Deletion Of Signal Transducer And Activator Of Transcription 3 Research Articles

2'-Hydroxycinnamaldehyde Alleviates Intestinal Inflammation by Attenuating Intestinal Mucosal Barrier Damage Via Directly Inhibiting STAT3.

The currently available clinical therapeutic drugs for ulcerative colitis (UC) are considered inadequate owing to certain limitations. There have been reports on the anti-inflammatory effects of 2'-hydroxycinnamaldehyde (HCA). However, whether HCA can improve UC is still unclear. Here, we aimed to investigate the pharmacological effects of HCA on UC and its underlying molecular mechanisms. The pharmacological effects of HCA were comprehensively investigated in 2 experimental setups: mice with dextran sulfate sodium (DSS)-induced colitis and lipopolysaccharide (LPS)-treated fetal human colon (FHC) cells. Furthermore, the interaction between HCA and signal transducer and activator of transcription 3 (STAT3) was investigated using molecular docking. The FHC cells with STAT3 knockdown or overexpression and mice with intestinal epithelium-specific STAT3 deletion (STAT3ΔIEC) were used to evaluate whether STAT3 mediated the pharmacological effects of HCA. 2'-Hydroxycinnamaldehyde attenuated dysregulated expression of inflammatory cytokines in a dose-dependent manner while increasing the expression of tight junction proteins, reducing the apoptosis of intestinal epithelial cells, and effectively alleviating inflammation both in vivo and in vitro. 2'-Hydroxycinnamaldehyde bound directly to STAT3 and inhibited its activation. The modulation of STAT3 activation levels due to STAT3 knockdown or overexpression influenced the mitigating effects of HCA on colitis. Further analysis indicated that the remission effect of HCA was not observed in STAT3ΔIEC mice, indicating that STAT3 mediated the anti-inflammatory effects of HCA. We present a novel finding that HCA reduces colitis severity by attenuating intestinal mucosal barrier damage via STAT3. This discovery holds promise as a potential new strategy to alleviate UC.

IL-6R/Signal Transducer and Activator of Transcription 3 Signaling in Keratinocytes rather than in T Cells Induces Psoriasis-Like Dermatitis in Mice

Signal transducer and activator of transcription 3 (STAT3) is important for psoriasis pathogenesis because STAT3 signaling downstream of IL-6, IL-21, IL-22, and IL-23 contributes to T helper type 17 cell development and because transgenic mice with keratinocyte (KC) STAT3 expression (K14-Stat3C mice) develop psoriasis-like dermatitis. In this study, the relative contribution of STAT3 signaling in KCs versus in T cells was evaluated in the imiquimod model of psoriasis-like dermatitis. Mice with STAT3-inducible deletion in KCs (K5-Stat3-/- mice) had decreased psoriasis-like dermatitis and epidermal STAT3 phosphorylation compared with wild-type mice, whereas mice with constitutive deletion of STAT3 in all T cells were similar to wild-type mice. Interestingly, mice with KC-inducible deletion of IL-6Rα had similar findings to those of K5-Stat3-/- mice, identifying IL-6/IL-6R as a predominant upstream signal for KC STAT3-induced psoriasis-like dermatitis. Moreover, psoriasis-like dermatitis inversely associated with type 1 immune gene products, especially CXCL10, whereas CXCL10 limited psoriasis-like dermatitis, suggesting that KC STAT3 signaling promoted psoriasis-like dermatitis by restricting downstream CXCL10 expression. Finally, treatment of mice with the pan-Jak inhibitor, tofacitinib, reduced psoriasis-like dermatitis and epidermal STAT3 phosphorylation. Taken together, STAT3 signaling in KCs rather than in T cells was a more important determinant for psoriasis-like dermatitis in a mechanism that involved upstream KC IL-6R signaling and downstream inhibition of type 1 immunity‒associated CXCL10 responses.

