SREBP isoform and SREBP target gene expression during rat primary hepatocyte culture

Abstract

Expression of mRNA encoding sterol regulatory element binding protein (SREBP) isoforms (SREBP-1a, -1c, -2) and seven SREBP target genes decreased dramatically as a result of isolation and subsequent culture of primary rat hepatocytes. In standard maintenance medium (MM) expression remained low but when cultured in HepatoZYME (HZM), there was a selective increase in mRNA encoding SREBP-2 and a subset of SREBP target genes, a group characterised by promoters containing adjacent sterol regulatory element and nuclear factor Y (NF-Y) binding sequences. Quantification of all three NF-Y transcripts showed that expression of nuclear factor Y alpha subunit and nuclear factor Y beta subunit mRNA increased during culture in HZM (in contrast to the situation with MM) whilst specificity protein 1, liver-x-receptor and hepatocyte nuclear factor-4 alpha mRNA exhibited equivalent decreased expression in both HZM and MM. Our data indicate that HZM exerts a selective preservation of hepatocyte phenotype through actions on NF-Y expression directly or via an effect secondary to actions on SREBP-2 expression. These data add to the molecular dissection of the causes of hepatocyte dedifferentiation during culture and address means to develop approaches to prevent/limit phenotype change.