The RNA polymerase III subunit Polr3b is required for the maintenance of small intestinal crypts in mice.

BACKGROUND & AIMS: The continuously self-renewing mammalian intestinal epithelium, with high cellular turnover, depends on adequate protein synthesis for its proliferative capacity. RNA polymerase III activity is closely related to cellular growth and proliferation. Here, we studied the role of Polr3b, a large RNA polymerase III subunit, in the mammalian intestinal epithelium. METHODS: We derived mice with an intestinal epithelium-specific hypomorphic mutation of the Polr3b gene, using VillinCre-mediated gene ablation. Phenotypic consequences of the Polr3b mutation on the intestinal epithelium in mice were assessed using histological and molecular methodologies, including genetic lineage tracing. RESULTS: The Polr3b mutation severely reduced survival and growth in mice during the first postnatal week, the period when the expansion of the intestinal epithelium, and thus the requirement for protein synthesis, are highest. The neonatal intestinal epithelium of Polr3bloxP/loxP;VillinCre mice was characterized by areas with reduced proliferation, abnormal epithelial architecture, loss of Wnt signaling and a dramatic increase in apoptotic cells in crypts. Genetic lineage tracing using Polr3bLoxP/LoxP;Rosa26-lox-stop-lox-YFP;VillinCre mice demonstrated that in surviving mutant mice, Polr3b-deficient dying crypts were progressively replaced by 'Cre-escaper' cells that had retained wild type Polr3b function. In addition, enteroids cultured from Polr3bloxP/loxP;VillinCre mice show reduced proliferative activity and increased apoptosis. CONCLUSIONS: We provide evidence for an essential role of the Pol III subunit Polr3b in orchestrating the maintenance of the intestinal crypt during early postnatal development in mice.

CAP2 in cardiac conduction, sudden cardiac death and eye development.

Sudden cardiac death kills 180,000 to 450,000 Americans annually, predominantly males. A locus that confers a risk for sudden cardiac death, cardiac conduction disease, and a newly described developmental disorder (6p22 syndrome) is located at 6p22. One gene at 6p22 is CAP2, which encodes a cytoskeletal protein that regulates actin dynamics. To determine the role of CAP2 in vivo, we generated knockout (KO) mice. cap2(-)/cap2(-) males were underrepresented at weaning and ~70% died by 12 weeks of age, but cap2(-)/cap2(-) females survived at close to the expected levels and lived normal life spans. CAP2 knockouts resembled patients with 6p22 syndrome in that mice were smaller and they developed microphthalmia and cardiac disease. The cardiac disease included cardiac conduction disease (CCD) and, after six months of age, dilated cardiomyopathy (DCM), most noticeably in the males. To address the mechanisms underlying these phenotypes, we used Cre-mediated recombination to knock out CAP2 in cardiomyocytes. We found that the mice developed CCD, leading to sudden cardiac death from complete heart block, but no longer developed DCM or the other phenotypes, including sex bias. These studies establish a direct role for CAP2 and actin dynamics in sudden cardiac death and cardiac conduction disease.

Protein tyrosine phosphatase of liver regeneration-1 is required for normal timing of cell cycle progression during liver regeneration.

Protein tyrosine phosphatase of liver regeneration-1 (Prl-1) is an immediate-early gene that is significantly induced during liver regeneration. Several in vitro studies have suggested that Prl-1 is important for the regulation of cell cycle progression. To evaluate its function in liver regeneration, we ablated the Prl-1 gene specifically in mouse hepatocytes using the Cre-loxP system. Prl-1 mutant mice (Prl-1(loxP/loxP);AlfpCre) appeared normal and fertile. Liver size and metabolic function in Prl-1 mutants were comparable to controls, indicating that Prl-1 is dispensable for liver development, postnatal growth, and hepatocyte differentiation. Mutant mice demonstrated a delay in DNA synthesis after 70% partial hepatectomy, although ultimate liver mass restoration was not affected. At 40 h posthepatectomy, reduced protein levels of the cell cycle regulators cyclin E, cyclin A2, cyclin B1, and cyclin-dependent kinase 1 were observed in Prl-1 mutant liver. Investigation of the major signaling pathways involved in liver regeneration demonstrated that phosphorylation of protein kinase B (AKT) and signal transducer and activator of transcription (STAT) 3 were significantly reduced at 40 h posthepatectomy in Prl-1 mutants. Taken together, this study provides evidence that Prl-1 is required for proper timing of liver regeneration after partial hepatectomy. Prl-1 promotes G1/S progression via modulating expression of several cell cycle regulators through activation of the AKT and STAT3 signaling pathway.

