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Robert H Costa

Publications and source records attributed to Robert H Costa.

At least 19 recordsLinked to original sources
PubMed2006

A cell-penetrating ARF peptide inhibitor of FoxM1 in mouse hepatocellular carcinoma treatment.

The forkhead box m1 (Foxm1) transcription factor is essential for initiation of carcinogen-induced liver tumors; however, whether FoxM1 constitutes a therapeutic target for liver cancer treatment remains unknown. In this study, we used diethylnitrosamine/phenobarbital treatment to induce hepatocellular carcinomas (HCCs) in either WT mice or Arf(-/-)Rosa26-FoxM1b Tg mice, in which forkhead box M1b (FoxM1b) is overexpressed and alternative reading frame (ARF) inhibition of FoxM1 transcriptional activity is eliminated. To pharmacologically reduce FoxM1 activity in HCCs, we subjected these HCC-bearing mice to daily injections of a cell-penetrating ARF(26-44) peptide inhibitor of FoxM1 function. After 4 weeks of this treatment, HCC regions displayed reduced tumor cell proliferation and angiogenesis and a significant increase in apoptosis within the HCC region but not in the adjacent normal liver tissue. ARF peptide treatment also induced apoptosis of several distinct human hepatoma cell lines, which correlated with reduced protein levels of the mitotic regulatory genes encoding polo-like kinase 1, aurora B kinase, and survivin, all of which are transcriptional targets of FoxM1 that are highly expressed in cancer cells and function to prevent apoptosis. These studies indicate that ARF peptide treatment is an effective therapeutic approach to limit proliferation and induce apoptosis of liver cancer cells in vivo.

ADP-Ribosylation Factors↗
PubMed2006

Chk2 mediates stabilization of the FoxM1 transcription factor to stimulate expression of DNA repair genes.

The forkhead box M1 (FoxM1) transcription factor regulates expression of cell cycle genes essential for DNA replication and mitosis during organ repair and cancer progression. Here, we demonstrate that FoxM1-deficient (-/-) mouse embryonic fibroblasts and osteosarcoma U2OS cells depleted in FoxM1 levels by small interfering RNA transfection display increased DNA breaks, as evidenced by immunofluorescence focus staining for phosphospecific histone H2AX. FoxM1-deficient cells also exhibit stimulation of p53 transcriptional activity, as evidenced by increased expression of the p21(cip1) gene. FoxM1-deficient cells display reduced expression of the base excision repair factor X-ray cross-complementing group 1 (XRCC1) and breast cancer-associated gene 2 (BRCA2), the latter of which is involved in homologous recombination repair of DNA double-strand breaks. Furthermore, FoxM1 protein is phosphorylated by checkpoint kinase 2 (Chk2) in response to DNA damage. This phosphorylation of FoxM1 on serine residue 361 caused increased stability of the FoxM1 protein with corresponding increased transcription of XRCC1 and BRCA2 genes, both of which are required for repair of DNA damage. These results identify a novel role for FoxM1 in the transcriptional response during DNA damage/checkpoint signaling and show a novel mechanism by which Chk2 protein regulates expression of DNA repair enzymes.

Amino Acid Sequence↗
PubMed2006

Identification of a chemical inhibitor of the oncogenic transcription factor forkhead box M1.

The oncogenic transcription factor forkhead box M1 (FoxM1) is overexpressed in a number of different carcinomas, whereas its expression is turned off in terminally differentiated cells. For this reason, FoxM1 is an attractive target for therapeutic intervention in cancer treatment. As a first step toward realizing this goal, in this study, using a high-throughput, cell-based assay system, we screened for and isolated the antibiotic thiazole compound Siomycin A as an inhibitor of FoxM1. Interestingly, we observed that Siomycin A was able to down-regulate the transcriptional activity as well as the protein and mRNA abundance of FoxM1. Consequently, we found that the downstream target genes of FoxM1, such as Cdc25B, Survivin, and CENPB, were repressed. Also, we observed that consistent with earlier reports of FoxM1 inhibition, Siomycin A was able to reduce anchorage-independent growth of cells in soft agar. Furthermore, we found that Siomycin A was able to induce apoptosis selectively in transformed but not normal cells of the same origin. Taken together, our data suggest that FoxM1 inhibitor Siomycin A could represent a useful starting point for the development of anticancer therapeutics.

