Changes in annexin I and II levels during the postnatal development of rat pancreatic islets

Annexin A1 Is a Key Modulator of Mesenchymal Stromal Cell-Mediated Improvements in Islet Function

We have previously demonstrated that coculture of islets with mesenchymal stromal cells (MSCs) enhanced islet insulin secretory capacity in vitro, correlating with improved graft function in vivo. To identify factors that contribute to MSC-mediated improvements in islet function, we have used an unbiased quantitative RT-PCR screening approach to identify MSC-derived peptide ligands of G-protein-coupled receptors that are expressed by islets cells. We demonstrated high expression of annexin A1 (ANXA1) mRNA by MSCs and confirmed expression at the protein level in lysates and MSC-conditioned media by Western blot analysis and ELISA. Preculturing islets with exogenous ANXA1 enhanced glucose-stimulated insulin secretion (GSIS), thereby mimicking the beneficial influence of MSC preculture in vitro. Small interfering RNA-mediated knockdown of ANXA1 in MSCs reduced their capacity to potentiate GSIS. MSCs derived from ANXA1(-/-) mice had no functional capacity to enhance GSIS, in contrast to wild-type controls. Preculturing islets with ANXA1 had modest effects on their capacity to regulate blood glucose in streptozotocin-induced diabetic mice, indicating that additional MSC-derived factors are required to fully mimic the beneficial effects of MSC preculture in vivo. These findings demonstrate the feasibility of harnessing the MSC secretome as a defined, noncellular strategy to improve the efficiency of clinical islet transplantation protocols.

Expression and prognostic significance of gastric-specific annexin A10 in diffuse- and intestinal-type gastric carcinoma

BACKGROUND AND AIMS

Annexin A10 (ANXA10) and its liver-specific short isoform (ANXA10S) had tissue-restricted expression. The downregulation of ANXA10S is correlated with tumor progression and poor prognosis in hepatocellular carcinoma. The aim of the present study was to validate the tissue distribution and explore the role of the ANXA10 protein expression in gastric carcinoma.

METHODS

We examined the ANXA10 protein expression in human and animal tissues and 356 resected primary gastric carcinomas, using specific mouse and rabbit polyclonal antibodies, by immunohistochemical staining.

RESULTS

The ANXA10 protein is a nuclear protein specifically expressed in fetal and adult gastric mucosa and Brunner's gland across species, including humans, minipigs, woodchucks, and mice, and is commonly lost in gastric mucosa with intestinal metaplasia. The ANXA10 protein was expressed in 43.5% (155 cases) of gastric carcinomas; 74.2% (98/132) in the diffuse-type gastric carcinoma (DGC), 73.7% (28/38) in the mixed-type gastric carcinoma, and significantly lower in the intestinal-type gastric carcinoma (IGC) and indeterminate groups, 16.8% (28/167) and 5.3% (1/19), respectively (P<1×10(-8)). IGC with ANXA10 expression was correlated with a higher stage (P=0.049), particularly higher in stage IIIA/IIIB/IV IGC than lower-stage (IA/IB/II) tumors (P=0.005), but was not correlated with age, sex, and nodal status. In contrast, DGC with ANXA10 expression was associated with younger age, female patients, and importantly, lower tumor stage and lymph node metastasis (P=0.007, P=0.065, P=0.024, and P=0.0014, respectively). Moreover, DGC with ANXA10 expression had a better 5-year patient survival (P=0.0048), whereas IGC with ANXA10 expression had a lower 5-year survival (P=0.034).

CONCLUSIONS

The ANXA10 protein expression is a novel marker of gastric differentiation, and is differentially expressed in IGC and DGC, with opposite prognostic significance.

Src activation generates reactive oxygen species and impairs metabolism-secretion coupling in diabetic Goto-Kakizaki and ouabain-treated rat pancreatic islets

AIMS/HYPOTHESIS

Na(+)/K(+)-ATPase inhibition by ouabain suppresses ATP production by generating reactive oxygen species (ROS) and impairs glucose-induced insulin secretion from pancreatic islets. To clarify the signal-transducing function of Na(+)/K(+)-ATPase in decreasing ATP production by the generation of ROS in pancreatic islets, the involvement of Src was examined. In addition, the significance of Src activation in diabetic islets was examined.

