WO1994007994A1 - Insulin-dependent yeast or fungi - Google Patents
Insulin-dependent yeast or fungi Download PDFInfo
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- WO1994007994A1 WO1994007994A1 PCT/US1993/009504 US9309504W WO9407994A1 WO 1994007994 A1 WO1994007994 A1 WO 1994007994A1 US 9309504 W US9309504 W US 9309504W WO 9407994 A1 WO9407994 A1 WO 9407994A1
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07K—PEPTIDES
- C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
- C07K14/435—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans
- C07K14/575—Hormones
- C07K14/62—Insulins
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- C—CHEMISTRY; METALLURGY
- C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
- C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
- C12N1/00—Microorganisms, e.g. protozoa; Compositions thereof; Processes of propagating, maintaining or preserving microorganisms or compositions thereof; Processes of preparing or isolating a composition containing a microorganism; Culture media therefor
- C12N1/14—Fungi; Culture media therefor
- C12N1/16—Yeasts; Culture media therefor
- C12N1/18—Baker's yeast; Brewer's yeast
- C12N1/185—Saccharomyces isolates
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- C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
- C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
- C12N15/00—Mutation or genetic engineering; DNA or RNA concerning genetic engineering, vectors, e.g. plasmids, or their isolation, preparation or purification; Use of hosts therefor
- C12N15/09—Recombinant DNA-technology
- C12N15/63—Introduction of foreign genetic material using vectors; Vectors; Use of hosts therefor; Regulation of expression
- C12N15/79—Vectors or expression systems specially adapted for eukaryotic hosts
- C12N15/80—Vectors or expression systems specially adapted for eukaryotic hosts for fungi
- C12N15/81—Vectors or expression systems specially adapted for eukaryotic hosts for fungi for yeasts
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- C—CHEMISTRY; METALLURGY
- C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
- C12R—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES C12C - C12Q, RELATING TO MICROORGANISMS
- C12R2001/00—Microorganisms ; Processes using microorganisms
- C12R2001/645—Fungi ; Processes using fungi
- C12R2001/85—Saccharomyces
- C12R2001/865—Saccharomyces cerevisiae
Definitions
- the present invention relates to mutant strains of yeast or fungi.
- insulin Most of the effects of insulin are cell- and tissue-specific and involve only a discrete subset of proteins in differentiated systems. In mammals, insulin synthesis and secretion coupled to nutrient sensing is compartmentalized to the beta cells of the pancreas, whereas insulin action is primarily exerted in peripheral target tissues.
- Diabetes mellitus and sequelae e.g. cardiovascular, renal, ocular, neural and congenital disorders
- proliferative diseases e.g. cardiovascular, renal, ocular, neural and congenital disorders
- insulin e.g. insulinomas
- insulinomas have multifactorial etiologies. Some of these diseases result from aberrant insulin secretion or defects in insulin structure or processing. In other forms of disease, the receptor is defective in number, hormone binding properties or protein tyrosine kinase activity.
- Various genetic systems are available for studying insulin action in this complex group of diseases. The first is represented by human diabetics (or animal models of diabetes) whose disease possesses a heritable component. In the recent past, transgenic mice have been developed to address specific genetic lesions associated with the diabetic phenotype. Another genetically amenable organism for analyzing insulin action is the fruit fly Drosophila melanogaster. Homologues of insulin signaling elements have been identified in Drosophila ,
- the present invention is therefore directed to a yeast or fungal strain which possesses different growth, morphology or viability properties in the presence of insulin than the parent strain from which it was derived.
- a preferred yeast or fungus is one which grows better than Saccharomyces cerevisiae ( S . cerevisiae) strain S288c in the presence of insulin at a concentration of 10 -6 M at a temperature between 17°C to 37°C.
- the yeast or fungus grows at least 10% better, more preferably at least 50% better and most preferably at least 100% better (2 fold better) than S.
- cerevisiae strain S288c when cultivated in a rich medium containing insulin (YPD+I medium) for 24 hours at 30°C when 1 ⁇ 10 5 cells are inoculated into 100 ml of media to yield a final density 1 ⁇ 10 3 cells/ml.
- the mutant yeast strain may also have at least one of the following characteristics: a response to a compound known to be an insulin secretagogue for mammals
- the present invention is also directed to a method for isolating a mutant yeast strain which comprises mutating yeast cells and selecting a mutant in said yeast cells which possesses different growth, morphology or viability properties in the presence of insulin than the parent strain from which it was derived.
