The diabetes susceptibility gene Clec16a regulates mitophagy.

Clec16a has been identified as a disease susceptibility gene for type 1 diabetes, multiple sclerosis, and adrenal dysfunction, but its function is unknown. Here we report that Clec16a is a membrane-associated endosomal protein that interacts with E3 ubiquitin ligase Nrdp1. Loss of Clec16a leads to an increase in the Nrdp1 target Parkin, a master regulator of mitophagy. Islets from mice with pancreas-specific deletion of Clec16a have abnormal mitochondria with reduced oxygen consumption and ATP concentration, both of which are required for normal ß cell function. Indeed, pancreatic Clec16a is required for normal glucose-stimulated insulin release. Moreover, patients harboring a diabetogenic SNP in the Clec16a gene have reduced islet Clec16a expression and reduced insulin secretion. Thus, Clec16a controls ß cell function and prevents diabetes by controlling mitophagy. This pathway could be targeted for prevention and control of diabetes and may extend to the pathogenesis of other Clec16a- and Parkin-associated diseases.

Effects of Sotagliflozin Added to Insulin in Patients with Type 1 Diabetes.

BACKGROUND: In most patients with type 1 diabetes, adequate glycemic control is not achieved with insulin therapy alone. We evaluated the safety and efficacy of sotagliflozin, an oral inhibitor of sodium-glucose cotransporters 1 and 2, in combination with insulin treatment in patients with type 1 diabetes. METHODS: In this phase 3, double-blind trial, which was conducted at 133 centers worldwide, we randomly assigned 1402 patients with type 1 diabetes who were receiving treatment with any insulin therapy (pump or injections) to receive sotagliflozin (400 mg per day) or placebo for 24 weeks. The primary end point was a glycated hemoglobin level lower than 7.0% at week 24, with no episodes of severe hypoglycemia or diabetic ketoacidosis after randomization. Secondary end points included the change from baseline in glycated hemoglobin level, weight, systolic blood pressure, and mean daily bolus dose of insulin. RESULTS: A significantly larger proportion of patients in the sotagliflozin group than in the placebo group achieved the primary end point (200 of 699 patients [28.6%] vs. 107 of 703 [15.2%], P<0.001). The least-squares mean change from baseline was significantly greater in the sotagliflozin group than in the placebo group for glycated hemoglobin (difference, -0.46 percentage points), weight (-2.98 kg), systolic blood pressure (-3.5 mm Hg), and mean daily bolus dose of insulin (-2.8 units per day) (P≤0.002 for all comparisons). The rate of severe hypoglycemia was similar in the sotagliflozin group and the placebo group (3.0% [21 patients] and 2.4% [17], respectively). The rate of documented hypoglycemia with a blood glucose level of 55 mg per deciliter (3.1 mmol per liter) or below was significantly lower in the sotagliflozin group than in the placebo group. The rate of diabetic ketoacidosis was higher in the sotagliflozin group than in the placebo group (3.0% [21 patients] and 0.6% [4], respectively). CONCLUSIONS: Among patients with type 1 diabetes who were receiving insulin, the proportion of patients who achieved a glycated hemoglobin level lower than 7.0% with no severe hypoglycemia or diabetic ketoacidosis was larger in the group that received sotagliflozin than in the placebo group. However, the rate of diabetic ketoacidosis was higher in the sotagliflozin group. (Funded by Lexicon Pharmaceuticals; inTandem3 ClinicalTrials.gov number, NCT02531035 .).

miR-211 is a prosurvival microRNA that regulates chop expression in a PERK-dependent manner.

MicroRNAs typically function at the level of posttranscriptional gene silencing within the cytoplasm; however, increasing evidence suggests that they may also function in nuclear, Argonaut-containing complexes, to directly repress target gene transcription. We have investigated the role of microRNAs in mediating endoplasmic reticulum (ER) stress responses. ER stress triggers the activation of three signaling molecules: Ire-1α/ß, PERK, and ATF6, whose function is to facilitate adaption to the ensuing stress. We demonstrate that PERK induces miR-211, which in turn attenuates stress-dependent expression of the proapoptotic transcription factor chop/gadd153. MiR-211 directly targets the proximal chop/gadd153 promoter, where it increases histone methylation and represses chop expression. Maximal chop accumulation ultimately correlates with miR-211 downregulation. Our data suggest a model in which PERK-dependent miR-211 induction prevents premature chop accumulation and thereby provides a window of opportunity for the cell to re-establish homeostasis prior to apoptotic commitment.

