Rationale, design and baseline characteristics of the effect of canagliflozin in patients with type 2 diabetes and microalbuminuria in the Japanese population: The CANPIONE study.

AIM: To evaluate the effect of canagliflozin, a sodium-glucose co-transporter-2 (SGLT2) inhibitor, on albuminuria and the decline of estimated glomerular filtration rate (eGFR) in participants with type 2 diabetes and microalbuminuria. METHODS: The CANPIONE study is a multicentre, randomized, parallel-group and open-labelled study consisting of a unique 24-week preintervention period, during which the rate of eGFR decline before intervention is estimated, followed by a 52-week intervention and a 4-week washout period. Participants with a geometric mean urinary albumin-to-creatinine ratio (UACR) of 50 and higher and less than 300 mg/g in two consecutive first-morning voids at two different time points, and an eGFR of 45 ml/min/1.73m2 or higher, are randomly assigned to receive canagliflozin 100 mg daily or to continue guideline-recommended treatment, except for SGLT2 inhibitors. The first primary outcome is the change in UACR, and the second primary outcome is the change in eGFR slope. RESULTS: A total of 258 participants were screened and 98 were randomized at 21 sites in Japan from August 2018 to May 2021. The mean baseline age was 61.4 years and 25.8% were female. The mean HbA1c was 7.9%, mean eGFR was 74.1 ml/min/1.73m2 and median UACR was 104.2 mg/g. CONCLUSIONS: The CANPIONE study will determine whether the SGLT2 inhibitor canagliflozin can reduce albuminuria and slow eGFR decline in participants with type 2 diabetes and microalbuminuria.

Protein Kinase C (Pkc)-δ Mediates Arginine-Induced Glucagon Secretion in Pancreatic α-Cells.

The pathophysiology of type 2 diabetes involves insulin and glucagon. Protein kinase C (Pkc)-δ, a serine-threonine kinase, is ubiquitously expressed and involved in regulating cell death and proliferation. However, the role of Pkcδ in regulating glucagon secretion in pancreatic α-cells remains unclear. Therefore, this study aimed to elucidate the physiological role of Pkcδ in glucagon secretion from pancreatic α-cells. Glucagon secretions were investigated in Pkcδ-knockdown InR1G9 cells and pancreatic α-cell-specific Pkcδ-knockout (αPkcδKO) mice. Knockdown of Pkcδ in the glucagon-secreting cell line InR1G9 cells reduced glucagon secretion. The basic amino acid arginine enhances glucagon secretion via voltage-dependent calcium channels (VDCC). Furthermore, we showed that arginine increased Pkcδ phosphorylation at Thr505, which is critical for Pkcδ activation. Interestingly, the knockdown of Pkcδ in InR1G9 cells reduced arginine-induced glucagon secretion. Moreover, arginine-induced glucagon secretions were decreased in αPkcδKO mice and islets from αPkcδKO mice. Pkcδ is essential for arginine-induced glucagon secretion in pancreatic α-cells. Therefore, this study may contribute to the elucidation of the molecular mechanism of amino acid-induced glucagon secretion and the development of novel antidiabetic drugs targeting Pkcδ and glucagon.

Cell Autonomous Dysfunction and Insulin Resistance in Pancreatic α Cells.

To date, type 2 diabetes is considered to be a "bi-hormonal disorder" rather than an "insulin-centric disorder," suggesting that glucagon is as important as insulin. Although glucagon increases hepatic glucose production and blood glucose levels, paradoxical glucagon hypersecretion is observed in diabetes. Recently, insulin resistance in pancreatic α cells has been proposed to be associated with glucagon dysregulation. Moreover, cell autonomous dysfunction of α cells is involved in the etiology of diabetes. In this review, we summarize the current knowledge about the physiological and pathological roles of glucagon.

Association of Renal Function and Statin Therapy with Lipoprotein(a) in Patients with Type 2 Diabetes.