- the present invention is also directed to a method for production of insulin or an insulin-like peptide comprising culturing a yeast or fungus which overexpresses said insulin or insulin-like peptide and recovering insulin or insulin-like peptide from said strain or said culture medium.
- the present invention is also directed to a method for production of insulin, which comprises i) providing a mutant yeast strain in which the response to insulin observed for wild-type yeast has been abrogated; i i ) transforming said mutant yeast strain with DNA which expresses an insulin gene; iii) culturing the transformed mutant yeast strain from step (ii) under conditions which provide for efficient expression of said insulin gene; and iv) recovering the insulin produced by the culture of step (iii).
- the present invention is also directed to a method for detecting an insulin secretagogue which comprises i) culturing cells of a mutant yeast strain wherein a response to said secretagogue is altered so as to be an exaggerated response, in a medium lacking said
- the present invention is also directed to a method for identifying elements in the insulin sensing/signaling pathway or to detect agents which modulate the activity of the components or elements of the pathway which comprises culturing the yeast; and analyzing basal status of said components; and adding an agent to said yeast; and measuring the status of said components; and comparing said status with said basal status.
- the present invention is further directed to a method for making a mutant yeast strain which comprises mutating a yeast culture and selecting a mutant in said yeast culture which grows better in the presence of insulin than the yeast from which said mutant was derived.
- the present invention is further directed to method for production of insulin comprising culturing a mutant yeast strain which is transformed with a gene for mammalian insulin in a culture medium and recovering insulin from said mutant strain or said culture medium.
- FIG. 1 is a schematic diagram of a four phase model for an insulin sensing/signaling pathway
- FIG. 2 is a summary of a procedure for mutagenizing yeast and isolating insulin-dependent mutants
- FIG. 3 is a graph showing plating efficiency curves at three different plating densities
- FIGS. 4-9 illustrate representative plates having (YPD+D/YPD or (YNB+D/YNB ratios as indicated in the Figures.
- FIGS. 10A through 10G shows the elevation of intracellular cAMP of cultured S. cerevisiae S288c in response to the addition of various nutrients.
- FIGS. 11A through 11D shows the proliferation response of cultured S. cerevisiae S288c in response to the addition of various nutrients.
- FIGS. 12A through 12D shows the TCA precipitable phosphate in actively growing versus phosphate arrested yeast cultures.
- FIG. 13 shows the results of DNA synthesis of growing yeast cultures and cultures arrested by phosphate depletion analysed by cell sorting.
- FIG. 14 shows the results of phosphoamino acid analysis of actively growing yeast cultures compared to cultures arrested by phosphate depletion.
- FIG. 15 shows a Western blot with anti-phosphotyrosine antibody of total proteins of yeast throughout the life cycle (inoculation-exponential phase-stationary phase-redilution) of a yeast culture.
- the invention comprises mutant yeast cells, preferably Saccharomyces cerevisiae, which have an altered response to insulin, insulin secretagogues and insulinomimetic compounds compared to wild-type yeasts.
- the response to insulin and insulinomimetic compounds can be abrogated or enhanced.
- the mutations which affect response to insulin and insulinomimetic compounds may be distributed throughout the biochemical pathways which act to bind the compound and then produce a physiological change in metabolism in response to that binding.
- Elements of this pathway include (but are not limited to) secretagogue receptors, such as glucose transporter and proteins which bind to sulfonylurea compounds, protein kinase C, phospholipase C, proteins involved in phosphatidylinositol turnover, other proteins involved in second messenger signaling, such as adenylate cyclase and phosphodiesterase, enzymes involved in synthesis, intracellular transport and secretion of the yeast insulin-like protein, the membrane-localized insulin receptor-like protein (IRP) for insulin and insulin-like proteins, and proteins which act downstream of the IRP that transduce the signal of ligand binding to the IRP to reprogram cell physiology, such as the product of the CDC25 gene, phosphatidylinositol kinase, and other as yet unidentified proteins.
- secretagogue receptors such as glucose transporter and proteins which bind to sulfonylurea compounds, protein kinase C, phospho
- the "downstream” proteins can be of two classes, those which interact directly with the IRP and those which are even further “downstream”, such as transcription factors and the proteins which carry biochemical signals from the plasma membrane to the nucleus.
- Other sites of mutation include enzymes involved in cell wall biosynthesis, as permeability of the cell wall to insulin has an influence on insulin transport from the culture medium to the cell membrane.
- the secretion of insulin-like peptide may be altered so as to decrease secretion of insulin-like peptide in response to secretagogue stimulation or the secretion of insulin-like peptide may be altered so as to result in constitutive secretion of insulin-like peptide.