Animals↗
PubMed2006

The FoxM1 transcription factor is required to maintain pancreatic beta-cell mass.

The FoxM1 transcription factor is highly expressed in proliferating cells and activates several cell cycle genes, although its requirement appears to be limited to certain tissue types. Embryonic hepatoblast-specific inactivation of Foxm1 results in a dramatic reduction in liver outgrowth and subsequent late gestation lethality, whereas inactivation of Foxm1 in adult liver impairs regeneration after partial hepatectomy. These results prompted us to examine whether FoxM1 functions similarly in embryonic outgrowth of the pancreas and beta-cell proliferation in the adult. We found that FoxM1 is highly expressed in embryonic and neonatal endocrine cells, when many of these cells are proliferating. Using a Cre-lox strategy, we generated mice in which Foxm1 was inactivated throughout the developing pancreatic endoderm by embryonic d 15.5 (Foxm1(Deltapanc)). Mice lacking Foxm1 in their entire pancreas were born with normal pancreatic and beta-cell mass; however, they displayed a gradual decline in beta-cell mass with age. Failure of postnatal beta-cell mass expansion resulted in impaired islet function by 6 wk of age and overt diabetes by 9 wk. The decline in beta-cell mass in Foxm1(Deltapanc) animals is due to a dramatic decrease in postnatal beta-cell replication and a corresponding increase in nuclear localization of the cyclin-dependent kinase inhibitor, p27(Kip1), a known target of FoxM1 inhibition. We conclude that Foxm1 is essential to maintain normal beta-cell mass and regulate postnatal beta-cell turnover. These results suggest that mechanisms regulating embryonic beta-cell proliferation differ from those used postnatally to maintain the differentiated cell population.

Animals↗
PubMed2006

The Forkhead Box m1 transcription factor stimulates the proliferation of tumor cells during development of lung cancer.

The proliferation-specific Forkhead Box m1 (Foxm1 or Foxm1b) transcription factor (previously called HFH-11B, Trident, Win, or MPP2) regulates expression of cell cycle genes essential for progression into DNA replication and mitosis. Expression of Foxm1 is found in a variety of distinct human cancers including hepatocellular carcinomas, intrahepatic cholangiocarcinomas, basal cell carcinomas, ductal breast carcinomas, and anaplastic astrocytomas and glioblastomas. In this study, we show that human Foxm1 protein is abundantly expressed in highly proliferative human non-small cell lung cancers (NSCLC) as well as in mouse lung tumors induced by urethane. To determine the role of Foxm1 during the development of mouse lung tumors, we used IFN-inducible Mx-Cre recombinase transgene to delete mouse Foxm1 fl/fl-targeted allele before inducing lung tumors with urethane. We show that Mx-Cre Foxm1-/- mice exhibit diminished proliferation of lung tumor cells causing a significant reduction in number and size of lung adenomas. Transient transfection experiments with A549 lung adenocarcinoma cells show that depletion of Foxm1 levels by short interfering RNA caused diminished DNA replication and mitosis and reduced anchorage-independent growth of cell colonies on soft agar. Foxm1-depleted A549 cells exhibit reduced expression of cell cycle-promoting cyclin A2 and cyclin B1 genes. These data show that Foxm1 stimulates the proliferation of tumor cells during progression of NSCLC.

Adenocarcinoma↗
PubMed2006

Increased levels of the FoxM1 transcription factor accelerate development and progression of prostate carcinomas in both TRAMP and LADY transgenic mice.

