PKR associates with 4.1R to promote anchorage-independent growth of hepatocellular carcinoma and lead to poor prognosis.

RNA-dependent protein kinase (PKR) may have a positive regulatory role in controlling tumor growth and progression in hepatocellular carcinoma (HCC). However, the downstream substrates and the molecular mechanism of PKR in the growth and progression of HCC have not been clarified. In this study, mass spectrometry analysis was performed with immunoprecipitated samples, and 4.1R was identified as a protein that binds to PKR. In transfected COS7 cells, an immunoprecipitation experiment showed that 4.1R binds to wild-type PKR, but not to a kinase-deficient mutant PKR, suggesting that PKR binds to 4.1R in a kinase activity-dependent manner. In HCC cell lines, HuH7 and HepG2, the expression level of 4.1R protein was shown to be regulated by protein expression and activation of PKR. Interestingly, high expression of 4.1R, as well as PKR, is associated with a worse prognosis in HCC. PKR increased HCC cell growth in both anchorage-dependent and anchorage-independent manners, whereas 4.1R was involved in HCC cell growth only in an anchorage-independent manner, not in an anchorage-dependent manner. The rescue experiment indicated that increased anchorage-independent growth of HCC cells by PKR might be caused by 4.1R. In conclusion, PKR associates with 4.1R and promotes anchorage-independent growth of HCC. The PKR-4.1R axis might be a new therapeutic target in HCC.