Non‐muscle (NM) Myosin II Mediates the Formation of Adhesome Signaling Complexes in Response to Contractile Stimulation of Airway Smooth Muscle (ASM)

Contractile stimulation of ASM induces the recruitment of vinculin and paxillin to integrin adhesion junctions (adhesomes) (Huang JBC 2011; Zhang JBC 2012). Vinculin binds to talin in adhesomes and undergoes phosphorylation and activation. The recruitment of vinculin and paxillin to adhesome complexes and their activation is required for actin polymerization and ASM contraction. NM myosin II is expressed in ASM and has been implicated in focal adhesion assembly in NM cells. We hypothesized that NM myosin II might mediate the recruitment vinculin and paxillin to adhesomes during ASM contraction. The NM myosin II heavy chain tail domain mediates its assembly into filaments, and undergoes phosphorylation at ser 1943 near its COOH terminal. Stimulation of ASM tissues with ACh increased NM myosin Ser 1943 phosphorylation. We expressed the phosphorylation deficient mutant NM myosin S1943A in ASM tissues. NM myosin S1943A expression inhibited endogenous NM myosin II phosphorylation at Ser 1943 and prevented the ACh stimulated recruitment of vinculin and paxillin to adhesomes. NM myosin II S1943A expression also suppressed vinculin and paxillin phosphorylation in response to ACh and inhibited ASM contraction. S100A4 binds to the C‐terminal of NM myosin II and may also regulate NM Myosin II filament assembly. siRNA was used to deplete the endogenous S100A4 in ASM tissues. S100A4 depletion inhibited ACh stimulated recruitment of vinculin and paxillin, reduced vinculin and paxillin phosphorylation and inhibited ASM contraction. The results suggest that NM myosin II plays a role in the assembly of adhesome signalling complexes in ASM that are critical for the activation of cytoskeletal signalling pathways required for ASM contraction.