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

The product of the retinoblastoma tumor-suppressor gene (pRB), a nuclear phosphoprotein that regulates transcription factors such as E2F, is involved in cell cycle control and differentiation. Its activity is regulated by phosphorylation; the underphosphorylated form inhibits transcription whereas the highly phosphorylated form is inactive. Cyclin D1 and its associated kinase (CDK 4/6) phosphorylate pRB in vitro, and therefore are thought to contribute to the regulation of pRB function. To examine the effect of cyclin D1 overexpression on pRB in primary tumor tissue, we studied pRB expression in low-grade B-cell neoplasms, with particular regard to mantle cell lymphoma, which is characterized by cyclin D1 (bcl-1) overexpression. pRB expression was studied by immunostaining with a well-characterized anti-pRB antibody; the phosphorylation status of pRB was examined by immunoblots; and the functional binding capacity of pRB was examined by in vitro binding to adenovirus E1A protein. We studied 3 reactive lymph nodes, 28 low grade B-cell lymphomas, 4 cases of hairy cell leukemia (HCL) and 3 plasmacytomas. Reactive lymph nodes showed intense pRB staining of germinal centers, with strongest (2+) staining in the large cells (centroblasts) of the proliferating (dark) zone and weak or no staining of small lymphocytes, including those of the mantle zone. In B-chronic lymphocytic leukemia (B-CLL) (4 cases), follicular lymphoma (3 cases) and mucosa-associated (MALT) lymphoma (3 cases) strong (2+) pRB staining was limited to centroblasts in reactive and neoplastic follicles and occasional proliferation centers, with only faint staining of small lymphoid cells. In contrast, 15 of 16 cases of mantle cell lymphoma showed strong (1-2+) staining of most cells; one blastoid mantle cell lymphoma showed only faint pRB staining. All cases of (HCL) and plasmacytoma showed strong pRB staining. Although most lymphomas with strong pRB expression were cyclin D1(+), three cyclin D1(+) cases showed only weak pRB expression (1 B-CLL, 1 blastoid mantle cell, 1 unclassifiable low grade B-cell lymphoma). Conversely, of the 4 pRB(+) HCLs and 3 pRB(+) plasmacytomas, only 1 of each was cyclin D1(+). pRB appeared to exist primarily in the underphosphorylated (fastest migrating) form on Western blot, despite the fact that cyclin D1 was complexed to CDK4, a form in which it normally phosphorylates pRB. In addition, pRB appeared to be unmutated, because it bound normally to the adenovirus E1A protein and showed nuclear localization by immunostaining. We conclude that most cases of mantle cell lymphoma, HCL, and plasmacytoma show high levels of pRB in contrast to follicle center lymphoma and small lymphocytic lymphoma; however, pRB expression does not appear to be consistently related to cyclin D1 overexpression. The pRB appears to be unmutated and underphosphorylated, and therefore should be in its active form. Our data from primary lymphoma tissue suggests that overexpression of cyclin D1, whereas tumorigenic, does not lead to pRB loss or hyperphosporylation. Thus, the mechanism by which cyclin D1 contributes to tumorigenesis and the significance of the restricted expression of pRB in low-grade lymphoid neoplasms remain to be determined.
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PMID:Expression of the retinoblastoma protein in low-grade B-cell lymphoma: relationship to cyclin D1. 870 83

The CDKN2A gene located on chromosome region 9p21 encodes the cyclin-dependent kinase-4 inhibitor p16/INK4A, a negative cell cycle regulator. We analyzed p16/INK4A expression in different types of non-Hodgkin's lymphoma to determine whether the absence of this protein is involved in lymphomagenesis, while also trying to characterize the genetic events underlying this p16/INK4A loss. To this end, we investigated the levels of p16/INK4A protein using immunohistochemical techniques in 153 cases of non-Hodgkin's lymphoma, using as reference the levels found in reactive lymphoid tissue. The existence of gene mutation, CpG island methylation, and allelic loss were investigated in a subset of 26 cases, using single-strand conformational polymorphism and direct sequencing, Southern Blot, polymerase chain reaction, and microsatellite analysis, respectively. Loss of p16/INK4A expression was detected in 41 of the 112 non-Hodgkin's lymphomas studied (37%), all of which corresponded to high-grade tumors. This loss of p16/INK4A was found more frequently in cases showing tumor progression from mucosa-associated lymphoid tissue low-grade lymphomas (31 of 37) or follicular lymphomas (4 of 4) into diffuse large B-cell lymphomas. Analysis of the status of the p16/INK4A gene showed different genetic alterations (methylation of the 5'-CpG island of the p16/INK4A gene, 6 of 23 cases; allelic loss at 9p21, 3 of 16 cases; and nonsense mutation, 1 of 26 cases). In all cases, these events were associated with loss of the p16/INK4A protein. No case that preserved protein expression contained any genetic change. Our results demonstrate that p16/INK4A loss of expression contributes to tumor progression in lymphomas. The most frequent genetic alterations found were 5'-CpG island methylation and allelic loss.
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PMID:Loss of p16/INK4A protein expression in non-Hodgkin's lymphomas is a frequent finding associated with tumor progression. 973 37

Mantle cell lymphoma (MCL) is an aggressive neoplasm characterized by the deregulated expression of cyclin D1 by t(11;14). The molecular mechanisms responsible for MCL's clinical behavior remain unclear. The authors have investigated the expression of p53, E2F-1, and the CDK inhibitors p27 and p21 in 110 MCLs, relating their expression to proliferative activity (Ki-67). For comparison, they have similarly analyzed low-grade (12 MALT, 16 CLL/SLL) and high-grade (19 DLCL) lymphomas. p53 was detected more frequently in large-cell MCL (l-MCL; 5 of 7) than in classical MCL (s-MCL; 13 of 103) and DLCL (8 of 19). In MCL and DLCL, the percentage of E2F-1+ nuclei was high, correlating with high Ki-67 expression. Most MCLs (91 of 112) and DLCLs (12 of 19) showed a loss of p27; MALT and CLL/SLL, however, were p27 positive. Reverse transcription-polymerase chain reaction and in vitro protein degradation assays demonstrated that MCLs have normal p27 mRNA expression but increased p27 protein degradation activity via the proteasome pathway. Correlation of MCL p53 and p27 expression with clinical data showed an association between reduced overall survival rates and the overexpression of p53 (P =.001), the loss of p27 (P =. 002), or both. Loss of p27 identified patients with a worse clinical outcome among p53 negative cases (P =.002). These findings demonstrated that MCL has a distinct cell cycle protein expression similar to that of high-grade lymphoma. The loss of p27 and the overexpression of p53 in MCL are prognostic markers that identify patients at high risk. The demonstration that low levels of p27 in MCL result from enhanced proteasome-mediated degradation should encourage additional clinical trials. (Blood. 2000;95:619-626) (Blood. 2000;95:619-626)
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PMID:Increased proteasome degradation of cyclin-dependent kinase inhibitor p27 is associated with a decreased overall survival in mantle cell lymphoma. 1062 71