The role of the cytoskeleton in differentially regulating pressure-mediated effects on malignant colonocyte focal adhesion signaling and cell adhesion

ZINC40099027 activates human focal adhesion kinase by accelerating the enzymatic activity of the FAK kinase domain

Focal adhesion kinase (FAK) regulates gastrointestinal epithelial restitution and healing. ZINC40099027 (Zn27) activates cellular FAK and promotes intestinal epithelial wound closure in vitro and in mice. However, whether Zn27 activates FAK directly or indirectly remains unknown. We evaluated Zn27 potential modulation of the key phosphatases, PTP-PEST, PTP1B, and SHP2, that inactivate FAK, and performed in vitro kinase assays with purified FAK to assess direct Zn27-FAK interaction. In human Caco-2 cells, Zn27-stimulated FAK-Tyr-397 phosphorylation despite PTP-PEST inhibition and did not affect PTP1B-FAK interaction or SHP2 activity. Conversely, in vitro kinase assays demonstrated that Zn27 directly activates both full-length 125 kDa FAK and its 35 kDa kinase domain. The ATP-competitive FAK inhibitor PF573228 reduced basal and ZN27-stimulated FAK phosphorylation in Caco-2 cells, but Zn27 increased FAK phosphorylation even in cells treated with PF573228. Increasing PF573228 concentrations completely prevented activation of 35 kDa FAK in vitro by a normally effective Zn27 concentration. Conversely, increasing Zn27 concentrations dose-dependently activated kinase activity and overcame PF573228 inhibition of FAK, suggesting the direct interactions of Zn27 with FAK may be competitive. Zn27 increased the maximal activity (Vmax ) of FAK. The apparent Km of the substrate also increased under laboratory conditions less relevant to intracellular ATP concentrations. These results suggest that Zn27 is highly potent and enhances FAK activity via allosteric interaction with the FAK kinase domain to increase the Vmax of FAK for ATP. Understanding Zn27 enhancement of FAK activity will be important to redesign and develop a clinical drug that can promote mucosal wound healing.

Regulation of Src Family Kinases during Colorectal Cancer Development and Its Clinical Implications

Src family kinases (SFKs) are non-receptor kinases that play a critical role in the pathogenesis of colorectal cancer (CRC). The expression and activity of SFKs are upregulated in patients with CRC. Activation of SFKs promotes CRC cell proliferation, metastases to other organs and chemoresistance, as well as the formation of cancer stem cells (CSCs). The enhanced expression level of Src is associated with decreased survival in patients with CRC. Src-mediated regulation of CRC progression involves various membrane receptors, modulators, and suppressors, which regulate Src activation and its downstream targets through various mechanisms. This review provides an overview of the current understanding of the correlations between Src and CRC progression, with a special focus on cancer cell proliferation, invasion, metastasis and chemoresistance, and formation of CSCs. Additionally, this review discusses preclinical and clinical strategies to improve the therapeutic efficacy of drugs targeting Src for treating patients with CRC.

ZINC4085554 inhibits cancer cell adhesion by interfering with the interaction of Akt1 and FAK

Perioperative or circulatory forces enhance disseminated cancer cell adhesiveness by modulating focal adhesion kinase (FAK)-Akt1 interaction. Selectively blocking FAK-Akt1 interaction by a peptide derived from the FAK-Four-point-one, ezrin, radixin, moesin (FERM) domain reduces colon cancer cell adhesion in vitro and in mice. A preliminary in silico screening identified two small molecules resembling a peptide that may inhibit pressure-stimulated SW620 cancer cell adhesion to collagen I. The present study selected ZINC4085554 for further study to validate its proposed mechanism of action, using human SW620 colon cancer cells as a model system. At 25 and 50 µM, ZINC4085554 inhibited the pressure-stimulated adhesion of SW620 colon cancer cells to collagen I. This molecule prevented pressure-stimulated FAK-Tyr-397 phosphorylation; however, it did not affect Akt1-Ser-473 phosphorylation, indicating that ZINC4085554 acts downstream of Akt1, while Akt-Thr-308 remains unchanged in the presence of pressure and or ZINC4085554. Indeed, ZINC4085554 inhibited FAK-Akt1 interaction in response to increased extracellular pressure, consistent with the proposed mechanism. ZINC4085554 did not inhibit FAK-Tyr-397 phosphorylation in response to cell adhesion to collagen I, indicating the specificity of the inhibitory effects towards force-stimulated pathways. Finally, the present study confirmed that ZINC4085554 at 50 µM prevented pressure-activation of adhesion to surgical wounds in vivo in parallel to its ablation of intracellular signaling. In summary, ZINC4085554 is a small molecule mimicking part of the structure of FAK that reduces cancer cell adhesion by impairing pressure-stimulated FAK-Akt1 interaction and its downstream consequences. ZINC4085554 does not inhibit conventional outside-in FAK signaling and may be less toxic than global FAK inhibitors, and ZINC4085554 may be an important step towards the inhibition of metastasis.

