Lasp-1, a Novel Type of Actin-Binding Protein Accumulating in Cell Membrane Extensions

Tandem LIM domain-containing proteins, LIMK1 and LMO1, directly bind to force-bearing keratin intermediate filaments

The cytoskeleton of the cell is constantly exposed to physical forces that regulate cellular functions. Selected members of the LIM (Lin-11, Isl-1, and Mec-3) domain-containing protein family accumulate along force-bearing actin fibers, with evidence supporting that the LIM domain is solely responsible for this force-induced interaction. However, LIM domain's force-induced interactions are not limited to actin. LIMK1 and LMO1, both containing only two tandem LIM domains, are recruited to force-bearing keratin fibers in epithelial cells. This unique recruitment is mediated by their LIM domains and regulated by the sequences outside the LIM domains. Based on in vitro reconstitution of this interaction, LIMK1 and LMO1 directly interact with stretched keratin 8/18 fibers. These results show that LIM domain's mechano-sensing abilities extend to the keratin cytoskeleton, highlighting the diverse role of LIM proteins in force-regulated signaling.

Cholesterol uptake in the intestine is regulated by the LASP1-AKT-NPC1L1 signaling pathway

Cholesterol is essential for the stability and architecture of the plasma membrane and a precursor of bile acids and steroid hormones in mammals. Excess dietary cholesterol uptake leads to hypercholesterolemia and atherosclerosis and plays a role in cancer development. The role of actin-binding scaffolding protein LIM and SH3 protein 1 (LASP1) in cholesterol trafficking has not been investigated previously. Cholesterol levels, its uptake, and excretion were studied in mice deficient for low-density lipoprotein receptor and Lasp1 (Ldlr-/-Lasp1-/- mice) upon feeding a high-fat diet, and in LASP1-knockdown, differentiated human intestinal epithelial CaCo-2 cells. When compared with diet-fed Ldlr-/- control mice, Ldlr-/-Lasp1-/- mice displayed a reduction in serum cholesterol levels. Mechanistically, we identified a new role of LASP1 in controlling the translocation of the intestinal cholesterol transporter Niemann-Pick C1-like 1 (NPC1L1) to the apical cell surface, which was limited in LASP1-knockdown human CaCo-2 enterocytes and in the intestine of Ldlr-/- Lasp1-/- compared with Ldlr-/- mice, linked to LASP1-pAKT signaling but not CDC42 activation. In line, a reduction in cholesterol reabsorption was noted in LASP1-knockdown CaCo-2 cells in vitro, and an enhanced cholesterol excretion via the feces was observed in Ldlr-/- Lasp1-/- mice. These data uncover a novel function of Lasp1 in cholesterol trafficking, promoting cholesterol reabsorption in the intestine. Targeting LASP1 locally could thus represent a novel targeting strategy to ameliorate hypercholesterolemia and associated diseases.NEW & NOTEWORTHY We here uncovered LASP1 as a novel regulator of the shuttling of the sterol transporter NPC1L1 to the cell surface in enterocytes to control cholesterol absorption. Accordingly, LASP1-deficient mice displayed lowered serum cholesterol levels under dietary cholesterol supplementation.

LASP1, CERS6, and Actin Form a Ternary Complex That Promotes Cancer Cell Migration

CERS6 is associated with metastasis and poor prognosis in non-small cell lung cancer (NSCLC) patients through d18:1/C16:0 ceramide (C16 ceramide)-mediated cell migration, though the detailed mechanism has not been elucidated. In the present study, examinations including co-immunoprecipitation, liquid chromatography, and tandem mass spectrometry analysis were performed to identify a novel binding partner of CERS6. Among the examined candidates, LASP1 was a top-ranked binding partner, with the LIM domain possibly required for direct interaction. In accord with those findings, CERS6 and LASP1 were found to co-localize on lamellipodia in several lung cancer cell lines. Furthermore, silencing of CERS6 and/or LASP1 significantly suppressed cell migration and lamellipodia formation, whereas ectopic addition of C16 ceramide partially rescued those phenotypes. Both LASP1 and CERS6 showed co-immunoprecipitation with actin, with those interactions markedly reduced when the LASP1-CERS6 complex was abolished. Based on these findings, it is proposed that LASP1-CERS6 interaction promotes cancer cell migration.

LASP1 in Cellular Signaling and Gene Expression: More than Just a Cytoskeletal Regulator

LIM and SH3 protein 1 was originally identified as a structural cytoskeletal protein with scaffolding function. However, recent data suggest additional roles in cell signaling and gene expression, especially in tumor cells. These novel functions are primarily regulated by the site-specific phosphorylation of LASP1. This review will focus on specific phosphorylation-dependent interaction between LASP1 and cellular proteins that orchestrate primary tumor progression and metastasis. More specifically, we will describe the role of LASP1 in chemokine receptor, and PI3K/AKT signaling. We outline the nuclear role for LASP1 in terms of epigenetics and transcriptional regulation and modulation of oncogenic mRNA translation. Finally, newly identified roles for the cytoskeletal function of LASP1 next to its known canonical F-actin binding properties are included.

Alterations of actin cytoskeleton and arterial protein level in patients with obstructive jaundice

Vascular hypo-responsiveness to vasopressors in patients with obstructive jaundice (OJ) is a common anesthetic event, which leads to perioperative complications and increased mortality. The cause of this clinical issue remains unclear. In this study, we estimated the actin cytoskeleton and arterial protein level in the artery of OJ patients by proteomic analysis. Ten patients with OJ due to bile duct diseases or pancreatic head carcinoma were enrolled, while another ten non-jaundice patients with chronic cholecystitis or liver hemangioma as the control group. Vascular reactivity to noradrenaline was measured before anesthesia on the day of surgery. Artery samples in adjacent tissues of removed tumor were collected and evaluated by 2-dimensional electrophoresis. Proteins with differential expression were detected by MALDI-TOF mass spectrometry with immunoblot confirmation. The results confirmed the phenomenon of vascular hypo-reactivity in OJ patients as suppressed aortic response to noradrenaline were existed in these patients. We also found that actin cytoskeleton and several actin-binding proteins were up- or down-regulated in the artery of OJ patients. These proteins changed in OJ patents might be the basic mechanism of vascular hypo-reactivity, further studies to uncover the role of these proteins in OJ is critical for clinical treatment of these patients.

The Mechanisms of Thin Filament Assembly and Length Regulation in Muscles

The actin containing tropomyosin and troponin decorated thin filaments form one of the crucial components of the contractile apparatus in muscles. The thin filaments are organized into densely packed lattices interdigitated with myosin-based thick filaments. The crossbridge interactions between these myofilaments drive muscle contraction, and the degree of myofilament overlap is a key factor of contractile force determination. As such, the optimal length of the thin filaments is critical for efficient activity, therefore, this parameter is precisely controlled according to the workload of a given muscle. Thin filament length is thought to be regulated by two major, but only partially understood mechanisms: it is set by (i) factors that mediate the assembly of filaments from monomers and catalyze their elongation, and (ii) by factors that specify their length and uniformity. Mutations affecting these factors can alter the length of thin filaments, and in human cases, many of them are linked to debilitating diseases such as nemaline myopathy and dilated cardiomyopathy.

LIM and SH3 protein 1 (LASP1) differentiates malignant chordomas from less malignant chondrosarcomas

PURPOSE

Chordomas are malignant tumors that develop along the neuraxis between skull-base and sacrum. Chondrosarcomas show similarities with chordomas, yet show less malignant behavior. LIM and SH3 protein 1 (LASP1) is a cytoskeletal protein known to promote the malignant behavior of tumors. LASP1 was previously identified as a possibly overexpressed protein in a chordoma proteomics experiment. In this study we compare LASP1 expression in chordoma and chondrosarcoma tissue.

