Id-1 regulates Bax and Bcl-2 expression through p53 and NF-κB signaling pathways in breast cancer cells

Abstract

Although increasing evidence supports the function of inhibitor of differentiation and DNA binding-1 (Id-1) as a survival factor, its molecular mechanism has not been fully understood. Here, we examined the direct role of Id-1 in MCF7 cells by ectopically overexpressing Id-1 and underlying pathways on the development of anticancer drug resistance in breast cancer. Methods The role of Id-1 investigated in breast cancer cell line MCF7 through ectopically overexpressing or inactivating Id-1 by stable transfection or retroviral infection, respectively. NF-κB and p53 pathway regulators are examined by immunoblot, reverse transcriptase-polymerase chain reaction (RT-PCR), real-time PCR and reporter assay. Cellular cytotoxicity was determined by MTT assay and DAPI staining. Results Id-1 expression resulted in augmented growth, reduced Bax expression, enhanced Bcl-2 expression, but no change in Bcl-xL expression. The expression of nuclear factor B (NF-κB) was augmented, while those of p53 and I B were reduced. Such changes in p53 and NF-κB pathways were also functional, as assessed by several assays of their known downstream regulators, p21 and IL-6, as well as Bax and Bcl-2 genes. Finally, Id-1 played a protective role against taxol-induced apoptosis in breast cancer cells upon taxol treatment. Reduced Bax expression and enhanced Bcl-2 expression by Id-1 were also noted in the presence of taxol. Conclusion Taken together, we present a molecular mechanism where Id-1 regulates p53 and NF-κB pathways, which in turn regulates Bax and Bcl-2 genes, thus providing a survival advantage under exogenous stress such as serum-free or taxol treatment in breast cancer cells. In this regard, inactivation of Id-1 may provide a potential therapeutic strategy leading to inhibition of breast cancer progression and anti-cancer drug resistance.