Stromal-Cell Deletion of STAT3 Protects Mice from Kidney Fibrosis by Inhibiting Pericytes Trans-Differentiation and Migration

Signal transducer and activator of transcription 3 (STAT3) is a key transcription factor implicated in the pathogenesis of kidney fibrosis. Although tubular Stat3 deletion in tubular epithelial cells is known to protect mice from kidney fibrosis, the exact function of STAT3 in stromal cells remains unknown. We utilized stromal-cell Stat3 knock-out (KO) mice, CRISPR and pharmacologic activators and inhibitors of STAT3 to investigate its function in pericyte-like cells. STAT3 is phosphorylated in tubular epithelial cells in acute kidney injury whereas its activation expanded to interstitial cells in chronic kidney disease in mice and humans. Stromal cell-specific deletion of Stat3 protects mice from folic acid- and aristolochic acid-induced kidney fibrosis. Mechanistically, STAT3 directly regulates the inflammatory pathway, differentiation of pericytes into myofibroblasts. Specifically, STAT3 activation leads to an increase in migration and profibrotic signaling in genome-edited pericyte-like cells, 10T1/2. Conversely, Stat3 KO or blocking STAT3 function inhibits detachment, spreading, migration, and profibrotic signaling. Furthermore, STAT3 binds to Collagen1a1 promoter of fibrotic mouse kidneys and in pericyte-like cells. Together, our study identifies a previously unknown function of STAT3 in stromal cells that promotes kidney fibrosis and may have therapeutic value in fibrotic kidney disease.

Effects of Cardiomyocyte-Specific Deletion of STAT3-A Murine Model of Heart Failure With Preserved Ejection Fraction.

Aims: There is a high incidence of heart failure with preserved ejection fraction (HFpEF), but the options of treatment are limited. A new animal model of HFpEF is urgently needed for in-depth research on HFpEF. Signal transducer and activator of transcription 3 (STAT3) may affect the passive stiffness of myocardium, which determines cardiac diastolic function. We hypothesized that cardiomyocyte-specific deletion of STAT3 increases cardiac passive stiffness, which results the murine features of HFpEF.Methods and Results: Cardiomyocyte-specific deletion of STAT3 (STAT3cKO) mice was generated by the Cre/FLOXp method. The STAT3cKO mice showed heavier cardiac fibrosis and cardiac hypertrophy comparing with wild-type (WT) mice. Furthermore, STAT3cKO mice showed increased serum brain natriuretic peptide (BNP) level, and growth stimulation expressed gene 2 (ST2) level. Other indicators reflecting cardiac passive stiffness and diastolic function, including end diastolic pressure volume relation, MV A value, MV E value, E/A and E/E' had different fold changes. All these changes were accompanied by decreasing levels of protein kinase G (PKG). Bioinformatic analysis of STAT3cKO mice hearts suggested cGMP-PKG signaling pathway might participate in the pathogenesis of HFpEF by means of adjusting different biological functions.Conclusions: Cardiomyocyte-specific deletion of STAT3 results in a murine HFpEF model which imitates the clinical characteristics partly by affecting cardiac PKG levels. Better understanding of the factors influencing HFpEF may finally provided innovative therapies.

Osteoblastic STAT3 Is Crucial for Orthodontic Force Driving Alveolar Bone Remodeling and Tooth Movement.

Mechanical force is essential to shape the internal architecture and external form of the skeleton by regulating the bone remodeling process. However, the underlying mechanism of how the bone responds to mechanical force remains elusive. Here, we generated both orthodontic tooth movement (OTM) model in vivo and a cyclic stretch-loading model in vitro to investigate biomechanical regulation of the alveolar bone. In this study, signal transducer and activator of transcription 3 (STAT3) was screened as one of the mechanosensitive proteins by protein array analysis of cyclic stretch-loaded bone mesenchymal stem cells (BMSCs) and was also proven to be activated in osteoblasts in response to the mechanical force during OTM. With an inducible osteoblast linage-specific Stat3 knockout model, we found that Stat3 deletion decelerated the OTM rate and reduced orthodontic force-induced bone remodeling, as indicated by both decreased bone resorption and formation. Both genetic deletion and pharmacological inhibition of STAT3 in BMSCs directly inhibited mechanical force-induced osteoblast differentiation and impaired osteoclast formation via osteoblast-osteoclast cross-talk under mechanical force loading. According to RNA-seq analysis of Stat3-deleted BMSCs under mechanical force, matrix metalloproteinase 3 (Mmp3) was screened and predicted to be a downstream target of STAT3. The luciferase and ChIP assays identified that Stat3 could bind to the Mmp3 promotor and upregulate its transcription activity. Furthermore, STAT3-inhibitor decelerated tooth movement through inhibition of the bone resorption activity, as well as MMP3 expression. In summary, our study identified the mechanosensitive characteristics of STAT3 in osteoblasts and highlighted its critical role in force-induced bone remodeling during orthodontic tooth movement via osteoblast-osteoclast cross-talk. © 2022 American Society for Bone and Mineral Research (ASBMR).

