The transcription factor, signal transducer and activator of transcription-3 (STAT-3) contributes to various physiological processes. Here we show that mice with liver-specific deficiency in STAT-3, achieved using the Cre-loxP system, show insulin resistance associated with increased hepatic expression of gluconeogenic genes. Restoration of hepatic STAT-3 expression in these mice, using adenovirus-mediated gene transfer, corrected the metabolic abnormalities and the alterations in hepatic expression of gluconeogenic genes. Overexpression of STAT-3 in cultured hepatocytes inhibited gluconeogenic gene expression independently of peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1 alpha), an upstream regulator of gluconeogenic genes. Liver-specific expression of a constitutively active form of STAT-3, achieved by infection with an adenovirus vector, markedly reduced blood glucose, plasma insulin concentrations and hepatic gluconeogenic gene expression in diabetic mice. Hepatic STAT-3 signaling is thus essential for normal glucose homeostasis and may provide new therapeutic targets for diabetes mellitus.

The protein p27(Kip1) regulates cell cycle progression in mammals by inhibiting the activity of cyclin-dependent kinases (CDKs). Here we show that p27(Kip1) progressively accumulates in the nucleus of pancreatic beta cells in mice that lack either insulin receptor substrate 2 (Irs2(-/-)) or the long form of the leptin receptor (Lepr(-/-) or db/db). Deletion of the gene encoding p27(Kip1) (Cdkn1b) ameliorated hyperglycemia in these animal models of type 2 diabetes mellitus by increasing islet mass and maintaining compensatory hyperinsulinemia, effects that were attributable predominantly to stimulation of pancreatic beta-cell proliferation. Thus, p27(Kip1) contributes to beta-cell failure during the development of type 2 diabetes in Irs2(-/-) and Lepr(-/-) mice and represents a potential new target for the treatment of this condition.

Polycomb genes in Drosophila maintain the repressed state of homeotic and other developmentally regulated genes by mediating changes in higher-order chromatin structure. M33, a mouse homologue of Polycomb, was isolated by means of the structural similarity of its chromodomain. The fifth exon of M33 contains a region of homology shared by Drosophila and Xenopus. In Drosophila, its deletion results in the loss of Polycomb function. Here we have disrupted M33 in mice by inserting a poly(A) capture-type neo(r) targeting vector into its fifth exon. More than half of the resultant M33cterm/M33cterm mutant mice died before weaning, and survivors showed male-to-female sex reversal. Formation of genital ridges was retarded in both XX and XY M33cterm/M33cterm embryos. Gonadal growth defects appeared near the time of expression of the Y-chromosome-specific Sry gene, suggesting that M33 deficiency may cause sex reversal by interfering with steps upstream of Sry. M33cterm/M33cterm mice may be a valuable model in which to test opposing views regarding sex determination.

Recent studies have demonstrated the importance of insulin or insulin-like growth factor 1 (IGF-1) for regulation of pancreatic ␤-cell mass. Given the role of tuberous sclerosis complex 2 (TSC2) as an upstream molecule of mTOR (mammalian target of rapamycin), we examined the effect of TSC2 deficiency on ␤-cell function. Here, we show that mice deficient in TSC2, specifically in pancreatic ␤ cells (␤TSC2 ؊/؊ mice), manifest increased IGF-1-dependent phosphorylation of p70 S6 kinase and 4E-BP1 in islets as well as an initial increased islet mass attributable in large part to increases in the sizes of individual ␤ cells. These mice also exhibit hypoglycemia and hyperinsulinemia at young ages (4 to 28 weeks). After 40 weeks of age, however, the ␤TSC2 ؊/؊ mice develop progressive hyperglycemia and hypoinsulinemia accompanied by a reduction in islet mass due predominantly to a decrease in the number of ␤ cells. These results thus indicate that TSC2 regulates pancreatic ␤-cell mass in a biphasic manner.

The total mass of islets of Langerhans is reduced in individuals with type 2 diabetes, possibly contributing to the pathogenesis of this condition. Although the regulation of islet mass is complex, recent studies have suggested the importance of a signaling pathway that includes the insulin or insulin-like growth factor-1 receptors, insulin receptor substrate and phosphatidylinositol (PI) 3-kinase. 3-Phosphoinositide-dependent protein kinase 1 (PDK1) is a serine-threonine kinase that mediates signaling downstream of PI 3-kinase. Here we show that mice that lack PDK1 specifically in pancreatic beta cells (betaPdk1-/- mice) develop progressive hyperglycemia as a result of a loss of islet mass. The mice show reductions in islet density as well as in the number and size of cells. Haploinsufficiency of the gene for the transcription factor Foxo1 resulted in a marked increase in the number, but not the size, of cells and resulted in the restoration of glucose homeostasis in betaPdk1-/- mice. These results suggest that PDK1 is important in maintenance of pancreatic cell mass and glucose homeostasis.

