Increased expression of hepatocyte nuclear factor 6 stimulates hepatocyte proliferation during mouse liver regeneration.
OBJECTIVE
The hepatocyte nuclear factor 6 (HNF6 or ONECUT-1) protein is a cell-type specific transcription factor that regulates expression of hepatocyte-specific genes. Using hepatocytes for chromatin immunoprecipitation (ChIP) assays, the HNF6 protein was shown to associate with cell cycle regulatory promoters. Here, we examined whether increased levels of HNF6 stimulate hepatocyte proliferation during mouse liver regeneration.


METHODS
Tail vein injection of adenovirus expressing the HNF6 complementary DNA was used to increase hepatic HNF6 levels during mouse liver regeneration induced by partial hepatectomy, and DNA replication was determined by bromodeoxyuridine incorporation. Cotransfection and ChIP assays were used to determine transcriptional target promoters.


RESULTS
Elevated expression of HNF6 during mouse liver regeneration causes a significant increase in the number of hepatocytes entering DNA replication (S phase), and mouse hepatoma Hepa1-6 cells diminished for HNF6 levels by small interfering RNA transfection exhibit a 50% reduction in S phase following serum stimulation. This stimulation in hepatocyte S-phase progression was associated with increased expression of the hepatocyte mitogen tumor growth factor alpha and the cell cycle regulators cyclin D1 and Forkhead box m1 (Foxm1) transcription factor. Cotransfection and ChIP assays show that tumor growth factor alpha, cyclin D1, and HNF6 promoter regions are direct transcriptional targets of the HNF6 protein. Coimmunoprecipitation assays with regenerating mouse liver extracts reveal an association between HNF6 and FoxM1 proteins, and cotransfection assays show that HNF6 stimulates Foxm1 transcriptional activity.


CONCLUSIONS
These mouse liver regeneration studies show that increased HNF6 levels stimulate hepatocyte proliferation through transcriptional induction of cell cycle regulatory genes.
Tan
Yongjun
Y
Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago College of Medicine, Chicago, Illinois 60607-7170, USA.
Yoshida
Yuichi
Y
Hughes
Douglas E
DE
Costa
Robert H
RH
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D047369:Chromatin Immunoprecipitation; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D004261:DNA Replication; D004357:Drug Synergism; D000072278:Forkhead Box Protein M1; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism; D018014:Gene Transfer Techniques; D005822:Genetic Vectors; D051559:Hepatocyte Nuclear Factor 6 / Q000235:genetics / Q000378:metabolism*; D022781:Hepatocytes / Q000166:cytology*; D008099:Liver / Q000378:metabolism*; D008115:Liver Regeneration / Q000502:physiology*; D051379:Mice; D008815:Mice, Inbred Strains; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic; D016211:Transforming Growth Factor alpha / Q000235:genetics / Q000378:metabolism
D000072278:Forkhead Box Protein M1; D051858:Forkhead Transcription Factors; C491524:Foxm1 protein, mouse; D051559:Hepatocyte Nuclear Factor 6; D016211:Transforming Growth Factor alpha; D019938:Cyclin D1; D051357:Cyclin-Dependent Kinase 2