Physical and functional association of migfilin with cell-cell adhesions

Migfilin: Cell Adhesion Effect and Comorbidities

Cell adhesion manifests as cell linkages to neighboring cells and/or the extracellular matrix (ECM). Migfilin is a widely expressed adhesion protein. It comprises three LIM domains in the C-terminal region and one proline-rich sequence in the N-terminal region. Through interplay with its various binding partners, such as Kindlin-2, Filamin, vasodilator-stimulated phosphoprotein (VASP) protein and the transcription factor CSX, Migfilin facilitates the dynamic association of connecting actomyosin fibers, orchestrating cell morphogenetic movement and cell adhesion, proliferation, migration, invasion, differentiation and signal transduction. In this review, to further elucidate the functional contributions of and pathogenesis induced by Migfilin, we focused on the structure of Migfilin and the targets which it directly binds with. We also summarized the role of Migfilin and its binding partners in the progression of different diseases and malignancies. As a possible candidate for coordinating various cellular processes and because of its association with both the pathogenesis and progression of certain tumors, Migfilin likely has utility as a therapeutic target against multiple diseases in the clinic.

Update on the genetics of nonbacterial osteomyelitis in humans

PURPOSE OF REVIEW

To summarize the current advances in our understanding or the genetic basis of nonbacterial osteomyelitis.

RECENT FINDINGS

Chronic recurrent multifocal osteomyelitis (CRMO) is a complex genetic disorder. Past discoveries identified several single gene defects (LPIN2, Pstpip2 and IL1RN) that cause IL-1-mediated sterile multifocal osteomyelitis. Recently Lorden et al.'s studies show that LIPIN2 deficiency can activate the NLRP3 inflammasome through alterations in the function of P2X7 receptor providing evidence that Majeed syndrome is an NLRP3 inflammasomopathy. New gene discoveries include the identification of FBLIM1 as a CRMO susceptibility gene. Mutations in FBLIM1 were found in a consanguineous family with CRMO. Fblim1 is one of the most significantly differentially expressed gene in bone from chronic multifocal osteomyelitis (cmo) mice, plays a role in IL-10-driven anti-inflammatory responses, and is involved in the physiology of bone remodeling. Lastly, new data on the putative CRMO susceptibility locus on chromosome 18 is presented here. Using Sanger sequencing, rather than microsatellite analysis, the DS18S60 susceptibility region could not be replicated in a larger cohort.

SUMMARY

CRMO occurs in humans, nonhuman primates, dogs and mice. There is a genetic component to disease but the genetic basis has only been identified for a small percentage of all cases.

First approaches for the transplantation of hepatocytes from Wistar rat preneoplastic livers into healthy recipients

BACKGROUND

the shortage of donors of hepatocyte transplantation therapy led to the use of so-called marginal donors. Some donors may have a hepatic illnesses that is associated with hepatic preneoplasia with foci of altered hepatocytes (FAH).

AIMS

to determine whether recipients developed FAH upon transplantation with hepatocytes from a preneoplastic liver and whether FAH progresses to a preneoplastic hepatocyte-derived tumor (PHDT), up to 60 days after transplantation.

MATERIAL AND METHODS

male Wistar adult rats were used as donors and recipients. Donors underwent a 2-phase model of liver preneoplasia for hepatocyte isolation. Recipients underwent a partial two thirds hepatectomy and received 150,000 hepatocytes. Recipients were euthanized seven and 60 days after transplantation. The number of FAH per liver area, percentage of liver occupied by FAH, the hepatic enzymatic profile, the percentage of prothrombin time (PT), the proliferative index (PI) and liver morphology were analyzed.

RESULTS

recipients developed few and very isolated FAH. No statistical differences were found between hepatic enzyme activities and PT. There were no differences between the groups with regard to the number of FAH per liver area and percentage of liver occupied by FAH after 60 days. The PI decreased on day 60 compared to day seven. No morphological alterations were found.

CONCLUSIONS

recipients developed few FAH that did not increase in number or size, nor did they progress to PHDT and had normal plasma biochemical features and liver morphology up to 60 days post-transplant. Additional studies are needed to determine whether FAH development constitutes a risk for recipients while waiting for whole organ transplant.

FBLIM1 enhances oral cancer malignancy via modulation of the epidermal growth factor receptor pathway

Filamin-binding LIM protein 1 (FBLIM1) is related to regulation of inflammatory responses, such as chronic recurrent multifocal osteomyelitis; however, the relevance of FBLIM1 in oral squamous cell carcinoma (OSCC) is unknown. The aim of the current study was to elucidate the possible role of FBLIM1 in the carcinogenesis of OSCC. We analyzed FBLIM1 expression using quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR), immunoblot analysis, and immunohistochemistry. The expression levels of FBLIM1 were up-regulated significantly (P < 0.05) in OSCC-derived cell lines and primary OSCCs specimens compared with normal counterparts. FBLIM1 expression also was correlated with the primary tumoral size (P < 0.05) and vascular invasion (P < 0.05). We then assessed tumoral progression after treatment with FBLIM1 siRNA and clopidogrel, an antiplatelet agent. Similar to the FBLIM1 knockdown effect, clopidogrel-treated cells had attenuated functions of proliferation, migration, and invasiveness. Interestingly, clopidogrel treatment led to down-regulation of epidermal growth factor receptor (EGFR) and FBLIM1. These findings identify FBLIM1 as a putative therapeutic target by using clopidogrel for inhibiting over activation of EGFR signaling to prevent OSCC malignancy.

circFBLIM1 act as a ceRNA to promote hepatocellular cancer progression by sponging miR-346

BACKGROUD

Accumulating evidences indicate that circular RNAs (circRNAs), a class of non-coding RNAs, play important roles in tumorigenesis. However, the function of circRNAs in hepatocellular cancer (HCC) is largely unknown.