Abstract PO-054: A stromal PTEN/STAT3 signaling axis promotes immune evasion and tumor progression in pancreatic cancer

Abstract Pancreatic adenocarcinoma (PDAC) is among the most lethal cancer types, with more than 90% of patients succumbing to the disease within five years of diagnosis. The most notable hallmark of PDAC tumors is an inordinately dense stromal reaction comprised of extracellular matrix proteins, immune infiltrates, endothelial cells, and activated fibroblasts. The stroma experiences a dramatic expansion in parallel with the progression of the tumor, suggesting it is an active participant in PDAC development. However, key studies targeting stromal development through Hedgehog signaling revealed tumor-suppressive functions of the stroma, further complicating the strategy to target the stroma as a single component. Thus, our understanding of the complex relationship between the tumor and its microenvironment and how to effectively target the stroma itself remains incomplete. Previous work by our lab demonstrates that phosphatase and tensin homolog (PTEN) expression is lost in approximately 25% of patients in a PDAC cohort, and lower PTEN expression correlates with worsened patient outcome. Additionally, inhibition of Hedgehog signaling results in loss of PTEN expression and subsequent activation of Akt signaling pathways, and increased tumor growth. The purpose of the current study is to determine the effect of PTEN loss in PDAC cancer-associated fibroblasts (CAFs) on tumor progression and dissemination, and immune evasion. Using a combination of in vitro and in vivo experiments, we have found robust activation of Signal Transducer and Activator of Transcription 3 (STAT3) in PTEN-null pancreatic fibroblasts. We also see selective alterations in the secretome of pancreatic fibroblasts, including a marked increase in IL-6, CXCL1, and CXCL2. Our group has developed a genetically engineered mouse model of PDAC using a dual recombinase system in which the fibroblast-specific protein-1 (FspCre) transgene is used to conditionally delete genes of interest in the fibroblasts of Pdx1Flpki/+;FSF-KrasG12D/+;p53frt/+ (KPF) mice while driving tumorigenesis in the pancreatic epithelium. Conditional deletion of STAT3 in stromal fibroblasts of these mice results in increased overall survival, reduced tumor progression, and alterations within the immune landscape of the tumor microenvironment. Based on our current findings, we believe that a PTEN/STAT3/CXCL1/2 signaling axis within stromal CAFs produces an immunosuppressive tumor microenvironment that favors PDAC progression. Future experiments are needed to validate and confirm this conclusion, including defining the exact mechanisms by which PTEN loss leads to STAT3 activation and elevated secretion of CXCL1/2. This project further highlights the nuanced and complex relationship between PDAC tumor and stroma, and may serve to advance our understanding of how the stroma can be more precisely and effectively targeted to reduce tumor burden and increase the efficacy of immune therapy. Citation Format: Catherine B. MarElia-Bennett, Julia E. Lefler, Michael C. Ostrowski. A stromal PTEN/STAT3 signaling axis promotes immune evasion and tumor progression in pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-054.

JAK/STAT inhibition in macrophages promotes therapeutic resistance by inducing expression of protumorigenic factors

Tumor-associated macrophages contribute to tumor progression and therapeutic resistance in breast cancer. Within the tumor microenvironment, tumor-derived factors activate pathways that modulate macrophage function. Using in vitro and in vivo models, we find that tumor-derived factors induce activation of the Janus kinase (JAK)/signal transducer and activator of transcription 3 (STAT3) pathway in macrophages. We also demonstrate that loss of STAT3 in myeloid cells leads to enhanced mammary tumorigenesis. Further studies show that macrophages contribute to resistance of mammary tumors to the JAK/STAT inhibitor ruxolitinib in vivo and that ruxolitinib-treated macrophages produce soluble factors that promote resistance of tumor cells to JAK inhibition in vitro. Finally, we demonstrate that STAT3 deletion and JAK/STAT inhibition in macrophages increases expression of the protumorigenic factor cyclooxygenase-2 (COX-2), and that COX-2 inhibition enhances responsiveness of tumors to ruxolitinib. These findings define a mechanism through which macrophages promote therapeutic resistance and highlight the importance of understanding the impact of targeted therapies on the tumor microenvironment.