AIM: A high level of serum lipoprotein(a) [Lp(a)] is associated with kidney disease development in patients with type 2 diabetes (T2DM). Recent studies have suggested that statins may affect serum levels of Lp(a). However, the statin effect is not well-defined in patients with T2DM with kidney dysfunction. This retrospective study aimed to investigate the relevance of kidney dysfunction and statin therapy to Lp(a) in patients with T2DM. METHODS: Japanese patients with T2DM (n=149, 96 men and 53 women) were divided into two groups: statin users (n=79) and non-statin users (n=70). Multiple logistic regression analyses were performed with Lp(a) as the objective variable and estimated glomerular filtration rate (eGFR), hemoglobin A1c, age, gender, and body mass index as the explanatory variables. RESULTS: Lp(a) serum levels were higher in statin users than in non-statin users (P=0.022). Multivariate regression analysis results showed an inverse correlation of eGFR to log Lp(a) in all patients (P=0.009) and in non-statin users (P=0.025), but not in statin users. In a multiple logistic regression analysis for median Lp(a), there was an inverse association between eGFR and Lp(a) level (odds ratio, 0.965; 95% confidence interval, 0.935-0.997; P=0.030) in non-statin users as well as in all participants, but not in statin users. CONCLUSIONS: The present study suggests that a high Lp(a) level in patients with T2DM, except in statin users, is significantly associated with decreased eGFR, indicating that the increased Lp(a) levels under statin therapy might diminish the relationship between Lp(a) and eGFR.

Targeting cyclophilin D and the mitochondrial permeability transition enhances beta-cell survival and prevents diabetes in Pdx1 deficiency.

Mutations of the pancreatic duodenal homeobox gene-1, Pdx1, cause heritable diabetes in humans and mice. A central abnormality with Pdx1 deficiency is increased death of beta-cells, leading to decreased beta-cell mass. We show that lentiviral suppression of Pdx1 increases death of mouse insulinoma MIN6 beta-cells associated with dissipation of the mitochondrial inner membrane electrochemical gradient, Deltapsi(m). Preventing mitochondrial permeability transition pore opening with the cyclophilin D inhibitor cyclosporin A restored Deltapsi(m) and rescued cell viability. Reduced beta-cell mass, markers of beta-cell apoptosis, necrosis, and decreased proliferation are present in Pdx1 haploinsufficient mice. Genetic ablation of the Ppif gene, encoding cyclophilin D, restored beta-cell mass and decreased TUNEL and complement complex labeling without affecting beta-cell proliferation. In adult mice maintained on a high-fat diet, Ppif ablation normalized fasting glucose and glucose and insulin responses to acute glucose challenge. Thus, cyclophilin D and the mitochondrial permeability transition are critical regulators of beta-cell death caused by Pdx1 insufficiency.

Temporal and Spatial Cellular Distribution of Neural Crest Derivatives and Alpha Cells during Islet Development.

Recent studies have revealed that signals from neural crest (NC) derivatives regulate the mass, proliferation, and maturation of beta cells in developing fetal pancreas. However, little is known about the cellular distribution of NC derivatives during pancreatic development or the process whereby the developing islets are enclosed. We studied the temporal and spatial distribution of NC derivatives and endocrine cells at each developmental stage. At embryonic day 10.5 (E10.5) of mouse embryo, NC derivatives that migrated to the prospective pancreatic region were distributed in close proximity to pancreatic epithelial cells. As development advanced, most NC derivatives progressively surrounded endocrine rather than exocrine cells, and were distributed in closer proximity to alpha cells rather than to beta cells. At E20, approximately 70% of the NC derivatives enclosing endocrine cells were distributed in close proximity to alpha cells. Moreover, the expression of SynCAM, a Ca(2+)-independent homophilic trans-cell adhesion molecule, was confirmed from E16.5 on and was more remarkable at the cell boundaries of alpha cells and NC derivatives. These findings suggest that NC derivatives might be distributed in close proximity to alpha cells as a result of homophilic binding of SynCAM expressed by alpha cells and NC derivatives during islet development.