Genome-wide location analysis reveals distinct transcriptional circuitry by paralogous regulators Foxa1 and Foxa2.

Gene duplication is a powerful driver of evolution. Newly duplicated genes acquire new roles that are relevant to fitness, or they will be lost over time. A potential path to functional relevance is mutation of the coding sequence leading to the acquisition of novel biochemical properties, as analyzed here for the highly homologous paralogs Foxa1 and Foxa2 transcriptional regulators. We determine by genome-wide location analysis (ChIP-Seq) that, although Foxa1 and Foxa2 share a large fraction of binding sites in the liver, each protein also occupies distinct regulatory elements in vivo. Foxa1-only sites are enriched for p53 binding sites and are frequently found near genes important to cell cycle regulation, while Foxa2-restricted sites show only a limited match to the forkhead consensus and are found in genes involved in steroid and lipid metabolism. Thus, Foxa1 and Foxa2, while redundant during development, have evolved divergent roles in the adult liver, ensuring the maintenance of both genes during evolution.

p21-Activated kinase 1 (Pak1) phosphorylates BAD directly at serine 111 in vitro and indirectly through Raf-1 at serine 112.

BACKGROUND: Cell survival depends on the balance between protective and apoptotic signals. When the balance of signals tips towards apoptosis, cells undergo programmed cell death. This balance has profound implications in diseases including cancer. Oncogenes and tumor suppressors are mutated to promote cell survival during tumor development, and many chemotherapeutic drugs kill tumor cells by stimulating apoptosis. BAD is a pro-apoptotic member of the Bcl-2 family of proteins, which can be phosphorylated on numerous sites to modulate binding to Bcl-2 and 14-3-3 proteins and inhibit its pro-apoptotic activities. One of the critical phosphorylation sites is the serine 112 (S112), which can be phosphorylated by several kinases including Pak1. METHODOLOGY/PRINCIPAL FINDINGS: We mapped the Pak phosphorylation sites by making serine to alanine mutations in BAD and testing them as substrates in in vitro kinase assays. We found that the primary phosphorylation site is not S112 but serine 111 (S111), a site that is sometimes found phosphorylated in vivo. In transfection assays of HEK293T cells, we showed that Pak1 required Raf-1 to stimulate phosphorylation on S112. Mutating either S111 or S112 to alanine enhanced binding to Bcl-2, but the double mutant S111/112A bound better to Bcl-2. Moreover, BAD phosphorylation at S111 was observed in several other cell lines, and treating one of them with the Pak1 inhibitor 2,2'-Dihydroxy-1,1'-dinaphthyldisulfide (IPA-3) reduced phosphorylation primarily at S112 and to a smaller extent at S111, while Raf inhibitors only reduced phosphorylation at S112. CONCLUSION/SIGNIFICANCE: Together, these findings demonstrate that Pak1 phosphorylates BAD directly at S111, but phosphorylated S112 through Raf-1. These two sites of BAD serve as redundant regulatory sites for Bcl-2 binding.

Foxa1 and Foxa2 control the differentiation of goblet and enteroendocrine L- and D-cells in mice.

