MAPK signaling during Müller glial cell development in retina explant cultures

The Müller cell is the only glial cell type generated from the retinal neuroepithelium. This cell type controls normal retina homeostasis and has been suggested to play a neuroprotective role. Recent evidence suggests that mammalian Müller cells can de-differentiate and return to a progenitor or stem cell stage following injury or disease. In vivo exploration of the molecular mechanisms of Müller cell differentiation and proliferation will add essential information to manipulate Müller cell functions. Signal transduction pathways that regulate Müller cell responses and activity are a critical part of their cellular machinery. In this study, we focus on mitogen-activated protein kinase (MAPK) signaling pathway during Müller glial cell differentiation and proliferation. We found that both MAPK and STAT3 signaling pathways are present during Müller glial cell development. Ciliary neurotrophic factor (CNTF)-stimulated Müller glial cell proliferation is associated with early developmental stages. Specific inhibition of MAPK phosphorylation significantly reduced the number of Müller glial cells with or without CNTF stimulation. These results suggested that the MAPK signal transduction pathway is important in the formation of Müller glial cells during retina development.

Effect of baicalin on the JAK-STAT3 signaling pathway in human hepatocellular carcinoma cell line SMMC-7721

AIM: To investigate the effect of baicalin on the JAK-STAT3 signaling pathway in human hepatocellular carcinoma cell line SMMC-7721.

METHODS: SMMC-7721 cells were divided into four groups: blank control group, baicalin group, AG490 group, and baicalin plus AG490 group. The mRNA expressional level of STAT3 in SMMC-7721 cells was measured by RT-PCR. The protein expression levels of STAT3 and p-STAT3 in SMMC-7721 cells were measured by Western blot.

RESULTS: The expressional level of STAT3 mRNA in SMMC-7721 cells was significantly lower in the baicalin group than in the blank control group (0.505 ± 0.111 vs 0.697 ± 0.145, P < 0.05). The protein expressional levels of STAT3 and p-STAT3 in SMMC-7721 cells were also significantly lower in the baicalin group than in the blank control group (0.879 ± 0.012 vs 1.087 ± 0.015, 0.983 ± 0.085 vs 1.103 ± 0.074, both P < 0.05). Compared to the baicalin group, the protein expressional level of p-STAT3 in SMMC-7721 cells was significantly decreased in the baicalin plus AG490 (0.756 ± 0.103 vs 0.983 ± 0.085, P < 0.05).

CONCLUSION: Baicalin could significantly down-regulate the mRNA and protein expressional levels of STAT3 and p-STAT3 and inhibit the activation of STAT3 protein in SMMC-7721 cells.

High fat diet-induced obesity leads to proinflammatory response associated with higher expression of NOD2 protein

Obesity has been reported to be associated with low grade inflammatory status. In this study, we investigated the inflammatory response as well as associated signaling molecules in immune cells from diet-induced obese mice. Four-week-old C57BL mice were fed diets containing 5% fat (control) or 20% fat and 1% cholesterol (HFD) for 24 weeks. Splenocytes (1 × 10⁷ cells) were stimulated with 10 µg/mL of lipopolysaccharide (LPS) for 6 or 24 hrs. Production of interleukin (IL)-1β, IL-6, and TNF-α as well as protein expression levels of nucleotide-binding oligomerization domain (NOD)2, signal transducer and activator of transcription (STAT)3, and pSTAT3 were determined. Mice fed HFD gained significantly more body weight compared to mice fed control diet (28.2 ± 0.6 g in HFD and 15.4 ± 0.8 g in control). After stimulation with LPS for 6 hrs, production of IL-1β was significantly higher (P = 0.001) and production of tumor necrosis factor (TNF)-α tended to be higher (P < 0.064) in the HFD group. After 24 hrs of LPS stimulation, splenocytes from the HFD group produced significantly higher levels of IL-6 (10.02 ± 0.66 ng/mL in HFD and 7.33 ± 0.56 ng/mL in control, P = 0.005) and IL-1β (121.34 ± 12.72 pg/mL in HFD and 49.74 ± 6.58 pg/mL in control, P < 0.001). There were no significant differences in the expression levels of STAT3 and pSTAT3 between the HFD and the control groups. However, the expression level of NOD2 protein as determined by Western blot analysis was 60% higher in the HFD group compared with the control group. NOD2 contributes to the induction of inflammation by activation of nuclear factor κB. These findings suggest that diet-induced obesity is associated with increased inflammatory response of immune cells, and higher expression of NOD2 may contribute to these changes.

