Expression of the transcription factor STAT-1 alpha in insulinoma cells protects against cytotoxic effects of multiple cytokines

The relationship between gestational diabetes mellitus and interleukin 1beta gene polymorphisms in southwest of China

Gestational diabetes mellitus (GDM) is a kind of chronic inflammatory condition with carbohydrate metabolism disorder. Interleukin-1beta (IL-1β) plays an important role in inflammatory response, but its role in GDM development remains unknown. The aim of this study was to analyze the association between Interleukin 1beta (IL1B) rs1143623 and rs16944 polymorphisms and susceptibility to GDM.In total, 300 pregnant women with GDM and 261 healthy pregnant women were included in the study. In both groups, single nucleotide polymorphism (SNP) rs1143623 and rs16944 were analyzed by using snapshot technology. IL-1β serum values were determined by ELISA.Serum IL-1β levels involvement in GDM development. According to the results, we found the association between the IL1B rs1143623 polymorphism and susceptibility to GDM. In further analysis, IL1B rs1143623 GG genotype had a higher level of total cholesterol (TCHO) and lower level of high density lipoprotein (HDL) in GDM patients compared with the CC/GC genotypes. However, there were no statistically significant difference between the GDM and healthy control groups in terms of rs16944 polymorphism.Our results indicated that rs1143623 in IL1B gene may lead to GDM in the southwest of china. However, no significant difference was found between GDM and rs16944. The rs1143623 genotype may significantly impact the fat metabolism, especially the levels of TCHO and HDL. We believe that our findings will contribute to understanding of the etiology and possible novel prognostic markers for GDM.

Regulation of iNOS gene transcription by IL-1β and IFN-γ requires a coactivator exchange mechanism

The proinflammatory cytokines IL-1β and IFN-γ decrease functional islet β-cell mass in part through the increased expression of specific genes, such as inducible nitric oxide synthase (iNOS). Dysregulated iNOS protein accumulation leads to overproduction of nitric oxide, which induces DNA damage, impairs β-cell function, and ultimately diminishes cellular viability. However, the transcriptional mechanisms underlying cytokine-mediated expression of the iNOS gene are not completely understood. Herein, we demonstrated that individual mutations within the proximal and distal nuclear factor-κB sites impaired cytokine-mediated transcriptional activation. Surprisingly, mutating IFN-γ-activated site (GAS) elements in the iNOS gene promoter, which are classically responsive to IFN-γ, modulated transcriptional sensitivity to IL-1β. Transcriptional sensitivity to IL-1β was increased by generation of a consensus GAS element and decreased correspondingly with 1 or 2 nucleotide divergences from the consensus sequence. The nuclear factor-κB subunits p65 and p50 bound to the κB response elements in an IL-1β-dependent manner. IL-1β also promoted binding of serine-phosphorylated signal transducer and activator of transcription-1 (STAT1) (Ser727) but not tyrosine-phosphorylated STAT1 (Tyr701) to GAS elements. However, phosphorylation at Tyr701 was required for IFN-γ to potentiate the IL-1β response. Furthermore, coactivator p300 and coactivator arginine methyltransferase were recruited to the iNOS gene promoter with concomitant displacement of the coactivator CREB-binding protein in cells exposed to IL-1β. Moreover, these coordinated changes in factor recruitment were associated with alterations in acetylation, methylation, and phosphorylation of histone proteins. We conclude that p65 and STAT1 cooperate to control iNOS gene transcription in response to proinflammatory cytokines by a coactivator exchange mechanism. This increase in transcription is also associated with signal-specific chromatin remodeling that leads to RNA polymerase II recruitment and phosphorylation.

Polymorphism M55V in gene encoding small ubiquitin-like modifier 4 (SUMO4) protein associates with susceptibility to type 1 (and type 2) diabetes

BACKGROUND

The association between small ubiquitin-like modifier 4 (SUMO4) gene polymorphism and type 1 diabetes mellitus (T1DM) or type 2 diabetes mellitus (T2DM) has been investigated in several studies. We conducted a meta-analysis to evaluate the association of SUMO4 gene polymorphism with T1DM and T2DM susceptibility.

METHODS

A meta-analysis was performed on the published studies before August 2011. The association of SUMO4 M55V polymorphism with T1DM and T2DM was evaluated. Meta-analysis was performed for genotypes AA versus GG, AA versus AG, AA versus AG + GG and A allele versus G allele in a fixed/random effect model. The combined odds ratio (OR) with 95% confidence interval (95% CI) was calculated to estimate the strength of the association.

RESULTS

Sixteen case-control studies including 9190 cases and 10 456 healthy controls were included. T1DM patients were divided into Asian and Caucasian subgroup. We detected a significant association of SUMO4 M55V polymorphism with T1DM in Asian population (A versus G: OR = 0.79, 95%CI = 0.72-0.86, p = 0.000) and a significant association of SUMO4 M55V polymorphism with T1DM in Caucasian population (A versus G: OR = 0.84, 95%CI = 0.73-0.97, p = 0.007). Included T2DM patients were all Asian. Meanwhile, a significant association of SUMO4 M55V polymorphism with T2DM was also found (A versus G: OR = 0.86, 95%CI = 0.79-0.94, p = 0.001).

