Hyperactivated Jnk Is A Therapeutic Target In Pvhl-Deficient Renal Cell Carcinoma

Clear cell renal cell carcinomas (RCC), the major histologic subtype of RCC accounting for more than 80% of cases, are typified by biallelic inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene. Although accumulation of hypoxia-inducible factor alpha (HIF-alpha) is the most well-studied effect of VHL inactivation, direct inhibition of HIF alpha or restoration of wild-type pVHL protein expression has not proved readily feasible, given the limitations associated with pharmacologic targeting of transcription factors (i.e., HIF-a) and gene replacement therapy of tumor suppressor genes (i.e., VHL). Here, we have established that phosphorylated c-Jun, a substrate of the c-Jun-NH2-kinase (JNK), is selectively activated in clear cell RCC patient specimens. Using multiple isogenic cell lines, we show that HIF-alpha-independent JNK hyperactivation is unique to the pVHL-deficient state. Importantly, pVHL-deficient RCCs are dependent upon JNK activity for in vitro and in vivo growth. A multistep signaling pathway that links pVHL loss to JNK activation involves the formation of a CARD9/BCL10/TRAF6 complex as a proximal signal to sequentially stimulate TAK1 (MAPKKK), MKK4 (MAPKK), and JNK (MAPK). JNK stimulates c-Jun phosphorylation, activation, and dimerization with c-Fos to form a transcriptionally competent AP1 complex that drives transcription of the Twist gene and induces epithelial-mesenchymal transition. Thus, JNK represents a novel molecular target that is selectively activated in and drives the growth of pVHL-deficient clear cell RCCs. These findings can serve as the preclinical foundation for directed efforts to characterize potent pharmacologic inhibitors of the JNK pathway for clinical translation. Cancer Res; 73(4); 1374-85. (C) 2012 AACR.