- administering may not result in said yeast entering a cycle of DNA replication. This may be because the yeast does not commit to the start portion of said cycle of DNA replication.
- the mutant yeast strain has a mutant insulin-like receptor
- the insulin-like receptor may not be able to interact with downstream effector proteins.
- “Secretagogues” generally are compounds which elicit secretion of a hormone or other factor from a cell when the cell is exposed to them.
- secretagogue is used to denote a compound which elicits secretion of "insulin-like protein” from a yeast cell.
- Examples of such secretagogues are nutrients such as glucose, oleic acid, amino acids such as leucine, lysine and arginine, nucleotides such as adenine, and sulfonylurea compounds and derivatives of sulfonylurea compounds: [Caro, Am. J. Med., 89.17S-25S (1990); Easom et al, J. Biol. Chem., 265:4938-14946 (1990); Fleischer et al, In Molecular and Cellular Biology of Diabetes
- IPP insulin-like protein
- This receptor-ligand interaction begins a physiological response which alters carbohydrate and lipid metabolism in the yeast and also stimulates entry into the cell cycle culminating in DNA replication and budding.
- Over-exposure of the cell to insulin or insulinomimetic compounds that can bind to the receptor can result in insulinemia or insulin resistance (i.e. a diabetes-like state) in a culture of yeast, with concomitant disruption of the normal cellular metabolism and death of the cells.
- Yeast unlike higher eukaryotic cells, can be grown to high densities in inexpensive, defined nutrient media.
- scale-up of the culture can be used to overcome the limited quantities of starting materials from which to isolate the insulin signaling/sensing proteins.
- the precise role of these proteins can be determined in mutant strains of yeast defective in normal insulin related functions.
- molecular biology techniques can be employed to introduce into yeast mammalian homologues of the insulin signal transducing proteins for identification of common, fundamental functions in evolutionarily diverse organisms. Insight into the molecular mechanism of insulin action should pave the way for discovery and development of novel classes of therapeutic agents that circumvent the receptor in mediating an insulin signal. The availability of such agents would be useful for treatment of
- diabetes mellitus and other diseases of cell proliferation and metabolism related to insulin are diseases of cell proliferation and metabolism related to insulin.
- yeast is known to possess many of the proteins proposed to transduce the insulin signals in mammals. Therefore, advanced molecular biological techniques available with this organism could be used to establish the role of the proposed transducing proteins, and would permit identification of second-site mutations in as yet unknown elements of the insulin signal transduction pathway.
- Yeast has been exploited for study of fundamental aspects of cell biology including control of cell division, protein secretion and signal transduction through a mating factor receptor. However, demonstration of endogenous, molecular components related to insulin production and action was required before yeast could be used to study the mechanism of insulin action.
- yeast and fungi of the class Ascomycetes may be useful parent strains to be mutated.
- Representative yeast include yeasts from the genera Saccharomyces, Schizosaccharomyces, Aspergillus, Penicillium, Neurospora , Candida, Torulaspora, and Torulopsis .
- Other species of S. cerevisiae may include carlsbergensis and ellipsoideus var.
- yeast and fungal strains which may be useful are described in the American Type Culture Collection CATALOGUE OF FUNGI/YEASTS, Seventeenth Edition (1987).
- Mutations were generated using ethyl methanesulfonate as the mutagenic agent.
- mutagens include nitrous acid, N-nitrosoguanidine, ultraviolet radiation and transposon insertion mutagenesis.
- the insulin dependent mutants of the present invention include any mutant which grows better in the presence of insulin than the parent strain from which it was derived.
- Preferred mutants are those which have a YPD+I/YPD and a YNB+I/YNB ratio of 2.0 or more as measured by the plating assays described herein at a temperature of 17°C, 23°C, 30°C or 37°C.
- Some yeast mutants have the same YPD+I/YPD ratio and YNB+I/YNB ratio at all four of the above temperatures. These yeast show a "temperature independent insulin response”. Other yeast show a progressive increasing or decreasing ratio with increasing temperature. This may be a result of a single site temperature sensitive mutation. These yeast show a "temperature dependent insulin response”.
- Some mutants demonstrate fluctuating ratios as a funtion of temperature suggesting mutations at multiple loci.
- mutant yeast or fungi of the present invention is as a parent (host) strain, which is transformed with a gene for vertebrate or mammalian insulin (e.g. human insulin, bovine insulin, etc.) or for elements of the insulin sensing/signaling system.
- the yeast can be mutated to increase its ability to grow in the presence of insulin either before or after transformation with the mammalian insulin gene.
