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Adapting to changes in nutrient availability and environmental conditions is a fundamental property of cells. This adaptation requires a multi-directional coordination between metabolism, growth, and the cell cycle regulators (consisting of the family of cyclin-dependent kinases (CDKs), their regulatory subunits known as cyclins, CDK inhibitors, the retinoblastoma family members, and the E2F transcription factors). Deciphering the mechanisms accountable for this coordination is crucial for understanding various patho-physiological processes. While it is well established that metabolism and growth affect cell division, this review will focus on recent observations that demonstrate how cell cycle regulators coordinate metabolism, cell cycle progression, and growth. We will discuss how the cell cycle regulators directly regulate metabolic enzymes and pathways and summarize their involvement in the endolysosomal pathway and in the functions and dynamics of mitochondria.

To determine if p53 abnormalities could be involved in the pathogenesis of T- or natural killer (NK)-cell lymphomas, we investigated 51 cases of these lymphomas for the expression of p53 and its relationship with p53 gene mutations, the expression of the p21 protein as well as the proliferative and apoptotic indices. Overexpression of p53 was found in 19 cases (37%), whereas mutations of the p53 gene were observed in only 5 of 28 tested cases. The analysis of immunohistochemical data showed some entity-related phenotypic profiles. Anaplastic large cell lymphomas showed a frequent overexpression of p53 (7/8 cases) and p21 (6/8 cases) proteins and rare p53 mutations (1/7 cases), suggesting accumulation of a functional wild type p53 protein able to induce p21 expression. Nodal peripheral T-cell lymphomas unspecified showed relatively frequent overexpression of p53 protein (5/7 cases), infrequent p21 expression (2/7 cases), and rare p53 gene mutations (1/6 cases). In angioimmunoblastic lymphomas, the common phenotype was p53-/p21- (15/17 cases), with only a few scattered p53-positive cells, which, on the basis of double staining results, were mostly Epstein-Barr virus-infected B cells. A p53 gene mutation was only found in 1 case (1/8 cases) of angioimmunoblastic lymphoma, which showed cytologic tumor progression. Mycosis fungoides showed p53 overexpression in 2 of 4 cases, including 1 case with p53 gene mutation and features of cytologic tumor progression. Nasal NK/T lymphomas showed p53 overexpression in 2 of 5 cases, 1 of which had a p53 gene mutation. Finally, all lymphoblastic T-cell lymphomas (5 cases) and gammadelta hepatosplenic T-cell lymphomas (3 cases) were negative for expression of p53 and p21 proteins. We conclude that p53 protein overexpression is a common finding in some entities of T- and T/NK-cell lymphomas, whereas a p53 gene mutation is a rare, sporadic, and rather late event associated with tumor progression in some instances. The p53/p21 expression pattern appears to be variable in T- and T/NK-cell lymphoma entities, reinforcing the concept of distinct, entity-related mechanisms of pathogenesis in these tumors. Hum Pathol

Overexpression of a constitutively active mutant of the mitogen-activated protein kinase kinase MEK1 (caMEK1) in epithelial Madin-Darby canine kidney (MDCK)-C7 cells disrupts morphogenesis, induces an invasive phenotype, and is associated with a reduced rate of cell proliferation. The role of cell-cell adhesion molecules and cell cycle proteins in these processes, however, has not been investigated. We now report loss of E-cadherin expression as well as a marked reduction of beta- and alpha-catenin expression in transdifferentiated MDCK-C7 cells stably expressing caMEK1 (C7caMEK1) compared with epithelial mock-transfected MDCK-C7 (C7Mock1) cells. At least part of the remaining alpha-catenin was coimmunoprecipitated with beta-catenin, whereas no E-cadherin was detected in beta-catenin immunoprecipitates. In both cell types, the proteasome-specific protease inhibitors N-acetyl-Leu-Leu-norleucinal (ALLN) and lactacystin led to a time-dependent accumulation of beta-catenin, including the appearance of high-molecular-weight beta-catenin species. Quiescent as well as serum-stimulated C7caMEK1 cells showed a higher cyclin D expression than epithelial C7Mock1 cells. The MEK inhibitor U-0126 inhibited extracellular signal-regulated kinase phosphorylation and cyclin D expression in C7caMEK1 cells and almost abolished their already reduced cell proliferation rate. We conclude that the transdifferentiated and invasive phenotype of C7caMEK1 cells is associated with a diminished expression of proteins involved in cell-cell adhesion. Although beta-catenin expression is reduced, C7caMEK1 cells show a higher expression of U-0126-sensitive cyclin D protein.