CONCLUSIONS

Our study demonstrates significant associations of SUMO4 M55V polymorphism with T1DM in Asian and Caucasian population and with T2DM in Asian population.

In vitro phenotypic, genomic and proteomic characterization of a cytokine-resistant murine β-TC3 cell line

Type 1 diabetes mellitus (T1DM) is caused by the selective destruction of insulin-producing β-cells. This process is mediated by cells of the immune system through release of nitric oxide, free radicals and pro-inflammatory cytokines, which induce a complex network of intracellular signalling cascades, eventually affecting the expression of genes involved in β-cell survival.

The aim of our study was to investigate possible mechanisms of resistance to cytokine-induced β-cell death. To this purpose, we created a cytokine-resistant β-cell line (β-TC3R) by chronically treating the β-TC3 murine insulinoma cell line with IL-1β + IFN-γ. β-TC3R cells exhibited higher proliferation rate and resistance to cytokine-mediated cell death in comparison to the parental line. Interestingly, they maintained expression of β-cell specific markers, such as PDX1, NKX6.1, GLUT2 and insulin. The analysis of the secretory function showed that β-TC3R cells have impaired glucose-induced c-peptide release, which however was only moderately reduced after incubation with KCl and tolbutamide. Gene expression analysis showed that β-TC3R cells were characterized by downregulation of IL-1β and IFN-γ receptors and upregulation of SOCS3, the classical negative regulator of cytokines signaling. Comparative proteomic analysis showed specific upregulation of 35 proteins, mainly involved in cell death, stress response and folding. Among them, SUMO4, a negative feedback regulator in NF-kB and JAK/STAT signaling pathways, resulted hyper-expressed. Silencing of SUMO4 was able to restore sensitivity to cytokine-induced cell death in β-TC3R cells, suggesting it may play a key role in acquired cytokine resistance by blocking JAK/STAT and NF-kB lethal signaling.

In conclusion, our study represents the first extensive proteomic characterization of a murine cytokine-resistant β-cell line, which might represent a useful tool for studying the mechanisms involved in resistance to cytokine-mediated β-cell death. This knowledge may be of potential benefit for patients with T1DM. In particular, SUMO4 could be used as a therapeutical target.

Interleukin 1β gene single-nucleotide polymorphisms and susceptibility to pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumors (pNETs) are rare neoplasms with not fully understood etiology. Interleukin 1β (IL1β) plays an important role in pancreatic pathology, especially carcinogenesis, but its role in pNET development remains unknown. The aim of this study was to analyze the association between IL1β polymorphisms and susceptibility to pNETs. IL1β -511 C/T and +3954 C/T single-nucleotide polymorphisms (SNPs) were analyzed by real-time polymerase chain reaction-SNP analysis. IL1β serum values in pNET patients were also determined. Association between high-expression C/T -511 IL1β genotype and susceptibility to pNET (p=0.042) was found, especially with functional pNET (p=0.014), where it was associated with the T allele (p=0.016). Combination of genotype analyses confirmed carriers of -511/+3954 CTCT to be at risk of developing functional pNETs (p=0.006) and carriers of -511/+3954 CTCC at risk of developing nonfunctional pNETs (p=0.019). IL1β serum levels of all patients were below the limit of detection. Our results suggest IL1β involvement in pNET development, and we also found association between the IL1β -511 SNP and susceptibility to pNET, especially functional pNETs. Nonfunctional pNETs seem to have inferior prognosis when compared with functional pNETs. It is possible that they differ in tumor microenvironment and that nonfunctional tumors share similarities with adenocarcinoma. We believe that our findings will contribute to understanding of the etiology and possible novel prognostic markers for pNETs when future studies investigating the serum and tumor tissue IL1β levels are done.

The induction of STAT1 gene by activating transcription factor 3 contributes to pancreatic beta-cell apoptosis and its dysfunction in streptozotocin-treated mice

It is well established that the IFN-gamma/STAT1 pathway plays an important role in the pancreatic beta-cell apoptosis that is observed in STZ-induced type 1 diabetes; however, the upstream regulatory proteins involved have not been understood. Here, we investigated whether activating transcription factor 3 (ATF3) affects STAT1-mediated beta-cell dysfunction and apoptosis in streptozotocin-treated mice. To this, STZ (80 mg/kg, i.p.) was administered to wild-type and STAT1(-/-) or IFN-gamma(-/-) mice for 5 days and the mice were euthanized after 14 days. STZ-induced beta-cell dysfunction and apoptosis were associated with increased STAT1/IRF-1 and ATF3 expression and were correlated with elevated IFN-gamma levels. Genetic depletion using IFN-gamma(-/-) or STAT1(-/-) mice strongly inhibited the reduction of islet cell mass or insulin synthesis/secretion and the increase of beta-cell apoptosis observed in STZ-treated wild-type mice. ATF3 overexpression, especially the C-terminal domain, strongly enhanced beta-cell dysfunction and apoptosis by enhancing STAT1 activation and its accumulation, which were abolished with an ATF3-specific siRNA or C-terminal-deleted ATF3. The STZ induction of ATF3 was completely depleted in IFN-gamma(-/-) mice, but not in STAT1(-/-) mice. Furthermore, STAT1 did not affect ATF3 expression, but STAT1 depletion or its inactivation inhibited STZ-induced ATF3 nuclear translocation and beta-cell apoptosis. Interestingly, ATF3 also increased STAT1 transcription by directly binding to a putative binding region (-116 to -96 bp) in the STAT1 promoter. Our results suggest that ATF3 functions as a potent upstream regulator of STAT1 and ATF3 may play a role in STZ-induced beta-cell dysfunction by enhancing the steady state abundance of STAT1.