METHODS

Biopsies of primary tumors were collected from surgically treated chordoma (n = 6) and chondrosarcoma (n = 6) patients, flash-frozen upon collection and collectively analyzed for LASP1 RNA (real-time PCR) and protein expression (western blotting). Additionally, tissue micro array (TMA)-based immunohistochemistry was applied to an archive of 31 chordoma and 1 chondrosarcoma specimen.

RESULTS

In chordoma samples, LASP1 mRNA was detected in 4/6 cases and a strong 36 kDa immunoreactive protein band was observed in 4/5 cases. In contrast, 0/6 chondrosarcoma samples showed detectable levels of LASP1 mRNA and only a weak 36 kDa band was observed in 4/5 cases. Immunohistochemical analysis showed LASP1 expression in all chordoma samples, whereas chondrosarcoma specimen did not show immunoreactivity.

CONCLUSION

LASP1 is strongly expressed in the majority of chordoma cases and shows low expression in chondrosarcoma tissue. Since LASP1 is known to function as oncogene and regulate cell proliferation in other tumor types, this study implicates a role for LASP1 in chordoma biology. Further studies are warranted to improve understanding of LASP1's expression and functioning within chordoma, both in vitro and in vivo.

p21-activated kinase 4 promotes the progression of esophageal squamous cell carcinoma by targeting LASP1

Esophageal squamous cell carcinoma (ESCC) is one of the most common malignant tumors of the digestive tract in humans. Several studies have indicated that PAK4 is associated with the risk of ESCC and may be a potential druggable kinase for ESCC treatment. However, the underlying mechanism remains largely unknown. The aim of our study is to identify the functional role of PAK4 in ESCC. To determine the expression of PAK4 in ESCC, Western blot analysis and immunohistochemistry were performed, and the results showed that PAK4 is significantly upregulated in ESCC tissues and cell lines compared with normal controls and normal esophageal epithelial cell line. To further investigate the role of PAK4 in ESCC, cell viability assays, anchorage-independent cell growth assays, wound healing assays, cellular invasion assays, in vivo xenograft mouse models, and metastasis assays were conducted, and the results showed that PAK4 can significantly facilitate ESCC proliferation and metastasis in vitro and in vivo. To determine the potential target of PAK4 in ESCC progression, a pull-down assay was performed, and the results showed that LASP1 may be a potential target of PAK4. An immunoprecipitation assay and confocal microscopy analysis confirmed that PAK4 can bind to and colocalize with LASP1 in vitro and in cells. Notably, rescue experiments further illustrated the mechanistic network of PAK4/LASP1. Our research reveals the oncogenic roles of PAK4 in ESCC and preliminarily elucidates the mechanistic network of PAK4/LASP1 in ESCC.

LIM and SH3 protein 1 localizes to the leading edge of protruding lamellipodia and regulates axon development

The actin cytoskeleton drives cell motility and is essential for neuronal development and function. LIM and SH3 protein 1 (LASP1) is a unique actin-binding protein that is expressed in a wide range of cells including neurons, but its roles in cellular motility and neuronal development are not well understood. We report that LASP1 is expressed in rat hippocampus early in development, and this expression is maintained through adulthood. High-resolution imaging reveals that LASP1 is selectively concentrated at the leading edge of lamellipodia in migrating cells and axonal growth cones. This local enrichment of LASP1 is dynamically associated with the protrusive activity of lamellipodia, depends on the barbed ends of actin filaments, and requires both the LIM domain and the nebulin repeats of LASP1. Knockdown of LASP1 in cultured rat hippocampal neurons results in a substantial reduction in axonal outgrowth and arborization. Finally, loss of the Drosophila homologue Lasp from a subset of commissural neurons in the developing ventral nerve cord produces defasciculated axon bundles that do not reach their targets. Together, our data support a novel role for LASP1 in actin-based lamellipodial protrusion and establish LASP1 as a positive regulator of both in vitro and in vivo axon development.

The CXCR4-Dependent LASP1-Ago2 Interaction in Triple-Negative Breast Cancer

The CXCR4-LASP1 axis is an emerging target in the field of breast cancer metastasis. C-X-C chemokine receptor type 4 (CXCR4) mediates directed cell migration when activated by its cognate ligand CXCL12. LIM and SH3 Protein 1 (LASP1) is a critical node in the CXCR4 signaling pathway, as its deficiency blocks CXCR4-dependent Matrigel invasion. The mechanism by which LASP1 facilitates this invasive ability of tumor cells when CXCR4 is activated is unknown. Our previous proteomics work had revealed several components of the RNA interference (RNAi) machinery as being potential LASP1 interacting proteins. Here we report that argonaute 2 (Ago2), a protein with central involvement in RNAi, associates with LASP1 in triple-negative breast cancer (TNBC) cells. We demonstrate that LASP1 co-immunoprecipitates with Ago2 endogenously in a CXCL12-dependent manner, with further confirmation of this interaction by proximity ligation assay. Furthermore, this association is specific to CXCR4 as it can be abrogated by the CXCR4 antagonist, AMD3465. By GST-pulldown approach, we identify that LASP1 directly binds to Ago2 through its LIM and SH3 domains, and that this binding is dictated by the S146 and Y171 phosphorylation sites of LASP1. Additionally, the phosphorylation status of LASP1 affected tumor suppressor microRNA (miRNA) Let-7a-guided Ago2 activity. Levels of several endogenous targets of Let-7a were found to be altered including C-C chemokine receptor type 7 (CCR7), which is another critical chemokine receptor involved in metastasis to lymph nodes. Our results suggest a novel role for the LASP1-Ago2 module in shaping the RNAi landscape, functionally impacting the invasive ability of cancer cells.

Nebulin: big protein with big responsibilities

Nebulin, encoded by NEB, is a giant skeletal muscle protein of about 6669 amino acids which forms an integral part of the sarcomeric thin filament. In recent years, the nebula around this protein has been largely lifted resulting in the discovery that nebulin is critical for a number of tasks in skeletal muscle. In this review, we firstly discussed nebulin’s role as a structural component of the thin filament and the Z-disk, regulating the length and the mechanical properties of the thin filament as well as providing stability to myofibrils by interacting with structural proteins within the Z-disk. Secondly, we reviewed nebulin’s involvement in the regulation of muscle contraction, cross-bridge cycling kinetics, Ca²⁺-homeostasis and excitation contraction (EC) coupling. While its role in Ca²⁺-homeostasis and EC coupling is still poorly understood, a large number of studies have helped to improve our knowledge on how nebulin affects skeletal muscle contractile mechanics. These studies suggest that nebulin affects the number of force generating actin-myosin cross-bridges and may also affect the force that each cross-bridge produces. It may exert this effect by interacting directly with actin and myosin and/or indirectly by potentially changing the localisation and function of the regulatory complex (troponin and tropomyosin). Besides unravelling the biology of nebulin, these studies are particularly helpful in understanding the patho-mechanism of myopathies caused by NEB mutations, providing knowledge which constitutes the critical first step towards the development of therapeutic interventions. Currently, effective treatments are not available, although a number of therapeutic strategies are being investigated.