Inhibition of pressure-activated cancer cell adhesion by FAK-derived peptides

Forces within the surgical milieu or circulation activate cancer cell adhesion and potentiate metastasis through signaling requiring FAK-Akt1 interaction. Impeding FAK-Akt1 interaction might inhibit perioperative tumor dissemination, facilitating curative cancer surgery without global FAK or AKT inhibitor toxicity. Serial truncation and structurally designed mutants of FAK identified a seven amino acid, short helical structure within FAK that effectively competes with Akt1-FAK interaction. Adenoviral overexpression of this FAK-derived peptide inhibited pressure-induced FAK phosphorylation and AKT-FAK coimmunoprecipitation in human SW620 colon cancer cells briefly exposed to 15mmHg increased pressure, consistent with laparoscopic or post-surgical pressures. Adenoviral FAK-derived peptide expression prevented pressure-activation of SW620 adhesion not only to collagen-I-coated plates but also to murine surgical wounds. A scrambled peptide did not. Finally, we modeled operative shedding of tumor cells before irrigation and closure by transient cancer cell adhesion to murine surgical wounds before irrigation and closure. Thirty minute preincubation of SW620 cells at 15mmHg increased pressure impaired subsequent tumor free survival in mice exposed to cells expressing the scrambled peptide. The FAK-derived sequence prevented this. These results suggest that blocking FAK-Akt1 interaction may prevent perioperative tumor dissemination and that analogs or mimics of this 7 amino acid FAK-derived peptide could impair metastasis.

α-Tubulin acetylation elevated in metastatic and basal-like breast cancer cells promotes microtentacle formation, adhesion, and invasive migration

Metastatic cases of breast cancer pose the primary challenge in clinical management of this disease, demanding the identification of effective therapeutic strategies that remain wanting. In this study, we report that elevated levels of α-tubulin acetylation are a sufficient cause of metastatic potential in breast cancer. In suspended cell culture conditions, metastatic breast cancer cells exhibited high α-tubulin acetylation levels that extended along microtentacle (McTN) protrusions. Mutation of the acetylation site on α-tubulin and enzymatic modulation of this posttranslational modification exerted a significant impact on McTN frequency and the reattachment of suspended tumor cells. Reducing α-tubulin acetylation significantly inhibited migration but did not affect proliferation. In an analysis of more than 140 matched primary and metastatic tumors from patients, we found that acetylation was maintained and in many cases increased in lymph node metastases compared with primary tumors. Proteomic analysis of an independent cohort of more than 390 patient specimens further documented the relationship between increased α-tubulin acetylation and the aggressive behaviors of basal-like breast cancers, with a trend toward increased risk of disease progression and death in patients with high-intensity α-tubulin acetylation in primary tumors. Taken together, our results identify a tight correlation between acetylated α-tubulin levels and aggressive metastatic behavior in breast cancer, with potential implications for the definition of a simple prognostic biomarker in patients with breast cancer.

Effect of Spilanthes acmella hydroethanolic extract activity on tumour cell actin cytoskeleton

Numerous natural products have pharmacological activity such that many biologically active compounds have led to the development of cancer chemotherapy drugs. Spilanthes acmella (Asteraceae) is widely cultivated in the State of Pará, Brazil, being employed in folk medicine for its anti-inflammatory, antimicrobial, antioxidant, analgesic, insecticide, and larvicidal properties. However, its cytotoxicity and influence on actin cytoskeleton organisation in tumour cell lines are practically nonexistent. We have verified the cytotoxicity of a hydroethanolic extract of the inflorescence of S. acmella, and examined its effects on the cytoskeleton of tumour cells. Decreasing concentrations of the extract (250, 500 and 1,000 µg/mL) were given to cultures of neoplastic cells (HEp-2). Cytotoxicity was assessed by the MTT test, and the influence on cytoskeleton organisation was examined by fluorescence microscopy. The IC50 of the hydroethanolic extract was 513 µg/mL, confirming the data obtained from the MTT assay that gave high cytotoxicity. The actin cytoskeleton arrangement of HEp2 cells at 500 and 1,000 µg/mL showed depolymerisation of the filaments, causing loss of morphology and consequently compromising cell adhesion.

