Embryonic but not postnatal reexpression of hepatocyte nuclear factor 1alpha (HNF1alpha) can reactivate the silent phenylalanine hydroxylase gene in HNF1alpha-deficient hepatocytes

HNF1α upregulation and promoter hypermethylation as a cause of glucose dysregulation: a case-control study of Kashmiri MODY population

AIM

HNF1α transcription factor regulates a network of genes involved in the development of β-cells and also serves as a model for transcription defects in pancreatic β-cells; mutations in this gene cause MODY. The goal of this study was to assess the promoter methylation and expression profile of the most common MODY causing gene, HNF1α, in Kashmiri MODY patients, as factors responsible for glucose dysregulation, as no such study had been performed on MODY patients in Kashmir previously.

METHODS

The study included 85 Kashmiri subjects. Samples were extracted for DNA and RNA using standard protocols. The HNF1α promoter methylation profile was assessed by bisulfite conversion of the DNA followed by MSP, whereas qPCR was used for expression analysis.

RESULTS

The expression of HNF1α was found to be upregulated (p value 0.0349*) in majority of MODY (60%) and T1D (72%) cases (p value 0.0349*). HNF1α expression was 1.33-fold higher in MODY cases with hypermethylated HNF1α promoters (p value 0.0360*). HNF1α expression was upregulated by 2.3-fold in MODY patients with HbA1c levels > 7% (p value 0.0025**). MODY cases with FBS levels > 7.7 mmol/l were upregulated by 0.646-fold than those with FBS levels ≤ 7.7 mmol/l (p value 0.0161*).

CONCLUSION

In this study, we found that as glucose dysregulation progresses, blood FBS, RBS, and HbA1c levels rise, and that at higher levels, HNF1α expression rises as well. From the results obtained, we may conclude that HNF1α is strongly upregulated in MODY, thus indicating the deleterious effect of over expression of HNF1α gene on glucose regulation.

Chromatin changes on the GSTP1 promoter associated with its inactivation in prostate cancer

Glutathione-S-transferases (GSTs) are metabolic enzymes that help detoxify and eliminate harmful chemicals. In prostate tumors, expression of GST pi (encoded by GSTP1) is frequently lost because of promoter hypermethylation. Here we analyze the native GSTP1 promoter in cancerous and noncancerous human prostate cells to identify structural features associated with its cancer-related transcriptional silencing. We find that in noncancerous prostate cells (RWPE-1 and PWR-1E) GSTP1 is constitutively expressed, not methylated, highly accessible, bound by transcription factors and associated with histones with activating modifications (histone H3 methylated at lysine 4 and acetylated histones H3 and H4). In contrast, in cancerous prostate cells (LNCaP) GSTP1 is not expressed, extensively methylated, inaccessible, lacks bound transcription factors and is not associated with histones with activating modifications. We do not detect significant levels of histones with repressive modifications (histone H3 methylated at lysine 9 or 27) on GSTP1 in any cell line indicating that they are not associated with cancer-related GSTP1 silencing. Treatment of LNCaP cells with 5-azacytidine restores activating histone modifications on GSTP1 and reactivates transcription. We conclude that, in the process of prostate carcinogenesis, activating histone modifications on GSTP1 are lost and the DNA becomes methylated and inaccessible resulting in transcriptional silencing.

Gata4 and Hnf1alpha are partially required for the expression of specific intestinal genes during development

The terminal differentiation phases of intestinal development in mice occur during cytodifferentiation and the weaning transition. Lactase-phlorizin hydrolase (LPH), liver fatty acid binding protein (Fabp1), and sucrase-isomaltase (SI) are well-characterized markers of these transitions. With the use of gene inactivation models in mature mouse jejunum, we have previously shown that a member of the zinc finger transcription factor family (Gata4) and hepatocyte nuclear factor-1alpha (Hnf1alpha) are each indispensable for LPH and Fabp1 gene expression but are both dispensable for SI gene expression. In the present study, we used these models to test the hypothesis that Gata4 and Hnf1alpha regulate LPH, Fabp1, and SI gene expression during development, specifically focusing on cytodifferentiation and the weaning transition. Inactivation of Gata4 had no effect on LPH gene expression during either cytodifferentiation or suckling, whereas inactivation of Hnf1alpha resulted in a 50% reduction in LPH gene expression during these same time intervals. Inactivation of Gata4 or Hnf1alpha had a partial effect ( approximately 50% reduction) on Fabp1 gene expression during cytodifferentiation and suckling but no effect on SI gene expression at any time during development. Throughout the suckling period, we found a surprising and dramatic reduction in Gata4 and Hnf1alpha protein in the nuclei of absorptive enterocytes of the jejunum despite high levels of their mRNAs. Finally, we show that neither Gata4 nor Hnf1alpha mediates the glucocorticoid-induced precocious maturation of the intestine but rather are downstream targets of this process. Together, these data demonstrate that specific intestinal genes have differential requirements for Gata4 and Hnf1alpha that are dependent on the developmental time frame in which they are expressed.