Crystal structure of the lipid flippase MurJ in a "squeezed" form distinct from its inward- and outward-facing forms.

The bacterial peptidoglycan enclosing the cytoplasmic membrane is a fundamental cellular architecture. The integral membrane protein MurJ plays an essential role in flipping the cell wall building block Lipid II across the cytoplasmic membrane for peptidoglycan biosynthesis. Previously reported crystal structures of MurJ have elucidated its V-shaped inward- or outward-facing forms with an internal cavity for substrate binding. MurJ transports Lipid II using its cavity through conformational transitions between these two forms. Here, we report two crystal structures of inward-facing forms from Arsenophonus endosymbiont MurJ and an unprecedented crystal structure of Escherichia coli MurJ in a "squeezed" form, which lacks a cavity to accommodate the substrate, mainly because of the increased proximity of transmembrane helices 2 and 8. Subsequent molecular dynamics simulations supported the hypothesis that the squeezed form is an intermediate conformation. This study fills a gap in our understanding of the Lipid II flipping mechanism.

The Plasticity of Pancreatic ß-Cells.

Type 2 diabetes is caused by impaired insulin secretion and/or insulin resistance. Loss of pancreatic ß-cell mass detected in human diabetic patients has been considered to be a major cause of impaired insulin secretion. Additionally, apoptosis is found in pancreatic ß-cells; ß-cell mass loss is induced when cell death exceeds proliferation. Recently, however, ß-cell dedifferentiation to pancreatic endocrine progenitor cells and ß-cell transdifferentiation to α-cell was reported in human islets, which led to a new underlying molecular mechanism. Hyperglycemia inhibits nuclear translocation and expression of forkhead box-O1 (FoxO1) and induces the expression of neurogenin-3 (Ngn3), which is required for the development and maintenance of pancreatic endocrine progenitor cells. This new hypothesis (Foxology) is attracting attention because it explains molecular mechanism(s) underlying ß-cell plasticity. The lineage tracing technique revealed that the contribution of dedifferentiation is higher than that of ß-cell apoptosis retaining to ß-cell mass loss. In addition, islet cells transdifferentiate each other, such as transdifferentiation of pancreatic ß-cell to α-cell and vice versa. Islet cells can exhibit plasticity, and they may have the ability to redifferentiate into any cell type. This review describes recent findings in the dedifferentiation and transdifferentiation of ß-cells. We outline novel treatment(s) for diabetes targeting islet cell plasticity.

Associations of Homocysteine with B Vitamins and Zinc in Serum Levels of Patients with Type 2 Diabetes Mellitus: A Cross-Sectional Study.

The association of homocysteine metabolism-related nutrients along with renal function to homocysteine levels is not well known in patients with type 2 diabetes mellitus (T2DM). We investigated the relevance of kidney function, albuminuria, and nutritional factors to serum homocysteine in T2DM patients. This cross-sectional study enrolled 149 T2DM patients (96 men and 53 postmenopausal women), and patient characteristics and laboratory data including kidney-related data [glomerular filtration rate (eGFR), urinary albumin excretion (UACR), uric acid] and metabolism parameters (hemoglobin A1c and lipids) were collected from the medical record and serum levels of vitamin B12, folic acid, zinc, homocysteine and UACR were also acquired. In total subjects, serum levels of homocysteine, vitamin B12, and folic acid were within reference intervals, but zinc levels were close to lower limits of its reference interval. A multivariate-adjusted analysis showed that gender (ß=-0.259, p<0.001), uric acid (ß=0.267, p<0.001), eGFR (ß=-0.188, p=0.001), log UACR (ß=0.190, p=0.002), log folic acid (ß=-0.259, p<0.001), log vitamin B12 (ß=-0.224, p<0.001) and zinc (ß=-0.169, p=0.006) were correlated to log homocysteine. In multiple regression analysis by gender, these correlations were found similarly in men, but neither log folic acid nor zinc showed correlations with log homocysteine in women. The present study suggests that renal function parameters and the certain nutritional factors have a possible influence on serum homocysteine, in T2DM patients including diabetes kidney disease.

