Regulation of paxillin family members during epithelial-mesenchymal transformation: a putative role for paxillin delta

Paxillin regulates liver fibrosis via actin polymerization and ERK activation in hepatic stellate cells

Liver injury leads to fibrosis and cirrhosis. The primary mechanism underlying the fibrogenic response is the activation of hepatic stellate cells (HSCs), which are 'quiescent' in normal liver but become 'activated' after injury by transdifferentiating into extracellular matrix (ECM)-secreting myofibroblasts. Given that integrins are important in HSC activation and fibrogenesis, we hypothesized that paxillin, a key downstream effector in integrin signaling, might be critical in the fibrosis pathway. Using a cell-culture-based model of HSC activation and in vivo models of liver injury, we found that paxillin is upregulated in activated HSCs and fibrotic livers. Overexpression of paxillin (both in vitro and in vivo) led to increased ECM protein expression, and depletion of paxillin in a novel conditional mouse injury model reduced fibrosis. The mechanism by which paxillin mediated this effect appeared to be through the actin cytoskeleton, which signals to the ERK pathway and induces ECM protein production. These data highlight a novel role for paxillin in HSC biology and fibrosis.

TATA-box-binding protein promotes hepatocellular carcinoma metastasis through epithelial-mesenchymal transition

BACKGROUND

HCC characterizes malignant metastasis with high incidence and recurrence. Thus, it is pivotal to discover the mechanisms of HCC metastasis. TATA-box-binding protein (TBP), a general transcriptional factor (TF), couples with activators and chromatin remodelers to sustain the transcriptional activity of target genes. Here, we investigate the key role of TBP in HCC metastasis.

METHODS

TBP expression was measured by PCR, western blot, and immunohistochemistry. RNA-sequencing was performed to identify downstream proteins. Functional assays of TBP and downstream targets were identified in HCC cell lines and xenograft models. Luciferase reporter and chromatin immunoprecipitation assays were used to demonstrate the mechanism mediated by TBP.

RESULTS

HCC patients showed high expression of TBP, which correlated with poor prognosis. Upregulation of TBP increased HCC metastasis in vivo and in vitro, and muscleblind-like-3 (MBNL3) was the effective factor of TBP, positively related to TBP expression. Mechanically, TBP transactivated and enhanced MBNL3 expression to stimulate exon inclusion of lncRNA-paxillin (PXN)-alternative splicing (AS1) and, thus, activated epithelial-mesenchymal transition for HCC progression through upregulation of PXN.

CONCLUSIONS

Our data revealed that TBP upregulation is an HCC enhancer mechanism that increases PXN expression to drive epithelial-mesenchymal transition.

Therapeutic potential of TRPM8 channels in cancer treatment

Cancer is a multifactorial process associated with changes in signaling pathways leading to cell cycle variations and gene expression. The transient receptor potential melastatin 8 (TRPM8) channel is a non-selective cation channel expressed in neuronal and non-neuronal tissues, where it is involved in several processes, including thermosensation, differentiation, and migration. Cancer is a multifactorial process associated with changes in signaling pathways leading to variations in cell cycle and gene expression. Interestingly, it has been shown that TRPM8 channels also participate in physiological processes related to cancer, such as proliferation, survival, and invasion. For instance, TRPM8 channels have an important role in the diagnosis, prognosis, and treatment of prostate cancer. In addition, it has been reported that TRPM8 channels are involved in the progress of pancreatic, breast, bladder, colon, gastric, and skin cancers, glioblastoma, and neuroblastoma. In this review, we summarize the current knowledge on the role of TRPM8 channels in cancer progression. We also discuss the therapeutic potential of TRPM8 in carcinogenesis, which has been proposed as a molecular target for cancer therapy.

The role of Actopaxin in tumor metastasis

Actopaxin is a newly discovered focal adhesions (FAs) protein, actin-binding protein and pseudopodia-enriched molecule. It can not only bind to a variety of FAs proteins (such as Paxillin, ILK and PINCH) and non-FAs proteins (such as TESK1, CdGAP, β2-adaptin, G3BP2, ADAR1 and CD29), but also participates in multiple signaling pathways. Thus, it plays a crucial role in regulating important processes of tumor metastasis, including matrix degradation, migration, and invasion, etc. This review covers the latest progress in the structure and function of Actopaxin, its interaction with other proteins as well as its involvement in regulating tumor development and metastasis. Additionally, the current limitations for Actopaxin related studies and the possible research directions on it in the future are also discussed. It is hoped that this review can assist relevant researchers to obtain a deep understanding of the role that Actopaxin plays in tumor progression, and also enlighten further research and development of therapeutic approaches for the treatment of tumor metastasis.

The explorations of dynamic interactions of paxillin at the focal adhesions

Paxillin is one of the most important adapters in integrin-mediated adhesions that performs numerous crucial functions relying on its dynamic interactions. Its structural behavior serves different purposes, providing a base for several activities. The various domains of paxillin display different functions in the whole process of cell movements and have a significant role in cell adhesion, migration, signal transmission, and protein-protein interactions. On the other hand, some paxillin-associated proteins provide a unique spatiotemporal mechanism for regulating its dynamic characteristics in the tissue homeostasis and make it a more complex and decisive protein at the focal adhesions. This review briefly describes the structural adaptations and molecular mechanisms of recruitment of paxillin into adhesions, explains paxillin's binding dynamics and impact on adhesion stability and turnover, and reveals a variety of paxillin-associated regulatory mechanisms and how paxillin is embedded into the signaling networks.

Inhibition of epithelial-mesenchymal transition in retinal pigment epithelial cells by a retinoic acid receptor-α agonist

Epithelial-mesenchymal transition (EMT) in retinal pigment epithelial (RPE) cells plays a key role in proliferative retinal diseases such as age-related macular degeneration by contributing to subretinal fibrosis. To investigate the potential role of retinoic acid receptor-α (RAR-α) signaling in this process, we have now examined the effects of the RAR-α agonist Am580 on EMT induced by transforming growth factor-β2 (TGF-β2) in primary mouse RPE cells cultured in a three-dimensional type I collagen gel as well as on subretinal fibrosis in a mouse model. We found that Am580 inhibited TGF-β2-induced collagen gel contraction mediated by RPE cells. It also attenuated the TGF-β2-induced expression of the mesenchymal markers α-smooth muscle actin, fibronectin, and collagen type I; production of pro-matrix metalloproteinase 2 and interleukin-6; expression of the focal adhesion protein paxillin; and phosphorylation of SMAD2 in the cultured RPE cells. Finally, immunofluorescence analysis showed that Am580 suppressed both the TGF-β2-induced translocation of myocardin-related transcription factor-A (MRTF-A) from the cytoplasm to the nucleus of cultured RPE cells as well as subretinal fibrosis triggered by laser-induced photocoagulation in a mouse model. Our observations thus suggest that RAR-α signaling inhibits EMT in RPE cells and might attenuate the development of fibrosis associated with proliferative retinal diseases.

Paxillin knockdown suppresses metastasis and epithelial‑mesenchymal transition in colorectal cancer via the ERK signalling pathway

Paxillin (PXN) is a cytoplasmic protein that plays an important role in regulating focal adhesion, cytoskeletal rearrangements and cell motility. The present study aimed to investigate the role of PXN in the metastasis of human colorectal cancer (CRC) and its possible mechanisms. Immunohistochemical staining of tissues from 102 surgical CRC patients revealed that high PXN expression was positively correlated with tumour‑node‑metastasis (TNM) stage, lymph node metastasis, distant metastasis, and recurrence at distant sites after radical surgery. In 24 cases of stage IV CRC, PXN expression in liver metastasis was higher than that in the matched primary tumour. The knockdown of PXN inhibited the proliferation, migration and invasion potential of SW480 cells in vitro and in vivo. Transmission electron microscopy revealed the effect of PXN on ultrastructural characteristics, observed mainly in microvilli and desmosomes. The downregulation of PXN decreased the activation of extracellular regulated protein kinase (ERK) and suppressed the epithelial‑mesenchymal transition (EMT) process. Following the downregulation of PXN, the addition of an ERK activator or inhibitor restored or further suppressed EMT, respectively, accompanied by corresponding changes in cell migration and invasion. Collectively, the present results confirmed the important role of PXN in CRC metastasis and revealed that PXN regulated EMT progression via the ERK signalling pathway. PXN may represent a future therapeutic strategy to prevent the EMT‑associated progression and invasion of CRC.

