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)

The melanocyte is a neural crest-derived cell that localizes in humans to several organs including the epidermis, eye, inner ear and leptomeninges. In the skin, melanocytes synthesize and transfer melanin pigments to surrounding keratinocytes, leading to skin pigmentation and protection against solar exposure. We have investigated the process of replicative senescence and accompanying irreversible cell cycle arrest, in melanocytes in culture. As was found in other cell types, progressive telomere shortening appears to trigger replicative senescence in normal melanocytes. In addition, senescence is associated with increased binding of the cyclin-dependent kinase inhibitor (CDK-I) p16(INK4a) to CDK4, down-regulation of cyclin E protein levels (and consequent loss of cyclin E/CDK2 activity), underphosphorylation of the retinoblastoma protein RB and subsequent increased levels of E2F4-RB repressive complexes. In contrast to fibroblasts, however, the CDK-Is p21(Waf-1) and p27(Kip-1) are also down-regulated. These changes appear to be important for replicative senescence because they do not occur in melanocytes that overexpress the catalytic subunit of the enzyme telomerase (hTERT), or in melanomas, which are tumors that originate from melanocytes or melanoblasts. In contrast to unmodified melanocytes, hTERT overexpressing (telomerized) melanocytes displayed telomerase activity, stable telomere lengths and an extended replicative life span. However, telomerized melanocytes show changes in cell cycle regulatory proteins, including increased levels of cyclin E, p21(Waf-1) and p27(Kip-1). Cyclin E, p21(Waf-1) and p27(Kip-1) are also elevated in many primary melanomas, whereas p16(INK4a) is mutated or deleted in many invasive and metastatic melanomas. Thus, the molecular mechanisms leading to melanocyte senescence and transformation differ significantly from fibroblasts. This suggests that different cell types may use different strategies to halt the cell cycle in response to telomere attrition and thus prevent replicative immortality.
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PMID:The human melanocyte: a model system to study the complexity of cellular aging and transformation in non-fibroblastic cells. 1160 3

With increasing frequency during serial passage in culture, primary human keratinocytes express p16(INK4A) (p16) and undergo senescence arrest. Keratinocytes engineered to express hTERT maintain long telomeres but typically are not immortalized unless, by mutation or other heritable event, they avoid or greatly reduce p16 expression. We have confirmed that keratinocytes undergo p16-related senescence during growth in culture, whether in the fibroblast feeder cell system or in the specialized K-sfm medium formulation, and that this mechanism can act as a barrier to immortalization following hTERT expression. We have characterized the p16-related arrest mechanism more precisely by interfering specifically with several regulators of cell cycle control. Epidermal, oral mucosal, corneal limbal, and conjunctival keratinocytes were transduced to express a p16-insensitive mutant cdk4 (cdk4(R24C)), to abolish p16 control, and/or a dominant negative mutant p53 (p53DD), to abolish p53 function. Expression of either cdk4(R24C) or p53DD alone had little effect on life span, but expression of both permitted cells to divide 25 to 43 population doublings (PD) beyond their normal limit. Keratinocytes from a p16(+/-) individual transduced to express p53DD alone displayed a 31-PD life span extension associated with selective growth of variants that had lost the wild-type p16 allele. Cells in which both p53 and p16 were nonfunctional divided rapidly during their extended life span but experienced telomere erosion and ultimately ceased growth with very short telomeres. Expression of hTERT in these cells immortalized them. Keratinocytes engineered to express cdk4(R24C) and hTERT but not p53DD did not exhibit an extended life span. Rare immortal variants exhibiting p53 pathway defects arose from them, however, indicating that the p53-dependent component of keratinocyte senescence is telomere independent. Mutational loss of p16 and p53 has been found to be a frequent early event in the development of squamous cell carcinoma. Our results suggest that such mutations endow keratinocytes with extended replicative potential which may serve to increase the probability of neoplastic progression.
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PMID:A two-stage, p16(INK4A)- and p53-dependent keratinocyte senescence mechanism that limits replicative potential independent of telomere status. 1207 43