Cytokine signalling in the beta-cell: a dual role for IFNgamma

IFNgamma (interferon gamma), a cytokine typically secreted by infiltrating immune cells in insulitis in Type 1 diabetes, is by itself not detrimental to beta-cells, but, together with other cytokines, such as IL-1beta (interleukin 1beta) and TNFalpha (tumour necrosis factor alpha), or dsRNA (double-stranded RNA), it induces beta-cell apoptosis. The complex gene and protein networks that are altered by the combination of cytokines clearly point towards synergisms between these agents. IFNgamma acts mostly via JAK (Janus kinase) activation, with the transcription factors STAT-1 (signal transducer and activator of transcription-1) and IRF-1 (IFNgamma regulatory factor-1) playing a central role in the downstream pathway. The study of mice with a disruption of these transcription factors has revealed a possible dual role for IFNgamma in beta-cell destruction by cytokines or dsRNA. We demonstrated that the absence of STAT-1 from beta-cells completely protects against IFNgamma+IL-1beta- and IFNgamma+dsRNA-mediated beta-cell death in vitro, whereas absence of IRF-1 does not prevent cytokine-induced beta-cell apoptosis. In vivo, a lack of the IRF-1 gene in pancreatic islets even promotes low-dose streptozotocin-induced diabetes, whereas lack of STAT-1 confers resistance against beta-cell death following low-dose streptozotocin-induced diabetes. Additionally, IRF-1(-/-) islets are more sensitive to PNF (primary islet non-function) after transplantation in spontaneously diabetic NOD (non-obese diabetic) mice, whereas STAT-1(-/-) islets are fully protected. Moreover, proteomic analysis of beta-cells exposed to IFNgamma or IFNgamma+IL-1beta confirms that very different pathways are activated by IFNgamma alone compared with the combination. We conclude that IFNgamma may play a dual role in immune-induced beta-cell destruction. Transcription factors drive this dual role, with STAT-1 driving beta-cell destruction and IRF-1 possibly playing a role in up-regulation of protective pathways induced by IFNgamma.

Iterative exposure of clonal BRIN-BD11 cells to ninhydrin enables selection of robust toxin-resistant cells but with decreased gene expression of insulin secretory function

OBJECTIVES

Prevention of pancreatic beta-cell destruction combined with preservation of insulin secretory function is an important goal for cell-based diabetes therapy. This study describes the generation and characteristics of toxin-resistant beta-cells.

METHODS

By using iterative exposures to ninhydrin, a new class of robust ninhydrin-tolerant insulin-secreting BRIN-BD11 ninhydrin-tolerant (BRINnt) cells was generated. Low- and high-passage BRINnt cells were used to evaluate beta-cell function and tolerance against toxins in comparison with native BRIN-BD11 cells. Differences in viability, gene expression, insulin secretory function, antioxidant enzyme activity, DNA damage, and DNA repair efficiency were compared.

RESULTS

BRIN-BD11 ninhydrin-tolerant cells exhibited resistance toward ninhydrin and hydrogen peroxide but not streptozotocin (STZ). Both total superoxide dismutase (SOD) and catalase enzyme activities of BRINnt cells were significantly enhanced, and ninhydrin-induced DNA damage was decreased. BRIN-BD11 ninhydrin-tolerant cells also exhibited enhanced DNA repair efficiency. However, this was accompanied by loss of secretagogue-induced insulin release, decreased cellular insulin content, and deficits in insulin and glucose transporter 2 gene expression. Prolonged culture of BRINnt cells in the absence of ninhydrin reversed the degenerated function of BRINnt cells but restored ninhydrin susceptibility.

CONCLUSIONS

These data illustrate dissociation between beta-cell toxin resistance and secretory function, indicating difficulties in generation of robust and well-functioning cells using this approach.

SUMO4 and its role in type 1 diabetes pathogenesis

Susceptibility to type 1 diabetes (T1D) is determined by interactions of multiple genes with unknown environmental factors. Despite the characterization of over 20 susceptibility regions for T1D, identification of specific genes in these regions is still a formidable challenge. In 2004, we first reported the cloning of a novel, small ubiquitin-like modifier (SUMO) gene, SUMO4, in the IDDM5 interval on chromosome 6q25, and presented strong genetic and functional evidence suggesting that SUMO4 is a T1D susceptibility gene. Subsequent studies have consistently confirmed this association in multiple Asian populations despite controversial observations in Caucasians. In this review, we will update the genetic evidence supporting SUMO4 as a T1D susceptibility gene and discuss the possible explanations for the discrepant associations observed in Caucasians. We will then discuss the mechanisms through which SUMO4 contributes to the pathogenesis of T1D.

Essential role for signal transducer and activator of transcription-1 in pancreatic beta-cell death and autoimmune type 1 diabetes of nonobese diabetic mice

OBJECTIVE

We have reported important roles for signal transducer and activator of transcription-1 (STAT1) in pancreatic beta-cell death by cytokines in vitro. However, in vivo evidence supporting the role for STAT1 in natural type 1 diabetes has not been reported. We studied whether STAT1 plays an important role in the development of natural type 1 diabetes.