Change in distribution of cytoskeleton-associated proteins, lasp-1 and palladin, during uterine receptivity in the rat endometrium

The epithelium of the uterine lumen is the first point of contact with the blastocyst before implantation. To facilitate pregnancy, these uterine epithelial cells (UECs) undergo morphological changes specific to the receptive uterus. These changes include basal, lateral and apical alterations in the plasma membrane of UECs. This study looked at the cytoskeletal and focal adhesion-associated proteins, lasp-1 and palladin, in the uterus during early pregnancy in the rat. Two palladin isoforms, 140 kDa and 90 kDa, were analysed, with the migration-associated 140-kDa isoform increasing significantly at the time of implantation when compared with the time of fertilisation. Lasp-1 was similarly increased at this time, whilst also being located predominantly apically and laterally in the UECs, suggesting a role in the initial contact between the UECs and the blastocyst. This is the first study to investigate palladin and lasp-1 in the uterine luminal epithelium and suggests an importance for these cytoskeletal proteins in the morphological changes the UECs undergo for pregnancy to occur.

New Frontiers for the Cytoskeletal Protein LASP1

In the recent two decades, LIM and SH3 protein 1 (LASP1) has been developed from a simple actin-binding structural protein to a tumor biomarker and subsequently to a complex, nuclear transcriptional regulator. Starting with a brief historical perspective, this review will mainly compare and contrast LASP1 and LASP2 from the angle of the newest data and importantly, examine their role in transcriptional regulation. We will summarize the current knowledge through pictorial models and tables including the roles of different microRNAs in the differential regulation of LASP1 levels and patient outcome rather than specify in detail all tumor entities. Finally, the novel functional roles of LASP1 in secretion of vesicles, expression of matrix metalloproteinases and transcriptional regulation as well as the activation of survival and proliferation pathways in different cancer types are described.

Regulation of matrix metalloproteinases (MMPs) expression and secretion in MDA-MB-231 breast cancer cells by LIM and SH3 protein 1 (LASP1)

The process of tumor invasion requires degradation of extracellular matrix by proteolytic enzymes. Cancer cells form protrusive invadopodia, which produce and release matrix metalloproteinases (MMPs) to degrade the basement membrane thereby enabling metastasis. We investigated the effect of LASP1, a newly identified protein in invadopodia, on expression, secretion and activation of MMPs in invasive breast tumor cell lines.

By analyzing microarray data of in-house generated control and LASP1-depleted MDA-MB-231 breast cancer cells, we observed downregulation of MMP1, -3 and -9 upon LASP1 depletion. This was confirmed by Western blot analysis. Conversely, rescue experiments restored in part MMP expression and secretion. The regulatory effect of LASP1 on MMP expression was also observed in BT-20 breast cancer cells as well as in prostate and bladder cancer cell lines.

In line with bioinformatic FunRich analysis of our data, which mapped a high regulation of transcription factors by LASP1, public microarray data analysis detected a correlation between high LASP1 expression and enhanced c-Fos levels, a protein that is part of the transcription factor AP-1 and known to regulate MMP expression. Compatibly, in luciferase reporter assays, AP-1 showed a decreased transcriptional activity after LASP1 knockdown.

Zymography assays and Western blot analysis revealed an additional promotion of MMP secretion into the extracellular matrix by LASP1, thus, most likely, altering the microenvironment during cancer progression.

The newly identified role of LASP1 in regulating matrix degradation by affecting MMP transcription and secretion elucidated the migratory potential of LASP1 overexpressing aggressive tumor cells in earlier studies.

Silencing of LIM and SH3 Protein 1 (LASP-1) Inhibits Thyroid Cancer Cell Proliferation and Invasion

LIM and SH3 protein 1 (LASP-1) is a specific focal adhesion protein that was first identified in breast cancer and then reported to be involved in cell proliferation and migration. Many studies have demonstrated the essential role of LASP-1 in cancer progression. However, there have been no studies on the association of LASP-1 with thyroid cancer. In this study, we investigated the expression pattern and biological function of LASP-1 in thyroid cancer. We found that LASP-1 was highly expressed in thyroid cancer tissues and cell lines. LASP-1 silencing had antiproliferative and anti-invasive effects on thyroid cancer cells. Moreover, tumor xenograft experiments showed that LASP-1 silencing suppressed thyroid cancer cell growth in vivo. We also demonstrated that LASP-1 silencing decreased the protein expression of p-PI3K and p-Akt. In conclusion, these findings suggest LASP-1 to be an oncogene and a potential therapeutic target in thyroid cancer.

LIM and SH3 protein 1 promotes tumor proliferation and metastasis in lung carcinoma

Lung cancer is the most frequently diagnosed cancer and the leading cause of cancer-related mortality worldwide. In the present study, we focused on LIM and SH3 protein 1 (LASP-1), a key molecule involved in the development of multiple cancers, and attempted to elucidate its effect on the oncogenesis of lung cancer. We determined the expression level of LASP-1 in lung cancer using reverse transcription-quantitative polymerase chain reaction and western blot analysis, and also studied the potential function of LASP-1 in lung cancer cell growth, apoptosis and migration by small interfering RNA transfection. The results revealed that the levels of LASP-1 mRNA and protein were abnormally high in lung cancer cells. Following RNA interference of LASP-1, the proliferation and migration ability of the human cancer cell line A549 were significantly decreased. In addition, fluorescence-activated cell sorting analysis indicated that the apoptotic process in the A549 cell line was induced by the silencing of LASP-1. Our study is the first to investigate the potential of LASP-1 in lung cancer, and revealed its significant role in regulating the growth and metastasis of lung cancer cells. The present study suggests that LASP-1 has potential as a therapeutic target in the treatment of lung cancer in the clinic.

Suppression of LASP-1 attenuates the carcinogenesis of prostatic cancer cell lines: Key role of the NF-κB pathway

Prostate cancer (PCa) is one of the most frequently diagnosed cancers among males worldwide and causes a considerable number of deaths each year. One of the newly explored targets for the development of therapies against PCa is LIM and SH3 protein 1 (LASP-1). In the present study, the function of LASP-1 in the oncogenesis and metastasis of PCa was investigated using a series of in vitro experiments. Moreover, the mechanism through which LASP-1 exerted its effect on the carcinogenesis of PCa was also explored. The expression levels of LASP-1 in clinical PCa specimens were determined both at the mRNA and protein levels. Afterwards, the activity of LASP-1 in human PCa cell lines PC3 and DU145 was inhibited using a short hairpin RNA (shRNA) interfering method. The effects of LASP-1 knockdown on the cell growth, apoptosis, cell cycle distribution, migration and invasion were assessed. It was demonstrated that the expression of LASP-1 was significantly higher in the clinical PCa tissues than the level in the corresponding para-carcinoma tissues. Following the knockdown of the LASP-1 gene in human PCa cell lines, the viability, migration and invasion of the cancer cells were decreased. It was also demonstrated that the change in the cell viability and motile ability were associated with an induction of cell apoptosis and G1 phase cell cycle arrest. Based on the results of the detection of the expression of NF-κB-related factors, it was indicated that LASP-1 may affect the carcinogenesis of PCa through a NF-κB inhibition-dependent manner. Although the detailed explanation of the mechanism of LASP-1 in the carcinogenesis of PCa requires further elucidation, the present study highlights the potential of LASP-1 as a promising therapeutic target to ameliorate the oncogenesis and metastasis of PCa.

