Selective Deletion of <i>Pten</i> in Pancreatic β Cells Leads to Increased Islet Mass and Resistance to STZ-Induced Diabetes

Stiles, Bangyan L.; Kuralwalla-Martinez, Christine; Guo, Wei; Gregorian, Caroline; Wang, Ying; Tian, Jide; Magnuson, Mark A.; Wu, Hong

doi:10.1128/mcb.26.7.2772-2781.2006

Cited by 121 publications

(147 citation statements)

References 65 publications

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“…In the presence of LY294002, an increase in the number of propidium iodide-positive cells was detected (Fig. 7, A and B), supporting the notion that the PI 3-kinase is important for ␤-cell survival (5,46). Inhibiting Akt caused an increase in ␤-cell death, but to a lesser extent compared with the Raf-1 inhibitor (Fig.…”

Section: Roles and Mechanisms Of Raf-1 And Pi 3-kinase/akt Signaling supporting

confidence: 63%

Inhibition of Raf-1 Alters Multiple Downstream Pathways to Induce Pancreatic β-Cell Apoptosis

Alejandro¹,

Johnson

2008

Journal of Biological Chemistry

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The serine threonine kinase Raf-1 plays a protective role in many cell types, but its function in pancreatic ␤-cells has not been elucidated. In the present study, we examined whether primary ␤-cells possess Raf-1 and tested the hypothesis that Raf-1 is critical for ␤-cell survival. Using reverse transcriptase-PCR, Western blot, and immunofluorescence, we identified Raf-1 in human islets, mouse islets, and in the MIN6 ␤-cell line. Blocking Raf-1 activity using a specific Raf-1 inhibitor or dominant-negative Raf-1 mutants led to a time-and dose-dependent increase in cell death, assessed by real-time imaging of propidium iodide incorporation, TUNEL, PCR-enhanced DNA laddering, and Caspase-3 cleavage. Although the rapid increase in apoptotic cell death was associated with decreased Erk phosphorylation, studies with two Mek inhibitors suggested that the classical Erkdependent pathway could explain only part of the cell death observed after inhibition of Raf-1. An alternative Erk-independent pathway downstream of Raf-1 kinase involving the pro-apoptotic protein Bad has recently been characterized in other tissues. Inhibiting Raf-1 in ␤-cells led to a striking loss of Bad phosphorylation at serine 112 and an increase in the protein levels of both Bad and Bax. Together, our data strongly suggest that Raf-1 signaling plays an important role regulating ␤-cell survival, via both Erk-dependent and Bad-dependent mechanisms. Conversely, acutely inhibiting phosphatidylinositol 3-kinase Akt had more modest effects on ␤-cell death. These studies identify Raf-1 as a critical anti-apoptotic kinase in pancreatic ␤-cells and contribute to our understanding of survival signaling in this cell type.A reduction in pancreatic ␤-cell survival is a critical pathogenic event in type 1 diabetes, type 2 diabetes, and rare monogenic forms of the disease. Moreover, increased ␤-cell death has been implicated in the failure of clinical islet transplantation (1-3). Several kinases have been investigated for their possible roles in ␤-cell survival, with PI 3 3-kinase and Akt receiving the most attention to date (4 -8). Transgenic mice that overexpress constitutively active Akt in their ␤-cells are protected against streptozotocin-induced diabetes (9, 10) and overexpression of constitutively active Akt protects INS-1 cells from free fatty acid-induced apoptosis (11). However, mice with an 80% reduction in islet Akt activity did not show increased apoptosis or reduced ␤-cell mass (12, 13), suggesting the possibility that other kinases may contribute to ␤-cell survival.The Ras-Raf-mitogen-activated protein kinase cascade mediates pro-survival signals in many cell types. However, this signaling pathway remains understudied in pancreatic ␤-cells. Members of this pathway are found in human and mouse islets, as well as in ␤-cell lines (14 -17). The Raf kinase is a critical hub in this cascade, as it integrates multiple upstream signals and controls several downstream effectors. All three Raf isoforms (A-Raf, B-Raf, and C-Raf/Raf-1) share a common structu...

