Ethanol inhibition of angiotensin II-stimulated Tyr705 and Ser727 STAT3 phosphorylation in cultured rat hepatocytes: relevance to activation of p42/44 mitogen-activated protein kinase

Cellular Substrates for Cell-Based Tissue Engineering of Human Corneal Endothelial Cells

Corneal endothelial tissue engineering aims to find solutions for blindness due to endothelial dysfunction. A suitable combination of endothelial cells, substrates and environmental cues should be deployed for engineering functional endothelial tissues. This manuscript reviews up-to-date topics of corneal endothelial tissue engineering with special emphasis on biomaterial substrates and their properties, efficacy, and mechanisms of supporting functional endothelial cells in vitro.

P300-dependent STAT3 acetylation is necessary for angiotensin II-induced pro-fibrotic responses in renal tubular epithelial cells

AIM

To explore the signal transducer and activator of transcription 3 (STAT3) signaling pathway, especially STAT3 acetylation, in angiotensin II (Ang II)-induced pro-fibrotic responses in renal tubular epithelial cells.

METHODS

Rat renal tubular epithelial cell line (NRK-52E) was used. STAT3 acetylation and phosphorylation, as well as the expression of fibronectin, collagen IV and transforming growth factor-β1 (TGF-β1) were examined using Western blotting. The level and localization of STAT3 phosphorylation on Tyr705 were detected with fluorescence immunocytochemistry. The cells were transfected with a plasmid vector carrying p300 gene or siRNA targeting p300 to regulate p300 expression.

RESULTS

Overexpression of p300 significantly increased STAT3 acetylation on Lys685, STAT3 phosphorylation on Tyr705, and the expression of TGF-β1, collagen IV and fibronectin in the cells. Treatment of the cells with Ang II (1 μmol/L) significantly increased STAT3 phosphorylation on Tyr705 through JAK2 activation, and dose-dependently increased the expression of fibronectin, collagen IV and TGF-β1. Pretreatment with curcumin, an inhibitor of JAK2 and p300, blocked Ang II-induced effects. Knockdown of p300 significantly decreased STAT3 acetylation on Lys685, and abolished Ang II-stimulated STAT3 phosphorylation on Tyr705, whereas pretreatment of the cells with C646, a selective inhibitor of p300, inhibited Ang II-induced STAT3 nuclear translocation and the expression of TGF-β1, collagen IV and fibronectin. Pretreatment of the cells with AG490, a JAK2 inhibitor, markedly inhibited Ang II-induced STAT3 phosphorylation on Tyr705 and fibronectin expression.

CONCLUSION

p300-dependent STAT3 acetylation is necessary for Ang II-induced STAT3 phosphorylation and the consequent pro-fibrotic responses in renal tubular epithelial cells in vitro.

Inhibition of STAT3 acetylation is associated with angiotesin renal fibrosis in the obstructed kidney

AIM

To explore the relationship between the signal transducer and activator of transcription 3 (STAT3) signaling and renal fibrosis.

METHODS

Rat renal tubular epithelial NRK-52E cells were treated with angiotesin II (Ang II), nicotinamide (an inhibitor of NAD+-dependent class III protein deacetylases, SIRT1-7), or resveratrol (an activator of SIRT1). Mice underwent unilateral ureteral obstruction (UUO) were used for in vivo studies. Renal interstitial fibrosis was observed with HE and Masson's trichrome staining. STAT3 acetylation and phosphorylation, fibronectin, collagen I, collagen IV, and α-smooth muscle actin (α-SMA) levels were examined using Western blotting.

RESULTS

Nicotinamide (0.625-10 mmol/L) dose-dependently increased STAT3 acetylation on Lys685 and phosphorylation on Tyr705 in NRK-52E cells, accompanied by accumulation of fibronectin and collagen IV. Ang II increased STAT3 phosphorylation on Tyr705 and the expression of fibronectin, collagen IV and α-SMA in the cells. Pretreatment with resveratrol (12.5 μmol/L) blocked Ang II-induced effects in the cells. UUO induced marked STAT3 phosphorylation, fibronectin, collagen IV and α-SMA accumulation, and renal interstitial fibrosis in the obstructed kidneys, which were significantly attenuated by daily administration of resveratrol (100 mg/kg).

CONCLUSION

STAT3 acetylation plays an important role in activation of STAT3 signaling pathway and consequent renal fibrosis.