RESEARCH DESIGN AND METHODS

We produced nonobese diabetic (NOD)/STAT1(-/-) mice by backcrossing and studied the in vivo role of STAT1 in beta-cell death and type 1 diabetes.

RESULTS

STAT1(-/-) islet cells were resistant to death by interferon (IFN)-gamma/tumor necrosis factor (TNF)-alpha or IFN-gamma/interleukin (IL)-1 beta combination. Cytochrome c translocation by IFN-gamma/TNF-alpha was abrogated in STAT1(-/-) islet cells. The induction of X-linked inhibitor of apoptosis protein by TNF-alpha was inhibited by IFN-gamma in STAT1(+/-) islet cells but not in STAT1(-/-) islet cells. Inducible nitric oxide (NO) synthase induction and NO production by IFN-gamma/IL-1 beta were impaired in STAT1(-/-) islet cells. Strikingly, diabetes and insulitis were completely abrogated in NOD/STAT1(-/-) mice. Development of diabetes after CD4(+) diabetogenic T-cell transfer was inhibited in those mice. STAT1(-/-) neonatal pancreata were not destroyed when grafted into diabetic NOD/BDC2.5 mice that developed CD4(+) T-cell-dependent islet cell death. In NOD/STAT1(-/-) mice, autoreactive T-cell priming was not impaired, but Th1 differentiation was impaired. A janus kinase (JAK) 2 inhibitor upstream of STAT1 attenuated islet cell death by IFN-gamma/TNF-alpha or IFN-gamma/IL-1 beta and delayed diabetes onset in NOD/BDC2.5-SCID mice.

CONCLUSIONS

These data demonstrate a critical role for STAT1 in beta-cell death, T-cell immunoregulation, and type 1 diabetes in vivo and suggest potential therapeutic values of STAT1 or JAK inhibitors in the treatment/prevention of type 1 diabetes.

Streptozotocin-resistant BRIN-BD11 cells possess wide spectrum of toxin tolerance and enhanced insulin-secretory capacity

Since streptozotocin (STZ) exhibits beta-cell toxicity, mediated through diverse mechanisms, multiple toxin resistance can be expected in insulin-secretory cells rendered STZ-resistant. RINm5F, but not all cell lines surviving STZ treatment, possess higher insulin content than native parental cells and additional tolerance against alloxan. To understand the impact of STZ tolerant cell selection on toxin resistance and insulin-secretory function, STZ-resistant BRIN-BD11 cells were generated by iterative acute exposure to 20 mM STZ. These cells, denoted BRINst cells, exhibited resistance to toxic challenges from STZ, H(2)O(2), and ninhydrin. Insulin content and both glucose and arginine-stimulated insulin secretion were significantly enhanced in BRINst cells. The toxin-resistance of BRINst cells was gradually lost during continuous cultivation without STZ challenge. However, enhanced insulin secretory capacity at high passage in BRINst cells persisted. Although total SOD activity was decreased, catalase activity was increased and appeared to be important for the ninhydrin and STZ resistance of BRINst cells. This was associated with reductions of both STZ- and ninhydrin-induced DNA damage, although DNA repair was abolished. Further characterization of cells exhibiting multiple toxin tolerance and an enhanced insulin secretory function could provide useful lessons for understanding of beta-cell survival.

Tyk2 tyrosine kinase expression is required for the maintenance of mitochondrial respiration in primary pro-B lymphocytes

Tyk2, a member of the Jak family of protein tyrosine kinases, is critical for the biological actions of alpha/beta interferon (IFN-alpha/beta). Although Tyk2(-/-) mice are phenotypically normal, they exhibit abnormal responses to inflammatory challenges in a variety of cells isolated from Tyk2(-/-) mice. The reported phenotypic alterations in both Tyk2-null cells and mice are consistent with the possibility that the expression of this tyrosine kinase may regulate mitochondrial function. We report here that Tyk2-null pro-B cells are markedly deficient in basal oxygen consumption and exhibit a significant decrease in steady-state cellular ATP levels compared to wild-type cells. Tyk2-null cells also exhibit impaired complex I, III, and IV function of the mitochondrial electron transport chain. Reconstitution of Tyk2-null pro-B cells with either the wild type or a kinase-inactive mutant of Tyk2 restores basal mitochondrial respiration. By contrast, the kinase activity of Tyk2 is required for maintenance of both complex I-dependent mitochondrial respiration as well as induction of apoptosis in cells incubated with IFN-beta. Consistent with the role of Tyk2 in the regulation of tyrosine phosphorylation of Stat3, expression of a constitutively active Stat3 can restore the mitochondrial respiration in Tyk2-null cells treated with IFN-beta. Finally, Tyk2(-/-) mice show decreased exercise tolerance compared to wild-type littermates. Our results implicate a novel role for Tyk2 kinase and Stat3 phosphorylation in mitochondrial respiration.