Over-expression of CKS1B activates both MEK/ERK and JAK/STAT3 signaling pathways and promotes myeloma cell drug-resistance

Here we demonstrate the crucial role of CKS1B in multiple myeloma (MM) progression and define CKS1B-mediated SKP2/p27^Kip1-independent down-stream signaling pathways. Forced-expression of CKS1B in MM cells increased cell multidrug-resistance. CKS1B activates STAT3 and MEK/ERK pathways. In contrast, SKP2 knockdown or p27^Kip1 over-expression resulted in activation of the STAT3 and MEK/ERK pathways. Further investigations showed that BCL2 is a downstream target of MEK/ERK signaling. Stimulation of STAT3 and MEK/ERK signaling pathways partially abrogated CKS1B knockdown induced MM cell death and growth inhibition. Targeting STAT3 and MEK/ ERK signaling pathways by specific inhibitors induced significant MM cell death and growth inhibition in CKS1B-overexpressing MM cells and their combinations resulted in synergy. Thus, our findings provide a rationale for targeting STAT3 and MEK/ERK/ BCL2 signaling in aggressive CKS1B-overexpressing MM.

Signal transducer and activator of transcription 3 in liver diseases: a novel therapeutic target

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that is activated by many cytokines and growth factors and plays a key role in cell survival, proliferation, and differentiation. STAT3 activation is detected virtually in all rodent models of liver injury and in human liver diseases. In this review, we highlight recent advances of STAT3 signaling in liver injury, steatosis, inflammation, regeneration, fibrosis, and hepatocarcinogenesis. The cytokines and small molecules that activate STAT3 in hepatocytes may have therapeutic benefits to treat acute liver injury, fatty liver disease, and alcoholic hepatitis, while blockage of STAT3 may have a therapeutic potential to prevent and treat liver cancer.

Upregulation of the signal transducers and activators of transcription 3 (STAT3) pathway in lymphatic metastases of papillary thyroid cancer

Papillary thyroid cancer (PTC) has an impressive propensity for lymphatic spread. Signal transducers and activators of transcription 3 (STAT3), constitutively activated in many different cancers, may play a role in PTC lymphatic metastases. We examined 49 patients with PTC, 22 with and 27 without lymphatic metastases. All patients had a total thyroidectomy with lymph node dissection to document true node negative cases. The level of STAT3 expression in benign, non-neoplastic thyroid tissue is barely detectable by immunohistochemistry. Only 11 of the 35 (31%) specimens exhibited weak immunostainingfor STAT3 and pSTAT3 was found weakly positive in 3 of 35 (9%) benign specimens. Expression of STAT3 in all PTC primary tumors was 98% (40/41) and thus significantly higher than corresponding benign thyroid tissue (p=0.0001). pSTAT3 was found in 37% of primary tumors (15/41) and this was significantly higher than pSTAT3 expression in benign tissue (p=0.006). Comparing node-positive and node-negative primary tumors, there was no difference in staining intensity for STAT3 where strong (2+) staining was seen 12/19 node-positive tumors and 13/22 node-negative tumors (p=1). Regarding pSTAT3 expression in primary PTC tumors, node negative cases (n=22) exhibited significantly less staining compared to node positive cases (n=19). Only 4 of 22 (18%) cases in the node-negative group were weakly (1+) positive for pSTAT3 while 12 of 19 (58%) cases in the node-positive group were positive (p=0.011) with 45% of these specimens exhibiting strong (2+) staining. Lymphatic metastases were highly positive (>93%) for both STAT3 and pSTAT3. The STAT3 pathway is ubiquitous in PTC and activated pSTAT3 is significantly upregulated in PTC tumors with metastatic disease. This study is the first to suggest a potential role for activated pSTAT3 in lymphatic metastases in thyroid cancer.

Eupatilin Inhibits Gastric Cancer Cell Growth by Blocking STAT3-Mediated VEGF Expression

PURPOSE

Eupatilin is an antioxidative flavone and a phytopharmaceutical derived from Artemisia asiatica. It has been reported to possess anti-tumor activity in some types of cancer including gastric cancer. Eupatilin may modulate the angiogenesis pathway which is part of anti-inflammatory effect demonstrated in gastric mucosal injury models. Here we investigated the anti-tumor effects of eupatilin on gastric cancer cells and elucidated the potential underlying mechanism whereby eupatilin suppresses angiogenesis and tumor growth.