Autophagy regulates pancreatic beta cell death in response to Pdx1 deficiency and nutrient deprivation.

There are three types of cell death; apoptosis, necrosis, and autophagy. The possibility that activation of the macroautophagy (autophagy) pathway may increase beta cell death is addressed in this study. Increased autophagy was present in pancreatic islets from Pdx1(+/-) mice with reduced insulin secretion and beta cell mass. Pdx1 expression was reduced in mouse insulinoma 6 (MIN6) cells by delivering small hairpin RNAs using a lentiviral vector. The MIN6 cells died after 7 days of Pdx1 deficiency, and autophagy was evident prior to the onset of cell death. Inhibition of autophagy prolonged cell survival and delayed cell death. Nutrient deprivation increased autophagy in MIN6 cells and mouse and human islets after starvation. Autophagy inhibition partly prevented amino acid starvation-induced MIN6 cell death. The in vivo effects of reduced autophagy were studied by crossing Pdx1(+/-) mice to Becn1(+/-) mice. After 1 week on a high fat diet, 4-week-old Pdx1(+/-) Becn1(+/-) mice showed normal glucose tolerance, preserved beta cell function, and increased beta cell mass compared with Pdx1(+/-) mice. This protective effect of reduced autophagy had worn off after 7 weeks on a high fat diet. Increased autophagy contributes to pancreatic beta cell death in Pdx1 deficiency and following nutrient deprivation. The role of autophagy should be considered in studies of pancreatic beta cell death and diabetes and as a target for novel therapeutic intervention.

Coexistence of aldosterone-producing adrenocortical adenoma and pheochromocytoma in an ipsilateral adrenal gland.

A 40-year-old female, diagnosed as essential hypertension, demonstrated a 2 cm mass in left adrenal gland by computed tomography without abnormal endocrinological findings. (131)I-adosterol and (123)I-metaiodobenzylguanidine (MIBG) scintigraphy at 39 years of age showed no abnormal accumulation. Follow up (131)I-adosterol scintigraphy performed one year later showed apparently abnormal uptake and slightly elevated uptake in left adrenal gland. Her physical examination was unremarkable except for mild hypertension. Routine blood chemistry was normal except for hypokalemia. Endocrinological date revealed suppressed plasma renin activity, and elevated plasma aldosterone concentration, and noradrenalin levels. Serial T2-weighted magnetic resonance imaging clearly demonstrated two distinct tumors. Furthermore, selective adrenal venous sampling with intravenous ACTH infusion indicated aldosterone-producing adrenocortical adenoma (APA) in left adrenal gland. During operation of adrenal tumor, blood pressure elevated markedly and complication of pheochromocytoma (PC) was suspected. Immunohistochemical findings after left adrenolectomy revealed that the adrenal mass was compatible with APA and PC. Risk of operation against undiagnosed PC is very high and, therefore, it must be diagnosed before surgery. Herein, we present an extremely rare case of the simultaneous occurrence of both APA and PC in an ipsilateral adrenal gland.

Genetic association of glutathione peroxidase-1 with coronary artery calcification in type 2 diabetes: a case control study with multi-slice computed tomography.