The proliferation-specific Forkhead Box M1 (FoxM1 or FoxM1b) transcription factor is overexpressed in a number of aggressive human carcinomas. Mouse hepatocytes deficient in FoxM1 fail to proliferate and are highly resistant to developing carcinogen-induced liver tumors. We previously developed a transgenic (TG) mouse line in which the ubiquitous Rosa26 promoter was used to drive expression of the human FoxM1b cDNA transgene in all mouse cell types. To investigate the role of FoxM1b in prostate cancer progression, we bred Rosa26-FoxM1b mice with both TRAMP and LADY TG mouse models of prostate cancer. We show that increased expression of FoxM1b accelerated development, proliferation, and growth of prostatic tumors in both TRAMP and LADY double TG mice. Furthermore, development of prostate carcinomas in TRAMP/Rosa26-FoxM1b double TG mice required high levels of FoxM1 protein to overcome sustained expression of the alternative reading frame tumor suppressor, a potent inhibitor of FoxM1 transcriptional activity. Depletion of FoxM1 levels in prostate cancer cell lines PC-3, LNCaP, or DU-145 by small interfering RNA transfection caused significant reduction in proliferation and anchorage-independent growth on soft agar. This phenotype was associated with increased nuclear levels of the cyclin-dependent kinase inhibitor protein p27(Kip1) and diminished expression of S-phase promoting cyclin A2 and M-phase promoting cyclin B1 proteins. Finally, we show that elevated levels of FoxM1 protein correlate with high proliferation rates in human prostate adenocarcinomas. Our results suggest that the FoxM1 transcription factor regulates development and proliferation of prostate tumors, and that FoxM1 is a novel target for prostate cancer treatment.

Adenocarcinoma↗
PubMed2006

C/EBPalpha and HNF6 protein complex formation stimulates HNF6-dependent transcription by CBP coactivator recruitment in HepG2 cells.

We previously demonstrated that formation of complexes between the DNA-binding domains of hepatocyte nuclear factor 6 (HNF6) and forkhead box a2 (Foxa2) proteins stimulated Foxa2 transcriptional activity. Here, we used HepG2 cell cotransfection assays to demonstrate that HNF6 transcriptional activity was stimulated by CCAAT/enhancer-binding protein alpha (C/EBPalpha), but not by the related C/EBPbeta or C/EBPdelta proteins. Formation of the C/EBPalpha-HNF6 protein complex required the HNF6 cut domain and the C/EBPalpha activation domain (AD) 1/AD2 sequences. This C/EBPalpha-HNF6 transcriptional synergy required both the N-terminal HNF6 polyhistidine and serine/threonine/proline box sequences, as well as the C/EBPalpha AD1/AD2 sequences, the latter of which are known to recruit the CREB binding protein (CBP) transcriptional coactivator. Consistent with these findings, adenovirus E1A-mediated inhibition of p300/CBP histone acetyltransferase activity abrogated C/EBPalpha-HNF6 transcriptional synergy in cotransfection assays. Co-immunoprecipitation assays with liver protein extracts demonstrate an association between the HNF6 and C/EBPalpha transcription factors and the CBP coactivator protein in vivo. Furthermore, chromatin immunoprecipitation assays with hepatoma cells demonstrated that increased levels of both C/EBPalpha and HNF6 proteins were required to stimulate association of these transcription factors and the CBP coactivator protein with the endogenous mouse Foxa2 promoter region. In conclusion, formation of the C/EBPalpha-HNF6 protein complex stimulates recruitment of the CBP coactivator protein for expression of Foxa2, a transcription factor critical for regulating expression of hepatic gluconeogenic genes during fasting.

Amino Acid Sequence↗
PubMed2006

Increased expression of hepatocyte nuclear factor 6 stimulates hepatocyte proliferation during mouse liver regeneration.

BACKGROUND & AIMS: 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.

Adenoviridae↗
PubMed2006

Endothelial cell-restricted disruption of FoxM1 impairs endothelial repair following LPS-induced vascular injury.