Macrophage Migration and Phagocytosis Are Controlled by Kindlin-3's Link to the Cytoskeleton

Major myeloid cell functions from adhesion to migration and phagocytosis are mediated by integrin adhesion complexes, also known as adhesome. The presence of a direct integrin binding partner Kindlin-3 is crucial for these functions, and its lack causes severe immunodeficiency in humans. However, how Kindlin-3 is incorporated into the adhesome and how its function is regulated is poorly understood. In this study, using nuclear magnetic resonance spectroscopy, we show that Kindlin-3 directly interacts with paxillin (PXN) and leupaxin (LPXN) via G43/L47 within its F0 domain. Surprisingly, disruption of Kindlin-3-PXN/LPXN interactions in Raw 264.7 macrophages promoted cell spreading and polarization, resulting in upregulation of both general cell motility and directed cell migration, which is in a drastic contrast to the consequences of Kindlin-3 knockout. Moreover, disruption of Kindlin-3-PXN/LPXN binding promoted the transition from mesenchymal to amoeboid mode of movement as well as augmented phagocytosis. Thus, these novel links between Kindlin-3 and key adhesome members PXN/LPXN limit myeloid cell motility and phagocytosis, thereby providing an important immune regulatory mechanism.

Alternative mechanisms of translation initiation: An emerging dynamic regulator of the proteome in health and disease

Eukaryotic mRNAs were historically thought to rely exclusively on recognition and binding of their 5' cap by initiation factors to effect protein translation. While internal ribosome entry sites (IRESs) are well accepted as necessary for the cap-independent translation of many viral genomes, there is now recognition that eukaryotic mRNAs also undergo non-canonical modes of translation initiation. Recently, high-throughput assays have identified thousands of mammalian transcripts with translation initiation occurring at non-canonical start codons, upstream of and within protein coding regions. In addition to IRES-mediated events, regulatory mechanisms of translation initiation have been described involving alternate 5' cap recognition, mRNA sequence elements, and ribosome selection. These mechanisms ensure translation of specific mRNAs under conditions where cap-dependent translation is shut down and contribute to pathological states including cardiac hypertrophy and cancer. Such global and gene-specific dynamic regulation of translation presents us with an increasing number of novel therapeutic targets. While these newly discovered modes of translation initiation have been largely studied in isolation, it is likely that several act on the same mRNA and exquisite coordination is necessary to maintain 'normal' translation. In this short review, we summarize the current state of knowledge of these alternative mechanisms of eukaryotic protein translation, their contribution to normal and pathological cell biology, and the potential of targeting translation initiation therapeutically in human disease.

Seed targeting with tiny anti-miR-1297 inhibits EMT in melanoma cells

MicroRNAs (miRNAs) are small, noncoding RNAs that have tissue- and cell-specific expression. They have the ability to regulate the malignant proliferation and transformation of tumour cells. The research focussed on the expression and role of miR-1297 in melanoma. We firstly found that miR-1297 is up-regulated in melanoma tissues and cell lines. Functionally, phosphatase and tension homology deleted on chromsome ten gene (PTEN) was used as a potential target for miR-1297 and detected using Western blotting and immunohistochemistry (IHC). We then used chemical synthesis of anti-miR1297 to explore the influence on melanoma cells and examined the effects on A375 cell proliferation using MTT and western blotting methods. The results showed that anti-miR-1297 transfected A375 cells could inhibit the growth. Furthermore, transfection with anti-miR-1297 reduced PTEN protein expression and partially restrained A375 cells proliferation, migration and reversed Epithelial-Mesenchymal Transition (EMT) progression. In conclusion, we tentatively put forward that miR-1297 might be the key oncomiR in melanoma, and seed-targeted anti-miR-1297 might serve as a new tactic for miR-1297-based therapies.

Hic-5 expression is a major indicator of cancer cell morphology, migration, and plasticity in three-dimensional matrices

The focal adhesion proteins Hic-5 and paxillin have been previously identified as key regulators of MDA-MB-231 breast cancer cell migration and morphologic mesenchymal-amoeboid plasticity in three-dimensional (3D) extracellular matrices (ECMs). However, their respective roles in other cancer cell types have not been evaluated. Herein, utilizing 3D cell-derived matrices and fibronectin-coated one-dimensional substrates, we show that across a variety of cancer cell lines, the level of Hic-5 expression serves as the major indicator of the cells primary morphology, plasticity, and in vitro invasiveness. Domain mapping studies reveal sites critical to the functions of both Hic-5 and paxillin in regulating phenotype, while ectopic expression of Hic-5 in cell lines with low endogenous levels of the protein is sufficient to induce a Rac1-dependent mesenchymal phenotype and, in turn, increase amoeboid-mesenchymal plasticity and invasion. We show that the activity of vinculin, when coupled to the expression of Hic-5 is required for the mesenchymal morphology in the 3D ECM. Taken together, our results identify Hic-5 as a critical modulator of tumor cell phenotype that could be utilized in predicting tumor cell migratory and invasive behavior in vivo.

Altered translation initiation of Gja1 limits gap junction formation during epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is activated during development, wound healing, and pathologies including fibrosis and cancer metastasis. Hallmarks of EMT are remodeling of intercellular junctions and adhesion proteins, including gap junctions. The GJA1 mRNA transcript encoding the gap junction protein connexin43 (Cx43) has been demonstrated to undergo internal translation initiation, yielding truncated isoforms that modulate gap junctions. The PI3K/Akt/mTOR pathway is central to translation regulation and is activated during EMT, leading us to hypothesize that altered translation initiation would contribute to gap junction loss. Using TGF-β-induced EMT as a model, we find reductions in Cx43 gap junctions despite increased transcription and stabilization of Cx43 protein. Biochemical experiments reveal suppression of the internally translated Cx43 isoform, GJA1-20k in a Smad3 and ERK-dependent manner. Ectopic expression of GJA1-20k does not halt EMT, but is sufficient to rescue gap junction formation. GJA1-20k localizes to the Golgi apparatus, and using superresolution localization microscopy we find retention of GJA1-43k at the Golgi in mesenchymal cells lacking GJA1-20k. NativePAGE demonstrates that levels of GJA1-20k regulate GJA1-43k hexamer oligomerization, a limiting step in Cx43 trafficking. These findings reveal alterations in translation initiation as an unexplored mechanism by which the cell regulates Cx43 gap junction formation during EMT.

Hic-5 regulates epithelial to mesenchymal transition in ovarian cancer cells in a TGFβ1-independent manner

The molecular basis of epithelial ovarian cancer (EOC) dissemination is still poorly understood. We have previously identified the hydrogen peroxide-inducible clone-5 (Hic-5) gene as hypomethylated in high-grade (HG) serous EOC tumors, compared to normal ovarian tissues. Hic-5 is a focal adhesion scaffold protein and has been primarily studied for its role as a key mediator of TGF-β–induced epithelial-to-mesenchymal transition (EMT) in epithelial cells of both normal and malignant origin; however, its role in EOC has been never investigated.

Here we demonstrate that Hic-5 is overexpressed in advanced EOC, and that Hic-5 is upregulated upon TGFβ1 treatment in the EOC cell line with epithelial morphology (A2780s), associated with EMT induction. However, ectopic expression of Hic-5 in A2780s cells induces EMT independently of TGFβ1, accompanied with enhancement of cellular proliferation rate and migratory/invasive capacity and increased resistance to chemotherapeutic drugs. Moreover, Hic-5 knockdown in the EOC cells with mesenchymal morphology (SKOV3) was accompanied by induction of mesenchymal-to-epithelial transition (MET), followed by a reduction of their proliferative, migratory/invasive capacity, and increased drugs sensitivity in vitro, as well as enhanced tumor cell colonization and metastatic growth in vivo. The modulation of Hic-5 expression in EOC cells resulted in altered regulation of numerous EMT-related canonical pathways and was indicative for a possible role of Hic-5 in controlling EMT through a RhoA/ROCK mediated mechanism.

To our knowledge, this is the first report examining the role of Hic-5 in EOC, and its role in maintaining the mesenchymal phenotype of EOC cells independently of exogenous TGFβ1 treatment.

Integrin-mediated traction force enhances paxillin molecular associations and adhesion dynamics that increase the invasiveness of tumor cells into a three-dimensional extracellular matrix

Mammary tumor cells adopt a basal-like phenotype when invading through a dense, stiffened, 3D matrix. These cells exert higher integrin-mediated traction forces, consistent with a physical motor-clutch model, display an altered molecular organization at the nanoscale, and recruit a suite of paxillin-associated proteins implicated in metastasis.

