Seroreactivity Against Tyrosine Phosphatase PTPRN Links Type 2 Diabetes and Colorectal Cancer and Identifies a Potential Diagnostic and Therapeutic Target.

Colorectal cancer (CRC) and diabetes are two of the most prevalent chronic diseases worldwide with dysregulated receptor tyrosine kinase signaling and strong co-occurrence correlation. Plasma autoantibodies represent a promising early diagnostic marker for both diseases before symptoms appear. In this study, we explore the value of autoantibodies against receptor-type tyrosine-protein phosphatase-like N (PTPRN; full-length or selected domains) as diagnostic markers using a cohort of individuals with type 2 diabetes (T2D), CRC, or both diseases or healthy individuals. We show that PTPRN autoantibody levels in plasma discriminated between patients with T2D with and without CRC. Consistently, high PTPRN expression correlated with decreased survival of patients with CRC. Mechanistically, PTPRN depletion significantly reduced invasiveness of CRC cells in vitro and liver homing and metastasis in vivo by means of a dysregulation of the epithelial-mesenchymal transition and a decrease of the insulin receptor signaling pathway. Therefore, PTPRN autoantibodies may represent a particularly helpful marker for the stratification of patients with T2D at high risk of developing CRC. Consistent with the critical role played by tyrosine kinases in diabetes and tumor biology, we provide evidence that tyrosine phosphatases such as PTPRN may hold potential as therapeutic targets in patients with CRC.

Rab35 regulates insulin secretion via phogrin in pancreatic ß cells.

Dysfunction of pancreatic ß cell insulin secretion is related to the pathogenesis of type 2 diabetes (T2D). Rab proteins have been shown to be key players in insulin secretion by pancreatic ß cells, and phogrin is a marker for the processes of exocytosis and insulin secretion. The purposes of this study were to clarify the regulatory role of Rab35 in insulin secretion and analyse the Rab35/phogrin interaction mechanism in ß-TC-6 cells. We studied the effects of Rab35 gene overexpression and interference on insulin secretion and phogrin expression and levels in ß-TC-6 cells. The Rab35/phogrin interaction was verified by GST pulldown, co-IP and co-localisation experiments. Here, we report that Rab35 is mainly distributed in the ß-TC-6-cell plasma membrane and cytoplasm. Rab35 overexpression promotes insulin secretion and decreases phogrin expression in ß-TC-6 cells, whereas its silencing significantly inhibits insulin secretion, promotes phogrin expression (p < 0.05) and causes phogrin redistribution. Furthermore, Rab35 silencing suppresses exocytosis of insulin. Rab35 interacts with phogrin, and both proteins co-localise in the plasma membranes and cytoplasm of ß-TC-6 cells. Our study presents novel evidence that Rab35 regulates insulin secretion by inhibiting phogrin expression and causing intracellular phogrin redistribution in pancreatic ß cells.

Expression and function of IA-2 family proteins, unique neuroendocrine-specific protein-tyrosine phosphatases.

IA-2 (also known as islet cell antigen ICA-512) and IA-2 beta (also known as phogrin, phosphatase homologue in granules of insulinoma) are major autoantigens in insulin-dependent diabetes mellitus (IDDM). Autoantibodies against both proteins are expressed years before clinical onset, and they become predictive markers for high-risk subjects. However, the role of these genes in the IDDM pathogenesis has been reported fairly negative by recent studies. IA-2 and IA-2 beta are type I transmembrane proteins that possess one inactive protein-tyrosine phosphatase (PTP) domain in the cytoplasmic region, and act as one of the constituents of regulated secretory pathways in various neuroendocrine cell types including pancreatic beta-cells. Existence of IA-2 homologues in different species suggests a fundamental role in neuroendocrine function. Studies of knockout animals have shown their involvement in maintaining hormone content, however, their specific steps in the secretory pathway IA-2 functions as well as their molecular mechanisms in the hormone content regulation are still unknown. More recent studies have suggested a novel function showing that they contribute to pancreatic beta-cell growth. This review attempts to show the possible biological functions of IA-2 family, focusing on their expression and localization in the neuroendocrine cells.

Insulinoma-associated protein 2-deficient mice develop severe forms of diabetes induced by multiple low doses of streptozotocin.

Insulinoma-associated protein 2 (IA-2) is the major autoantigen that contributes to the pathogenesis of type 1 diabetes (T1D). IA-2-deficient (IA-2-/-) mice showed impaired insulin secretion after intraperitoneal injection of glucose as well as elevated glucose level in a glucose tolerance test. Despite the fact that 70% of newly diagnosed T1D patients have an antibody against IA-2, the role of IA-2 in the pathogenesis of T1D is largely unknown. In this study, the sensitivity to diabetes induced by streptozotocin (STZ) of IA-2-/- mice was compared with that of wild-type (WT) mice. STZ injection to IA-2-/- mice caused significant elevation of blood glucose and depressed insulin concentration in the pancreas. Furthermore, abnormal ultrastructure in the beta cells of the IA-2-/- mice was revealed by electron microscopy, showing a decreased number of insulin containing vesicles and dilation of the ER-Golgi complex. These results demonstrated that IA-2-/- mice had higher sensitivity to STZ, suggesting a role of IA-2 not only in the secretion but also in the production of insulin.

Deletion of the secretory vesicle proteins IA-2 and IA-2beta disrupts circadian rhythms of cardiovascular and physical activity.