T Cell-Specific Knockout of STAT3 Ameliorates Dextran Sulfate Sodium-Induced Colitis by Reducing the Inflammatory Response.

Signal transducer and activator of transcription 3 (STAT3) has a crucial role in various autoimmune disorders including, inflammatory bowel disease (IBD). Our previous study demonstrated that STAT3 activation by IL-6 in colonic epithelial cells exacerbates experimental ulcerative colitis. Activated T lymphocytes are also found in ulcerative colitis patients with intestinal inflammation, but the role of STAT3 in T cells remains elusive. To determine the STAT3 function of T cells in intestinal inflammation, we generated T cell-specific STAT3 knockout (KO) mice and used dextran sulfate sodium (DSS) to induce colitis. In this study, we demonstrated that T cell-specific STAT3 deletion alleviated DSS-induced colitis in mice, resulting in reduced histological scores and myeloperoxidase (MPO) activity. Importantly, the population of T cells in the spleen and lymph nodes was significantly decreased in the control and DSS-induced groups of STAT3 KO mice. In addition, STAT3 deficiency in T cells markedly reduced the production of interferon (IFN)-γ, IL-6, and IL-17A, whereas IL-10 secretion was increased. Collectively, the results suggest that STAT3 in T cells may be a therapeutic target in ulcerative colitis by balancing the immune response through T cell homeostasis.

Epidermal growth factor signaling protects from cholestatic liver injury and fibrosis

We have demonstrated that the signal transducer and activator of transcription 3 (STAT3) protects from cholestatic liver injury. Specific ablation of STAT3 in hepatocytes and cholangiocytes (STAT3∆hc) aggravated liver damage and fibrosis in the Mdr2−/− (multidrug resistance 2) mouse model for cholestatic disease. Upregulation of bile acid biosynthesis genes and downregulation of epidermal growth factor receptor (EGFR) expression were observed in STAT3∆hc Mdr2−/− mice but the functional consequences of these processes in cholestatic liver injury remained unclear. Here, we show normal canalicular architecture and bile flow but increased amounts of bile acids in the bile of STAT3∆hc Mdr2−/− mice. Moreover, STAT3-deficient hepatocytes displayed increased sensitivity to bile acid-induced apoptosis in vitro. Since EGFR signaling has been reported to protect hepatocytes from bile acid-induced apoptosis, we generated mice with hepatocyte/cholangiocyte-specific ablation of EGFR (EGFR∆hc) and crossed them to Mdr2−/− mice. Importantly, deletion of EGFR phenocopied deletion of STAT3 and led to aggravated liver damage, liver fibrosis, and hyperproliferation of K19+ cholangiocytes. Our data demonstrate hepatoprotective functions of the STAT3-EGFR signaling axis in cholestatic liver disease.Key messageSTAT3 is a negative regulator of bile acid biosynthesis.STAT3 protects from bile acid-induced apoptosis and regulates EGFR expression.EGFR signaling protects from cholestatic liver injury and fibrosis.

Ablation of STAT3 in the B Cell Compartment Restricts Gammaherpesvirus Latency In Vivo.

ABSTRACTA challenging property of gammaherpesviruses is their ability to establish lifelong persistence. The establishment of latency in B cells is thought to involve active virus engagement of host signaling pathways. Pathogenic effects of these viruses during latency or following reactivation can be devastating to the host. Many cancers, including those associated with members of the gammaherpesvirus family, Kaposi’s sarcoma-associated herpesvirus and Epstein-Barr virus, express elevated levels of active host signal transducer and activator of transcription-3 (STAT3). STAT3 is activated by tyrosine phosphorylation in response to many cytokines and can orchestrate effector responses that include proliferation, inflammation, metastasis, and developmental programming. However, the contribution of STAT3 to gammaherpesvirus pathogenesis remains to be completely understood. This is the first study to have identified STAT3 as a critical host determinant of the ability of gammaherpesvirus to establish long-term latency in an animal model of disease. Following an acute infection, murine gammaherpesvirus 68 (MHV68) established latency in resident B cells, but establishment of latency was dramatically reduced in animals with a B cell-specific STAT3 deletion. The lack of STAT3 in B cells did not impair germinal center responses for immunoglobulin (Ig) class switching in the spleen and did not reduce either total or virus-specific IgG titers. Although ablation of STAT3 in B cells did not have a global effect on these assays of B cell function, it had long-term consequences for the viral load of the host, since virus latency was reduced at 6 to 8 weeks postinfection. Our findings establish host STAT3 as a mediator of gammaherpesvirus persistence.