Recovery of endothelial integrity after vascular injury is vital for endothelial barrier function and vascular homeostasis. However, little is known about the molecular mechanisms of endothelial barrier repair following injury. To investigate the functional role of forkhead box M1 (FoxM1) in the mechanism of endothelial repair, we generated endothelial cell-restricted FoxM1-deficient mice (FoxM1 CKO mice). These mutant mice were viable and exhibited no overt phenotype. However, in response to the inflammatory mediator LPS, FoxM1 CKO mice displayed significantly protracted increase in lung vascular permeability and markedly increased mortality. Following LPS-induced vascular injury, FoxM1 CKO lungs demonstrated impaired cell proliferation in association with sustained expression of p27(Kip1) and decreased expression of cyclin B1 and Cdc25C. Endothelial cells isolated from FoxM1 CKO lungs failed to proliferate, and siRNA-mediated suppression of FoxM1 expression in human endothelial cells resulted in defective cell cycle progression. Deletion of FoxM1 in endothelial cells induced decreased expression of cyclins, Cdc2, and Cdc25C, increased p27(Kip1) expression, and decreased Cdk activities. Thus, FoxM1 plays a critical role in the mechanism of the restoration of endothelial barrier function following vascular injury. These data suggest that impairment in FoxM1 activation may be an important determinant of the persistent vascular barrier leakiness and edema formation associated with inflammatory diseases.

Animals↗
PubMed2005

Functional characterization of evolutionarily conserved DNA regions in forkhead box f1 gene locus.

The Forkhead Box f1 (Foxf1) transcription factor (previously known as HFH-8 or Freac-1) is expressed in the septum transversum and splanchnic (visceral) mesoderm and is required for proper development of gut-derived organs. Sequence comparisons of mouse and human Foxf1 genes have revealed highly conserved DNA sequences located within the -5.3-kb Foxf1 promoter region and the 400-nucleotide regulatory element located 1 kb 3' to the Foxf1 gene (3'RE). To examine their transcriptional activity during mouse embryonic development, we generated transgenic mice in which the expression of the beta-galactosidase transgene was controlled by the -2.7-kb Foxf1 promoter region, the -5.3-kb Foxf1 promoter region, or the -5.3-kb Foxf1 promoter region fused to the 3'RE. The -5.3-kb Foxf1 promoter sequences induced appropriate transgene expression in the midgut and developing intestine, whereas the -2.7-kb Foxf1 promoter region was transcriptionally inactive. Addition of 3'RE to the -5.3-kb Foxf1 promoter restored proper transgene expression in the foregut, liver, and lung mesenchyme and prevented ectopic transgene expression in the developing nervous system. Cotransfection studies demonstrated that FoxA2 protein bound to the 3'RE region (+4506/+4529 bp) and was sufficient to inhibit expression of the -5.3-kb Foxf1 promoter. Furthermore, C/EBPbeta and HNF-6 proteins bound to the 3'RE region (+4647/+4694 bp) and provided synergistic transcriptional activation of the -5.3-kb Foxf1 promoter in cotransfection assays. These studies demonstrated that the conserved Foxf1 3'RE region is essential for proper tissue-specific regulation of the Foxf1 promoter region during mouse embryogenesis.

Animals↗
PubMed2005

The forkhead box m1 transcription factor is essential for embryonic development of pulmonary vasculature.

Transgenic and gene knock-out studies demonstrated that the mouse Forkhead Box m1 (Foxm1 or Foxm1b) transcription factor (previously called HFH-11B, Trident, Win, or MPP2) is essential for hepatocyte entry into mitosis during liver development, regeneration, and liver cancer. Targeted deletion of Foxm1 gene in mice produces an embryonic lethal phenotype due to severe abnormalities in the development of liver and heart. In this study, we show for the first time that Foxm1(-/-) lungs exhibit severe hypertrophy of arteriolar smooth muscle cells and defects in the formation of peripheral pulmonary capillaries as evidenced by significant reduction in platelet endothelial cell adhesion molecule 1 staining of the distal lung. Consistent with these findings, significant reduction in proliferation of the embryonic Foxm1(-/-) lung mesenchyme was found, yet proliferation levels were normal in the Foxm1-deficient epithelial cells. Severe abnormalities of the lung vasculature in Foxm1(-/-) embryos were associated with diminished expression of the transforming growth factor beta receptor II, a disintegrin and metalloprotease domain 17 (ADAM-17), vascular endothelial growth factor receptors, Polo-like kinase 1, Aurora B kinase, laminin alpha4 (Lama4), and the Forkhead Box f1 transcription factor. Cotransfection studies demonstrated that Foxm1 stimulates transcription of the Lama4 promoter, and this stimulation requires the Foxm1 binding sites located between -1174 and -1145 bp of the mouse Lama4 promoter. In summary, development of mouse lungs depends on the Foxm1 transcription factor, which regulates expression of genes essential for mesenchyme proliferation, extracellular matrix remodeling, and vasculogenesis.

