Premature Expression of the Winged Helix Transcription Factor HFH-11B in Regenerating Mouse Liver Accelerates Hepatocyte Entry into S Phase

Abstract

Two-thirds partial hepatectomy (PH) induces differentiated cells in the liver remnant to proliferate and regenerate to its original size. The proliferation-specific HNF-3/fork head homolog-11B protein (HFH-11B; also known as Trident and Win) is a family member of the winged helix/fork head transcription factors and in regenerating liver its expression is reactivated prior to hepatocyte entry into DNA replication (S phase). To examine whether HFH-11B regulates hepatocyte proliferation during liver regeneration, we used the ؊3-kb transthyretin (TTR) promoter to create transgenic mice that displayed ectopic hepatocyte expression of HFH-11B. Liver regeneration studies with the TTR-HFH-11B mice demonstrate that its premature expression resulted in an 8-h acceleration in the onset of hepatocyte DNA replication and mitosis. This liver regeneration phenotype is associated with protracted expression of cyclin D1 and C/EBP␤, which are involved in stimulating DNA replication and premature expression of M phase promoting cyclin B1 and cdc2. Consistent with the early hepatocyte entry into S phase, regenerating transgenic livers exhibited earlier expression of DNA repair genes (XRCC1, mHR21spA, and mHR23B). Furthermore, in nonregenerating transgenic livers, ectopic HFH-11B expression did not elicit abnormal hepatocyte proliferation, a finding consistent with the retention of the HFH-11B transgene protein in the cytoplasm. We found that nuclear translocation of the HFH-11B transgene protein requires mitogenic signalling induced by PH and that its premature availability in regenerating transgenic liver allowed nuclear translocation to occur 8 h earlier than in wild type.The mammalian liver is one of the few adult organs capable of completely regenerating itself in response to cellular injury from toxins, viral infections, or tissue removal (15,38,46). Liver regeneration after two-thirds partial hepatectomy (PH) represents a balance between hepatocyte proliferation and the maintenance of hepatocyte-specific gene expression required for liver homeostasis (22,46). A potent activation of hepatocyte immediate early transcription factors is observed during liver regeneration and includes c-Jun, c-Fos, c-Myc, NF-B, signal transducers, and activators of transcription 3 (stat3) and the CCAAT/enhancer protein ␤ (C/EBP␤) genes (7,9,25,46). Furthermore, maintenance of hepatocyte-specific gene transcription is coincident with sustained expression of hepatocyte nuclear factor genes (16,20,41). More recent genetic data demonstrated that the cytokine interleukin-6 (IL-6) plays an important role in establishing responsiveness of hepatocytes to growth factors which are released after liver injury (8,54). In a PH model of liver regeneration, homozygous null interleukin-6 (IL-6) or type 1 tumor necrosis factor receptor (TNFR-I) mice exhibited a 70% reduction in hepatocyte replication and this proliferation defect was eliminated by an intraperitoneal injection of IL-6 prior to surgery (8,43,54). This proliferation defect was accompanied by a failur...

Transgenic expression of the forkhead box M1 transcription factor induces formation of lung tumors

“…One possible explanation for this discrepancy is that Foxm1 transgenic protein is transcriptionally inactive in quiescent lungs. It was previously demonstrated (Ye et al, 1999) that in quiescent cells transgenic Foxm1 protein localizes in cytoplasm and needs an activation signal (injury-induced proliferative stimuli) to be translocated Figure 3 Gene expression profile in Rosa26-Foxm1 transgenic lungs after 3-methylcholanthrene (MCA)/butylated hydroxytoluene (BHT) treatment. Total RNA was prepared from left lung lobes of untreated or MCA/BHT-treated wild-type (WT) and Rosa26-Foxm1 mice.…”

In vivo regulation of murine CYP7A1 by HNF-6: A novel mechanism for diminished CYP7A1 expression in biliary obstruction

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Foxf1 +/− mice exhibit defective stellate cell activation and abnormal liver regeneration following CCl4 injury

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“…20 The mice were killed by CO 2 asphyxiation; liver tissue was used to prepare total RNA and protein cell extract, or livers were fixed overnight in 4% paraformaldehyde at 4°C and then paraffin embedded as described previously. 21 National Institutes of Health Guidelines for Animal Care were followed during CCl 4 mouse liver injury experiments.…”