JAK-STAT and the renin-angiotensin system: The role of the JAK-STAT pathway in blood pressure and intrarenal renin-angiotensin system regulation

The renin-angiotensin system (RAS) plays important roles in blood pressure control and tissue disease. An inappropriate local angiotensin II elevation in the kidneys leads to the development of hypertension, tissue damage and chronic injury. Studies have demonstrated that the JAK-STAT pathway mediates angiotensin II-triggered gene transcription. The JAK-STAT pathway in turn, acting as an amplifying system, contributes to further intrarenal RAS activation. These observations prompt the suggestion that the JAK-STAT pathway may be of importance in elucidating the mechanisms RAS-associated tissue injury. Accordingly, this review provides a brief overview of the interactions between the JAK-STAT pathway and the RAS, specifically the RAS expressed in the kidneys.

MEK inhibition affects STAT3 signaling and invasion in human melanoma cell lines

Elevated activity of the mitogen-activated protein kinase (MAPK) signaling cascade is found in the majority of human melanomas and is known to regulate proliferation, survival and invasion. Current targeted therapies focus on decreasing the activity of this pathway; however, we do not fully understand how these therapies impact tumor biology, especially given that melanoma is a heterogeneous disease. Using a three-dimensional (3D), collagen-embedded spheroid melanoma model, we observed that MEK and BRAF inhibitors can increase the invasive potential of ∼20% of human melanoma cell lines. The invasive cell lines displayed increased receptor tyrosine kinase (RTK) activity and activation of the Src/FAK/signal transducers and activators of transcription-3 (STAT3) signaling axis, also associated with increased cell-to-cell adhesion and cadherin engagement following MEK inhibition. Targeting various RTKs, Src, FAK and STAT3 with small molecule inhibitors in combination with a MEK inhibitor prevented the invasive phenotype, but only STAT3 inhibition caused cell death in the 3D context. We further show that STAT3 signaling is induced in BRAF-inhibitor-resistant cells. Our findings suggest that MEK and BRAF inhibitors can induce STAT3 signaling, causing potential adverse effects such as increased invasion. We also provide the rationale for the combined targeting of the MAPK pathway along with inhibitors of RTKs, SRC or STAT3 to counteract STAT3-mediated resistance phenotypes.

Angiotensin II protects primary rat hepatocytes against bile salt-induced apoptosis

Angiotensin II (AT-II) is a pro-fibrotic compound that acts via membrane-bound receptors (AT-1R/AT-2R) and thereby activates hepatic stellate cells (HSCs). AT-II receptor blockers (ARBs) are thus important candidates in the treatment of liver fibrosis. However, multiple case reports suggest that AT-1R blockers may induce hepatocyte injury. Therefore, we investigated the effect of AT-II and its receptor blockers on cytokine-, oxidative stress- and bile salt-induced cell death in hepatocytes. Primary rat hepatocytes were exposed to TNF-α/Actinomycin D, the ROS-generating agent menadione or the bile salts: glycochenodeoxycholic acid (GCDCA) and tauro-lithocholic acid-3 sulfate (TLCS), to induce apoptosis. AT-II (100 nmol/L) was added 10 minutes prior to the cell death-inducing agent. AT-1R antagonists (Sartans) and the AT-2R antagonist PD123319 were used at 1 µmol/L. Apoptosis (caspase-3 activity, acridine orange staining) and necrosis (Sytox green staining) were quantified. Expression of CHOP (marker for ER stress) and AT-II receptor mRNAs were quantified by Q-PCR. AT-II dose-dependently reduced GCDCA-induced apoptosis of hepatocytes (−50%, p<0.05) without inducing necrosis. In addition, AT-II reduced TLCS-induced apoptosis of hepatocytes (−50%, p<0.05). However, AT-II did not suppress TNF/Act-D and menadione-induced apoptosis. Only the AT-1R antagonists abolished the protective effect of AT-II against GCDCA-induced apoptosis. AT-II increased phosphorylation of ERK and a significant reversal of the protective effect of AT-II was observed when signaling kinases, including ERK, were inhibited. Moreover, AT-II prevented the GCDCA-induced expression of CHOP (the marker of the ER-mediated apoptosis).