Proteomic analysis of naturally-sourced biological scaffolds

A key challenge to the clinical implementation of decellularized scaffold-based tissue engineering lies in understanding the process of removing cells and immunogenic material from a donor tissue/organ while maintaining the biochemical and biophysical properties of the scaffold that will promote growth of newly seeded cells. Current criteria for evaluating whole organ decellularization are primarily based on nucleic acids, as they are easy to quantify and have been directly correlated to adverse host responses. However, numerous proteins cause immunogenic responses and thus should be measured directly to further understand and quantify the efficacy of decellularization. In addition, there has been increasing appreciation for the role of the various protein components of the extracellular matrix (ECM) in directing cell growth and regulating organ function. We performed in-depth proteomic analysis on four types of biological scaffolds and identified a large number of both remnant cellular and ECM proteins. Measurements of individual protein abundances during the decellularization process revealed significant removal of numerous cellular proteins, but preservation of most structural matrix proteins. The observation that decellularized scaffolds still contain many cellular proteins, although at decreased abundance, indicates that elimination of DNA does not assure adequate removal of all cellular material. Thus, proteomic analysis provides crucial characterization of the decellularization process to create biological scaffolds for future tissue/organ replacement therapies.

Roles of Nebulin Family Members in the Heart

The members of the nebulin protein family, including nebulin, nebulette, LASP-1, LASP-2, and N-RAP, contain various numbers of nebulin repeats and bind to actin, but are otherwise heterogeneous with regard to size, expression pattern, and function. This review focuses on the roles of nebulin family members in the heart. Nebulin is the largest member predominantly expressed in skeletal muscle, where it stretches along the thin filament. In heart, nebulin is detectable only at low levels and its absence has no apparent effects. Nebulette is similar in structure to the nebulin C-terminal Z-line region and specifically expressed in heart. Nebulette gene mutations have been identified in dilated cardiomyopathy patients and transgenic mice overexpressing nebulette mutants partially recapitulate the human pathology. In contrast, nebulette knockout mice show no functional phenotype, but exhibit Z-line widening. LASP-2 is an isoform of nebulette expressed in multiple tissues, including the heart. It is present in the Z-line and intercalated disc and able to bind and cross-link filamentous actin. LASP-1 is similar in structure to LASP-2, but expressed only in non-muscle tissue. N-RAP is present in myofibril precursors during myofibrillogenesis and thought to be involved in myofibril assembly, while it is localized at the intercalated disc in adult heart. Additional in vivo models are required to provide further insights into the functions of nebulin family members in the heart.

LASP1, a Newly Identified Melanocytic Protein with a Possible Role in Melanin Release, but Not in Melanoma Progression

The LIM and SH3 protein 1 (LASP1) is a focal adhesion protein. Its expression is increased in many malignant tumors. However, little is known about the physiological role of the protein. In the present study, we investigated the expression and function of LASP1 in normal skin, melanocytic nevi and malignant melanoma. In normal skin, a distinct LASP1 expression is visible only in the basal epidermal layer while in nevi LASP1 protein is detected in all melanocytes. Melanoma exhibit no increase in LASP1 mRNA compared to normal skin. In melanocytes, the protein is bound to dynamin and mainly localized at late melanosomes along the edges and at the tips of the cell. Knockdown of LASP1 results in increased melanin concentration in the cells. Collectively, we identified LASP1 as a hitherto unknown protein in melanocytes and as novel partner of dynamin in the physiological process of membrane constriction and melanosome vesicle release.

Molecular characterization of LASP-1 expression reveals vimentin as its new partner in human hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is the third most common cause of cancer-related mortality worldwide. We have previously reported that LASP-1 is a downstream protein of the urokinase type plasminogen activator (uPA). Here we investigated the role of LASP-1 in HCC by a molecular and biological characterization of LASP-1 expression in human HCC specimens and in cultured HCC cells. We determined the LASP-1 mRNA expression levels in 55 HCC cases with different hepatic background disease. We identified 3 groups of patients with high, equal or low LASP-1 mRNA levels in HCC tissues compared to the peritumoral (PT) tissues. In particular we found that i) the HCCs displayed a higher LASP-1 mRNA level in HCC compared to PT tissues; ii) the expression levels of LASP-1 mRNA in female HCCs were significantly higher compared to male HCCs; iii) the cirrhotic HCCs displayed a higher LASP-1 mRNA. Further, the biological characterization of the ectopic LASP-1 overexpression in HCC cells, using MALDI-TOF mass spectrometer on the LASP-1 co-immunoprecipitated fractions, displayed vimentin as a novel putative partner of LASP-1. Our results suggest that LASP-1 mRNA overexpression may be mainly implicated in female HCCs and cirrhotic HCCs; and that LASP1 may play its role with vimentin in HCC cells.

LASP1 is a HIF1α target gene critical for metastasis of pancreatic cancer

LASP1 is an actin-binding protein associated with actin assembly dynamics in cancer cells. Here, we report that LASP1 is overexpressed in pancreatic ductal adenocarcinoma (PDAC) where it promotes invasion and metastasis. We found that LASP1 overexpression in PDAC cells was mediated by HIF1α through direct binding to a hypoxia response element in the LASP1 promoter. HIF1α stimulated LASP1 expression in PDAC cells in vitro and mouse tumor xenografts in vivo. Clinically, LASP1 overexpression in PDAC patient specimens was associated significantly with lymph node metastasis and overall survival. Overall, our results defined LASP1 as a direct target gene for HIF1α upregulation that is critical for metastatic progression of PDAC.

LIM and SH3 domain protein 1 (LASP-1) overexpression was associated with aggressive phenotype and poor prognosis in clear cell renal cell cancer

Background

LIM and SH3 protein 1 (LASP-1) is a specific focal adhesion protein that is known to be involved in numerous biological and pathological processes. LASP-1 overexpression has been described in several types of cancers, but its expression and role in clear cell renal cell cancer (ccRCC) remains unknown.

Methods

Using immunohistochemistry, we analyzed LASP-1 protein expression in 216 clinicopathologically characterized ccRCC cases. We also examined LASP-1 expression in 20 paired ccRCC tissues and in 2 cell lines by real-time PCR and Western blot. Using RNA interference, we investigated the effects of LASP-1 depletion on tumor cell behavior in vitro. Statistical analyses were used to determine the associations between LASP-1 levels, tumor features and patient outcomes.

Results

LASP-1 overexpression was observed in ccRCC tissues (P<0.0001) compared to adjuvant nontumorous tissues, and its expression levels were closely correlated with overall survival and recurrence-free survival (P = 0.044 and 0.006, respectively) in patients with ccRCC. RNA interference-mediated silencing of the LASP-1 gene in 786–0 ccRCC cells significantly inhibited cell migration.

Conclusions

The results of the present study indicate that LASP-1 may serve as a prognostic biomarker for ccRCC patients and may be a promising target for the treatment of ccRCC.

Investigating lasp-2 in cell adhesion: new binding partners and roles in motility

Focal adhesions are intricate protein complexes that facilitate cell attachment, migration, and cellular communication. Lasp-2 (LIM-nebulette), a member of the nebulin family of actin-binding proteins, is a newly identified component of these complexes. To gain further insights into the functional role of lasp-2, we identified two additional binding partners of lasp-2: the integral focal adhesion proteins vinculin and paxillin. Of interest, the interaction of lasp-2 with its binding partners vinculin and paxillin is significantly reduced in the presence of lasp-1, another nebulin family member. The presence of lasp-2 appears to enhance the interaction of vinculin and paxillin with each other; however, as with the interaction of lasp-2 with vinculin or paxillin, this effect is greatly diminished in the presence of excess lasp-1. This suggests that the interplay between lasp-2 and lasp-1 could be an adhesion regulatory mechanism. Lasp-2's potential role in metastasis is revealed, as overexpression of lasp-2 in either SW620 or PC-3B1 cells-metastatic cancer cell lines-increases cell migration but impedes cell invasion, suggesting that the enhanced interaction of vinculin and paxillin may functionally destabilize focal adhesion composition. Taken together, these data suggest that lasp-2 has an important role in coordinating and regulating the composition and dynamics of focal adhesions.

