Filamin A regulates focal adhesion disassembly and suppresses breast cancer cell migration and invasion

Evidence for calpains in cancer metastasis

Metastatic dissemination represents the final stage of tumor progression as well as the principal cause of cancer-associated deaths. Calpains are a conserved family of calcium-dependent cysteine proteinases with ubiquitous or tissue-specific expression. Accumulating evidence indicates a central role for calpains in tumor migration and invasion via participating in several key processes, including focal adhesion dynamics, cytoskeletal remodeling, epithelial-to-mesenchymal transition, and apoptosis. Activated after the increased intracellular calcium concentration ( [ Ca 2 + ] i ) induced by membrane channels and extracellular or intracellular stimuli, calpains induce the limited cleavage or functional modulation of various substrates that serve as metastatic mediators. This review covers established literature to summarize the mechanisms and underlying signaling pathways of calpains in cancer metastasis, making calpains attractive targets for aggressive tumor therapies.

Global Signaling Profiling in a Human Model of Tumorigenic Progression Indicates a Role for Alternative RNA Splicing in Cellular Reprogramming

Intracellular signaling is controlled to a large extent by the phosphorylation status of proteins. To determine how human breast cells can be reprogrammed during tumorigenic progression, we profiled cell lines in the MCF10A lineage by phosphoproteomic analyses. A large cluster of proteins involved in RNA splicing were hypophosphorylated as cells progressed to a hyperplastic state, and then hyperphosphorylated after progression to a fully metastatic phenotype. A comprehensive transcriptomic approach was used to determine whether alterations in splicing factor phosphorylation status would be reflected in changes in mRNA splicing. Results indicated that the degree of mRNA splicing trended with the degree of tumorigenicity of the 4 cell lines tested. That is, highly metastatic cell cultures had the greatest number of genes with splice variants, and these genes had greater fluctuations in expression intensities. Genes with high splicing indices were mapped against gene ontology terms to determine whether they have known roles in cancer. This group showed highly significant associations for angiogenesis, cytokine-mediated signaling, cell migration, programmed cell death and epithelial cell differentiation. In summary, data from global profiling of a human model of breast cancer development suggest that therapeutics should be developed which target signaling pathways that regulate RNA splicing.

Copy number profiling of Oncotype DX genes reveals association with survival of breast cancer patients

Copy number variations (CNVs) are key contributors in breast cancer initiation and progression. However, to date, no CNV-based gene signature is developed for breast cancer. 21-gene Oncotype DX, a clinically validated signature, was identified using only RNA expression data in breast cancer patients. In this study, we evaluated whether CNVs of Oncotype DX genes can be used to predict the prognosis of breast cancer patients. Transcriptomic data of 547 and genomic data of 816 of breast cancer patients were downloaded from The Cancer Genome Atlas database. To establish the prognostic relevance between the CNVs of Oncotype DX genes and clinicopathological features, statistical analysis including Pearson Correlation, Fisher-exact, Chi square, Kaplan-Meier survival and Cox regression analyses were performed. 86% genes showed positive CNV-expression correlation. CNVs in 52% and 47.6% genes showed association with ER+ and PR+ status, respectively. 71% of the genes (including ERBB2, CTSV, CD68, GRB7, MKI67, MMP1, PGR, RPLP0, TFRC, BAG1, BCL2, BIRC5, FLNB, GSTM1 and SCUBE2) showed association with poor overall survival. 14% of the genes (including CTSV, RPLP0 and BIRC5) genes showed association with disease free survival. Cox regression analysis revealed ESR1, metastasis and node stage as independent prognostic factors for overall survival of breast cancer patients. The results suggested that CNV-based assay of Oncotype DX genes can be used to predict the survival of breast cancer patients. In future, identifying new gene signatures for better breast cancer prognosis using CNV level information will be worth investigating.

Detection and benchmarking of somatic mutations in cancer genomes using RNA-seq data

To detect functional somatic mutations in tumor samples, whole-exome sequencing (WES) is often used for its reliability and relative low cost. RNA-seq, while generally used to measure gene expression, can potentially also be used for identification of somatic mutations. However there has been little systematic evaluation of the utility of RNA-seq for identifying somatic mutations. Here, we develop and evaluate a pipeline for processing RNA-seq data from glioblastoma multiforme (GBM) tumors in order to identify somatic mutations. The pipeline entails the use of the STAR aligner 2-pass procedure jointly with MuTect2 from genome analysis toolkit (GATK) to detect somatic variants. Variants identified from RNA-seq data were evaluated by comparison against the COSMIC and dbSNP databases, and also compared to somatic variants identified by exome sequencing. We also estimated the putative functional impact of coding variants in the most frequently mutated genes in GBM. Interestingly, variants identified by RNA-seq alone showed better representation of GBM-related mutations cataloged by COSMIC. RNA-seq-only data substantially outperformed the ability of WES to reveal potentially new somatic mutations in known GBM-related pathways, and allowed us to build a high-quality set of somatic mutations common to exome and RNA-seq calls. Using RNA-seq data in parallel with WES data to detect somatic mutations in cancer genomes can thus broaden the scope of discoveries and lend additional support to somatic variants identified by exome sequencing alone.

An alternative splicing switch in FLNB promotes the mesenchymal cell state in human breast cancer

Alternative splicing of mRNA precursors represents a key gene expression regulatory step and permits the generation of distinct protein products with diverse functions. In a genome-scale expression screen for inducers of the epithelial-to-mesenchymal transition (EMT), we found a striking enrichment of RNA-binding proteins. We validated that QKI and RBFOX1 were necessary and sufficient to induce an intermediate mesenchymal cell state and increased tumorigenicity. Using RNA-seq and eCLIP analysis, we found that QKI and RBFOX1 coordinately regulated the splicing and function of the actin-binding protein FLNB, which plays a causal role in the regulation of EMT. Specifically, the skipping of FLNB exon 30 induced EMT by releasing the FOXC1 transcription factor. Moreover, skipping of FLNB exon 30 is strongly associated with EMT gene signatures in basal-like breast cancer patient samples. These observations identify a specific dysregulation of splicing, which regulates tumor cell plasticity and is frequently observed in human cancer.

As the human body develops, countless cells change from one state into another. Two important cell states are known as epithelial and mesenchymal. Cells in the epithelial state tend to be tightly connected and form barriers, like skin cells. Mesenchymal state cells are loosely organized, move around more and make up connective tissues. Some cells alternate between these states via an epithelial-to-mesenchymal transition (EMT for short) and back again. Without this transition, certain organs would not develop and wounds would not heal. Yet, cancer cells also use this transition to spread to distant sites of the body. Such cancers are often the most aggressive, and therefore the most deadly.

The epithelial-to-mesenchymal transition is dynamically regulated in a reversible manner. For example, the genes for some proteins might only be active in the epithelial state and further reinforce this state by turning on other ‘epithelial genes’. Alternatively, there might be differences in the processing of mRNA molecules – the intermediate molecules between DNA and protein – that result in the production of different proteins in epithelial and mesenchymal cells.

Li, Choi et al. wanted to know which of the thousands of human genes can endow epithelial state cells with mesenchymal characteristics. A better understanding of the switch could help to prevent cancers undergoing an epithelial-to-mesenchymal transition.

From a large-scale experiment in human breast cancer cells, Li, Choi et al. found that a group of proteins that bind and modify mRNA molecules are important for the epithelial-to-mesenchymal transition. Two proteins in particular promoted the transition, most likely by binding to the mRNA of a third protein called FLNB and removing a small piece of it. FLNB normally works to prevent the epithelial-to-mesenchymal transition, but the smaller protein encoded by the shorter mRNA promoted the transition by turning on ‘mesenchymal genes’.

