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A7260 - Alpha- and Beta-Parvin Isoforms Regulate Phenotype Switching in Canine Airway Smooth Muscle
Author Block: Y. Huang, S. J. Gunst; Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN, United States.
Extracellular stimuli can induce ASM smooth muscle to modulate its phenotype between a synthetic and a differentiated state. The inflammatory mediators IL-13 and IL-4 promote a synthetic phenotype characterized by Akt activation and cytokine secretion and suppress the expression of smooth muscle phenotype-specific contractile proteins such as smooth muscle myosin heavy chain (SmMHC) (Desai, 2011; Wu, 2016). In contrast, acetylcholine (ACh) stimulation activates signaling pathways that mediate tension development and promotes the expression of contractile proteins. α-parvin and β-parvin are components of stable heterotrimeric signaling modules that also contain integrin-link-kinase (ILK) and PINCH (IPP), and that localize to integrin adhesion junction complexes. The activation of Akt requires its binding to ILK within the IPP complex (Wu, 2008). We hypothesized that α-IPP and β-IPP complexes differentially regulate the activation of Akt, secretion of eotaxin and the expression of the differentiated phenotype in ASM tissues. Using immunoprecipitation and in situ Proximity Ligation Assays (PLA) in canine tracheal ASM tissues and dissociated cells, we found that the association of α- and β-IPP complexes with Akt is differentially regulated by IL-4, which stimulates the interaction of Akt with α-IPP, and ACh, which stimulates the interaction of β-IPP to Akt. The depletion of α-parvin by siRNA inhibited Akt activation, decreased eotaxin secretion and increased SmMHC expression (synthetic phenotype), whereas the depletion of β-parvin by siRNA potentiated Akt activation and increased eotaxin secretion, but decreased SmMHC expression (differentiated phenotype). In ASM, the activation of focal adhesion kinase (FAK) and its substrate, paxillin, promote a differentiated ASM phenotype (Wu, 2016). We found ACh and IL-4 differentially regulate the interaction of α-IPP and β-IPP complexes with Akt by differentially regulating FAK activation and paxillin phosphorylation: ACh is a much more potent stimulus for FAK activation and paxillin phosphorylation than IL-4. Expression of the paxillin Y31/118F mutant in ASM prevented paxillin phosphorylation in response to ACh and promoted the binding of Akt to α-IPP complexes, promoting a synthetic phenotype. These results suggest that ACh and IL-4 differentially regulate ASM phenotype as a result of their different effects on paxillin phosphorylation. We conclude that α and β isoforms of parvins form distinct IPP complexes that are differentially activated by extracellular conditions to modulate ASM phenotype, i.e. IL-4 promotes the interaction of Akt with α-IPP complexes and the synthetic phenotype, whereas ACh promotes the interaction of Akt with β-IPP complexes and the differentiated phenotype.Supported by NIH R01 HL029289, HL109629, HL048522