Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.22 (cdc2)
 8,319 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We studied spheroid (multicellular aggregate) formation by hepatocytes and the expression of liver-specific functions such as albumin secretion when hepatocytes were cultured with various extracellular matrices. Hepatocytes cultured on Primaria(R) and poly-D-lysine coated dishes, and in the presence of a polymer, Eudragit, formed spheroids, and they also exhibited higher liver-specific functions and poor growth compared to monolayer cultures. The results indicated that the cell morphological change and cell-cell interaction caused by the spheroid formation were key factors promoting the expression of the liver-specific functions. To elucidate the mechanism underlying the poor growth in spheroids, we examined the HGF signaling pathway. Phosphorylation and down-regulation of the HGF receptor (c-Met proto-oncogene product) were observed for the cells from both monolayer and spheroid cultures, but Ras activation was partly blocked in spheroids. Furthermore, we found that CDK inhibitors, p21 and p27, were highly expressed in spheroids. These results suggested that the reduced Ras signaling and high expression of the CDK inhibitors might cause the lower growth in spheroids. We then examined the relationship between liver-enriched transcription factors (C/EBPalpha and beta) and liver-specific functions. The results revealed that the high expression of C/EBPalpha was maintained during cultures when hepatocytes formed spheroids. Antisense oligonucleotides of C/EBPalpha repressed albumin secretion and the expression of p21, suggesting that the transcription factor, C/EBPalpha, may play a crucial role in the growth and differentiation of hepatocytes in spheroids.
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PMID:Differentiation and proliferation of primary rat hepatocytes cultured as spheroids. 979 21

When exposed to diverse growth conditions in vitro, cells can respond by entering states of proliferation, quiescence, differentiation or apoptosis. While the choices among these states can be influenced by proto-oncogene expression, how these disparate outcomes are achieved remains poorly understood. To address these issues, we have generated rodent fibroblast cell lines that harbor a human c-myc gene under the control of a tetracycline-regulated promoter. When Myc-induced cells are deprived of serum growth factors, they rapidly become apoptotic with the onset of apoptosis preceded by a large, transient increase in cdk2 kinase activity that is associated with the induction of cdc25A phosphatase and the later accumulation of p27Kip1 kinase inhibitor. Surprisingly, serum starvation in the absence of myc overexpression, (which leads to quiescence instead of apoptosis) also causes a marked transient elevation in cdk2 kinase activity, an induction of cdc25A and a delayed increase in p27Kip1. Transient elevations in cdk2 kinase activity and cdc25A abundance are required for cell cycle progression, but it is evident that these changes also precede entry to either apoptosis or quiescence in serum-starved cells. These findings suggest that the pathways to both quiescence and apoptosis share regulatory machinery with cell cycle control mechanisms. In addition, the abundance of Myc protein can be critical in the choices among these cellular states.
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PMID:Quiescence versus apoptosis: Myc abundance determines pathway of exit from the cell cycle. 979 26

Confluent 3T3-L1 preadipocytes differentiate to adipocytes in the presence of insulin, dexamethasone, and isobutylmethylxanthine (IDI). A transient increase of DNA synthesis is induced in 3T3-L1 cells 18 h after addition of IDI, followed by an arrest in the G1 phase of the cell cycle. Growth arrested cells express the proto-oncogene c-myc and the gene for the CCAAT/enhancer binding protein (C/EBPalpha) between day 2 and 5. While c-Myc is strongly implicated in cell proliferation, C/EBPalpha: is a differentiation-specific transcription factor with antiproliferative activity. Here we have characterized the cell cycle arrest in differentiating 3T3-L1 cells. Arrested cells express the Cdk inhibitors p21 and p27, but, at the same time, show hyperphosphorylation of Rb and expression of the E2F-regulated thymidine kinase gene. The addition of new serum to arrested cells resulted in cyclin A expression and Cdk2 activity, but not in DNA synthesis. Simian virus 40 large tumor antigen (LTAg) is a potent mitogen. The mutant LTAg-K1, deficient in binding of pocket proteins and unable to induce DNA synthesis in serum-starved 3T3-L1 cells, efficiently induced DNA synthesis in differentiating 3T3-L1 cells. This indicates that pocket proteins are probably not involved in the control of the cell cycle arrest during 3T3-L1 cell differentiation. Our data suggest that the differentiation-specific cell cycle block in 3T3-L1 cells is resistant to high levels of c-Myc, inactivation of pocket proteins, upregulation of cyclin A levels, and Cdk2 activation, but can be abolished by a function of LTAg that is independent of binding to pocket proteins.
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PMID:Analysis of cell cycle arrest in adipocyte differentiation. 992 2

