The Cdk5 activator P39 specifically links muskelin to myosin II and regulates stress fiber formation and actin organization in lens

Abstract

Cyclin dependent kinase 5 (Cdk5), a proline-directed serine/threonine kinase, requires p39 for its enzymatic activity, and is implicated in cytoskeletal organization and contraction in numerous cell types. The C-terminus of p39 binds muskelin, a multi-domain scaffolding protein known to affect cytoskeletal organization, but the mechanism(s) by which muskelin affects cytoskeletal organization remain unclear. The present study sought to determine whether p39 might serve as an adaptor protein that links muskelin to stress fibers and to investigate the possible biological relevance of such an interaction. Double immunoprecipitation showed that muskelin, p39, and myosin II are components of a single intracellular complex, and suppressing p39 abrogated the interaction between muskelin and the myosin subunits, demonstrating that p39 is required to link muskelin to myosin II. Muskelin is colocalized with myosin regulatory light chain (MRLC) and on stress fibers. The suppression of muskelin reduced Rho-GTP, MRLC phosphorylation, disrupted stress fiber organization, and promoted cell migration, all of which closely mimics the effect of Cdk5 inhibition. Moreover, suppressing muskelin and inhibiting Cdk5 together has no additional effect, indicating that muskelin plays an important role in Cdk5-dependent signaling. P39 is necessary and sufficient for Cdk5-dependent regulation of MRLC phosphorylation, as suppression of p39, but not p35, reduced MRLC phosphorylation. Together, these results demonstrate that p39 specifically links muskelin to myosin II and consequently, to stress fibers and reveal a novel role for muskelin in regulating myosin phosphorylation and cytoskeletal organization.

Mechanistic insights into Nav1.7‐dependent regulation of rat prostate cancer cell invasiveness revealed by toxin probes and proteomic analysis

“…In addition, it was found that all the eight proteins are correlated with the two GTPases. Fascin, muskelin, annexin A2, and cofilin‐1 have been known to be involved in regulating cell morphology and motility of tumor cells, and also are closely associated with Rho GTPase‐related cancer migration and invasion . For example, Fascin is a critical component downstream of Rac1 that is needed for actin cytoskeletal organization and cell motility .…”

Targeting the cyclin-dependent kinase 5 in metastatic melanoma

“…Depending on the study, CDK5 was shown to promote migration of cancer cells by phosphorylating actin-binding/regulatory proteins such as caldesmon, talin, or FAK, phosphatidylinositol 4-phosphate 5-kinase type I γ (PIPKIγ90), PIKE-A, a transcription factor USF2, or to indirectly activate small GTP-ases RalA and RalB (11,50,51,(58)(59)(60)(61)(62)(63). In contrast, other authors concluded that CDK5 serves to inhibit cancer cell migration and to suppress metastasis by phosphorylating a tumor-suppressor DLC1, a scaffold protein muskelin, a transmembrane glycoprotein PDPN, an epigenetic regulator EZH2, or a protein phosphatase PP2A (64)(65)(66)(67)(68). Again, these studies mainly utilized nonspecific inhibitors, dominant-negative CDK5 constructs, or shRNAs.…”

MKLN1 splicing defect in dogs with lethal acrodermatitis

“…In the rat lens, muskelin 1 is a substrate of Cdk5 and interacts with the Cdk5 activator p39 [ 28 ]. Also in lens, it was shown that p39 links muskelin 1 to myosin II and stress fibers [ 29 ].…”