Id-1 expression promotes cell survival through activation of NF-κB signalling pathway in prostate cancer cells

The growth-promoting effect of Id-1 (inhibitor of differentiation/DNA binding) has been demonstrated in a number of human cancers. However, the mechanisms responsible for its action are not clear. In this study, we report that in prostate cancer cells, Id-1 promotes cell survival through activation of nuclear factor- κ B (NF- κ B) signalling pathway. After stable expression of Id-1 protein in LNCaP cells, we found that the Id-1 transfectants showed increased resistance to apoptosis induced by TNF α through inactivation of Bax and caspase 3. In addition, in the LNCaP cells expressing ectopic Id-1 protein, we also observed increased NF- κ B transactivation activity and nuclear translocation of the p65 and p50 proteins, which was accompanied by upregulation of their downstream effectors Bcl-xL and ICAM-1. These results indicate that the Id-1-induced antiapoptotic effect may be via NF- κ B signalling transduction pathway in these cells. In addition, inactivation of Id - 1 by its antisense oligonucleotide and retroviral construct in DU145 cells resulted in the decrease of nuclear level of p65 and p50 proteins, which was associated with increased sensitivity to TNF α -induced apoptosis. Our results strongly suggest that Id-1 may be one of the upstream regulators of NF- κ B and activation of NF- κ B signalling pathway may be essential for Id-1 induced cell proliferation through protection against apoptosis. Our findings also suggest a potential therapeutic strategy in which inactivation of Id-1 may lead to sensitization of prostate cancer cells to chemotherapeutic drug-induced apoptosis.