Effects of bile acids and cholestasis on major histocompatibility complex class I in human and rat hepatocytes

Major histocompatibility complex (MHC) class I molecules, which are normally poorly expressed on the surface of hepatocytes, are overexpressed during cholestasis. The mechanisms responsible for this overexpression were examined.

The expression of class I molecules, assessed by flow cytofluorimetry, and the class I messenger RNA (mRNA) transcripts, assessed by Northern blot analysis, were measured on normal human hepatocytes in primary culture.

Chenodeoxycholic acid induced an overexpression of MHC class I molecules, whereas ursodeoxycholic acid did not. The level of class I mRNA closely reflected that of the membrane protein. Moreover, cholestasis, induced in the rat by ligation-section of the common bile duct, increased the MHC class I mRNA level. Actinomycin D inhibited bile acid-induced class I transcription of rat hepatocytes in primary culture, whereas cycloheximide did not. Finally, class I mRNA expression was induced in hepatocytes by phorbol myristate acetate and by forskolin. This hyperexpression, as well as that observed with chenodeoxycholic acid, was suppressed by an inhibitor of protein kinase C and protein kinase A.

Taken together, these results suggest that chenodeoxycholic acid, as interferon, activates protein kinase C and protein kinase A, resulting in the induction of MHC class I expression.