Transcriptional repression of E2F gene by proteasome inhibitors in human osteosarcoma cells

Abstract

E2F family of transcription factors regulates the transcription of genes required for DNA synthesis. E2F is itself controlled by a series of transcriptional and post-transcriptional pathways. Here we provide evidence that proteasome inhibitor-mediated E2F1 gene down-regulation is regulated by transcriptional events. Using the proteasome-specific inhibitors, MG132 and lactacystin, we show that the p53, the cdk inhibitors p21 and p27, and cyclin A are degraded by the ubiquitin-proteasome pathway in human osteosarcoma cells. Interestingly, the expression levels of E2F1 and E2F2 are down-regulated by proteasome inhibitors. E2F promoter and RT-PCR assay clearly demonstrated that proteasome inhibitors could reduce E2F transcriptional activation. However, MG132-induced repression of E2F1 and E2F2 is not associated with ROS generation.