BACKGROUND: Although oxidative stress by accumulation of reactive oxygen species (ROS) in diabetes has become evident, it remains unclear what genes, involved in redox balance, would determine susceptibility for development of atherosclerosis in diabetes. This study evaluated the effect of genetic polymorphism of enzymes producing or responsible for reducing ROS on coronary artery calcification in type 2 diabetes (T2D). METHODS: An index for coronary-arteriosclerosis, coronary artery calcium score (CACS) was evaluated in 91 T2D patients using a multi-slice computed tomography. Patients were genotyped for ROS-scavenging enzymes, Glutathione peroxidase-1 (GPx-1), Catalase, Mn-SOD, Cu/Zn-SOD, as well as SNPs of NADPH oxidase as ROS-promoting elements, genes related to onset of T2D (CAPN10, ADRB3, PPAR gamma, FATP4). Age, blood pressure, BMI, HbA1c, lipid and duration of diabetes were evaluated for a multivariate regression analysis. RESULTS: CACS with Pro/Leu genotype of the GPx-1 gene was significantly higher than in those with Pro/Pro (744 +/- 1,291 vs. 245 +/- 399, respectively, p = 0.006). In addition, genotype frequency of Pro/Leu in those with CACS >or= 1000 was significantly higher than in those with CACS < 1000 (45.5% vs. 18.8%; OR = 3.61, CI = 0.97-13.42; p = 0.045) when tested for deviation from Hardy-Weinberg's equilibrium. Multivariate regression analyses revealed that CACS significantly correlated with GPx-1 genotypes and age. CONCLUSION: The presence of Pro197Leu substitution of the GPx-1 gene may play a crucial role in determining genetic susceptibility to coronary-arteriosclerosis in T2D. The mechanism may be associated with a decreased ability to scavenge ROS with the variant GPx-1.

In vitro and pathological investigations of MODY5 with the R276X-HNF1beta (TCF2) mutation.

Maturity-onset diabetes of the young type 5 (MODY5) is caused by mutation of hepatocyte nuclear factor 1beta (HNF1 beta) (TCF2) gene, resulting in a wide range of phenotypes including diabetes and renal abnormalities, but little is known about the pathogenesis of the clinical spectrum. We describe a 27-year-old Japanese male with the MODY phenotype including an atrophic kidney and multiple renal cysts. Genetic analysis revealed the patient to be heterozygous for a nonsense mutation in codon 276 of the HNF1beta gene (CGA or Arginine to TGA or stop codon; R276X). To clarify the pathophysiological relevance of this mutation, we conducted an in vitro study monitoring human C-peptide secretion after transfecting both the HNF1beta mutant cDNA and preproinsulin cDNA into a murine beta cell line, MIN6. Functional studies of the transformed MIN6 cells indicated that expression of the R276X caused a significant decrease in glucose-stimulated insulin secretion but no change in either KCl-stimulated or basal insulin secretion. These results suggest that the R276X functions in a negative manner in regard to metabolic responses of insulin secretion in beta cells. Analysis with light and electron microscopy on biopsied kidney specimens suggested that the origin of the cysts might be glomeruli but the primary lesion could be tubules.

Gene and cell-based therapy for diabetes mellitus: endocrine gene therapeutics.

Recently, islet transplantation in the treatment of type 1 diabetes has been revisited with improved results. This approach has the potential to restore the regulatory unit of endocrine pancreas, but it cannot be a definite solution because of its limitation for the use of toxic immune-suppressive agents and limited number of donors. One possible way to restore the insulin secretion safely is with cell therapy using tissue engineering of a patient's own somatic cells by transduction of the corresponding gene of interest, in which extrapancreatic cells are engineered to secrete insulin. We constructed a somatic cell therapy system using a furin-cleavable insulin gene and somatic cells of mesenchymal origin. We also tested a semipermeable chamber that can contain allo- or xenogeneic insulin-secreting cells and found that the device could be helpful for cell therapy. This novel approach should provide a feasible method for treatment of diabetes mellitus without the use of any toxic agent or of embryonic stem cells that involve ethical implications.

Novel hormonal delivery method using the ink-jet technology: application to pulmonary insulin therapies.

