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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Fission yeast cell division is initiated by the cdc2/cdc13-cyclin protein kinase which in its catalytically active state comprises the mitotic inducer. During interphase the cdc2/cyclin complex is assembled in an inactive state that requires cdc25+ gene function for M-phase activation. The cdc25+ product, a 76 kd phosphoprotein, is shown to oscillate in abundance during the cell cycle, reaching a peak at G2/M, and to be sensitive to nitrogen starvation. The level of cdc25 is subject to feedback regulation involving both cdc25 and cdc2.
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PMID:Fission yeast cdc25 is a cell-cycle regulated protein. 217 10

Human autoimmune sera specific for proliferating cell nuclear antigen (PCNA)/cyclin (auxiliary protein for DNA polymerase delta) demonstrated the presence of epitopes within the macro- and micronuclei of the hypotrichous ciliated protozoa Euplotes eurystomus. Tightly bound PCNA/cyclin was localized at the site of DNA synthesis in macronuclei, the rear zone of the replication band. Starvation or heat shock, conditions that reduce macronuclear replication, resulted in a decrease of PCNA/cyclin in replication bands. Micronuclei also exhibited PCNA/cyclin localization which persisted for a large proportion of the vegetative cell cycle and exhibited significant resistance to adverse culture conditions. Immunoprecipitation of 35S-labeled soluble Euplotes proteins with PCNA/cyclin autoimmune sera revealed a spectrum of low molecular mass proteins. PCNA/cyclin-like proteins have now been observed in the widely divergent species: human, rat, amphibian, yeast, and ciliated protozoa.
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PMID:Proliferating cell nuclear antigen/cyclin in the ciliate Euplotes eurystomus: localization in the replication band and in micronuclei. 247 76

We have used monoclonal antibodies to statin (S-44) and a cyclin-like protein (S-132) to examine the distribution of these two antigens in proliferating and in nonproliferating populations of cells. We have found that this cyclin-like protein is present in proliferating fibroblasts, whereas statin is absent from these same cell populations; in contrast, in senescent populations of fibroblasts the cyclin-like antigen disappears and statin labeling of nuclei appears. During myogenesis in rat muscle cell cultures, S-132 labeling is present in proliferating myoblasts and disappears after cells fuse and differentiate as multinucleated myotubes. In contrast, statin is absent from proliferating myoblasts, but appears when these cells become postmitotic and begin to differentiate. Similar results were seen during chick myogenesis. We have also found similar results during serum-starvation-induced differentiation in neuroblastoma cells. These results indicate that the cyclin-like protein disappears and statin appears upon commitment to differentiation in vitro, and the presence or the absence of these proteins appears to provide cellular markers for the transition from the proliferative to the nonproliferative state during differentiation.
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PMID:The disappearance of a cyclin-like protein and the appearance of statin is correlated with the onset of differentiation during myogenesis in vitro. 289 89

The cdc2+ gene product (p34cdc2) is a protein kinase that regulates entry into mitosis in all eukaryotic cells. The role that p34cdc2 plays in the cell cycle has been extensively investigated in a number of organisms, including the fission yeast Schizosaccharomyces pombe. To study the degree of functional conservation among evolutionarily distant p34cdc2 proteins, we have constructed a S. pombe strain in which the yeast cdc2+ gene has been replaced by its Drosophila homologue CDC2Dm (the CDC2Dm strain). This CDC2Dm S. pombe strain is viable, capable of mating and producing four viable meiotic products, indicating that the fly p34CDC2Dm recognizes all the essential S. pombe cdc2+ substrates, and that it is recognized by cyclin partners and other elements required for its activity. The p34CDC2Dm protein yields a lethal phenotype in combination with the mutant B-type cyclin p56cdc13-117, suggesting that this S. pombe cyclin might interact less efficiently with the Drosophila protein than with its native p34cdc2 counterpart. This CDC2Dm strain also responds to nutritional starvation and to incomplete DNA synthesis, indicating that proteins involved in these signal transduction pathways, interact properly with p34CDC2Dm (and/or that p34cdc2-independent pathways are used). The CDC2Dm gene produces a 'wee' phenotype, and it is largely insensitive to the action of the S. pombe wee1+ mitotic inhibitor, suggesting that Drosophila wee1+ homologue might not be functionally conserved. This CDC2Dm strain is hypersensitive to UV irradiation, to the same degree as wee1-deficient mutants. A strain which co-expresses the Drosophila and yeast cdc2+ genes shows a dominant wee phenotype, but displays a wild-type sensitivity to UV irradiation, suggesting that p34cdc2 triggers mitosis and influences the UV sensitivity by independent mechanisms.
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PMID:Functional analysis of the Drosophila CDC2 Dm gene in fission yeast. 747 62

