RESUMO
BCL2A1 is an anti-apoptotic member of the BCL-2 family that contributes to chemoresistance in a subset of tumors. BCL2A1 has a short half-life due to its constitutive processing by the ubiquitin-proteasome system. This constitutes a major tumor-suppressor mechanism regulating BCL2A1 function. However, the enzymes involved in the regulation of BCL2A1 protein stability are currently unknown. Here, we provide the first insight into the regulation of BCL2A1 ubiquitination. We present evidence that TRIM28 is an E3 ubiquitin-ligase for BCL2A1. Indeed, endogenous TRIM28 and BCL2A1 bind to each other at the mitochondria and TRIM28 knock-down decreases BCL2A1 ubiquitination. We also show that TRIM17 stabilizes BCL2A1 by blocking TRIM28 from binding and ubiquitinating BCL2A1, and that GSK3 is involved in the phosphorylation-mediated inhibition of BCL2A1 degradation. BCL2A1 and its close relative MCL1 are thus regulated by common factors but with opposite outcome. Finally, overexpression of TRIM28 or knock-out of TRIM17 reduced BCLA1 protein levels and restored sensitivity of melanoma cells to BRAF-targeted therapy. Therefore, our data describe a molecular rheostat in which two proteins of the TRIM family antagonistically regulate BCL2A1 stability and modulate cell death.
Assuntos
Apoptose/genética , Antígenos de Histocompatibilidade Menor/genética , Neoplasias/genética , Proteínas Proto-Oncogênicas c-bcl-2/genética , Proteínas com Motivo Tripartido/genética , Proteína 28 com Motivo Tripartido/genética , Ubiquitina-Proteína Ligases/genética , Morte Celular/genética , Linhagem Celular Tumoral , Doxiciclina/farmacologia , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Quinase 3 da Glicogênio Sintase/genética , Humanos , Neoplasias/tratamento farmacológico , Neoplasias/patologia , Fosforilação/genética , Complexo de Endopeptidases do Proteassoma/genética , Ligação Proteica/genética , Estabilidade Proteica , Proteólise/efeitos dos fármacos , Ubiquitinação/genéticaRESUMO
Hypoxia-inducible factor (HIF-1α) protein is over-expressed in many human cancers and is a major cause of resistance to drugs. HIF-1α up-regulation decreases the effectiveness of several anticancer agents, including 5-fluorouracil (5-FU), because it induces the expression of drug efflux transporters, alters DNA repair mechanisms and modifies the balance between pro- and antiapoptotic factors. These findings suggest that inhibition of HIF-1α activity may sensitize cancer cells to cytotoxic drugs. We previously reported that l-carnosine reduces HIF-1α expression by inhibiting the proliferation of colon cancer cells. In the present study we investigated the effect of l-carnosine on HT29 colon cancer cells with acquired resistance to 5-FU. We found that l-carnosine reduces colon cancer cell viability, decreases HIF-1α and multi-drug resistant protein MDR1-pg expression, and induces apoptosis. Moreover, the l-carnosine/5-FU combination lowers the expression of some chemoresistance markers. The combination index evaluated in vitro on the HT29-5FU cell line by median drug effect analysis reveals a significant synergistic effect.