• Human constitutive androstane receptor represses liver cancer development and hepatoma cell proliferation by inhibiting erythropoietin signaling.

      Li, Zhihui; Kwon, So Mee; Li, Daochuan; Li, Linhao; Peng, Xiwei; Zhang, Junran; Sueyoshi, Tatsuya; Raufman, Jean-Pierre; Negishi, Masahiko; Wang, Xin Wei; et al. (Elsevier, 2022-03-30)
      The constitutive androstane receptor (CAR) is a nuclear receptor that plays a crucial role in regulating xenobiotic metabolism and detoxification, energy homeostasis, and cell proliferation by modulating the transcription of numerous target genes. CAR activation has been established as the mode of action by which phenobarbital-like non-genotoxic carcinogens promote liver tumor formation in rodents. This paradigm, however, appears to be unrelated to the function of human CAR (hCAR) in hepatocellular carcinoma (HCC), which remains poorly understood. Here, we show that hCAR expression is significantly lower in HCC than that in adjacent non-tumor tissues and, importantly, reduced hCAR expression is associated with a worse HCC prognosis. We also show overexpression of hCAR in human hepatoma cells (HepG2 and Hep3B) profoundly suppressed cell proliferation, cell cycle progression, soft-agar colony formation, and the growth of xenografts in nude mice. RNA-seq analysis revealed that the expression of erythropoietin (EPO), a pleiotropic growth factor, was markedly repressed by hCAR in hepatoma cells. Addition of recombinant EPO in HepG2 cells partially rescued hCAR-suppressed cell viability. Mechanistically, we showed that overexpressing hCAR repressed mitogenic EPO-EPOR signaling through dephosphorylation of STAT3, AKT, and ERK1/2. Furthermore, we found that hCAR downregulates EPO expression by repressing the expression and activity of HNF4α, a key transcription factor regulating EPO expression. Collectively, our results suggest that hCAR plays a tumor suppressive role in HCC development which differs from that of rodent CAR and offers insight into the hCAR-HNF4α-EPO axis in human liver tumorigenesis.