Effects of dexamethasone on VEGF-induced MUC5AC expression in human primary bronchial epithelial cells: Implications for asthma.

Mucins are major macromolecular components of lung mucus that are mainly responsible for the viscoelastic property of mucus. MUC5AC is a major mucin glycoprotein that is hypersecreted in asthmatic individuals. Vascular endothelial growth factor (VEGF) has been implicated in inflammatory and airway blood vessel remodeling in asthmatics. Our previous studies indicate that VEGF upregulates MUC5AC expression by interacting with VEGF receptor 2 (VEGFR2). It has been shown that dexamethasone (Dex) downregulates MUC5AC expression; however, the underlying mechanisms have not been completely elucidated. Therefore, we sought to investigate the effect of Dex on MUC5AC expression induced by VEGF and study the underlying mechanisms. We tested the effects of Dex on VEGFR2 and RhoA activation, caveolin-1 expression, and the association of caveolin-1 and VEGFR2 in primary bronchial epithelial cells. Dex downregulated MUC5AC mRNA and protein levels in a dose- and time-dependent manner, and suppressed the activation of VEGFR2 and RhoA induced by VEGF. Additionally, Dex upregulated caveolin-1 protein levels in a dose- and time-dependent manner. Furthermore, phospho-VEGFR2 expression was decreased through overexpression of caveolin-1 and increased after caveolin-1 knockdown. Dex treatment attenuated the VEGF-decreased association of caveolin-1 and VEGFR2. Collectively, our findings suggest that Dex downregulates VEGF-induced MUC5AC expression by inactivating VEGFR2 and RhoA. Furthermore, decreased MUC5AC expression by Dex was related to the increased association of caveolin-1 with VEGFR2. Further studies characterizing these mechanisms are required to facilitate the development of improved treatment strategies for asthma.

Upregulation of MUC5AC by VEGF in human primary bronchial epithelial cells: implications for asthma.

BACKGROUND: Airway mucus hypersecretion is an important pathophysiological feature in asthma. Mucins are glycoproteins that are mainly responsible for the viscoelastic property of mucus, and MUC5AC is a major mucin glycoprotein that is overproduced in asthma. Vascular endothelial growth factor (VEGF) has been implicated in inflammatory and airway blood vessel remodeling in asthmatics. Therefore, we sought to investigate the effect of VEGF on MUC5AC expression and study the underlying mechanisms. METHODS: In order to elucidate the precise mechanism underlying the effect of VEGF on MUC5AC expression, we tested the effects of VEGF on RhoA activation and the association of caveolin-1 and VEGFR2 in Primary Bronchial Epithelial Cells. RESULTS: VEGF up-regulated MUC5AC mRNA and protein levels in a dose- and time-dependent manner, and activated RhoA. Additionally, VEGF-induced MUC5AC expression and RhoA activation were enhanced by disrupting caveolae with cholesterol depletion and reversed by cholesterol repletion, and inhibited by a selective VEGF receptor 2 (VEGFR2) inhibitor SU1498. Furthermore, phospho-VEGFR2 expression was decreased via overexpression of caveolin-1. VEGF treatment reduced the association of caveolin-1 and VEGFR2. CONCLUSION: Collectively, our findings suggest that VEGF up-regulates MUC5AC expression and RhoA activation by interaction with VEGFR2, and this phenomenon was related with the association of caveolin-1 and VEGFR2. Further studies on these mechanisms are needed to facilitate the development of treatments for asthma.

The p70S6K Specific Inhibitor PF-4708671 Impedes Non-Small Cell Lung Cancer Growth.

BACKGROUND: As a serine/threonine protein kinase, p70S6K plays an important role in tumor cells. Evidence has revealed overexpression of p70S6K and phosphorylated p70S6K (p-p70S6K) in various tumor tissues, with these proteins identified as independent prognostic markers in non-small cell lung cancer (NSCLC). In this study, we explored the role of the p70S6K specific inhibitor PF-4708671 in NSCLC. METHODS: Three NSCLC cell lines (A549, SK-MES-1, and NCI-H460) were treated with PF-4708671 at five different concentrations, including 0.1µM, 0.3µM, 1µM, 3µM and 10µM, and protein levels were determined by Western-blot. Then, PF-4708671's effects were assessed both in vitro (cell proliferation, apoptosis, cell cycle distribution, and invasion) and in vivo. RESULTS: The expression levels of p-p70S6K and the downstream effector S6 were significantly reduced by PF-4708671. Diametrically opposite, the downstream protein levels of BAD, Caspase3 and ERK had increased after treatment with PF-4708671. In addition, PF-4708671 drastically inhibited cell proliferation and invasion ability in A549, SK-MES-1 and NCI-H460 cells in vitro, causing cell cycle arrest in G0-G1 phase. Limited effects of PF-4708671 were observed on apoptosis in the three NSCLC cell lines assessed. Importantly, PF-4708671 could inhibit tumorigenesis in nude mice in vivo. CONCLUSION: These findings demonstrated that the p70S6K specific inhibitor PF-4708671 has inhibitory effects on NSCLC tumorigenesis in vitro and in vivo. Therefore, P70S6K should be considered a new potential therapeutic target, and PF-470867 may be used as targeted drug for cancer treatment.