Deregulation of the retinoblastoma (pRB) tumor suppressor pathway and telomerase activation have been identified as rate-limiting steps for immortalization of primary human epithelial cells. However, additional molecular aberrations including p53 inactivation, ras activation, and deregulation of protein phosphatase 2A activity are necessary for full transformation of immortalized epithelial cells. Genomic instability is observed in most human tumors and constitutes an important mechanism to allow emerging tumor cells to acquire additional mutations to efficiently overcome selection barriers during carcinogenic progression. In an attempt to model oral cancer in a human cell-based system, we analyzed normal oral epithelial keratinocytes with the pRB pathway dysregulated by loss of expression of the cyclin-dependent kinase (cdk) 4/cdk6 inhibitor p16(INK4A) and/or ectopic expression of cdk4 or expression of the human papillomavirus (HPV) type 16 E7 oncoprotein. Ectopic expression of cdk4 and HPV-16 E7 was equally efficient in extending the life span of normal oral keratinocytes, and each was able to cooperate with telomerase (hTERT) to immortalize these cells. HPV-16 E7/hTERT-immortalized normal oral keratinocytes showed centrosome abnormalities, whereas populations of cdk4/hTERT-immortalized cells or hTERT-immortalized cells that had lost expression of p16INK4A showed no such abnormalities. These results demonstrate that disruption of the p16INK4A/pRB checkpoint of epithelial cell immortalization does not necessarily lead to centrosome-associated genomic instability.
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PMID:Abrogation of the retinoblastoma tumor suppressor checkpoint during keratinocyte immortalization is not sufficient for induction of centrosome-mediated genomic instability. 1254 5

As telomeres play a role in protecting DNA, there is the possibility that telomerase activity is involved with cellular response to DNA-damaging agents. This study was designed to investigate the association between telomerase and the doxorubicin altered cell cycle in drug resistant gastric carcinoma cell lines. Three doxorubicin resistant gastric carcinoma cell lines and their parent cell lines (SNU-1, SNU-16 and SNU-620) were incubated with doxorubicin at the final concentration induced resistance and ten times final concentration for 24 h. Telomerase activity and hTERT mRNA expression were lowered by doxorubicin treatment in parent cell lines, but in drug resistant cell lines, telomerase activity and hTERT mRNA expression were not repressed by doxorubicin treatment. Bcl-2 protein expression, which is known to regulate telomerase activity, did not change in doxorubicin resistant cell lines but decreased in parent cell lines by doxorubicin treatment. Cell cycle analysis revealed that the parent cell lines had an increased fraction of cells in G2/M phase after doxorubicin treatment and doxorubicin resistant cell lines had maintained fractions in G0/G1 phase. Doxorubicin treatment did not alter cyclin B or cdc2 protein level, which is known as the essential component of G2/M transition. G2/M arrest in the parent cell lines was associated with an increase in inhibitory phosphorylation of Tyr15 on cdc2. In summary, the parent cell lines showed G2/M arrest and a reduction of telomerase activity after doxorubicin treatment. In contrast, reduced telomerase activity, Bcl-2 expression and G2/M arrest after doxorubicin treatment did not appear in resistant cell lines. Therefore, relative resistance to doxorubicin may be related to high levels of bcl-2 or intact cell cycle and consequently high telomerase activity.
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PMID:Telomerase activity, expression of Bcl-2 and cell cycle regulation in doxorubicin resistant gastric carcinoma cell lines. 1257 37

A therapeutic approach being investigated for a variety of pathologies is tissue regeneration using a patient's own cells. Such studies have been hampered due to the difficulty in growing epithelial cells for prolonged periods in culture. Replicative senescence due to short telomeres and p16 induced by culture stress work together to inhibit cell growth. Forced expression of telomerase (hTERT) can prevent replicative senescence, and expression of the cell cycle protein cdk4 can sequester p16, thereby immortalizing epithelial cells in culture. In the present study, we used this method to immortalize human bronchial epithelial cells (HBECs) to determine whether immortalized HBECs retain the ability to differentiate normally. HBECs were plated atop contracted collagen gels containing lung fibroblasts. This three-dimensional (3D) tissue model was cultured initially submerged, then raised to the air/liquid interface for up to 28 days. Normal differentiation was assessed by the presence of ciliated cells, goblet (mucin-producing) cells, and basal epithelial cells. Scanning electron microscopic observations revealed both ciliated and non-ciliated cells in these 3D tissues. Histological examination revealed the presence of mucin-producing cells, and immunohistochemistry using antibodies against p63 and keratin 14 showed the presence of basal cells. These results demonstrate that immortalized HBECs retain the capacity to differentiate into each of three cell types: basal, mucin-producing, and columnar ciliated epithelial cells. Such cells will be useful cellular reagents for research in aging, cancer progression, as well as normal bronchial epithelial differentiation and will help progress the use of engineered cells to enhance tissue regeneration.
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PMID:A three-dimensional model of differentiation of immortalized human bronchial epithelial cells. 1668 84