Overexpression of LASP1 is associated with proliferation, migration and invasion in esophageal squamous cell carcinoma

LIM and SH3 protein 1 (LASP1) is an actin-binding protein which is overexpressed in many types of cancers and plays important roles in cancer progression. however, the role of LASP1 in esophageal squamous cell carcinoma (ESCC) is still unknown. We sought to analyze the expression level of LASP1 in ESCC, and the role of LASP1 in the development of ESCC was further investigated. We evaluated the expression levels of LASP1 in 89 ESCC tissues and two ESCC cell lines using quantitative real-time polymerase chain reaction, western blotting and immunohistochemistry. The effects of LASP1 depletion on tumor cell behavior were investigated using gene transfection and small interfering RNA (siRNA) in ESCC cell lines in vitro. The expression levels of LASP1 at the mRNA and protein levels were significantly higher in ESCC tissues and ESCC cell lines compared to adjacent tissues. Immunohistochemistry showed that LASP1 was localized in the cytoplasm and nuclei of tumor epithelia. Silencing of LASP1 in ECA109 and KYSE510 cell lines significantly inhibited cell proliferation, migration and invasion when compared with the negative control cells in vitro. LASP1 may play an important role in the pathogenesis of ESCC and shows promise as a treatment target in ESCC.

LIM and SH3 protein 1, a promoter of cell proliferation and migration, is a novel independent prognostic indicator in hepatocellular carcinoma

LIM and SH3 protein 1 (LASP-1) plays a significant role in the formation of several malignant tumours. However, the biological and clinical significances of LASP-1 in hepatocellular carcinoma (HCC) remain largely unknown. Using immunohistochemistry, we analysed LASP-1 expression in 144 clinicopathologically characterised HCC cases. Using gene and transfection and RNA interference, we investigated the effects of LASP-1 overexpression and depletion on tumour cellular behaviour in vitro. LASP-1 expression was detected in not only cytoplasm and but also nucleus of HCC and liver cells. The positive rates of both cytosolic and nuclear LASP-1 expression in HCC were higher than adjacent non-tumourous tissues. Statistical analysis showed that heterogeneous LASP-1 expression is associated with hepatitis B surface antigen (HBsAg) and serum alpha-fetoprotein (AFP) level of HCC patients. A significant trend was identified between cytosolic LASP-1 overexpression in HCC and worsening clinical prognosis. Multivariate survival analysis showed that cytosolic LASP-1 expression was recognised as an independent prognostic factor of patient's survival. In vitro study showed LASP-1 promoted cell proliferation and migration, and resulted in aggressive phenotypes of cancer cells. LASP-1 is a valuable marker of HCC progression. High cytosolic LASP-1 expression is associated with poor overall survival in HCC patients.

cDNA cloning and characterization of LASP1 from silkworm, Bombyx mori, involved in cytoplasmic polyhedrosis virus infection

Full-length cDNA of a LIM and SH3 contained protein 1 (named BmLASP1) was identified from the silkworm, Bombyx mori, for the first time by rapid amplification of cDNA ends. The full-length cDNA of BmLASP1 is 2094 bp, consisting of a 5'-terminal untranslated region (UTR) of 117 bp, and a 3'-UTR of 610 bp with two poly-adenylation signal sequence AATAAA and a poly (A) tail. The BmLASP1 cDNA encodes a polypeptide comprising 455 amino acids, including a LIM domain, two nebulin domains and an SH3 domain. The theoretical isoelectric point is 7.07 and the predicted molecular weight is 51.8 kDa. BmLASP1 has no signal peptide but three potential N-glycosylation sites. Sequence similarity and phylogenic analyses indicated that BmLASP1 belonged to the group of insect LASP1 with a longer linker region which is different from vertebrate LASP1. The LASP1 in silkworm contained eight exons in its coding regions, and the last exon-intron boundary was conserved the same as in mammalian and Ciona intestinalis LASP1 genes. By fluorescent quantitative real-time polymerase chain reaction, the mRNA transcripts of BmLASP1 were mainly detected in the gonad, head, and spiracle, and slightly in the silk gland, vasa mucosa, midgut, fat body, and hemocytes. After silkworm larvae were infected by B. mori cytoplasmic polyhedrosis virus (BmCPV), the relative expression level of BmLASP1 was down-regulated in the midgut. This result suggested that BmLASP1 may play an important role in the response of silkworm to BmCPV infection.

Lasp-1 regulates podosome function

Eukaryotic cells form a variety of adhesive structures to connect with their environment and to regulate cell motility. In contrast to classical focal adhesions, podosomes, highly dynamic structures of different cell types, are actively engaged in matrix remodelling and degradation. Podosomes are composed of an actin-rich core region surrounded by a ring-like structure containing signalling molecules, motor proteins as well as cytoskeleton-associated proteins. Lasp-1 is a ubiquitously expressed, actin-binding protein that is known to regulate cytoskeleton architecture and cell migration. This multidomain protein is predominantely present at focal adhesions, however, a second pool of Lasp-1 molecules is also found at lamellipodia and vesicle-like microdomains in the cytosol.In this report, we show that Lasp-1 is a novel component and regulator of podosomes. Immunofluorescence studies reveal a localization of Lasp-1 in the podosome ring structure, where it colocalizes with zyxin and vinculin. Life cell imaging experiments demonstrate that Lasp-1 is recruited in early steps of podosome assembly. A siRNA-mediated Lasp-1 knockdown in human macrophages affects podosome dynamics as well as their matrix degradation capacity. In summary, our data indicate that Lasp-1 is a novel component of podosomes and is involved in the regulation of podosomal function.

MicroRNA-1 is a candidate tumor suppressor and prognostic marker in human prostate cancer

We previously reported that miR-1 is among the most consistently down-regulated miRs in primary human prostate tumors. In this follow-up study, we further corroborated this finding in an independent data set and made the novel observation that miR-1 expression is further reduced in distant metastasis and is a candidate predictor of disease recurrence. Moreover, we performed in vitro experiments to explore the tumor suppressor function of miR-1. Cell-based assays showed that miR-1 is epigenetically silenced in human prostate cancer. Overexpression of miR-1 in these cells led to growth inhibition and down-regulation of genes in pathways regulating cell cycle progression, mitosis, DNA replication/repair and actin dynamics. This observation was further corroborated with protein expression analysis and 3'-UTR-based reporter assays, indicating that genes in these pathways are either direct or indirect targets of miR-1. A gene set enrichment analysis revealed that the miR-1-mediated tumor suppressor effects are globally similar to those of histone deacetylase inhibitors. Lastly, we obtained preliminary evidence that miR-1 alters the cellular organization of F-actin and inhibits tumor cell invasion and filipodia formation. In conclusion, our findings indicate that miR-1 acts as a tumor suppressor in prostate cancer by influencing multiple cancer-related processes and by inhibiting cell proliferation and motility.

