4.6 Article

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

Journal

JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 298, Issue 5, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.jbc.2022.101885

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Funding

  1. National Institutes of Health, United States [R01 CA262084, GM121550, ZIA-BC010313, ZIA-BC010876, ZIA BC 010877, ZIA BC 011870, Z01ES1005-01]
  2. Intramural Research Program of the National Institutes of Health, United States [BX004890]
  3. Department of Veterans Affairs Biomedical Laboratory Research and Development Program, United States

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The study reveals that reduced expression of human CAR is associated with worse prognosis in hepatocellular carcinoma. Overexpression of CAR in human hepatoma cells can significantly suppress cell proliferation and growth, and affects cell growth through multiple mechanisms.
The constitutive androstane receptor (CAR) is a nuclear receptor that plays a crucial role in regulating xenobiotic meta-bolism and detoxification, energy homeostasis, and cell prolif-eration by modulating the transcription of numerous target genes. CAR activation has been established as the mode of action by which phenobarbital-like nongenotoxic 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 under-stood. Here, we show that hCAR expression is significantly lower in HCC than that in adjacent nontumor 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 pleio-tropic growth factor, was markedly repressed by hCAR in hep-atoma cells. Addition of recombinant EPO in HepG2 cells partially rescued hCAR-suppressed cell viability. Mechanisti-cally, we showed that overexpressing hCAR repressed mitogenic EPO-EPO receptor signaling through dephosphorylation of signal transducer and activator of transcription 3, AKT, and extracellular signal-regulated kinase 1/2. Furthermore, we found that hCAR downregulates EPO expression by repressing the expression and activity of hepatocyte nuclear factor 4 alpha, 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-hepatocyte nuclear factor 4 alpha- EPO axis in human liver tumorigenesis.

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