The ubiquitin-proteasome pathway and its role in cancer
ABSTRACT Critical cellular processes are regulated, in part, by maintaining the appropriate intracellular levels of proteins. Whereas de novo protein synthesis is a comparatively slow process, proteins are rapidly degraded at a rate compatible with the control of cell cycle transitions and cell death induction. A major pathway for protein degradation is initiated by the addition of multiple 76-amino acid ubiquitin monomers via a three-step process of ubiquitin activation and substrate recognition. Polyubiquitination targets proteins for recognition and processing by the 26S proteasome, a cylindrical organelle that recognizes ubiquitinated proteins, degrades the proteins, and recycles ubiquitin. The critical roles played by ubiquitin-mediated protein turnover in cell cycle regulation makes this process a target for oncogenic mutations. Oncogenes of several common malignancies, for example colon and renal cell cancer, code for ubiquitin ligase components. Cervical oncogenesis by human papillomavirus is also mediated by alteration of ubiquitin ligase pathways. Protein degradation pathways are also targets for cancer therapy, as shown by the successful introduction of bortezomib, an inhibitor of the 26S proteasome. Further work in this area holds great promise toward our understanding and treatment of a wide range of cancers.
SourceAvailable from: Jaudah Al-Maghrabi[Show abstract] [Hide abstract]
ABSTRACT: Background Recent studies suggest that aberrations in cell cycle checkpoint controllers are a common feature in human malignancies and predict prognosis independent of stage. Objectives This study correlated two cell cycle regulators (p27 and p21) with clinical and pathological variables in colorectal cancer (CRC) patients to assess their role as prognostic factors. Patients and Methods A series of 65 CRC patients were analyzed for p27 and p21 expression in their tumors using immunohistochemistry. Results Forty-six percent of tumors showed positive nuclear p27 expression, whereas 72% of cases were completely p21 negative. There were no significant correlations between p27 and p21 expression and gender, age, lymph node involvement, stage, and grade. However, p27 (but not p21) expression revealed highly significant correlation with tumor location (p<0.01), depth of invasion (p<0.03), and lympho-vascular invasion (p<0.02). Tumors with high p27 expression showed a higher recurrence rate than tumors with no expression (p<0.03). In Kaplan–Meier survival analysis, there was a significant (p=0.046) difference in disease-free survival (DFS) between p27-positive and p27- negative tumors in favor of the latter. p21 did not show any predictive value of DFS (p<0.7). Neither p27 nor p21 did predict disease-specific survival (DSS) in Kaplan–Meier analysis, but DSS time was much shorter for p27-positive tumors. In multivariate (Cox) model, p27 lost its value as independent predictor of DFS, and none of the covariates were independent predictors of DSS. Conclusion p27 expression seems to be more powerful than p21 expression in providing useful prognostic information in CRC, particularly in predicting the patients at high risk for recurrent disease. Larger cohort and longer follow-up are needed to fully elucidate the value of p27 (and p21) as independent predictors of disease outcome.
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ABSTRACT: Benzo(a)pyrene (BaP) is a ubiquitously distributed environmental pollutant. BaP is a known carcinogen and can induce malignant transformation of rodent and human cells. Many evidences suggest that inhibitor of poly(ADP-ribose) glycohydrolase (PARG) is potent anticancer drug candidate. However, the effect of PARG on BaP carcinogenesis remains unclear. We explored this question in a PARG-deficient human bronchial epithelial cell line (shPARG cells) treated with various concentration of BaP for 15 weeks. Soft agar assay was used to examine BaP-induced cell malignancy of human bronchial epithelial cells and shPARG cells. Mechanistic investigations were used by 2D-DIGE and mass spectrometry. Western blot analysis and Double immunofluorescence detection were used to confirm some of the results obtained from DIGE experiments. We found that PARG silencing could dramatically inhibit BaP-induced cell malignancy of human bronchial epithelial cells in soft agar assay. Altered levels of expression induced by BaP were observed within shPARG cells for numerous proteins, including proteins required for cell mobility, stress response, DNA repair and cell proliferation pathways. Among these proteins, TCTP and Cofilin-1 involved in malignancy, were validated by western blot analysis and immunofluorescence assay. PARG inhibition contributed to down-regulation of TCTP and Cofilin-1. This is the first experimental demonstration of a link between PARG silencing and reduced cell migration after BaP exposure. We propose that PARG silencing might down-regulate TCTP and Cofilin-1 associated with metastasis in BaP carcinogenesis.
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ABSTRACT: Renal cell carcinoma (RCC) is the most common primary malignancy of the kidney and one of the most lethal genitourinary malignancies. Clear-cell renal cell carcinoma (ccRCC) has an extremely poor prognosis because of a high potential for tumor growth, vascular invasion, metastasis and recurrence. Unfortunately, the mechanism of RCC growth and metastasis is not well understood. In this report, we for the first time demonstrated ubiquitin protein ligase E3C (UBE3C) as a driving factor for RCC growth and metastasis. UBE3C expression was increased in ccRCC tissues compared with adjacent normal tissues. ccRCC patients with high UBE3C protein expression in tumors were associated with significantly worse postoperative survival. Knockdown of UBE3C expression in ACHN cells inhibited cell proliferation, migrations and invasiveness in vitro while overexpression of UBE3C in 786-O cells exerted the opposite effects. UBE3C up-regulated β-catenin protein levels and promoted β-catenin nuclear accumulation, leading to the activation of the Wnt/β-catenin signal pathway in RCC cells. Collectively, these observations suggest that UBE3C plays an important role in RCC development and progression, and UBE3C may be a novel target for prevention and treatment of ccRCC.PLoS ONE 02/2015; 10(2):e0115622. DOI:10.1371/journal.pone.0115622 · 3.53 Impact Factor