Metastasis requires tumor cells to navigate through a stiff stroma and squeeze through confined microenvironments. Whether tumors exploit unique biophysical properties to metastasize remains unclear. Data show that invading mammary tumor cells, when cultured in a stiffened three-dimensional extracellular matrix that recapitulates the primary tumor stroma, adopt a basal-like phenotype. Metastatic tumor cells and basal-like tumor cells exert higher integrin-mediated traction forces at the bulk and molecular levels, consistent with a motor-clutch model in which motors and clutches are both increased. Basal-like nonmalignant mammary epithelial cells also display an altered integrin adhesion molecular organization at the nanoscale and recruit a suite of paxillin-associated proteins implicated in invasion and metastasis. Phosphorylation of paxillin by Src family kinases, which regulates adhesion turnover, is similarly enhanced in the metastatic and basal-like tumor cells, fostered by a stiff matrix, and critical for tumor cell invasion in our assays. Bioinformatics reveals an unappreciated relationship between Src kinases, paxillin, and survival of breast cancer patients. Thus adoption of the basal-like adhesion phenotype may favor the recruitment of molecules that facilitate tumor metastasis to integrin-based adhesions. Analysis of the physical properties of tumor cells and integrin adhesion composition in biopsies may be predictive of patient outcome.

Paxillin: a crossroad in pathological cell migration

Paxilllin is a multifunctional and multidomain focal adhesion adapter protein which serves an important scaffolding role at focal adhesions by recruiting structural and signaling molecules involved in cell movement and migration, when phosphorylated on specific Tyr and Ser residues. Upon integrin engagement with extracellular matrix, paxillin is phosphorylated at Tyr31, Tyr118, Ser188, and Ser190, activating numerous signaling cascades which promote cell migration, indicating that the regulation of adhesion dynamics is under the control of a complex display of signaling mechanisms. Among them, paxillin disassembly from focal adhesions induced by extracellular regulated kinase (ERK)-mediated phosphorylation of serines 106, 231, and 290 as well as the binding of the phosphatase PEST to paxillin have been shown to play a key role in cell migration. Paxillin also coordinates the spatiotemporal activation of signaling molecules, including Cdc42, Rac1, and RhoA GTPases, by recruiting GEFs, GAPs, and GITs to focal adhesions. As a major participant in the regulation of cell movement, paxillin plays distinct roles in specific tissues and developmental stages and is involved in immune response, epithelial morphogenesis, and embryonic development. Importantly, paxillin is also an essential player in pathological conditions including oxidative stress, inflammation, endothelial cell barrier dysfunction, and cancer development and metastasis.

Evolution and Expression of Paxillin Genes in Teleost Fish

Background

Paxillin family proteins regulate intracellular signaling downstream of extracellular matrix adhesion. Tissue expression patterns and cellular functions of Paxillin proteins during embryo development remain poorly understood. Additionally, the evolution of this gene family has not been thoroughly investigated.

Results

This report characterizes the evolution and expression of a novel Paxillin gene, called Paxillin-b, in Teleosts. Alignments indicate that Teleost Paxillin-a and Paxillin-b proteins are highly homologous to each other and to human Paxillin. Phylogenetic and synteny analyses suggest that these genes originated from the duplication of an ancestral Paxillin gene that was in a common ancestor of Teleosts and Tetrapods. Analysis of the spatiotemporal expression profiles of Paxillin-a and Paxillin-b using zebrafish revealed both overlapping and distinct domains for Paxillin-a and Paxillin-b during embryo development. Localization of zebrafish Paxillin orthologs expressed in mammalian cells demonstrated that both proteins localize to focal adhesions, similar to mammalian Paxillin. This suggests these proteins regulate adhesion-dependent processes in their endogenous tissues.

Conclusion

Paxillin-a and Paxillin-b were generated by duplication in Teleosts. These genes likely play similar roles as Paxillin genes in other organisms. This work provides a framework for functional investigation of Paxillin family members during development using the zebrafish as an in vivo model system.

Uterine focal adhesions are retained at implantation after rat ovarian hyperstimulation

Controlled ovarian hyperstimulation is an essential component of IVF techniques to ensure proliferation and development of multiple ovarian follicles, but the effects of these hormones on the endometrium are largely unknown. During normal pregnancy in rats, there are significant changes in the basal plasma membrane of uterine epithelial cells (UECs) at the time of receptivity, including loss of focal adhesions. This enables the UECs to be removed from the implantation chamber surrounding the blastocyst, thus allowing invasion into the underlying stroma. This study investigated the influence of ovarian hyperstimulation (OH) on the basal plasma membrane of UECs during early pregnancy in the rat. Immunofluorescence results demonstrate the presence of paxillin, talin, integrin β1 and phosphorylated FAK (Y397FAK) in the basal portion of UECs at the time of implantation in OH pregnancy. TEM analysis demonstrated a flattened basal lamina and the presence of focal adhesions on the basal surface at this time in OH pregnancy. Significantly low full-length paxillin, high paxillin δ and integrin β1 were seen at the time of implantation in OH compared with those in normal pregnancy. The increase in paxillin δ suggests that these cells are less mobile, whereas the increase in integrin β1 and Y397FAK suggests the retention of a stable FA complex. Taken together with the increase in morphological focal adhesions, this represents a cell type that is stable and less easily removed for blastocyst implantation. This may be one mechanism explaining lower implantation rates after fresh embryo transfers compared with frozen cycles.

Cytoskeletal signaling in TGFβ-induced epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is a physiological process that plays an important role in embryonic development and wound healing and is appropriated during pathological conditions including fibrosis and cancer metastasis. EMT can be initiated by a variety of factors, including transforming growth factor (TGF)-β, and is characterized by loss of epithelial features including cell-cell contacts and apicobasal polarity and acquisition of a motile, mesenchymal phenotype. A key feature of EMT is reorganization of the cytoskeleton and recent studies have elucidated regulation mechanisms governing this process. This review describes changes in gene expression patterns of cytoskeletal associated proteins during TGFβ-induced EMT. It further reports TGFβ-induced intracellular signaling cascades that regulate cytoskeletal reorganization during EMT. Finally, it highlights how changes in cytoskeletal architecture during EMT can regulate gene expression, thus further promoting EMT progression.

Micropillar arrays as potential drug screens: Inhibition of micropillar-mediated activation of the FAK-Src-paxillin signaling pathway by the CK2 inhibitor CX-4945

Here, we demonstrate the possible applications of micropillar arrays in screening anti-metastasis drugs. Human lung adenocarcinoma A549 cells incubated in multiwell plates containing micropillars exhibited markedly different physical/biochemical behavior depending on pillar dimensions. In particular, A549 cells grown in plates containing 2-μm diameter, 16-μm pitched pillar arrays showed epithelial-to-mesenchymal transition (EMT)-like behavior; cell body elongation, and highly increased activation of the focal adhesion kinase (FAK)-Src-paxillin signaling cascade. FAK is the most prominent kinase involved in dynamic regulation of the actin cytoskeleton and cell adhesion, migration, and invasion. Activation of FAK, a hallmark of cancer cell adhesion and migration, is normally induced by various growth factors, such as transforming growth factor-β (TGF-β). Here, we found that pillar-mediated activation of signaling molecules mimicked that induced by TGF-β. Notably, micropillar arrays with specific dimensions accelerated the elongation of cells, an effect linked to the activation of signaling molecules related to EMT. Micropillar-induced FAK activation could be arrested by the casein kinase-2 (CK2) inhibitor CX-4945, a drug candidate with activity against TGF-β-induced cancer cell metastasis, demonstrating the possibility of using inorganic microstructures for cell-based drug screening.

STATEMENT OF SIGNIFICANCE

In this work, we have fabricated flexible substrates with regular arrays of micrometersized pillars, and used them to grow A549 human lung adenocarcinoma cells. Cells exhibit dramatically different behavior depending on the intervals of pillars. Especially, cells grown in certain pillar structures show epithelial-to mesenchmal transition (EMT)-like morphology and related molecules, which is similar to the activation obtained using expensive cytokine TGF-β. Based on the fact that pillar arrays may activate EMT like transition, screening of anti-cancer drug using pillar arrays have demonstrated as well in our work. Our study confirms that mechanical stimulation may exert similar effects with chemical stimulation, and such mechanical structures could be used as a large-scale drug screening platforms. Cell morphogenesis on engineered substrate is not new, but the present work could be distinguished with its unique fabrication process that can mass produce the structures and it could be applied for high-throughput drug screening. Also, we suggest the formation of focal adhesions on pillar structures and consequent strain as the possible mechanism behind the observed EMT-like transition. Currently, we are working on full-scale profiling of metabolomics and proteomics of cells grown in large-scale pillar arrays as well.