DPP-4 inhibition has beneficial effects on the heart after myocardial infarction

AimsDipeptidyl peptidase-4 (DPP-4) inhibitors are reported to have protective effects on various cells but it is unclear how DPP-4 inhibitors have cardioprotective effects. Our aim was to study the mechanisms of cardioprotective effects by DPP-4 inhibition. Methods and resultsC57BL/6 mice and DPP-4 knockout (DPP-4KO) mice were subjected to left coronary artery ligation to produce acute myocardial infarction (MI). C57BL/6 mice were then treated with vehicle or DPP-4 inhibitor. Left ventricular function, infarct size, the number of vessels, and myocardial ischemia were assessed at 5days after MI. The treatment with DPP-4 inhibitor significantly improved cardiac function and decreased the infarct size. DPP-4 inhibitor increased the ratio of endothelial cell numbers to a cardiomyocyte. The extent of myocardial ischemia and the number of TUNEL-positive cells in the border area were significantly decreased by DPP-4 inhibitor. Stromal cell-derived factor-1α (SDF-1α) level in myocardium was significantly increased by DPP-4 inhibitor. Those cardioprotective effects after MI were also recognized in DPP-4KO mice. DPP-4 protein was expressed on rat neonatal cardiomyocytes and DPP-4 inhibitor significantly reduced hypoxia-induced apoptosis in the cardiomyocytes. However, this effect was abolished by the pretreatment with a CXCR4 antagonist or a signal transducer and activator of transcription 3 (STAT3) inhibitor. The beneficial effects of DPP-4 inhibitor on heart failure after MI were abolished by cardiomyocyte-specific deletion of STAT3. ConclusionsDPP-4 inhibition may have direct protective effects on the post-MI heart by inducing an antiapoptotic effect and inhibiting a decrease in vessel number through the SDF-1α/CXCR4-mediated STAT3 signaling pathway.

Leptin Suppresses the Rewarding Effects of Running via STAT3 Signaling in Dopamine Neurons

The adipose hormone leptin potently influences physical activity. Leptin can decrease locomotion and running, yet the mechanisms involved and the influence of leptin on the rewarding effects of running ("runner's high") are unknown. Leptin receptor (LepR) signaling involves activation of signal transducer and activator of transcription-3 (STAT3), including in dopamine neurons of the ventral tegmental area (VTA) that are essential for reward-relevant behavior. We found that mice lacking STAT3 in dopamine neurons exhibit greater voluntary running, an effect reversed by viral-mediated STAT3 restoration. STAT3 deletion increased the rewarding effects of running whereas intra-VTA leptin blocked it in a STAT3-dependent manner. Finally, STAT3 loss-of-function reduced mesolimbic dopamine overflow and function. Findings suggest that leptin influences the motivational effects of running via LepR-STAT3 modulation of dopamine tone. Falling leptin is hypothesized to increase stamina and the rewarding effects of running as an adaptive means to enhance the pursuit and procurement of food.

Differential roles of STAT3 in the initiation and growth of lung cancer.

Signal transducer and activator of transcription 3 (STAT3) is linked to multiple cancers, including pulmonary adenocarcinoma. However, the role of STAT3 in lung cancer pathogenesis has not been determined. Using lung epithelial-specific inducible knockout strategies, we demonstrate that STAT3 plays contrasting roles in the initiation and growth of both chemically and genetically induced lung cancers. Selective deletion of lung epithelial STAT3 in mice prior to cancer induction by the smoke carcinogen, urethane, resulted in increased lung tissue damage and inflammation, K-Ras oncogenic mutations, and tumorigenesis. Deletion of lung epithelial STAT3 after establishment of lung cancer inhibited cancer cell proliferation. Simultaneous deletion of STAT3 and expression of oncogenic K-Ras in mouse lung elevated pulmonary injury, inflammation, and tumorigenesis, but reduced tumor growth. These studies indicate that STAT3 prevents lung cancer initiation by maintaining pulmonary homeostasis under oncogenic stress, whereas it facilitates lung cancer progression by promoting cancer cell growth. These studies also provide a mechanistic basis for targeting STAT3 to lung cancer therapy.