A conditional model reveals that induction of hepatocyte nuclear factor-1alpha in Hnf1alpha-null mutant beta-cells can activate silenced genes postnatally, whereas overexpression is deleterious

Humans with heterozygous loss-of-function mutations in the hepatocyte nuclear factor-1alpha (HNF1alpha) gene develop beta-cell-deficient diabetes (maturity-onset diabetes of the young type 3), indicating that HNF1alpha gene dosage is critical in beta-cells. However, whether increased HNF1alpha expression might be beneficial or deleterious for beta-cells is unknown. Furthermore, although it is clear that HNF1alpha is required for beta-cell function, it is not known whether this role is cell autonomous or whether there is a restricted developmental time frame for HNF1alpha to elicit gene activation in beta-cells. To address this, we generated a tetracycline-inducible mouse model that transcribes HNF1alpha selectively in beta-cells in either wild-type or Hnf1alpha-null backgrounds. Short-term induction of HNF1alpha in islets from adult Hnf1alpha(-/-) mice that did not express HNF1alpha throughout development resulted in the activation of target genes, indicating that HNF1alpha has beta-cell-autonomous functions that can be rescued postnatally. However, transgenic induction throughout development, which inevitably resulted in supraphysiological levels of HNF1alpha, strikingly caused a severe reduction of cellular proliferation, increased apoptosis, and consequently beta-cell depletion and diabetes. Thus, HNF1alpha is sensitive to both reduced and excessive concentrations in beta-cells. This finding illustrates the paramount importance of using the correct concentration of a beta-cell transcription factor in both gene therapy and artificial differentiation strategies.

Hepatocyte nuclear factor-1alpha is required for expression but dispensable for histone acetylation of the lactase-phlorizin hydrolase gene in vivo

Hepatocyte nuclear factor-1alpha (HNF-1alpha) is a modified homeodomain-containing transcription factor that has been implicated in the regulation of intestinal genes. To define the importance and underlying mechanism of HNF-1alpha for the regulation of intestinal gene expression in vivo, we analyzed the expression of the intestinal differentiation markers and putative HNF-1alpha targets lactase-phlorizin hydrolase (LPH) and sucrase-isomaltase (SI) in hnf1alpha null mice. We found that in adult jejunum, LPH mRNA in hnf1alpha(-/-) mice was reduced 95% compared with wild-type controls (P < 0.01, n = 4), whereas SI mRNA was virtually identical to that in wild-type mice. Furthermore, SI mRNA abundance was unchanged in the absence of HNF-1alpha along the length of the adult mouse small intestine as well as in newborn jejunum. We found that HNF-1alpha occupies the promoters of both the LPH and SI genes in vivo. However, in contrast to liver and pancreas, where HNF-1alpha regulates target genes by recruitment of histone acetyl transferase activity to the promoter, the histone acetylation state of the LPH and SI promoters was not affected by the presence or absence of HNF-1alpha. Finally, we showed that a subset of hypothesized intestinal target genes is regulated by HNF-1alpha in vivo and that this regulation occurs in a defined tissue-specific and developmental context. These data indicate that HNF-1alpha is an activator of a subset of intestinal genes and induces these genes through an alternative mechanism in which it is dispensable for chromatin remodeling.

The transcriptional regulation of phosphoenolpyruvate carboxykinase gene in the kidney requires the HNF-1 binding site of the gene

The transcription of the cytosolic form of phosphoenolpyruvate carboxykinase (PEPCK-C) gene is differentially regulated in each of the several PEPCK-C-expressing tissues. In the kidney, it is regulated by glucocorticoids and acidosis. Previously, we reported that in LLC-PK1 and derived kidney cell lines, mutation of the hepatic nuclear factor 1 (HNF-1) binding site in PEPCK-C gene promoter markedly reduced both the basal activity of the gene promoter and its response to acidic pH. Using the same kidney cell line, we now report that nuclear receptors robustly stimulate transcription from the PEPCK-C gene promoter. This stimulation is markedly reduced by mutation of the accessory factor 1 (AF1) site in the glucocorticoid responsive unit (GRU) residing within the glucocorticoid-responsive domain. The stimulation is likewise reduced by mutation of the HNF-1 site, residing outside the nuclear receptor-responsive domain of the PEPCK-C gene promoter. There is no binding similarity between HNF-1 and AF1 binding sites, as is evident from gel shift assays showing a lack of competition of either site for the binding of renal nuclear proteins to the other. We further assessed that the regulation of PEPCK-C gene transcription by acidosis is not mediated by nuclear receptors. This became evident from studies of transgenic mice harboring a rat PEPCK-C transgene driven by truncated 5' flanking region of the gene, which contains the HNF-1 site but lacks the glucocorticoid responsive domain. The full transcriptional response of this transgene to acidosis establishes that the truncated 5' flanking region (362 bp) of the PEPCK-C gene contains the information required for the acidosis-mediated regulation independent of the glucocorticoid domain. Taking together the previous and present results, it appears that acidosis and nuclear receptors regulate the renal transcription of the PEPCK-C gene via two independent domains in the 5' flanking region of the gene. These two modulations, as well as the basal activity of the gene, require intact HNF-1 binding site in the gene promoter.