METHODS

We performed circRNA microarrays to identify circRNAs that are aberrantly expressed in HCC tissues. Expression levels of a significantly upregulated circRNA, circFBLIM1, was detected by quantitative real-time PCR (qRT-PCR) in HCC cell lines and tissues. Then, we examined the functions of circFBLIM1 in HCC by cell proliferation, apoptosis, invasion and mouse xenograft assay. In addition, luciferase assay and RNA immunoprecipitation (RIP) assay were used to explore the miRNA sponge function of circFBLIM1 in HCC.

RESULTS

Microarray analysis and qRT-PCR verified a circRNA termed circFBLIM1 that was upregulated in HCC tissues and cell lines. Knockdown of circFBLIM1 inhibited proliferation, invasion and promoted apoptosis in HCC. Via luciferase reporter assays, circFBLIM1 and FBLIM1 were observed to directly bind to miR-346. Subsequent experiments showed that circFBLIM1 and FBLIM1 regulated the expression of each other by sponging miR-346.

CONCLUSIONS

Taken together, we conclude that circFBLIM1 may function as a competing endogenous RNA (ceRNA) to regulate FBLIM1 expression through sponging miR-346 to exert regulatory functions in HCC. circFBLIM1 may be a diagnostic biomarker and potential target for HCC therapy.

Possible involvement of a cell adhesion molecule, Migfilin, in brain development and pathogenesis of autism spectrum disorders

Migfilin, encoded by FBLIM1 at the 1p36 locus, is a multi-domain adaptor protein essential for various cellular processes such as cell morphology and migration. Small deletions and duplications at the 1p36 locus, monosomy of which results in neurodevelopmental disorders and multiple congenital anomalies, have also been identified in patients with autism spectrum disorder (ASD). However, the impact of FBLIM1, the gene within 1p36, on the pathogenesis of ASD is unknown. In this study, we performed morphological analyses of migfilin to elucidate its role in brain development. Migfilin was detected specifically in the embryonic and perinatal stages of the mouse brain. Either silencing or overexpression of migfilin in embryos following in utero electroporation disrupted Neocortical neuronal migration. Additionally, neurite elongation was impaired when migfilin was silenced in cultured mouse hippocampal neurons. We then screened FBLIM1 for rare exonic deletions/duplications in 549 Japanese ASD patients and 824 controls, detecting one case of ASD and intellectual delay that harbored a 26-kb deletion at 1p36.21 that solely included the C-terminal exon of FBLIM1. The FBLIM1 mRNA expression level in this case was reduced compared to levels in individuals without FBLIM1 deletion. Our findings indicate that tightly regulated expression of migfilin is essential for neuronal development and that FBLIM1 disruption may be related to the phenotypes associated with ASD and related neurodevelopmental disorders.

Recessive coding and regulatory mutations in FBLIM1 underlie the pathogenesis of chronic recurrent multifocal osteomyelitis (CRMO)

Chronic recurrent multifocal osteomyelitis (CRMO) is a rare, pediatric, autoinflammatory disease characterized by bone pain due to sterile osteomyelitis, and is often accompanied by psoriasis or inflammatory bowel disease. There are two syndromic forms of CRMO, Majeed syndrome and DIRA, for which the genetic cause is known. However, for the majority of cases of CRMO, the genetic basis is unknown. Via whole-exome sequencing, we detected a homozygous mutation in the filamin-binding domain of FBLIM1 in an affected child with consanguineous parents. Microarray analysis of bone marrow macrophages from the CRMO murine model (cmo) determined that the Fblim1 ortholog is the most differentially expressed gene, downregulated over 20-fold in the cmo mouse. We sequenced FBLIM1 in 96 CRMO subjects and found a second proband with a novel frameshift mutation in exon 6 and a rare regulatory variant. In SaOS2 cells, overexpressing the regulatory mutation showed the flanking region acts as an enhancer, and the mutation ablates enhancer activity. Our data implicate FBLIM1 in the pathogenesis of sterile bone inflammation and our findings suggest CRMO is a disorder of chronic inflammation and imbalanced bone remodeling.

Vasodilator-Stimulated Phosphoprotein (VASP) depletion from breast cancer MDA-MB-231 cells inhibits tumor spheroid invasion through downregulation of Migfilin, β-catenin and urokinase-plasminogen activator (uPA)

A hallmark of cancer cells is their ability to invade surrounding tissues and form metastases. Cell-extracellular matrix (ECM)-adhesion proteins are crucial in metastasis, connecting tumor ECM with actin cytoskeleton thus enabling cells to respond to mechanical cues. Vasodilator-stimulated phosphoprotein (VASP) is an actin-polymerization regulator which interacts with cell-ECM adhesion protein Migfilin, and regulates cell migration. We compared VASP expression in MCF-7 and MDA-MB-231 breast cancer (BC) cells and found that more invasive MDA-MB-231 cells overexpress VASP. We then utilized a 3-dimensional (3D) approach to study metastasis in MDA-MB-231 cells using a system that considers mechanical forces exerted by the ECM. We prepared 3D collagen I gels of increasing concentration, imaged them by atomic force microscopy, and used them to either embed cells or tumor spheroids, in the presence or absence of VASP. We show, for the first time, that VASP silencing downregulated Migfilin, β-catenin and urokinase plasminogen activator both in 2D and 3D, suggesting a matrix-independent mechanism. Tumor spheroids lacking VASP demonstrated impaired invasion, indicating VASP's involvement in metastasis, which was corroborated by Kaplan-Meier plotter showing high VASP expression to be associated with poor remission-free survival in lymph node-positive BC patients. Hence, VASP may be a novel BC metastasis biomarker.