This switching between different FLNB proteins happens in some of the more aggressive breast cancers, which also contain mesenchymal cells. Finding out which FLNB protein is made in a given cancer may provide an indication of its aggressiveness. Also, looking for drugs that can target the mRNA-binding proteins or FLNB may one day lead to new treatments for some of the most aggressive breast cancers.

Endosomal sorting and c-Cbl targeting of paxillin to autophagosomes regulate cell-matrix adhesion turnover in human breast cancer cells

Post-translational mechanisms regulating cell-matrix adhesion turnover during cell locomotion are not fully elucidated. In this study, we uncovered an essential role of Y118 site-specific tyrosine phosphorylation of paxillin, an adapter protein of focal adhesion complexes, in paxillin recruitment to autophagosomes to trigger turnover of peripheral focal adhesions in human breast cancer cells. We demonstrate that the Rab-7 GTPase is a key upstream regulator of late endosomal sorting of tyrosine118-phosphorylated paxillin, which is subsequently recruited to autophagosomes via the cargo receptor c-Cbl. Essentially, this recruitment involves a direct and selective interaction between Y118-phospho-paxillin, c-Cbl, and LC3 and is independent from c-Cbl E3 ubiquitin ligase activity. Interference with the Rab7-paxillin-autophagy regulatory network using genetic and pharmacological approaches greatly impacted focal adhesion stability, cell locomotion and progression to metastasis using a panel of human breast cancer cells. Together, these results provide novel insights into the requirement of phospho-site specific post-translational mechanism of paxillin for autophagy targeting to regulate cell-matrix adhesion turnover and cell locomotion in breast cancer cells.

Signaling regulation and role of filamin A cleavage in Ca2+-stimulated migration of androgen receptor-deficient prostate cancer cells

Ca²⁺, a ubiquitous cellular signal, and filamin A, an actin-binding protein, play an important role in the regulation of cell adhesion, shape and motility. Using transwell filters to analyze cell migration, we found that extracellular Ca²⁺ (Ca_o²⁺) promotes the migration of androgen receptor (AR)-deficient and highly metastatic prostate cancer cell lines (DU145 and PC-3) compared to AR-positive and relatively less metastatic prostate cancer cells (LNCaP). Furthermore, we found that expression of filamin A is up-regulated in DU145 and PC-3 cells, and that Ca_o²⁺ significantly induces the cleavage of filamin A. Silencing expression of Ca²⁺-sensing receptor (CaR) and p115RhoGEF, and treating with leupeptin, a protease inhibitor, and ALLM, a calpain specific inhibitor, we further demonstrate that Ca_o²⁺-induced filamin A cleavage occurs via a CaR- p115RhoGEF-calpain dependent pathway. Our data show that Ca_o²⁺ via CaR- mediated signaling induces filamin A cleavage and promotes the migration in AR-deficient and highly metastatic prostate cancer cells.

RSK2 activity mediates glioblastoma invasiveness and is a potential target for new therapeutics

In glioblastoma (GBM), infiltration of primary tumor cells into the normal tissue and dispersal throughout the brain is a central challenge to successful treatment that remains unmet. Indeed, patients respond poorly to the current therapies of tumor resection followed by chemotherapy with radiotherapy and have only a 16-month median survival. It is therefore imperative to develop novel therapies. RSK2 is a kinase that regulates proliferation and adhesion and can promote metastasis. We demonstrate that active RSK2 regulates GBM cell adhesion and is essential for cell motility and invasion of patient-derived GBM neurospheres. RSK2 control of adhesion and migration is mediated in part by its effects on integrin-Filamin A complexes. Importantly, inhibition of RSK2 by either RSK inhibitors or shRNA silencing impairs invasion and combining RSK2 inhibitors with temozolomide improves efficacy in vitro. In agreement with the in vitro data, using public datasets, we find that RSK2 is significantly upregulated in vivo in human GBM patient tumors, and that high RSK2 expression significantly correlates with advanced tumor stage and poor patient survival. Together, our data provide strong evidence that RSK inhibitors could enhance the effectiveness of existing GBM treatment, and support RSK2 targeting as a promising approach for novel GBM therapy.

Quantitative mass spectrometry analysis reveals a panel of nine proteins as diagnostic markers for colon adenocarcinomas

Adenocarcinomas are cancers originating from the gland forming cells of the colon and rectal lining, and are known to be the most common type of colorectal cancers. The current diagnosis strategies for colorectal cancers include biopsy, laboratory tests, and colonoscopy which are time consuming. Identification of protein biomarkers could aid in the detection of colon adenocarcinomas (CACs). In this study, tissue proteome of colon adenocarcinomas (n = 11) was compared with the matched control specimens (n = 11) using isobaric tags for relative and absolute quantitation (iTRAQ) based liquid chromatography-mass spectrometry (LC-MS/MS) approach. A list of 285 significantly altered proteins was identified in colon adenocarcinomas as compared to its matched controls, which are associated with growth and malignancy of the tumors. Protein interaction analysis revealed the association of altered proteins in colon adenocarcinomas with various transcription factors and their targets. A panel of nine proteins was validated using multiple reaction monitoring (MRM). Additionally, S100A9 was also validated using immunoblotting. The identified panel of proteins may serve as potential biomarkers and thereby aid in the detection of colon adenocarcinomas.

Keap1 Inhibits Metastatic Properties of NSCLC Cells by Stabilizing Architectures of F-Actin and Focal Adhesions

Low expression of the tumor suppressor Kelch-like ECH-associated protein 1 (KEAP1) in non-small cell lung cancer (NSCLC) often results in higher malignant biological behavior and poor prognosis; however, the underlying mechanism remains unclear. The present study demonstrates that overexpression of Keap1 significantly suppresses migration and invasion of three different lung cancer cells (A549, H460, and H1299). Highly expressed Keap1, compared with the control, promotes formation of multiple stress fibers with larger mature focal adhesion complexes in the cytoplasm where only fine focal adhesions were observed in the membrane under control conditions. RhoA activity significantly increased when Keap1 was overexpressed, whereas Myosin 9b expression was reduced but could be rescued by proteasome inhibition. Noticeably, mouse tumor xenografts with Keap1 overexpression were smaller in size and less metastatic relative to the control group. Taken together, these results demonstrate that Keap1 stabilizes F-actin cytoskeleton structures and inhibits focal adhesion turnover, thereby restraining the migration and invasion of NSCLC. Therefore, increasing Keap1 or targeting its downstream molecules might provide potential therapeutic benefits for the treatment of patients with NSCLC.Implications: This study provides mechanistic insight on the metastatic process in NSCLC and suggests that Keap1 and its downstream molecules may be valuable drug targets for NSCLC patients. Mol Cancer Res; 16(3); 508-16. ©2018 AACR.

Filamin A (FLNA) regulates autophagy of bladder carcinoma cell and affects its proliferation, invasion and metastasis

PURPOSE

This research intended to explore the effect of FLNA on cell proliferation, invasion and migration in bladder carcinoma (BC).

METHODS

Microarray analysis was performed with the TCGA data, and the results were confirmed on 20 paired BC tissues and adjacent tissues using qRT-PCR and immunohistochemistry. Transmission electron microscope (TEM) and cell fluorescence assay were used to observe the quantity of autophagosomes. The expression of autophagy-related protein (LC3-I/II, p62) was detected by western blot. Cell proliferation was detected using CCK-8 and colony formation. The invasion and migration ability of the cell were tested by transwell and wound-healing assay. Tumor xenograft in BALB/c nude mice and HE staining were utilized to probe into the effects of FLNA-induced regulation of volume, weight and metastasis of tumors.

