Retinoic acid receptors (RAR; α, β, and γ), members of the nuclear receptor superfamily, mediate the pleiotropic effects of the vitamin A metabolite retinoic acid (RA) and derivatives (retinoids) in normal and cancer cells. Abnormal expression and function of RARs are often involved in the growth and development of cancer. However, the underlying molecular mechanisms remain largely elusive. Here, we report that levels of RARγ were significantly elevated in tumor tissues from a majority of human hepatocellular carcinoma (HCC) and in HCC cell lines. Overexpression of RARγ promoted colony formation by HCC cells in vitro and the growth of HCC xenografts in animals. In HepG2 cells, transfection of RARγ enhanced, whereas downregulation of RARγ expression by siRNA approach impaired, the effect of RA on inducing the expression of α-fetoprotein, a protein marker of hepatocarcinogenesis. In studying the possible mechanism by which overexpression of RARγ contributed to liver cancer cell growth and transformation, we observed that RARγ resided mainly in the cytoplasm of HCC cells, interacting with the p85α regulatory subunit of phosphatidylinositol 3-kinase (PI3K). The interaction between RARγ and p85α resulted in activation of Akt and NF-κB, critical regulators of the growth and survival of cancer cells. Together, our results show that overexpression of RARγ plays a role in the growth of HCC cells through nongenomic activation of the PI3K/Akt and NF-κB signaling pathways. Cancer Res; 70(6); 2285–95

Interleukin-35 (IL-35) exerts immunosuppressive effects in rheumatoid arthritis (RA), but its direct impact on synovial fibroblasts (SFs) remains unclear.