Increased expression of kindlin-2 is correlated with hematogenous metastasis and poor prognosis in patients with clear cell renal cell carcinoma

Kindlin‐2 is involved in activating the integrin signaling pathway which plays an important role in regulating cancer cell invasion. However, the role of kindlin‐2 may vary among cancer types. The aim of this study was to explore the possible association between kindlin‐2 and clear cell renal cell carcinoma (ccRCC), and its potential role in the prognosis of ccRCC. Immunohistochemistry assays were used to examine kindlin‐2 expression levels in cancer tissues obtained from 336 patients with ccRCC. The correlation between kindlin‐2 expression levels and pathologic variables was then analyzed. In addition, the association between kindlin‐2 expression levels and survival time was analyzed by Kaplan–Meier survival curves and log‐rank tests. Of 336 ccRCC patients, 199 had high levels of kindlin‐2 expression, while 137 had low kindlin‐2 expression levels. Patients at a late stage of ccRCC (stage III or IV) were more likely to have high kindlin‐2 expression levels than those at an early stage (stage I or II) (χ² = 4.72, P = 0.03). Patients with high levels of kindlin‐2 expression had higher risk of hematogenous metastasis (χ² = 6.70, P = 0.01) than those with low levels of kindlin‐2 expression. In addition, the survival time was significantly shorter for patients with high levels of kindlin‐2 expression than for those with low levels of kindlin‐2 expression (P = 0.001 for overall survival [OS] and P = 0.002 for disease‐free survival [DFS]). Multivariate survival analysis based on the Cox proportional hazards model showed that high kindlin‐2 expression levels had a hazard risk (HR) of 1.76 for OS (95% CI 1.19–2.62, P = 0.005) and an HR of 1.47 for DFS (95% CI = 1.05–2.06, P = 0.026). By comparison, lymph node metastasis had an HR of 1.48 for OS (95% CI 1.04–2.10, P = 0.029) and an HR of 1.41 for DFS (95% CI 1.04–1.93, P = 0.029). This study provided strong evidence that increased kindlin‐2 expression might be involved in promoting tumor invasiveness and leading to a poor prognosis of ccRCC.

Converging and Unique Mechanisms of Mechanotransduction at Adhesion Sites

The molecular mechanisms by which physical forces control tissue development are beginning to be elucidated. Sites of adhesion between both cells and the extracellular environment [extracellular matrix (ECM) or neighboring cells] contain protein complexes capable of sensing fluctuations in tensile forces. Tension-dependent changes in the dynamics and composition of these complexes mark the transformation of physical input into biochemical signals that defines mechanotransduction. It is becoming apparent that, although the core constituents of these different adhesions are distinct, principles and proteins involved in mechanotransduction are conserved. Here, we discuss the current knowledge of overlapping and distinct aspects of mechanotransduction between integrin and cadherin adhesion complexes.

Experimental evidence of Migfilin as a new therapeutic target of hepatocellular carcinoma metastasis

Migfilin is a novel cell-matrix adhesion protein known to interact with Vasodilator Stimulated Phosphoprotein (VASP) and be localized both at cell-matrix and cell-cell adhesions. To date there is nothing known about its role in hepatocellular carcinoma (HCC). As matrix is important in metastasis, we aimed to investigate the Migfilin׳s role in HCC metastasis using two human HCC cell lines that differ in their metastatic potential; non-invasive Alexander cells and the highly invasive HepG2 cells. We silenced Migfilin by siRNA and studied its effect on signaling and metastasis-related cellular properties. We show that Migfilin׳s expression is elevated in HepG2 cells and its silencing leads to upregulation of actin reorganization-related proteins, namely phosphor-VASP (Ser157 and Ser239), Fascin-1 and Rho-kinase-1, promoting actin polymerization and inhibiting cell invasion. Phosphor-Akt (Ser473) is decreased contributing to the upregulation of free and phosphor-β-catenin (Ser33/37Thr41) and inducing proliferation. Migfilin elimination upregulates Extracellular Signal-regulated kinase, which increases cell adhesion in HepG2 and reduces invasiveness. This is the first study to reveal that Migfilin inhibition can halt HCC metastasis in vitro, providing the molecular mechanism involved and presenting Migfilin as potential therapeutic target against HCC metastasis.

Selective miRNA expression profile in chronic myeloid leukemia K562 cell-derived exosomes

BACKGROUND

Chronic myeloid leukemia (CML) is a myeloproliferative disorder of hematopoietic stem cell scarrying the Philadelphia (Ph) chromosome and an oncogenic BCR-ABL1 fusion gene. The tyrosine kinase inhibitor (TKI) of BCR-ABL1 kinase is a treatment of choice for control of CML.

OBJECTIVE

Recent studies have demonstrated that miRNAs within exosomes from cancer cells play crucial roles in initiation and progression. This study was performed to assess miRNAs within exosomes of K562 cells.

