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Dynamic reorganization of the actin cytoskeleton at the leading edge is required for directed cell migration. Cofilin, a small actin-binding protein with F-actin severing activities, is a key enzyme initiating such actin remodeling processes. Cofilin activity is tightly regulated by phosphorylation and dephosphorylation events that are mediated by LIM kinase (LIMK) and the phosphatase slingshot (SSH), respectively. Protein kinase D (PKD) is a serine/threonine kinase that inhibits actin-driven directed cell migration by phosphorylation and inactivation of SSH. Here, we show that PKD can also regulate LIMK through direct phosphorylation and activation of its upstream kinase p21-activated kinase 4 (PAK4). Therefore, active PKD increases the net amount of phosphorylated inactive cofilin in cells through both pathways. The regulation of cofilin activity at multiple levels may explain the inhibitory effects of PKD on barbed end formation as well as on directed cell migration.

The interaction of astral microtubules with cortical actin networks is essential for the correct orientation of the mitotic spindle; however, little is known about how the cortical actin organization is regulated during mitosis. LIM kinase-1 (LIMK1) regulates actin dynamics by phosphorylating and inactivating cofilin, an actin-depolymerizing protein. LIMK1 activity increases during mitosis. Here we show that mitotic LIMK1 activation is critical for accurate spindle orientation in mammalian cells. Knockdown of LIMK1 suppressed a mitosis-specific increase in cofilin phosphorylation and caused unusual cofilin localization in the cell cortex in metaphase, instability of cortical actin organization and astral microtubules, irregular rotation and misorientation of the spindle, and a delay in anaphase onset. Similar results were obtained by treating the cells with a LIMK1 in hibitor peptide or latrunculin A or by overexpressing a non-phosphorylatable cofilin(S3A) mutant. Furthermore, localization of LGN (a protein containing the repetitive Leu-Gly-Asn tripeptide motifs), an important regulator of spindle orientation, in the crescent-shaped cortical regions was perturbed in LIMK1 knockdown cells. Our results suggest that LIMK1-mediated cofilin phosphorylation is required for accurate spindle orientation by stabilizing cortical actin networks during mitosis.

Cofilin and its closely related protein, actin-depolymerizing factor (ADF), are key regulators of actin cytoskeleton dynamics that have been implicated in growth cone motility and neurite extension. Cofilin/ADF are inactivated by LIM kinase (LIMK)-catalyzed phosphorylation and reactivated by Slingshot (SSH)-catalyzed dephosphorylation. Here we examined the roles of cofilin/ADF, LIMKs (LIMK1 and LIMK2), and SSHs (SSH1 and SSH2) in nerve growth factor (NGF)-induced neurite extension. Knockdown of cofilin/ADF by RNA interference almost completely inhibited NGF-induced neurite extension from PC12 cells, and double knockdown of SSH1/SSH2 significantly suppressed both NGF-induced cofilin/ADF dephosphorylation and neurite extension from PC12 cells, thus indicating that cofilin/ADF and their activating phosphatases SSH1/SSH2 are critical for neurite extension. Interestingly, NGF stimulated the activities of both LIMK1 and LIMK2 in PC12 cells, and suppression of LIMK1/LIMK2 expression or activity significantly reduced NGF-induced neurite extension from PC12 cells or chick dorsal root ganglion (DRG) neurons. Inhibition of LIMK1/LIMK2 activity reduced actin filament assembly in the peripheral region of the growth cone of chick DRG neurons. These results suggest that proper regulation of cofilin/ADF activities through control of phosphorylation by LIMKs and SSHs is critical for neurite extension and that LIMKs regulate actin filament assembly at the tip of the growth cone.