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Section: Roles and Mechanisms Of Raf-1 And Pi 3-kinase/akt Signaling supporting

confidence: 63%

Inhibition of Raf-1 Alters Multiple Downstream Pathways to Induce Pancreatic β-Cell Apoptosis

Alejandro¹,

Johnson

2008

Journal of Biological Chemistry

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“…Adipocyte-specific deletion of PTEN further results in increased energy expenditure and body temperature (Komazawa et al, 2004). Loss of PTEN specifically in pancreatic ␤-cells also protects from streptozotocin-induced diabetes, although these mice are significantly smaller than control littermates (Stiles et al, 2006). Finally, PTEN +/-mice are also protected from diabetes caused by knocking out insulin receptor substrate 2 (IRS2) (Kushner et al, 2005).…”

Section: New Animal Modelsmentioning

confidence: 90%

New insights into PTEN

Tamgüney

Stokoe

2007

Journal of Cell Science

222

216

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The functions ascribed to PTEN have become more diverse since its discovery as a putative phosphatase mutated in many human tumors. Although it can dephosphorylate lipids and proteins, it also has functions independent of phosphatase activity in normal and pathological states. In addition, control of PTEN function is very complex. It is positively and negatively regulated at the transcriptional level, as well as post-translationally by phosphorylation, ubiquitylation, oxidation and acetylation. Although most of its tumor suppressor activity is likely to be caused by lipid dephosphorylation at the plasma membrane, PTEN also resides in the cytoplasm and nucleus, and its subcellular distribution is under strict control. Deregulation of PTEN function is implicated in other human diseases in addition to cancer, including diabetes and autism. Journal of Cell Science 4072 and protein levels (but decreases phosphorylation of PTEN at S370 and S385, and its stability), and the ability of SPRY2 to restrain proliferation is abolished in PTEN-negative cells (Edwin et al., 2006).Resistin, a cytokine involved in inflammation and insulin resistance, increases PTEN expression in human aortic vascular endothelial cells by activating p38 MAPK and activating transcription factor 2 (ATF2), which leads to decreased activation of PKB and of its target, endothelial nitric oxide synthase (eNOS, also known as NOS3). This provides a potential mechanism for resistin-mediated impairment of insulin signaling and of its role in cardiovascular diseases (Shen et al., 2006). Furthermore, phytoestrogens such as genistein (in soy), resveratrol (in red wine) and quercetin (in fruit and vegetables) also lead to increased PTEN expression, with a concomitant decrease in phospho-PKB levels and increase in levels of the CDK inhibitor p27 (Waite et al., 2005). Epidemiological data suggest that phytoestrogen consumption can protect against cancer (Park and Surh, 2004;Verheus et al., 2007). Upregulation of PTEN expression might therefore be one basis for these beneficial effects. Indeed, mammary glands of rats fed with soy protein or a genistein-supplemented diet display higher PTEN levels and a higher apoptotic index (Dave et al., 2005). The same is true for MCF-7 cells cultured in serum from such rats (Dave et al., 2005). Similarly, indole-3-carbinol, a phytochemical derived from cruciferous vegetables such as broccoli, upregulates PTEN expression in the cervical epithelium in a mouse model for cervical cancer (Qi et al., 2005). Negative regulation of PTEN transcriptionMost of the data so far have demonstrated positive regulation of PTEN transcription. Negative regulation of PTEN expression has also been shown, however (Fig. 1). Mitogenactivated protein kinase kinase-4 (MKK4) inhibits PTEN transcription by activating NFB, which binds to a site in the PTEN promoter (Xia et al., 2007). Transforming growth factor (TGF)␤ also decreases PTEN transcription in pancreatic cancer cells (Chow et al., 2007) , 2006). Phytoestrogens, such as genistein from soybea...