METHODS

miRNA microarray analysis of K562 cells and K562 cell-derived exosomes was conducted with the 6th generation miRCURYTM LNA Array (v.16.0). Gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were also carried out. GO terms and signaling pathways were categorized into 66 classes (including homophilic cell adhesion, negative regulation of apoptotic process, cell adhesion) and 26 signaling pathways (such as Wnt).

RESULTS

In exosomes, 49 miRNAs were up regulated as compared to K562 cells, and two of them were further confirmed by quantitative real-time PCR. There are differentially expressed miRNAs between K562 cell derived-exosomes and K562 cells.

CONCLUSION

Selectively expressed miRNAs in exosomes may promote the development of CML via effects on interactions (e.g. adhesion) of CML cells with their microenvironment.

Kindlin binds migfilin tandem LIM domains and regulates migfilin focal adhesion localization and recruitment dynamics

Focal adhesions (FAs), sites of tight adhesion to the extracellular matrix, are composed of clusters of transmembrane integrin adhesion receptors and intracellular proteins that link integrins to the actin cytoskeleton and signaling pathways. Two integrin-binding proteins present in FAs, kindlin-1 and kindlin-2, are important for integrin activation, FA formation, and signaling. Migfilin, originally identified in a yeast two-hybrid screen for kindlin-2-interacting proteins, is a LIM domain-containing adaptor protein found in FAs and implicated in control of cell adhesion, spreading, and migration. By binding filamin, migfilin provides a link between kindlin and the actin cytoskeleton. Here, using a combination of kindlin knockdown, biochemical pulldown assays, fluorescence microscopy, fluorescence resonance energy transfer (FRET), and fluorescence recovery after photobleaching (FRAP), we have established that the C-terminal LIM domains of migfilin dictate its FA localization, shown that these domains mediate an interaction with kindlin in vitro and in cells, and demonstrated that kindlin is important for normal migfilin dynamics in cells. We also show that when the C-terminal LIM domain region is deleted, then the N-terminal filamin-binding region of the protein, which is capable of targeting migfilin to actin-rich stress fibers, is the predominant driver of migfilin localization. Our work details a correlation between migfilin domains that drive kindlin binding and those that drive FA localization as well as a kindlin dependence on migfilin FA recruitment and mobility. We therefore suggest that the kindlin interaction with migfilin LIM domains drives migfilin FA recruitment, localization, and mobility.

Mechanosensitivity and compositional dynamics of cell-matrix adhesions

Cells perceive information about the biochemical and biophysical properties of their tissue microenvironment through integrin-mediated cell-matrix adhesions, which connect the cytoskeleton with the extracellular matrix and thereby allow cohesion and long-range mechanical connections within tissues. The formation of cell-matrix adhesions and integrin signalling involves the dynamic recruitment and assembly of an inventory of proteins, collectively termed the 'adhesome', at the adhesive site. The recruitment of some adhesome proteins, most notably the Lin11-, Isl1- and Mec3-domain-containing proteins, depends on mechanical tension generated by myosin II-mediated contractile forces exerted on cell-matrix adhesions. When exposed to force, mechanosensitive adhesome proteins can change their conformation or expose cryptic-binding sites leading to the recruitment of proteins, rearrangement of the cytoskeleton, reinforcement of the adhesive site and signal transduction. Biophysical methods and proteomics revealed force ranges within the adhesome and cytoskeleton, and also force-dependent changes in adhesome composition. In this review, we provide an overview of the compositional dynamics of cell-matrix adhesions, discuss the most prevalent functional domains in adhesome proteins and review literature and concepts about mechanosensing mechanisms that operate at the adhesion site.

Migfilin sensitizes cisplatin-induced apoptosis in human glioma cells in vitro

AIM

Filamin binding LIM protein 1, also known as migfilin, is a skeleton organization protein that binds to mitogen-inducible gene 2 at cell-extracellular matrix adhesions. The aim of this study was to investigate the role of migfilin in cisplatin-induced apoptosis in human glioma cells, to determine the functional domains of migfilin, and to elucidate the molecular mechanisms underlying the regulation of cisplatin-related chemosensitivity.

METHODS

The human glioma cell lines Hs683, H4, and U-87 MG were transfected with pEGFP-C2-migfilin to elevate the expression level of migfilin. RNA interference was used to reduce the expression of migfilin. To determine the functional domains of migfilin, U-87 MG cells were transfected with plasmids of migfilin deletion mutants. After treatment with cisplatin (40 μmol/L) for 24 h, the cell viability was assessed using the MTS assay, and the cell apoptotic was examined using the DAPI staining assay and TUNEL analysis. Expression levels of apoptosis-related proteins were detected by Western blot analysis.

RESULTS

Overexpression of migfilin significantly enhanced cisplatin-induced apoptosis in Hs683, H4, and U-87 MG cells, whereas downregulation of migfilin expression inhibited the chemosensitivity of these cell lines. The N-terminal region of migfilin alone was able to enhance the cisplatin-induced apoptosis. However, despite the existence of the N-terminal region, mutants of migfilin with any one of three LIM domains deleted led to a function loss. Furthermore, apoptotic proteins (PARP and caspase-3) and the anti-apoptotic protein Bcl-xL were modulated by the expression level of migfilin in combination with cisplatin.