MATERIALS AND METHODS

The impact of eupatilin on the expression of angiogenesis pathway proteins was assessed using western blots in MKN45 cells. Using a chromatin immunoprecipitation assay, we tested whether eupatilin affects the recruitment of signal transducer and activator of transcription 3 (STAT3), aryl hydrocarbon receptor nuclear translocator (ARNT) and hypoxia-inducible factor-1α (HIF-1α) to the human VEGF promoter. To investigate the effect of eupatilin on vasculogenesis, tube formation assays were conducted using human umbilical vein endothelial cells (HUVECs). The effect of eupatilin on tumor suppression in mouse xenografts was assessed.

RESULTS

Eupatilin significantly reduced VEGF, ARNT and STAT3 expression prominently under hypoxic conditions. The recruitment of STAT3, ARNT and HIF-1α to the VEGF promoter was inhibited by eupatilin treatment. HUVECs produced much foreshortened and severely broken tubes with eupatilin treatment. In addition, eupatilin effectively reduced tumor growth in a mouse xenograft model.

CONCLUSIONS

Our results indicate that eupatilin inhibits angiogenesis in gastric cancer cells by blocking STAT3 and VEGF expression, suggesting its therapeutic potential in the treatment of gastric cancer.

Connective tissue growth factor reacts as an IL-6/STAT3-regulated hepatic negative acute phase protein

AIM

To investigate the mechanisms involved in a possible modulator role of interleukin (IL)-6 signalling on CYR61-CTGF-NOV (CCN) 2/connective tissue growth factor (CTGF) expression in hepatocytes (PC) and to look for a relation between serum concentrations of these two parameters in patients with acute inflammation.

METHODS

Expression of CCN2/CTGF, p-STAT3, p-Smad3/1 and p-Smad2 was examined in primary freshly isolated rat or cryo-preserved human PC exposed to various stimuli by Western blotting, electrophoretic mobility shift assay (EMSA), reporter-gene-assays and reverse-transcriptase polymerase chain reaction.

RESULTS

IL-6 strongly down-regulated CCN2/CTGF protein and mRNA expression in PC, enhanceable by extracellular presence of the soluble IL-6 receptor gp80, and supported by an inverse relation between IL-6 and CCN2/CTGF concentrations in patients' sera. The inhibition of TGFβ1 driven CCN2/CTGF expression by IL-6 did not involve a modulation of Smad2 (and Smad1/3) signalling. However, the STAT3 SH2 domain binding peptide, a selective inhibitor of STAT3 DNA binding activity, counteracted the inhibitory effect of IL-6 on CCN2/CTGF expression much more pronounced than pyrrolidine-dithiocarbamate, an inhibitor primarily of STAT3 phosphorylation. An EMSA confirmed STAT3 binding to the proposed proximal STAT binding site in the CCN2/CTGF promoter.

CONCLUSION

CCN2/CTGF is identified as a hepatocellular negative acute phase protein which is down-regulated by IL-6 via the STAT3 pathway through interaction on the DNA binding level.

NDRG2-mediated Modulation of SOCS3 and STAT3 Activity Inhibits IL-10 Production

Background

N-myc downstream regulated gene 2 (NDRG2) is a member of the NDRG gene family. Our previous report indicated a possible role for NDRG2 in regulating the cytokine, interleukin-10 (IL-10), which is an important immunosuppressive cytokine. Several pathways, including p38-MAPK, NF-κB, and JAK/STAT, are used for IL-10 production, and the JAK/STAT pathway can be inhibited in a negative feedback loop by the inducible protein, SOCS3. In the present study, we investigated the effect of NDRG2 gene expression on IL-10 signaling pathway that is modulated via SOCS3 and STAT3.

Methods

We generated NDRG2-overexpressing U937 cell line (U937-NDRG2) and treated the cells with PMA to investigate the role of NDRG2 in IL-10 production. U937 cells were also transfected with SOCS3- or NDRG2-specific siRNAs to examine whether the knockdown of SOCS3 or NDRG2 influenced IL-10 expression. Lastly, STAT3 and SOCS3 induction was measured to identify the signaling pathway that was associated with IL-10 production.

