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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.

SUBMITTER: Storbeck CJ

PROVIDER: S-EPMC2754931 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Interphase microtubules are organized into a radial array with centrosome in the center. This organization is a subject of cellular regulation that can be driven by protein phosphorylation. Only few protein kinases that regulate microtubule array in interphase cells have been described. Ste20-like protein kinase LOSK (SLK) was identified as a microtubule and centrosome-associated protein. In this study we have shown that the inhibition of LOSK activity by dominant-negative mutant K63R-DeltaT or by LOSK depletion with RNAi leads to unfocused microtubule arrangement. Microtubule disorganization is prominent in Vero, CV-1, and CHO-K1 cells but less distinct in HeLa cells. The effect is a result neither of microtubule stabilization nor of centrosome disruption. In cells with suppressed LOSK activity centrosomes are unable to anchor or to cap microtubules, though they keep nucleating microtubules. These centrosomes are depleted of dynactin. Vero cells overexpressing K63R-DeltaT have normal dynactin "comets" at microtubule ends and unaltered morphology of Golgi complex but are unable to polarize it at the wound edge. We conclude that protein kinase LOSK is required for radial microtubule organization and for the proper localization of Golgi complex in various cell types.

| S-EPMC2366846 | biostudies-literature

Ste20-like protein kinase SLK (LOSK) regulates microtubule organization by targeting dynactin to the centrosome.

Project description:The microtubule- and centrosome-associated Ste20-like kinase (SLK; long Ste20-like kinase [LOSK]) regulates cytoskeleton organization and cell polarization and spreading. Its inhibition causes microtubule disorganization and release of centrosomal dynactin. The major function of dynactin is minus end-directed transport along microtubules in a complex with dynein motor. In addition, dynactin is required for maintenance of the microtubule radial array in interphase cells, and depletion of its centrosomal pool entails microtubule disorganization. Here we demonstrate that SLK (LOSK) phosphorylates the p150(Glued) subunit of dynactin and thus targets it to the centrosome, where it maintains microtubule radial organization. We show that phosphorylation is required only for centrosomal localization of p150(Glued) and does not affect its microtubule-organizing properties: artificial targeting of nonphosphorylatable p150(Glued) to the centrosome restores microtubule radial array in cells with inhibited SLK (LOSK). The phosphorylation site is located in a microtubule-binding region that is variable for two isoforms (1A and 1B) of p150(Glued) expressed in cultured fibroblast-like cells (isoform 1B lacks 20 amino acids in the basic microtubule-binding domain). The fact that SLK (LOSK) phosphorylates only a minor isoform 1A of p150(Glued) suggests that transport and microtubule-organizing functions of dynactin are distinctly divided between the two isoforms. We also show that dynactin phosphorylation is involved in Golgi reorientation in polarized cells.

| S-EPMC3806656 | biostudies-literature

Role of the Ste20-like kinase SLK in Podocyte Adhesion

Project description:SLK controls the cytoskeleton, cell adhesion and migration. Analysis of a protein kinase phosphorylation site dataset showed that podocyte adhesion proteins – paxillin, vinculin and talin-1 may be potential SLK substrates. The project examines if these adhesion proteins are substrates of SLK.

2024-01-22 | PXD046962 | Pride

Caspase 3 cleavage of the Ste20-related kinase SLK releases and activates an apoptosis-inducing kinase domain and an actin-disassembling region.

Project description:We have demonstrated that a novel Ste20-related kinase, designated SLK, mediates apoptosis and actin stress fiber dissolution through distinct domains generated by caspase 3 cleavage. Overexpression of SLK in C2C12 myoblasts stimulated the disassembly of actin stress fibers and focal adhesions and induced apoptosis, as determined by annexin V binding and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling analysis. SLK was cleaved by caspase 3 in vitro and in vivo during c-Myc-, tumor necrosis factor alpha, and UV-induced apoptosis. Furthermore, cleavage of SLK released two domains with distinct activities: an activated N-terminal kinase domain that promoted apoptosis and cytoskeletal rearrangements and a C-terminus domain that disassembled actin stress fibers. Moreover, our analysis has identified a novel conserved region (termed the AT1-46 homology domain) that efficiently promotes stress fiber disassembly. Finally, transient transfection of SLK also activated the c-Jun N-terminal kinase signaling pathway. Our results suggest that caspase-activated SLK represents a novel effector of cytoskeletal remodeling and apoptosis.

| S-EPMC85169 | biostudies-literature

Transforming growth factor ?-induced epithelial to mesenchymal transition requires the Ste20-like kinase SLK independently of its catalytic activity.