Aldehyde dehydrogenase 2 deficiency ameliorates alcoholic fatty liver but worsens liver inflammation and fibrosis in mice

Aldehyde dehydrogenase 2 (ALDH2) is the major enzyme that metabolizes acetaldehyde produced from alcohol metabolism. Approximately 40-50% of East Asians carry an inactive ALDH2 gene and exhibit acetaldehyde accumulation after alcohol consumption. However, the role of ALDH2 deficiency in the pathogenesis of alcoholic liver injury remains obscure. In the present study, wild-type and ALDH2(-/-) mice were subjected to ethanol feeding and/or carbon tetrachloride (CCl4 ) treatment, and liver injury was assessed. Compared with wild-type mice, ethanol-fed ALDH2(-/-) mice had higher levels of malondialdehyde-acetaldehyde (MAA) adduct and greater hepatic inflammation, with higher hepatic interleukin (IL)-6 expression but surprisingly lower levels of steatosis and serum alanine aminotransferase (ALT). Higher IL-6 levels were also detected in ethanol-treated precision-cut liver slices from ALDH2(-/-) mice and in Kupffer cells isolated from ethanol-fed ALDH2(-/-) mice than those levels in wild-type mice. In vitro incubation with MAA enhanced the lipopolysaccharide (LPS)-mediated stimulation of IL-6 production in Kupffer cells. In agreement with these findings, hepatic activation of the major IL-6 downstream signaling molecule signal transducer and activator of transcription 3 (STAT3) was higher in ethanol-fed ALDH2(-/-) mice than in wild-type mice. An additional deletion of hepatic STAT3 increased steatosis and hepatocellular damage in ALDH2(-/-) mice. Finally, ethanol-fed ALDH2(-/-) mice were more prone to CCl4 -induced liver inflammation and fibrosis than ethanol-fed wild-type mice. ALDH2(-/-) mice are resistant to ethanol-induced steatosis but prone to inflammation and fibrosis by way of MAA-mediated paracrine activation of IL-6 in Kupffer cells. These findings suggest that alcohol, by way of acetaldehyde and its associated adducts, stimulates hepatic inflammation and fibrosis independent from causing hepatocyte death, and that ALDH2-deficient individuals may be resistant to steatosis and blood ALT elevation, but are prone to liver inflammation and fibrosis following alcohol consumption.

Neither Signal Transducer and Activator of Transcription 3 (STAT3) or STAT5 Signaling Pathways Are Required for Leptin's Effects on Fertility in Mice

The hormone leptin is critical for the regulation of energy balance and fertility. The long-form leptin receptor (LepR) regulates multiple intracellular signaling cascades, including the classic Janus kinase-signal transducer and activator of transcription (STAT) pathways. Previous studies have shown that deletion of STAT3 or the closely related STAT5 from the brain results in an obese phenotype, but their roles in fertility regulation are not clear. This study tested whether STAT3 and STAT5 pathways of leptin signaling are required for fertility, and whether absence of one pathway might be compensated for by the other in a redundant manner. A Cre-loxP approach was used to generate 3 models of male and female transgenic mice with LepR-specific deletion of STAT3, STAT5, or both STAT3 and STAT5. Body weight, puberty onset, estrous cyclicity, and fertility were measured in all knockout (KO) mice and their control littermates. Knocking out STAT3 or both STAT3 and 5 from LepR expressing cells, but not STAT5 alone, led to significant increase in body weight. All STAT3 and STAT5 single KO mice exhibited normal puberty onset and subsequent fertility compared to their control littermates. Surprisingly, all STAT3 and STAT5 double KO mice also exhibited normal puberty onset, estrous cyclicity, and fertility, although they had severely disrupted body weight regulation. These results suggest that, although STAT3 signaling is crucial for body weight regulation, neither STAT3 nor STAT5 is required for the regulation of fertility by leptin. It remains to be determined what other signaling molecules mediate this effect of leptin, and whether they interact in a redundant manner.