Neurofibromin is a neurofibromatosis type 1 (NF1) tumor suppressor gene product with a domain that acts as a GTPase-activating protein and functions, in part, as a negative regulator of Ras. Loss of neurofibromin expression in NF1 patients is associated with elevated Ras activity and increased cell proliferation, predisposing to a variety of tumors of the peripheral and central nervous systems. We show here, using the small interfering RNA (siRNA) technique, that neurofibromin dynamically regulates actin cytoskeletal reorganization, followed by enhanced cell motility and gross cell aggregation in Matrigel matrix. NF1 siRNA induces characteristic morphological changes, such as excessive actin stress fiber formation, with elevated negative phosphorylation levels of cofilin, which regulates actin cytoskeletal reorganization by depolymerizing and severing actin filaments. We found that the elevated phosphorylation of cofilin in neurofibromin-depleted cells is promoted by activation of a Rho-ROCK-LIMK2 pathway, which requires Ras activation but is not transduced through three major Ras-mediated downstream pathways via Raf, phosphatidylinositol 3-kinase, and RalGEF. In addition, the exogenous expression of the NF1-GTPase-activating protein-related domain suppressed the NF1 siRNA-induced phenotypes. Neurofibromin was demonstrated to play a significant role in the machinery regulating cell proliferation and in actin cytoskeletal reorganization, which affects cell motility and adhesion. These findings may explain, in part, the mechanism of multiple neurofibroma formation in NF1 patients.

LIM kinases (LIMKs) are mainly in the cytoplasm and regulate actin dynamics through cofilin phosphorylation. Recently, it has been reported that nuclear localization of LIMKs can mediate suppression of cyclin D1 expression. Using immunofluorescence monitoring of enhanced green fluorescent protein-tagged LIMK2 in combination with photobleaching techniques and leptomycin B treatment, we demonstrate that LIMK2 shuttles between the cytoplasm and the nucleus in endothelial cells. Sequence analysis predicted two PKC phosphorylation sites in LIMK2 but not in LIMK1. One site at Ser-283 is present between the PDZ and the kinase domain, and the other site at Thr-494 is within the kinase domain. Activation of PKC by phorbol ester treatment of endothelial cells stimulated LIMK2 phosphorylation at Ser-283 and inhibited nuclear import of LIMK2 and the PDZ kinase construct of LIMK2 (amino acids 142-638) but not of LIMK1. The PKC-delta isoform phosphorylated LIMK2 at Ser-283 in vitro. Mutational analysis indicated that LIMK2 phosphorylation at Ser-283 but not Thr-494 was functional. Serum stimulation of endothelial cells also inhibited nuclear import of PDZK-LIMK2 by protein kinase C-dependent phosphorylation of Ser-283. Our study shows that phorbol ester and serum stimulation of endothelial cells inhibit nuclear import of LIMK2 but not LIMK1. This effect was dependent on PKC-delta-mediated phosphorylation of Ser-283. Since phorbol ester enhanced cyclin D1 expression and subsequent G1-to-S-phase transition of endothelial cells, we suggest that the PKC-mediated exclusion of LIMK2 from the nucleus might be a mechanism to relieve suppression of cyclin D1 expression by LIMK2.

Two characteristics of highly malignant cells are their increased motility and secretion of proteinases allowing these cells to penetrate surrounding basement membranes and metastasize. Activation of 21-kDa activated kinases (PAKs) is an important mechanism for increasing cell motility. Recently, we reported that binding of receptor-recognized forms of the proteinase inhibitor alpha2-macroglobulin (alpha2M*) to GRP78 on the cell surface of 1-LN human prostate cancer cells induces mitogenic signaling and cellular proliferation. In the current study, we have examined the ability of alpha2M* to activate PAK-1 and PAK-2. Exposure of 1-LN cells to alpha2M* caused a 2- to 3-fold increase in phosphorylated PAK-2 and a similar increase in its kinase activity toward myelin basic protein. By contrast, the phosphorylation of PAK-1 was only negligibly affected. Silencing the expression of the GRP78 gene, using either of two different mRNA sequences, greatly attenuated the appearance of phosphorylated PAK-2 in alpha2M*-stimulated cells. Treatment of 1-LN cells with alpha2M* caused translocation of PAK-2 in association with NCK to the cell surface as evidenced by the co-immunoprecipitation of PAK-2 and NCK in the GRP78 immunoprecipitate from plasma membranes. alpha2M*-induced activation of PAK-2 was inhibited by prior incubation of the cells with specific inhibitors of tyrosine kinases and phosphatidylinositol 3-kinase. PAK-2 activation was accompanied by significant increases in the levels of phosphorylated LIMK and phosphorylated cofilin. Silencing the expression of the PAK-2 gene greatly attenuated the phosphorylation of LIMK. In conclusion, we show for the first time the activation of PAK-2 in 1-LN prostate cancer cells by a proteinase inhibitor, alpha2-macroglobulin. These studies suggest a mechanism by which alpha2M* enhances the metastatic potential of these cells.