BACKGROUND & AIMS: The winged helix transcription factors Foxa1 and Foxa2 are expressed in all epithelia of the gastrointestinal tract from its embryonic origin into adulthood. In vitro studies have shown that Foxa1/a2 can transactivate the promoters of Mucin 2 (Muc2), which is expressed in goblet cells, and of preproglucagon, which is expressed in enteroendocrine cells. These findings suggest Foxa1/a2 as critical factors in the differentiation of gut epithelial cells. METHODS: Mice with intestine-specific simultaneous deletion of Foxa1 and Foxa2 were derived using the Cre-loxP system and analyzed using histologic and molecular means. RESULTS: Both Foxa1 and Foxa2 were deleted successfully in the epithelia of the small intestine and colon using Villin-Cre mice. Immunohistochemical staining showed that Foxa1/a2 mutants lack glucagon-like peptide-1- and peptide-2-expressing cells (L-cells), and have reduced numbers of somatostatin (D-cells) and peptide YY-expressing cells (L-cells). Preproglucagon, somatostatin, and peptide YY messenger RNA (mRNA) levels also were reduced significantly in Foxa1/a2 mutants. Thus, Foxa1 and Foxa2 are essential regulators of these enteroendocrine lineages in vivo. The mRNA levels of transcription factors Islet-1 and Pax6 were reduced significantly in the small intestine, showing that Foxa1 and Foxa2 impact on a transcription factor network in the enteroendocrine lineage. In addition, deletion of Foxa1/a2 caused a reduction in goblet cell number with altered expression of the secretory mucins Muc2, Mucin5b, Mucin5ac, and Mucin 6. CONCLUSIONS: The winged helix factors Foxa1 and Foxa2 are essential members of the transcription factor network that govern secretory cell differentiation in the mammalian gastrointestinal tract.

MafA expression and insulin promoter activity are induced by nicotinamide and related compounds in INS-1 pancreatic beta-cells.

Nicotinamide has been reported to induce differentiation of precursor/stem cells toward a beta-cell phenotype, increase islet regeneration, and enhance insulin biosynthesis. Exposure of INS-1 beta-cells to elevated glucose leads to reduced insulin gene transcription, and this is associated with diminished binding of pancreatic duodenal homeobox factor 1 (PDX-1) and mammalian homologue of avian MafA/l-Maf (MafA). Nicotinamide and other low-potency poly(ADP-ribose) polymerase (PARP) inhibitors were thus tested for their ability to restore insulin promoter activity. The low-potency PARP inhibitors nicotinamide, 3-aminobenzamide, or PD128763 increased expression of a human insulin reporter gene suppressed by elevated glucose. In contrast, the potent PARP-1 inhibitors PJ34 or INO-1001 had no effect on promoter activity. Antioxidants, including N-acetylcysteine, lipoic acid, or quercetin, only minimally induced the insulin promoter. Site-directed mutations of the human insulin promoter mapped the low-potency PARP inhibitor response to the C1 element, which serves as a MafA binding site. INS-1 cells exposed to elevated glucose had markedly reduced MafA protein and mRNA levels. Low-potency PARP inhibitors restored MafA mRNA and protein levels, but they had no affect on PDX-1 protein levels or binding activity. Increased MafA expression by low-potency PARP inhibitors was independent of increased MafA protein or mRNA stability. These data suggest that low-potency PARP inhibitors increase insulin biosynthesis, in part, through a mechanism involving increased MafA gene transcription.

Elevated glucose attenuates human insulin gene promoter activity in INS-1 pancreatic beta-cells via reduced nuclear factor binding to the A5/core and Z element.

