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OBJECTIVE--Phogrin and IA-2, autoantigens in insulin-dependent diabetes, have been shown to be involved in insulin secretion in pancreatic β-cells; however, implications at a molecular level are confusing from experiment to experiment. We analyzed biological functions of phogrin in β-cells by an RNA interference technique. RESEARCH DESIGN AND METHODS--Adenovirus-mediated expression of short hairpin RNA specific for phogrin (shPhogrin) was conducted using cultured p-cell lines and mouse islets. Both glucose-stimulated insulin secretion and cell proliferation rate were determined in the phogrin-knockdown cells. Furthermore, protein expression was profiled in these cells. To see the binding partner of phogrin in β-cells, coimmunoprecipitation analysis was carried out. RESULTS--Adenoviral expression of shPhogrin efficiently decreased its endogenous expression in pancreatic β-cells. Silencing of phogrin in β-cells abrogated the glucose-mediated mitogenic effect, which was accompanied by a reduction in the level of insulin receptor substrate 2 (IRS2) protein, without any changes in insulin secretion. Phogrin formed a complex with insulin receptor at the plasma membrane, and their interaction was promoted by high-gincose stimulation that in turn led to stabilization of IRS2 protein. Corroboratively, phogrin knockdown had no additional effect on the proliferation of p-cell line derived from the insulin receptor-knockout mouse. CONCLUSIONS--Phogrin is involved in p-cell growth via regulating stability of IRS2 protein by the molecular interaction with insulin receptor. We propose that phogrin and IA-2 function as an essential regulator of autocrine insulin action in pancreatic β-cells., Glucose is a principle regulator pancreatic B-cell survival and growth as well as insulin secretion (1). It is a potent mitogen on pancreatic B-cells and regulates islet β-cells mass through [...]

Parathyroid hormone-related protein (PTHrP) increases the content and mRNA level of insulin in a mouse β-cell line, MIN6, and primary-cultured mouse islets. We examined the mechanism of PTHrP-induced insulin expression. The PTHrP effect was markedly augmented by SB203580, a mitogen-activated protein (MAP) kinase inhibitor, and SB203580 itself increased insulin expression extensively, even without PTHrP. Because SB203580 inhibits both p38 and c-jun N[H.sub.2]-terminal kinases (JNKs), we investigated the JNK-specific inhibitor SP600125. SP600125 also increased insulin content and its mRNA level. PTHrP induced dephosphorylation of JNK1/2, and PTHrP-induced insulin expression was blocked by a dominant-negative type JNK-APF. We suspected that dual specificity MAP kinase phosphatases (MKPs) may be involved in the PTHrP-induced insulin expression by inactivating JNK1/2. MIN6 cells contained at least five MKPs, among which only MKP-1 was inducible by PTHrP. PTHrP-induced insulin expression was blocked by the MKP-1 expression inhibitor Ro-31-8220, indicating that the PTHrP effect is mediated by MKP-1. Indeed, adenoviral MKP-1 expression increased insulin expression by decreasing a phosphorylation form of JNKs and a resulting phosphorylated form of c-jun in MIN6 cells. The phosphorylated form of c-jun is known to repress cAMP-dependent insulin gene promoter activity. Thus, MKP-1 controls the insulin expression by downregulating a JNK/c-jun pathway., Parathyroid hormone-related protein (PTHrP) controls the growth and differentiation of pancreatic β-cells (1-3). Previously, we demonstrated the effect of PTHrP using the well-differentiated mouse pancreatic β-cell line MIN6 (4). PTHrP [...]

Autosomal dominant diabetes in the Akita mouse is caused by mutation of the insulin 2 gene, whose product replaces a cysteine residue that is engaged in the formation of an intramolecular disulfide bond. These heterozygous mice exhibit severe insulin deficiency despite coexpression of normal insulin molecules derived from three other wild-type alleles of the insulin 1 and 2 genes. Although the results of our previous study suggested that the mutant proinsulin 2 is misfolded and blocked in the transport from the endoplasmic reticulum to the Golgi apparatus, its dominant negative nature has not been fully characterized. In the present study, we investigated the possible pathogenic mechanisms induced by the mutant proinsulin 2. There is no evidence that the mutant proinsulin 2 attenuates the overall protein synthesis rate or promotes the formation of aberrant disulfide bonds. The trafficking of constitutively secreted alkaline phosphatase, however, is significantly decreased in the islets of Akita mice, indicating that the function of early secretory pathways is nonspecifically impaired. Morphological analysis has revealed that secretory pathway organelle architecture is progressively devastated in the β-cells of Akita mice. These findings suggest that the organelle dysfunction resulting from the intracellular accumulation of misfolded proinsulin 2 is primarily responsible for the defect of coexisting wild-type insulin secretion in Akita β-cells., Defective folding of membrane-bound and soluble proteins is known to be the basis of many inherited diseases (1). Synthesized cargo proteins are first inserted into the endoplasmic reticulum (ER) and [...]

One form of maturity-onset diabetes of the young, MODY3, is characterized by a severe insulin secretory defect, compared with MODY2, a glucokinase-deficient diabetes. It has recently been shown that mutations [...]

We have previously reported that in the well-differentiated Β-cell line MIN6 cells, the Β-cell-specific differentiated characteristics, such as insulin content, expression of prohormone convertases PC2 and PC3, and glucose-regulated insulin [...]

The receptor-type protein tyrosine kinases in murine pancreatic islets were screened to identify possible growth/differentiation factors in pancreatic Β-cells. The analysis revealed that insulin receptor-related receptor (IRR) is highly expressed [...]

The phenotype of the insulin receptor substrate (IRS)-2 knockout mouse indicates that an IRS-2-mediated signaling pathway controls the compensatory increase in pancreatic [Beta]-cell mass in insulin-resisrant states. To identify the [...]

The molecular pathogenesis of diabetes remains poorly understood because of the genetic complexity of the disease. One possibly effective approach to elucidate the pathogenesis is to study an animal model [...]

The molecular pathogenesis of diabetes remains poorly understood because of the genetic complexity of the disease. One possibly effective approach to elucidate the pathogenesis is to study an animal model [...]

Comparison of genes expressed in pancreatic [Alpha] and [Beta] cell lines has revealed a novel rabphilin3-1ike gene, named granuphilin. The domain structure of the protein products of granuphilin is similar [...]

FKHR is a mammalian homologue of C. elegans gene daf16. By genetic analysis of C. elegans, daf16 is known to be controlled by daf2, age-1, akt-1 and akt-2, which are [...]

Recent studies have revealed mutations in the gene encoding the transcription factor hepatocyte nuclear factor (HNF)-1[Alpha] to be the cause of one form of maturity-onset diabetes of the young (MODY), [...]

Maturity-onset diabetes of the young (MODY) is a monogenic form of NIDDM characterized by an early age of onset, often in childhood or adolescence and usually [is less than] 25 [...]