Expression of the human HIN-200 family member IFI 16 has been reported to suppress cell growth and contribute to the onset of cellular senescence. However the molecular events involved in this process have not been fully characterised. We fused IFI 16 to the estrogen receptor ligand-binding domain to establish an inducible model for studying the molecular events that cause these phenomena. In cells induced to express the ER-IFI 16 within the nucleus there was a decrease in cellular proliferation and concomitant growth arrest in the G1 phase of the cell cycle. Unlike previous reports, this did not appear to involve the p53-p21(WAF1/CIP1)-cdk2-pRb pathway. Following nuclear expression of ER-IFI 16 we noted senescence-like morphological changes and expression of senescence-associated beta-galactosidase in growth arrested cells. Importantly, we also found a marked reduction in telomerase activity in arrested cells compared to controls. Moreover, IFI 16 and hTERT co-localised within the nucleus and these two proteins physically interacted in vivo and in vitro. Together, these data suggest that IFI 16 may act as an endogenous regulator of telomerase activity and, through its interaction with hTERT, contributes to the inhibition of proliferation and induces a senescence-like state.
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PMID:Inducible activation of IFI 16 results in suppression of telomerase activity, growth suppression and induction of cellular senescence. 1988 68

The MYC and RAS oncogenes are frequently activated in cancer and, together, are sufficient to transform rodent cells. The basis for this cooperativity remains unclear. We found that although Ras interfered with Myc-induced apoptosis, Myc repressed Ras-induced senescence, together abrogating two main barriers of tumorigenesis. Inhibition of cellular senescence required phosphorylation of Myc at Ser-62 by cyclin E/cyclin-dependent kinase (Cdk) 2. Cdk2 interacted with Myc at promoters, where it affected Myc-dependent regulation of genes, including Bmi-1, p16, p21, and hTERT, which encode proteins known to control senescence. Repression of senescence by Myc was abrogated by the Cdk inhibitor p27Kip1, which is induced by antiproliferative signals like IFN-gamma or by pharmacological inhibitors of Cdk2 but not by inhibitors of other Cdks. In contrast, a phospho-mimicking Myc-S62D mutant was resistant to these manipulations. Inhibition of cyclin E/Cdk2 reversed the senescence-associated gene expression pattern imposed by Myc/cyclin E/Cdk2. This indicates a role of Cdk2 as a transcriptional cofactor and activator of the antisenescence function of Myc and provides mechanistic insight into the Myc-p27Kip1 antagonism. Finally, our findings highlight that pharmacological inhibition of Cdk2 activity is a potential therapeutical principle for cancer therapy, in particular for tumors with activated Myc or Ras.
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PMID:Phosphorylation by Cdk2 is required for Myc to repress Ras-induced senescence in cotransformation. 1996