The role of focal adhesion kinase in the regulation of cellular mechanical properties

The regulation of mechanical properties is necessary for cell invasion into connective tissue or intra- and extravasation through the endothelium of blood or lymph vessels. Cell invasion is important for the regulation of many healthy processes such as immune response reactions and wound healing. In addition, cell invasion plays a role in disease-related processes such as tumor metastasis and autoimmune responses. Until now the role of focal adhesion kinase (FAK) in regulating mechanical properties of cells and its impact on cell invasion efficiency is still not well known. Thus, this review focuses on mechanical properties regulated by FAK in comparison to the mechano-regulating protein vinculin. Moreover, it points out the connection between cancer cell invasion and metastasis and FAK by showing that FAK regulates cellular mechanical properties required for cellular motility. Furthermore, it sheds light on the indirect interaction of FAK with vinculin by binding to paxillin, which then impairs the binding of paxillin to vinculin. In addition, this review emphasizes whether FAK fulfills regulatory functions similar to vinculin. In particular, it discusses the differences and the similarities between FAK and vinculin in regulating the biomechanical properties of cells. Finally, this paper highlights that both focal adhesion proteins, vinculin and FAK, synergize their functions to regulate the mechanical properties of cells such as stiffness and contractile forces. Subsequently, these mechanical properties determine cellular invasiveness into tissues and provide a source sink for future drug developments to inhibit excessive cell invasion and hence, metastases formation.

Procedures for the biochemical enrichment and proteomic analysis of the cytoskeletome

The cell cytoskeleton is composed of microtubules, intermediate filaments, and actin that provide a rigid support structure important for cell shape. However, it is also a dynamic signaling scaffold that receives and transmits complex mechanosensing stimuli that regulate normal physiological and aberrant pathophysiological processes. Studying cytoskeletal functions in the cytoskeleton's native state is inherently difficult due to its rigid and insoluble nature. This has severely limited detailed proteomic analyses of the complex protein networks that regulate the cytoskeleton. Here, we describe a purification method that enriches for the cytoskeleton and its associated proteins in their native state that is also compatible with current mass spectrometry-based protein detection methods. This method can be used for biochemical, fluorescence, and large-scale proteomic analyses of numerous cell types. Using this approach, 2346 proteins were identified in the cytoskeletal fraction of purified mouse embryonic fibroblasts, of which 635 proteins were either known cytoskeleton proteins or cytoskeleton-interacting proteins. Functional annotation and network analyses using the Ingenuity Knowledge Database of the cytoskeletome revealed important nodes of interconnectivity surrounding well-established regulators of the actin cytoskeleton and focal adhesion complexes. This improved cytoskeleton purification method will aid our understanding of how the cytoskeleton controls normal and diseased cell functions.

Novel mechanistic link between focal adhesion remodeling and glucose-stimulated insulin secretion

Actin cytoskeleton remodeling is well known to be positively involved in glucose-stimulated pancreatic β cell insulin secretion. We have observed glucose-stimulated focal adhesion remodeling at the β cell surface and have shown this to be crucial for glucose-stimulated insulin secretion. However, the mechanistic link between such remodeling and the insulin secretory machinery remained unknown and was the major aim of this study. MIN6B1 cells, a previously validated model of primary β cell function, were used for all experiments. Total internal reflection fluorescence microscopy revealed the glucose-responsive co-localization of focal adhesion kinase (FAK) and paxillin with integrin β1 at the basal cell surface after short term stimulation. In addition, blockade of the interaction between β1 integrins and the extracellular matrix with an anti-β1 integrin antibody (Ha2/5) inhibited short term glucose-induced phosphorylation of FAK (Tyr-397), paxillin (Tyr-118), and ERK1/2 (Thr-202/Tyr-204). Pharmacological inhibition of FAK activity blocked glucose-induced actin cytoskeleton remodeling and glucose-induced disruption of the F-actin/SNAP-25 association at the plasma membrane as well as the distribution of insulin granules to regions in close proximity to the plasma membrane. Furthermore, FAK inhibition also completely blocked short term glucose-induced activation of the Akt/AS160 signaling pathway. In conclusion, these results indicate 1) that glucose-induced activation of FAK, paxillin, and ERK1/2 is mediated by β1 integrin intracellular signaling, 2) a mechanism whereby FAK mediates glucose-induced actin cytoskeleton remodeling, hence allowing docking and fusion of insulin granules to the plasma membrane, and 3) a possible functional role for the Akt/AS160 signaling pathway in the FAK-mediated regulation of glucose-stimulated insulin secretion.