Although Dictyostelium differentiation occurs in the absence of external nutrients, two periods of mitosis occur, one during early development and one during the formation of the migrating pseudoplasmodium. We showed previously that cyclin B mRNA levels vary in a cell cycle dependent manner during vegetative cell growth. In the present study, we report that cyclin B mRNA levels change dramatically during development, reaching a maximum at the tipped aggregate stage. However, amounts of cyclin B protein vary only slightly, peaking during early development and decreasing during late aggregation and pseudoplasmodial formation. Cdc2 protein levels also remain relatively constant during development. Cdc2-histone H1 kinase activity was considerably higher in vegetative cell extracts of transformants that expressed large amounts of truncated cyclin B protein in comparison to extracts of the parental Ax-2 cells. These results suggest that Cdc2 kinase activity is dependent upon the level of cyclin B in vegetative cells. This result is consistent with the idea that variations in the level of cyclin B during growth regulate the cell cycle. When Cdc2 histone H1 kinase activity was determined during development, it was also found that activity correlated reasonably well with the amount of cyclin B protein. Thus, there was an increase in Cdc2 histone H1 kinase activity early in development, and then levels decreased as development progressed. The increase in Cdc2 histone H1 kinase activity that occurs early in development following starvation may be important in accelerating G2-phase cells through into mitosis. There was no increase in Cdc2 histone H1 kinase that accompanied the previously reported late developmental mitosis.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cyclin B and Cdc2 expression and Cd2 kinase activity during Dictyostelium differentiation. 757 76

Genes encoding cdk1 (p34cdc2), cyclin A, cyclin B, and the tumor suppressor gene Rb are fundamental regulators of cell cycle progression which associate as a complex with the transcription factor E2F. Expression of many of these proteins has previously been shown to be repressed by okadaic acid, a specific inhibitor of protein phosphatases 1/2A (PP1/PP2A), resulting in growth arrest in nontransformed but immortalized cells. We have investigated levels of mRNA encoding cdk1 (p34cdc2), cyclin A, cyclin B, Rb, GAPDH, c-myc, and histone H4 genes for sensitivity to okadaic acid in HeLa cells to determine if transformation altered their regulation. Serum starvation slowed growth and diminished mRNA levels for all genes tested except c-myc and GAPDH. When starved cells were subsequently exposed to 19 nM okadaic acid or refed 10% serum, mRNA levels of cyclin A, cyclin B, cdk1, and Rb dramatically increased while mRNA levels for c-myc and GAPDH were largely unaffected. Histone H4 mRNA levels and the rate of DNA synthesis were greatly enhanced by serum addition but not affected appreciably by okadaic acid. Okadaic acid was also effective in blocking proliferation of exponentially growing HeLa cells at G2/M and S phase. Despite the cell cycle phase-specific block, elevated mRNA levels for cdk1, cyclin A, cyclin B, Rb, and suppression of H4 mRNA levels were detected and persisted for at least 12 hr following okadaic acid removal. The results demonstrate that cell cycle progression is blocked and several cell cycle regulatory genes, encoding transcription factor E2F-associated proteins, experience elevation of mRNA levels through mechanisms sensitive to okadaic acid likely through a PP1/PP2A-sensitive mechanism. Data from transformed cells contrast with data from immortalized but nontransformed cells in which okadaic acid also blocks cell cycle progression during G2/M phase but suppresses expression of these genes. Such contrasts may be correlated with reduced growth factor dependence and transformation.
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PMID:Selective induction of cell cycle regulatory genes cdk1 (p34cdc2), cyclins A/B, and the tumor suppressor gene Rb in transformed cells by okadaic acid. 762 88

The baker's yeast Saccharomyces cerevisiae can undergo pseudohyphal differentiation upon limited starvation for nitrogen. This differentiation is characterized by a hyperpolarized cell growth that gives rise to elongated cells. These elongated cells can form chains that penetrate an agar surface. The study of the grr1 mutant, affected in the degradation of the G1 cyclins, showed that the stabilization of Cln1 and Cln2 leads to a similar hyperpolarized cell growth. We suggest that G1 cyclin stability is a key element controlling cellular morphogenesis. Examination of G1 cyclin turnover during pseudohyphal growth strongly supports this hypothesis. Saccharomyces cerevisiae is thus an interesting model for studying the interconnections between cell cycle control and cellular differentiation.
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PMID:[G1 cyclin degradation and cell differentiation in Saccharomyces cerevisiae]. 775 3