Results

RT-PCR and ELISA assays showed that IL-10 was increased in U937-mock cells upon stimulation with PMA, but IL-10 was inhibited by overexpression NDRG2. After PMA treatment, STAT3 phosphorylation was decreased in a time-dependent manner in U937-mock cells, whereas it was maintained in U937-NDRG2 cells. SOCS3 was markedly reduced in U937-NDRG2 cells compared with U937-mock cells. IL-10 production after PMA stimulation was reduced in U937 cells when SOCS3 was inhibited, but this effect was less severe when NDRG2 was inhibited.

Conclusion

NDRG2 expression modulates SOCS3 and STAT3 activity, eventually leading to the inhibition of IL-10 production.

Additive effect on survival of Raf kinase inhibitor protein and signal transducer and activator of transcription 3 in high-grade glioma

BACKGROUND

Animal studies have shown cooperative contribution of the Ras/Raf/MAPK and PI3K/Akt/mTOR signaling pathways in glioblastoma formation. However, this joint action has not yet been confirmed in human studies.

METHODS

The expression of Raf kinase inhibitory protein (RKIP) was examined in 159 patients with high-grade and low-grade gliomas and correlated with previously obtained data on the activation of signal transducer and activator of transcription 3 (STAT3), a downstream effector of the PI3K/Akt/mTOR signaling pathway.

RESULTS

RKIP expression was associated with a longer overall survival in high-grade glioma cases without showing a direct or inverse correlation with tyrosine-705 phosphorylation of STAT3 (pSTAT3). Notably, RKIP-positive and pSTAT3 negative cases demarcate a patients group with exceptionally long survival, exceeding the prognostic impact of each single marker.

CONCLUSIONS

The results of this study indicated that 1) RKIP expression correlates with tumor grade and is a marker for good prognosis in high-grade gliomas; 2) RKIP expression and lack of pSTAT3 have a cumulative prognostic impact; and 3) RKIP and pSTAT3 are likely to operate independently to influence survival. These findings represented the first human evidence of an additive effect of 2 distinct signaling pathways in high-grade glioma, suggesting that simultaneous inhibition of multiple pathways should be considered as a treatment strategy for these patients.

Identification of a New Series of STAT3 Inhibitors by Virtual Screening

The signal transducer and activator of transcription 3 (STAT3) is considered to be an attractive therapeutic target for oncology drug development. We identified a N-[2-(1,3,4-oxadiazolyl)]-4-quinolinecarboxamide derivative, STX-0119, as a novel STAT3 dimerization inhibitor by a virtual screen using a customized version of the DOCK4 program with the crystal structure of STAT3. In addition, we used in vitro cell-based assays such as the luciferase reporter gene assay and the fluorescence resonance energy transfer-based STAT3 dimerization assay. STX-0119 selectively abrogated the DNA binding activity of STAT3 and suppressed the expression of STAT3-regulated oncoproteins such as c-myc and survivin in cancer cells. In contrast, a truncated inactive analogue, STX-0872, did not exhibit those activities. Oral administration of STX-0119 effectively abrogated the growth of human lymphoma cells in a SCC-3 subcutaneous xenograft model without visible toxicity. Structure-activity relationships of STX-0119 derivatives were investigated using the docking model of the STAT3-SH2 domain/STX-0119.

Overexpression of sonic hedgehog pathway molecules and STAT3 activation in colonic tumors

AIM: To determine the expression pattern of sonic hedgehog (SHH) signaling pathway molecules and analyze their relationship with STAT3 activation in colonic tumors.

METHODS: Paraffin-embedded tissue sections of 20 normal colon tissue specimens, 42 colonic adenoma specimens, and 77 colonic adenoma adenocarcinoma specimens were used in the study. The expression of SHH, GLI1, PTCH1, HHIP and P-STAT3 in these specimens was detected by immunohistochemistry. The correlation of the expression of HH molecules with clinicopathological parameters and P-STAT3 expression was then evaluated.