Myricetin inhibits advanced glycation end product (AGE)-induced migration of retinal pericytes through phosphorylation of ERK1/2, FAK-1, and paxillin in vitro and in vivo

Advanced glycation end products (AGE) have been implicated in the development of diabetic retinopathy. Characterization of the early stages of diabetic retinopathy is retinal pericytes loss, which is the result of pericytes migration. In this study, we investigated the pathological mechanisms of AGE on the migration of retinal pericytes and confirmed the inhibitory effect of myricetin on migration in vitro and in vivo. Migration assays of bovine retinal pericytes (BRP) were induced using AGE-BSA and phosphorylation of Src, ERK1/2, focal adhesion kinase (FAK-1) and paxillin were determined using immunoblot analysis. Sprague-Dawley rats (6 weeks old) were injected intravitreally with AGE-BSA and morphological and immunohistochemical analysis of p-FAK-1 and p-paxillin were performed in the rat retina. Immunoblot analysis and siRNA transfection were used to study the molecular mechanism of myricetin on BRP migration. AGE-BSA increased BRP migration in a dose-dependent manner via receptor for AGEs (RAGE)-dependent activation of the Src kinase-ERK1/2 pathway. AGE-BSA-induced migration was inhibited by an ERK1/2 specific inhibitor (PD98059), but not by p38 and Jun N-terminal kinase inhibitors. AGE-BSA increased FAK-1 and paxillin phosphorylation in a dose- and time-dependent manner. These increases were attenuated by PD98059 and ERK1/2 siRNA. Phosphorylation of FAK-1 and paxillin was increased in response to AGE-BSA-induced migration of rat retinal pericytes. Myricetin strongly inhibited ERK1/2 phosphorylation and significantly suppressed pericytes migration in AGE-BSA-injected rats. Our results demonstrate that AGE-BSA participated in the pathophysiology of retinal pericytes migration likely through the RAGE-Src-ERK1/2-FAK-1-paxillin signaling pathway. Furthermore, myricetin suppressed phosphorylation of ERK 1/2-FAK-1-paxillin and inhibited pericytes migration.

A novel aminothiazole KY-05009 with potential to inhibit Traf2- and Nck-interacting kinase (TNIK) attenuates TGF-β1-mediated epithelial-to-mesenchymal transition in human lung adenocarcinoma A549 cells

Transforming growth factor (TGF)-β triggers the epithelial-to-mesenchymal transition (EMT) of cancer cells via well-orchestrated crosstalk between Smad and non-Smad signaling pathways, including Wnt/β-catenin. Since EMT-induced motility and invasion play a critical role in cancer metastasis, EMT-related molecules are emerging as novel targets of anti-cancer therapies. Traf2- and Nck-interacting kinase (TNIK) has recently been considered as a first-in-class anti-cancer target molecule to regulate Wnt signaling pathway, but pharmacologic inhibition of its EMT activity has not yet been studied. Here, using 5-(4-methylbenzamido)-2-(phenylamino)thiazole-4-carboxamide (KY-05009) with TNIK-inhibitory activity, its efficacy to inhibit EMT in cancer cells was validated. The molecular docking/binding study revealed the binding of KY-05009 in the hinge region of TNIK, and the inhibitory activity of KY-05009 against TNIK was confirmed by an ATP competition assay (Ki, 100 nM). In A549 cells, KY-05009 significantly and strongly inhibited the TGF-β-activated EMT through the attenuation of Smad and non-Smad signaling pathways, including the Wnt, NF-κB, FAK-Src-paxillin-related focal adhesion, and MAP kinases (ERK and JNK) signaling pathways. Continuing efforts to identify and validate potential therapeutic targets associated with EMT, such as TNIK, provide new and improved therapies for treating and/or preventing EMT-based disorders, such as cancer metastasis and fibrosis.

Hic-5 influences genomic and non-genomic actions of the androgen receptor in prostate myofibroblasts

There is extensive knowledge of androgen receptor (AR) signaling in cancer cells, but less regarding androgen action in stromal cells of the tumor microenvironment. We report here the genome-wide effects of a stromal cell specific molecular adapter and AR coregulator, hydrogen peroxide-inducible gene 5 (Hic-5/TGFB1I1), on AR function in prostate myofibroblasts. Following androgen stimulation, Hic-5 rapidly translocates to the nucleus, coincident with increased phosphorylation of focal adhesion kinase. As a coregulator, Hic-5 acted to amplify or inhibit regulation of approximately 50% of AR target genes, affected androgen regulation of growth, cell adhesion, motility and invasion. These data suggest Hic-5 as a transferable adaptor between focal adhesions and the nucleus of prostate myofibroblasts, where it acts a key mediator of the specificity and sensitivity of AR signaling. We propose a model in which Hic-5 coordinates AR signaling with adhesion and extracellular matrix contacts to regulate cell behavior in the tumor microenvironment.

Dynamics of focal adhesions and reorganization of F-actin in VEGF-stimulated NSCs under varying differentiation states

Precise migration of neural stem/progenitor cells (NSCs) is crucially important for neurogenesis and repair in the nervous system. However, the detailed mechanisms are not clear. Our previous results showed that NSCs in varying differentiation states possess different migratory ability to vascular endothelial growth factor (VEGF). In this study, we demonstrate the different dynamics of focal adhesions (FAs) and reorganization of F-actin in NSCs during spreading and migration stimulated by VEGF. We found that the migrating NSCs of 0.5 and 1 day differentiation possess more FAs at leading edge than cells of other states. Moreover, the phosphorylation of focal adhesion kinase (FAK) and paxillin in NSCs correlates closely with their differentiation states. VEGF promotes FA formation with broad lamellipodium generation at the leading edge in chemotaxing cells of 0, 0.5, and 1 day differentiation, but not in cells of 3 days differentiation. Furthermore, cells of 1 day differentiation show a maximal asymmetry of FAs between lamella and cell rear, orchestrating cell polarization and directional migration. Time-lapse video analysis shows that the disassembly of FAs and the cell tail detachment in NSCs of 1 day differentiation are more rapid, along with the concurrent enlarged size of FAs at the leading edge, leading to the most effective chemotactic response to VEGF. Collectively, these results indicate that the dynamics of FAs and reorganization of F-actin in NSCs that undergo directional migration correlate closely with their differentiation states, contributing to the different chemotactic responses of these cells to VEGF.

Transglutaminase-2 in cell adhesion: all roads lead to paxillin?

Cell-matrix adhesion is a fundamental biological process that governs survival, migration, and proliferation of living eukaryotic cells. Paxillin is an important central player in a network of adhesome proteins that form focal adhesion complexes. Phosphorylation of tyrosine and serine residues in paxillin is critical for the coordinated sequential recruitment of other adaptor and kinase proteins to adhesion complexes. Recently, the phosphorylation of serine178 in paxillin has been shown to be vital for epithelial cell adhesion and migration. In vivo and in vitro evidence have shown that transglutaminase (TG)-2 positively regulates this phosphorylation. Here, we propose three possible mechanisms that may explain these observations. First, TG-2 itself may be an adhesome member directly interacting with paxillin in a non-covalent way. Second, TG-2 may cross link a mitogen-activated protein kinase kinase kinase (MAP3K), which eventually activates c-Jun N-terminal kinase (JNK), and the latter phosphorylates paxillin. Lastly, TG-2 may have intrinsic kinase activity that phosphorylates paxillin. Future studies investigating these hypotheses on TG-2-paxillin relationships are necessary in order to address this fundamental process in cell matrix adhesion signaling.

CK2 inhibitor CX-4945 blocks TGF-β1-induced epithelial-to-mesenchymal transition in A549 human lung adenocarcinoma cells

BACKGROUND

The epithelial-to-mesenchymal transition (EMT) is a major phenotype of cancer metastasis and invasion. As a druggable cancer target, the inhibition of protein kinase CK2 (formally named to casein kinase 2) has been suggested as a promising therapeutic strategy to treat EMT-controlled cancer metastasis. This study aimed to evaluate the effect of the CK2 inhibitor CX-4945 on the processes of cancer migration and invasion during the EMT in A549 human lung adenocarcinoma cells.

MATERIALS AND METHODS

The effect of CX-4945 on TGF-β1-induced EMT was evaluated in A549 cells treated with TGF-β1 (5 ng/ml) and CX-4945. The effect of CX-4945 on TGF-β1-induced cadherin switch and activation of key signaling molecules involved in Smad, non-Smad, Wnt and focal adhesion signaling pathways were investigated by Western blot analysis, immunocytochemistry and reporter assay. Additionally, the effect of CX-4945 on TGF-β1-induced migration and invasion was investigated by wound healing assay, Boyden chamber assay, gelatin zymography, and the quantitative real-time PCR.