The Nkx6.1 homeodomain transcription factor suppresses glucagon expression and regulates glucose-stimulated insulin secretion in islet beta cells

We have previously described rat insulinoma INS-1-derived cell lines with robust or poor glucose-stimulated insulin secretion (GSIS). In the current study, we have further resolved these lines into three classes: class 1, glucose-unresponsive/glucagon-expressing; class 2, glucose-unresponsive/glucagon-negative; and class 3, glucose-responsive/glucagon-negative. The transcription factor Nkx2.2 was expressed with relative abundance of 3.3, 1.0, and 1.0 in class 1, class 2, and class 3 cells, respectively, whereas Nkx6.1 expression had the opposite trend: 1.0, 2.6, and 6.4 in class 1, class 2, and class 3 cells, respectively. In class 1 cells, overexpressed Nkx6.1 suppressed glucagon expression but did not affect the levels of several other prominent beta cell transcription factors. RNA interference (RNAi)-mediated suppression of Nkx6.1 in class 3 cells resulted in a doubling of glucagon mRNA, with no effect on Pdx1 levels, whereas suppression of Pdx1 in class 3 cells caused a 12-fold increase in glucagon transcript levels, demonstrating independent effects of Nkx6.1 and Pdx1 on glucagon expression in beta cell lines. RNAi-mediated suppression of Nkx6.1 expression in class 3 cells also caused a decrease in GSIS from 13.9- to 3.7-fold, whereas suppression of Pdx1 reduced absolute amounts of insulin secretion without affecting fold response. Finally, RNAi-mediated suppression of Nkx6.1 mRNA in primary rat islets was accompanied by a significant decrease in GSIS relative to control cells. In sum, our studies have revealed roles for Nkx6.1 in suppression of glucagon expression and control of GSIS in islet beta cells.

Toxin-based selection of insulin-producing cells with improved defense properties for islet cell transplantation

Insulin-producing pancreatic beta-cells are known to be extremely susceptible to destruction, primarily by autoimmune mechanisms, infectious agents, and by chemical toxins that cause overt type I diabetes. As development of highly protected insulin-producing cells would be important for successful cell therapy of diabetic patients, gene transfection technique was utilized by several investigators in order to improve the defense properties of transplanted cells. In this article, we summarize other approaches based on a selection strategy that has been developed in our laboratory and by other research groups that engineer pancreatic beta-cells to provide protection against diabetogenic toxins (streptozotocin and alloxan), oxidative stress and cytokines. Selection strategies based on acute repeated or long-term continuous treatment of cell lines with cytotoxic agents have resulted in the selection of highly resistant cell subpopulations. We discuss possible involvement of different expression of cytoprotective genes in the selection of cell subpopulations, which demonstrate a broad spectrum of resistance. Importantly, toxin-based selection did not impair functional activity of the cells as it was shown in vitro. In addition, selected cells preserved their improved metabolic characteristics following encapsulation in alginate and subsequent implantation in diabetic animals. Identifying the mechanisms through which cell defense properties act will help clarify the process responsible for beta-cell regeneration in type I diabetes patients. Such knowledge might be useful in developing strategies focusing on the regeneration of beta-cell resistant populations.

Requirement of Histone Deacetylase Activity for Signaling by STAT1

STAT1 is a transcription factor that plays a crucial role in signaling by interferons (IFNs). In this study we demonstrated that inhibitors of histone deacetylase (HDAC) activity, butyrate, trichostatin A, and suberoylanilide hydroxamic acid, prevented IFNgamma-induced JAK1 activation, STAT1 phosphorylation, its nuclear translocation, and STAT1-dependent gene activation. Furthermore, we showed that silencing of HDAC1, HDAC2, and HDAC3 through RNA interference markedly decreased IFNgamma-driven gene activation and that overexpression of HDAC1, HDAC2, and HDAC3 enhanced STAT1-dependent transcriptional activity. Our data therefore established the essential role of deacetylase activity in STAT1 signaling. Induction of IRF-1 by IFNgamma requires functional STAT1 signaling and was abrogated by butyrate, trichostatin A, suberoylanilide hydroxamic acid, and STAT1 small interfering RNA. In contrast, silencing of STAT1 did not interfere with IFNgamma-induced expression of STAT2 and caspase-7, and HDAC inhibitors did not preclude IFNgamma-induced expression of STAT1, STAT2, and caspase-7, suggesting that HDAC inhibitors impede the expression of IFNgamma target genes whose expression depends on STAT1 but do not interfere with STAT1-independent signaling by IFNgamma. Finally, we showed that inhibitors of deacetylase activity sensitized colon cancer cells to IFNgamma-induced apoptosis through cooperative negative regulation of Bcl-x expression, demonstrating that interruption of the balance between STAT1-dependent and STAT1-independent signaling significantly alters the biological activity of IFNgamma.