RESULTS: All the SHH signaling pathway molecules examined were overexpressed in colonic adenomas and adenocarcinomas when compared with normal colon tissue (95.2% and 75.3% vs 0.0%, both P < 0.05; 66.7% and 84.4% vs 0.0%, both P < 0.05; 23.8% and 58.4% vs 0.0%, both P < 0.05; 42.9% and 36.4% vs 25.0%, both P < 0.05). SHH and GLI1 expression was correlated with tumor grade (both P < 0.05). There was a significant correlation between SHH and GLI1 expression in colonic adenomas and adenocarcinomas (r = 0.498, P < 0.01). Overexpression of activated STAT3 (P-STAT3) was significantly correlated with SHH and GLI1 expression in colonic adenocarcinomas (r = 0.525, P < 0.01; r = 0,637, P < 0.01).

CONCLUSION: SHH signaling pathway may play a role in the progression of colonic tumors. The finding that SHH overexpression is correlated with STAT3 activation in colonic tumors indicates that there may be a synergetic effect between the two signaling pathways.

STAT3 upregulates the protein expression and transcriptional activity of β-catenin in breast cancer

The expression of β-catenin detectable by immunohistochemistry has been reported to be prognostically important in breast cancer. In this study, we investigated the mechanism by which β-catenin is regulated in breast cancer cells. Our analysis of the gene promoter of β-catenin revealed multiple putative STAT3 binding sites. In support of the concept that STAT3 is a transcriptional regulator for β-catenin, results from our chromatin immunoprecipitation studies showed that STAT3 binds to two of the three potential STAT3-binding sites in the gene promoter of β-catenin (-856 and -938). Using our generated MCF-7 cell clones that carry an inducible STAT3C construct, we found that the expression levels of STAT3C significantly correlated with the transcriptional activity of β-catenin. Similar observations were made when we subjected two breast cancer cell lines (MCF-7 and BT-474) to STAT3 knock-down or transient gene transfection of STAT3C. Using immunohistochemistry, we found that pSTAT3 and β-catenin significantly correlated with each other (p=0.003, Fisher's exact test) in a cohort of primary breast tumors (n=129). To conclude, our results support the concept that STAT3 upregulates the protein expression and transcriptional activity of β-catenin in breast cancer, and these two proteins may cooperate with each other in exerting their oncogenic effects in these tumors.

Interplay of hepatic and myeloid signal transducer and activator of transcription 3 in facilitating liver regeneration via tempering innate immunity

Liver regeneration triggered by two-thirds partial hepatectomy is accompanied by elevated hepatic levels of endotoxin, which contributes to the regenerative process, but liver inflammation and apoptosis remain paradoxically limited. Here, we show that signal transducer and activator of transcription 3 (STAT3), an important anti-inflammatory signal, is activated in myeloid cells after partial hepatectomy and its conditional deletion results in an enhanced inflammatory response. Surprisingly, this is accompanied by an improved rather than impaired regenerative response with increased hepatic STAT3 activation, which may contribute to the enhanced liver regeneration. Indeed, conditional deletion of STAT3 in both hepatocytes and myeloid cells results in elevated activation of STAT1 and apoptosis of hepatocytes, and a dramatic reduction in survival after partial hepatectomy, whereas additional global deletion of STAT1 protects against these effects.

CONCLUSION

An interplay of myeloid and hepatic STAT3 signaling is essential to prevent liver failure during liver regeneration through tempering a strong innate inflammatory response mediated by STAT1 signaling.

Extracellular Signal-regulated Kinase Activation Is Required for Serine 727 Phosphorylation of STAT3 in Schwann Cells in vitro and in vivo

In the peripheral nerves, injury-induced cytokines and growth factors perform critical functions in the activation of both the MEK/ERK and JAK/STAT3 pathways. In this study, we determined that nerve injury-induced ERK activation was temporally correlated with STAT3 phosphorylation at the serine 727 residue. In cultured Schwann cells, we noted that ERK activation is required for the serine phosphorylation of STAT3 by neuropoietic cytokine interleukin-6 (IL-6). Serine phosphorylated STAT3 by IL-6 was transported into Schwann cell nuclei, thereby indicating that ERK may regulate the transcriptional activity of STAT3 via the induction of serine phosphorylation of STAT3. Neuregulin-1 (NRG) also induced the serine phosphorylation of STAT3 in an ERK-dependent fashion. In contrast with the IL-6 response, serine phosphorylated STAT3 induced by NRG was not detected in the nucleus, thus indicating the non-nuclear function of serine phosphorylated STAT3 in response to NRG. Finally, we determined that the inhibition of ERK prevented injury-induced serine phosphorylation of STAT3 in an ex-vivo explants culture of the sciatic nerves. Collectively, the results of this study show that ERK may be an upstream kinase for the serine phosphorylation of STAT3 induced by multiple stimuli in Schwann cells after peripheral nerve injury.

