Transcription factor AP-1 promotes growth and radioresistance in prostate cancer cells

Expression of AP-1 proteins has been associated with a more aggressive clinical outcome in prostate cancer. However, their role and regulation by upstream kinase pathways in response to ionizing radiation has remained elusive. Here, we show that constitutive AP-1 activity in prostate cancer cells is dependent on the activities of EGF-R and PI3K. While inhibition of EGF-R is associated with suppression of c-Jun expression and proliferation, inhibition of PI3K pathway suppresses expression of several AP-1 subunits and proliferation, and also sensitizes prostate cancer cells to gamma-radiation. The importance of AP-1 as a mediator of proliferation and radiation responses is demonstrated by the findings that the expression of JunD, Fra-1 and Fra-2 siRNAs in prostate cancer cells suppress these cellular responses. Together, the findings show that AP-1 activity in prostate cancer cells mediates EGF-R and PI3K signalling, is essential for their proliferation, and confers protection against radiation-induced cell death. Thus, its inhibition would be a lucrative target for therapy in this widely increasing cancer type.