Pancreatic islets and insulinoma cells express a novel isoform of group VIA phospholipase A2 (iPLA2 beta) that participates in glucose-stimulated insulin secretion and is not produced by alternate splicing of the iPLA2 beta transcript

Many cells express a group VIA 84 kDa phospholipase A(2) (iPLA(2)beta) that is sensitive to inhibition by a bromoenol lactone (BEL) suicide substrate. Inhibition of iPLA(2)beta in pancreatic islets and insulinoma cells suppresses, and overexpression of iPLA(2)beta in INS-1 insulinoma cells amplifies, glucose-stimulated insulin secretion, suggesting that iPLA(2)beta participates in secretion. Western blotting analyses reveal that glucose-responsive 832/13 INS-1 cells express essentially no 84 kDa iPLA(2)beta-immunoreactive protein but predominantly express a previously unrecognized immunoreactive iPLA(2)beta protein in the 70 kDa region that is not generated by a mechanism of alternate splicing of the iPLA(2)beta transcript. To determine if the 70 kDa-immunoreactive protein is a short isoform of iPLA(2)beta, protein from the 70 kDa region was digested with trypsin and analyzed by mass spectrometry. Such analyses reveal several peptides with masses and amino acid sequences that exactly match iPLA(2)beta tryptic peptides. Peptide sequences identified in the 70 kDa tryptic digest include iPLA(2)beta residues 7-53, suggesting that the N-terminus is preserved. We also report here that the 832/13 INS-1 cells express iPLA(2)beta catalytic activity and that BEL inhibits secretagogue-stimulated insulin secretion from these cells but not the incorporation of arachidonic acid into membrane PC pools of these cells. These observations suggest that the catalytic iPLA(2)beta activity expressed in 832/13 INS-1 cells is attributable to a short isoform of iPLA(2)beta and that this isoform participates in insulin secretory but not in membrane phospholipid remodeling pathways. Further, the finding that pancreatic islets also express predominantly a 70 kDa iPLA(2)beta-immunoreactive protein suggests that a signal transduction role of iPLA(2)beta in the native beta-cell might be attributable to a 70 kDa isoform of iPLA(2)beta.

JAK/STAT, Raf/MEK/ERK, PI3K/Akt and BCR-ABL in cell cycle progression and leukemogenesis

The roles of the JAK/STAT, Raf/MEK/ERK and PI3K/Akt signal transduction pathways and the BCR-ABL oncoprotein in leukemogenesis and their importance in the regulation of cell cycle progression and apoptosis are discussed in this review. These pathways have evolved regulatory proteins, which serve to limit their proliferative and antiapoptotic effects. Small molecular weight cell membrane-permeable drugs that target these pathways have been developed for leukemia therapy. One such example is imatinib mesylate, which targets the BCR-ABL kinase as well as a few structurally related kinases. This drug has proven to be effective in the treatment of CML patients. However, leukemic cells have evolved mechanisms to become resistant to this drug. A means to combat drug resistance is to target other prominent signaling components involved in the pathway or to inhibit BCR-ABL by other mechanisms. Treatment of imatinib-resistant leukemia cells with drugs that target Ras (farnysyl transferase inhibitors) or with the protein destabilizer geldanamycin has proven to be a means to inhibit the growth of resistant cells. This review will tie together three important signal transduction pathways involved in the regulation of hematopoietic cell growth and indicate how their expression is dysregulated by the BCR-ABL oncoprotein.

Understanding of basic mechanisms of beta-cell function and survival: prelude to new diabetes therapies

Type 1 and type 2 diabetes are both diseases of insulin insufficiency, although they develop by distinct pathways. The recent surge in the incidence of type 2 diabetes and the chronic ailments confronted by patients with either form of the disease highlight the need for better understanding of beta-cell biology. In this review, we present recent work focused on this goal. Our hope is that basic research being conducted in this and other laboratories will ultimately contribute to the development of methods for enhancing beta-cell function and survival in the context of both major forms of diabetes. Our strategy for understanding the beta-cell involves a multidisciplinary approach in which tools from the traditional fields of biochemistry, enzymology, and physiology are teamed with newer technologies from the fields of molecular biology, gene discovery, cell and developmental biology, and biophysical chemistry. We have focused on two important aspects of beta-cell biology in our studies: beta-cell function, specifically the metabolic regulatory mechanisms involved in glucose-stimulated insulin secretion, and beta-cell resistance to immune attack, with emphasis on resistance to inflammatory cytokines and reactive oxygen species.

Discrete and complementary mechanisms of protection of beta-cells against cytokine-induced and oxidative damage achieved by bcl-2 overexpression and a cytokine selection strategy

We have been investigating the potential utility of engineered cell lines as surrogates for primary islet cells in treatment of type 1 diabetes. To this end, two strategies that have emerged for procuring cell lines with resistance to immune-mediated damage are 1) selection of cytokine-resistant cell lines by growth of INS-1 insulinoma cells in iteratively increasing concentrations of interleukin (IL)-1beta + gamma-interferon (IFN-gamma), and 2) stable overexpression of the anti-apoptotic gene bcl-2 in INS-1 cells. Herein, we show that bcl-2-overexpressing cells are resistant to the cytotoxic effects of reactive oxygen and nitrogen species (ROS/RNS), but are only modestly protected against high concentrations of IL-1beta + INF-gamma, whereas the converse is true in cytokine selected cells. We also found that the combination of bcl-2 expression and cytokine selection confers a broader spectrum of resistance than either procedure alone, such that the resultant cells are highly resistant to cytokines and ROS/RNS, with no impairment in glucose-stimulated insulin secretion. INS-1-derived cells with combined bcl-2 expression and cytokine selection are also more resistant to damage induced by coculture with mitogen-activated peripheral blood mononuclear cells. Surprisingly, application of the cytokine selection procedure to bcl-2-overexpressing cells does not result in impairment of nuclear factor-kappaB translocation, iNOS expression, and NO production, as clearly occurs upon application of the selection procedure to cells without bcl-2 overexpression. Further investigation of the diverse pathways involved in the development of cytokine and ROS/RNS resistance may define simplified and specific strategies for preservation of beta-cell mass.