Chronic exposure of pancreatic beta-cells to elevated glucose reduces insulin gene promoter activity, and this is associated with diminished binding of two beta-cell-enriched transcription factors, Pdx-1 and MafA. In this study using INS-1 beta-cells, overexpression of MafA, but not Pdx-1, was able to restore expression of a human insulin reporter gene (-327 to +30 bp) suppressed by elevated glucose. At issue, however, was that MafA also markedly stimulated an insulin reporter gene (-230 to +30 bp) that was only marginally suppressed by glucose, suggesting that glucose-mediated suppression of the insulin promoter involved elements upstream of -230. Using serial truncations and mini-enhancer constructs of the human insulin promoter, the majority of glucose suppression was localized to regulatory elements between -327 and -261. Nuclear extracts from INS-1 cells exposed to elevated glucose had reduced binding activities to the A5/core (-319 to -307), and to a palindrome (-284 to -267) and an E box (-273 to -257, E3) contained within the Z element. The A5/core binding complex was determined to contain MafA, Pdx-1, and an A2-like binding factor. Two mini-enhancer constructs containing the A5/core were suppressed by glucose and strongly activated by MafA. Glucose-mediated suppression of the Z mini-enhancer was not attenuated by overexpression of MafA or Pdx-1. Site-directed mutation of the A5/core, palindrome, and E3 elements attenuated glucose-mediated suppression. These data indicate that glucose suppression of human insulin promoter activity in INS-1 cells involves reduced binding of MafA to the A5/core. Changes in nuclear factor binding to the Z element, which functions as a strong activator element in primary islets and a negative regulatory element in simian virus 40 or T antigen transformed beta-cell lines, also participate in glucose suppression of insulin promoter activity.

Function and regulation of endothelin-1 and its receptors in salt sensitive hypertension induced by sensory nerve degeneration.

To determine the role of endothelin-1 (ET-1) and its receptors in salt-sensitive hypertension induced by sensory nerve degeneration, selective ET(A) antagonist (ABT-627) and ET(B) antagonist (A-192621) were used. Newborn Wistar rats were given vehicle or 50 mg/kg capsaicin subcutaneously on the first and second days of life. After the weaning period, male rats were divided into eight groups, and subjected to the following treatments for 2 weeks: control + normal salt diet (Con+NS, 0.5%), control + high salt diet (Con+HS, 4%), control + high salt diet + ABT-627 (Con+HS+ABT-627), control + high salt diet + A-192621 (Con+HS+A-192621), capsaicin + normal salt diet (Cap+NS), capsaicin + high salt diet (Cap+HS), capsaicin + high salt diet + ABT-627 (Cap+HS+ABT-627), capsaicin + high salt diet + A-192621 (Cap+HS+A-192621). Both ABT-627 (5 mg/kg/d) and A-192621 (30 mg/kg/d) were given by oral gavage twice a day. Mean arterial pressure (MAP, mm Hg) was higher in Con+HS+A-192621 (141 +/-11) than in Con+NS (94 +/- 10), Con+HS (95 +/- 5), and Con+HS+ABT-627 (97 +/- 6) (P<0.05). MAP was also higher in Cap+HS (152 +/- 6) and Cap+HS+A-192621 (180 +/- 7) than in Cap+NS (99 +/- 3) and Cap+HS+ABT-627 (104 +/- 5) (P<0.05), and it was higher in Cap+HS+A-192621 than in Cap+HS (P<0.05). Enzyme immunometric assay showed that ET-1 plasma concentration (pg/mL) was higher in Con+HS+A-192621 (7.59 +/- 0.78) than in Con+NS (2.68 +/- 0.56), Con+HS (2.50 +/- 0.92), and Con+HS+ABT-627 (3.54 +/- 0.79) (P<0.05). ET-1 plasma concentration was also higher in Cap+HS (8.95 +/-.16), Cap+HS+ABT-627 (9.82 +/- 1.22) and Cap+HS+A-192621 (10.97 +/- 0.57) than in Cap+NS (3.06 +/- 0.73) (P<0.05). We conclude that blockade of the ET(A) receptor prevents the development of salt sensitive hypertension induced by sensory nerve degeneration, indicating that activation of the ET(A) receptor by increased plasma ET-1 level contributes to elevation of blood pressure in this model. In contrast, blockade of the ET(B) receptor leads to an increase in blood pressure in both normal and sensory nerve degenerated rats fed a high salt diet. These results suggest that ET(B) plays an antihypertensive role in response to high salt intake under both normal and sensory nerve degenerated conditions.