RESULTS

CX-4945 inhibits the TGF-β1-induced cadherin switch and the activation of key signaling molecules involved in Smad (Smad2/3, Twist and Snail), non-Smad (Akt and Erk), Wnt (β-catenin) and focal adhesion signaling pathways (FAK, Src and paxillin) that cooperatively regulate the overall process of EMT. As a result, CX-4945 inhibits the migration and invasion of A549 cells accompanied with the downregulation of MMP-2 and 9.

CONCLUSIONS

Clinical evaluation of CX-4945 in humans as a single agent in solid tumors and multiple myeloma has established its promising pharmacokinetic, pharmacodynamic, and safety profiles. Beyond regression of tumor mass, CX-4945 may be advanced as a new therapy for cancer metastasis and EMT-related disorders.

Zebrafish keratocyte explant cultures as a wound healing model system: differential gene expression & morphological changes support epithelial-mesenchymal transition

The control of collective cell migration of zebrafish keratocyte sheets in explant culture is of interest for cell migration and epithelial wound healing and depends on the gene expression profile. In a zebrafish genome array, ∼17.5% of the probe sets were differentially expressed greater than two-fold (p≤0.003) between 1 and 7 days of explant culture. Among the differentially expressed genes were a variety of wound healing-related genes and many of the biomarkers for epithelial-mesenchymal transition (EMT), including a switch from keratin and E-cadherin to vimentin and N-cadherin expression and several EMT-related transcription factors were found to be differentially expressed. Supporting evidence for EMT is seen in both morphological change and rearrangement of the actin cytoskeleton and in expression of cadherins during explant culture with a visible disassembly of the cell sheet. TGFβ1 and TNFα expression were analyzed by qPCR at various time points and peak differential expression of both cytokines occurred at 3 days, indicating that the EMT process is ongoing under conditions routinely used in the study of fish keratocyte motility. These data establish that an EMT process is occurring during zebrafish keratocyte explant culture and support the use of this system as a wound healing model.

Diverse roles for the paxillin family of proteins in cancer

The paxillin family of intracellular scaffold proteins includes paxillin, Hic-5, and leupaxin, and all have been identified as key regulators of the cellular migration machinery in both 2- and 3-dimensional microenvironments. Herein, we provide insight into the roles of these proteins during tumorigenesis and metastasis, highlighting their functions in cancer initiation as well as tumor cell dissemination and survival. Furthermore, we speculate on the potential of paxillin family proteins as both future prognostic and therapeutic targets.

Hic-5 affects proliferation, migration and invasion of B16 murine melanoma cells

Hic-5 is a shuttling protein between the cell membrane and the nucleus which functions as a focal adhesion adaptor protein and a nuclear receptor coactivator. Although several studies have shown its involvement in other types of cancer, the role of Hic-5 in melanoma is unknown. Herein, we show for the first time that Hic-5 is expressed in B16-F1 murine melanoma cells. To determine its function in melanoma cells, we used shRNA-mediated RNA interference and established stable clones with down-regulated Hic-5 expression. These clones had impaired growth and metastatic potential compared with controls in vivo, which correlated with decreased proliferation, migration and invasion in vitro. Moreover, silencing of Hic-5 expression in B16-F1 activated RhoA with an amoeboid phenotypic change, indicating that Hic-5 is a key regulator of B16-F1 metastasis in the context of Rho-dependent motility. These results provide new evidence that Hic-5 is a possible molecular target for treatment of melanoma.

C(16)-Ceramide-induced F-actin regulation stimulates mouse embryonic stem cell migration: involvement of N-WASP/Cdc42/Arp2/3 complex and cofilin-1/α-actinin

Ceramide, a major structural element in the cellular membrane, is a key regulatory factor in various cellular behaviors that are dependent on ceramide-induced association of specific proteins. However, molecular mechanisms that regulate ceramide-induced embryonic stem cell (ESC) migration are still not well understood. Thus, we investigated the effect of ceramide on migration and its related signal pathways in mouse ESCs. Among ceramide species with different fatty acid chain lengths, C(16)-Cer increased migration of mouse ESCs in a dose- (≥1μM) and time-dependent (≥8h) manners, as determined by the cell migration assay. C(16)-Cer (10μM) increased protein-kinase C (PKC) phosphorylation. Subsequently, C(16)-Cer increased focal adhesion kinase (FAK) and Paxillin phosphorylation, which were inhibited by PKC inhibitor Bisindolylmaleimide I (1μM). When we examined for the downstream signaling molecules, C(16)-Cer activated small G protein (Cdc42) and increased the formation of complex with Neural Wiskott-Aldrich Syndrome Protein (N-WASP)/Cdc42/Actin-Related Protein 2/3 (Arp2/3). This complex formation was disrupted by FAK- and Paxillin-specific siRNAs. Furthermore, C(16)-Cer-induced increase of filamentous actin (F-actin) expression was inhibited by Cdc42-, N-WASP-, and Arp2/3-specific siRNAs, respectively. Indeed, C(16)-Cer increased cofilin-1/F-actin interaction or F-actin/α-actinin-1 and α-actinin-4 interactions in the cytoskeleton compartment, which was reversed by Cdc42-specific siRNA. Finally, C(16)-Cer-induced increase of cell migration was inhibited by knocking down each signal pathway-related molecules with siRNA or inhibitors. In conclusion, C(16)-Cer enhances mouse ESC migration through the regulation of PKC and FAK/Paxillin-dependent N-WASP/Cdc42/Arp2/3 complex formation as well as through promoting the interaction between cofilin-1 or α-actinin-1/-4 and F-actin.

Structural basis for paxillin binding and focal adhesion targeting of β-parvin

β-Parvin is a cytoplasmic adaptor protein that localizes to focal adhesions where it interacts with integrin-linked kinase and is involved in linking integrin receptors to the cytoskeleton. It has been reported that despite high sequence similarity to α-parvin, β-parvin does not bind paxillin, suggesting distinct interactions and cellular functions for these two closely related parvins. Here, we reveal that β-parvin binds directly and specifically to leucine-aspartic acid repeat (LD) motifs in paxillin via its C-terminal calponin homology (CH2) domain. We present the co-crystal structure of β-parvin CH2 domain in complex with paxillin LD1 motif to 2.9 Å resolution and find that the interaction is similar to that previously observed between α-parvin and paxillin LD1. We also present crystal structures of unbound β-parvin CH2 domain at 2.1 Å and 2.0 Å resolution that show significant conformational flexibility in the N-terminal α-helix, suggesting an induced fit upon paxillin binding. We find that β-parvin has specificity for the LD1, LD2, and LD4 motifs of paxillin, with K(D) values determined to 27, 42, and 73 μM, respectively, by surface plasmon resonance. Furthermore, we show that proper localization of β-parvin to focal adhesions requires both the paxillin and integrin-linked kinase binding sites and that paxillin is important for early targeting of β-parvin. These studies provide the first molecular details of β-parvin binding to paxillin and help define the requirements for β-parvin localization to focal adhesions.

Linear motifs: lost in (pre)translation

Pretranslational modification by alternative splicing, alternative promoter usage and RNA editing enables the production of multiple protein isoforms from a single gene. A large quantity of data now supports the notion that short linear motifs (SLiMs), which are protein interaction modules enriched within intrinsically disordered regions, are key for the functional diversification of these isoforms. The inclusion or removal of these SLiMs can switch the subcellular localisation of an isoform, promote cooperative associations, refine the affinity of an interaction, coordinate phase transitions within the cell, and even create isoforms of opposing function. This article discusses the novel functionality enabled by the addition or removal of SLiM-containing exons by pretranslational modifications, such as alternative splicing and alternative promoter usage, and how these alterations enable the creation and modulation of complex regulatory and signalling pathways.