Microtubule (MT) destabilization promotes the formation of actin stress fibers and enhances the contractility of cells; however, the mechanism involved in the coordinated regulation of MTs and the actin cytoskeleton is poorly understood. LIM kinase 1 (LIMK1) regulates actin polymerization by phosphorylating the actin depolymerization factor, cofilin. Here we report that LIMK1 is also involved in the MT destabilization. In endothelial cells endogenous LIMK1 co-localizes with MTs and forms a complex with tubulin via the PDZ domain. MT destabilization induced by thrombin or nocodazole resulted in a decrease of LIMK1 colocalization with MTs. Overexpression of wild type LIMK1 resulted in MT destabilization, whereas the kinase-dead mutant of LIMK1 (KD) did not affect MT stability. Importantly, down-regulation of endogenous LIMK1 by small interference RNA resulted in abrogation of the thrombin-induced MTs destabilization and the inhibition of thrombin-induced actin polymerization. Expression of Rho kinase 2, which phosphorylates and activates LIMK1, dramatically decreases the interaction of LIMK1 with tubulin but increases its interaction with actin. Interestingly, expression of KD-LIMK1 or small interference RNA-LIMK1 prevents thrombin-induced microtubule destabilization and F-actin formation, suggesting that LIMK1 activity is required for thrombin-induced modulation of microtubule destabilization and actin polymerization. Our findings indicate that LIMK1 may coordinate microtubules and actin cytoskeleton.

Yersinia bacteria can take control of the host cell by injecting so-called Yop effector proteins into the cytosol of the cells to which they adhere. Using Yersinia enterocolitica strains that are deficient for one or more Yops, we could show that YopE and, to a lesser extent, YopT interfere with the caspase-1-mediated maturation of prointerleukin-1beta in macrophages. In addition, overexpression of YopE and YopT was shown to prevent the autoproteolytic activation of caspase-1 in a way that is dependent on their inhibitory effect on Rho GTPases. Expression of constitutive-active or dominant-negative Rho GTPase mutants or treatment with Rho GTPase inhibitors confirmed the role of Rho GTPases and, in particular, Rac1 in the autoactivation of caspase-1. Rac1-induced caspase-1 activation was mediated by its effect on LIM kinase-1, which is targeting the actin cytoskeleton. Rac-1 and LIM kinase-1 dominant-negative mutants were shown to inhibit caspase-1 activation induced by overexpression of Asc, which is a caspase-1-activating adaptor protein. Moreover, Rac1 as well as YopE and YopT significantly modulated caspase-1 oligomerization. These results highlight a previously unknown function of Rho GTPases in the activation of caspase-1 and give new insight on the role of YopE in immune-escape mechanisms of Yersinia.

LIM kinase 1 (LIMK1), a novel member of a subclass of the protein-serine/threonine kinases, is known to play a role in the development and maintenance of neuronal circuits that mediate cognitive function. Genetic studies have implicated a mutation of LIMK1 as a causative factor in the impairment of visuospatial cognition in a neurodevelopmental disorder, Williams syndrome. A transcriptional factor, cAMP-responsive element-binding protein (CREB), is thought to be involved in the formation of many types of synaptic plasticity involving learning and memory. In the present study we show that the LIMK1 activity is markedly induced during the differentiation of immortalized hippocampal progenitor (H19-7) cells. We found that the addition of neurogenic growth factor to H19-7 cells induces specific binding between LIMK1 and active CREB, that LIMK1 directly phosphorylates CREB, and that this leads to the stimulation of subsequent cAMP-responsive element-mediated gene transcription during H19-7 cell neuronal differentiation. In addition, we also found that LIMK1 activation occurs through Rac/Cdc42- and p21-activated kinase-mediated signaling pathways. Moreover, when the plasmid encoding kinase-inactive LIMK1 was transfected to block the activation of endogenous LIMK1, the neuronal differentiation of H19-7 cells was significantly suppressed. These findings suggest that LIMK1 activation and subsequent CREB phosphorylation are important in the neuronal differentiation of central nervous system hippocampal progenitor cells.