RESULTS

We confirmed that FLNA was down-regulated in BC tissues. TEM and fluorescence analysis proved that FLNA overexpression promoted autophagy in BC cells. Colony formation assay and CCK-8 experiment showed that FLNA overexpression suppressed the proliferation of BC cells. In addition, FLNA blocked cell cycle and promoted apoptosis of BC cell. Transwell assay and wound-healing assay further proved that FLNA suppressed invasion and migration ability in BC cell. Meanwhile, in vivo study indicated that FLNA inhibited the tumor growth.

CONCLUSION

Overexpression of FLNA suppressed the proliferation, migration and invasion of the BC cell, suggesting the potential role of FLNA in clinical treatment.

Matrix Stiffness Differentially Regulates Cellular Uptake Behavior of Nanoparticles in Two Breast Cancer Cell Lines

Matrix stiffness regulates cell behavior in various biological contexts. In breast tumors, the deposition of extracellular matrix correlates with increasing matrix stiffness and poor survival. Nanoparticulate carriers represent a promising therapeutic vehicle for disease diagnosis and efficient anticancer drug delivery. However, how matrix stiffness influences cellular uptake of nanoparticles remains largely unexplored. Here, we selected photopolymerized polyacrylamide gels with varying stiffnesses as model substrates and studied the impact of matrix stiffness on cell morphology and nanoparticle uptake efficiency in two representative breast cancer cell lines with varying invasiveness, that is, MCF-7 with low invasiveness and MDA-MB-231 with high invasiveness. In our study, both cell lines showed similar morphological changes with changing stiffness. MCF-7 cells adhered on compliant substrates (1 kPa) showed a roundlike morphology with the lowest cell uptake efficiency among four stiffnesses under investigation at each given time point, whereas for MDA-MB-231 cells, the uptake efficiency showed no significant differences across varying stiffnesses. The percentages of MCF-7 cell proliferation on a 1 kPa substrate were significantly decreased at 48 and 72 h as compared to those on stiff substrates and coverslips. When treated with pluronic/d-α-tocopheryl polyethylene glycol 1000 succinate mixed micelle-loaded paclitaxel, cells on stiff substrates of 7, 20, and 25 kPa showed higher cell apoptosis rates as compared to those of cells on 1 kPa substrates. To sum up, our work presents an example of how physical cues impact specific cellular behavior and function, which may further contribute to engineering nanoparticulate delivery systems for more efficient delivery in vivo.

Filamin A upregulation correlates with Snail-induced epithelial to mesenchymal transition (EMT) and cell adhesion but its inhibition increases the migration of colon adenocarcinoma HT29 cells

Filamin A (FLNA) is actin filament cross-linking protein involved in cancer progression. Its importance in regulating cell motility is directly related to the epithelial to mesenchymal transition (EMT) of tumor cells. However, little is known about the mechanism of action of FLNA at this early stage of cancer invasion. Using immunochemical methods, we evaluated the levels and localization of FLNA, pFLNA[Ser2152], β1 integrin, pβ1 integrin[Thr788/9], FAK, pFAK[Y379], and talin in stably transfected HT29 adenocarcinoma cells overexpressing Snail and looked for the effect of Snail in adhesion and migration assays on fibronectin-coated surfaces before and after FLNA silencing. Our findings indicate that FLNA upregulation correlates with Snail-induced EMT in colorectal carcinoma. FLNA localizes in the cytoplasm and at the sites of focal adhesion (FA) of invasive cells. Silencing of FLNA inhibits Snail-induced cell adhesion, reduces the size of FA sites, induces the relocalization of talin from the cytoplasm to the membrane area and augments cell migratory properties. Our findings suggest that FLNA may not act as a classic integrin inhibitor in invasive carcinoma cells, but is involved in other pro-invasive pathways. FLNA upregulation, which correlates with cell metastatic properties, maybe an additional target for combination therapy in colorectal carcinoma tumor progression.

Runx3 inhibits melanoma cell migration through regulation of cell shape change

The transcription factor Runx3 is a known tumor suppressor gene, and its expression is frequently lost in melanoma. However, the potential contribution of the loss of Runx3 expression to melanoma development and progression remains unclear. In this in vitro study, we demonstrated that ectopic Runx3 re-expression in B16-F10 melanoma cells changed the cell shape from elongated and branched to spread and unbranched, which enhanced stress fiber formation, increased the number of mature and fibrillar focal adhesions, and up-regulated fibronectin expression. In association with the cell shape change, the Runx3 re-expression in B16-F10 melanoma cells inhibited cell migration. Moreover, the phenotype of the Runx3 induced cell shape change was partially resembled when the melanoma cells were cultured on a fibronectin-coated coverslip, suggesting that fibronectin may mediate the Runx3 induced cell shape change of the melanoma cells. Taken together, our findings suggest that Runx3 may regulate cell shape to inhibit melanoma cell migration partly through enhancing stress fiber formation and ECM protein production. Our present study provides further evidence for the idea that cell shape change is potentially correlated with melanoma development and progression.

Filamin A is required for spindle migration and asymmetric division in mouse oocytes

Dynamic changes in the actin network are crucial for the cortical migration of spindles and establishment of polarity, to ensure asymmetric division during meiotic maturation. In this study, filamin A (FLNA) was found to be an essential actin regulator that controlled spindle migration and asymmetric division during oocyte meiosis. FLNA was localized in the cytoplasm and enriched at the cortex and near the chromosomes. Knockdown of FLNA impaired meiotic asymmetric division and spindle migration with a decrease in the amount of cytoplasmic actin mesh and cortical actin levels. Moreover, FLNA knockdown reduced the phosphorylation of cofilin and Rho kinase (ROCK) near the spindle. Similar phenotypes, such as decreased filament actin levels, impaired spindle migration and polar body extrusion, were observed when active cofilin (S3A) was overexpressed or ROCK was inhibited. Notably, we found that FLNA and ROCK interacted directly in mouse oocytes. Taken together, our results show that FLNA plays crucial roles in asymmetric division during meiotic maturation by regulating ROCK-cofilin-mediated actin reorganization.-Wang, H., Guo J., Lin, Z., Namgoong, S., Oh, J. S., Kim, N.-H. Filamin A is required for spindle migration and asymmetric division in mouse oocytes.

Ectopic overexpression of filamin C scaffolds MEK1/2 and ERK1/2 to promote the progression of human hepatocellular carcinoma

Hepatocellular carcinoma (HCC) invasion and metastasis are mediated by a complicated signal transduction network and downstream cytoskeletal and adhesion molecules. In this study, a microarray-based analysis revealed a dramatic increase in filamin C (FLNC), which is commonly expressed in muscle rather than in liver cells, in the two metastatic HCC cell lines MHCC97L and HCCLM3. Clinicopathological studies showed that increased FLNC expression was associated with microvascular invasion and poor prognosis. Specific hypomethylation was identified within the FLNC promoter region in HCC cell lines and patient tumor samples, which might contribute to the ectopic overexpression of FLNC. FLNC downregulation inhibited cell migration and impaired cell proliferation and promoted apoptosis. Mechanistic studies suggested that FLNC interacts with mitogen-activated extracellular signal-regulated kinase 1/2 (MEK1/2) and extracellular signal-regulated kinase 1/2 (ERK1/2) and that FLNC downregulation inhibited MEK1/2 and ERK1/2 activation. Xenographic tumor transplantation experiments in nude mice further confirmed the role of FLNC in HCC progression and metastasis. Our results reveal a novel mechanism by which the cytoskeletal protein FLNC enhances the mitogen-activated protein kinase signaling pathway during tumorigenesis.

