Regulation of TRAF2 Activity in Normal and Tumor Cells

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TRAF2 is a key adaptor protein that regulates the IKK, JNK and p38 signaling pathways in response to cytokines and stress, leading to activation of the critical transcription factors AP-1 and NF-kB. Human tumors often exhibit either elevated expression or altered localization of TRAF2, resulting in constitutive IKK activation and increased resistance to stress-induced apoptosis. The mechanism that brings about such deregulation of TRAF2 stability and activity in cancer cells is still elusive. In earlier studies we demonstrated the role of Siah2 in regulating TRAF2 stability in resonse to stress stimulation. We also demonstratedthat TRAF2's own RING-dependent ubiquitination induces its translocation to membrane rafts and concomitant activation of JNK, but not of IKK. However, the molecular mechanism underlying the regulation of TRAF2 activity is far from being understood. We mapped TNFa-induced and Akt/PKC-mediated TRAF2 phosphorylation sites. Importantly, TRAF2 phosphorylation within the RING finger domain is required for TRAF2-mediated activation of IKK, whereas phosphorylation within the TRAF domain was found important for limiting TNFa-induced IKK activation. These findings provide the foundation to our hypothesis that TRAF2-mediated signaling is tightly regulated by a post-translational phosphorylation. In this second revision, we will focus on Akt/PKC-mediated TRAF2 phosphorylation and elucidate its physiological and pathophysiological significance in TRAF2-mediated activation of diverse signaling pathways, with which we propose to carry out the following specific aims: 1. Characterize the mechanism by which newly identified TRAF2 phosphorylation regulates TNFa-induced and TRAF2-mediated activation of the JNK and NF-kB pathways. 2. Assess the role of Akt and PKC in the phosphorylation of TRAF2 and TRAF2-mediated activation of the JNK and NF-kB pathways. 3. Define the relationship between Akt- and PKC-mediated TRAF2 phosphorylation and stress-induced cell death. Aim-4. Assess the pathophysiological relevance of TRAF2 phosphorylation in melanoma cell resistance to stress-induced cell death. Our work will shed new light on the regulation of TRAF2 phosphorylation by PKC and Akt and their role in the regulation of tumor cell resistance to stress-induced cell death.