CONCLUSION

The LIM1-3 domains of migfilin play a key role in sensitizing glioma cells to cisplatin-induced apoptosis through regulation of apoptosis-related proteins.

Critical role of filamin-binding LIM protein 1 (FBLP-1)/migfilin in regulation of bone remodeling

Bone remodeling is a complex process that must be precisely controlled to maintain a healthy life. We show here that filamin-binding LIM protein 1 (FBLP-1, also known as migfilin), a kindlin- and filamin-binding focal adhesion protein, is essential for proper control of bone remodeling. Genetic inactivation of FBLIM1 (the gene encoding FBLP-1) in mice resulted in a severe osteopenic phenotype. Primary FBLP-1 null bone marrow stromal cells (BMSCs) exhibited significantly reduced extracellular matrix adhesion and migration compared with wild type BMSCs. Loss of FBLP-1 significantly impaired the growth and survival of BMSCs in vitro and decreased the number of osteoblast (OB) progenitors in bone marrow and OB differentiation in vivo. Furthermore, the loss of FBLP-1 caused a dramatic increase of osteoclast (OCL) differentiation in vivo. The level of receptor activator of nuclear factor κB ligand (RANKL), a key regulator of OCL differentiation, was markedly increased in FBLP-1 null BMSCs. The capacity of FBLP-1 null bone marrow monocytes (BMMs) to differentiate into multinucleated OCLs in response to exogenously supplied RANKL, however, was not different from that of WT BMMs. Finally, we show that a loss of FBLP-1 promotes activating phosphorylation of ERK1/2. Inhibition of ERK1/2 activation substantially suppressed the increase of RANKL induced by the loss of FBLP-1. Our results identify FBLP-1 as a key regulator of bone homeostasis and suggest that FBLP-1 functions in this process through modulating both the intrinsic properties of OB/BMSCs (i.e., BMSC-extracellular matrix adhesion and migration, cell growth, survival, and differentiation) and the communication between OB/BMSCs and BMMs (i.e., RANKL expression) that controls osteoclastogenesis.

The diverse biofunctions of LIM domain proteins: determined by subcellular localization and protein-protein interaction

The LIM domain is a cysteine- and histidine-rich motif that has been proposed to direct protein-protein interactions. A diverse group of proteins containing LIM domains have been identified, which display various functions including gene regulation and cell fate determination, tumour formation and cytoskeleton organization. LIM domain proteins are distributed in both the nucleus and the cytoplasm, and they exert their functions through interactions with various protein partners.

Kindlin-2: a novel adhesion protein related to tumor invasion, lymph node metastasis, and patient outcome in gastric cancer

BACKGROUND

Kindlin-2 has been confirmed as an essential element of bidirectional integrin signaling. In recent years, the relationship between Kindlin-2 expression and cancers has been a focus of interest. However, the relationship between Kindlin-2 expression in gastric cancer and tumor invasion, metastasis, and the outcome of patients have not been studied.

METHODS

Kindlin-2 expression at protein and RNA levels were detected by Western blot and real-time polymerase chain reaction in 40 pairs of gastric cancer samples. In addition, the correlations between Kindlin-2 expression and clinicopathologic factors as well as the prognosis of the patients were analyzed. Multivariate Cox regression was used to study the effect of Kindlin-2 expression on overall and progression-free survival.

RESULTS

We found that Kindlin-2 was up-regulated both at RNA (P = .027) and protein levels (P = .014) in gastric cancer tissues. Tumor samples with high Kindlin-2 expression (Kindlin-2/β-actin:tumor tissue/paraneoplastic tissue, ≥2) was observed in 55% of the patients. Moreover, Kindlin-2 expression had a significant positive correlation with tumor stromal invasion (P = .014), lymph node metastasis (P = .007), and TNM stage (P = .014). Patients with high Kindlin-2 expression had significantly poorer overall survival (P = .012) and progression-free survival (P = .012). High Kindlin-2 expression was an independent risk factor of progression-free survival (hazard ratio, 5.2; 95% confidence interval, 1.1-3.3; P = .032).

CONCLUSIONS

Kindlin-2 may play an important role in the development of gastric cancer and it is a potential factor that could be used to evaluate the outcome of gastric cancer. Kindlin-2 may shed new light on evaluating the prognosis and targeted therapy of gastric cancer.

Quantitative proteomics of the integrin adhesome show a myosin II-dependent recruitment of LIM domain proteins

A characteristic of integrins is their ability to transfer chemical and mechanical signals across the plasma membrane. Force generated by myosin II makes cells able to sense substrate stiffness and induce maturation of nascent adhesions into focal adhesions. In this paper, we present a comprehensive proteomic analysis of nascent and mature adhesions. The purification of integrin adhesion complexes combined with quantitative mass spectrometry enabled the identification and quantification of known and new adhesion-associated proteins. Furthermore, blocking adhesion maturation with the myosin II inhibitor blebbistatin markedly impaired the recruitment of LIM domain proteins to integrin adhesion sites. This suggests a common recruitment mechanism for a whole class of adhesion-associated proteins, involving myosin II and the zinc-finger-type LIM domain.