During spermatogenesis, germ cells execute two meiotic divisions, then withdraw from the cell cycle and initiate postmeiotic differentiation. We show that the gene roughex (rux) is a dose-dependent regulator of meiosis II during Drosophila spermatogenesis. rux mutant germ cells execute the two meiotic divisions, but then undergo an additional M phase resembling an extra meiosis II. Conversely, germ cells with excess rux function fail to undergo meiosis II. rux does not appear to act directly at meiosis II. Rather, rux appears to act through cyclin A during premeiotic G2 to regulate meiosis II. We propose that cyclin A-cdc2 kinase at the G2 to M transition of meiosis I activates a target necessary for meiosis II, thereby coupling the two meiotic divisions.

Ataxia telangiectasia is a hereditary pleiomorphic syndrome caused by loss of Atm, a phosphoprotein involved in multiple signaling pathways. Here, we propose a novel role for atm in cultured epithelial cells, namely the regulation of cell growth by contact inhibition. We show that atm is upregulated in epithelial cells reaching confluence. Conditional expression of the PI 3-Kinase domain of atm in non-confluent Tac-2 epithelial cells increases the expression of the anti-proliferative gene Tis-21 and downregulates key cell cycle regulator genes, such as cyclins A, B1, B2, E and E2. Finally, we demonstrate that upregulation of atm, and thus Tis-21, in confluent Tac-2 cells can be inhibited by an E-cadherin antibody blocking specifically homophilic E-cadherin interactions between adjacent cell surfaces. Altogether, these results suggest that atm could participate in a molecular pathway linking extracellular signalling to cell cycle control and may help further clarify the role of Atm in epithelial cell biology and carcinogenesis.

A study of laryngeal carcinomas was performed in order to analyze (a) the expression of p53/p21, cyclin D1/cyclin E, p21/p27 (b) the relation of normal and abnormal protein expression, with the proliferation status, as determined by the expression of Ki67 and PCNA and (c) the correlation of our findings with prognosis. We performed a retrospective analysis of 57 cases of squamous cell carcinomas of the larynx. We applied monoclonal antibodies against p53, p21, p27, cyclin D1, cyclin E, Ki67 and PCNA, using streptavidin-biotin method. Analysis of the p53/p21 proteins, revealed abnormalities in 25/37 cases (67.57%), while 12/37 (32.43%) cases displayed normal phenotype (p53-/p21-). Analysis of cyclins revealed overexpression in 17/48 cases (35.42), while the majority 31/48(64.58%) displayed normal phenotype (cyclin D1-/cyclin E-). Concerning CDKIs expression, the majority 30/50(60%) presented high levels of both inhibitors (p21+/p27+). Cases with simultaneous overexpression of CDKIs demonstrated significantly higher levels of Ki67 protein (p = 0.05). Analysis of p53/p21, cyclin D/cyclin E, p21/p27 patterns showed no association between the presence of one or two alterations and prognosis. In conclusion, we demonstrated that p53 tumor suppressor pathway is frequently disrupted in laryngeal cancer. Furthermore, levels of CDKIs, although they act as cell cycle activity blockers, are not reliable markers for the estimation of laryngeal neoplastic cells growth fraction. J Exp Clin Cancer Res

BACKGROUND: Cell cycle proteins are important markers in predicting tumor behavior in urothelial carcinoma of the bladder. The objectives of this study were 1) to determine the expression levels of some of those markers in a series of patients with bladder carcinoma, 2) to define their value in distinguishing T1a (minimally invasive) from T1b (invasive) tumors, and 3) to evaluate their use as predictive factors in the progression of T1a and T1b tumors. METHODS: Tumor specimens from 101 patients were included (22 Ta specimens, 34 T1a specimens, 15 T1b specimens, and 30 T2 specimens). A tissue microarray from the 101 paraffin embedded tissue blocks was constructed. Immunohistochemistry for p16, p27, p21, p53, cyclin D1, and Ki-67 were performed. To evaluate T1a and T1b tumor progression, clinical and follow-up data were available for all 49 patients. RESULTS: Cyclin D1 and p27 were the only markers that showed a significant association with tumor stage and tumor grade (cyclin D1: P = 0.002 and P > 0.00, respectively; p27: P = 0.024 and P = 0.031, respectively). The results indicated that a combination of p21 (odds ratio, 5.7; 95% confidence interval [95% CI], 1.3-24.8 [P = 0.022]) and p16 (odds ratio, 3.7; 95% CI, 0.8-16.5 [P = 0.081]) may have potential use in distinguishing T1b tumors from T1a tumors. Finally, none of the markers examined were found to have predictive value for T1a and T1b tumor progression. CONCLUSIONS: The expression of cyclin D1 and p27 was associated with the most important prognostic factors (tumor stage and grade). The combination of p21 and p16 may have value in distinguishing T1b tumors from T1a tumors, although this finding must be evaluated in much larger series. Finally, none of the markers studied appeared to have predictive value for disease progression in patients with T1a and T1b urothelial bladder tumors.