STAT1 deficiency unexpectedly and markedly exacerbates the pathophysiological actions of IFN-alpha in the central nervous system

Although signal transducer and activator of transcription 1 (STAT1) is an essential signaling molecule in many IFN-alpha-regulated processes, some biological responses to IFN-alpha can occur independently of STAT1. To establish the role of STAT1 in mediating the biological actions of IFN-alpha in the CNS, transgenic mice [termed glial fibrillary acidic protein (GFAP)-IFN-alpha] with astrocyte production of IFN-alpha were bred to be null for the STAT1 gene. Surprisingly, GFAP-IFN-alpha mice deficient for STAT1 developed earlier onset and more severe neurological disease with increased lethality compared with GFAP-IFN-alpha mice sufficient for STAT1. Whereas the brain of 2- to 3-month-old GFAP-IFN-alpha mice showed little, if any abnormality, the brain from GFAP-IFN-alpha mice deficient for STAT1 had severe neurodegeneration, inflammation, calcification with increased apoptosis, and glial activation. However, the cerebral expression of a number of IFN-regulated STAT1-dependent genes increased in GFAP-IFN-alpha mice but was reduced markedly in GFAP-IFN-alpha STAT1-null mice. Of many other signaling molecules examined, STAT3 alone was activated significantly in the brain of GFAP-IFN-alpha STAT1-null mice. Thus, in the absence of STAT1, alternative signaling pathways mediate pathophysiological actions of IFN-alpha in the living brain, giving rise to severe encephalopathy. Finally, STAT1 or a downstream component of the JAKSTAT pathway may protect against such IFN-alpha-mediated injury in the CNS.

While tinkering with the beta-cell...metabolic regulatory mechanisms and new therapeutic strategies: American Diabetes Association Lilly Lecture, 2001

A common feature of the two major forms of human diabetes is the partial or complete loss of insulin secretion from beta-cells in the pancreatic islets of Langerhans. In this article, we review the development of a set of tools for studying beta-cell biology and their application to understanding of fuel-mediated insulin secretion and enhancement of beta-cell survival. Insights into these basic issues are likely to be useful for the design of new drug and cell-based diabetes therapies.

Fatty acids potentiate interleukin-1beta toxicity in the beta-cell line INS-1E

Evidence for "lipotoxicity," i.e., negative effects of fatty acids (FA) on pancreatic beta-cells is incomplete. Here, we tested whether non-toxic concentrations of FA potentiate toxic effects of interleukin-1beta (IL-1beta). Culture of INS-1E clonal beta-cells for 2-6 days with 70 microM docosahexaenoic acid (DHA), eicosapentaenoic acid, arachidonic acid, 0.1mM linoleic acid, or 0.1-0.2mM oleic acid exerted no or minor negative effects on cell viability (MTT assay). Viability was reduced by 0.5 ng/ml IL-1beta. All tested FA significantly aggravated this effect after 6 days of culture. IL-1beta also exerted negative effects on cellular insulin content and DHA and oleic acid aggravated these effects. L-NAME, an inhibitor of constitutive nitric oxide (NO) synthase, reduced the negative effects of IL-1beta per se but did not abolish the potentiating effects of FA.

CONCLUSION

FA potentiate toxic effects of IL-1beta on beta-cells by mechanisms that include NO-independent ones.

Mechanisms for regulation of cellular responsiveness to human IFN-beta1a

Interferons (IFNs) are potent, pleiotropic cytokines, and therefore it is likely that the cell has mechanisms to modulate IFN activity in response to excessive or prolonged IFN exposure. To investigate this question, Jurkat T cells were exposed to IFN-beta1a in vitro. The effect of dose and frequency of IFN treatment on receptor expression, the signal transduction pathway, and biologic activity was examined. Results demonstrate that at even modest doses of IFN (60 IU/ml), cell surface expression of the IFN receptor subunit, IFNAR-1, decreased significantly, and the cells were unresponsive to further IFN treatment. More interestingly, after an initial treatment with very low concentrations of IFN (<10 IU/ml), even when receptor levels remained normal and phosphorylation of signaling molecules occurred, cells were still refractory to further IFN treatment. After withdrawal of IFN, full cellular responsiveness was a progressive but surprisingly slow process. Cells retreated 2 days or 4 days after the initial IFN treatment were still refractory to even high doses (500 IU/ml) of IFN. Cells retreated 1 week after the initial IFN treatment were fully responsive. High levels of Stat1 and Stat2 correlated with the block in transcriptional activation of IFN-dependent genes and may be a mechanism by which cells can downmodulate an IFN response. Similar results were obtained when fresh peripheral blood mononuclear cells (PBMC) were treated with IFN and expression of the endogenous IFN-dependent gene, MxA, was examined. Cell surface levels of IFNAR-1 decreased and Stat1 levels increased after IFN-beta treatment, and retreatment with IFN resulted in an attenuated induction of Mx protein expression. In the context of using IFNs as therapeutic agents in the treatment of human disease, our data suggest that increasing the amount or frequency of IFN administration may not yield desired biologic effects. Thus, issues concerning the dosage and the frequency of IFN-beta administration deserve careful consideration.

