The Role of STATs in Apoptosis

Signal transducers and activators of transcription (STATs) are transcription factors that mediate cytokine and growth factor induced signals that culminate in various biological responses, including proliferation and differentiation. Recent studies indicate a role for STATs in apoptosis as well. Depending upon the particular stimulus or cell type, STATs can mediate either pro-apoptotic signals or anti-apoptotic signals. STAT1 and, under some circums-tances, STAT3 are important for transducing pro-apoptotic signals whereas STAT3 and STAT5 have been implicated in promoting cell survival. Recent studies demonstrate that regulation of apoptotic pathways by STATs is largely due to transcriptional activation of genes that encode proteins that mediate or trigger the cell death process, such as Bcl-xL, caspases, Fas and TRAIL as well as those that regulate cell cycle progression, such as p21waf1. Interestingly, STAT proteins may also regulate apoptosis through a non-transcriptional mechanism by inhibiting the anti-apoptotic protein NF-kB. Considering that dysregulation of the STAT signaling pathway is commonly found in clinical tumor samples, understanding the mechanisms underlying STAT regulation of cell survival may lead to successful strategies for targeting STATs in cancer therapy.