Improving the scientific rigour of nutritional recommendations for adults with type 2 diabetes: A comprehensive review of the American Diabetes Association guideline-recommended eating patterns.

AIMS: The global rate of type 2 diabetes (T2D) continues to rise. Guidelines that influence the worldwide treatment of this disease are central to changing this trajectory. We sought in this review to evaluate the appropriateness of sources cited in the American Diabetes Association's (ADA) guidelines on eating patterns for T2D management, identify additional relevant sources, and evaluate the evidence. MATERIALS AND METHODS: We reviewed the evidence behind the ADA's recommendations on eating patterns in the 2018 and 2019 ADA Standards of Care and the 2014 ADA Nutrition Therapy Recommendations for Adults with Diabetes. Additionally, we conducted a comprehensive search to identify any additional studies not included in the cited evidence. To determine appropriateness of inclusion in the guidelines, the following criteria were applied: 1) it was a clinical trial or systematic review/meta-analysis of clinical trials; 2) it involved persons with T2D; 3) one of the study arms followed one of the eating patterns currently recommended; 4) its reported outcomes included glycaemic control; 5) outcomes were reported separately for persons with T2D. RESULTS: We found a wide variation in the evidence for each eating pattern. Issues that have hampered the guideline process include: lack of a rigorous literature review, resulting in the omission of pertinent studies; an overreliance on prospective cohort studies; inconsistent standards for evidence; inclusion of studies not on persons with T2D; and bias. CONCLUSIONS: The ADA Guidelines recommended eating patterns fall short of rigorous standards of scientific review according to state-of-the-art systematic review and guideline creation practices.

Dose-dependent glycometabolic effects of sotagliflozin on type 1 diabetes over 12 weeks: The inTandem4 trial.

AIMS: To assess the dose-related effects of sotagliflozin, a novel dual inhibitor of sodium-glucose co-transporters-1 and -2, in type 1 diabetes (T1D). MATERIALS AND METHODS: In this 12-week, multicentre, randomized, double-blind, placebo-controlled dose-ranging trial, adults with T1D were randomized to once-daily placebo (n = 36) or sotagliflozin 75 mg (n = 35), 200 mg (n = 35) or 400 mg (n = 35). Insulin was maintained at baseline doses. The primary endpoint was least squares mean (LSM) change in glycated haemoglobin (HbA1c) from baseline. Other endpoints included proportion of participants with ≥0.5% HbA1c reduction and assessments of 2-hour postprandial glucose (PPG), weight, and urinary glucose excretion (UGE). RESULTS: From a mean baseline of 8.0% ± 0.8% (full study population), placebo-adjusted LSM HbA1c decreased by 0.3% (P = .07), 0.5% (P < .001) and 0.4% (P = .006) with sotagliflozin 75 mg, 200 mg and 400 mg, respectively, at week 12. In the placebo and sotagliflozin 75 mg, 200 mg and 400 mg groups, 33.3%, 37.1%, 80.0% and 65.7% of participants achieved an HbA1c reduction ≥0.5%. Placebo-adjusted PPG decreased by 22.2 mg/dL (P = .28), 28.7 mg/dL (P = .16) and 50.2 mg/dL (P = .013), UGE increased by 41.8 g/d (P = .006), 57.7 g/d (P < .001) and 70.5 g/d (P < .001), and weight decreased by 1.3 kg (P = .038), 2.4 kg (P < .001) and 2.6 kg (P < .001) with sotagliflozin 75 mg, 200 mg and 400 mg, respectively. One case of severe hypoglycaemia occurred in each sotagliflozin group and one case of diabetic ketoacidosis (DKA) occurred with sotagliflozin 400 mg. CONCLUSIONS: Combined with stable insulin doses, sotagliflozin 200 mg and 400 mg improved glycaemic control and weight in adults with T1D. Sotagliflozin 400 mg reduced PPG levels. UGE increased with all sotagliflozin doses. Rates of severe hypoglycaemia and DKA were low (NCT02459899).