Expression of the signal transducer and activator of transcription factor 3 and Janus kinase 3 in colorectal carcinomas, colonic adenomas and ulcerative colitis

BACKGROUND AND STUDY AIMS

Despite the growing understanding of the involvement of protooncogenes and tumour suppressor genes in the oncogenesis of CRC, the exact biological and molecular mechanisms underpinning this process remain poorly understood. The signal transducer and activator of transcription (STAT3) has been implicated in the regulation of growth and malignant transformation. Accumulating evidences have come to indicate that abnormalities in the Janus kinase (JAK)/STAT pathway are involved in oncogenesis of several cancers. The aim of this study was to investigate the expression of JAK3 and STAT3 in both normal and activated forms by immunohistochemistry in adenomas of the colon, ulcerative colitis and CRC compared to normal colonic mucosa.

PATIENTS AND METHODS

Tissues from 30 cases with primary CRC and seven cases with ulcerative colitis (UC), removed by colectomy, were included. In addition, tissues from 10 colonic adenomas, 15 CRC and eight cases with UC, obtained by endoscopic biopsies, were examined histopathologically. Immunohistochemical evaluation of STAT3, p-STAT3, JAK3 and p-JAK3 expression in tissue sections was completed. Statistical analysis and correlation of data were then performed.

RESULTS

Normal colonic mucosa showed expression of STAT3 only. Immunoreactivity of p-JAK3 increased significantly (p<0.05) and correlated with the degree of dysplasia in colonic adenomas. Immunoreactivity of p-STAT3 increased significantly (p<0.05) and correlated with the degree of dysplasia in cases with UC. In CRC a significant positive correlation was found between p-STAT3 expression and grading, STAT3, JAK3 and p-JAK3 and TNM or Dukes' staging, and p-STAT3 and nodal status excluding distant metastasis (p<0.05).

CONCLUSION

JAK3 and STAT3, and particularly their activated forms, were found to correlate significantly with the degree of dysplasia in adenomas and UC, indicating their potential role in colorectal carcinogenesis. They also correlate with anaplasia and invasion, suggesting a definitive role in progression of CRC.

Janus Kinase 2 Inhibitor AG490 Inhibits the STAT3 Signaling Pathway by Suppressing Protein Translation of gp130

The binding of interleukin-6 (IL-6) cytokine family ligands to the gp130 receptor complex activates the Janus kinase (JAK)/ signal transducer and activator of transcription 3 (STAT3) signal transduction pathway, where STAT3 plays an important role in cell survival and tumorigenesis. Constitutive activation of STAT3 has been frequently observed in many cancer tissues, and thus, blocking of the gp130 signaling pathway, at the JAK level, might be a useful therapeutic approach for the suppression of STAT3 activity, as anticancer therapy. AG490 is a tyrphostin tyrosine kinase inhibitor that has been extensively used for inhibiting JAK2 in vitro and in vivo. In this study, we demonstrate a novel mechanism associated with AG490 that inhibits the JAK/STAT3 pathway. AG490 induced downregulation of gp130, a common receptor for the IL-6 cytokine family compounds, but not JAK2 or STAT3, within three hours of exposure. The downregulation of gp130 was not caused by enhanced degradation of gp130 or by inhibition of mRNA transcription. It most likely occurred by translation inhibition of gp130 in association with phosphorylation of the eukaryotic initiation factor-2alpha . The inhibition of protein synthesis of gp130 by AG490 led to immediate loss of mature gp130 in cell membranes, due to its short half-life, thereby resulting in reduction in the STAT3 response to IL-6. Taken together, these results suggest that AG490 blocks the STAT3 activation pathway via a novel pathway.

Pravastatin prevents aortic atherosclerosis via modulation of signal transduction and activation of transcription 3 (STAT3) to attenuate interleukin-6 (IL-6) action in ApoE knockout mice

The purpose of this study was to determine whether pravastatin’s prevention of aortic atherosclerosis via attenuation of IL-6 action depends on modulation of STAT3 activity. Male apoE knockout (apoE-/-) mice fed on a diet containing 1.25% cholesterol (wt/wt) were divided into pravastatin group provided with pravastatin (80 mg kg^-1 per day) and atherosclerosis group. After eight weeks, pravastatin significantly prevented atherosclerotic lesion and reduced levels of IL-6 in serum and lesion, and significantly decreased expressions of phosphorylated STAT3 (pSTAT3) and increased suppressor of cytokine signaling 3 (SOCS3) expressions in lesions. Our results suggested that pravastatin’s aortic atherosclerosis preventing action via attenuation of IL-6 action may partially depend on modulation of STAT3 activity.