A Molecular Link Between Interleukin 22 and Intestinal Mucosal Wound Healing

Interleukin 22 (IL-22) and signal transducer and activator of transcription 3 (STAT3) are two important regulators of inflammation. Crohn's disease and ulcerative colitis are considered inflammatory bowel diseases (IBDs), due to the belief that these diseases result from dysregulated responses of the intestinal immune system to bacteria present in the commensal flora. It is debated whether a breakdown of immune tolerance is the primary cause of these diseases or occurs downstream of an initial defect of the intestinal barrier and intestinal epithelial cells (IECs). Recent reports suggest a crucial role for IL-22 in the regulation of gut inflammation as well as epithelial barrier integrity. Local IL-22 gene delivery enhances expression of its downstream effector, STAT3, within colonic epithelial cells and induces both STAT3-dependent expression of mucus-associated molecules and restitution of mucus-producing goblet cells. IEC-specific deletion of STAT3 results in significant susceptibility to experimental colitis with a striking defect in epithelial restitution. STAT3 activation, thus, may regulate immune homeostasis in the gut by promoting IL-22-dependent mucosal wound healing. The importance of IL-22/STAT3 signaling in IEC wound healing suggests a critical role for epithelial homeostasis in IBDs. Effective healing of the IECs could be considered a primary target in the development of treatments for IBDs. IL-22/STAT3 signaling exerts a protective role in the process of intestinal mucosal wound healing and may thereby provide a promising therapeutic approach to the treatment of IBDs.

Signal Transducer and Activator of Transcription 3 (STAT3) Protein Suppresses Adenoma-to-carcinoma Transition in Apcmin/+ Mice via Regulation of Snail-1 (SNAI) Protein Stability

STAT3 was recently reported to suppress tumor invasion in Apc(min)(/+) mice. We investigated the mechanisms by which STAT3 inhibits intestinal epithelial tumors using Apc(min)(/+)/Stat3(IEC-KO) mice (intestinal epithelial cell (IEC)-specific deletion of STAT3 in the Apc(min)(/+) background) to determine the role of STAT3 in carcinogenesis in vivo as well as colorectal cancer cell lines in vitro. To inhibit invasion of IEC tumors, STAT3 functions as a molecular adaptor rather than a transcription factor. Accordingly, the tumors in Apc(min)(/+)/Stat3(IEC-KO) mice undergo adenoma-to-carcinoma transition and acquire an invasive phenotype. Similarly, STAT3 knockdown in a colorectal cell line enhances IEC invasion. We demonstrate that STAT3 down-regulates SNAI (Snail-1) expression levels and hence suppresses epithelial-mesenchymal transition of colorectal cancer cells. Mechanistically, STAT3 facilitates glycogen synthase kinase (GSK) 3β-mediated degradation of SNAI by regulating phosphorylation of GSK3β. Our data identified a new role for STAT3 in the adenoma-to-carcinoma sequence of intestinal tumors.

Inflammation-associated interleukin-6/signal transducer and activator of transcription 3 activation ameliorates alcoholic and nonalcoholic fatty liver diseases in interleukin-10-deficient mice.

Alcoholic and nonalcoholic steatohepatitis are characterized by fatty liver plus inflammation. It is generally believed that steatosis promotes inflammation, whereas inflammation in turn aggregates steatosis. Thus, we hypothesized the deletion of interleukin (IL)-10, a key anti-inflammatory cytokine, exacerbates liver inflammation, steatosis, and hepatocellular damage in alcoholic and nonalcoholic fatty liver disease models that were achieved via feeding mice with a liquid diet containing 5% ethanol for 4 weeks or a high-fat diet (HFD) for 12 weeks, respectively. IL-10 knockout (IL-10(-/-)) mice and several other strains of genetically modified mice were generated and used. Compared with wild-type mice, IL-10(-/-) mice had greater liver inflammatory response with higher levels of IL-6 and hepatic signal transducer and activator of transcription 3 (STAT3) activation, but less steatosis and hepatocellular damage after alcohol or HFD feeding. An additional deletion of IL-6 or hepatic STAT3 restored steatosis and hepatocellular damage but further enhanced liver inflammatory response in IL-10(-/-) mice. In addition, the hepatic expression of sterol regulatory element-binding protein 1 and key downstream lipogenic proteins and enzymes in fatty acid synthesis were down-regulated in IL-10(-/-) mice. Conversely, IL-10(-/-) mice displayed enhanced levels of phosphorylated adenosine monophosphate-activated protein kinase and its downstream targets including phosphorylated acetyl-coenzyme A carboxylase and carnitine palmitoyltransferase 1 in the liver. Such dysregulations were corrected in IL-10(-/-) IL-6(-/-) or IL-10(-/-) STAT3(Hep-/-) double knockout mice. IL-10(-/-) mice are prone to liver inflammatory response but are resistant to steatosis and hepatocellular damage induced by ethanol or HFD feeding. Resistance to steatosis in these mice is attributable to elevation of inflammation-associated hepatic IL-6/STAT3 activation that subsequently down-regulates lipogenic genes but up-regulates fatty acid oxidation-associated genes in the liver.

