Impeding two p53-pathways fosters HCC initiation via MTHFD1L-RNA m6A-elicited autonomous cell growth and immune evasion

Background and Aims: HCC develop from mature hepatocytes in chronic liver injuries, during which dynamic regulation of p53 activity is crucial for ensuring normal liver regeneration while preventing HCC initiation. Yet, it remains unaddressed if and how impairing p53 response might trigger HCC initiation. Two p53 regulatory pathways, ribosomal proteins (RPs)-MDM2 and 14-3-3-MDMX, are shown to activate p53 in response to multiple stresses. We investigated the role of the p53-pathways in HCC initiaition, and determined how dynamic p53 activation is required for preventing HCC initiation. Approach and Results: We generated double knock-in (DKI) mice harboring impaired RPs-MDM2- and 14-3-3-MDMX- p53 pathways, and employed DEN and NASH-induced HCC mouse models. Correlation between the p53-pathways and HCC prevention in human cirrhosis was also assessed. We demonstrated that carcinogen- or unhealthy diet-induced HCC initiation is accelerated in DKI mice, and the p53- pathways are activated in human cirrhotic livers. We futher identified a one-carbon metabolism (1CM) enzyme methylenetetrahydrofolate dehydrogenase 1 like (MTHFD1L) as the p53-suppressed player in HCC initiation. MTHFD1L promotes HCC initiation by enhancing autonomous cell growth and immune evasion of HCC progenitor cells (HcPCs). With Nanopore RNA sequencing, we unveiled that MTHFD1L fulfills these bi-functions by fueling methionine cycle that produces methyl groups to maintain mRNA m6A of cell growth mediators Prickle1 and Snail, and B2m, a light chain of MHC-I critical for antigen presentation. Conclusions: Stress-MDM2/MDMX-p53-MTHFD1L-RNA m6A pathways are crucial for preventing HCC initiation by reversing 1CM reprogramming-boosted cell autonomous growth and immune evasion.