p57Kip2 is the only cyclin-dependent kinase (Cdk) inhibitor shown to be essential for mouse embryogenesis. The fact suggests that p57 has a specific role that cannot be compensated by other Cdk inhibitors. LIM-kinase 1 (LIMK-1) is a downstream effector of the Rho family of GTPases that phosphorylates and inactivates an actin depolymerization factor, cofilin, to induce the formation of actin fiber. Here we demonstrate that p57 regulates actin dynamics by binding and translocating LIMK-1 from the cytoplasm into the nucleus, which in turn results in a reorganization of actin fiber. The central region of p57, a unique feature among the Cdk inhibitors, and the N-terminal region of LIMK-1, which contains the LIM domains were essential for the interaction. Expression of p57, but not p27Kip1 or a p57 mutant, with a deletion in the central region was shown to induce marked reorganization of actin filament and a translocation of LIMK-1. Our findings indicate p57 may act as a key regulator in embryogenesis by bearing two distinct functions, the regulation of cell cycle through binding to Cdks and the regulation of actin dynamics through binding to LIMK-1, both of which should be important in developmental procedure.

Receptor-mediated endocytosis is a constitutive high capacity pathway for the reabsorption of proteins from the glomerular filtrate by the renal proximal tubule. ClC-5 is a voltage-gated chloride channel found in the proximal tubule where it has been shown to be essential for protein uptake, based on evidence from patients with Dent's disease and studies in ClC-5 knockout mice. To further delineate the role of ClC-5 in albumin uptake, we performed a yeast two-hybrid screen with the C-terminal tail of ClC-5 to identify any interactions of the channel with proteins involved in endocytosis. We found that the C-terminal tail of ClC-5 bound the actin depolymerizing protein, cofilin, a result that was confirmed by GST-fusion pulldown assays. In cultured proximal tubule cells, cofilin was distributed in nuclear, cytoplasmic, and microsomal fractions and co-localized with ClC-5. Phosphorylation of cofilin by overexpressing LIM kinase 1 resulted in a stabilization of the actin cytoskeleton. Phosphorylation of cofilin in two proximal tubule cell models (porcine renal proximal tubule and opossum kidney) was also accompanied by a pronounced inhibition of albumin uptake. This study identifies a novel interaction between the C-terminal tail of ClC-5 and cofilin, an actin-associated protein that is crucial in the regulation of albumin uptake by the proximal tubule.

Mammalian LIM kinase 1 (LIMK1) is involved in reorganization of actin cytoskeleton through inactivating phosphorylation of the ADF family protein cofilin, which depolymerizes actin filaments. Maintenance of the actin dynamics in an ordered fashion is essential for stabilization of cell shape or promotion of cell motility depending on the cell type. These are the two key phenomena that may become altered during acquisition of the metastatic phenotype by cancer cells. Here we show that LIMK1 is overexpressed in prostate tumors and in prostate cancer cell lines, that the concentration of phosphorylated cofilin is higher in metastatic prostate cancer cells, and that a partial reduction of LIMK1 altered cell proliferation by arresting cells at G2/M, changed cell shape, and abolished the invasiveness of metastatic prostate cancer cells. We also show that the ectopic expression of LIMK1 promotes acquisition of invasive phenotype by the benign prostate epithelial cells. Our data provide evidence of a novel role of LIMK1 in regulating cell division and invasive property of prostate cancer cells and indicate that the effect is not mediated by phosphorylation of cofilin. Our study correlates with the recent observations showing a metastasis-associated chromosomal gain on 7q11.2 in prostate cancer, suggesting a possible gain in LIMK1 DNA (7q11.23).

During cytokinesis the actomyosin-based contractile ring is formed at the equator, constricted, and then disassembled prior to cell abscission. Cofilin stimulates actin filament disassembly and is implicated in the regulation of contractile ring dynamics. However, little is known about the mechanism controlling cofilin activity during cytokinesis. Cofilin is inactivated by phosphorylation on Ser-3 by LIM-kinase-1 (LIMK1) and is reactivated by a protein phosphatase Slingshot-1 (SSH1). Here we show that the phosphatase activity of SSH1 decreases in the early stages of mitosis and is elevated in telophase and cytokinesis in HeLa cells, a time course correlating with that of cofilin dephosphorylation. SSH1 co-localizes with F-actin and accumulates onto the cleavage furrow and the midbody. Expression of a phosphatase-inactive SSH1 induces aberrant accumulation of F-actin and phospho-cofilin near the midbody in the final stage of cytokinesis and frequently leads to the regression of the cleavage furrow and the formation of multinucleate cells. Co-expression of cofilin rescued the inhibitory effect of phosphatase-inactive SSH1 on cytokinesis. These results suggest that SSH1 plays a critical role in cytokinesis by dephosphorylating and reactivating cofilin in later stages of mitosis.

