Cancer Science & Therapy

The Proto-Oncoprotein c-Cbl Protects Cells against Oxidative Stress by Down-Regulating Apoptosis and is Highly Expressed in Several Cancers

Abstract

Sadok Yakoub, Nisrine El-Chami, Krisztian Kaszas, Mouhannad Malek, Mohamed El Sirkasi, Colin A. Smith, Elias Baydoun, Eric Tabone, Serge N Manié and Daniel C.L. Régnier

Objective: To determine the role of c-Cbl in the apoptotic process, using several means, stressing the role of oxidative stress in cancer cells.

Methods: Prostatic epithelial cell apopotosis of c-Cbl-/-mice were compared to wildtype mice (n: 6 per condition), upon testosterone-antagonist flutamide. c-Cbl-deficient mouse embryonic fibroblasts (MEFs) were compared to wild type MEFs under etoposide or hydrogen peroxide treatments. The use of c-Cbl RNA silencing in the human prostate adenocarcinoma cell line LNCaP allowed to reveal c-Cbl’s role in LNCaPs’ apoptosis. The role of the p38-MAPK stress pathway in the LNCAP c-Cbl anti-apoptotic effect as well as its relationship with the well-documented Grb2-associated Tyrosine-Kinase-Receptor (TKR) down-regulation were investigated, using c-Cbl and/or Grb2 RNA silencing. Human c-Cbl protein expression was analysed by Western blotting and immunostaining, comparing prostatic adenocarcinoma (x22) to benign prostatic hypertrophia (x6). In situ tissue microarrays were used to assess several human malignancies (x17 and x6 spots/tissue) and to compare the magnitude of c-Cbl and oxidative stress expression.

Results: The cellular apoptotic threshold decreased in Mouse c-Cbl-/-prostatic cells and c-Cbl-/- MEFs. Only hydrogen peroxide in c-Cbl-/-MEFs induced apoptosis up to six times more than controls. Similar results were found in LNCaPs. c-Cbl down-regulates the activation of the apoptotic ASK1-p38MAPK stress pathway. c-Cbl is overexpressed in prostate, ovary, uterus, brain, lung, colon, rectum adenocarcinoma and in rhabdomyosarcoma. We found a correlation between malignant oxidative stress and c-Cbl over-expression.

Conclusions: c-Cbl increases the cellular apoptotic threshold of wild type MEFs and mouse prostate cells. c-Cbl behaves as a strong cellular protector against oxidative stress in MEFs and LNCaPs. The p38-MAPK pathway is down-regulated by c-Cbl, possibly independently of the Grb2-associated TKR down-regulation. A high c-Cbl expression in several cancers often associated with high oxidative stress expression has been found, suggesting that c-Cbl could thereby promote their survival.