- Such transformed mutants are considered to be within the scope of this patent.
- Techniques for transforming yeast with foreign (heterologous) DNA are described in U.S. Patent 5,108,925 to Enari et al which issued on April 28, 1992.
- Preparation of transformant yeast which express the human insulin gene is described in U.S. Patent 4,916,212 to Markussen et al which issued on April 10, 1990. The entire contents of both of these patents are hereby incorporated by reference.
- EXAMPLE 1 Isolation and characterization of yeast strains having an altered response to insulin
- Newly created and isolated mutant strains of the present invention were derived from S . cerevisiae wild-type strain S288c (MATa mal mel gal2 CUP1 SUC2) available from the Yeast Genetics Stock Center
- Ethyl methanesulfonate is an alkylating agent that can generate as many as 10 2 -10 4 mutations per gene without significant inactivation. Thus, isolates may be defective at multiple genetic loci.
- the primary targets of ethyl methanesulfonate are keto oxygens at position six of guanine to yield 0-6 ethyl guanine and at position four of thymine to yield 0-4 ethyl thymine. Modification at these positions leads to mispairing of guanine with thymine resulting in GC ⁇ AT transitions.
- the mutagenesis procedure is initiated with parent cells grown to a mid-logarithmic phase density of 2 ⁇ 10 8 /ml in YPD broth consisting of 1% (w/v) yeast extract, 2% (w/v) Bacto-peptone and 2% (w/v) glucose. Cells harvested by centrifugation at 3,000 ⁇ g at room temperature were washed and resuspended in sterile, phosphate buffered saline (PBS) to a concentration of 2 ⁇ 10 8 /ml.
- PBS phosphate buffered saline
- YPD agar plates (15 ml) are supplemented with 0.15 ml of bovine insulin (10 -4 M) which was dissolved in 10 mM HCl, neutralized in PBS and emulsified with 1 % Emulphor ® (Hoffmann-LaRoche).
- the thus prepared insulin stock solution is sterilized through 0.2 ⁇ m cellulose acetate filter and spread with a sterile glass rod over the surface of the plate. Under no circumstances is insulin added to the medium prior to autoclaving the medium. Control plates were spread with a similar solution lacking insulin.
- Mutagenized and control cell suspensions were diluted by a factor of 10 5 and aliquots of 0.1, 0.2 and 0.4 ml were plated in 10 replicates on both types of media.
- the plates were inverted and incubated at room temperature (approximately 23°C). After 24, 48, 72 and 96 hours of incubation, plates were examined for growth. Representative recoveries of cells are presented in Figure 3. Following 72 hours of incubation, isolates appearing as colonies on YPD plus insulin (YPD+I) plates were streaked on YPD or YPD+I plates to demonstrate the degree of insulin dependence.
- YPD+I YPD plus insulin
- the mutants demonstrated varying degrees of dependence or insensitivity to supraphysiological concentrations (e.g. 10 -6 M) of insulin, and some of the phenotypes observed between the permissive
- YPD may contain insulin or insulinomimetic substances
- the mutant strains of S. cerevisiae were also tested for insulin dependence by cultivation on complex, defined medium, YNB .
- the chemical composition of the medium designated YNB is presented in Table I.
- yeast nitrogen base without amino acids (Difco, Catalog No. 0919) supplemented with 5 g/L ammonium sulfate and 20 g/L glucose.
- the results of incubation at various temperatures on rich, complex YPD or defined YNB media are presented in Table II.
- the wild-type parental strain S288c is characterized by vigorous growth with a doubling time of 2 to 2.5 hours in YPD and YNB media, respectively.
- the colonies are pearly white to buff colored, relatively large (1-5 mm) in diameter, luxurious and thick.
- Each of the mutants possess a distinct colony or individual cellular morphology (See Table III). Whereas single cells of S288c are ellipsoid or round and approximately 5-10 ⁇ m in diameter, the mutants do not conform to the wild-type characteristics.
- the growth rates are generally slower than for S288c, although for some mutants, 10 -6 M insulin restores growth characteristics of the wild-type.
- the morphology of selected insulin-dependent mutants which have a YNB+I/YNB growth rate ratio of 2 or more is described in the following Table.
- Mutant strains are maintained by freezing using the following protocol. 200 ⁇ l of a previously frozen stock or stock YPD+I plate stored at 4°C for less than one month, is inoculated into 200 ml of YPD media with insulin. The inoculated media is put on a shaker at 30°C until cells reach the mid-logarithmic phase of growth (optical density at 600 nm between 0.5-1.0). The culture is transferred to four 50 ml sterile tubes and centrifuged at 3,000 x g for 15 min. The supernatant is removed by pipetting until between 10-15 ml is left in each tube. The pellet is resuspended in the same YPD+I media (the 10-15 ml).
