Oncogenic RARγ Isoforms Promote Head and Neck Cancer Proliferation Through Vinexin-β-mediated Cell Cycle Acceleration and Autocrine Activation of EGFR Signal

Results of retinoid-based therapies in head and neck cancer (HNC) are generally disappointing, indicating a lack of understanding of retinoic acid signaling. The role of retinoic acid receptor gamma (RARγ) and its isoforms in HNC is yet to be established. In this study, we found that RARγ1, 2, 4 are the predominant RARγ isoforms expressed in various types of human cancers, including HNC. The mechanistic study revealed that RARγ1, 2, 4 enhanced the proliferation of HNC cells by accelerating cell cycle progression through interaction with vinexin-β, as well as by ligand-dependent activation of EGFR with downstream Akt, ERK, Src, and YAP signaling pathways. Retinoic acid binding and CDK7-dependent phosphorylation on specific serine residue at the AF-1 domain are mandatory for RARγ-mediated growth promotion of HNC. Knockdown of RARγ abolished proliferation of cultured HNC cells, and completely prevented tumor growth in xenografted nude mice. Similar effects were observed in various human cancer types other than HNC. Our results indicate that RARγ-targeting approach could be a promising therapeutic and chemopreventive strategy for human cancers.