METHODS

Isolated islets from Wistar rats and diabetic Goto-Kakizaki (GK) rats (a model for diabetes) were used. ROS was measured by 5-(and 6)-chloromethyl-2',7'-dichlorofluorescein fluorescence using dispersed islet cells. After lysates were immunoprecipitated by anti-Src antibody, immunoblotting was performed.

RESULTS

Ouabain caused a rapid Tyr(418) phosphorylation, indicating activation of Src in the presence of high glucose. The specific Src inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) restored the ouabain-induced decrease in ATP content and the increase in ROS production. Both PP2 and ROS scavenger restored the impaired insulin release and impaired ATP elevation in GK islets, but had no such effect in control islets. PP2 reduced the high glucose-induced increase in ROS generation in GK islet cells but had no effect on that in control islet cells. Moreover, ouabain had no effect on ATP content and ROS production in the presence of high glucose in GK islets.

CONCLUSIONS/INTERPRETATION

These results indicate that Src plays a role in the signal-transducing function of Na(+)/K(+)-ATPase, in which ROS generation decreases ATP production in control islets. Moreover, ROS generated by Src activation plays an important role in impaired glucose-induced insulin secretion in GK islets, in which Src is endogenously activated independently of ouabain.

Inhibitory role of Src family tyrosine kinases on Ca2+-dependent insulin release

Both neurotransmitter release and insulin secretion occur via regulated exocytosis and share a variety of similar regulatory mechanisms. It has been suggested that Src family tyrosine kinases inhibit neurotransmitter release from neuronal cells (H. Ohnishi, S. Yamamori, K. Ono, K. Aoyagi, S. Kondo, and M. Takahashi. Proc Natl Acad Sci USA 98: 10930-10935, 2001). Thus the potential role of Src family kinases in the regulation of insulin secretion was investigated in this study. Two structurally different inhibitors of Src family kinases, SU-6656 and PP2, but not the inactive compound, PP3, enhanced Ca2+-induced insulin secretion in both rat pancreatic islets and INS-1 cells in a concentration-dependent and time-dependent manner. Furthermore, Src family kinase-mediated insulin secretion appears to be dependent on elevated intracellular Ca2+ and independent of glucose metabolism, the ATP-dependent K+ channel, adenylyl cyclase, classical PKC isoforms, extracellular signal-regulated kinase 1/2, and insulin synthesis. The sites of action for Src family kinases seem to be distal to the elevation of intracellular Ca2+ level. These results indicate that one or more Src family tyrosine kinases exert a tonic inhibitory role on Ca2+-dependent insulin secretion.

Down-regulation of annexin A10 in hepatocellular carcinoma is associated with vascular invasion, early recurrence, and poor prognosis in synergy with p53 mutation

Annexins (ANXs) are a large group of calcium-binding proteins participating in diverse important biological processes. ANXA10 is the least expressed new member of unknown function. We showed that ANXA10 mRNA was expressed in adult liver and hepatocellular carcinoma (HCC), but not in multiple adult and fetal tissues, cholangiocarcinoma, and several other common carcinomas. Of 182 unifocal primary HCCs, ANXA10 mRNA was dramatically reduced in 121 (66%), and the down-regulation correlated with p53 mutation (P = 0.024), early intrahepatic tumor recurrence (P = 0.0007), and lower 4-year survival (P = 0.0014). Down-regulation of ANXA10 was twofold more frequent in large than small HCCs (P = 0.0012), in grade II to III than grade I HCC (P < 0.00001), and in stage IIIA to IV than stage I to II HCC (P < 0.00001). Moreover, ANXA10 down-regulation and p53 mutation acted synergistically toward high-grade (P < 0.00001), high-stage HCC (P < 0.00001), and poorer prognosis (P = 0.0025). Our results indicate that the expression of the tissue- and tumor-restricted ANXA10 is a marker of liver cell differentiation and growth arrest, and its down-regulation associated with malignant phenotype of hepatocytes, vascular invasion, and progression of HCC, leading to poor prognosis. Thus, ANXA10 might serve as a new potential target of gene therapy for HCC.

