STAT3 inhibitory activity of naphthoquinones isolated from Tabebuia avellanedae

The extract of Tabebuia avellanedae has been used as a folk medicine, and the various biological activities of T. avellanedae have been extensively studied. However, few studies have reported which natural products play a role in their biological effects. In this study, we evaluated representative naphthoquinones isolated from T. avellanedae and found that furanonaphthoquinones were the key structures required to exhibit STAT3 phosphorylation inhibitory activities. Our SAR analysis indicated that removal of a hydroxyl group enhanced the STAT3 phosphorylation inhibitory activity. In addition, the combined results of a mobility shift assay, SH2 domain binding assay, and docking simulation by Autodock 4.2.6 suggested that (S)-5-hydroxy-2-(1-hydroxyethyl)naphtho[2,3-b]furan-4,9-dione (1) could directly bind to the hinge region of STAT3.     

Design and characterization of non-phosphopeptide inhibitors for Src family SH2 domains

The development of novel non-phosphopeptide inhibitors for the Src family SH2 domain is described. Several commercially available hydroxyl aromatic acids have been appended off the N-terminus of pYEEIE and the potent phosphopeptide inhibitors of GST-Lck-SH2 were identified via ELISA. The most potent inhibitor, caffeic acid-pYEEIE, exhibited approximately 30-fold more binding activity than Ac-pYEEIE. Non-phosphopeptides were synthesized by replacing phosphotyrosine of caffeic acid-pYEEIE with tyrosine or 3,4-dihydroxyphenylalanine (DOPA). Caffeic acid-DOPA-EEIE that did not contain phosphotyrosine and its isosteres exhibited less than 20 times decreased binding affinity for GST-Lck-SH2 than Ac-pYEEIE. Moreover, it had a similar binding affinity for the GST-Lck-SH2, GST-Src-SH2, and GST-Fyn-SH2 domains. This study showed that the pY-1 positions of the phosphopeptide inhibitors and of the non-phosphopeptide inhibitors played an important role in the binding for the SH2 domain and that the non-phosphopeptide inhibitor must be a new lead in the development of SH2 inhibitors.     

Analyses of putative anti-cancer potential of three STAT3 signaling inhibitory compounds derived from Salvia officinalis

The extract of Salvia officinalis (Common Sage) exhibited inhibitory activity of STAT3 signal after screening of several plants extracts using the STAT3-responsive reporter system. Cirsiliol, luteolin, and carnosol were identified from the methanol extract of Silvia officinalis as inhibitors of STAT3 signaling and the effects of these three compounds on STAT3 protein or growth inhibition on cancer cells was compared. Luteolin at the dose of 90 μM clearly suppressed the phosphorylation of STAT3 induced by IL-6, while carnosol was prone to decrease total STAT3 proteins at high doses (>90 μM). Cirsiliol had almost no effect. Since the three compounds exhibited similar concentration-dependent suppression patterns in the reporter assay except for cirsiliol became plateau beyond 30 μM, these compounds appeared to function as STAT3 inhibitory factors in different ways. The direct anti-proliferative activity of three compounds was examined with or without the anti-cancer drug gefitinib using HepG2 and A549 cells. The anti-proliferative effect of the three compounds was additively enhanced by gefitinib. At the doses of 3.6 μM, statistically significant suppression of proliferation was observed in HepG2 cells only by cirsiliol among the three compounds in the absence of gefitinib but all three compounds were prone to suppress the proliferation of HepG2 cells and A549 cells dose-dependently although cirsiliol showed a modest dose-dependency and this suppression of proliferation was enhanced by the addition of gefitinib. Cirsiliol, a dimethyoxylated flavone, activated the natural killer activity of KHYG-1 cells against erythroleukemia K562 cells like a hexamethoxylated flavone, nobiletin, suggesting that it may also have an indirect anti-cancer potential through activation of NK cells. These results shed light on the putative anti-cancer potential of Salvia officinalis.     

IL-9 Induces CCL11 Expression via STAT3 Signalling in Human Airway Smooth Muscle Cells

Background

Previous findings support the concept that IL-9 may play a significant role in mediating both pro-inflammatory and changes in airway responsiveness that characterizes the atopic asthmatic state. We previously demonstrated that human airway smooth muscle (ASM) cells express a functional IL-9R that mediate CCL11 expression. However, the signaling pathway governing this effect is not well understood.

Methodology/Principal Findings

In this study, we showed that IL-9 mediated CCL11 expression in ASM cells does not rely on STAT6 or STAT5 but on STAT3 pathway. IL-9 induced rapid STAT3 activation in primary ASM cells that was not observed in case of STAT6 or STAT5. STAT3 binding to CCL11 promoter was also observed in vivo upon IL-9 stimulation of ASM cells. Disruption of STAT3 activity with SH2 domain binding inhibitory peptide results in significant reduction of IL-9 mediated CCL11 promoter activity. DN STAT3β over-expression in ASM cells, but not Ser 727 STAT3 or STAT6 DN, abolishes IL-9 mediated CCL11 promoter activity. Finally, STAT3 but not STAT6 silenced ASM cells showed significant reduction in IL-9 mediated CCL11 promoter activity and mRNA expression.

Conclusion/Significance

Taken together, our results indicate that IL-9 mediated CCL11 via STAT3 signalling pathway may play a crucial role in airway inflammatory responses.