B-myb is a highly conserved member of the myb proto-oncogene family that encodes a ubiquitously expressed 110-kDa sequence-specific DNA-binding protein. Transactivation of Myb-inducible promoters by B-Myb is repressed by a regulatory domain located at the C-terminus of the protein. Cyclin A/Cdk2-mediated phosphorylation apparently releases the negative constraint and triggers B-Myb transactivation potential. Two-dimensional tryptic phosphopeptide analysis indicated that the majority of the sites phosphorylated in vivo are targeted in vitro by cyclin A/Cdk2. Six sites in B-Myb fulfil the requirements for recognition by Cdk2. Using point mutation of the phosphorylation sites to nonphosphorylatable amino acids, we show that five of these sites are targets for Cdk2 in vivo. Mutation of one of these residues (T524) to alanine diminished the ability of B-Myb to promote transcription of a reporter gene, suggesting that phosphorylation of B-Myb at this site is important for the regulation of its activity by cyclin A/Cdk2.
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PMID:Identification of cyclin A/Cdk2 phosphorylation sites in B-Myb. 1009 72

c-myc is a cellular proto-oncogene associated with a variety of human cancers and is strongly implicated in the control of cellular proliferation, programmed cell death, and differentiation. We have previously reported the first isolation of a c-myc-null cell line. Loss of c-Myc causes a profound growth defect manifested by the lengthening of both the G1 and G2 phases of the cell cycle. To gain a clearer understanding of the role of c-Myc in cellular proliferation, we have performed a comprehensive analysis of the components that regulate cell cycle progression. The largest defect observed in c-myc-/- cells is a 12-fold reduction in the activity of cyclin D1-Cdk4 and -Cdk6 complexes during the G0-to-S transition. Downstream events, such as activation of cyclin E-Cdk2 and cyclin A-Cdk2 complexes, are delayed and reduced in magnitude. However, it is clear that c-Myc affects the cell cycle at multiple independent points, because restoration of the Cdk4 and -6 defect does not significantly increase growth rate. In exponentially cycling cells the absence of c-Myc reduces coordinately the activities of all cyclin-cyclin-dependent kinase complexes. An analysis of cyclin-dependent kinase complex regulators revealed increased expression of p27(KIP1) and decreased expression of Cdk7 in c-myc-/- cells. We propose that c-Myc functions as a crucial link in the coordinate adjustment of growth rate to environmental conditions.
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PMID:c-Myc regulates cyclin D-Cdk4 and -Cdk6 activity but affects cell cycle progression at multiple independent points. 1037 16

The INK4a/ARF locus on human chromosome 9p resides at the nexus of two critical cell cycle regulatory pathways, the p53 pathway and the retinoblastoma (pRb) gene pathway. Through the use of shared coding regions and alternative reading frames two distinct proteins are produced: INK4a is a cyclin-dependent kinase inhibitor whereas ARF binds the MDM2 proto-oncogene and stabilizes p53. We have examined the expression patterns of the INK4a/ARF locus at the RNA level in normal human and murine tissues to determine if these genes are coordinately regulated. We found that both INK4a and ARF were expressed in most tissues at low levels detectable only by RT-PCR. The pancreas was an exception in that it expressed no detectable ARF mRNA but expressed high levels of INK4a mRNA. Furthermore, human pancreas expressed an additional previously unrecognized splice variant of INK4a, termed p12, through the use of an alternative splice donor site within intron 1. The p12 transcript produced a 12 kD protein composed of INK4a exon 1alpha and a novel intron-derived C-terminus. This novel protein did not interact with cdk4 but was capable of suppressing growth in a pRb-independent manner. The implications of the capacity of the INK4a/ARF locus to encode a third transcript, and for pancreatic cancer, in which the INK4a/ARF locus is nearly always altered, are considered.
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PMID:Tissue-specific alternative splicing in the human INK4a/ARF cell cycle regulatory locus. 1044 44

A novel, brain-specific cDNA, denoted CROC-4, was cloned from human brain by a contingent replication of cDNA procedure capable of detecting transcriptional activators of the human c-fos proto-oncogene promoter. CROC-4 encoded an 18-kDa serine/threonine-rich polypeptide containing a P-loop motif and an SH3-binding region with phosphorylation sites for a variety of protein kinases (cdc2, CDK2, MAPK, CDK5, protein kinase C, Ca(2+)/calmodulin protein kinase 2, casein kinase 2) involved in cell proliferation and differentiation. Immunohistochemistry revealed that during early development, expression was associated with proliferating and migrating cells throughout the rodent brain, initially appearing in the proliferative ventricular zones. During late development and in adult human brain, CROC-4 was expressed in diverse brain regions including the thalamus, subthalamic nucleus, corpus callosum, substantia nigra, caudate nucleus, amygdala, and hippocampus. The association of CROC-4 expression with proliferating regions of developing brain and retention in regions of the adult brain, as well as the punctate nuclear location, suggest that CROC-4 participates in brain-specific c-fos signaling pathways involved in cellular remodeling of brain architecture.
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PMID:CROC-4: a novel brain specific transcriptional activator of c-fos expressed from proliferation through to maturation of multiple neuronal cell types. 1099 46