In the fission yeast Schizosaccharomyces pombe, the cdc10+/SWI family members constitute the cell cycle 'start' genes. res1+ and res2+ are the newly identified members of this family and encode putative association partners of the Cdc10 protein. The Pat1 kinase plays a pivotal role in switching between vegetative growth and sexual development, and its inactivation in haploid cells induces unconditional growth arrest and subsequent meiosis. We have identified as an extragenic suppressor of a temperature sensitive pat1-114 mutant, a new B-type cyclin that negatively regulates conjugation by interacting with these 'start' genes. This cyclin, named Cyc17, is highly homologous with Cdc13, but has no detectable activity as a mitotic cyclin. Deletion of cyc17+ markedly enhances conjugation, despite the presence of nitrogen source, and accelerates growth arrest in G1 upon nitrogen starvation. Conversely, overexpression of the cyc17+ gene strongly inhibits conjugation. The cyc17+ gene is transcribed into 3.2 kb poly(A)+ and 3.0 kb poly(A)- RNAs. Only the poly(A)+ species is expressed during vegetative growth and periodically with a peak in the G1 and S phases of the cell cycle. On the other hand, the poly(A)- transcript is highly induced during conjugation. This induction is lost in res2- cells, whereas the poly(A)+ transcript is significantly reduced in res1- cells. However, the mating inhibition as well as the ability to rescue the pat1 mutation by overexpression of res1+ and res2+ are totally abolished in cyc17- cells. Thus, in S.pombe, a B-type cyclin, regulated by the newly identified cell cycle 'start' genes, plays a crucial role in the control of sexual development.
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PMID:A B-type cyclin negatively regulates conjugation via interacting with cell cycle 'start' genes in fission yeast. 790 13

In normal human fibroblast cells, the primary cell cycle regulators, the cyclin-dependent kinases (CDKs), exist predominantly in multiple quaternary complexes, each consisting of a CDK, a cyclin, proliferating cell nuclear antigen (PCNA) and p21. p21 encodes a universal inhibitor of cyclin-dependent kinases. Here we show that the level of p21 mRNA and the interaction of p21 protein with cyclin-CDK enzymes are regulated during the cell cycle. When normal human fibroblast IMR90 cells were released from serum starvation, p21 mRNA reached its highest level immediately following serum stimulation, began to decrease at the G1/S boundary, fell to its lowest level during S phase, and accumulated again as cells exited from S phase. p21 protein associates with each cyclin-CDK complex in a cell cycle dependent manner. Cyclin A-CDK2-p21-PCNA and Cyclin B1-CDC2-p21-PCNA complexes are assembled in early S and G2 phase, respectively, indicating that p21 and/or PCNA regulates the enzymatic activity of each kinase at the time of their functioning. Cyclin D1-CDK4-p21-PCNA complexes, on the other hand, persist throughout the cell cycle, suggesting that cyclin D1-CDK4 quaternary complexes may play a role in monitoring an event(s) that may occur at any time, rather than at a specific stage of the cell cycle. The level of p21 mRNA in early passage Li-Fraumeni cells that are heterozygous for p53 mutation remained similar to that in normal fibroblasts, but was undetectable in immortalized Li-Fraumeni cells homozygous for mutant p53. This finding provides a plausible molecular explanation for the loss of genetic stability associated with cells homozygous, but not heterozygous, for p53 mutation.
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PMID:Cell cycle expression and p53 regulation of the cyclin-dependent kinase inhibitor p21. 791 44

The puc1+ gene, encoding a G1-type cyclin from the fission yeast Schizosaccharomyces pombe, was originally isolated by complementation in the budding yeast Saccharomyces cerevisiae. Here, we report the molecular characterization of this gene and analyse its role in S. pombe. We fail to identify any function of this cyclin at the mitotic G1/S transition in S. pombe, but demonstrate that it does function in exit from the mitotic cycle. Expression of the puc1+ gene is increased during nitrogen starvation, and puc1 affects the timing of sexual development in response to starvation. Overexpression of the puc1 protein blocks sexual development, and rescues pat1ts cells, which would otherwise undergo a lethal meiosis. We conclude that puc1 contributes to negative regulation of the timing of sexual development in fission yeast, and functions at the transition between cycling and non-cycling cells.
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PMID:Analysis of the Schizosaccharomyces pombe cyclin puc1: evidence for a role in cell cycle exit. 800 74


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