Loss of annexin A7 leads to alterations in frequency-induced shortening of isolated murine cardiomyocytes

Annexin A7 has been proposed to function in the fusion of vesicles, acting as a Ca(2+) channel and as Ca(2+)-activated GTPase, thus inducing Ca(2+)/GTP-dependent secretory events. To understand the function of annexin A7, we have performed targeted disruption of the Anxa7 gene in mice. Matings between heterozygous mice produced offspring showing a normal Mendelian pattern of inheritance, indicating that the loss of annexin A7 did not interfere with viability in utero. Mice lacking annexin A7 showed no obvious phenotype and were fertile. To assay for exocytosis, insulin secretion from isolated islets of Langerhans was examined. Ca(2+)-induced and cyclic AMP-mediated potentiation of insulin secretion was unchanged in the absence of annexin A7, suggesting that it is not directly implicated in vesicle fusion. Ca(2+) regulation studied in isolated cardiomyocytes, showed that while cells from early embryos displayed intact Ca(2+) homeostasis and expressed all of the components required for excitation-contraction coupling, cardiomyocytes from adult Anxa7(-/-) mice exhibited an altered cell shortening-frequency relationship when stimulated with high frequencies. This suggests a function for annexin A7 in electromechanical coupling, probably through Ca(2+) homoeostasis.

Annexin XI may be involved in Ca2+ - or GTP-gammaS-induced insulin secretion in the pancreatic beta-cell

The aim of this study was to investigate possible involvement of annexin XI in the insulin secretory machinery. In fluorescence immunocytochemistry, annexin XI was found in the cytoplasm of pancreatic endocrine cells and a pancreatic beta-cell line, MIN6, in a granular pattern. MIN6 cells also possessed weak and diffused annexin XI immunoreactivity in the cytoplasm. Immunoelectron microscopy revealed annexin XI in the insulin granules. Insulin secretion from streptolysin-O-permeabilized MIN6 cells was inhibited by anti-annexin XI antibody, when the release was stimulated by either Ca2+ or GTP-gammaS, but not by a protein kinase C-activating phorbol ester. Inhibition of insulin release by anti-annexin XI antibody was reproduced in permeabilized rat islets. These findings suggest that annexin XI may be involved in the regulation of insulin secretion from the pancreatic beta-cells.

Polarized localizations of annexins I, II, VI and XIII in epithelial cells of intestinal, hepatic and pancreatic tissues

The cellular and subcellular localizations of annexins I, II, VI and XIII in the rabbit intestine, liver and pancreas were studied by performing immunofluorescence labeling on thin frozen tissue sections using specific monoclonal antibodies. The expression of annexins was found to be finely regulated. Annexins XIII and I were expressed exclusively in the small intestine and the colon, respectively, whereas annexin II was present in all the tissues tested and annexin VI specifically in the liver and pancreas. These different annexins were concentrated in the basolateral domain of polarized cells, and some of them had an extra-apical localization: annexin XIII was concentrated in the lower 3/4 of enterocyte brush border microvilli; annexin II was present in the upper part of the terminal web in intestinal absorbent cells as well as in the bile canalicular area in hepatocytes, whereas annexin VI was detected on some apical vesicles concentrated around the bile canaliculi. In pancreatic acinar cells, the presence of annexin II on some zymogen granules provides further evidence that annexin II may be involved in exocytic events. In conclusion, this study shows that the basolateral domain of polarized cells appears to be the main site where annexins are located, and they may therefore be involved in the important cellular events occurring at this level.

Annexin II tetramer: structure and function

The annexins are a family of proteins that bind acidic phospholipids in the presence of Ca2+. The interaction of these proteins with biological membranes has led to the suggestion that these proteins may play a role in membrane trafficking events such as exocytosis, endocytosis and cell-cell adhesion. One member of the annexin family, annexin II, has been shown to exist as a monomer, heterodimer or heterotetramer. The ability of annexin II tetramer to bridge secretory granules to plasma membrane has suggested that this protein may play a role in Ca(2+)-dependent exocytosis. Annexin II tetramer has also been demonstrated on the extracellular face of some metastatic cells where it mediates the binding of certain metastatic cells to normal cells. Annexin II tetramer is a major cellular substrate of protein kinase C and pp60src. Phosphorylation of annexin II tetramer is a negative modulator of protein function.