- the suspensions are transferred to one 50 ml sterile tube and centrifuged as above for 15 min (to obtain 1 pellet). The supernatant is removed and resuspended in 5.5 ml of YPD media supplemented with insulin and 20% glycerol. 500 ⁇ l of suspension is dispensed into each vial. The cultures are checked for contamination by light microscopy under oil immersion. The cultures are then frozen at
- Yeast strains 2.1D2, 2.2C5 and 2.4B1 described above were deposited at the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Maryland 20852, USA, on October 5, 1992 under the conditions of the Budapest Treaty. The strains were assigned the following designations ATCC 74189 (2.1D2), ATCC 74190 (2.2C5) and ATCC 74191 (2.4B1), respectively. Strain 2.1D2 was selected because it was insulin sensitive. Strain 2.2C5 was selected because it demonstrated a strong insulin- and temperature-dependent phenotype on YNB. Strain 2.4B1 was selected because it was unaffected or improved with respect to viability by extended term culture in the presence of supraphysiological concentrations of insulin. EXAMPLE 2 : Use of yeasts as a secretagogue sensing system
- mutant yeasts as isolated and described in Example 1 may be employed.
- those mutants which show an enhanced or stabilized response would be desirable to be used.
- a mutant which demonstrated a rapid rise in 3',5'-cyclic adenosine monophosphate (cAMP) level which did not subsequently decay, and thus maintained a high, stable level of intracellular cAMP would be particularly useful.
- a mutant which showed an increased amount of tyrosine phosphorylation of total cellular proteins or of the IRP would be most useful as a nutrient sensor cell.
- YNB without glucose medium 1.7 grams of Difco Yeast Nitrogen Base and 5.0 grams of ammonium sulfate were dissolved in 1 liter distilled, deionized water. When all solids have dissolved the solution is made up to 1 liter with distilled water and sterilized through a 0.2 micropore Fisher filter and stored in an autoclaved bottle in a refrigerator. For YNBM plus glucose, 20 grams of dextrose (Sigma) was added per liter. 2.
- aliquots of the starter culture were transferred into two 250 ml flasks; one contained YNBM with 2% (w/v) glucose while the other contained YNBM without glucose.
- Yeast incubated in the presence of glucose were diluted frequently in YNBM before assay to maintain a maximum cell density of 3 ⁇ 10 6 /ml.
- Cells prepared in the absence of glucose were diluted in YNBM minus glucose to allow six to seven generations of growth on intracellular glycogen before arrest at 3 ⁇ 10 6 /ml.
- YNBM medium lacking glucose cells were maintained at 30°C with shaking at 250 rpm for a period of sixteen hours to ensure a starved depleted state.
- D-glucose solution was added to each flask containing 100 ml of YNBM to give a final concentration of 110 mM glucose.
- ana l og s o f g l u c o s e , i n c l ud i ng 3-O-methyl-D-glucopyranoside (110 mM) and 2-deoxy-D-glucose (110 mM) were added to glucose starved and continuously fed cultures.
- cAMP content of the supernatants was quantitated by a scintillation proximity technique using a kit, (Amersham, Catalog No. RPA.538, Arlington Heights, IL) as described by the manufacturer. Prior to assay, supernatants were vacuum evaporated to dryness, resuspended in assay buffer and acetylated with acetic anhydride and trimethylamine to stabilize the cyclic nucleotide.
- samples (1 ml) were also withdrawn from flasks at each time point and fixed with 0.05% glutaraldehyde in YNB. The contents fixed for 3 minutes and were then centrifuged for 2 mins at 13,000 ⁇ g. The pellets were resuspended in 4% formaldehyde in PBS, and stored frozen at -20°C. Budding was quantitated by counting, under a light microscope, the number of buds per one hundred cells sampled.
- step four sulfonylureas supplemented glucose in the following concentrations: into first set of cultures (YNB with glucose), tolbutamide 0.025 mM (with 110 mM glucose), chlorpropamide 0.025 mM (with 110 mM glucose), and glyburide 2.5 ⁇ M (with 110 mM) were added; into the second set of cultures (starved) the same concentrations of sulfonylureas were added but with 5 mM of glucose instead of 110 mM. Again all steps of the cAMP extraction were
- Yeast grown in the presence of glucose are insensitive to further stimulation by additional glucose.