Tyrphostin ErbB2 Inhibitors AG825 and AG879 Have Non-specific Suppressive Effects on gp130/ STAT3 Signaling

Although the interaction between gp130 and the ErbB family has frequently been shown in cancer cells, the mechanism of this interaction remains unclear and controversial. In the present study, we found that specific tyrphostin inhibitors of ErbB2 (AG825 and AG879), but not ErbB1 inhibitor (AG1478), suppressed IL-6-induced tyrosine phosphorylation of STAT3 in schwannoma cells. However, biochemical evidence for transactivation of ErbB2 by IL-6 was not observed. Additionally, the inhibition of ErbB2 expression, with either a specific RNAi or transfection of an ErbB2 mutant lacking the intracellular domain did not inhibit the IL-6-induced tyrosine phosphorylation of STAT3. Thus, it seems that tyrphostins, which are known as specific inhibitors of the ErbB2 kinase, may have non-specific suppressive effects on the IL-6/STAT3 pathway.

Role of STAT3 in inflammatory bowel disease

Signal transducers and activators of transcription 3 (STAT3) play an important role in various autoimmune disorders including inflammatory bowel disease (IBD). Recent studies have revealed that STAT3 activation plays distinctly different roles between innate immune responses and acquired immune responses in colitis. STAT3-mediated activation of acquired immune responses plays a pathogenic role in colitis by enhancing the survival of pathogenic T cells. In contrast, STAT3-mediated activation of innate responses contributes to the suppression of colitis. This review will summarize the current understanding of the roles of STAT3 in IBD and the potential of targeting STAT3 for the treatment of IBD, emphasizing recent observations.

STAT3 activation in pressure-overloaded feline myocardium: role for integrins and the tyrosine kinase BMX

Growth, survival and cytoskeletal rearrangement of cardiomyocytes are critical for cardiac hypertrophy. Signal transducer and activator of transcription-3 (STAT3) activation is an important cardioprotective factor associated with cardiac hypertrophy. Although STAT3 activation has been reported via signaling through Janus Kinase 2 (JAK2) in several cardiac models of hypertrophy, the importance of other nonreceptor tyrosine kinases (NTKs) has not been explored. Utilizing an in vivo feline right ventricular pressure-overload (RVPO) model of hypertrophy, we demonstrate that in 48 h pressure-overload (PO) myocardium, STAT3 becomes phosphorylated and redistributed to detergent-insoluble fractions with no accompanying JAK2 activation. PO also caused increased levels of phosphorylated STAT3 in both cytoplasmic and nuclear fractions. To investigate the role of other NTKs, we used our established in vitro cell culture model of hypertrophy where adult feline cardiomyocytes are embedded three-dimensionally (3D) in type-I collagen and stimulated with an integrin binding peptide containing an Arg-Gly-Asp (RGD) motif that we have previously shown to recapitulate the focal adhesion complex (FAC) formation of 48 h RVPO. RGD stimulation of adult cardiomyocytes in vitro caused both STAT3 redistribution and activation that were accompanied by the activation and redistribution of c-Src and the TEC family kinase, BMX, but not JAK2. However, infection with dominant negative c-Src adenovirus was unable to block RGD-stimulated changes on either STAT3 or BMX. Further analysis in vivo in 48 h PO myocardium showed the presence of both STAT3 and BMX in the detergent-insoluble fraction with their complex formation and phosphorylation. Therefore, these studies indicate a novel mechanism of BMX-mediated STAT3 activation within a PO model of cardiac hypertrophy that might contribute to cardiomyocyte growth and survival.

Effect of knockdown of STAT3 gene expression by shRNA on the characteristics of gastric cancer cell line MKN-45 in vitro and in vivo

AIM: To determine the effect of knockdown of STAT3 expression by shRNA on the characteristics of human gastric carcinoma cell line MKN-45 in vitro and in vivo.