Analysis of dynamic tyrosine phosphoproteome in LFA-1 triggered migrating T-cells

The ordered, directional migration of T-lymphocytes is a key process during immune surveillance and response. This requires cell adhesion to the high endothelial venules or to the extracellular matrix by a series of surface receptor/ligand interactions involving adhesion molecules of the integrin family including lymphocyte function associated molecule-1 (LFA-1) and intercellular adhesion molecules (ICAMs). Reversible protein phosphorylation is emerging as a key player in the regulation of biological functions with tyrosine phosphorylation playing a crucial role in signal transduction. Thus, the study of this type of post-translational modification at the proteomic level has great biological significance. In this work, phospho-enriched cell lysates from LFA-1-triggered migrating human T-cells were subjected to immunoaffinity purification of tyrosine phosphorylated proteins, mass spectrometric, and bioinformatic analysis. In addition to the identification of several well-documented proteins, the analysis suggested involvement of a number of new and novel proteins in LFA-1 induced T-cell migration. This dataset expands the list of the signaling components of the LFA-1 induced phosphotyrosine protein complexes in migrating T-cells that will be extremely useful in the study of their specific roles within LFA-1 associated signaling pathways. Identification of proteins previously not reported in the context of LFA-1 stimulated signal transduction might provide new insights into understanding the LFA-1 signaling networks and aid in the search for new potential therapeutic targets.

Nuclear localisation of LASP-1 correlates with poor long-term survival in female breast cancer

BACKGROUND

LIM and SH3 protein 1 (LASP-1) is a nucleo-cytoplasmatic signalling protein involved in cell proliferation and migration and is upregulated in breast cancer in vitro studies have shown that LASP-1 might be regulated by prostate-derived ETS factor (PDEF), p53 and/or LASP1 gene amplification. This current study analysed the prognostic significance of LASP-1 on overall survival (OS) in 177 breast cancer patients and addressed the suggested mechanisms of LASP-1-regulation.

METHODS

Nucleo-cytoplasmatic LASP-1-positivity of breast carcinoma samples was correlated with long-term survival, clinicopathological parameters, Ki67-positivity and PDEF expression. Rate of LASP1 amplification was determined in micro-dissected primary breast cancer cells using quantitative RT-PCR. Cell-phase dependency of nuclear LASP-1-localisation was studied in synchronised cells. In addition, LASP-1, PDEF and p53 expression was compared in cell lines of different tumour entities to define principles for LASP-1-regulation.

RESULTS

We showed that LASP-1 overexpression is not due to LASP1 gene amplification. Moreover, no correlation between p53-mutations or PDEF-expression and LASP-1-status was observed. However, nuclear LASP-1-localisation in breast carcinomas is increased during proliferation with peak in G2/M-phase and correlated significantly with Ki67-positivity and poor OS.

CONCLUSION

Our results provide evidence that nuclear LASP-1-positivity may serve as a negative prognostic indicator for long-term survival of breast cancer patients.

Cigarette smoke extract induced protein phosphorylation changes in human microvascular endothelial cells in vitro

Phosphorylation is the most widely studied posttranslational modification (PTM) and is an important regulatory mechanism used during cellular responses to external stimuli. The kinases and phosphatases that regulate protein phosphorylation are known to be affected in many human diseases. Cigarette smoking causes cardiovascular disease (CVD). Endothelial cells play a pivotal role in CVD initiation and development; however, there have been limited investigations of the specific signaling cascades and protein phosphorylations activated by cigarette smoke in endothelial cells. The purpose of this research was to better understand the differential protein phosphorylation in endothelial cells stimulated with extracts of cigarette smoke total particulate matter (CS-TPM) in vitro. Human microvascular endothelial cells were exposed in vitro to CS-TPM at concentrations that were shown to cause endothelial cell dysfunction. The phosphorylated proteins were isolated using phosphoprotein-specific chromatography, followed by enzymatic digestion and nano-flow capillary liquid chromatography (ncap-LC) coupled to high resolution mass spectrometry. This study putatively identified 94 proteins in human microvascular endothelial cells that were differentially bound to a phosphoprotein-specific chromatography column following exposure to CS-TPM suggesting differential phosphorylation. Pathway analysis has also been conducted and confirmations of several observations have been made using immunoaffinity-based techniques (e.g., Western blotting).

Lasp1 gene disruption is linked to enhanced cell migration and tumor formation

Lasp1 is an actin-binding, signaling pathway-regulated phosphoprotein that is overexpressed in several cancers. siRNA knockdown in cell lines retards cell migration, suggesting the possibility that Lasp1 upregulation influences cancer metastasis. Herein, we utilized a recently developed gene knockout model to assess the role of Lasp1 in modulating nontransformed cell functions. Wound healing and tumor initiation progressed more rapidly in Lasp1(-/-) mice compared with Lasp1(+/+) controls. Embryonic fibroblasts (MEFs) derived from Lasp1(-/-) mice also migrated more rapidly in vitro. These MEFs characteristically possessed increased focal adhesion numbers and displayed more rapid attachment compared with wild-type MEFs. Differential microarray analyses revealed alterations in message expression for proteins implicated in cell migration, adhesion, and cytoskeletal organization. Notably, the focal adhesion protein, lipoma preferred partner (LPP), a zyxin family member and putative Lasp1 binding protein, was increased about twofold. Because LPP gene disruption reduces cell migration, we hypothesize that LPP plays a role in enhancing the migratory capacity of Lasp1(-/-) MEFs, perhaps by modifying the subcellular localization of other motility-associated proteins. The striking contrast in the functional effects of loss of Lasp1 in innate cells compared with cell lines reveals distinct differences in mechanisms of motility and attachment in these models.

Proteomic identification of LASP-1 down-regulation after RNAi urokinase silencing in human hepatocellular carcinoma cells

In human hepatocellular carcinoma (HCC), the high expression of urokinase-type plasminogen activator (uPA) is an unfavorable prognostic factor and a therapeutic target. To identify the downstream effects of uPA silencing by RNA interference, we studied proteome modifications of uPA-inhibited SKHep1C3 cells, an HCC-derived cell line. The study with two-dimensional difference gel electrophoresis and matrix-assisted laser desorption/ionization-time of flight-mass spectrometry showed Lim and SH3 protein 1 (LASP-1), cytokeratin 1 (CK-1), cytokeratin 10 (CK-10), and heterogeneous nuclear ribonucleoprotein H1 down-modulation after uPA inhibition. LASP-1, CK-1, and CK-10 are involved in cytoskeleton dynamics as heterogeneous nuclear ribonucleoprotein H1 takes part in the mRNA processing and stability. We first confirmed the proteomic data by Western blot and immunoflorescence and then explored the link between uPA and LASP-1. The ectopic expression of uPA and LASP-1 supported the proteomic results and showed that uPA up-regulation increased LASP-1 expression and that both were implicated in SKHep1C3 motility. siRNA LASP-1 inhibition showed that LASP-1 was involved in actin microfilaments organization of SKHep1C3 cells. The disruption of the actin microfilaments after LASP-1 depletion increased uPA secretion and SKHep1C3 motility. Our results would suggest the hypothesis that uPA and LASP-1 expression may be coordinated in HCC-derived cells. In summary, the proteomic identification of a set of uPA downstream proteins provides new insight into the function of uPA in HCC cells.

LIM and SH3 protein 1 (Lasp1) is a novel p53 transcriptional target involved in hepatocellular carcinoma

BACKGROUND/AIMS

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death worldwide with poor prognosis associated with tumor invasion and metastasis. The tumor suppressor p53 plays critical roles in tumor development, but there is increasing evidence for its involvement in tumor metastasis with the underlying mechanisms largely unexplored.

METHODS

Using combinatorial analysis of a p53 binding database with HCC microarray expression profile, we identified a novel metastasis-related gene Lasp1 as a potential p53 target.