Autocrine CCL2 promotes cell migration and invasion via PKC activation and tyrosine phosphorylation of paxillin in bladder cancer cells

The amount of monocyte chemoattractant protein-1 (MCP-1/CCL2) produced by a transitional cell carcinoma is directly correlated with high recurrence and poor prognosis in bladder cancer. However, the mechanisms underlying the effects of CCL2 on tumor progression remain unexplored. To investigate the role played by CCL2, we examined cell migration in various bladder cancer cell lines. We found that high-grade cancer cells expressing high levels of CCL2 showed more migration activity than low-grade bladder cancer cells expressing low levels of the chemokine. Although the activation of CCL2/CCR2 signals did not appreciably affect cell growth, it mediated cell migration and invasion via the activation of protein kinase C and phosphorylation of tyrosine in paxillin. Blocking CCL2 and CCR2 with small hairpin RNA (shCCL2) or a specific inhibitor reduced CCL2/CCR2-mediated cell migration. The antagonist of CCR2 promoted the survival of mice bearing MBT2 bladder cancer cells, and CCL2-depleted cells showed low tumorigenicity compared with shGFP cells. In addition to observing high-levels of CCL2 in high-grade human bladder cancer cells, we showed that the CCL2/CCR2 signaling pathway mediated migratory and invasive activity, whereas blocking the pathway decreased migration and invasion. In conclusion, high levels of CCL2 expressed in bladder cancer mediates tumor invasion and is involved with advanced tumorigenesis. Our findings suggest that this CCL2/CCR2 pathway is a potential candidate for the attenuation of bladder cancer metastases.

Hic-5 promotes invadopodia formation and invasion during TGF-β-induced epithelial-mesenchymal transition

The focal adhesion protein Hic-5 acts through RhoC to promote TGF-β–stimulated invadopodia formation, cell migration, and invasion.

Transforming growth factor β (TGF-β)–stimulated epithelial–mesenchymal transition (EMT) is an important developmental process that has also been implicated in increased cell invasion and metastatic potential of cancer cells. Expression of the focal adhesion protein Hic-5 has been shown to be up-regulated in epithelial cells in response to TGF-β. Herein, we demonstrate that TGF-β–induced Hic-5 up-regulation or ectopic expression of Hic-5 in normal MCF10A cells promoted increased extracellular matrix degradation and invasion through the formation of invadopodia. Hic-5 was tyrosine phosphorylated in an Src-dependent manner after TGF-β stimulation, and inhibition of Src activity or overexpression of a Y38/60F nonphosphorylatable mutant of Hic-5 inhibited matrix degradation and invasion. RhoC, but not RhoA, was also required for TGF-β– and Hic-5–induced matrix degradation. Hic-5 also induced matrix degradation, cell migration, and invasion in the absence of TGF-β via Rac1 regulation of p38 MAPK. These data identify Hic-5 as a critical mediator of TGF-β–stimulated invadopodia formation, cell migration, and invasion.

Nanog and Oct4 overexpression increases motility and transmigration of melanoma cells

PURPOSE

Melanoma tumors are highly heterogeneous and can undergo phenotypic modifications depending on their plasticity and the microenvironment, with shifts between proliferative and invasive states. We have shown that melanoma cells, grown as spheroids in a neural crest cell medium, polarize toward an invasive and motile phenotype, in agreement with transcriptomic modulations, including the up-regulation of Nanog and Oct4. Overexpression of these genes was shown to be associated with poor prognosis and metastatic forms of some cancers. We thus investigated implication of Nanog and Oct4, two embryonic transcription factors, in melanoma motility.

METHODS

Our team used stable transfection of Nanog or Oct4 in A375 melanoma cell line to investigate motility in a wound healing assay and a transendothelial migration assay. Using semiquantitative RT-PCR, expression of two gene panels involved either in mesenchymal motility or in amoeboid migration was studied.

RESULTS

Strongly enhanced capacities of motility and extravasation were observed with cells overexpressing Oct4 and Nanog. The A375 cell line has been described as having a mesenchymal migration type. However, in the Oct4 and Nanog transfectants, several amoeboid migration markers are strongly induced. Accordingly, amoeboid migration inhibitors decrease significantly the transmigration of Oct4- and Nanog-expressing cells through endothelial cells.

CONCLUSIONS

We propose here that Nanog and Oct4 pluripotency marker expression in melanoma cells increases the transmigration capacity of these cells through the gain of amoeboid motility, leading to higher invasiveness and aggressiveness.

The H4 histamine receptor agonist, clobenpropit, suppresses human cholangiocarcinoma progression by disruption of epithelial mesenchymal transition and tumor metastasis

Cholangiocarcinoma (CCA) is a biliary cancer arising from damaged bile ducts. Epithelial-mesenchymal transition (EMT) occurs as epithelial cells begin to resemble mesenchymal cells leading to increased invasion potential as the extracellular matrix (ECM) degrades. Histamine exerts its effects by way of four receptors (H1-H4 HRs). Clobenpropit, a potent H4HR agonist, inhibits mammary adenocarcinoma growth. We have shown that (1) cholangiocytes and CCA cells express H1-H4 HRs and (2) the H3HR decreases CCA proliferation. We evaluated the effects of clobenpropit on CCA proliferation, invasion, EMT phenotypes, and ECM degradation. In vitro, we used CCA cell lines to study proliferation, signaling pathways, and the morphological invasive potential. Gene and protein expression of the hepatobiliary epithelial markers CK-7, CK-8, and CK-19, the focal contact protein paxillin, and the mesenchymal markers fibronectin, s100A4, and vimentin were evaluated. Cell invasion across an ECM layer was quantitated and matrix metalloproteinase-1, -2, -3, -9, and -11 gene and protein expression was examined. Evaluation of the specific role of H4HR was performed by genetic knockdown of the H3HR and overexpression of H4HR. Proliferation was evaluated by proliferating cellular nuclear antigen immunoblotting. In vivo, xenograft tumors were treated with either vehicle or clobenpropit for 39 days. Tumor volume was recorded every other day. Clobenpropit significantly decreased CCA proliferation by way of a Ca(2+) -dependent pathway and altered morphological development and invasion. Loss of H3HR expression or overexpression of H4HR significantly decreased CCA proliferation. In vivo, clobenpropit inhibited xenograft tumor growth compared with controls.

CONCLUSION

Modulation of H4HR by clobenpropit disrupts EMT processes, ECM breakdown, and invasion potential and decreases tumor growth. Interruption of tumorigenesis and invasion by histamine may add to therapeutic advances for CCAs.

Expression and localization of paxillin in rat pancreas during development

AIM: To investigate the expression and localization of paxillin in rat pancreas during development.

METHODS: Pancreata from Sprague Dawley rat fetuses, embryos, young animals, and adult animals were used in this study. Expression levels of paxillin in pancreata of different development stages were detected by reverse transcription polymerase chain reaction and Western blotting. To identify the cell location of paxillin in the developing rat pancreas, immunohistochemistry and double-immunofluorescent staining were performed using antibodies for specific cell markers and paxillin, respectively.

RESULTS: The highest paxillin mRNA level was detected at E15.5 (embryo day 15.5) following a decrease in the later developmental periods (P < 0.05 vs E18.5, P0 and adult, respectively), and a progressively increased paxillin protein expression through the transition from E15.5 to adult was detected. The paxillin positive staining was mainly localized in rat islets of Langerhans at each stage tested during pancreas development.

CONCLUSION: The dynamic expression of paxillin in rat pancreas from different stages indicates that paxillin might be involved in some aspects of pancreatic development.

Paxillin enables attachment-independent tyrosine phosphorylation of focal adhesion kinase and transformation by RAS

Paxillin and HIC5 are closely related adapter proteins that regulate cell migration and are tyrosine-phosphorylated by focal adhesion kinase (FAK). Paxillin, HIC5, and FAK tyrosine phosphorylation increase upon cell attachment and decrease upon detachment from extracellular matrix. Unexpectedly, we found that although FAK tyrosine phosphorylation in attached cells did not require paxillin, in detached fibroblasts there was remaining FAK tyrosine phosphorylation that required expression of paxillin and was not supported by HIC5. The support of attachment-independent FAK tyrosine phosphorylation required the paxillin LIM domains and suggested that paxillin might facilitate oncogenic transformation. Paxillin but not HIC5 augmented anchorage-independent cell proliferation induced by RAS. Both anchorage-independent FAK tyrosine phosphorylation and RAS-induced colony formation required multiple docking sites on paxillin, including LD4 (docking sites for FAK-Src and GIT1/2-PIX-NCK-PAK complex), LD5, and all four carboxyl-terminal LIM domains (that bind tubulin and PTP-PEST). Analysis using paxillin mutants dissociated domains of paxillin that are required for regulation of cell migration from domains that are required for anchorage-independent cell proliferation and demonstrated essential functions of the paxillin LIM domains that are not found in HIC5 LIM domains. These results highlight the role of paxillin in facilitating attachment-independent signal transduction implicated in cancer.

Distinct roles for paxillin and Hic-5 in regulating breast cancer cell morphology, invasion, and metastasis

This study reveals novel roles for the focal adhesion proteins paxillin and Hic-5 in regulating breast cancer invasion strategies and metastasis. Depletion of paxillin promotes a hypermesenchymal phenotype while dysregulating 3D adhesion dynamics. In contrast, RNAi of Hic-5 induces a hyperamoeboid phenotype with dysregulated RhoA/pMLC signaling.