Regulation of signal transducer and activator of transcription and suppressor of cytokine-signaling gene expression in the brain of mice with astrocyte-targeted production of interleukin-12 or experimental autoimmune encephalomyelitis

Interleukin (IL)-12 and interferon (IFN)-gamma are implicated in the pathogenesis of immune disorders of the central nervous system (CNS). To define the basis for the actions of these cytokines in the CNS, we examined the temporal and spatial regulation of key signal transducers and activators of transcription (STATs) and suppressors of cytokine signaling (SOCS) in the brain of transgenic mice with astrocyte production of IL-12 or in mice with experimental autoimmune encephalomyelitis (EAE). In healthy mice, with the exception of STAT4 and STAT6, the expression of a number of STAT and SOCS genes was detectable. However, in symptomatic transgenic mice and in EAE significant up-regulation of STAT1, STAT2, STAT3, STAT4, IRF9, and SOCS1 and SOCS3 RNA transcripts was observed. Although the increased expression of STAT1 RNA was widely distributed and included neurons, astrocytes, and microglia, STAT4 and STAT3 and SOCS1 and SOCS3 RNA was primarily restricted to the infiltrating mononuclear cell population. The level and location of the STAT1, STAT3, and STAT4 proteins overlapped with their corresponding RNA and additionally showed nuclear localization indicative of activation of these molecules. Thus, in both the glial fibrillary acidic protein-IL-12 mice and in EAE the CNS expression of key STAT and SOCS genes that regulate IL-12 (STAT4) and IFN-gamma (STAT1, SOCS1, and SOCS3) receptor signaling is highly regulated and compartmentalized. We conclude the interaction between these positive and negative signaling circuits and their distinct cellular locations likely play a defining role in coordinating the actions of IL-12 and IFN-gamma during the pathogenesis of type 1 immune responses in the CNS.

gamma-Interferon signaling in pancreatic beta-cells is persistent but can be terminated by overexpression of suppressor of cytokine signaling-1

Proinflammatory cytokines, including gamma-interferon (IFN-gamma), have been implicated in the destruction of beta-cells in autoimmune diabetes. IFN-gamma signaling is transient in some cell types, but there is indirect evidence that it may be prolonged in beta-cells. In this study, we have shown that IFN-gamma signaling, measured by signal transducer and activator of transcription-1 (STAT1) activation and the expression of IFN-gamma-responsive genes, is persistent in beta-cells for as long as the cytokine is present. Because members of the suppressor of cytokine signaling (SOCS) family may regulate the duration of IFN-gamma signaling, their expression was investigated in beta-cells. We found that cytokine-inducible SH2-containing protein, SOCS-1, and SOCS-2 are expressed in primary islets and NIT-1 insulinoma cells, both at the mRNA and protein levels, after treatment with IFN-gamma and other proinflammatory cytokines. Transfected SOCS-1 was found to inhibit responses to IFN-gamma in NIT-1 insulinoma cells, including STAT1 activation, class I major histocompatibility complex upregulation, and IFN-gamma-induced cell death, but only when expressed at levels higher than those found in untransfected cells. Consistent with this, IFN-gamma signaling was not affected in SOCS-1-deficient beta-cells. Therefore, persistent IFN-gamma signaling in beta-cells is associated with SOCS-1 expression that is not sufficient to terminate signaling. Because overexpression of SOCS-1 can suppress responses to IFN-gamma, this may be a useful strategy for protecting beta-cells from cytotoxicity mediated by IFN-gamma and possibly other proinflammatory cytokines.

Suppressor of cytokine signaling 3 (SOCS-3) protects beta -cells against interleukin-1beta - and interferon-gamma -mediated toxicity

Suppressor of cytokine signaling 3 (SOCS-3) is a negative feedback regulator of IFN-gamma signaling, shown up-regulated in mouse bone marrow cells by the proinflammatory cytokines interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and IFN-gamma. IL-1beta and IFN-gamma alone, or potentiated by TNF-alpha, are cytotoxic to the insulin producing pancreatic beta-cells and beta-cell lines in vitro and suggested to contribute to the specific beta-cell destruction in Type-1 diabetes mellitus (T1DM). Using a doxycycline-inducible SOCS-3 expression system in the rat beta-cell line INS-1, we demonstrate that the toxic effect of both IL-1beta or IFN-gamma at concentrations that reduced the viability by 50% over 3 days, was fully preventable when SOCS-3 expression was turned on in the cells. At cytokine concentrations or combinations more toxic to the cells, SOCS-3 overexpression yielded a partial protection. Whereas SOCS-3-mediated inhibition of IFN-gamma signaling is described in other cell systems, SOCS-3 mediated inhibition of IL-1beta signaling has not previously been described. In addition we show that SOCS-3 prevention of IL-1beta-induced toxicity is accompanied by inhibited transcription of the inducible nitric oxide synthase (iNOS) by 80%, resulting in 60% decreased formation of the toxic nitric oxide (NO). Analysis of isolated native rat islets exposed to IL-1beta revealed a naturally occurring but delayed up-regulated SOCS-3 transcription. Influencing SOCS-3 expression thus represents an approach for affecting cytokine-induced signal transduction at a proximal step in the signal cascade, potentially useful in future therapies aimed at reducing the destructive potential of beta-cell cytotoxic cytokines in T1DM, as well as other cytokine-dependent diseases.