Targeted deletion of IA-2 and IA-2beta, major autoantigens in type 1 diabetes and transmembrane secretory vesicle proteins, results in impaired secretion of hormones and neurotransmitters. In the present study, we evaluated the effect of these deletions on daily rhythms in blood pressure, heart rate, core body temperature, and spontaneous physical and neuronal activity. We found that deletion of both IA-2 and IA-2beta profoundly disrupts the usual diurnal variation of each of these parameters, whereas the deletion of either IA-2 or IA-2beta alone did not produce a major change. In situ hybridization revealed that IA-2 and IA-2beta transcripts are highly but nonrhythmically expressed in the suprachiasmatic nuclei, the site of the brain's master circadian oscillator. Electrophysiological studies on tissue slices from the suprachiasmatic nuclei showed that disruption of both IA-2 and IA-2beta results in significant alterations in neuronal firing. From these studies, we concluded that deletion of IA-2 and IA-2beta, structural proteins of secretory vesicles and modulators of neuroendocrine secretion, has a profound effect on the circadian system.

Dense-core vesicle proteins IA-2 and IA-2{beta} affect renin synthesis and secretion through the {beta}-adrenergic pathway.

IA-2 and IA-2beta, major autoantigens in type 1 diabetes, are transmembrane proteins in dense-core vesicles, and their expression influences the secretion of hormones and neurotransmitters. The present experiments were performed to examine whether IA-2 and IA-2beta modulate the release of renin from dense-core vesicles of juxtaglomerular granular cells in the kidney. Plasma renin concentration (PRC; ng angiotensin I.ml(-1).h(-1)) was significantly reduced in mice with null mutations in IA-2, IA-2beta, or both IA-2 and IA-2beta compared with wild-type mice (876 +/- 113, 962 +/- 130, and 596 +/- 82 vs. 1,367 +/- 93; P < 0.01, P < 0.02, and P < 0.001). Renin mRNA levels were reduced to 26.4 +/- 5.1, 39 +/- 5.4, and 35.3 +/- 5.5% of wild-type in IA-2-/-, IA-2beta-/-, and IA-2/IA-2beta-/- mice. Plasma aldosterone levels were not significantly different among genotypes. The regulation of PRC by furosemide and salt intake, and of aldosterone by salt intake, was maintained in all genotypes. IA-2 and IA-2beta expression did not colocalize with renin but showed overlapping immunoreactivity with tyrosine hydroxylase. While propranolol reduced PRC in wild-type mice, it had no effect on PRC in IA-2/ IA-2beta-/- mice. Renal tyrosine hydroxylase mRNA and immunoreactivity were reduced in IA-2/IA-2beta-/- mice as was the urinary excretion of catecholamines. We conclude that IA-2 and IA-2beta are required to maintain normal levels of renin expression and renin release, most likely by permitting normal rates of catecholamine release from sympathetic nerve terminals.

ICA512 signaling enhances pancreatic beta-cell proliferation by regulating cyclins D through STATs.

Changes in metabolic demands dynamically regulate the total mass of adult pancreatic beta-cells to adjust insulin secretion and preserve glucose homeostasis. Glucose itself is a major regulator of beta-cell proliferation by inducing insulin secretion and activating beta-cell insulin receptors. Here, we show that islet cell autoantigen 512 (ICA512)/IA-2, an intrinsic tyrosine phosphatase-like protein of the secretory granules, activates a complementary pathway for beta-cell proliferation. On granule exocytosis, the ICA512 cytoplasmic domain is cleaved and the resulting cytosolic fragment (ICA512-CCF) moves into the nucleus where it enhances the levels of phosphorylated STAT5 and STAT3, thereby inducing insulin gene transcription and granule biogenesis. We now show that knockdown of ICA512 decreases cyclin D1 levels and proliferation of insulinoma INS-1 cells, whereas beta-cell regeneration is reduced in partially pancreatectomized ICA512-/- mice. Conversely, overexpression of ICA512-CCF increases both cyclin D1 and D2 levels and INS-1 cell proliferation. Up-regulation of cyclin D1 and D2 by ICA512-CCF is affected by knockdown of STAT3 and STAT5, respectively, whereas it does not require insulin signaling. These results identify ICA512 as a regulator of cyclins D and beta-cell proliferation through STATs and may have implication for diabetes therapy.

PTP-NP, a new member of the receptor protein tyrosine phosphatase family, implicated in development of nervous system and pancreatic endocrine cells.

The regulation of protein tyrosine phosphorylation is an important mechanism for developmental control. We describe here a new member of the protein tyrosine phosphatase (PTP) family, called PTP-NP (for neural and pancreatic). The cDNA sequence indicates a receptor-type transmembrane molecule. At early organogenesis, in situ hybridization with a probe for the PTP-NP extracellular region detects expression confined to the region of the developing pancreas, an organ of medical importance, but poorly understood with regard to molecular mechanisms of developmental control. This localized expression appears early, even before morphological differentiation of the pancreas, and is found in presumptive precursors of the endocrine cells by the earliest times that they can be distinguished. In neural development, an alternate RNA with a different or missing extracellular region is expressed transiently at early stages of neurogenesis and the full-length PTP-NP RNA appears later. To search for a ligand of PTP-NP, a fusion protein probe was made with the extracellular domain fused to an alkaline phosphatase tag. This probe bound strongly to pancreatic islets, providing evidence for a ligand-receptor interaction that could be involved in endocrine cell regulation. The results show PTP-NP is an especially early marker for pancreatic development and suggest it may be a receptor that could control the development of pancreatic endocrine cells.