Hepatic circadian and differentiation factors control liver susceptibility for fatty liver disease and tumorigenesis

Hepatocellular carcinoma (HCC) is a leading cause of cancer deaths, and the most common primary liver malignancy to present in the clinic. With the exception of liver transplant, treatment options for advanced HCC are limited, but improved tumor stratification could open the door to new treatment options. Previously, we demonstrated that the circadian regulator Aryl Hydrocarbon-Like Receptor Like 1 (ARNTL, or Bmal1) and the liver-enriched nuclear factor 4 alpha (HNF4 alpha) are robustly co-expressed in healthy liver but incompatible in the context of HCC. Faulty circadian expression of HNF4 alpha- either by isoform switching, or loss of expression- results in an increased risk for IICC, while BMAL1 gain-of-function in HNF4 alpha-positive HCC results in apoptosis and tumor regression. We hypothesize that the transcriptional programs of HNF4 alpha and BMAL1 are antagonistic in liver disease and HCC. Here, we study this antagonism by generating a mouse model with inducible loss of hepatic HNF4 alpha and BMAL1 expression. The results reveal that simultaneous loss of HNF4 alpha and BMAL1 is protective against fatty liver and HCC in carcinogen-induced liver injury and in the "STAM" model of liver disease. Furthermore, our results suggest that targeting Bmall expression in the absence of HNF4 alpha inhibits HCC growth and progression. Specifically, pharmacological suppression of Bmal1 in HNF4 alpha-deficient, BMAL1-positive HCC with REV-ERB agonist SR9009 impairs tumor cell proliferation and migration in a REV-ERB-dependent manner, while having no effect on healthy hepatocytes. Collectively, our results suggest that stratification of HCC based on HNF4 alpha and BMAL1 expression may provide a new perspective on HCC properties and potential targeted therapeutics.