Inhibition of permeability transition pore opening by mitochondrial STAT3 and its role in myocardial ischemia/reperfusion

The signal transducer and activator of transcription 3 (STAT3) contributes to cardioprotection by ischemic pre- and postconditioning. Mitochondria are central elements of cardioprotective signaling, most likely by delaying mitochondrial permeability transition pore (MPTP) opening, and STAT3 has recently been identified in mitochondria. We now characterized the mitochondrial localization of STAT3 and its impact on respiration and MPTP opening. STAT3 was mainly present in the matrix of subsarcolemmal and interfibrillar cardiomyocyte mitochondria. STAT1, but not STAT5 was also detected in mitochondria under physiological conditions. ADP-stimulated respiration was reduced in mitochondria from mice with a cardiomyocyte-specific deletion of STAT3 (STAT3-KO) versus wildtypes and in rat mitochondria treated with the STAT3 inhibitor Stattic (STAT3 inhibitory compound, 6-Nitrobenzo[b]thiophene 1,1-dioxide). Mitochondria from STAT3-KO mice and Stattic-treated rat mitochondria tolerated less calcium until MPTP opening occurred. STAT3 co-immunoprecipitated with cyclophilin D, the target of the cardioprotective agent and MPTP inhibitor cyclosporine A (CsA). However, CsA reduced infarct size to a similar extent in wildtype and STAT3-KO mice in vivo. Thus, STAT3 possibly contributes to cardioprotection by stimulation of respiration and inhibition of MPTP opening.

Abstract 228: Cucurbitacin-I (JSI-124) induces apoptosis in chronic lymphocytic leukemia (CLL) cells through inhibiting STAT3 activation and XIAP expression

Abstract Abstract AACR April-2010 Cucurbitacin-I (JSI-124) induces apoptosis in Chronic Lymphocytic Leukemia (CLL) cells through inhibiting STAT3 activation and XIAP expression. Ganchimeg Ishdorj, James B Johnston and Spencer B Gibson Manitoba Institute of Cell Biology, University of Manitoba, Winnipeg, Canada Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in North America. Current therapies control the disease but eventually the disease recurs and becomes drug resistant. Phosphorylation of signal transducer and activator of transcription 3 (STAT3) plays a pivotal role in cell survival and induces proliferation, whereas deletion of STAT3 results in cell death. Constitutive phosphorylation of STAT3 on tyrosine 705 residues has been found in a number of solid tumors and hematologic malignancies. Unlike other tumors, STAT3 is constitutively phosphorylated (p) on serine 727 but not on tyrosine residues in CLL. These observations lead to investigation of the effect of STAT3/JAK2 inhibitor Cucurbitacin-I (JSI-124) in CLL cells. We proposed that the targeting STAT3 phosphorylation may induce apoptosis in CLL cells. We studied B-cell lines (BJAB, I-83, NALM-6) and primary B-cells from patients with CLL using immunoprecipitation and found that JSI-124 suppressed serine pSTAT3 and induced apoptosis of these cells as determined by FACS analysis and membrane permeability assay. Using western blotting analysis, caspase-8 activation was observed in these cells after JSI-124 treatment. Since the activation of caspases are inhibited by members of the inhibitor of apoptosis (IAP) and Bcl-2 protein families and STAT3 has been shown to regulate their expression, we investigated anti-apoptotic members of these families. JSI-124 treatment led to downregulation of IAP protein XIAP, while Bcl-xL and Mcl-1 levels remained unchanged. In addition, JSI-124 selectively induced activation of JNK signaling pathways in CLL cells. Taken together, our results indicate that JSI-124 causes apoptosis through alterations in signal transduction pathways and could be a useful treatment in CLL. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 228.