- a period of starvation for glucose, followed by refeeding results in a transient 5-to 10-fold increase in intracellular cAMP, over the basal cAMP level.
- Refeeding with 2-deoxyglucose generates a 2- to 3-fold rise in cAMP in the starved cells.
- 3-O-methylglucopyranoside and galactose do not alter cAMP levels.
- Amino acids recognized as secretagogues in mammalian cells including L-arginine, L-leucine and L-lysine, induce cAMP transients of 2-, 10- and 2-fold, respectively. Similar to transients induced by glucose, the timing of the cAMP pulse is centered around 30 seconds. L-arginine also stimulates growth, but this effect is observed clearly only after 6 hours of culture. L-glutamine and L-glutamate do not promote cAMP pulses, but these amino acids effectively stimulate growth. Conversely, cysteine reduced cAMP levels ascompared to basal levels and interfered with traversal through the cell cycle.
- adenine, oleic acid and potassium phosphate induce a cAMP transient.
- the magnitude of stimulation by adenine was 4-fold at 15 seconds.
- Oleic acid caused a protracted rise of 7- to 10-fold by 1 hr. of incubation, which was accompanied by a stimulation of cell proliferation.
- Potassium phosphate which is required for insulin secretion in mammals, supported a 15- to 30-fold elevation in cAMP level within 30 seconds in cells starved for phosphate in the presence of glucose.
- cAMP pulses comparable in magnitude and duration as those observed in cells starved and replenished with glucose.
- Glyburide generates the highest response, stimulating a 5-fold increase over basal levels.
- Tolbutamide also elevates cAMP levels, though only 2- to 3 -fold.
- Chlorpropamide is able to stimulate cAMP transients in both starved cells and cells continuously fed glucose. Stimulation of cAMP elevation by chlorpropamide is preferentially observed in continuously fed cells and apparently is elicited by a mechanism different from that through which glucose operates.
- Insulin treatment of cells starved for glucose and refed glucose suppressed the transient rise in cAMP noted in the absence of the hormone.
- cells exposed to insulin achieved a growth rate approximately 50% more rapid than the starved and refed control cultures.
- This observation correlates with the time of appearance of their endogenous insulin-like peptide, ILP in the growth medium, which occurs at approximately 1-2 hours.
- the highest specific activity of the ILP is greatest just at commencement of exponential growth of the cells.
- Glycogen biosynthesis in response to glucose feeding was inhibited for approximately 10-30 minutes, the time when cAMP transients were at their peak levels. Addition of ILP and insulin at physiological concentrations exacerbated the initial inhibition of glycogen synthesis.
- Protein tyrosine phosphorylation is a central motif in eukaryotic cell regulation, implicated in cell cycle control, transformation, differentiation, neurotroph signaling, and immune cell activation. Growth factor receptor activation by autophosphorylation on tyrosine residues is one well-documented physiological role. The strongest link between protein tyrosine phosphorylation and function is the activation of insulin, insulin-like growth factor I (IGF-I), epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) hormone receptors that possess intrinsic tyrosine protein kinase activities in normal mammalian cells.
- IGF-I insulin-like growth factor I
- EGF epidermal growth factor
- PDGF platelet-derived growth factor
- Strain S288c was grown in YNB medium (Difco) at 30°C with shaking at 250 rpm to a cell density of 3 ⁇ 10 6 /ml.
- a starter culture was inoculated at 4 ⁇ 10 3 /ml into YNB, or comparable medium formulated from separate components (Difco Manual) , and buffered with 50 mM 2-(N-morpholino)-ethanesulfonic acid (MES), pH 6.0, to exclude KH 2 PO 4 .
- MES 2-(N-morpholino)-ethanesulfonic acid
- Cells harvested by centrifugation were resuspended to 5 ⁇ 10 6 /ml in fresh YNB or MES-buffered medium with indicated concentrations of KH 2 PO 4 and 0.125 mCi/MI 32 PO 4 .
- aliquots of cells were removed and phosphate uptake was terminated with ice-cold TCA (10% w/v). Extracts were washed 3x in ice-cold phosphate buffered saline, neutralized with 0. 1N NAOH and scintillation counted.
- Figure 12 shows TCA precipitable counts measured from actively growing or phosphate-arrested cultures supplemented with (A) 100% KH 2 PO 4 , (B) 25% KH 2 PO 4 , (C) 10% KH 2 PO 4 and (D) KH 2 PO 4 -deficient MES-buffered medium.