RESULTS

In this study, we demonstrate that Lasp1 is indeed a bona fide p53 target by validating the functional repression effect of p53 on Lasp1 via a p53 response element. Transient transfection of wild-type p53 but not the mutant form suppressed Lasp1 in Hep3B (p53-/-) cells, while p53 siRNA up-regulated its expression in HepG2 (p53+/+) cells. p53 mutations at key residues involved in DNA binding abrogates the p53-mediated suppression of Lasp1 expression. In addition, Lasp1 regulates HCC cell growth as well as cell migration and invasion ability.

CONCLUSIONS

p53 transcriptionally represses Lasp1, which is a partner protein in affecting HCC cell motility. This suggests that p53 may play a role in influencing tumor metastasis through Lasp1.

The actin-binding protein Lasp promotes Oskar accumulation at the posterior pole of the Drosophila embryo

During Drosophila oogenesis, Oskar mRNA is transported to the posterior pole of the oocyte, where it is locally translated and induces germ-plasm assembly. Oskar protein recruits all of the components necessary for the establishment of posterior embryonic structures and of the germline. Tight localization of Oskar is essential, as its ectopic expression causes severe patterning defects. Here, we show that the Drosophila homolog of mammalian Lasp1 protein, an actin-binding protein previously implicated in cell migration in vertebrate cell culture, contributes to the accumulation of Oskar protein at the posterior pole of the embryo. The reduced number of primordial germ cells in embryos derived from lasp mutant females can be rescued only with a form of Lasp that is capable of interacting with Oskar, revealing the physiological importance of the Lasp-Oskar interaction.

Ectopic expression of LIM-nebulette (LASP2) reveals roles in cell migration and spreading

LIM-nebulette (LASP2) is a small focal adhesion protein and a member of the nebulin family of actin binding proteins. This recently identified splice variant of the nebulette locus is widely expressed and highly enriched in neuronal tissue. Other than that LIM-nebulette is a focal adhesion protein and interacts with zyxin, nothing is known about its function. Given that LIM-nebulette has an identical modular organization and overlapping tissue distributions to that of LASP1, we have analyzed the role of LIM-nebulette in comparison with that of LASP1. We find that LIM-nebulette is a dynamic focal adhesion protein that increases the rate of attachment and spreading of fibroblasts on fibronectin coated surfaces. Additionally, LIM-nebulette is recruited from the cortical cytoskeleton in non-motile cells to focal adhesions at the leading edge of stimulated cells. In confluent cultures of HeLa and NIH3T3 cells, LIM-nebulette co-localizes with alpha-catenin in putative adherens junctions, whereas LASP1 is devoid of these areas. Interestingly, overexpression of LIM-nebulette in PC6 cells inhibits neurite outgrowth in response to growth factors. Collectively, our data indicate that LIM-nebulette and LASP1 have distinct roles in the actin cytoskeleton.

Targeted disruption of the Lasp-1 gene is linked to increases in histamine-stimulated gastric HCl secretion

Lasp-1 (LIM and SH3 domain protein 1) is a multidomain actin-binding protein that is differentially expressed within epithelial tissues and brain. In the gastric mucosa, Lasp-1 is highly expressed in the HCl-secreting parietal cell, where it is prominently localized within the F-actin-rich subcellular regions. Histamine-induced elevation of parietal cell [cAMP]i increases Lasp-1 phosphorylation, which is correlated with activation of HCl secretion. To determine whether Lasp-1 is involved in the regulation of HCl secretion in vivo, we generated a murine model with a targeted disruption of the Lasp-1 gene. Lasp-1-null mice had slightly lower body weights but developed normally and had no overt phenotypic abnormalities. Basal HCl secretion was unaffected by loss of Lasp-1, but histamine stimulation induced a more robust acid secretory response in Lasp-1-null mice compared with wild-type littermates. A similar effect of histamine was observed in isolated gastric glands on the basis of measurements of accumulation of the weak base [14C]aminopyrine. In addition, inhibition of the acid secretory response to histamine by H2 receptor blockade with ranitidine proceeded more slowly in glands from Lasp-1-null mice. These findings support the conclusion that Lasp-1 is involved in the regulation of parietal HCl secretion. We speculate that cAMP-dependent phosphorylation of Lasp-1 alters interactions with F-actin and/or endocytic proteins that interact with Lasp-1, thereby regulating the trafficking/activation of the H+, K+-ATPase (proton pump).

Global gene expression analysis identifies PDEF transcriptional networks regulating cell migration during cancer progression

Prostate derived ETS factor (PDEF) is an ETS (epithelial-specific E26 transforming sequence) family member that has been identified as a potential tumor suppressor. In multiple invasive breast cancer cells, PDEF expression inhibits cell migration by preventing the acquisition of directional morphological polarity conferred by changes in cytoskeleton organization. In this study, microarray analysis was used to identify >200 human genes that displayed a common differential expression pattern in three invasive breast cancer cell lines after expression of exogenous PDEF protein. Gene ontology associations and data mining analysis identified focal adhesion, adherens junctions, cell adhesion, and actin cytoskeleton regulation as cell migration-associated interaction pathways significantly impacted by PDEF expression. Validation experiments confirmed the differential expression of four cytoskeleton-associated genes with known functional associations with these pathways: uPA, uPAR, LASP1, and VASP. Significantly, chromatin immunoprecipitation studies identified PDEF as a direct negative regulator of the metastasis-associated gene uPA and phenotypic rescue experiments demonstrate that exogenous urokinase plasminogen activator (uPA) expression can restore the migratory ability of invasive breast cancer cells expressing PDEF. Furthermore, immunofluorescence studies identify the subcellular relocalization of urokinase plasminogen activator receptor (uPAR), LIM and SH3 protein (LASP1), and vasodilator-stimulated protein (VASP) as a possible mechanism accounting for the loss of morphological polarity observed upon PDEF expression.

A lasp family protein of Ciona intestinalis

Lasp-1 and lasp-2 are actin-binding proteins that contain a LIM domain, nebulin repeats, and an SH3 domain and they are significantly conserved in mammalian and avian. Lasp-1 is widely expressed in nonmuscle tissues and lasp-2 is specifically expressed in the brain. Genes encoding proteins homologous to lasp-1 and lasp-2 were deposited in the genome/cDNA database of invertebrates such as sea urchins, nematodes, and insects; however, function of their proteins have not been studied in detail. In this study, we analyzed the gene structure, actin-binding activity, and expression of the lasp protein of the ascidian Ciona intestinalis (Ci lasp). A single gene encoding lasp protein was found in the ascidian, and the amino acid sequences of Ci lasp and other invertebrate lasp proteins exhibited similarity to vertebrate lasp-1 and lasp-2 to the same extent. A part of the exon-intron boundaries was conserved between the vertebrate lasp-1, the vertebrate lasp-2 and the invertebrate lasp genes. Ci lasp exhibited actin-binding activity in a co-sedimentation assay. In situ hybridization revealed that the expression of Ci lasp mRNA was apparent in nervous system of early embryos and was detected in various tissues in young adults. This suggests that the functions of invertebrate lasp proteins might include the functions of vertebrate lasp-1 and lasp-2.

Nuclear localization and cytosolic overexpression of LASP-1 correlates with tumor size and nodal-positivity of human breast carcinoma

Background

LIM and SH3 protein 1 (LASP-1), initially identified from human breast cancer, is a specific focal adhesion protein involved in cell proliferation and migration, which was reported to be overexpressed in 8–12 % of human breast cancers and thought to be exclusively located in cytoplasm.