Outcomes, care utilization, and expenditures in adolescent pregnancy complicated by diabetes.

BACKGROUND AND OBJECTIVE: Adolescence and pregestational diabetes separately increase risks of adverse pregnancy outcomes, but little is known about their combined effect. To analyze pregnancy outcomes, healthcare utilization, and expenditures in adolescent pregnancies with and without pregestational diabetes using a national claims database. METHODS: Retrospective study using Truven Health MarketScan Commercial Claims and Encounters Database, 2011 to 2015. Females 12 to 19 years old, continuously enrolled for at least 12 months before a livebirth until 2 months after, were included. Pregestational diabetes, diabetes complications (ketoacidosis, retinopathy, neuropathy, nephropathy), comorbidities, and pregnancy outcomes (preeclampsia, preterm delivery, high birthweight, cesarean delivery) were identified using claims data algorithms. Healthcare utilization and payer expenditure were tabulated per enrollee. Multivariate logistic regressions assessed pregnancy outcomes; multivariate OLS regression assessed payer expenditures. RESULTS: About 33 502 adolescents were included. Adolescents without diabetes had pregnancy outcomes consistent with national estimates. Adolescents with uncomplicated diabetes had increased odds of preeclampsia adjusted odds ratios 2.41 (95% confidence interval 1.93-3.02), preterm delivery 1.50 (1.21-1.87), high birthweight 1.84 (1.50-2.27), and cesarean delivery 1.81 (1.52-2.15). Diabetes with ketoacidosis and/or end-organ damage had higher odds of preeclampsia 5.62 (2.77-11.41), preterm delivery 5.81 (3.00-11.25), high birthweight 2.38 (1.08-5.24), and cesarean delivery 3.43 (1.78-6.64). Adolescents with diabetes utilized significantly more outpatient and inpatient care during pregnancy. Payer expenditures increased by 45.3% (34.8-55.9%) among adolescents with diabetes and by 82.6% (49.1-116.0%) among adolescents with diabetes complicated by ketoacidosis and/or end-organ damage. CONCLUSION: Compared with normal adolescent pregnancies, pregestational diabetes significantly increases risks of adverse pregnancy outcomes and significantly escalates healthcare utilization and cost.

Type I interferons mediate pancreatic toxicities of PERK inhibition.

The great preclinical promise of the pancreatic endoplasmic reticulum kinase (PERK) inhibitors in neurodegenerative disorders and cancers is marred by pancreatic injury and diabetic syndrome observed in PERK knockout mice and humans lacking PERK function and suffering from Wolcott-Rallison syndrome. PERK mediates many of the unfolded protein response (UPR)-induced events, including degradation of the type 1 interferon (IFN) receptor IFNAR1 in vitro. Here we report that whole-body or pancreas-specific Perk ablation in mice leads to an increase in IFNAR1 protein levels and signaling in pancreatic tissues. Concurrent IFNAR1 deletion attenuated the loss of PERK-deficient exocrine and endocrine pancreatic tissues and prevented the development of diabetes. Experiments using pancreas-specific Perk knockouts, bone marrow transplantation, and cultured pancreatic islets demonstrated that stabilization of IFNAR1 and the ensuing increased IFN signaling in pancreatic tissues represents a major driver of injury triggered by Perk loss. Neutralization of IFNAR1 prevented pancreatic toxicity of PERK inhibitor, indicating that blocking the IFN pathway can mitigate human genetic disorders associated with PERK deficiency and help the clinical use of PERK inhibitors.

Rebranding asymptomatic type 1 diabetes: the case for autoimmune beta cell disorder as a pathological and diagnostic entity.

