CRISPR-Cas9/phosphoproteomics identifies Myosin Light Chain Kinase dependent signaling in kidney epithelial cells

ABSTRACT: Prior studies have implicated myosin light chain kinase (MLCK) in the regulation of aqua-porin-2 (AQP2) in the renal collecting duct. To discover signaling targets of MLCK, we deleted the Mylk- gene to obtain MLCK-null mpkCCD cells and carried out comprehensive phosphopro-teomics using the SILAC method for quantification. Only 107 phosphopeptides were changed in abundance by MLCK deletion out of 1743 quantified over multiple replicates (29 decreased and 78 increased). One of the decreased phosphopeptides corresponded to the canonical target site in myosin regulatory light chain (MLC). Network analysis indicated that targeted phosphopro-teins clustered into distinct structural/functional groups: “acto-myosin,” “signaling,” “nuclear envelope,” “gene transcription,” “mRNA processing,” “energy metabolism,” “intermediate fila-ments,” “adherens junctions” and “tight junctions.” There was significant overlap between the derived MLCK signaling network and a previously determined PKA signaling network. Phalloidin labeling revealed that MLCK deletion inhibited the normal effect of vasopressin to depolymer-ize F-actin. Immunocytochemistry and electron microscopy demonstrated a defect in pro-cessing of early endosomes to late endosomes. In contrast, surface biotinylation studies showed no effect of MLCK deletion on AQP2 endocytosis. We conclude that MLCK is part of a multi-component signaling pathway that includes much more than simple regulation of conven-tional non-muscle myosins through MLC phosphorylation. Furthermore, vasopressin signaling in collecting duct cells involves both MLCK-dependent signaling and PKA-dependent signaling, which display significant overlap. Mapping MLCK targets revealed potential roles in both nu-cleus and cytoplasm. The latter includes proteins that regulate both actin polymerization and AQP2-endosomal processing from early to late endosomes.

INSTRUMENT(S): LTQ Orbitrap Elite

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Epithelial Cell

SUBMITTER: CHIN-RANG YANG  

LAB HEAD: Mark A Knepper

PROVIDER: PXD014985 | Pride | 2020-03-04

REPOSITORIES: Pride