Methods

In the present work we analyzed the cellular and histological expression pattern of LASP-1 and its involvement in biological behavior of human breast cancer through correlation with standard clinicopathological parameters and expression of c-erbB2 (HER-2/neu), estrogen- (ER) and progesterone-receptors (PR). For this purpose immunohistochemical staining intensity and percentage of stained cells were semi-quantitatively rated to define a LASP-1 immunoreactive score (LASP-1-IRS). LASP-1-IRS was determined in 83 cases of invasive ductal breast carcinomas, 25 ductal carcinomas in situ (DCIS) and 18 fibroadenomas. Cellular LASP-1 distribution and expression pattern was visualized by immunofluorescence and confocal microscopy and assessed through separate Western blots of nuclear and cytosol preparations of BT-20, MCF-7, MDA-MB231, and ZR-75/1 breast cancer cells.

Results

Statistical analysis revealed that the resulting LASP-1-IRS was significantly higher in invasive carcinomas compared to fibroadenomas (p = 0.0176). Strong cytoplasmatic expression of LASP-1 was detected in 55.4 % of the invasive carcinomas, which correlated significantly with nuclear LASP-1-positivity (p = 0.0014), increased tumor size (p = 0.0159) and rate of nodal-positivity (p = 0.0066). However, levels of LASP-1 expression did not correlate with average age at time point of diagnosis, histological tumor grading, c-erbB2-, ER- or PR-expression.

Increased nuclear localization and cytosolic expression of LASP-1 was found in breast cancer with higher tumor stage as well as in rapidly proliferating epidermal basal cells. Confocal microscopy and separate Western blots of cytosolic and nuclear preparations confirmed nuclear localization of LASP-1.

Conclusion

The current data provide evidence that LASP-1 is not exclusively a cytosolic protein, but is also detectable within the nucleus. Increased expression of LASP-1 in vivo is present in breast carcinomas with higher tumor stage and therefore may be related with worse prognosis concerning patients' overall survival.

Proteomic characterization of the site-dependent functional difference in the rat small intestine

To investigate the site-dependent functional difference in the small intestine, proteomic analysis was carried out on the three distinct parts of the rat small intestine. Male Wistar rats (7 weeks old) were fed a semi-purified diet ad libitum for 1 week. Intestinal tissues from the proximal, middle and distal regions of the small intestine were subjected to two-dimensional polyacrylamide gel electrophoresis, and the abundance of each spot was determined fluorometrically. MALDI-TOF/MS and LC-MS/MS analysis of the tryptic peptides were performed to identify the proteins. Many of the 180 identified proteins showed a distinctive distribution pattern along the small intestine. Glutathione S-transferase, Catechol O-methyltransferase and Villin 2 decreased gradually from the jejunum to the ileum, in contrast, non-specific dipeptidase and Keratin 19 increased gradually toward the ileum. The voltage-dependent anion channel 2 was most abundant in the duodenum while the L- and I-Fatty acid binding protein (FABP) and Cellular retinol binding protein (CRBP-II) were in the jejunum, and the Bile acid binding protein (BABP) was only observed in the ileum. The findings of these and of another proteins identified in this study may contribute to further understanding of the small intestinal function, and to clinical applications of small intestinal diseases.

Overexpression of LASP-1 mediates migration and proliferation of human ovarian cancer cells and influences zyxin localisation

LIM and SH3 protein 1 (LASP-1), initially identified from human breast cancer, is a specific focal adhesion protein involved in cell proliferation and migration. In the present work, we analysed the effect of LASP-1 on biology and function of human ovarian cancer cell line SKOV-3 using small interfering RNA technique (siRNA). Transfection with LASP-1-specific siRNA resulted in a reduced protein level of LASP-1 in SKOV-3 cells. The siRNA-treated cells were arrested in G(2)/M phase of the cell cycle and proliferation of the tumour cells was suppressed by 60-90% corresponding to around 70% of the cells being transfected successfully as seen by immunofluorescence. Moreover, transfected tumour cells showed a 40% reduced migration. LASP-1 silencing is accompanied by a reduced binding of the LASP-1-binding partner zyxin to focal contacts without changes in actin stress fibre and microtubule organisation or focal adhesion morphology as observed by immunofluorescence. In contrast, silencing of zyxin is not influencing cell migration and had neither influence on LASP-1 expression nor actin cytoskeleton and focal contact morphology suggesting that LASP-1 is necessary and sufficient for recruiting zyxin to focal contacts. The data provide evidence for an essential role of LASP-1 in tumour cell growth and migration, possibly through influencing zyxin localization.

Linker region of nebulin family members plays an important role in targeting these molecules to cellular structures

The nebulin family of actin-binding proteins plays an essential role in cytoskeletal dynamics and actin filament stability. All of the family members are modular proteins with their key defining structural feature being the presence of the 35-residue nebulin modules. The family members now include nebulin, nebulette, N-RAP, LASP-1, and LIM-nebulette. Nebulin and nebulette are associated with the thin filament/Z-line junction of striated muscle. LASP-1 and LIM-nebulette are found within focal adhesions, and N-RAP is associated with muscle cellular junctions. Although much investigation has focused on the role of the interactions between nebulin modules and actin, each of these proteins contains other domains that are essential for their cellular targeting and functions. The serine-rich linker region of nebulette has previously been shown to serve just such a purpose by targeting the association of the nebulin modules to the cardiac Z-line in cultured cardiomyocytes. In this report, we analyze the targeting functions of the homologous regions of LASP-1 and LIM-nebulette in their incorporation into focal adhesions. We have found that the linker region of LASP-1 is indeed important for its cellular localization and that the shortened linker region of LIM-nebulette drives the association of nebulin modules to focal adhesions.

Short-term retention of actin filament binding proteins on lamellipodial actin bundles

Actin filaments are organised into sub-compartments of meshwork and bundles in lamellipodia. Localisation of fascin, the LIM and SH3 domain protein 1 (lasp-1), and lasp-2 to the bundles suggest their involvement in that organisation; however, their contributions remain unclear. We have compared the turnover of these proteins with actin at the bundle. After photobleaching, EGFP-actin recovered inwards from the bundle tip, consistent with the retrograde flow by treadmilling. In contrast, the recovery of EGFP-fascin, -lasp-1 and -lasp-2 occurred from the anterograde direction. These results suggest that these molecules would participate in the stabilisation of bundles but not in initiation.

AP-1 differentially expressed proteins Krp1 and fibronectin cooperatively enhance Rho-ROCK-independent mesenchymal invasion by altering the function, localization, and activity of nondifferentially expressed proteins

The transcription factor AP-1, which is composed of Fos and Jun family proteins, plays an essential role in tumor cell invasion by altering gene expression. We report here that Krp1, the AP-1 up-regulated protein that has a role in pseudopodial elongation in v-Fos-transformed rat fibroblast cells, forms a novel interaction with the nondifferentially expressed actin binding protein Lasp-1. Krp1 and Lasp-1 colocalize with actin at the tips of pseudopodia, and this localization is maintained by continued AP-1 mediated down-regulation of fibronectin that in turn suppresses integrin and Rho-ROCK signaling and allows pseudopodial protrusion and mesenchyme-like invasion. Mutation analysis of Lasp-1 demonstrates that its SH3 domain is necessary for pseudopodial extension and invasion. The results support the concept of an AP-1-regulated multigenic invasion program in which proteins encoded by differentially expressed genes direct the function, localization, and activity of proteins that are not differentially expressed to enhance the invasiveness of cells.