We have previously reported that cofilin, an actin-binding protein, plays an important role in phagocyte functions, such as respiratory burst, phagocytosis, and chemotaxis. On the other hand, it was recently found that LIM motif-containing kinase (LIMK) phosphorylates cofilin. In this work, we investigated the roles of LIMK in activated phagocytes. The results of immunostaining showed that in dormant phagocytes the endogenous LIMK1 was diffusely distributed in the cytosol of macrophage-like U937 cells, and when activated by opsonized zymosan (OZ), it was translocated to plasma membranes. Green fluorescence protein (GFP)-conjugated LIMK was expressed in the phagocytes, and the GFP-positive cells were isolated by a fluorescence-activated cell sorter. The isolated wild-type LIMK-overexpressing cells produced superoxide at a rate that was 3.2-fold higher than that of only GFP-expressing control cells, whereas the respiratory burst of dominant negative LIMK1(D460A)-expressing cells decreased to 31% of that of the control cells. Phagocytic activity monitored by using Texas Red-labeled OZ was also decreased in the D460A-expressing cells. By immunoblotting using a specific anti-phosphorylated cofilin antibody, it was revealed that in the OZ-activated wild-type LIMK1-GFP-expressing cells, the phosphorylated cofilin increased by 2.3-fold, and that in the OZ-activated D460A-GFP-expressing cells, the phosphorylated cofilin decreased to 47% of that of only GFP-expressing cells (mock control). Furthermore, in the wild-type LIMK1-expressing cells, OZ-evoked increase in filamentous actin was markedly enhanced, whereas in the dominant negative LIMK1-expressing cells, the total level of F-actin was strongly suppressed. These results suggest that LIMK1 regulates the functions of phagocytes through phosphorylation of cofilin and enhances the formation of filamentous actin.

LIM kinases (LIMK1 and LIMK2) regulate actin cytoskeletal reorganization through cofilin phosphorylation downstream of distinct Rho family GTPases. Pak1 and ROCK, respectively, activate LIMK1 and LIMK2 downstream of Rac and Rho; however, an effector protein kinase for LIMKs downstream of Cdc42 remains to be defined. We now report evidence that LIMK1 and LIMK2 activities toward cofilin phosphorylation are stimulated in cells by the co-expression of myotonic dystrophy kinase-related Cdc42-binding kinase alpha (MRCKalpha), an effector protein kinase of Cdc42. In vitro, MRCKalpha phosphorylated the protein kinase domain of LIM kinases, and the site in LIMK2 phosphorylated by MRCKalpha proved to be threonine 505 within the activation segment. Expression of MRCKalpha induced phosphorylation of actin depolymerizing factor (ADF)/cofilin in cells, whereas MRCKalpha-induced ADF/cofilin phosphorylation was inhibited by the co-expression with the protein kinase-deficient form of LIM kinases. These results indicate that MRCKalpha phosphorylates and activates LIM kinases downstream of Cdc42, which in turn regulates the actin cytoskeletal reorganization through the phosphorylation and inactivation of ADF/cofilin.

LIM-kinase 1 (LIMK1) and LIM-kinase 2 (LIMK2) regulate actin cytoskeletal reorganization via cofilin phosphorylation downstream of distinct Rho family GTPases. We report our findings that ROCK, a downstream protein kinase of Rho, specifically activates LIMK2 but not LIMK1 downstream of RhoA. LIMK1 and LIMK2 activities toward cofilin phosphorylation were stimulated by co-expression with the active form of ROCK (ROCK-Delta3), whereas full-length ROCK selectively activates LIMK2 but not LIMK1. Activation of LIMK2 by RhoA was inhibited by Y-27632, a specific inhibitor of ROCK, but Rac1-mediated activation of LIMK1 was not. ROCK directly phosphorylated the threonine 505 residue within the activation segment of LIMK2 and markedly stimulated LIMK2 activity. A LIMK2 mutant with replacement of threonine 505 by valine abolished LIMK2 activities for cofilin phosphorylation and actin cytoskeletal changes, whereas replacement by glutamate enhanced the protein kinase activity and stress fiber formation by LIMK2. These results indicate that ROCK directly phosphorylates threonine 505 and activates LIMK2 downstream of RhoA and that this phosphorylation is essential for LIMK2 to induce actin cytoskeletal reorganization. Together with the finding that LIMK1 is regulated by Pak1, LIMK1 and LIMK2 are regulated by different protein kinases downstream of distinct Rho family GTPases.