ADAM Proteins↗
PubMed2005

New and unexpected: forkhead meets ARF.

Recent genetic studies demonstrate that mice deficient in the forkhead box m1b (Foxm1b) transcription factor are highly resistant to developing hepatocellular carcinoma, which is among the most lethal cancers worldwide. In addition, the Foxm1b transcription factor was identified as a novel inhibitory target of the p19ARF tumor suppressor during early stages of liver tumorigenesis, but p19ARF expression is extinguished in hepatic tumors that develop at later stages. Structure-function studies demonstrate that amino acids 26-46 of the p19ARF protein are sufficient to bind Foxm1b and reduce Foxm1b transcriptional activity by targeting it to the nucleolus. A peptide containing amino acids 24-46 of p19ARF, which was modified to enhance cellular uptake, is an effective inhibitor of Foxm1b transcriptional activity and prevents Foxm1b stimulation of anchorage-independent growth of cells on soft agar. Thus, the p19ARF peptide is an effective inhibitor of Foxm1b and represents a potential therapy for hepatocellular carcinoma.

Animals↗
PubMed2005

ARF directly binds DP1: interaction with DP1 coincides with the G1 arrest function of ARF.

The tumor suppressor ARF inhibits cell growth in response to oncogenic stress in a p53-dependent manner. Also, there is an increasing appreciation of ARF's ability to inhibit cell growth via multiple p53-independent mechanisms, including its ability to regulate the E2F pathway. We have investigated the interaction between the tumor suppressor ARF and DP1, the DNA binding partner of the E2F family of factors (E2Fs). We show that ARF directly binds to DP1. Interestingly, binding of ARF to DP1 results in an inhibition of the interaction between DP1 and E2F1. Moreover, ARF regulates the association of DP1 with its target gene, as evidenced by a chromatin immunoprecipitation assay with the dhfr promoter. By analyzing a series of ARF mutants, we demonstrate a strong correlation between ARF's ability to regulate DP1 and its ability to cause cell cycle arrest. S-phase inhibition by ARF is preceded by an inhibition of the E2F-activated genes. Moreover, we provide evidence that ARF inhibits the E2F-activated genes independently of p53 and Mdm2. Also, the interaction between ARF and DP1 is enhanced during oncogenic stress and "culture shock." Taken together, our results show that DP1 is a critical direct target of ARF.

Animals↗
PubMed2005

Forkhead box M1 regulates the transcriptional network of genes essential for mitotic progression and genes encoding the SCF (Skp2-Cks1) ubiquitin ligase.

The Forkhead box m1 (Foxm1) gene is critical for G(1)/S transition and essential for mitotic progression. However, the transcriptional mechanisms downstream of FoxM1 that control these cell cycle events remain to be determined. Here, we show that both early-passage Foxm1(-)(/)(-) mouse embryonic fibroblasts (MEFs) and human osteosarcoma U2OS cells depleted of FoxM1 protein by small interfering RNA fail to grow in culture due to a mitotic block and accumulate nuclear levels of cyclin-dependent kinase inhibitor (CDKI) proteins p21(Cip1) and p27(Kip1). Using quantitative chromatin immunoprecipitation and expression assays, we show that FoxM1 is essential for transcription of the mitotic regulatory genes Cdc25B, Aurora B kinase, survivin, centromere protein A (CENPA), and CENPB. We also identify the mechanism by which FoxM1 deficiency causes elevated nuclear levels of the CDKI proteins p21(Cip1) and p27(Kip1). We provide evidence that FoxM1 is essential for transcription of Skp2 and Cks1, which are specificity subunits of the Skp1-Cullin 1-F-box (SCF) ubiquitin ligase complex that targets these CDKI proteins for degradation during the G(1)/S transition. Moreover, early-passage Foxm1(-)(/)(-) MEFs display premature senescence as evidenced by high expression of the senescence-associated beta-galactosidase, p19(ARF), and p16(INK4A) proteins. Taken together, these results demonstrate that FoxM1 regulates transcription of cell cycle genes critical for progression into S-phase and mitosis.

