The incretin hormone GLP1 promotes islet-cell survival via the second messenger cAMP. Here we show that mice deficient in the activity of CREB, caused by expression of a dominant-negative A-CREB transgene in pan-creatic-cells, develop diabetes secondary to-cell apoptosis. Remarkably, A-CREB severely disrupted expression of IRS2, an insulin signaling pathway component that is shown here to be a direct target for CREB action in vivo. As induction of IRS2 by cAMP enhanced activation of the survival kinase Akt in response to insulin and IGF-1, our results demonstrate a novel mechanism by which opposing pathways cooperate in promoting cell survival. Supplemental material is available at http://www.genesdev.org.

A tumor homing peptide, LyP-1, selectively binds to tumorassociated lymphatic vessels and tumor cells in certain tumors and exhibits an antitumor effect. Here, we show that the protein known as p32 or gC1q receptor is the receptor for LyP-1. Various human tumor cell lines were positive for p32 expression in culture, and the expression was increased in xenograft tumors grown from the positive cell lines. Fluorescence-activated cell sorting analyses with anti-p32 antibodies showed that p32-positive cell lines expressed p32 at the cell surface. These cells bound and internalized LyP-1 peptide in proportion to the cell-surface expression level, which correlated with malignancy rather than total p32 expression in the cells. Like the LyP-1 peptide, p32 antibodies highlighted hypoxic areas in tumors, where they bound to both tumor cells and cells that expressed macrophage/myeloid cell markers and often seemed to be incorporated into the walls of tumor lymphatics. Significant p32 expression was common in human cancers and the p32 levels were often greatly elevated compared with the corresponding normal tissue. These results establish p32, particularly its cell-surface-expressed form, as a new marker of tumor cells and tumor-associated macrophages/myeloid cells in hypoxic/metabolically deprived areas of tumors. Its unique localization in tumors and its relative tumor specificity may make p32 a useful target in tumor diagnosis and therapy. [Cancer Res 2008;68(17):7210-8]

Bax inhibitor-1 (BI-1) is an evolutionarily conserved endoplasmic reticulum (ER) protein that suppresses cell death in both animal and plant cells. We characterized mice in which the bi-1 gene was ablated. Cells from BI-1-deficient mice, including fibroblasts, hepatocytes, and neurons, display selective hypersensitivity to apoptosis induced by ER stress agents (thapsigargin, tunicamycin, brefeldin A), but not to stimulators of mitochondrial or TNF/Fas-death receptor apoptosis pathways. Conversely, BI-1 overexpression protects against apoptosis induced by ER stress. BI-1-mediated protection from apoptosis induced by ER stress correlated with inhibition of Bax activation and translocation to mitochondria, preservation of mitochondrial membrane potential, and suppression of caspase activation. BI-1 overexpression also reduces releasable Ca(2+) from the ER. In vivo, bi-1(-/-) mice exhibit increased sensitivity to tissue damage induced by stimuli that trigger ER stress, including stroke and tunicamycin injection. Thus, BI-1 regulates a cell death pathway important for cytopreservation during ER stress.

Reperfusion after myocardial ischemia is associated with a rapid influx of calcium, leading to activation of various enzymes including calpain. Isolated perfused adult rabbit hearts subjected to global ischemia and reperfusion were studied. Calpain or a calpain-like activity was activated within 15 min after reperfusion, and preconditioning suppressed calpain activation. In contrast, caspase activation was not detected although cytochrome c was released after ischemia and reperfusion. The pro-apoptotic BH3-only Bcl-2 family member, Bid, was cleaved during ischemia/reperfusion in the adult rabbit heart. Recombinant Bid was cleaved by calpain to a fragment that was able to mediate cytochrome c release. The calpain cleavage site was mapped to a region within Bid that is extremely susceptible to proteolysis. These findings suggest that there is cross-talk between apoptotic and necrotic pathways in myocardial ischemia/reperfusion injury.Reperfusion after ischemia is accompanied by a rapid influx of calcium. Prevention of calcium influx is widely recognized in order to protect the myocardium. Preconditioning, in which a brief period of ischemia and reperfusion confers protection against a longer episode of ischemia, preserves tissue viability through attenuation of ionic fluxes (notably protons and calcium), preservation of energy charge (less consumption of ATP), and a variety of less well characterized enzymatic alterations (1-5). We have previously shown that preconditioning attenuates cytoplasmic acidification and calcium overload (3,6). A variety of calcium-dependent enzymes are activated after calcium influx, including the cysteine protease, calpain. Calpain has been implicated as a mediator of contractile dysfunction during ischemic injury, in part because of proteolysis of structural proteins (7,8). In addition, calpain has been reported to cleave Bax to an 18-kDa fragment that mediates cytochrome c release (9, 10), and calpain cleaves Bcl-x L to convert it to a pro-apoptotic form (11).Apoptosis has been reported to occur after ischemia/reperfusion injury, indicated by DNA fragmentation and TUNEL 1 staining (12-16). Preconditioning has been reported to reduce apoptosis (17). Caspase activation in ischemic and reperfused rat heart has been reported using an antibody that recognizes a neoepitope in activated caspase-3 (18). Other studies examining apoptosis in neonatal cardiomyocytes have described cytochrome c release and caspase activation (19,20). In this study we report that calpain is activated shortly after ischemia/reperfusion and that preconditioning attenuates calpain activation.In addition, we demonstrate a connection between calpain and mitochondrial dysfunction mediated by Bid. MATERIALS AND METHODSHeart Perfusion and Ischemia/Reperfusion Protocol-Male New Zealand White rabbits (2.0 -2.5 kg) were anesthetized and a midsternal thoracotomy was performed. The heart was rapidly excised and mounted onto a Langendorff heart perfusion apparatus using a protocol adapted from Tsuchida et al. (21). The heart w...

Summary Neuroendocrine (NE) phenotype, seen in >30% of prostate adenocarcinomas (PCa), and NE prostate tumors are implicated in aggressive prostate cancer. Formation of NE prostate tumors in the TRAMP mouse model was suppressed in mice lacking the ubiquitin ligase Siah2, which regulates HIF-1α availability. Cooperation between HIF-1α and FoxA2, a transcription factor expressed in NE tissue, promotes recruitment of p300 to transactivate select HIF-regulated genes, Hes6, Sox9 and Jmjd1a. These HIF-regulated genes are highly expressed in metastatic PCa and required for hypoxia-mediated NE phenotype, metastasis in PCa and the formation of NE tumors. Tissue-specific expression of FoxA2 combined with Siah2-dependent HIF-1α availability enables a transcriptional program required for NE prostate tumor development and NE phenotype in PCa.