The c-myc proto-oncogene encodes a transcription factor that participates in the regulation of cellular proliferation, differentiation, and apoptosis. Ectopic overexpression of c-Myc has been shown to sensitize cells to apoptosis. We report here that cells lacking c-Myc activity due to disruption of the c-myc gene by targeted homologous recombination are defective in DNA damage-initiated apoptosis in the G(2) phase of the cell cycle. The downstream effector of c-Myc is cyclin A, whose ectopic expression in c-myc(-/-) cells rescues the apoptosis defect. The kinetics of the G(2) response indicate that the induction of cyclin A and the concomitant activation of Cdk2 represent an early step during commitment to apoptosis. In contrast, expression of cyclins E and D1 does not rescue the apoptosis defect, and apoptotic processes in G(1) phase are not affected in c-myc(-/-) cells. These observations link DNA damage-induced apoptosis with cell cycle progression and implicate c-Myc in the functioning of a subset of these pathways.
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PMID:c-Myc is necessary for DNA damage-induced apoptosis in the G(2) phase of the cell cycle. 1143 50

The c-Mos proto-oncogene product plays an essential role during meiotic divisions in vertebrate eggs. In Xenopus, it is required for progression of oocyte maturation and meiotic arrest of unfertilized eggs. Its degradation after fertilization is essential to early embryogenesis. In this study we investigated the mechanisms involved in c-Mos degradation. We present in vivo evidence for ubiquitin-dependent degradation of c-Mos in activated eggs. We found that c-Mos degradation is not directly dependent on the anaphase-promoting factor activator Fizzy/cdc20 but requires cyclin degradation. We demonstrate that cyclin B/cdc2 controls in vivo c-Mos phosphorylation and stabilization. Moreover, we show that cyclin B/cdc2 is capable of directly phosphorylating c-Mos in vitro, inducing a similar mobility shift to the one observed in vivo. Tryptic phosphopeptide analysis revealed a practically identical in vivo and in vitro phosphopeptide map and allowed identification of serine-3 as the largely preferential phosphorylation site as previously described (Freeman et al., 1992). Altogether, these results demonstrate that, in vivo, stability of c-Mos is directly regulated by cyclin B/cdc2 kinase activity.
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PMID:Cyclin B/cdc2 induces c-Mos stability by direct phosphorylation in Xenopus oocytes. 1155 6

The proto-oncogene ErbB2 is known to be amplified and to play an important role in the development of about one-third of human breast cancers. Phosphatidylinositol 3-kinase (PI3K), which is often activated in ErbB2-overexpressing breast cancer cells, is known to regulate cell proliferation and cell survival. Selective inhibitors of the PI3K pathway were used to assess the relevance of PI3K signaling in the anchorage-independent growth of a series of human mammary carcinoma cell lines. Wortmannin, LY294002, and rapamycin at concentrations that did not affect MAPK phosphorylation but substantially inhibited PI3K, Akt, and p70(S6K) significantly suppressed the soft agar growth of tumor cell lines that overexpress ErbB2 but not the growth of tumor lines with low ErbB2 expression. A similar growth inhibition of ErbB2-overexpressing carcinoma lines was observed when a dominant negative p85(PI3K) mutant was introduced into these cells. Forced expression of ErbB2 in breast cancer lines originally expressing low ErbB2 levels augmented receptor expression and sensitized those lines to LY294002- and rapamycin-mediated inhibition of colony formation. Furthermore, treatment with LY294002 resulted in the selective increase of cyclin-dependent kinase inhibitors p21(Cip1) or p27(Kip1) and suppression of cyclin E-associated Cdk2 kinase activity in ErbB2-overexpressing lines, which may account for their hypersensitivity toward inhibitors of the PI3K pathway in anchorage-independent growth. Our results indicate that the PI3K/Akt/p70(S6K) pathway plays an enhanced role in the anchorage-independent growth of ErbB2-overexpressing breast cancer cells, therefore providing a molecular basis for the selective targeting of this signaling pathway in the treatment of ErbB2-related human breast malignancies.
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PMID:ErbB2-overexpressing human mammary carcinoma cells display an increased requirement for the phosphatidylinositol 3-kinase signaling pathway in anchorage-independent growth. 1170 27


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