Cytoskeletal Filamin A Differentially Modulates RNA Polymerase III Gene Transcription in Transformed Cell Lines

Cytoskeletal filamin A (FLNA) is an important protein involved in multiple cellular processes. Previous studies have shown that FLNA can promote or inhibit cancer growth and development; however, the mechanisms underlying these events are not fully understood. Here we show that, in both 293T and SaOS2 cells, knockdown of FLNA significantly enhanced transcription of RNA polymerase (pol) III-transcribed genes except for a subset of tRNA genes. In contrast, re-expression of FLNA in an FLNA-deficient melanoma cell line (A7) repressed transcription of all pol III-transcribed genes, suggesting that FLNA inhibits pol III transcription in a cell type-specific manner. Chromatin immunoprecipitation assays revealed that the repression of pol III gene transcription by FLNA correlates with the decreased occupancy of the RNA pol III transcription machinery at promoters. Immunofluorescence microscopy and coimmunoprecipitation assays revealed that FLNA can associate with the RNA pol III transcription machinery through its actin-binding domain within nuclei. Mechanistic analysis revealed that FLNA suppresses pol III gene transcription by confining the recruitment of the RNA pol III transcription machinery at the promoters of the genes that are sensitive to the alteration of FLNA expression. These findings not only extend the understanding of FLNA function in cells but also provide novel insights into the mechanism by which FLNA represses cell proliferation.

Genome-wide mutation profiles of colorectal tumors and associated liver metastases at the exome and transcriptome levels

To characterize the mutation profiles of colorectal cancer (CRC) primary tumors (PTs) and liver metastases (CLMs), we performed both whole-exome and RNA sequencing. Ten significantly mutated genes, including BMI1, CARD11, and NRG1, were found in 34 CRCs with CLMs. We defined three mutation classes (Class 1 to 3) based on the absence or presence of mutations during liver metastasis. Most mutations were classified into Class 1 (shared between PTs and CLMs), suggesting the common clonal origin of PTs and CLMs. Class 1 was more strongly associated with the clinical characteristics of advanced cancer and was more frequently superimposed with chromosomal deletions in CLMs than Class 2 (PT-specific). The integration of exome and RNA sequencing revealed that variant-allele frequencies (VAFs) of mutations in the transcriptome tended to have stronger functional implications than those in the exome. For instance, VAFs of the TP53 and APC mutations in the transcriptome significantly correlated with the expression level of their target genes. Additionally, mutations with high functional impact were enriched with high VAFs in the CLM transcriptomes. We identified 11 mutation-associated splicing events in the CRC transcriptomes. Thus, the integration of the exome and the transcriptome may elucidate the underlying molecular events responsible for CLMs.

Focal adhesion kinase overexpression and its impact on human osteosarcoma

Focal adhesion kinase (FAK) has been implicated in tumorigenesis in various malignancies. We sought to examine the expression patterns of FAK and the activated form, phosphorylated FAK (pFAK), in human osteosarcoma and to investigate the correlation of FAK expression with clinicopathologic parameters and prognosis. In addition, the functional consequence of manipulating the FAK protein level was investigated in human osteosarcoma cell lines. Immunohistochemical staining was used to detect FAK and pFAK in pathologic archived materials from 113 patients with primary osteosarcoma. Kaplan-Meier survival and Cox regression analyses were performed to evaluate the prognoses. The role of FAK in the cytological behavior of MG63 and 143B human osteosarcoma cell lines was studied via FAK protein knock down with siRNA. Cell proliferation, migration, invasiveness and apoptosis were assessed using the CCK8, Transwell and Annexin V/PI staining methods. Both FAK and pFAK were overexpressed in osteosarcoma. There were significant differences in overall survival between the FAK-/pFAK- and FAK+/pFAK- groups (P = 0.016), the FAK+/pFAK- and FAK+/pFAK+ groups (P = 0.012) and the FAK-/pFAK- and FAK+/pFAK+ groups (P < 0.001). There were similar differences in metastasis-free survival between groups. The Cox proportional hazards analysis showed that the FAK expression profile was an independent indicator of both overall and metastasis-free survival. SiRNA-based knockdown of FAK not only dramatically reduced the migration and invasion of MG63 and 143B cells, but also had a distinct effect on osteosarcoma cell proliferation and apoptosis. These results collectively suggest that FAK overexpression and phosphorylation might predict more aggressive biologic behavior in osteosarcoma and may be an independent predictor of poor prognosis.

Stroma derived COL6A3 is a potential prognosis marker of colorectal carcinoma revealed by quantitative proteomics

Colorectal cancer (CRC) represents the third most common cancer in males and second in females worldwide. Here, we performed a quantitative 8-plex iTRAQ proteomics analysis of the secreted proteins from five colonic fibroblast cultures and three colon cancer epithelial cell lines. We identified 1114 proteins at 0% FDR, including 587 potential secreted proteins. We further recognized 116 fibroblast-enriched proteins which were significantly associated with cell movement, angiogenesis, proliferation and wound healing, and 44 epithelial cell-enriched proteins. By interrogation of Oncomine database, we found that 20 and 8 fibroblast-enriched proteins were up- and downregulated in CRC, respectively. Western blots confirmed the fibroblast-specific secretion of filamin C, COL6A3, COL4A1 and spondin-2. Upregulated mRNA and stroma expression of COL6A3 in CRC, which were revealed by Oncomine analyses and tissue-microarray-immunohistochemistry, indicated poor prognosis. COL6A3 expression was significantly associated with Dukes stage, T stage, stage, recurrence and smoking status. Circulating plasma COL6A3 in CRC patients was upregulated significantly comparing with healthy peoples. Receiver operating characteristic curve analysis revealed that COL6A3 has better predictive performance for CRC with an area under the curve of 0.885 and the best sensitivity/specificity of 92.9%/81.3%. Thus we demonstrated that COL6A3 was a potential diagnosis and prognosis marker of CRC.

Predominant Rab-GTPase amplicons contributing to oral squamous cell carcinoma progression to metastasis

Metastatic oral squamous cell carcinoma (OSCC) is frequently associated with recurrent gene abnormalities at specific chromosomal loci. Here, we utilized array comparative genomic hybridization and genome-wide screening of metastatic and non-metastatic tongue tumors to investigate genes potentially contributing to OSCC progression to metastasis. We identified predominant amplifications of chromosomal regions that encompass the RAB5, RAB7 and RAB11 genes (3p24-p22, 3q21.3 and 8p11-12, respectively) in metastatic OSCC. The expression of these Rab GTPases was confirmed by immunohistochemistry in OSCC tissues from a cohort of patients with a follow-up of 10 years. A significant overexpression of Rab5, Rab7 and Rab11 was observed in advanced OSCC cases and co-overexpression of these Rabs was predictive of poor survival (log-rank test, P = 0.006). We generated a Rab interaction network and identified central Rab interactions of relevance to metastasis signaling, including focal adhesion proteins. In preclinical models, mRNA and protein expression levels of these Rab members were elevated in a panel of invasive OSCC cell lines, and their down-regulation prevented cell invasion at least in part via inhibition of focal adhesion disassembly. In summary, our results provide insights into the cooperative role of Rab gene amplifications in OSCC progression and support their potential utility as prognostic markers and therapeutic approach for advanced OSCC.