- Actively growing and phosphate starved exponential phase cells were grown to 3 ⁇ 10 6 /ml as described in A. At indicated times, 100 ⁇ l aliquots of cells were harvested and resuspended in citrate buffer-based fixative. Cells treated with 100 ⁇ g/ml RNase A and 5 ⁇ g/ml propidium iodide were analyzed at 625 nm on a Coulter Epics fluorescence activated cell sorter.
- Figure 13 depicts cell cycle progression of actively growing and phosphate arrested cells resuspended in MES-buffered medium with (A) 100% KH 2 PO 4 and (B) 10% KH 2 PO 4 .
- Exponential phase yeast were transferred at low density to phosphate-deficient medium.
- the yeast proliferated twelve to thirteen generations in phosphate-deficient conditions and displayed a slightly greater specific growth rate of 0.37, up to the point of arrest, than cells grown on standard phosphate-containing medium which demonstrated a specific growth rate of 0.35.
- Vacuolar phosphate stores constituting 35-40% of yeast cell dry weight (120 mm/kg wet weight; Griffin, Fungal Physiology, John Wiley & Sons, NY (1981)), were presumably mobilized during this period and seemed more readily utilized than phosphate from external sources.
- Yeast have been shown to liberate vacuolar polyphosphate reserves when transferred into medium containing disproportionately high nitrogen to phosphate levels. Thus, arrest must occur when both external and internal supplies are exhausted and intracellular phosphate pools are equilibrated. Phosphate-arrested cells, positioned at or before START of the cell cycle, were found to be unbudded and thermotolerant.
- FIG. 13A Flow cytometric analysis of phosphate- restricted cells revealed that DNA synthesis was reinitiated between 1-2 hours after fully replenishing medium phosphate content.
- Addition of 1x standard medium phosphate was adequate to re-initiate proliferation in 31% of phosphate-starved cells (FIG. 13A) while use of 0.1x standard medium phosphate induced proliferation in 9% of phosphate-limited cells (FIG. 13B).
- Tracer added alone to these cells was insufficient for growth induction.
- labelling macromolecules with radiolabelled phosphate is most efficient when exogenous and internal phosphate stores are negligible, these conditions are insufficient to support growth.
- phosphate-arrested cells positioned at the G1 phase, were stimulated with 0.1x standard medium phosphate. This condition achieved a balance between efficient labelling and re-entry into the cell cycle. Furthermore, arrest of logarithmic phase cells by phosphate limitation establishes a fixed metabolic position from which to initiate growth.
- phosphoamino acid analysis of mid-exponential phase yeast cells has demonstrated exceedingly weak signals from phosphotyrosine compared to those from phosphoserine and phosphothreonine (Castellanos et al, J. Biol. Chem., 260:8240 (1985); Dailey et al, Mol. Cell Biol., 10:6244 (1990); Schieven et al, Science, 231:390 (1986)).
- Exponential phase yeast cells depleted of vacuolar phosphate reserves, when refed 0.1x standard medium phosphate, displayed phosphotyrosine more prominently than the other phosphoamino acids. Under the conditions reported, threonine phosphorylation appears to be less actively involved in proliferative events, as evidenced by its virtual absence in phosphoamino acid analysis (FIG. 13) of growth-induced, phosphate restricted cells.
- Exponential phase cells (5 ⁇ 10 8 ) unrestricted for phosphate yielded 2.1 ⁇ 10 -7 moles of 3'-UMP and 1.2 ⁇ 10 -7 moles of phosphotyrosine.
- exponential cells 5 ⁇ 10 8
- restricted for phosphate 1 ⁇ 10 -7 moles of 3'-UMP and 1.1 ⁇ 10 -7 moles of phosphotyrosine were detected.
- phosphate is preferentially directed to tyrosine compared to serine or threonine in S. cerevisiae . Therefore, under conditions of growth induction, the ratio of phosphotyrosine to contaminants in cells grown to exponential phase and limited for phosphate prior to labelling, was greater than in the unrestricted cells.
- yeast proteins were probed with the monoclonal anti-phosphotyrosine antibody, 4G10
- Protein targets with tyrosine-specific phosphorylations were analyzed by Western blotting with monoclonal antibody 4G10 (FIG. 15).
- Yeast demonstrated numerous tyrosine phosphorylated proteins in every phase of growth. However, signals from bands at 95, 81 and 47 kD lost intensity as cells approached nutrientdependent saturation density. The proteins regained exponential phase intensity after introduction to fresh medium. Although generally less intense, similar proteins from starved cells were tyrosine phosphorylated upon replenishment with 0.1x standard medium phosphate and resumption of growth.