Individual metastatic tumor cells exhibit two interconvertible modes of cell motility during tissue invasion that are classified as either mesenchymal or amoeboid. The molecular mechanisms by which invasive breast cancer cells regulate this migratory plasticity have yet to be fully elucidated. Herein we show that the focal adhesion adaptor protein, paxillin, and the closely related Hic-5 have distinct and unique roles in the regulation of breast cancer cell lung metastasis by modulating cell morphology and cell invasion through three-dimensional extracellular matrices (3D ECMs). Cells depleted of paxillin by RNA interference displayed a highly elongated mesenchymal morphology, whereas Hic-5 knockdown induced an amoeboid phenotype with both cell populations exhibiting reduced plasticity, migration persistence, and velocity through 3D ECM environments. In evaluating associated signaling pathways, we determined that Rac1 activity was increased in cells devoid of paxillin whereas Hic-5 silencing resulted in elevated RhoA activity and associated Rho kinase–induced nonmuscle myosin II activity. Hic-5 was essential for adhesion formation in 3D ECMs, and analysis of adhesion dynamics and lifetime identified paxillin as a key regulator of 3D adhesion assembly, stabilization, and disassembly.

Proline-rich tyrosine kinase 2 (Pyk2) promotes cell motility of hepatocellular carcinoma through induction of epithelial to mesenchymal transition

AIMS

Proline-rich tyrosine kinase 2 (Pyk2), a non-receptor tyrosine kinase of the focal adhesion kinase (FAK) family, is up-regulated in more than 60% of the tumors of hepatocellular carcinoma (HCC) patients. Forced overexpression of Pyk2 can promote the proliferation and invasion of HCC cells. In this study, we aimed to explore the underlying molecular mechanism of Pyk2-mediated cell migration of HCC cells.

METHODOLOGY/PRINCIPAL FINDINGS

We demonstrated that Pyk2 transformed the epithelial HCC cell line Hep3B into a mesenchymal phenotype via the induction of epithelial to mesenchymal transition (EMT), signified by the up-regulation of membrane ruffle formation, activation of Rac/Rho GTPases, down-regulation of epithelial genes E-cadherin and cytokeratin as well as promotion of cell motility in presence of lysophosphatidic acid (LPA). Suppression of Pyk2 by overexpression of dominant negative PRNK domain in the metastatic HCC cell line MHCC97L transformed its fibroblastoid phenotype to an epithelial phenotype with up-regulation of epithelial genes, down-regulation of mesenchymal genes N-cadherin and STAT5b, and reduction of LPA-induced membrane ruffle formation and cell motility. Moreover, overexpression of Pyk2 in Hep3B cells promoted the phosphorylation and localization of mesenchymal gene Hic-5 onto cell membrane while suppression of Pyk2 in MHCC97L cells attenuated its phosphorylation and localization.

CONCLUSION

These data provided new evidence of the underlying mechanism of Pyk2 in controlling cell motility of HCC cells through regulation of genes associated with EMT.

Carbonic anhydrase IX (CA9) modulates tumor-associated cell migration and invasion

Expression of carbonic anhydrase IX (CA9) was shown to be strongly involved in high incidences of metastasis and poor prognosis in various human tumors. In this study, we investigated the possible role for CA9 in tumor metastases in vitro, using a gene transfection tool in the human cervical carcinoma cell line C33A. Gene expression profiling of CA9-transfected cells (C33A/CA9) and vector-transfected cells (C33A/Mock) was investigated by DNA microarray. The biological functions of differentially expressed genes between the C33A/CA9 and C33A/Mock cells included cell growth, regulation of cell-cell and cell-extracellular matrix adhesion and cytoskeletal organization. Immunofluorescent stain and Matrigel culture showed cytoskeletal remodeling, disassembled focal adhesion, weakened cell-cell adhesion and increased motility in C33A/CA9 cells. These invasive and metastatic phenotypes were associated with Rho-GTPase-related epithelial-mesenchymal transition. Inhibition of the Rho/Rho kinase pathway by a ROCK inhibitor (Y27632) and si-Rho (short interference RNA against RhoA) showed that Rho-GTPase signaling was involved in cellular morphologic and migratory changes. The effect of CA9 on Rho-GTPase signaling was also confirmed by silencing CA9 expression. Our results suggest that CA9 overexpression induces weakening of cell adhesions and augmented cell motility by aberrant Rho-GTPase signal transduction. Our study shows an underlying mechanism of CA9-related enhanced metastatic potential of tumor cells.

Calpain-mediated proteolysis of paxillin negatively regulates focal adhesion dynamics and cell migration

The dynamic turnover of integrin-mediated adhesions is important for cell migration. Paxillin is an adaptor protein that localizes to focal adhesions and has been implicated in cell motility. We previously reported that calpain-mediated proteolysis of talin1 and focal adhesion kinase mediates adhesion disassembly in motile cells. To determine whether calpain-mediated paxillin proteolysis regulates focal adhesion dynamics and cell motility, we mapped the preferred calpain proteolytic site in paxillin. The cleavage site is between the paxillin LD1 and LD2 motifs and generates a C-terminal fragment that is similar in size to the alternative product paxillin delta. The calpain-generated proteolytic fragment, like paxillin delta, functions as a paxillin antagonist and impairs focal adhesion disassembly and migration. We generated mutant paxillin with a point mutation (S95G) that renders it partially resistant to calpain proteolysis. Paxillin-deficient cells that express paxillin S95G display increased turnover of zyxin-containing adhesions using time-lapse microscopy and also show increased migration. Moreover, cancer-associated somatic mutations in paxillin are common in the N-terminal region between the LD1 and LD2 motifs and confer partial calpain resistance. Taken together, these findings suggest a novel role for calpain-mediated proteolysis of paxillin as a negative regulator of focal adhesion dynamics and migration that may function to limit cancer cell invasion.

p190RhoGEF (Rgnef) promotes colon carcinoma tumor progression via interaction with focal adhesion kinase

Focal adhesion kinase (FAK) functions downstream of integrins and growth factor receptors to promote tumor cell motility and invasion. In colorectal cancer, FAK is activated by amidated gastrin, a protumorigenic hormone. However, it is unclear how FAK receives signals from the gastrin receptor or other G-protein-coupled receptors that can promote cell motility and invasion. The Rho guanine-nucleotide exchange factor p190RhoGEF (Rgnef) binds FAK and facilitates fibroblast focal adhesion formation on fibronectin. Here we report that Rgnef mRNA and protein expression are significantly increased during colorectal tumor progression. In human colon carcinoma cells, Rgnef forms a complex with FAK and upon gastrin stimulation, FAK translocates to newly-forming focal adhesions where it facilitates tyrosine phosphorylation of paxillin. short hairpin (shRNA)-mediated knockdown of Rgnef or FAK, or pharmacological inhibition of FAK activity, is sufficient to block gastrin-stimulated paxillin phosphorylation, cell motility, and invadopodia formation in a manner dependent upon upstream cholecystokinin-2 receptor expression. Overexpression of the C-terminal region of Rgnef (Rgnef-C, amino acid 1,279-1,582) but not Rgnef-CΔFAK (amino acid 1,302-1,582 lacking the FAK binding site) disrupted endogenous Rgnef-FAK interaction and prevented paxillin phosphorylation and cell motility stimulated by gastrin. Rgnef-C-expressing cells formed smaller, less invasive tumors with reduced tyrosine phosphorylation of paxillin upon orthotopic implantation, compared with Rgnef-CΔFAK-expressing cells. Our studies identify Rgnef as a novel regulator of colon carcinoma motility and invasion, and they show that a Rgnef-FAK linkage promotes colon carcinoma progression in vivo.

Emerging role of paxillin-PKL in regulation of cell adhesion, polarity and migration

Cell adhesion and motility is of fundamental importance during development, normal physiology and pathologic conditions such as tumor metastasis. Focal adhesion proteins and their dynamic interactions play a critical role in the regulation of directed cell migration upon exposure to extracellular guidance cues. Using a combination of pharmacological inhibitors, knockout and knockdown cells and mutant protein expression, we recently reported that following adhesion and growth factor stimulation the dynamic interaction between paxillin and PKL(GIT2) is regulated by Src/FAK-dependent phosphorylation of PKL and that this interaction is necessary for the coordination of Rho family GTPase signaling controlling front-rear cell polarity and thus directional migration. Herein, we discuss the implications of these observations.