Project description:Invasion can be stimulated in vitro using the soluble ligand transforming growth factor-? (TGF?) to induce a process called epithelial-to-mesenchymal transition (EMT) characterized by cell-cell junction breakdown and an invasive phenotype. We have previously demonstrated a role for Ste20-like kinase SLK cell migration and invasion. Here we show that SLK depletion in NMuMG mammary epithelial cells significantly impairs their TGF?-induced migration and invasion. Immunofluorescence studies show that a fraction of SLK localizes to E-cadherin-positive adherens junction and that SLK impairs the breakdown of cell-cell contacts. We find that SLK-depleted cultures express significantly lower levels of vimentin protein as well as Snai1 and E-cadherin mRNA levels following TGF-? treatment. Surprisingly, our data show that SLK depletion does not affect the activation and nuclear translocation of Smad3. Furthermore, we show that expression of a dominant negative kinase does not impair tight junction breakdown and rescues Snai1 mRNA expression levels. Together these data suggest that SLK plays a novel role in TGF?-induced EMT, independent of Smads, in a kinase activity-independent manner.

| S-EPMC5716764 | biostudies-literature

Mammalian STE20?like kinase 1 regulates pancreatic cancer cell survival and migration through Mfn2?mediated mitophagy.

Project description:Mammalian STE20-like kinase 1 (MST1) plays an important role in pancreatic cancer progression, but its downstream targets are still unknown. In the present study, our results indicated that MST1 expression was significantly downregulated in pancreatic cancer cell lines (PANC?1, BxPC?3 and HPAC) compared with that in the normal ductal epithelial cell line (hTERT?HPNE). Moreover, MST1 overexpression in PANC?1 cells led to increased apoptosis as determined by MTT and TUNEL assays and inhibited cellular migration. Mechanistically, upregulation of MST1 expression caused mitochondrial dysfunction, decreased ATP production, and activation of the mitochondrial?dependent apoptotic pathway via inhibition of mitofusin 2 (Mfn2)?mediated mitophagy, which ultimately resulted in increased cellular apoptosis and decreased cellular migration. Collectively, the present study demonstrated that MST1 may regulate pancreatic cancer PANC?1 cell survival, invasion and migration through Mfn2?mediated mitophagy, laying the foundation for the exploration of novel therapeutic targets for pancreatic cancer.

| S-EPMC7248474 | biostudies-literature

Drosophila gene tao-1 encodes proteins with and without a Ste20 kinase domain that affect cytoskeletal architecture and cell migration differently.

Project description:Tao-1, the single representative of the Sterile 20 kinase subfamily in Drosophila, is best known for destabilizing microtubules at the actin-rich cortex, regulating the cytoskeletal architecture of cells. More recently, Tao-1 was shown to act in the Salvador-Warts-Hippo pathway by phosphorylating Hippo, regulating cell growth as well as cell polarity. Here, we show that tao-1 encodes two proteins, one with the Sterile 20 kinase domain (Tao-L) and one without it (Tao-S), and that they act in an antagonistic manner. Tao-L expression causes lamellipodia-like cell protrusions, whereas Tao-S expression results in filopodia-like structures that make cells stick to the surface they attach to. Ectopic Tao-1 expression in the anterior region of Drosophila embryos results in pole cell formation as normally observed at the posterior end. Tao-S expression causes primordial germ cells (PGCs) to adhere to the inner wall of the gut primordia and prevents proper transepithelial migration to the gonads. Conversely, RNAi knockdowns of Tao-1 cause disordered migration of PGCs out of the gut epithelium, their dispersal within the embryo and cell death. The results reveal a novel function of Tao-1 in cell migration, which is based on antagonistic activities of two proteins encoded by a single gene.

| S-EPMC4313371 | biostudies-literature

Site-specific proteolysis of the transcriptional coactivator HCF-1 can regulate its interaction with protein cofactors.