The asymptomatic phase of type 1 diabetes is recognised by the presence of beta cell autoantibodies in the absence of hyperglycaemia. We propose that an accurate description of this stage is provided by the name 'Autoimmune Beta Cell Disorder' (ABCD). Specifically, we suggest that this nomenclature and diagnosis will, in a proactive manner, shift the paradigm towards type 1 diabetes being first and foremost an immune-mediated disease and only later a metabolic disease, presaging more active therapeutic intervention in the asymptomatic stage of disease, before end-stage beta cell failure. Furthermore, we argue that accepting ABCD as a diagnosis will be critical in order to accelerate pharmaceutical, academic and public activities leading to clinical trials that could reverse beta cell autoimmunity and halt progression to symptomatic insulin-requiring type 1 diabetes. We recognize that there are both opportunities and challenges in the implementation of the ABCD concept but hope that the notion of 'asymptomatic autoimmune disease' as a disorder will be widely discussed and eventually accepted.

Extreme obesity induces massive beta cell expansion in mice through self-renewal and does not alter the beta cell lineage.

AIMS/HYPOTHESIS: Understanding the developmental biology of beta cell regeneration is critical for developing new diabetes therapies. Obesity is a potent but poorly understood stimulus for beta cell expansion. Current models of obesity are complicated by developmental compensation or concurrent diabetes, limiting their usefulness for identifying the lineage mechanism(s) of beta cell expansion. We aimed to determine whether acute inducible obesity stimulates beta cell expansion and to determine the lineage mechanism of beta cell growth in obesity. METHODS: We created whole-body tamoxifen-inducible leptin receptor (LepR)-deficient mice (Ubc-Cre (ERT2) LepR (loxP/loxP) ) as a novel model of acute obesity. Beta cell mass and proliferation were quantified after short-term LepR deletion. Clonal analysis of beta cell expansion using the Brainbow2.1 reporter was performed 6 months post tamoxifen initiation. RESULTS: LepR deficiency induced a doubling of body mass within 3 weeks, with moderate glucose intolerance (unlike typical LepR mutant mice [db/db], which have frank diabetes). Beta cell mass expanded threefold through increased beta cell proliferation, without evidence for contribution from specialised progenitors or stem cells (via sequential thymidine labelling and Brainbow2.1 reporter). Thus, self-renewal is the primary lineage mechanism in obesity-induced beta cell expansion. However, even the rapid beta cell proliferation could not exceed the restrictions of the replication refractory period. CONCLUSIONS/INTERPRETATION: In summary, we created a novel model of inducible obesity demonstrating that even extreme metabolic demand does not alter beta cell lineage.

Angiopoietin-like protein 8 (ANGPTL8)/betatrophin overexpression does not increase beta cell proliferation in mice.

AIMS/HYPOTHESIS: The identification of novel targets that stimulate endogenous regeneration of beta cells would represent a significant advance in the treatment of patients with diabetes. The betatrophin hypothesis suggests that increased expression of angiopoietin-like protein 8 (ANGPTL8) induces dramatic and specific beta cell proliferation and subsequent beta cell mass expansion with improved glucose tolerance. In light of recent controversy, we further investigated the effects of ANGPTL8 overexpression on beta cell proliferation. METHODS: We performed hydrodynamic tail vein injections of green fluorescent protein (GFP) or Angptl8 (also known as Gm6484) DNA in multiple cohorts of mice of different ages. We employed state-of-the-art methods to comprehensively quantify beta cell mass and proliferation, controlling for mouse age, genetic strain, source of DNA injected, Angptl8 gene expression and proliferation markers. RESULTS: In two young and two aged cohorts of B6.129 mice, no substantial change in beta cell replication, mass or glucose homeostasis was observed following ANGPTL8 overexpression. Even in mice with extremely elevated Angptl8 expression (26-fold increase), beta cell replication was not significantly altered. Finally, we considered mice on the ICR background exactly as studied by Melton and colleagues, and still no beta cell mitogenic effect was detected following ANGPTL8 overexpression. CONCLUSION/INTERPRETATION: ANGPTL8 does not stimulate beta cell replication in young or old mice.

Prediction and prevention of type 1 diabetes: update on success of prediction and struggles at prevention.