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“…4, b and d). Insulin was selected here for two reasons: one, it is a robust activator of AKT and, second, insulin resistance has been attributed to an increase in PTEN (31)(32)(33)(34)(35)(36). As seen in Fig.…”

Section: Mir-21 Targets Fasl and Pten During Hypoxia-pten Is A Validamentioning

confidence: 99%

MicroRNA-21 Is a Downstream Effector of AKT That Mediates Its Antiapoptotic Effects via Suppression of Fas Ligand

Sayed¹,

He²,

Hong³

et al. 2010

Journal of Biological Chemistry

287

213

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MicroRNA-21 (miR-21) is highly up-regulated during hypertrophic and cancerous cell growth. In contrast, we found that it declines in cardiac myocytes upon exposure to hypoxia. Thus, the objective was to explore its role during hypoxia. We show that miR-21 not only regulates phosphatase and tensin homologue deleted on chromosome 10 (PTEN), but also targets Fas ligand (FasL). During prolonged hypoxia, down-regulation of miR-21 proved necessary and sufficient for enhancing expression of both proteins. We demonstrate here for the first time that miR-21 is positively regulated via an AKT-dependent pathway, which is depressed during prolonged hypoxia. Accordingly, hypoxia-induced down-regulation of miR-21 and up-regulation of FasL and PTEN were reversed by activated AKT and reproduced by a dominant negative mutant, wortmannin, or PTEN. Moreover, the antiapoptotic function of AKT partly required miR-21, which was sufficient for inhibition of caspase-8 activity and mitochondrial damage. In consensus, overexpression of miR-21 in a transgenic mouse heart resulted in suppression of ischemia-induced up-regulation of PTEN and FasL expression, an increase in phospho-AKT, a smaller infarct size, and ameliorated heart failure. Thus, we have identified a unique aspect of the function of AKT by which it inhibits apoptosis through miR-21-dependent suppression of FasL. MicroRNA (miRNA)3 are molecules approximately twenty ribonucleotides long that specifically target mRNA through partial complementarity and, thereby, inhibit translation and/or induce their degradation. miR-21 is one of the most commonly and dramatically up-regulated miRNA in many cancers (1, 2) and has been implicated in the inhibition of programmed cell death (2). Some of its validated targets include tropomyosin 1 (3), PTEN (2, 4, 5), programmed cell death 4 (Pdcd4) (6, 7), TAp63 isoform of p53 family, and LRRFIP1, an inhibitor of NFB signaling (8). Similarly, miR-21 is one of the most highly and consistently up-regulated miRNA during cardiac hypertrophy (9 -12). Thum et al. (13) show that miR-21 is predominantly up-regulated in the myofibroblasts where it targets sprouty1 and enhances their survival and, thereby, fibrosis in the heart. Similarly, Roy et al. (14) show that miR-21 is elevated in the myofibroblast-infiltrated area 7 days after ischemia/ reperfusion and suppresses metalloprotease-2 via targeting PTEN. More recently, studies have shown that miR-21 exerts an antiapoptotic function in cardiac myocytes via inhibiting PDCD4 (15) and reduces infarct size via local viral delivery to the heart (16). However, the signaling pathway that regulates miR-21 has not been identified.Two of the molecules that play a major role in ischemic injury of the heart include PTEN and FasL. PTEN is a major negative regulator of AKT (17) whose activity is modulated by its abundance, oxidation, or phosphorylation (18). It is also targeted by miR-21, which provides a specific post-transcriptional mechanism for regulating its expression (2, 4, 5). PTEN has been regarded as the A...

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Selective Deletion of Pten in Pancreatic β Cells Leads to Increased Islet Mass and Resistance to STZ-Induced Diabetes

Cited by 121 publications

References 65 publications

Inhibition of Raf-1 Alters Multiple Downstream Pathways to Induce Pancreatic β-Cell Apoptosis

Inhibition of Raf-1 Alters Multiple Downstream Pathways to Induce Pancreatic β-Cell Apoptosis

New insights into PTEN

MicroRNA-21 Is a Downstream Effector of AKT That Mediates Its Antiapoptotic Effects via Suppression of Fas Ligand

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