Filamin-A is required to mediate SST2 effects in pancreatic neuroendocrine tumours

Somatostatin receptor type 2 (SST2) is the main pharmacological target of somatostatin (SS) analogues widely used in patients with pancreatic neuroendocrine tumours (P-NETs), this treatment being ineffective in a subset of patients. Since it has been demonstrated that Filamin A (FLNA) is involved in mediating GPCR expression, membrane anchoring and signalling, we investigated the role of this cytoskeleton protein in SST2 expression and signalling, angiogenesis, cell adhesion and cell migration in human P-NETs and in QGP1 cell line. We demonstrated that FLNA silencing was not able to affect SST2 expression in P-NET cells in basal conditions. Conversely, a significant reduction in SST2 expression (-43 ± 21%, P < 0.05 vs untreated cells) was observed in FLNA silenced QGP1 cells after long term SST2 activation with BIM23120. Moreover, the inhibitory effect of BIM23120 on cyclin D1 expression (-46 ± 18%, P < 0.05 vs untreated cells), P-ERK1/2 levels (-42 ± 14%; P < 0.05 vs untreated cells), cAMP accumulation (-24 ± 3%, P < 0.05 vs untreated cells), VEGF expression (-31 ± 5%, P < 0.01 vs untreated cells) and in vitro release (-40 ± 24%, P < 0.05 vs untreated cells) was completely lost after FLNA silencing. Interestingly, BIM23120 promoted cell adhesion (+86 ± 45%, P < 0.05 vs untreated cells) and inhibited cell migration (-24 ± 2%, P < 0.00001 vs untreated cells) in P-NETs cells and these effects were abolished in FLNA silenced cells. In conclusion, we demonstrated that FLNA plays a crucial role in SST2 expression and signalling, angiogenesis, cell adhesion and cell migration in P-NETs and in QGP1 cell line, suggesting a possible role of FLNA in determining the different responsiveness to SS analogues observed in P-NET patients.

Filamin C, a dysregulated protein in cancer revealed by label-free quantitative proteomic analyses of human gastric cancer cells

Gastric cancer (GC) is the fourth and fifth most common cancer in men and women, respectively. We identified 2,750 proteins at false discovery rates of 1.3% (protein) and 0.03% (spectrum) by comparing the proteomic profiles of three GC and a normal gastric cell lines. Nine proteins were significantly dysregulated in all three GC cell lines, including filamin C, a muscle-specific filamin and a large actin-cross-linking protein. Downregulation of filamin C in GC cell lines and tissues were verified using quantitative PCR and immunohistochemistry. Data-mining using public microarray datasets shown that filamin C was significantly reduced in many human primary and metastasis cancers. Transient expression or silencing of filamin C affected the proliferation and colony formation of cancer cells. Silencing of endogenous filamin C enhanced cancer cell migration and invasion, whereas ectopic expression of filamin C had opposing effects. Silencing of filamin C increased the expression of matrix metallopeptidase 2 and improved the metastasis of prostate cancer in a zebrafish model. High filamin C associated with better prognosis of prostate cancer, leukemia and breast cancer patients. These findings establish a functional role of filamin C in human cancers and these data will be valuable for further study of its mechanisms.

Profilin-1 overexpression in MDA-MB-231 breast cancer cells is associated with alterations in proteomics biomarkers of cell proliferation, survival, and motility as revealed by global proteomics analyses

Despite early screening programs and new therapeutic strategies, metastatic breast cancer is still the leading cause of cancer death in women in industrialized countries and regions. There is a need for novel biomarkers of susceptibility, progression, and therapeutic response. Global analyses or systems science approaches with omics technologies offer concrete ways forward in biomarker discovery for breast cancer. Previous studies have shown that expression of profilin-1 (PFN1), a ubiquitously expressed actin-binding protein, is downregulated in invasive and metastatic breast cancer. It has also been reported that PFN1 overexpression can suppress tumorigenic ability and motility/invasiveness of breast cancer cells. To obtain insights into the underlying molecular mechanisms of how elevating PFN1 level induces these phenotypic changes in breast cancer cells, we investigated the alteration in global protein expression profiles of breast cancer cells upon stable overexpression of PFN1 by a combination of three different proteome analysis methods (2-DE, iTRAQ, label-free). Using MDA-MB-231 as a model breast cancer cell line, we provide evidence that PFN1 overexpression is associated with alterations in the expression of proteins that have been functionally linked to cell proliferation (FKPB1A, HDGF, MIF, PRDX1, TXNRD1, LGALS1, STMN1, LASP1, S100A11, S100A6), survival (HSPE1, HSPB1, HSPD1, HSPA5 and PPIA, YWHAZ, CFL1, NME1) and motility (CFL1, CORO1B, PFN2, PLS3, FLNA, FLNB, NME2, ARHGDIB). In view of the pleotropic effects of PFN1 overexpression in breast cancer cells as suggested by these new findings, we propose that PFN1-induced phenotypic changes in cancer cells involve multiple mechanisms. Our data reported here might also offer innovative strategies for identification and validation of novel therapeutic targets and companion diagnostics for persons with, or susceptibility to, breast cancer.

Structural mechanism of integrin inactivation by filamin

Activation of heterodimeric (αβ) integrin is crucial for regulating cell adhesion. Binding of talin to the cytoplasmic face of integrin activates the receptor, but how integrin is maintained in a resting state to counterbalance its activation has remained obscure. Here, we report the structure of the cytoplasmic domain of human integrin αIIbβ3 bound to its inhibitor, the immunoglobin repeat 21 of filamin A (FLNa-Ig21). The structure reveals an unexpected ternary complex in which FLNa-Ig21 not only binds to the C terminus of the integrin β3 cytoplasmic tail (CT), as previously predicted, but also engages N-terminal helices of αIIb and β3 CTs to stabilize an inter-CT clasp that helps restrain the integrin in a resting state. Combined with functional data, the structure reveals a new mechanism of filamin-mediated retention of inactive integrin, suggesting a new framework for understanding regulation of integrin activation and adhesion.

Filamin B Enhances the Invasiveness of Cancer Cells into 3D Collagen Matrices

Numerous types of cancer cells migrate into extracellular tissues. This phenomenon is termed invasion, and is associated with poor prognosis in cancer patients. In this study, we demonstrated that filamin B (FLNb), an actin-binding protein, is highly expressed in cancer cell lines that exhibit high invasiveness, with a spindle morphology, into 3D collagen matrices. In addition, we determined that knockdown of FLNb in invasive cancer cells converts cell morphology from spindle-shaped, which is associated with high invasiveness, to round-shaped with low invasiveness. Furthermore, di-phosphorylation of myosin regulatory light chain (MRLC) and phosphorylation of focal adhesion kinase (FAK) are inhibited in FLNb-knockdown cancer cells. These results suggest that FLNb enhances invasion of cancer cells through phosphorylation of MRLC and FAK. Therefore, FLNb may be a new therapeutic target for invasive cancers.

MEK-ERK1/2-dependent FLNA overexpression promotes abnormal dendritic patterning in tuberous sclerosis independent of mTOR

Abnormal dendritic complexity is a shared feature of many neurodevelopmental disorders associated with neurological defects. Here, we found that the actin-crosslinking protein filamin A (FLNA) is overexpressed in tuberous sclerosis complex (TSC) mice, a PI3K-mTOR model of neurodevelopmental disease that is associated with abnormal dendritic complexity. Both under- and overexpression of FLNA in wild-type neurons led to more complex dendritic arbors in vivo, suggesting that an optimal level of FLNA expression is required for normal dendritogenesis. In Tsc1(null) neurons, knocking down FLNA in vivo prevented dendritic abnormalities. Surprisingly, FLNA overexpression in Tsc1(null) neurons was dependent on MEK1/2 but not mTOR activity, despite both pathways being hyperactive. In addition, increasing MEK-ERK1/2 activity led to dendritic abnormalities via FLNA, and decreasing MEK-ERK1/2 signaling in Tsc1(null) neurons rescued dendritic defects. These data demonstrate that altered FLNA expression increases dendritic complexity and contributes to pathologic dendritic patterning in TSC in an mTOR-independent, ERK1/2-dependent manner.