Cofilin promotes the depolymerization of actin filaments, which is required for a variety of cellular responses such as the formation of lamellipodia and chemotaxis. Phosphorylation of cofilin on serine residue 3 is known to block these activities. We now report that neutrophils contain a protein kinase that selectively catalyzes the phosphorylation of cofilin on serine 3 (/=70%) and a nonspecific kinase that recognizes multiple sites in this protein. The selective serine 3 cofilin kinase binds to a deoxyribonuclease I affinity column, whereas the nonspecific cofilin kinase does not. Deoxyribonuclease I forms a very tight complex with actin, and deoxyribonuclease affinity columns have been utilized to identify a variety of proteins that interact with the cytoskeleton. The serine 3 cofilin kinase did not react with antibodies to LIM kinase 1 or 2, which can catalyze the phosphorylation of cofilin in other cell types. The activity of the serine 3 cofilin kinase was insensitive to a variety of selective antagonists of protein kinases but was blocked by staurosporine. This pattern of inhibition is similar to that observed for the kinase that is active with cofilin in intact neutrophils. Thus, neutrophils contain a protein kinase distinct from LIM kinase-1/2 that selectively recognizes serine 3 in cofilin.

The LIM domain comprising two zinc-finger motifs is found in a variety of proteins and has been proposed to direct protein-protein interactions. During the identification of protein kinase C (PKC)-interacting proteins by a yeast two-hybrid assay, a novel protein containing three LIM domains, designated ENH, was shown to associate with PKC in an isoform-specific manner. Deletion analysis demonstrated that any single LIM domain of ENH associates with the NH2-terminal region of PKC. ENH associated with PKC in COS-7 cells and was phosphorylated by PKC in vitro. Upon treatment of the cells with phorbol ester, ENH in the membrane fraction was translocated to the cytosol fraction in vivo. Other LIM domain-containing proteins, such as Enigma and LIM-kinase 1, also interacted with PKC through their LIM domains. These results suggest that the LIM domain is one of the targets of PKC and that the LIM-PKC interaction may shed light on undefined roles of LIM domain-containing proteins.

We previously isolated human cDNA coding for LIMK1 (LIM motif-containing protein kinase-1), a putative protein kinase containing two LIM motifs at the N terminus and an unusual protein kinase domain at the C terminus. In the present study, we isolated human cDNA encoding LIMK2, a second member of a LIMK family, with a domain structure similar to LIMK1 and 50% overall amino acid identity with LIMK1. The protein kinase domains of LIMK1 and LIMK2 are unique in that they contain an unusual sequence motif Asp-Leu-Asn-Ser-His-Asn in subdomain VIB and a highly basic insert between subdomains VII and VIII. Expression patterns of LIMK1 and LIMK2 mRNAs in human tissues differ significantly. Chromosomal localization of human LIMK1 and LIMK2 genes was assigned to 7q11.23 and 22q12, respectively, by fluorescence in situ hybridization. The Myc epitope-tagged LIMK1 and LIMK2 proteins transiently expressed in COS cells exhibited serine/threonine-specific kinase activity toward myelin basic protein and histone in in vitro kinase assay. Immunofluorescence and subcellular fractionation analysis revealed that Myc-tagged LIMK1 and LIMK2 were localized mainly in the cytoplasm. The “native” LIMK1 protein endogenously expressed in A431 epidermoid carcinoma cells also exhibited serine/threonine kinase activity. The specific activity of native LIMK1 from A431 cells was apparently much higher than that of “recombinant” LIMK1 ectopically expressed in COS cells, hence, it is likely that there is a mechanism, by which native LIMK1 is activated. A 140-kDa tyrosine-phosphorylated protein (pp140) was co-immunoprecipitated with native LIMK1 from A431 cell lysates; therefore, pp140 may be a LIMK1-associated protein involved in the regulation of LIMK1 function.