Project description:Limited proteolytic processing is an important transcriptional regulatory mechanism. In various contexts, proteolysis controls the cytoplasmic-to-nuclear transport of important transcription factors or removes domains to produce factors with altered activities. The transcriptional coactivator host cell factor-1 (HCF-1) is proteolytically processed within a unique domain consisting of 20-aa reiterations. Site-specific cleavage within one or more repeats generates a family of amino- and carboxyl-terminal subunits that remain tightly associated. However, the consequences of HCF-1 processing have been undefined. In this study, it was determined that the HCF-1-processing domain interacts with several proteins including the transcriptional coactivator/corepressor four-and-a-half LIM domain-2 (FHL2). Analysis of this interaction has uncovered specificity with both sequence and context determinants within the reiterations of this processing domain. In cells, FHL2 interacts exclusively with the nonprocessed coactivator and costimulates transcription of an HCF-1-dependent target gene. The functional interaction of HCF-1 with FHL2 supports a model in which site-specific proteolysis regulates the interaction of HCF-1 with protein partners and thus can modulate the activity of this coactivator. This paradigm expands the biological significance of limited proteolytic processing as a regulatory mechanism in gene transcription.

| S-EPMC1440766 | biostudies-literature

Smad inhibition by the Ste20 kinase Misshapen.

Project description:The level of TGF-?/bone morphogenetic protein (BMP) signaling through Smad is tightly regulated to ensure proper embryonic patterning and homeostasis. Here we show that Smad activation by TGF-?/BMP is blocked by a highly conserved phosphorylation event in the ?-helix 1 region of Smad [T312 in Drosophila Smad1 (MAD)]. ?-helix 1 phosphorylation reduces Smad interaction with TGF-?/BMP receptor kinase and affects all receptor-activated Smads except Smad3. Tissue culture and transgenic studies in Drosophila further demonstrate that the biological activity of MAD is repressed by T312 phosphorylation in vivo. Through RNAi screening of the kinome, we have identified Misshapen (Msn) and the mammalian orthologs TNIK, MINK1, and MAP4K4 as the kinases responsible for ?-helix 1 phosphorylation. Targeted expression of an active form of Msn in the wing imaginal disk disrupted activation of endogenous MAD by Dpp and expression of the Dpp/MAD target gene. Msn kinases belong to the Ste20 kinase family that has been shown to act as MAP kinase kinase kinase kinase (MAP4K). Our findings thus reveal a function of Msn independent of its impact on MAP kinase cascades. This Smad inhibition mechanism by Msn likely has important implications for development and disease.

| S-EPMC3131379 | biostudies-literature

The SCL transcriptional network and BMP signaling pathway interact to regulate RUNX1 activity.

Project description:Hematopoietic stem cell (HSC) development is regulated by several signaling pathways and a number of key transcription factors, which include Scl/Tal1, Runx1, and members of the Smad family. However, it remains unclear how these various determinants interact. Using a genome-wide computational screen based on the well characterized Scl +19 HSC enhancer, we have identified a related Smad6 enhancer that also targets expression to blood and endothelial cells in transgenic mice. Smad6, Bmp4, and Runx1 transcripts are concentrated along the ventral aspect of the E10.5 dorsal aorta in the aorta-gonad-mesonephros region from which HSCs originate. Moreover, Smad6, an inhibitor of Bmp4 signaling, binds and inhibits Runx1 activity, whereas Smad1, a positive mediator of Bmp4 signaling, transactivates the Runx1 promoter. Taken together, our results integrate three key determinants of HSC development; the Scl transcriptional network, Runx1 activity, and the Bmp4/Smad signaling pathway.

| S-EPMC1783401 | biostudies-literature

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