Type 1 diabetes mellitus (T1DM) is the archetypal example of a T cell-mediated autoimmune disease characterized by selective destruction of pancreatic ß cells. The pathogenic equation for T1DM presents a complex interrelation of genetic and environmental factors, most of which have yet to be identified. On the basis of observed familial aggregation of T1DM, it is certain that there is a decided heritable genetic susceptibility for developing T1DM. The well-known association of T1DM with certain human histocompatibility leukocyte antigen (HLA) alleles of the major histocompatibility complex (MHC) was a major step toward understanding the role of inheritance in T1DM. Type 1 diabetes is a polygenic disease with a small number of genes having large effects (e.g., HLA) and a large number of genes having small effects. Risk of T1DM progression is conferred by specific HLA DR/DQ alleles [e.g., DRB1*03-DQB1*0201 (DR3/DQ2) or DRB1*04-DQB1*0302 (DR4/DQ8)]. In addition, the HLA allele DQB1*0602 is associated with dominant protection from T1DM in multiple populations. A concordance rate lower than 100% between monozygotic twins indicates a potential involvement of environmental factors on disease development. The detection of at least two islet autoantibodies in the blood is virtually pre-diagnostic for T1DM. The majority of children who carry these biomarkers, regardless of whether they have an a priori family history of the disease, will develop insulin-requiring diabetes. Facilitating pre-diagnosis is the timing of seroconversion which is most pronounced in the first 2 yr of life. Unfortunately the significant progress in improving prediction of T1DM has not yet been paralleled by safe and efficacious intervention strategies aimed at preventing the disease. Herein we summarize the chequered history of prediction and prevention of T1DM, describing successes and failures alike, and thereafter examine future trends in the exciting, partially explored field of T1DM prevention.

Haematopoietic stem cells do not asymmetrically segregate chromosomes or retain BrdU.

Stem cells are proposed to segregate chromosomes asymmetrically during self-renewing divisions so that older ('immortal') DNA strands are retained in daughter stem cells whereas newly synthesized strands segregate to differentiating cells. Stem cells are also proposed to retain DNA labels, such as 5-bromo-2-deoxyuridine (BrdU), either because they segregate chromosomes asymmetrically or because they divide slowly. However, the purity of stem cells among BrdU-label-retaining cells has not been documented in any tissue, and the 'immortal strand hypothesis' has not been tested in a system with definitive stem cell markers. Here we tested these hypotheses in haematopoietic stem cells (HSCs), which can be highly purified using well characterized markers. We administered BrdU to newborn mice, mice treated with cyclophosphamide and granulocyte colony-stimulating factor, and normal adult mice for 4 to 10 days, followed by 70 days without BrdU. In each case, less than 6% of HSCs retained BrdU and less than 0.5% of all BrdU-retaining haematopoietic cells were HSCs, revealing that BrdU has poor specificity and poor sensitivity as an HSC marker. Sequential administration of 5-chloro-2-deoxyuridine and 5-iodo-2-deoxyuridine indicated that all HSCs segregate their chromosomes randomly. Division of individual HSCs in culture revealed no asymmetric segregation of the label. Thus, HSCs cannot be identified on the basis of BrdU-label retention and do not retain older DNA strands during division, indicating that these are not general properties of stem cells.

Unsupervised Anomaly Detection to Characterize Heterogeneity in Type 2 Diabetes.

Diabetes is associated with heterogeneous behaviors affecting patients' clinical characteristics and trajectories. This study includes 21,288 patients with type 2 diabetes (women, ages 30 to 65). The cohort was filtered through a set of preprocessing heuristics in order to assure the cohort exhibited a similar clinical trajectory. Anomalous characteristics were then identified using dimensionality reduction and anomaly detection methods. Compared to the majority of the cohort, patients classified as anomalous were twice as likely to be admitted into the hospital (7.94[7.59 8.28] versus 3.12[3.06 3.17] times), have a higher incidence of comorbidities (2[1.64 2.36] times more), and be prescribed more insulin and less new and more expensive diabetes medications (such as Sodium glucose co-transporter 2 inhibitors). Patients with these anomalous characteristics may benefit from additional or specialized interventions to avert their risk for adverse outcomes.