Radiation-induced carcinogenesis is a major concern both for astronauts on long-term space missions and for cancer patients being treated with therapeutic radiation. Exposure to radiation induces oxidative stress and chronic inflammation, which are critical initiators and promoters of carcinogenesis. Many studies have demonstrated that non-steroidal anti-inflammatory drugs and antioxidants can reduce the risk of radiation-induced cancer. In this study, we found that a synthetic triterpenoid, CDDO-Me (bardoxolone methyl), was able to protect human colon epithelial cells (HCECs) against radiation-induced transformation. HCECs that were immortalized by ectopic expression of hTERT and cdk4 and exhibit trisomy for chromosome 7 (a non-random chromosome change that occurs in 37% of premalignant colon adenomas) can be transformed experimentally with one combined exposure to 2 Gy of protons at 1 GeV/nucleon followed 24 h later by 50 cGy of (56)Fe ions at 1 GeV/nucleon. Transformed cells showed an increase in proliferation rate and in both anchorage-dependent and independent colony formation ability. A spectrum of chromosome aberrations was observed in transformed cells, with 40% showing loss of 17p (e.g. loss of one copy of p53). Pretreatment of cells with pharmacological doses of CDDO-Me, which has been shown to induce antioxidative as well as anti-inflammatory responses, prevented the heavy-ion-induced increase in proliferation rate and anchorage-dependent and independent colony formation efficiencies. Taken together, these results demonstrate that experimentally immortalized human colon epithelial cells with a non-random chromosome 7 trisomy are valuable premalignant cellular reagents that can be used to study radiation-induced colorectal carcinogenesis. The utility of premalignant HCECs to test novel compounds such as CDDO-Me that can be used to protect against radiation-induced neoplastic transformation is also demonstrated.
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PMID:CDDO-Me protects against space radiation-induced transformation of human colon epithelial cells. 2068 96

Epithelial cell lines were established from the transition and peripheral zones of human prostate by transduction with cdk4 and hTERT. The properties of these lines were investigated using immunocytochemical markers, ability to generate anchorage-independent colonies and by spectral karyotyping (SKY). Cells were exposed to fractionated doses of gamma irradiation to investigate their ability to transform. Cell lines were established from the transition and peripheral zones of human prostate. The expression of CD133, CK5, CK14, CK18, p16, PSCA, p63 and c-myc varied between the lines from the two regions. The line derived from the peripheral zone exhibited properties of a tumour line. A similar pattern was observed in two separate transductions. It was thus unlikely to be an in vitro transformation event, which is very rarely observed with human cells in vitro, and thus more likely to be derived from the immortalisation of a quiescent tumour clone. Fractionated irradiation of the transition zone cell line resulted in forming of transformed colonies. The transformed and tumour line had marked chromosomal rearrangements as demonstrated by SKY analysis. Cell lines have been derived from different zones of human prostate for studies on radiation carcinogenesis. The unirradiated cell line derived from the peripheral zone exhibited chromosomal rearrangements similar to those observed in prostate carcinoma. The cell line derived from the transitional zone exhibited a near diploid karyotype and could be transformed following exposure to fractionated doses of gamma irradiation.
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PMID:Novel human prostate cell lines derived from the transition and peripheral zones of the prostate for carcinogenesis studies. 2110 66

Epithelial cell adhesion molecule (EpCAM) is overexpressed in a wide variety of human cancers including lung cancer, and its contribution to increased proliferation through upregulation of cell cycle accelerators such as cyclins A and E has been well established in breast and gastric cancers. Nevertheless, very little is known about its role in supporting the survival of cancer cells. In addition, the functional role of EpCAM in the pathogenesis of lung cancer remains to be explored. In this study, we show that RNAi-mediated knockdown of EpCAM suppresses proliferation and clonogenic growth of three EpCAM-expressing lung cancer cell lines (H3255, H358, and HCC827), but does not induce cell cycle arrest in any of these. In addition, EpCAM knockdown inhibits invasion in the highly invasive H358 but not in less invasive H3255 cells in a Transwell assay. Of note, the EpCAM knockdown induces massive apoptosis in the three cell lines as well as in another EpCAM-expressing lung cancer cell line, HCC2279, but to a much lesser extent in a cdk4/hTERT immortalized normal human bronchial epithelial cell line, HBEC4, suggesting that EpCAM could be a therapeutic target for lung cancer. Finally, EpCAM knockdown partially restores contact inhibition in HCC827, in association with p27(Kip1) upregulation. These results indicate that EpCAM could contribute substantially to the pathogenesis of lung cancer, especially cancer cell survival, and suggest that EpCAM targeted therapy for lung cancer may have potential.
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PMID:Pivotal role of epithelial cell adhesion molecule in the survival of lung cancer cells. 2153 18


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