Transcriptome-wide landscape of pre-mRNA alternative splicing associated with metastatic colonization

Metastatic colonization is an ominous feature of cancer progression. Recent studies have established the importance of pre-mRNA alternative splicing (AS) in cancer biology. However, little is known about the transcriptome-wide landscape of AS associated with metastatic colonization. Both in vitro and in vivo models of metastatic colonization were utilized to study AS regulation associated with cancer metastasis. Transcriptome profiling of prostate cancer cells and derivatives crossing in vitro or in vivo barriers of metastasis revealed splicing factors with significant gene expression changes associated with metastatic colonization. These include splicing factors known to be differentially regulated in epithelial-mesenchymal transition (ESRP1, ESRP2, and RBFOX2), a cellular process critical for cancer metastasis, as well as novel findings (NOVA1 and MBNL3). Finally, RNA-seq indicated a large network of AS events regulated by multiple splicing factors with altered gene expression or protein activity. These AS events are enriched for pathways important for cell motility and signaling, and affect key regulators of the invasive phenotype such as CD44 and GRHL1.

IMPLICATIONS

Transcriptome-wide remodeling of AS is an integral regulatory process underlying metastatic colonization, and AS events affect the metastatic behavior of cancer cells.

GATA2 as a potential metastasis-driving gene in prostate cancer

Effective treatment for metastatic prostate cancer is critically needed. The present study was aimed at identifying metastasis-driving genes as potential targets for therapy (oncotargets). A differential gene expression profile of metastatic LTL-313H and non-metastatic LTL-313B prostate cancer tissue xenografts, derived from one patient's specimen, was subjected to integrative analysis using the Ingenuity Upstream Regulator Analysis tool. Six candidate master regulatory genes were identified, including GATA2, a gene encoding a pioneer factor, a special transcription factor facilitating the recruitment of additional transcription factors. Elevated GATA2 expression in metastatic prostate cancer tissues correlated with poor patient prognosis. Furthermore, GATA2 gene silencing in human prostate cancer LNCaP cells led to a marked reduction in cell migration, tissue invasion, focal adhesion disassembly and to a dramatic change in cell transcriptomes, indicating that GATA2 plays a critical role in prostate cancer metastasis. As such, GATA2 could represent a prostate cancer metastasis-driving gene and a potential target for therapy of metastatic prostate cancer.

Dopamine and Somatostatin Analogues Resistance of Pituitary Tumors: Focus on Cytoskeleton Involvement

Pituitary tumors, that origin from excessive proliferation of a specific subtype of pituitary cell, are mostly benign tumors, but may cause significant morbidity in affected patients, including visual and neurologic manifestations from mass-effect, or endocrine syndromes caused by hormone hypersecretion. Dopamine (DA) receptor DRD2 and somatostatin (SS) receptors (SSTRs) represent the main targets of pharmacological treatment of pituitary tumors since they mediate inhibitory effects on both hormone secretion and cell proliferation, and their expression is retained by most of these tumors. Although long-acting DA and SS analogs are currently used in the treatment of prolactin (PRL)- and growth hormone (GH)-secreting pituitary tumors, respectively, clinical practice indicates a great variability in the frequency and entity of favorable responses. The molecular basis of the pharmacological resistance are still poorly understood, and several potential molecular mechanisms have been proposed, including defective expression or genetic alterations of DRD2 and SSTRs, or an impaired signal transduction. Recently, a role for cytoskeleton protein filamin A (FLNA) in DRD2 and SSTRs receptors expression and signaling in PRL- and GH-secreting tumors, respectively, has been demonstrated, first revealing a link between FLNA expression and responsiveness of pituitary tumors to pharmacological therapy. This review provides an overview of the known molecular events involved in SS and DA resistance, focusing on the role played by FLNA.

Tyrosyl phosphorylated serine-threonine kinase PAK1 is a novel regulator of prolactin-dependent breast cancer cell motility and invasion

Despite efforts to discover the cellular pathways regulating breast cancer metastasis, little is known as to how prolactin (PRL) cooperates with extracellular environment and cytoskeletal proteins to regulate breast cancer cell motility and invasion. We implicated serine-threonine kinase p21-activated kinase 1 (PAK1) as a novel target for PRL-activated Janus-kinase 2 (JAK2). JAK2-dependent PAK1 tyrosyl phosphorylation plays a critical role in regulation of both PAK1 kinase activity and scaffolding properties of PAK1. Tyrosyl phosphorylated PAK1 facilitates PRL-dependent motility via at least two mechanisms: formation of paxillin/GIT1/βPIX/pTyr-PAK1 complexes resulting in increased adhesion turnover and phosphorylation of actin-binding protein filamin A. Increased adhesion turnover is the basis for cell migration and phosphorylated filamin A stimulates the kinase activity of PAK1 and increases actin-regulating activity to facilitate cell motility. Tyrosyl phosphorylated PAK1 also stimulates invasion of breast cancer cells in response to PRL and three-dimensional (3D) collagen IV via transcription and secretion of MMP-1 and MMP-3 in a MAPK-dependent manner. These data illustrate the complex interaction between PRL and the cell microenvironment in breast cancer cells and suggest a pivotal role for PRL/PAK1 signaling in breast cancer metastasis.

Appreciating force and shape—the rise of mechanotransduction in cell biology

Although the shapes of organisms are encoded in their genome, the developmental processes that lead to the final form of vertebrates involve a constant feedback between dynamic mechanical forces, and cell growth and motility. Mechanobiology has emerged as a discipline dedicated to the study of the effects of mechanical forces and geometry on cell growth and motility—for example, during cell-matrix adhesion development—through the signalling process of mechanotransduction.

Targeting filamin B induces tumor growth and metastasis via enhanced activity of matrix metalloproteinase-9 and secretion of VEGF-A

Filamins regulate cell locomotion and associate with diverse signaling molecules. We have recently found that targeting filamin A (FLNA) reduces RAS-induced lung adenocarcinomas. In this study, we explored the role of another major filamin isoform, filamin B (FLNB), in tumor development. In contrast to FLNA, we report that targeting FLNB enhances RAS-induced tumor growth and metastasis which is associated with higher matrix metallopeptidase-9 (MMP-9) and extracellular signal-regulated kinase (ERK) activity. Flnb deficiency in mouse embryonic fibroblasts results in increased proteolytic activity of MMP-9 and cell invasion mediated by the RAS/ERK pathway. Similarly, silencing FLNB in multiple human cancer cells increases the proteolytic activity of MMP-9 and tumor cell invasion. Furthermore, we observed that Flnb-deficient RAS-induced tumors display more capillary structures that is correlated with increased vascular endothelial growth factor-A (VEGF-A) secretion. Inhibition of ERK activation blocks phorbol myristate acetate-induced MMP-9 activity and VEGF-A secretion in vitro. In addition, silencing FLNB in human ovarian cancer cells increases secretion of VEGF-A that induces endothelial cells to form more vascular structures in vitro. We conclude that FLNB suppresses tumor growth and metastasis by regulating the activity of MMP-9 and secretion of VEGF-A which is mediated by the RAS/ERK pathway.