Growth and regeneration of adult beta cells does not involve specialized progenitors.

Cellular progenitors remain poorly characterized in many adult tissues, limited in part by the lack of unbiased techniques to identify progenitors and their progeny. To address this fundamental problem, we developed a novel DNA analog-based lineage-tracing technique to detect multiple rounds of cell division in vivo. Here, we apply this technique to determine the adult lineage mechanism of the insulin-secreting beta cells of pancreatic islets, an important unresolved question in diabetes research. As expected, gastrointestinal and skin epithelia involve specialized progenitors that repeatedly divide to give rise to postmitotic cells. In contrast, specialized progenitors do not contribute to adult beta cells, not even during acute beta cell regeneration. Instead, beta cells are the products of uniform self-renewal, slowed by a replication refractory period that prevents beta cells from immediately redividing. Our approach provides unbiased resolution of previously inaccessible developmental niches and can elucidate lineage mechanisms without candidate markers.

Calcineurin signaling regulates human islet {beta}-cell survival.

The calcium-regulated phosphatase calcineurin intersects with both calcium and cAMP-mediated signaling pathways in the pancreatic ß-cell. Pharmacologic calcineurin inhibition, necessary to prevent rejection in the setting of organ transplantation, is associated with post-transplant ß-cell failure. We sought to determine the effect of calcineurin inhibition on ß-cell replication and survival in rodents and in isolated human islets. Further, we assessed whether the GLP-1 receptor agonist and cAMP stimulus, exendin-4 (Ex-4), could rescue ß-cell replication and survival following calcineurin inhibition. Following treatment with the calcineurin inhibitor tacrolimus, human ß-cell apoptosis was significantly increased. Although we detected no human ß-cell replication, tacrolimus significantly decreased rodent ß-cell replication. Ex-4 nearly normalized both human ß-cell survival and rodent ß-cell replication when co-administered with tacrolimus. We found that tacrolimus decreased Akt phosphorylation, suggesting that calcineurin could regulate replication and survival via the PI3K/Akt pathway. We identify insulin receptor substrate-2 (Irs2), a known cAMP-responsive element-binding protein target and upstream regulator of the PI3K/Akt pathway, as a novel calcineurin target in ß-cells. Irs2 mRNA and protein are decreased by calcineurin inhibition in both rodent and human islets. The effect of calcineurin on Irs2 expression is mediated at least in part through the nuclear factor of activated T-cells (NFAT), as NFAT occupied the Irs2 promoter in a calcineurin-sensitive manner. Ex-4 restored Irs2 expression in tacrolimus-treated rodent and human islets nearly to baseline. These findings reveal calcineurin as a regulator of human ß-cell survival in part through regulation of Irs2, with implications for the pathogenesis and treatment of diabetes following organ transplantation.

Effects of Sotagliflozin Combined with Intensive Insulin Therapy in Young Adults with Poorly Controlled Type 1 Diabetes: The JDRF Sotagliflozin Study.

Background: Young adults with type 1 diabetes (T1D) tend to have higher A1C than older adults and are at increased risk for diabetic ketoacidosis (DKA). Oral adjuncts to insulin have not been previously studied in this population. Methods: In this phase 2, multicenter, randomized, double-blind, placebo-controlled, parallel-group study, adults aged 18-30 years with T1D and A1C ≥9.0% were randomly assigned to placebo (n = 42) or sotagliflozin 400 mg (n = 43), in addition to insulin for 12 weeks. Insulin doses were adjusted to meet glucose targets (preprandial 80-130 mg/dL, postprandial <180 mg/dL). The primary endpoint was change from baseline in A1C at week 12. Results: From a baseline of 9.8%, mean A1C decreased by 1.0% with placebo and 1.3% with sotagliflozin (-0.4% [95% confidence interval (CI): -0.8 to 0.1]; P = 0.10 vs. placebo). In the prespecified A1C ≤10.0% subgroup, the treatment difference was -0.8% (-1.3 to -0.2; P = 0.006), favoring sotagliflozin. Overall, relative to placebo, postprandial glucose (PPG) decreased by 56.6 mg/dL (-89.7 to -23.6; P < 0.001) and weight decreased by 2.37 kg (-3.5 to -1.2; P < 0.001). More patients achieved an A1C <7.0% with sotagliflozin (16.3%) than placebo (2.4%; P = 0.026). Rates of documented hypoglycemia and severe hypoglycemia were similar between groups. One DKA event occurred with placebo, and none occurred with sotagliflozin. Conclusions: In young adults with T1D and suboptimal glycemic control, sotagliflozin plus insulin for 12 weeks numerically improved A1C and significantly improved A1C goal attainment, PPG, and body weight. Sotagliflozin plus insulin was generally well tolerated without any episodes of DKA (NCT02383940).