Molecular mechanisms of alcoholic liver disease: innate immunity and cytokines

Alcohol consumption is a predominant etiological factor in the pathogenesis of chronic liver diseases worldwide, causing fatty liver, alcoholic hepatitis, fibrosis/cirrhosis, and hepatocellular carcinoma. In the past few decades, significant progress has been made in our understanding of the molecular mechanisms underlying alcoholic liver injury. Activation of innate immunity components such as Kupffer cells, LPS/TLR4, and complements in response to alcohol exposure plays a key role in the development and progression of alcoholic liver disease (ALD). LPS activation of Kupffer cells also produces IL-6 and IL-10 that may play a protective role in ameliorating ALD. IL-6 activates signal transducer and activator of transcription 3 (STAT3) in hepatocytes and sinusoidal endothelial cells, while IL-10 activates STAT3 in Kupffer cells/macrophages, subsequently protecting against ALD. In addition, alcohol consumption also inhibits some components of innate immunity such as natural killer (NK) cells, a type of cells that play key roles in anti-viral, anti-tumor, and anti-fibrotic defenses in the liver. Ethanol inhibition of NK cells likely contributes significantly to the pathogenesis of ALD. Understanding the roles of innate immunity and cytokines in alcoholic liver injury may provide insight into novel therapeutic targets in the treatment of alcoholic liver disease.

Suppressor of cytokine signaling-2 gene disruption promotes Apc(Min/+) tumorigenesis and activator protein-1 activation

Epigenetic in vitro and in vivo studies suggest that suppressor of cytokine signaling-2 (SOCS2) may normally limit tumorigenesis in the intestine; however, this theory has not been directly tested. We hypothesized that SOCS2 deficiency promotes spontaneous intestinal tumorigenesis in Apc(Min/+) mice. Therefore, we quantified tumor number, size, and load in the small intestine and colon using SOCS2(+/+)/Apc(Min/+), SOCS2(+/-)/Apc(Min/+), and SOCS2(-/-)/Apc(Min/+) mice and assayed hematocrit as an indirect marker of disease severity. Biochemical and histological assays were used to assess mechanisms. Heterozygous and homozygous disruption of SOCS2 alleles promoted 166 and 441% increases in tumor load in the small intestine, respectively, accelerated development of colon tumors, and caused severe anemia. SOCS2 deletion promoted significant increases in intestinal insulin-like growth factor-I mRNA but did not affect plasma insulin-like growth factor-I. Western blots and immunohistochemical analysis demonstrated that tumor and nontumor intestinal tissue of SOCS2(-/-)/Apc(Min/+) mice had increased serine 727 phosphorylation of signal transducer and activator of transcription 3 compared with SOCS2(+/+)/Apc(Min/+) mice. Moreover, electromobility shift assays showed that SOCS2 deletion did not alter signal transducer and activator of transcription 3 DNA binding. However, tumors and small intestine from SOCS2(-/-)/Apc(Min/+) showed dramatic increases in activator protein-1 (AP-1) DNA binding, and SOCS2 overexpression in vitro reduced levels of AP-1. These studies indicate that SOCS2 deletion promotes the spontaneous development of intestinal tumors driven by mutations in the adenomatous polyposis coli/beta-catenin pathway and activates AP-1. Therefore, reduced expression or epigenetic silencing of SOCS2 may serve as a useful biomarker for colorectal cancer risk.

Activation of MEK 1/2 and p42/44 MAPK by angiotensin II in hepatocyte nucleus and their potentiation by ethanol

Hepato-subcellular effect of angiotensin II (Ang II) and ethanol on the p42/44 mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK 1/2) was investigated in the nucleus of rat hepatocytes. Hepatocytes were treated with ethanol (100 mM) for 24h and stimulated with Ang II (100 nM, 5 min). The levels of p42/44 MAPK and MEK 1/2 were monitored in the nuclear fraction using antibodies. Ang II itself caused significant accumulation of phosphorylated p42/44 MAPK (phospho-p42/44 MAPK) in the nucleus without any significant translocation of p42/44 MAPK protein thereby suggesting activation of p42/44 MAPK in the nucleus. Ang II caused marked accumulation of phosphorylated MEK 1/2 (phospho-MEK 1/2) in the nucleus without any significant accumulation of MEK 1/2 protein. Ratio of phospho-MEK 1/2 to MEK 1/2 protein in the nucleus after Ang II treatment was 2.4 times greater than control suggesting phosphorylation of MEK 1/2 inside the nucleus. Ethanol had no effect on the protein level or the activation of p42/44 MAPK in the nucleus. Ethanol treatment potentiated nuclear activation of p42/44 MAPK by Ang II but not translocation of p42/44 MAPK protein. This was accompanied by potentiation of Ang II-stimulated accumulation of phospho-MEK 1/2 in the nucleus by ethanol. MEK 1/2 inhibitor, U-0126 inhibited Ang II response and its potentiation by ethanol. These results suggest that Ang II-mediated accumulation of phospho-p42/44 MAPK in the hepatocyte nucleus involves MEK 1/2-dependent activation and this effect is potentiated by ethanol.