Tumourigenesis is the result of cell cycle disorganisation, leading to an uncontrolled cellular proliferation. Specific cellular processes-mechanisms that control cell cycle progression and checkpoint traversation through the intermitotic phases are deregulated. Normally, these events are highly conserved due to the existence of conservatory mechanisms and molecules such as cell cycle genes and their products: cyclins, cyclin dependent kinases (Cdks), Cdk inhibitors (CKI) and extra cellular factors (i.e. growth factors). Revolutionary techniques using laser cytometry and commercial software are available to quantify and evaluate cell cycle processes and cellular growth. S-phase fraction measurements, including ploidy values, using histograms and estimation of indices such as the mitotic index and tumour-doubling time indices, provide adequate information to the clinician to evaluate tumour aggressiveness, prognosis and the strategies for radiotherapy and chemotherapy in experimental researches. Int J Clin Pract

BACKGROUND: Apoptosis may be an important mechanism of hepatocyte death in chronic viral liver disease. METHODS: We studied apoptosis in liver biopsies from 30 patients with chronic viral hepatitis and 8 patients with viral cirrhosis by the TUNEL method. 12 cases of non-alcoholic steatohepatitis and 12 cases of primary biliary cirrhosis were used as non-viral disease controls. Immunohistochemical expression of p53, p21/waf1, bcl-2 and mdm-2 proteins was also studied in the same patients. RESULTS: A statistically significant increase of apoptotic liver cells was found in severe chronic viral hepatitis (5.3 +/- 0.3%), cirrhosis (3.4 +/- 0.5%) and PBC (4.4 +/- 0.4%) cases compared to patients with non-alcoholic steatohepatitis (0.8 +/- 0.3%). The expression of p53 protein was increased in the cases of viral cirrhosis and in chronic severe viral hepatitis whereas in the cases of chronic mild hepatitis, PBC and non-alcoholic steatohepatitis we found no expression of p53. P21/waf1 expression was increased in severe chronic hepatitis, cirrhosis and PBC cases compared to mild hepatitis and non-alcoholic steatohepatitis cases. However no induction of mdm-2 was observed in the subgroups of chronic liver disease. Bcl-2 was expressed only in epithelium of bile ducts and mononuclear cells of the portal tracts and liver lobules. A weaker Bcl-2 expression was noted in the epithelium of bile ducts of 7/12 PBC cases. CONCLUSION: Our results provide evidence of increased apoptosis in severe chronic viral liver disease, suggesting that apoptotic cell death might be involved in the pathogenesis of hepatocellular damage of viral hepatitis and cirrhosis. Furthermore we analysed part of the apoptotic pathways implicated in the above process and found an increased expression of p21/waf1, probably p53 mediated, without overexpression of the apoptosis inhibiting bcl-2 and mdm-2 proteins. By contrast p21/waf1 overexpression in PBC seems to be propagated by a p53 independent mechanism. Apoptosis

Growing incompetent mouse oocytes released from follicular cells are unable to spontaneously resume meiosis in vitro. To identify the reasons for meiotic incompetence in these cells, the levels of p34cdc2/cyclin B kinase and p42MAPK between incompetent and competent oocytes were compared. p34cdc2 was present at very low levels in incompetent oocytes and accumulated abruptly at the time of meiotic competence acquisition. By contrast, cyclin B and p42MAPK were present at similar concentrations in both types of oocytes. Okadaic acid induced centrosome phosphorylation and meiotic reinitiation in incompetent oocytes, without inducing an increase in p34cdc2 concentration. However, the p34cdc2 present in incompetent oocytes was activated and all events following germinal vesicle breakdown were induced up to the formation of a metaphase I spindle including p42MAPK activation, sustained increase in p34cdc2 kinase activity, and translational activation of a dormant mRNA. We suggest that a threshold level of p34cdc2 has to be reached for meiotic reinitiation to be spontaneously triggered: competence is restricted at a point preceding MPF activation. Whatever the mechanism involved in this restriction point, i.e., subthreshold concentration of p34cdc2 and/or lack of an activator or presence of an inhibitor, it is bypassed by okadaic acid. Downstream of this point meiosis progresses up to metaphase 1, even though p34cdc2 concentration remains low.