Irs2 inactivation suppresses tumor progression in Pten+/- mice.

Mutations in the phosphatase and tensin homologue (PTEN)/phosphatidylinositol-3 kinase-alpha (PI3K) signaling pathway are frequently found in human cancer. In addition, Pten(+/-) mice develop tumors in multiple organs because of the activation of the PI3K signaling cascade. Because activation of PI3K signaling leads to feedback inhibition of insulin receptor substrate-2 (IRS2) expression, an upstream activator of PI3K, we therefore anticipated that IRS2 expression would be low in tumors that lack PTEN. Surprisingly, however, an elevation of IRS2 was often detected in tumor samples in which PTEN levels were compromised. To determine the potential contribution of Irs2 to tumor progression, Pten(+/-) mice were crossed with Irs2(+/-) mice. Deletion of Irs2 did not affect the initiation of neoplasia found in Pten(+/-) mice but suppressed cancer cell growth, proliferation, and invasion through the basement membrane. Deletion of Irs2 also attenuated the expression of Myc in prostatic intraepithelial neoplasia in Pten(+/-) mice. In addition, the expression levels of IRS2 and MYC were highly correlated in human prostate cancer, and IRS2 could stimulate MYC expression in cultured cells. Our findings provide evidence that the PI3K-activating adaptor Irs2 contributes to tumor progression in Pten(+/-) mice by stimulating both Myc and DNA synthesis.

Identification of a WD40 repeat-containing isoform of PHIP as a novel regulator of beta-cell growth and survival.

The pleckstrin homology domain-interacting protein (PHIP) was originally identified as a 902-amino-acid (aa) protein that regulates insulin receptor-stimulated GLUT4 translocation in skeletal-muscle cells. Immunoblotting and immunohistological analyses of pancreatic beta-cells reveal prominent expression of a 206-kDa PHIP isoform restricted to the nucleus. Herein, we report the cloning of this larger, 1,821-aa isoform of PHIP (PHIP1), which represents a novel WD40 repeat-containing protein. We demonstrate that PHIP1 overexpression stimulates insulin-like growth factor 1-dependent and -independent proliferation of beta-cells, an event which correlates with transcriptional upregulation of the cyclin D2 promoter and the accumulation of cyclin D2 protein. RNA interference knockdown of PHIP1 in INS-1 cells abrogates insulin receptor substrate 2 (IRS2)-mediated DNA synthesis, providing for a specific role for PHIP1 in the enhancement of IRS2-dependent signaling responses leading to beta-cell growth. Finally, we provide evidence that PHIP1 overexpression blocks free fatty acid-induced apoptosis in INS-1 cells, which is accompanied by marked activation of phosphoprotein kinase B (PKB)/AKT and the concomitant inhibition of caspase-9 and caspase-3 cleavage. Our finding that the restorative effect of PHIP1 on beta-cell lipotoxicity can be attenuated by the overexpression of dominant-negative PKB suggests a key role for PKB in PHIP1-mediated cytoprotection. Taken together, these findings provide strong support for PHIP1 as a novel positive regulator of beta-cell function. We suggest that PHIP1 may be involved in the induction of long-term gene expression programs to promote beta-cell mitogenesis and survival.