Loss of migfilin expression has no overt consequences on murine development and homeostasis

Migfilin is a LIM-domain-containing protein of the zyxin family of adaptor proteins and is found at cell-matrix and cell-cell adhesion sites and in the nucleus. In vitro studies have suggested that migfilin promotes β1 integrin activity, regulates cell spreading and migration and induces cardiomyocyte differentiation. To test directly the function of migfilin in vivo, we generated a migfilin-null mouse strain. Here, we report that loss of migfilin expression permits normal development and normal postnatal aging. Fibroblasts and keratinocytes from migfilin-null mice display normal spreading and adhesion, and normal integrin expression and activation. The migration velocity and directionality of migfilin-null embryonic fibroblasts were normal, whereas the velocity of migfilin-null keratinocytes in wound scratch assays was slightly but significantly reduced. Our findings indicate that the roles of migfilin are functionally redundant during mouse development and tissue homeostasis.

GLI1 facilitates the migration and invasion of pancreatic cancer cells through MUC5AC-mediated attenuation of E-cadherin

The Krüppel-like zinc-finger protein GLI1 functions as a downstream transcription factor of Hedgehog signaling and plays a pivotal role in the cellular proliferation of many types of tumors, including pancreatic ductal adenocarcinoma (PDA). PDA develops from dysplastic lesions called pancreatic intraepithelial neoplasia (PanIN) through a multistep carcinogenesis process that changes its cellular characteristics, including a mucin expression profile. Increased expression of a gel-forming mucin, MUC5AC, was previously revealed as a major biomarker for the poor prognosis of PDA patients, but the molecular mechanisms responsible for its expression and correlation with poor prognosis are not fully understood. Here we show that MUC5AC is a direct transcriptional target of GLI1 in PDA cells. Overexpression of GLI1 enhanced MUC5AC expression, and a double knockdown of GLI1 and GLI2 suppressed endogenous MUC5AC expression in PDA cells. Luciferase reporter assays revealed that GLI1 and GLI2 can activate the MUC5AC promoter through its conserved CACCC-box-like cis-regulatory elements. We also found that GLI1-upregulated MUC5AC was expressed in the intercellular junction between cultured PDA cells and interfered with the membrane localization of E-cadherin, leading to decreased E-cadherin-dependent cell-cell adhesion and promoting the migration and invasion of PDA cells. Consistently, GLI1 induced the nuclear accumulation and target gene expression of β-catenin in a MUC5AC-dependent manner. Finally, immunohistochemical analysis revealed that GLI1 expression statistically correlated with MUC5AC expression and also with altered subcellular localization of E-cadherin and β-catenin in PanIN lesions and PDA. This evidence revealed a new aspect of GLI1 function in modulating E-cadherin/β-catenin-regulated cancer cell properties through the expression of a gel-forming mucin.

Reversion-induced LIM interaction with Src reveals a novel Src inactivation cycle

Aberrant Src activation plays prominent roles in cancer progression. However, how Src is activated in cancer cells is largely unknown. Genetic Src-activating mutations are rare and, therefore, are insufficient to account for Src activation commonly found in human cancers. In this study, we show that reversion-induced LIM (RIL), which is frequently lost in colon and other cancers as a result of epigenetic silencing, suppresses Src activation. Mechanistically, RIL suppresses Src activation through interacting with Src and PTPL1, allowing PTPL1-dependent dephosphorylation of Src at the activation loop. Importantly, the binding of RIL to Src is drastically reduced upon Src inactivation. Our results reveal a novel Src inactivation cycle in which RIL preferentially recognizes active Src and facilitates PTPL1-mediated inactivation of Src. Inactivation of Src, in turn, promotes dissociation of RIL from Src, allowing the initiation of a new Src inactivation cycle. Epigenetic silencing of RIL breaks this Src inactivation cycle and thereby contributes to aberrant Src activation in human cancers.

Expression of integrin-linked kinase and its binding partners in chondrosarcoma: association with prognostic significance

Integrin-linked kinase (ILK) and its binding partners alpha-parvin, beta-parvin, Mig-2 and Migfilin are important components of the cell-matrix adhesions implicated in cell motility, growth, survival and ultimately carcinogenesis. Herein, we investigated immunohistochemically the expression of these molecules in cartilaginous neoplasms and explored their involvement in chondrosarcoma pathobiology and behaviour. Our analyses revealed that ILK, alpha-parvin, beta-parvin and Mig-2 are expressed in the majority of chondrosarcomas but in a small proportion of enchondromas, implying that these proteins might have a role in the development and progression of chondrogenic neoplasms. Moreover, our findings highlight the possibilities that ILK might serve as biological marker that could accurately predict a high-grade tumour and that Mig-2 may function as a promising prognostic indicator of high-risk patients.

Role of Ena/VASP proteins in homeostasis and disease

The actin cytoskeleton is required for many important processes during embryonic development. In later stages of life, important homeostatic processes depend on the actin cytoskeleton, such as immune response, haemostasis and blood vessel preservation. Therefore, the function of the actin cytoskeleton must be tightly regulated, and aberrant regulation may cause disease. A growing number of proteins have been described to bind and regulate the actin cytoskeleton. Amongst them, Ena/VASP proteins function as anti-capping proteins, thereby directly modulating the actin ultrastructure. Ena/VASP function is regulated by their recruitment into protein complexes downstream of plasma membrane receptors and by phosphorylation. As regulators of the actin ultrastructure, Ena/VASP proteins are involved in crucial cellular functions, such as shape change, adhesion, migration and cell-cell interaction and hence are important targets for therapeutic intervention. In this chapter, we will first describe the structure, function and regulation of Ena/VASP proteins. Then, we will review the involvement of Ena/VASP proteins in the development of human diseases. Growing evidence links Ena/VASP proteins to important human diseases, such as thrombosis, cancer, arteriosclerosis, cardiomyopathy and nephritis. Finally, present and future perspectives for the development of therapeutic molecules interfering with Ena/VASP-mediated protein-protein interactions are presented.