In addition to T cell receptor (TCR) ligation, activation of CD28 coreceptor by costimulatory molecule B7 is required for transcription factor NF-κB induction and robust T cell activation, though exactly how CD28 contributes to this remains incompletely understood. We demonstrated here that phosphoinositide-dependent kinase 1 (PDK1) plays an essential role in integrating TCR and CD28 signals. Upon deletion of PDK1 in T cells, TCR-CD28 signals failed to induce NF-κB activation or protein kinase C θ (PKC-θ) phosphorylation, although T cell survival and pathways dependent on p38 and Jnk kinases or transcription factor NF-AT were unaffected. CD28 facilitated NF-κB activation by regulating PDK1 recruitment and phosphorylation, which are necessary for efficient binding of PDK1 to PKC-θ and CARMA1, and thus for NF-κB induction.

Cortactin is an actin filament-binding protein localizing at cortical regions of cells and a prominent substrate for Src family protein-tyrosine kinases in response to multiple extracellular stimuli. Human cortactin has been identified as a protein product of a putative oncogene, EMS1. In this report, we describe the identification of a Drosophila homolog of cortactin as a molecule that interacts with Drosophila ZO-1 using yeast twohybrid screening. Drosophila cortactin is a 559-amino acid protein highly expressed in embryos, larvae, and pupae but relatively underexpressed in adult flies. Deletion and substitution mutant analyses revealed that the SH3 domain of Drosophila cortactin binds to a PXXP motif in the proline-rich domain of Drosophila ZO-1. Colocalization of these proteins at cell-cell junction sites was evident under a confocal laser-scanning microscope. In vivo association was confirmed by coimmunoprecipitation of cortactin and ZO-1 from Drosophila embryo lysates. We also demonstrate an association for each of the murine homologs by immunoprecipitation analyses of mouse tissue lysates. Our previous work has demonstrated the involvement of ZO-1 in a signaling pathway that regulates expression of the emc gene in Drosophila. The potential roles of the cortactin⅐ZO-1 complex in cell adhesion and cell signaling are discussed.Cell-cell adhesions are essential for the development of the multicellular organisms. Among the proteins composing the cell-cell adhesion complexes, members of the membrane-associated guanylate kinase homologs (MAGUKs) 1 are widely found in Hydra, Caenorhabditis elegans, Drosophila, and mammals (1-3). MAGUKs have distinctive domains including one or three copies of the PDZ domain, an SH3 domain, and a domain homologous to guanylate kinase (GUK) and implicated in both formation of cell-cell junctions and signal transduction. One of the most intensively characterized members of the MAGUKs is the mammalian ZO-1, which is known to associate with several cellular proteins including the components of cell-cell junctions (occludin, ␤-catenin, and ZO-2) and the components of cytoskeletal networks (␣-spectrin and actin filaments (F-actin)) (4 -9). While ZO-1 has been considered as a homolog of a Drosophila tumor suppresser Dlg, its biological functions in the cell-cell junction and signal transduction remain obscure (10, 11).We recently identified a new Drosophila MAGUK protein, Tamou, and reported its significant homology with ZO-1 (12). We will refer to Tamou as Drosophila ZO-1 (DZO-1) because we also found that the transgenes of mouse ZO-1 could replace the tam gene function in Drosophila.2 The DZO-1 tam1 mutant flies exhibit the supernumerary mechanosensory organs. This is a similar phenotype to that of an extramacrochaetae (emc) mutation. The emc gene encodes a helix-loop-helix type transcriptional regulator and negatively regulates specification of sensory organ precursor cells (13-16). We have previously shown that DZO-1 locates at cell-cell junctions and is involved in the signaling p...

Pancreatic β cell failure is thought to underlie the progression from glucose intolerance to overt diabetes, and ER stress is implicated in such β cell dysfunction. We have now shown that the transcription factor CCAAT/ enhancer-binding protein β (C/EBPβ) accumulated in the islets of diabetic animal models as a result of ER stress before the onset of hyperglycemia. Transgenic overexpression of C/EBPβ specifically in β cells of mice reduced β cell mass and lowered plasma insulin levels, resulting in the development of diabetes. Conversely, genetic ablation of C/EBPβ in the β cells of mouse models of diabetes, including Akita mice, which harbor a heterozygous mutation in Ins2 (Ins2 WT/C96Y ), and leptin receptor-deficient (Lepr -/-) mice, resulted in an increase in β cell mass and ameliorated hyperglycemia. The accumulation of C/EBPβ in pancreatic β cells reduced the abundance of the molecular chaperone glucose-regulated protein of 78 kDa (GRP78) as a result of suppression of the transactivation activity of the transcription factor ATF6α, thereby increasing the vulnerability of these cells to excess ER stress. Our results thus indicate that the accumulation of C/EBPβ in pancreatic β cells contributes to β cell failure in mice by enhancing susceptibility to ER stress.