Animals↗
PubMed2004

The mouse Forkhead Box m1 transcription factor is essential for hepatoblast mitosis and development of intrahepatic bile ducts and vessels during liver morphogenesis.

Conditional deletion of the mouse Forkhead Box (Fox) m1b targeted allele in adult hepatocytes (Foxm1, previously called HFH-11B, Trident, Win, or MPP2) demonstrated that the Foxm1b transcription factor is essential for hepatocyte mitosis during liver regeneration. To determine the role of Foxm1b in liver development, we have generated Foxm1b -/- mice that deleted the Foxm1b exons encoding the winged helix DNA binding and transcriptional activation domains. Here, we show that all of the Foxm1b -/- embryos died in utero by 18.5 days postcoitum (dpc). Embryonic Foxm1b -/- livers displayed a 75% reduction in the number of hepatoblasts, resulting from diminished DNA replication and a failure to enter mitosis causing a polyploid phenotype. Reduced hepatoblast mitosis was associated with decreased protein levels of the Polo-like kinase 1 and Aurora B kinase, which phosphorylate regulatory proteins essential for orchestrating mitosis and cytokinesis. Diminished proliferation of Foxm1b -/- hepatoblasts contributed to abnormal liver development with significant reduction in the number of large hepatic veins compared to embryonic wild-type (WT) liver. Furthermore, embryonic Foxm1b -/- livers did not develop intrahepatic bile ducts, and these presumptive biliary hepatoblasts failed to express either biliary cytokeratins or nuclear levels of hepatocyte nuclear factor 1beta. These results suggest that Foxm1b is critical for hepatoblast precursor cells to differentiate toward biliary epithelial cell lineage. Finally, we used a hepatoblast-specific Cre recombinase transgene to mediate deletion of the Foxm1b fl/fl allele in the developing liver, and these embryos died in utero and exhibited diminished hepatoblast proliferation with similar abnormalities in liver morphogenesis, suggesting that the defect in liver development contributed to embryonic lethality.

Alleles↗
PubMed2004

Stability of the hepatocyte nuclear factor 6 transcription factor requires acetylation by the CREB-binding protein coactivator.

We previously demonstrated that the formation of complexes between the DNA binding domains of the hepatocyte nuclear factor 6 (HNF6) and Forkhead Box a2 (Foxa2) transcription factors resulted in synergistic transcriptional activation of a Foxa2 target promoter. This Foxa2.HNF6 transcriptional synergy was mediated by the recruitment of CREB-binding protein (CBP) coactivator through the HNF6 Cut-Homeodomain sequences. Although the HNF6 DNA binding domain sequences are sufficient to recruit CBP coactivator for HNF6.Foxa2 transcriptional synergy, paradoxically these HNF6 Cut-Homeodomain sequences were unable to stimulate the transcription of an HNF6-dependent reporter gene. Here, we investigated whether the CBP coactivator protein played a different role in regulating HNF6 transcriptional activity. We showed that acetylation of the HNF6 protein by CBP increased both HNF6 protein stability and its ability to stimulate transcription of the glucose transporter 2 promoter. Mutation of the HNF6 Cut domain lysine 339 residue to an arginine residue abrogated CBP acetylation, which is required for HNF6 protein stability. Furthermore, the HNF6 K339R mutant protein, which failed to accumulate detected protein levels, was transcriptionally inactive and could not be stabilized by inhibiting the ubiquitin proteasome pathway. Finally, increased HNF6 protein levels stabilized the Foxa2 protein, presumably through the formation of the Foxa2.HNF6 complex. These studies show for the first time that HNF6 protein stability is controlled by CBP acetylation and provides a novel mechanism by which the activity of the CBP coactivator may regulate steady levels of two distinct liver-enriched transcription factors.

Animals↗