BACKGROUND: A device developed based on ink-jet printer technology can precisely control the size and volume of droplets ejected. Here, we evaluated the application of this technology to the pulmonary administration of insulin mist as a therapeutic measure for diabetes. METHODS: Insulin ejected from the ink-jet device was initially characterized by high-performance liquid chromatography (HPLC) and mass spectrometry. Its effects on D-glucose uptake rate by L6 cells were then investigated. Next, different insulin solutions (with or without additives or ink-jet processing) were subcutaneously administered, and their pharmacodynamic features were evaluated. Finally, decreases in plasma glucose level in rats were examined after ventilator-assisted pulmonary administration of insulin mist. RESULTS: Neither the HPLC nor the mass spectrometry profile of insulin was altered by the ink-jet process. The D-glucose uptake rate by L6 cells that received the recovered aerosolized insulin solution was similar to that of cells treated with control insulin, at 107%. Neither the addition of additives nor the ink-jet process used for insulin aerosolization impaired the plasma glucose-lowering action of subcutaneously injected insulin. Similarly, the efficacy of pulmonary insulin administration was not affected by the additives or the ink-jet process. Plasma glucose levels showed a trend towards decreasing after ventilator-assisted pulmonary administration of insulin mist. Plasma insulin level increased 30 min after the inhalation. CONCLUSIONS: The ink-jet process did not affect the quality or biological activity of insulin, suggesting the potential use of the ink-jet device for insulin inhalation therapy for diabetes.

Loss of Nix in Pdx1-deficient mice prevents apoptotic and necrotic ß cell death and diabetes.

Mutations in pancreatic duodenal homeobox (PDX1) are linked to human type 2 diabetes and maturity-onset diabetes of the young type 4. Consistent with this, Pdx1-haploinsufficient mice develop diabetes. Both apoptosis and necrosis of ß cells are mechanistically implicated in diabetes in these mice, but a molecular link between Pdx1 and these 2 forms of cell death has not been defined. In this study, we introduced an shRNA into mouse insulinoma MIN6 cells to deplete Pdx1 and found that expression of proapoptotic genes, including NIP3-like protein X (Nix), was increased. Forced Nix expression in MIN6 and pancreatic islet ß cells induced programmed cell death by simultaneously activating apoptotic and mitochondrial permeability transition-dependent necrotic pathways. Preventing Nix upregulation during Pdx1 suppression abrogated apoptotic and necrotic ß cell death in vitro. In Pdx1-haploinsufficient mice, Nix ablation normalized pancreatic islet architecture, ß cell mass, and insulin secretion and eliminated reactive hyperglycemia after glucose challenge. These results establish Nix as a critical mediator of ß cell apoptosis and programmed necrosis in Pdx1-deficient diabetes.

Enhanced insulin secretion from engineered 3T3-L1 preadipocytes by induction of cellular differentiation.

We have established insulin-secreting cell line, L1-INS/fur cells, by engineering 3T3-L1 murine preadipocytes with human preproinsulin cDNA. Analysis with HPLC, mass spectrometry and immunological assay identified human insulin in the culture medium. Notably, secretion of insulin from L1-INS/fur cell was increased 8.2 times higher after induction of cellular differentiation. The increment of insulin secretion during differentiation was further enhanced by additive treatment with thiazolidinedione, a promoting agent of adipocyte differentiation. This observation strongly suggests that the enhancement of insulin secretion is tightly associated with cellular differentiation process itself. Expression rate of the insulin transgene was not changed after the additional treatment with thiazolidinedione. On the other hand, furin gene expression by Northern analysis showed an increase, and Western analysis revealed even more reduction in cellular content of proinsulin. These results indicate that mechanism of the observed enhancement in insulin secretion during the differentiation is mainly due to increased capacity of the proinsulin processing by induction of furin. Results of our present study will provide important information on cell-based therapy using undifferentiated progenitors and tissue stem cells.

Whole genome association study of rheumatoid arthritis using 27 039 microsatellites.