P21 functions to maintain quiescence of p27-deficient hepatocytes

Hepatocytes rarely proliferate in the healthy adult liver. We explored the roles of the cyclin kinase inhibitors p21 and p27 in maintaining hepatocyte quiescence. p27 is expressed throughout the wild-type liver, but the related protein p21 was not detected. However, p21 was detected in livers of p27-deficient mice. Increased p21 protein levels did not result from an increase in p21 mRNA expression, indicating that p21 expression is regulated post-transcriptionally. p21 protein levels increased in cultured primary hepatocytes treated with the proteasome inhibitor MG132 and cycloheximide, indicating that p21 expression is regulated at the level of protein stability in liver cells. Although increased expression of cyclin-dependent kinase (Cdk) 4, Cdk2, and proliferating cell nuclear antigen was detected in p27-deficient livers, increased hepatocyte proliferation was detected only in livers of mice deficient for both p21 and p27. In p27-deficient livers, p21 was found in complexes with Cdk2 and CdK4 and can compensate for the absence of p27. Our data indicate that cyclin kinase inhibitor activity is important for maintaining hepatocyte quiescence in the adult liver. Significant increases in p21 were detected in multiple tissues of mature p27-deficient mice compared with wild-type mice, suggesting that the ability of p21 to functionally substitute for p27 is not liver-specific.

Hepatocyte nuclear factor 1 alpha controls renal expression of the Npt1-Npt4 anionic transporter locus

Hepatocyte nuclear factor 1 alpha (HNF1alpha) is a transcription factor that is expressed in liver, pancreas, kidney and intestine. Mice lacking HNF1alpha are born normally but suffer from several defects including hyperphenylalaninemia, defective bile acid and cholesterol metabolism, an insulin secretion defect and renal Fanconi syndrome. The renal phenotype involves a defect in renal proximal tubule reabsorption, leading to polyuria, glucosuria, aminoaciduria and phosphaturia. We investigated the expression of genes encoding members of the sodium/phosphate cotransporter (Na(+)/Pi) family (namely Npt1, Npt2, Npt4 and Ram1). We show that Npt1 and Npt4 genes were expressed at reduced levels in the kidneys of HNF1alpha -/- mice, whereas the expression of Npt2, the major renal phosphate transporter, was not affected. Analysis of the Npt1 genomic sequence revealed the existence of several alternative promoters activated in liver and/or in kidney. All of these were down-regulated in the kidneys of HNF1alpha -/- animals. Several HNF1alpha binding sites (BS) play an important role in the transcriptional control of this locus, including low-affinity HNF1 BSs localised in a DNase I hypersensitivity site (HSS3). Transient transfection experiments confirmed that HNF1alpha directly transactivates the Npt1 promoter and that the HSS3 region contributes to this activation.

Hepatocyte nuclear factor 1alpha controls the expression of terminal complement genes

The terminal components of the complement system contribute to host defense by forming the multiprotein membrane attack complex (MAC) which is responsible for cell lysis and several noncytotoxic effects. Most of the complement proteins are synthesized in the liver, but the mechanisms controlling their tissue-specific expression have not been elucidated. In this study we show that mice lacking the hepatic transcription factor hepatocyte nuclear factor 1alpha (HNF1alpha) fail to transcribe C5 and C8A complement genes. In addition, mRNAs encoding for several other terminal complement components or subunits are expressed at lower levels, including C8beta, C8gamma, and C9. We next used a reconstitution assay involving human sera with selective complement deficiencies to assess mouse complement activity. Sera from HNF1alpha-deficient mice showed negligible hemolytic activity of both C5 and C8alpha-gamma subunits. The activity of C8beta was severely affected despite only a 50% reduction in C8beta mRNA levels in the liver. This is reminiscent of C8alpha-gamma-deficient patients who accumulate extremely low levels of the C8beta subunit. Our results demonstrate that HNF1alpha plays a key role in the expression of C5 and C8A genes, two terminal complement component genes that are essential for the assembly of MAC as a result of complement activation.