Increased cytoplasmic level of migfilin is associated with higher grades of human leiomyosarcoma

AIMS

Leiomyosarcomas (LMS) are malignant neoplasms composed of cells that exhibit distinct smooth muscle differentiation. The molecular and cytogenetic features of LMS are complex and no consistent aberrations have been reported to date. Mitogen inducible gene-2 (Mig-2), kindlin and migfilin are recently identified cell-matrix adhesion proteins. The aim was to determine the expression and distribution of these proteins in human smooth muscle tumours of somatic soft tissue.

METHODS AND RESULTS

Immunohistochemistry was performed on a human LMS tissue microarray and on sections of human leiomyomas (LM) and normal smooth muscle. Migfilin was barely detectable in normal smooth muscle cells, whereas increased levels of migfilin were observed in the majority of LM and LMS. Furthermore, the cytoplasmic level of migfilin was strongly associated with higher tumour grades. Additionally, the cytoplasmic levels of migfilin and Mig-2 were correlated with each other, suggesting an association between the two in the cytoplasm. Kindlin was expressed in normal smooth muscle, LM and LMS, and its level did not correlate with tumour grade.

CONCLUSIONS

Our results suggest a role for cytoplasmic migfilin in the progression of LMS and identify cytoplasmic migfilin as a potentially important biological marker for human LMS progression.

The MIG-2/integrin interaction strengthens cell-matrix adhesion and modulates cell motility

Integrin-mediated cell-matrix adhesion plays an important role in control of cell behavior. We report here that MIG-2, a widely expressed focal adhesion protein, interacts with beta1 and beta3 integrin cytoplasmic domains. Integrin binding is mediated by a single site within the MIG-2 FERM domain. Functionally, the MIG-2/integrin interaction recruits MIG-2 to focal adhesions. Furthermore, using alphaIIbbeta3 integrin-expressing Chinese hamster ovary cells, a well described model system for integrin activation, we show that MIG-2 promotes integrin activation and enhances cell-extracellular matrix adhesion. Although MIG-2 is expressed in many cell types, it is deficient in certain colon cancer cells. Expression of MIG-2, but not of an integrin binding-defective MIG-2 mutant, in MIG-2-null colon cancer cells strengthened cell-matrix adhesion, promoted focal adhesion formation, and reduced cell motility. These results suggest that the MIG-2/integrin interaction is an important element in the cellular control of integrin-mediated cell-matrix adhesion and that loss of this interaction likely contributes to high motility of colon cancer cells.

Use of an aggressive MCF-7 cell line variant, TMX2-28, to study cell invasion in breast cancer

An estrogen receptor-negative variant of the MCF-7 breast cancer cell line, TMX2-28, was used as a model in which to study breast cancer cell invasion. Using a reconstituted basement membrane (Matrigel) assay to evaluate cell invasion, we determined that TMX2-28 cells are more invasive than MCF-7 cells and that the invasiveness of TMX2-28 is similar to that of the aggressive MDA-MB-231 breast cancer cell line. TMX2-28 cells displayed a rounded, epithelial cell-like morphology, suggesting an amoeboid mode of cell invasion, in contrast to the mesenchymal mode of invasion characteristic of spindle-shaped, fibroblast-like MDA-MB-231 cells. Using real-time reverse transcription-PCR, we found that mitogen-inducible gene 2 (MIG2) is expressed at a 17-fold higher level in TMX2-28 cells than in nonaggressive MCF-7 cells and that MIG2 mRNA levels are low in the nontumorigenic human mammary epithelial cell line, 184. We determined that MIG2 plays a role in cell invasion by using small interfering RNA (siRNA) to suppress the expression of MIG2 mRNA levels in TMX2-28 cells. TMX2-28 cell invasion was reduced by 48% when the cells were transfected with siRNAs targeting MIG2, relative to cells transfected with siRNAs against glyceraldehyde-3-phosphate dehydrogenase. Finally, MIG2 expression was evaluated in reductive mammoplasty and breast tumor tissue. Although all 21 normal tissues from reduction mammoplasty showed immunoreactivity for MIG2, ranging from weak (62%) to strong (24%), only half of the 34 formalin-fixed breast tumors showed immunoreactivity for MIG2. Of these 17 positive cases, 10 were considered to overexpress MIG2 (moderate to strong staining). Examination of 30 frozen breast tumors supported the finding that MIG2 is overexpressed in a subset of breast cancers. We suggest that MIG2's normal regulation and function are disrupted in breast cancer.

Kindlin-1 is a phosphoprotein involved in regulation of polarity, proliferation, and motility of epidermal keratinocytes

A novel family of focal adhesion proteins, the kindlins, is involved in attachment of the actin cytoskeleton to the plasma membrane and in integrin-mediated cellular processes. Deficiency of kindlin-1, as a result of loss-of-function mutations in the KIND1 gene, causes Kindler syndrome, an autosomal recessive genodermatosis characterized by skin blistering, progressive skin atrophy, photosensitivity and, occasionally, carcinogenesis. Here we characterized authentic and recombinantly expressed kindlin-1 and show that it is localized in basal epidermal keratinocytes in a polar fashion, close to the cell surface facing the basement membrane, in the areas between the hemidesmosomes. We identified two forms of kindlin-1 in keratinocytes, with apparent molecular masses of 78 and 74 kDa, corresponding to phosphorylated and desphosphorylated forms of the protein. In kindlin-1-deficient skin, basal keratinocytes show multiple abnormalities: cell polarity is lost, proliferation is strongly reduced, and several cells undergo apoptosis. In vitro, deficiency of kindlin-1 in keratinocytes leads to strongly reduced cell proliferation, decreased adhesion, undirected motility, and intense protrusion activity of the plasma membrane. Taken together, these results show that kindlin-1 plays a role in keratinocyte adhesion, polarization, proliferation, and migration. It is involved in organization and anchorage of the actin cytoskeleton to integrin-associated signaling platforms.