A major goal of current human genome-wide studies is to identify the genetic basis of complex disorders. However, the availability of an unbiased, reliable, cost efficient and comprehensive methodology to analyze the entire genome for complex disease association is still largely lacking or problematic. Therefore, we have developed a practical and efficient strategy for whole genome association studies of complex diseases by charting the human genome at 100 kb intervals using a collection of 27,039 microsatellites and the DNA pooling method in three successive genomic screens of independent case-control populations. The final step in our methodology consists of fine mapping of the candidate susceptible DNA regions by single nucleotide polymorphisms (SNPs) analysis. This approach was validated upon application to rheumatoid arthritis, a destructive joint disease affecting up to 1% of the population. A total of 47 candidate regions were identified. The top seven loci, withstanding the most stringent statistical tests, were dissected down to individual genes and/or SNPs on four chromosomes, including the previously known 6p21.3-encoded Major Histocompatibility Complex gene, HLA-DRB1. Hence, microsatellite-based genome-wide association analysis complemented by end stage SNP typing provides a new tool for genetic dissection of multifactorial pathologies including common diseases.

Interaction of ATP sensor, cAMP sensor, Ca2+ sensor, and voltage-dependent Ca2+ channel in insulin granule exocytosis.

ATP, cAMP, and Ca(2+) are the major signals in the regulation of insulin granule exocytosis in pancreatic beta cells. The sensors and regulators of these signals have been characterized individually. The ATP-sensitive K(+) channel, acting as the ATP sensor, couples cell metabolism to membrane potential. cAMP-GEFII, acting as a cAMP sensor, mediates cAMP-dependent, protein kinase A-independent exocytosis, which requires interaction with both Piccolo as a Ca(2+) sensor and Rim2 as a Rab3 effector. l-type voltage-dependent Ca(2+) channels (VDCCs) regulate Ca(2+) influx. In the present study, we demonstrate interactions of these molecules. Sulfonylurea receptor 1, a subunit of ATP-sensitive K(+) channels, interacts specifically with cAMP-GEFII through nucleotide-binding fold 1, and the interaction is decreased by a high concentration of cAMP. Localization of cAMP-GEFII overlaps with that of Rim2 in plasma membrane of insulin-secreting MIN6 cells. Localization of Rab3 co-incides with that of Rim2. Rim2 mutant lacking the Rab3 binding region, when overexpressed in MIN6 cells, is localized exclusively in cytoplasm, and impairs cAMP-dependent exocytosis in MIN6 cells. In addition, Rim2 and Piccolo bind directly to the alpha(1)1.2-subunit of VDCC. These results indicate that ATP sensor, cAMP sensor, Ca(2+) sensor, and VDCC interact with each other, which further suggests that ATP, cAMP, and Ca(2+) signals in insulin granule exocytosis are integrated in a specialized domain of pancreatic beta cells to facilitate stimulus-secretion coupling.

Piccolo, a Ca2+ sensor in pancreatic beta-cells. Involvement of cAMP-GEFII.Rim2. Piccolo complex in cAMP-dependent exocytosis.

We have previously shown that cAMP-binding protein cAMP-guanidine nucleotide exchange factor II (GEFII) (or Epac2) interacting with Rim2 is involved in cAMP-dependent, protein kinase A-independent exocytosis in pancreatic beta-cells. The action of the cAMP-GEFII.Rim2 complex requires both intracellular cAMP and Ca(2+). Although Rim2 has C(2) domains, its role as a Ca(2+) sensor has remained unclear. In the present investigation, we have discovered that Piccolo, a CAZ (cytoskeletal matrix associated with the active zone) protein in neurons that is structurally related to Rim2, also binds to cAMP-GEFII and that it forms both homodimer and heterodimer with Rim2 in a Ca(2+)-dependent manner, whereas Rim2 alone does not form the homodimer. The association of Piccolo.Rim2 heterodimerization is stronger than Piccolo. Piccolo homodimerization. Treatment of pancreatic islets with antisense oligodeoxynucleotides against Piccolo inhibits insulin secretion induced by cAMP analog 8-bromo-cyclic AMP plus high glucose stimulation. These results suggest that Piccolo serves as a Ca(2+) sensor in exocytosis in pancreatic beta-cells and that the formation of a cAMP-GEFII.Rim2. Piccolo complex is important in cAMP-induced insulin secretion. In addition, this study suggests that CAZ proteins similar to those in neurons are also function in pancreatic beta-cells.