The pathophysiology of epithelial-mesenchymal transition induced by transforming growth factor-beta in normal and malignant mammary epithelial cells

Epithelial-mesenchymal transition (EMT) is an essential process that drives polarized, immotile mammary epithelial cells (MECs) to acquire apolar, highly migratory fibroblastoid-like features. EMT is an indispensable process that is associated with normal tissue development and organogenesis, as well as with tissue remodeling and wound healing. In stark contrast, inappropriate reactivation of EMT readily contributes to the development of a variety of human pathologies, particularly those associated with tissue fibrosis and cancer cell invasion and metastasis, including that by breast cancer cells. Although metastasis is unequivocally the most lethal aspect of breast cancer and the most prominent feature associated with disease recurrence, the molecular mechanisms whereby EMT mediates the initiation and resolution of breast cancer metastasis remains poorly understood. Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine that is intimately involved in regulating numerous physiological processes, including cellular differentiation, homeostasis, and EMT. In addition, TGF-beta also functions as a powerful tumor suppressor in MECs, whose neoplastic development ultimately converts TGF-beta into an oncogenic cytokine in aggressive late-stage mammary tumors. Recent findings have implicated the process of EMT in mediating the functional conversion of TGF-beta during breast cancer progression, suggesting that the chemotherapeutic targeting of EMT induced by TGF-beta may offer new inroads in ameliorating metastatic disease in breast cancer patients. Here we review the molecular, cellular, and microenvironmental factors that contribute to the pathophysiological activities of TGF-beta during its regulation of EMT in normal and malignant MECs.

Myosin II activity regulates vinculin recruitment to focal adhesions through FAK-mediated paxillin phosphorylation

FAK-mediated myosin-dependent paxillin phosphorylation is necessary to bring vinculin to maturing focal adhesions, reinforcing the link between the cytoskeleton and the ECM.

Focal adhesions (FAs) are mechanosensitive adhesion and signaling complexes that grow and change composition in response to myosin II–mediated cytoskeletal tension in a process known as FA maturation. To understand tension-mediated FA maturation, we sought to identify proteins that are recruited to FAs in a myosin II–dependent manner and to examine the mechanism for their myosin II–sensitive FA association. We find that FA recruitment of both the cytoskeletal adapter protein vinculin and the tyrosine kinase FA kinase (FAK) are myosin II and extracellular matrix (ECM) stiffness dependent. Myosin II activity promotes FAK/Src-mediated phosphorylation of paxillin on tyrosines 31 and 118 and vinculin association with paxillin. We show that phosphomimic mutations of paxillin can specifically induce the recruitment of vinculin to adhesions independent of myosin II activity. These results reveal an important role for paxillin in adhesion mechanosensing via myosin II–mediated FAK phosphorylation of paxillin that promotes vinculin FA recruitment to reinforce the cytoskeletal ECM linkage and drive FA maturation.

Hic-5 as a regulator of endothelial cell morphology and connective tissue growth factor gene expression

The functional role of the LIM-domain protein Hic-5 was investigated in microvascular endothelial cells using a siRNA approach. Knock down of Hic-5 reduced endothelial cell spreading and impaired structural organization of the cells on basement membrane extracts. Furthermore, Hic-5 was involved in the regulation of the multifunctional protein connective tissue growth factor (CTGF, CCN2). Upon Hic-5 down-regulation, induction of CTGF by lysophosphatidic acid or colchicine was reduced. Inhibition of CTGF expression was even more pronounced in cells treated with transforming growth factor beta and inhibitors of histone deacetylases. Treatment of endothelial cells with Hic-5 siRNA reduced CTGF promoter activity. Mutation analyses of the promoter revealed transcription factors binding to the basic control element as part of the proposed Hic-5-modulated transcription complex. Further analyses showed down-regulation of Hic-5 protein upon overnight treatment with inhibitors of histone deacetylases. These data suggest that the reduced expression of Hic-5 may contribute to the anti-angiogenic effects of histone deacetylase inhibitors.

Mechanisms of the epithelial-mesenchymal transition by TGF-beta

The formation of epithelial cell barriers results from the defined spatiotemporal differentiation of stem cells into a specialized and polarized epithelium, a process termed mesenchymal-epithelial transition. The reverse process, epithelial-mesenchymal transition (EMT), is a metastable process that enables polarized epithelial cells to acquire a motile fibroblastoid phenotype. Physiological EMT also plays an essential role in promoting tissue healing, remodeling or repair in response to a variety of pathological insults. On the other hand, pathophysiological EMT is a critical step in mediating the acquisition of metastatic phenotypes by localized carcinomas. Although metastasis clearly is the most lethal aspect of cancer, our knowledge of the molecular events that govern its development, including those underlying EMT, remain relatively undefined. Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine that oversees and directs all aspects of cell development, differentiation and homeostasis, as well as suppresses their uncontrolled proliferation and transformation. Quite dichotomously, tumorigenesis subverts the tumor suppressing function of TGF-beta, and in doing so, converts TGF-beta to a tumor promoter that stimulates pathophysiological EMT and metastasis. It therefore stands to reason that determining how TGF-beta induces EMT in developing neoplasms will enable science and medicine to produce novel pharmacological agents capable of preventing its ability to do so, thereby improving the clinical course of cancer patients. Here we review the cellular, molecular and microenvironmental mechanisms used by TGF-beta to mediate its stimulation of EMT in normal and malignant cells.

Ovarian hormones regulate expression of the focal adhesion proteins, talin and paxillin, in rat uterine luminal but not glandular epithelial cells

During early pregnancy in the rat, focal adhesions disassemble in uterine luminal epithelial cells at the time of implantation to facilitate their removal so that the implanting blastocyst can invade into the underlying endometrial decidual cells. This study investigated the effect of ovarian hormones on the distribution and protein expression of two focal adhesion proteins, talin and paxillin, in rat uterine luminal and glandular epithelial cells under various hormone regimes. Talin and paxillin showed a major distributional change between different hormone regimes. Talin and paxillin were highly concentrated along the basal cell surface of uterine luminal epithelial cells in response to oestrogen treatment. However, this prominent staining of talin and paxillin was absent and also a corresponding reduction of paxillin expression was demonstrated in response to progesterone alone or progesterone in combination with oestrogen, which is also observed at the time of implantation. In contrast, the distribution of talin and paxillin in uterine glandular epithelial cells was localised on the basal cell surface and remained unchanged in all hormone regimes. Thus, not all focal adhesions are hormonally dependent in the rat uterus; however, the dynamics of focal adhesion in uterine luminal epithelial cells is tightly regulated by ovarian hormones. In particular, focal adhesion disassembly in uterine luminal epithelial cells, a key component to establish successful implantation, is predominantly under the influence of progesterone.

c-Fos accelerates hepatocyte conversion to a fibroblastoid phenotype through ERK-mediated upregulation of paxillin-Serine178 phosphorylation

Transforming growth factor beta (TGF-beta) exerts an important role in the late steps of carcinogenesis by cooperating with Ras to induce cell motility and tumor invasion. The transcription complex AP-1 has been implicated in the regulation of genes involved in motility and invasion, by mechanisms not yet delineated. We utilized a model of immortalized human hepatocytes (IHH) overexpressing c-Fos (IHH-Fos) or not (IHH-C) to investigate the role of c-Fos on cell motility in response to a prolonged treatment with TGF-beta, EGF or a combination of both. Cotreatment with EGF and TGF-beta, but neither cytokine alone, induced the conversion of hepatocytes to a fibroblastoid phenotype and increased their motility in Boyden chambers. EGF/TGF-beta cotreatment induced a higher effect on ERK phosphorylation compared to TGF-beta treatment alone. It also induced an increase in total and phosphorylated Ser(178) paxillin, a protein previously implicated in cell motility. This response was inhibited by two specific MEK inhibitors, indicating the involvement of the ERK pathway in paxillin activation. Overexpression of c-Fos correlated with increased cell scattering and motility, higher levels of ERK activation and phospho Ser(178) paxillin, increased levels of EGF receptor (EGF-R) mRNA and higher EGF-R phosphorylation levels following EGF/TGF-beta cotreatment. Conversely, siRNA-mediated invalidation of c-Fos delayed the appearance of fibroblastoid cells, decreased EGF-R mRNA and downregulated ERK and Ser(178) paxillin phosphorylations, indicating that c-Fos activates hepatocyte motility through an EGF-R/ERK/paxillin pathway. Since c-Fos is frequently overexpressed in hepatocarcinomas, this newly identified mechanism might be involved in the progression of hepatic tumors in vivo.