- a protein of molecular weight 180 kDa was increasingly phosphorylated as cells entered stationary phase, and another high molecular weight protein at >220-240 kDa was phosphorylated to various extents in different phases of growth. Under varied conditions of growth, the profile of tyrosine phosphorylations in different phases were not consistent. Cells grown to late stationary phase, then transferred to fresh medium, exhibited intense phosphotyrosine signals upon growth resumption. This finding corroborates the result from phosphoamino acid analysis in which increased tyrosine phosphorylation is correlated with re-entry into the cell cycle.
- yeast cells in early logarithmic and stationary phases of growth were spiked with purified bovine serum albumin, bead beaten in denaturing sample buffer and the proteins analyzed by electrophoresis [(Laemmli, Nature, 227:680 (1970)].
- This experiment revealed extensive proteolytic digestion in stationary phase cells absent in logarithmic phase cells.
- Undefined media contain a large proportion of complex nitrogen substrates (e.g. peptone) and certain phosphate content is characteristically high when compared to that of defined medium.
- Certain nitrogen compositions promote protease activity, and a high nitrogen to phosphate ratio forces phosphate mobilization from the vacuole and enhanced scavenging phosphatase activity.
- Phosphate-starved yeast "sense" replenishment of phosphate through the RAS/CAMP pathway, and this signal transduction pathway, connected to nutrient availability, may be integrated with protein tyrosine phosphorylation-mediated signaling.
- Example 4 Use of the mutant yeasts to screen for antdiabetic agents
- any or all of the assay in the above Examples are performed in the presence of an agent with anti-diabetic, anti-proliferative and/or biological response modifying activities.
Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
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EP93923255A EP0666903A4 (en) | 1992-10-05 | 1993-10-05 | Insulin-dependent yeast or fungi. |
AU53209/94A AU5320994A (en) | 1992-10-05 | 1993-10-05 | Insulin-dependent yeast or fungi |
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US95629492A | 1992-10-05 | 1992-10-05 | |
US07/956,294 | 1992-10-05 |
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WO1994007994A1 true WO1994007994A1 (en) | 1994-04-14 |
WO1994007994A9 WO1994007994A9 (en) | 1994-06-09 |
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PCT/US1993/009504 WO1994007994A1 (en) | 1992-10-05 | 1993-10-05 | Insulin-dependent yeast or fungi |
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EP (1) | EP0666903A4 (en) |
AU (1) | AU5320994A (en) |
CA (1) | CA2146432A1 (en) |
WO (1) | WO1994007994A1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
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EP0967226A2 (en) * | 1998-05-08 | 1999-12-29 | Cohesion Technologies, Inc. | Methods for the production of fibrillar collagen |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4876197A (en) * | 1983-02-22 | 1989-10-24 | Chiron Corporation | Eukaryotic regulatable transcription |
US4880734A (en) * | 1984-05-11 | 1989-11-14 | Chiron Corporation | Eukaryotic regulatable transcription |
-
1993
- 1993-10-05 WO PCT/US1993/009504 patent/WO1994007994A1/en not_active Application Discontinuation
- 1993-10-05 AU AU53209/94A patent/AU5320994A/en not_active Abandoned
- 1993-10-05 CA CA002146432A patent/CA2146432A1/en not_active Abandoned
- 1993-10-05 EP EP93923255A patent/EP0666903A4/en not_active Withdrawn
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4876197A (en) * | 1983-02-22 | 1989-10-24 | Chiron Corporation | Eukaryotic regulatable transcription |
US4880734A (en) * | 1984-05-11 | 1989-11-14 | Chiron Corporation | Eukaryotic regulatable transcription |
Non-Patent Citations (2)
Title |
---|
See also references of EP0666903A4 * |
The Journal of Cell Biology, Volume 111, No. 5, Part 2, issued November 1990, M.A. McKENZIE et al., "An Insulin-Like Signal Transduction Pathway in Saccharomyces Cerevisiae", page 472A, see entire document. * |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0967226A2 (en) * | 1998-05-08 | 1999-12-29 | Cohesion Technologies, Inc. | Methods for the production of fibrillar collagen |
EP0967226A3 (en) * | 1998-05-08 | 2003-12-03 | Cohesion Technologies, Inc. | Methods for the production of fibrillar collagen |
Also Published As
Publication number | Publication date |
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CA2146432A1 (en) | 1994-04-14 |
EP0666903A1 (en) | 1995-08-16 |
EP0666903A4 (en) | 1997-06-04 |
AU5320994A (en) | 1994-04-26 |
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