Neurotherapeutic effects of novel HO-1 inhibitors in vitro and in a transgenic mouse model of Alzheimer's disease

Heme oxygenase-1 (HO-1) encoded by the HMOX1 gene is a 32-kDa stress protein that catabolizes heme to biliverdin, free iron, and carbon monoxide (CO). Glial HO-1 is over-expressed in the CNS of subjects with Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). The HMOX1 gene is exquisitely sensitive to oxidative stress and is induced in brain and other tissues in various models of disease and trauma. Induction of the glial HMOX1 gene may lead to pathological brain iron deposition, intracellular oxidative damage, and bioenergetic failure in AD and other human CNS disorders such as PD and MS. Therefore, targeted suppression of glial HO-1 hyperactivity may prove to be a rational and effective therapeutic intervention in AD and related neurodegenerative disorders. In this study, we report the effects of QC-47, QC-56, and OB-28, novel azole-based competitive and reversible inhibitors of HO-1, on oxidative damage to whole-cell and mitochondrial compartments in rat astrocytes transfected with the HMOX1 gene. We also report the effect of OB-28 on the behavior and neuropathology of APP(swe)/PS1(∆E9) mice. OB-28 was found to reduce oxidative damage to whole-cell and mitochondrial compartments in rat astrocytes transfected with the HMOX1 gene. Moreover, OB-28 was found to significantly counter behavioral deficits and neuropathological alterations in APP(swe)/PS1(∆E9) mice. Attenuation of AD-associated behavioral deficits and neuropathological changes suggests that HO-1 may be a promising target for neuroprotective intervention in AD and other neurodegenerative diseases. We propose that the targeted suppression of glial heme oxygenase-1 (HO-1) hyperactivity may prove to be a rational and effective therapeutic intervention in Alzheimer's disease (AD) and related neurodegenerative disorders. We report attenuation by a selective HO-1 inhibitor of oxidative damage to whole-cell and mitochondrial compartments in astrocytes in vitro and amelioration of behavioral anomalies in a transgenic mouse model of AD.

Clinical significance of FLNA and MMP-9 protein expression in gastric carcinoma

AIM: To detect the expression of filamin A (FLNA) and matrix metallopeptidase 9 (MMP-9) in gastric carcinoma and to analyze their clinical significance.

METHODS: Immunohistochemistry was used to detect FLNA and MMP-9 protein expression in 210 gastric cancer specimens and 50 normal tissues to study their correlations with clinical factors. The correlation between FLNA and MMMP-9 protein expression was also analyzed.

RESULTS: The level of FLNA protein expression was significantly lower in gastric cancer tissues than in normal tissues (P < 0.05). The level of MMP-9 protein expression was significantly higher in gastric cancer tissues than in normal tissues (P < 0.05). FLNA protein expression was not correlated with gender, age, or histological grade (P > 0.05), but correlated with lymph node metastasis, clinical stage and tumor invasion (P < 0.05). Moreover, there was a negative correlation between the expression of FLNA and MMP-9 protein in gastric cancer (r = -0.138, P = 0.044).

CONCLUSION: FLNA expression decreases in gastric cancer and correlates significantly with lymph node metastasis, clinical stage and tumor invasion, suggesting that FLNA may play an important role as a negative regulator of gastric carcinogenesis by promoting the degradation of MMP-9.

Grb7 and Filamin-a associate and are colocalized to cell membrane ruffles upon EGF stimulation

Grb7 is an adaptor molecule mediating signal transduction from multiple cell surface receptors to diverse downstream pathways. Grb7, along with Grb10 and Grb14, make up the Grb7 protein family. This protein family has been shown to be overexpressed in certain cancers and cancer cell lines. Grb7 and a receptor tyrosine kinase, ErbB2, are overexpressed in 20-30% of breast cancers. Grb7 overexpression has been linked to enhanced cell migration and metastasis, although the participants in these pathways have not been fully determined. In this study, we report the Grb7 protein interacts with Filamin-a, an actin-crosslinking component of the cell cytoskeleton. Additionally, we have demonstrated the interaction between Grb7 and Flna is specific to the RA-PH domains of Grb7, and the immunoglobulin-like repeat 16-19 domains of Flna. We demonstrate that full-length Grb7 and Flna interact in the mammalian cellular environment, as well as in vitro. Immunofluorescent microscopy shows potential co-localization of Grb7 and Flna in membrane ruffles upon epidermal growth factor stimulation. These studies are amongst the first to establish a clear connection between Grb7 signaling and cytoskeletal remodeling.

Distinct c-Met activation mechanisms induce cell rounding or invasion through pathways involving integrins, RhoA and HIP1

Many carcinomas have acquired oncogenic mechanisms for activating c-Met, including c-Met overexpression and excessive autocrine or paracrine stimulation with hepatocyte growth factor (HGF). However, the biological outcome of c-Met activation through these distinct modes remains ambiguous. Here, we report that HGF-mediated c-Met stimulation triggers a mesenchymal-type collective cell invasion. By contrast, the overexpression of c-Met promotes cell rounding. Moreover, in a high-throughput siRNA screen that was performed using a library of siRNAs against putative regulators of integrin activity, we identified RhoA and the clathrin-adapter protein HIP1 as crucial c-Met effectors in these morphological changes. Transient RhoA activation was necessary for the HGF-induced invasion, whereas sustained RhoA activity regulated c-Met-induced cell rounding. In addition, c-Met-induced cell rounding correlated with the phosphorylation of filamin A and the downregulation of active cell-surface integrins. By contrast, a HIP1-mediated increase in β1-integrin turnover was required for the invasion triggered by HGF. Taken together, our results indicate that c-Met induces distinct cell morphology alterations depending on the stimulus that activates c-Met.

Calpain 2 activation of P-TEFb drives megakaryocyte morphogenesis and is disrupted by leukemogenic GATA1 mutation

Megakaryocyte morphogenesis employs a "hypertrophy-like" developmental program that is dependent on P-TEFb kinase activation and cytoskeletal remodeling. P-TEFb activation classically occurs by a feedback-regulated process of signal-induced, reversible release of active Cdk9-cyclin T modules from large, inactive 7SK small nuclear ribonucleoprotein particle (snRNP) complexes. Here, we have identified an alternative pathway of irreversible P-TEFb activation in megakaryopoiesis that is mediated by dissolution of the 7SK snRNP complex. In this pathway, calpain 2 cleavage of the core 7SK snRNP component MePCE promoted P-TEFb release and consequent upregulation of a cohort of cytoskeleton remodeling factors, including α-actinin-1. In a subset of human megakaryocytic leukemias, the transcription factor GATA1 undergoes truncating mutation (GATA1s). Here, we linked the GATA1s mutation to defects in megakaryocytic upregulation of calpain 2 and of P-TEFb-dependent cytoskeletal remodeling factors. Restoring calpain 2 expression in GATA1s mutant megakaryocytes rescued normal development, implicating this morphogenetic pathway as a target in human leukemogenesis.

Hypoxia-induced and calpain-dependent cleavage of filamin A regulates the hypoxic response

The cellular response to hypoxia is regulated by hypoxia-inducible factor-1α and -2α (HIF-1α and -2α). We have discovered that filamin A (FLNA), a large cytoskeletal actin-binding protein, physically interacts with HIF-1α and promotes tumor growth and angiogenesis. Hypoxia induces a calpain-dependent cleavage of FLNA to generate a naturally occurring C-terminal fragment that accumulates in the cell nucleus. This fragment interacts with the N-terminal portion of HIF-1α spanning amino acid residues 1-390 but not with HIF-2α. In hypoxia this fragment facilitates the nuclear localization of HIF-1α, is recruited to HIF-1α target gene promoters, and enhances HIF-1α function, resulting in up-regulation of HIF-1α target gene expression in a hypoxia-dependent fashion. These results unravel an important mechanism that selectively regulates the nuclear accumulation and function of HIF-1α and potentiates angiogenesis and tumor progression.

