Differential expression of chicken dimerization cofactor of hepatocyte nuclear factor-1 (DcoH) and its novel counterpart, DcoHα

We have used differential display PCR to study altered gene expression in immortalized chicken embryo fibroblasts (CEFs) that have been established in our laboratory. This technique resulted in the cloning of a novel counterpart of the previously cloned chicken dimerization cofactor of hepatocyte nuclear factor (HNF)-1 (cDcoH), which was identified as cDcoH alpha. The steady-state mRNA levels of cDcoH alpha were up-regulated in all immortal CEFs tested compared with primary CEF cells, cDcoH and cDcoH alpha showed opposite patterns of mRNA expression due to differential regulation of transcription rates, but not mRNA half-lives, in primary and immortal CEFs. Expression of cDcoH alpha increased in the late G1 and early S phases of the cell cycle, while cDcoH mRNA increased in the late S and G2/M phases. In contrast with consistent expression of both genes in primary quiescent cells, cDcoH mRNA, but not cDcoH alpha mRNA, was dramatically decreased in primary senescent cells. The highest levels of cDcoH alpha mRNA were found in the kidney, liver, heart and ovarian follicles, while the major tissues expressing cDcoH were hypothalamus, kidney and liver. cDcoH and cDcoH alpha probes did not cross-hybridize to human hepatocyte mRNA. When transfected into human HepG2 cells, both cDcoH and cDcoH alpha showed similar functional activity as measured by increased expression of a reporter gene, as well as alpha-fetoprotein and albumin genes that both contain HNF-1 binding elements in their promoters. Our results suggest that the novel chicken DcoH alpha, might function as a transcriptional cofactor for HNF-1 in specific cellular-environmental states.