The Ldb1 and Ldb2 Transcriptional Cofactors Interact with the Ste20-like Kinase SLK and Regulate Cell Migration

Abstract

Cell migration involves a multitude of signals that converge on cytoskeletal reorganization, essential for development, immune responses, and tissue repair. Here, we show that the microtubule-associated Ste20 kinase SLK, required for cell migration, interacts with the LIM domain binding transcriptional cofactor proteins Ldb1/CLIM2 and Ldb2/CLIM1/NLI. We demonstrate that Ldb1 and 2 bind directly to the SLK carboxy-terminal AT1-46 homology domain in vitro and in vivo. We find that Ldb1 and -2 colocalize with SLK in migrating cells and that both knockdown and overexpression of either factor results in increased motility. Supporting this, knockdown of Ldb1 increases focal adhesion turnover and enhances migration in fibroblasts. We propose that Ldb1/2 function to maintain SLK in an inactive state before its activation. These findings highlight a novel function for Ldb1 and -2 and expand their role to include the control of cell migration.

SLK-mediated phosphorylation of paxillin is required for focal adhesion turnover and cell migration

“…However, in accordance with the derived dissociation constants of this structure, additional associations appear to be required to achieve efficient dimerization [77]. Interestingly, SLK has been shown to contain dimerization domains adjacent to the kinase region, where demonstrated LDB1/2-SLK binding [76,77]. Further investigation into this transhomodimerization has led to the discovery of two novel SLK phosphorylation sites namely S189 and T183, in which T183 was identified as an important site for SLK autophosphorylation [77].…”

“…Recent studies have shown that SLK localizes to the leading edge of migrating cells with vinculin and paxillin as well as with the LIM domain binding proteins, LDB1 and LDB2 following scratch-wounding of a confluent monolayer of fibroblasts [69,76,78]. This localization has been shown to occur in response to both the induction of wound-healing as well as the activation of the receptor tyrosine kinase ErbB2 [69,79].…”

“…The ATH domain however, exhibits a high degree of homology to the ATH1-46 protein of unknown function, and has also been found within both LOK and xPLKK1, suggesting that it may represent a novel motif [75]. In fact, recent studies have shown the ATH domain to be a region within SLK that mediates protein-protein interactions, both with itself to form SLK homodimers, as well as with binding partners such as the LIM domain binding proteins, LDB1 and LDB2 [76,77].…”

“…In vivo, overexpression assays using a kinase-inactive form of SLK as well as knockdown of the endogenous kinase, have been shown to negatively regulate both focal adhesion turnover and cell migration [69]. Conversely, disruption of the stoichiometry of the SLK kinase regulators LDB1 and LDB2 via over-expression or knockdown, has been shown to result in an increase in SLK kinase activity and the induction of focal adhesion disassembly and cell migration [76].…”

Germinal center kinases in immune regulation

“…124 SLK, which is similar to LOK, can regulate focal adhesion turnover through unknown mechanism that involves FAK. [125][126][127] The GCK-VIII subfamily member TAO2 is a mitogen-activated protein kinase kinase kinase which associates with and activates MAPK/extracellular signal-regulated kinase kinase 3 (MEK3) and MEK6 to activate p38. 128 Since p38 regulates the expression of inflammatory cytokines, TAO2 may be considered for therapeutic targeting for diseases such as autoimmunity.…”