METHODS: Specific shRNA plasmids to STAT3 were constructed and identified, then transfected into MKN-45. Cells were divided into three groups: control group, psiRNA-H1 group as the negative group and psiRNA-H1/STAT3 group. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting were used to detect the expression of STAT3 mRNA and protein respectively. MTT and flow cytometry were used to assess cell growth suppression and cell cycle distribution respectively. Models of xenograft in nude mice were established using the three-group cells, and the growth of stable ones was then observed.

RESULTS: Compared with the negative control cells, semi-quantitative RT-PCR and Western blotting showed that the expression of STAT3 mRNA (0.612 ± 0.074 vs 1.937 ± 0.043, P < 0.05) and protein (0.668 ± 0.054 vs 2.005 ± 0.064, P < 0.01) was down-regulated in the psiRNA-H1/STAT3 group. The subcloned recombinant plasmid expressing shRNA effectively inhibited MKN-45 cell growth and proliferation (25.42 ± 3.48 vs 33.54 ± 2.91, P < 0.05) while empty plasmid had no such specific effect. The volumes of xenografts in the psiRNA-H1/STAT3 transfection group were larger than those in the other groups (4.47 cm³ ± 0.18 cm³ vs 13.65 cm³ ± 5.64 cm³, P < 0.05).

CONCLUSION: Recombinant plasmid psiRNA-H1/STAT3 shRNA can specifically inhibit not only the expression of STAT3 mRNA and protein in vitro, but also the growth of cell line MKN-45 in vitro and in vivo.

Lipopolysaccharide-squamous cell carcinoma-monocyte interactions induce cancer-supporting factors leading to rapid STAT3 activation

Oral and oro-pharyngeal squamous cell carcinomas (OSCC) exhibit surface breach, and recent studies have demonstrated bacterial contamination of primary and metastatic OSCC. Increasing concentrations of inflammatory products, such as interleukin (IL)-6 and vascular endothelial growth factor (VEGF), correlate with, and contribute to, cancer progression, but their regulation in OSCC is poorly understood. We hypothesized that monocyte-lineage cells and bacterial contamination may contribute important inflammatory products that can support OSCC progression. We found that relative to non-specific chronic mucositis, oral carcinoma-in-situ/superficially-invasive OSCC contained more monocyte-lineage cells. In vitro, we used lipopolysaccharide (LPS) to model bacterial contamination, and evaluated the effects of oral and oropharyngeal (O)SCC-monocyte interactions and of LPS on OSCC cells and on the production of IL-6 and VEGF. OSCC cell lines varied in constitutive cytokine and chemokine production, and OSCC-monocyte interactions in the absence of LPS stimulated IL-6 and VEGF occasionally, while LPS-OSCC-monocyte interactions were always strongly stimulatory. Importantly, LPS independently stimulated some OSCC lines to secrete monocyte-dendritic cell chemoattractants CCL2 and/or CCL20, as well as IL-6 and/or VEGF. While very little constitutive Y705-STAT3 phosphorylation (pY705-STAT3) was detectable in HNSCC lines, IL-6 rapidly induced pY705-STAT3 in OSCC lines that produced little IL-6 constitutively. Supernatants from LPS-OSCC-monocyte co-cultures always rapidly and strongly activated STAT3, which was partly due to IL-6. We conclude that monocytes and microbial contamination have the potential to contribute to OSCC progression, as STAT3 activation in OSCC cells depends on soluble factors, which are consistently available through LPS-OSCC-monocyte interactions.

Pancreatitis-associated protein: From a lectin to an anti-inflammatory cytokine

Pancreatitis-associated protein (PAP) was discovered in the pancreatic juice of rats with acute pancreatitis. PAP is a 16 kDa secretory protein structurally related to the C-type lectins although classical lectin-related function has not been reported yet. Then, it was demonstrated that PAP expression may be activated in some tissues in a constitutive or injury- and inflammation-induced manner. More recently, it has been found that PAP acts as an anti-inflammatory factor in vitro and in vivo. PAP expression can be induced by several pro- and anti-inflammatory cytokines and by itself through a JAK/STAT3-dependent pathway. PAP is able to activate the expression of the anti-inflammatory factor SOCS3 through the JAK/STAT3-dependent pathway. The JAK/STAT3/SOCS3 pathway seems to be a common point between PAP and several cytokines. Therefore, it is reasonable to propose that PAP is a new anti-inflammatory cytokine.