The Kindlins: subcellular localization and expression during murine development

The three Kindlins are a novel family of focal adhesion proteins. The Kindlin-1 (URP1) gene is mutated in Kindler syndrome, the first skin blistering disease affecting actin attachment in basal keratinocytes. Kindlin-2 (Mig-2), the best studied member of this family, binds ILK and Migfilin, which links Kindlin-2 to the actin cytoskeleton. Kindlin-3 is expressed in hematopoietic cells. Here we describe the genomic organization, gene expression and subcellular localization of murine Kindlins-1 to -3. In situ hybridizations showed that Kindlin-1 is preferentially expressed in epithelia, and Kindlin-2 in striated and smooth muscle cells. Kindlins-1 and -2 are both expressed in the epidermis. While both localize to integrin-mediated adhesion sites in cultured keratinocytes Kindlin-2, but not Kindlin-1, colocalizes with E-cadherin to cell-cell contacts in differentiated keratinocytes. Using a Kindlin-3-specific antiserum and an EGFP-tagged Kindlin-3 construct, we could show that Kindlin-3 is present in the F-actin surrounding ring structure of podosomes, which are specialized adhesion structures of hematopoietic cells.

Migfilin interacts with vasodilator-stimulated phosphoprotein (VASP) and regulates VASP localization to cell-matrix adhesions and migration

Cell migration is a complex process that is coordinately regulated by cell-matrix adhesion and actin cytoskeleton. We report here that migfilin, a recently identified component of cell-matrix adhesions, is a biphasic regulator of cell migration. Loss of migfilin impairs cell migration. Surprisingly, overexpression of migfilin also reduces cell migration. Molecularly, we have identified vasodilator-stimulated phosphoprotein (VASP) as a new migfilin-binding protein. The interaction is mediated by the VASP EVH1 domain and a single L104PPPPP site located within the migfilin proline-rich domain. Migfilin and VASP form a complex in both suspended and adhered cells, and in the latter, they co-localize in cell-matrix adhesions. Functionally, migfilin facilitates VASP localization to cell-matrix adhesions. Using two different approaches (VASP-binding defective migfilin mutants and small interfering RNA-mediated VASP knockdown), we show that the interaction with VASP is crucially involved in migfilin-mediated regulation of cell migration. Our results identify migfilin as an important regulator of cell migration and provide new information on the mechanism by which migfilin regulates this process.

Migfilin and its binding partners: from cell biology to human diseases

Links between the plasma membrane and the actin cytoskeleton are essential for maintaining tissue integrity and for controlling cell morphology and behavior. Studies over the past several decades have identified dozens of components of such junctions. One of the most recently identified is migfilin, a widely expressed protein consisting of an N-terminal filamin-binding domain, a central proline-rich domain and three C-terminal LIM domains. Migfilin is recruited to cell-matrix contacts in response to adhesion and colocalizes with β-catenin at cell-cell junctions in epithelial and endothelial cells. Migfilin also travels from the cytoplasm into the nucleus, a process that is regulated by RNA splicing and calcium signaling. Through interactions with multiple binding partners, including Mig-2, filamin and VASP, migfilin links the cell adhesion structures to the actin cytoskeleton. It regulates actin remodeling, cell morphology and motility. In nuclei, migfilin interacts with the cardiac transcriptional factor CSX/NKX2-5 and promotes cardiomyocyte differentiation. It probably functions as a key regulator both at cell adhesion sites and nuclei, coordinating multiple cellular processes, and is implicated in the pathogenesis of several human diseases.

Assembly and Signaling of Adhesion Complexes

Cell-extracellular matrix (ECM) adhesion is crucial for control of cell behavior. It connects the ECM to the intracellular cytoskeleton and transduces bidirectional signals between the extracellular and intracellular compartments. The subcellular machinery that mediates cell-ECM adhesion and signaling is complex. It consists of transmembrane proteins (e.g., integrins) and at least several dozens of membrane-proximal proteins that assemble into a network through multiple protein interactions. Furthermore, despite sharing certain common components, cell-ECM adhesions exhibit considerable heterogeneity in different types of cells (e.g., the cell-ECM adhesions in cardiac myocytes are considerably different from those in fibroblasts). Here, we will first briefly describe the general properties of the integrin-mediated cell-ECM adhesion and signal transduction. Next, we will focus on one of the recently discovered cell-ECM adhesion protein complexes consisting of PINCH, integrin-linked kinase (ILK), and Parvin and use it as an example to illustrate the molecular basis underlying the assembly and functions of cell-ECM adhesions. Finally, we will discuss in detail the structure and regulation of cell-ECM adhesion complexes in cardiac myocytes, which illustrate the importance and complexity of the cell-ECM adhesion structures in organogenesis and diseases.