p90RSK2, a new MLCK mediates contractility in myosin light chain kinase null smooth muscle

Introduction: Phosphorylation of smooth muscle (SM) myosin regulatory light chain (RLC 20 ) is a critical switch leading to SM contraction. The canonical view held that only the short isoform kinase (MLCK1) catalyzed this reaction. It now accepted auxiliary kinases may contribute vascular tone and contractility. We have previously reported p90 ribosomal S6 (RSK2) functions as such kinase, in parallel with MLCK1, contributing ∼25% maximal myogenic force resistance arteries. Thus, RSK2 be instrumental regulation basal blood pressure. Here, we take advantage MLCK1 null mouse ( mylk1 −/− further test our hypothesis can function an MLCK, playing significant physiological role Methods: Using fetal (E14.5-18.5) tissues, embryos die at birth, investigated necessity MLCK for contractility development determined ability compensate lack characterized its signaling pathway SM. Results Discussion: Agonists induced contraction RLC phosphorylation was attenuated by inhibition. pCa-tension relationships permeabilized strips bladder showed no difference Ca 2+ sensitivity WT vs muscles, although magnitude responses considerably smaller absence MLCK. contractile similar upon addition GTPγS activate RhoA/ROCK or calyculinA inhibit phosphatase. -dependent tyrosine Pyk2, contributed RSK2-mediated phosphorylation. Proximity-ligation immunoprecipitation assays demonstrated association RSK2, PDK1 ERK1/2 actin. PDK1, formed complex on actin filament, positioning them interaction adjacent heads. component reflected agonist mediated increases , which activated Pyk2/PDK1/RSK2 cascade. −independent through activation Erk1/2/PDK1/RSK2 direct increase Overall, constitutes new third pathway, established /CaM/MLCK pathways regulate