The living aortic valve: From molecules to function

The aortic valve lies in a unique hemodynamic environment, one characterized by a range of stresses (shear stress, bending forces, loading forces and strain) that vary in intensity and direction throughout the cardiac cycle. Yet, despite its changing environment, the aortic valve opens and closes over 100,000 times a day and, in the majority of human beings, will function normally over a lifespan of 70–90 years. Until relatively recently heart valves were considered passive structures that play no active role in the functioning of a valve, or in the maintenance of its integrity and durability. However, through clinical experience and basic research the aortic valve can now be characterized as a living, dynamic organ with the capacity to adapt to its complex mechanical and biomechanical environment through active and passive communication between its constituent parts. The clinical relevance of a living valve substitute in patients requiring aortic valve replacement has been confirmed. This highlights the importance of using tissue engineering to develop heart valve substitutes containing living cells which have the ability to assume the complex functioning of the native valve.

The significance of dynamin 2 expression for prostate cancer progression, prognostication, and therapeutic targeting

Dynamin 2 (Dyn2) is essential for intracellular vesicle formation and trafficking, cytokinesis, and receptor endocytosis. In this study, we investigated the implication of Dyn2 as a prognostic marker and therapeutic target for progressive prostate cancer (PCA). We evaluated Dyn2 protein expression by immunohistochemistry in two cohorts: men with localized PCA treated by retropubic radical prostatectomy (n = 226), and men with advanced/castrate-resistant PCA (CRPC) treated by transurethral resection of prostate (TURP) (n = 253). The role of Dyn2 in cell invasiveness was assessed by in vitro and in vivo experiments using androgen-responsive and refractory PCA preclinical models. Dyn2 expression was significantly increased across advanced stages of PCA compared to benign prostate tissue (P < 0.0001). In the CRPC cohort, high Dyn2 was associated with higher Gleason score (P = 0.004) and marginally with cancer-specific mortality (P = 0.052). In preclinical models, Dyn2 gene silencing significantly reduced cell migration and invasion in vitro, as well as tumor size and lymph node metastases in vivo. In isolated PCA cells, Dyn2 was found to regulate focal adhesion turnover, which is critical for cell migration; this mechanism requires full Dyn2 compared to mutants deficient in GTPase activity. In conclusion, Dyn2 overexpression is associated with neoplastic prostate epithelium and is associated with poor prognosis. Inhibition of Dyn2 prevents cell invasiveness in androgen-responsive and -refractory PCA models, supporting the potential benefit of Dyn2 to serve as a therapeutic target for advanced PCA.

Pepper seed extract suppresses invasion and migration of human breast cancer cells

This study was performed to determine the antimetastatic activities of chili pepper seed on human breast cancer cells. The water extract of chili pepper seeds was prepared and it contained a substantial amount of phenols (131.12 mg%) and no capsaicinoids. Pepper seed extract (PSE) suppressed the proliferation of MDA-MB-231 and MCF-7 cells at the concentration of 10, 25, and 50 μg/ml (MDA-MB-231: IC50 = 20.1 μg/ml, MCF-7: IC50 = 14.7 μg/ml). PSE increased the expression level of E-cadherin up to 1.2-fold of the control in MCF-7 cells. PSE also decreased the secretion of matrix metalloproteinase (MMP)-2 and MMP-9 in MDA-MB-231 and MCF-7 cells at the concentration of 25 and 50 μg/ml. PSE treatment significantly suppressed the invasion of MDA-MB-231 and MCF-7 cells in a dose-dependent manner. The motility of cancer cells was apparently retarded in the wound healing assay by the PSE treatment. Although our data collectively demonstrate that PSE inhibits invasion and migration of breast cancer cells, further study is needed to identify specific mechanisms and bioactive components contributing to antimetastatic effects of chili pepper seed.

The dual role of filamin A in cancer: can't live with (too much of) it, can't live without it

Filamin A (FlnA) has been associated with actin as cytoskeleton regulator. Recently its role in the cell has come under scrutiny for FlnA's involvement in cancer development. FlnA was originally revealed as a cancer-promoting protein, involved in invasion and metastasis. However, recent studies have also found that under certain conditions, it prevented tumor formation or progression, confusing the precise function of FlnA in cancer development. Here, we try to decipher the role of FlnA in cancer and the implications for its dual role. We propose that differences in subcellular localization of FlnA dictate its role in cancer development. In the cytoplasm, FlnA functions in various growth signaling pathways, such as vascular endothelial growth factor, in addition to being involved in cell migration and adhesion pathways, such as R-Ras and integrin signaling. Involvement in these pathways and various others has shown a correlation between high cytoplasmic FlnA levels and invasive cancers. However, an active cleaved form of FlnA can localize to the nucleus rather than the cytoplasm and its interaction with transcription factors has been linked to a decrease in invasiveness of cancers. Therefore, overexpression of FlnA has a tumor-promoting effect, only when it is localized to the cytoplasm, whereas if FlnA undergoes proteolysis and the resulting C-terminal fragment localizes to the nucleus, it acts to suppress tumor growth and inhibit metastasis. Development of drugs to target FlnA and cause cleavage and subsequent localization to the nucleus could be a new and potent field of research in treating cancer.

Filamin A regulates neuronal migration through brefeldin A-inhibited guanine exchange factor 2-dependent Arf1 activation

Periventricular heterotopias is a malformation of cortical development, characterized by ectopic neuronal nodules around ventricle lining and caused by an initial migration defect during early brain development. Human mutations in the Filamin A (FLNA) and ADP-ribosylation factor guanine exchange factor 2 [ARFGEF2; encoding brefeldin-A-inhibited guanine exchange factor-2 (BIG2)] genes give rise to this disorder. Previously, we have reported that Big2 inhibition impairs neuronal migration and binds to FlnA, and its loss promotes FlnA phosphorylation. FlnA phosphorylation dictates FlnA-actin binding affinity and consequently alters focal adhesion size and number to effect neuronal migration. Here we show that FlnA loss similarly impairs migration, reciprocally enhances Big2 expression, but also alters Big2 subcellular localization in both null and conditional FlnA mice. FlnA phosphorylation promotes relocalization of Big2 from the Golgi toward the lipid ruffles, thereby activating Big2-dependent Arf1 at the cell membrane. Loss of FlnA phosphorylation or Big2 function impairs Arf1-dependent vesicle trafficking at the periphery, and Arf1 is required for maintenance of cell-cell junction connectivity and focal adhesion assembly. Loss of Arf1 activity disrupts neuronal migration and cell adhesion. Collectively, these studies demonstrate a potential mechanism whereby coordinated interactions between actin (through FlnA) and vesicle trafficking (through Big2-Arf) direct the assembly and disassembly of membrane protein complexes required for neuronal migration and neuroependymal integrity.

Targeting focal adhesion turnover in invasive breast cancer cells by the purine derivative reversine

Background:

The dynamics of focal adhesion (FA) turnover is a key determinant for the regulation of cancer cell migration. Here we investigated FA turnover in a panel of breast cancer models with distinct invasive properties and evaluated the impact of reversine on this turnover in relation to cancer cell invasion in in vitro and in vivo conditions.

Methods:

Live imaging and immunofluorescence assays were used to investigate FA turnover in breast cancer cells. Biochemical studies were used to investigate the impact of reversine on FA signalling and turnover. In vivo activity was investigated using orthotopic breast cancer mouse models.

Results:

Accelerated FA disassembly from plasma membrane protrusions was observed in invasive compared with non-invasive breast cancer cells or non-immortalised mammary epithelial cells. Reversine significantly inhibited FA disassembly leading to stable FAs, which was associated with reduced cell motility and invasion. The inhibitory effect of reversine on FA turnover accounted for a large part on its capacity to interfere with FAK function on regulating its downstream targets. In orthotopic breast cancer mouse models, reversine revealed a potent inhibitory activity on tumour progression to metastasis.

Conclusion:

These results support the utility of targeting FA turnover as a therapeutic approach for invasive breast cancer.