Comparative analysis of predictive models for nongenotoxic hepatocarcinogenicity using both toxicogenomics and quantitative structure-activity relationships

The primary testing strategy to identify nongenotoxic carcinogens largely relies on the 2-year rodent bioassay, which is time-consuming and labor-intensive. There is an increasing effort to develop alternative approaches to prioritize the chemicals for, supplement, or even replace the cancer bioassay. In silico approaches based on quantitative structure-activity relationships (QSAR) are rapid and inexpensive and thus have been investigated for such purposes. A slightly more expensive approach based on short-term animal studies with toxicogenomics (TGx) represents another attractive option for this application. Thus, the primary questions are how much better predictive performance using short-term TGx models can be achieved compared to that of QSAR models, and what length of exposure is sufficient for high quality prediction based on TGx. In this study, we developed predictive models for rodent liver carcinogenicity using gene expression data generated from short-term animal models at different time points and QSAR. The study was focused on the prediction of nongenotoxic carcinogenicity since the genotoxic chemicals can be inexpensively removed from further development using various in vitro assays individually or in combination. We identified 62 chemicals whose hepatocarcinogenic potential was available from the National Center for Toxicological Research liver cancer database (NCTRlcdb). The gene expression profiles of liver tissue obtained from rats treated with these chemicals at different time points (1 day, 3 days, and 5 days) are available from the Gene Expression Omnibus (GEO) database. Both TGx and QSAR models were developed on the basis of the same set of chemicals using the same modeling approach, a nearest-centroid method with a minimum redundancy and maximum relevancy-based feature selection with performance assessed using compound-based 5-fold cross-validation. We found that the TGx models outperformed QSAR in every aspect of modeling. For example, the TGx models' predictive accuracy (0.77, 0.77, and 0.82 for the 1-day, 3-day, and 5-day models, respectively) was much higher for an independent validation set than that of a QSAR model (0.55). Permutation tests confirmed the statistical significance of the model's prediction performance. The study concluded that a short-term 5-day TGx animal model holds the potential to predict nongenotoxic hepatocarcinogenicity.

Role of focal adhesion kinase in the pathogenesis of colorectal carcinoma

Focal adhesion kinase (FAK) was initially identified as a nonreceptor protein tyrosine kinase localized to the focal contact protein clusters. This enzyme has been shown to facilitate generation of integrin-stimulated signals to downstream targets. It has been reported that activation of FAK leads to a number of processes, including cell attachment, migration, proliferation, and survival. The expression of FAK in colon carcinoma is significantly higher than that in matched cancer-adjacent normal tissue, suggesting that FAK may be an important target for the therapy of colon carcinoma. The inhibition of FAK activation can interrupt many signal pathways involved in colon carcinogenesis and may represent a new therapy strategy for colon carcinoma.

Akt directly regulates focal adhesion kinase through association and serine phosphorylation: implication for pressure-induced colon cancer metastasis

Although focal adhesion kinase (FAK) is typically considered upstream of Akt, extracellular pressure stimulates cancer cell adhesion via Akt-dependent FAK activation. How Akt regulates FAK is unknown. We studied Akt-FAK interaction in colon cancer cells under 15 mmHg increased extracellular pressure. Pressure enhanced Akt-FAK association, blocked by inhibiting FAK or silencing Akt1 but not Akt2, and stimulated FAK serine phosphorylation in Caco-2 and human colon cancer cells from surgical specimens Akt1-dependently. FAK includes three serine (S517/601/695) and one threonine (T600)-containing consensus sequences for Akt phosphorylation. Studying S->A nonphosphorylatable point mutants suggests that these sites coordinately upregulate FAK Y397 tyrosine phosphorylation, which conventionally initiates FAK activation, and mediate pressure-induced cancer cell adhesion. FAK(T600A) mutation did not prevent pressure-induced FAK(Y397) phosphorylation or adhesion. Akt1 appeared to directly bind FAK, and this binding did not depend on the FAK autophosphorylation site (Y397). In addition, our results demonstrated that Akt phosphorylated FAK at three novel serine phosphorylation sites, which were also not required for FAK-Akt binding. This novel interaction suggests that FAK and Akt may be dual kinase targets to prevent cancer cell adhesion and metastasis.

Progress in researches about focal adhesion kinase in gastrointestinal tract

Focal adhesion kinase (FAK) is a 125-kDa non-receptor protein tyrosine. Growth factors or the clustering of integrins facilitate the rapid phosphorylation of FAK at Tyr-397 and this in turn recruits Src-family protein tyrosine kinases, resulting in the phosphorylation of Tyr-576 and Tyr-577 in the FAK activation loop and full catalytic FAK activation. FAK plays a critical role in the biological processes of normal and cancer cells including the gastrointestinal tract. FAK also plays an important role in the restitution, cell survival and apoptosis and carcinogenesis of the gastrointestinal tract. FAK is over-expressed in cancer cells and its over-expression and elevated activities are associated with motility and invasion of cancer cells. FAK has been proposed as a potential target in cancer therapy. Small molecule inhibitors effectively inhibit the kinase activity of FAK and show a potent inhibitory effect for the proliferation and migration of tumor cells, indicating a high potential for application in cancer therapy.

The effects of mechanical forces on intestinal physiology and pathology

The epithelial and non-epithelial cells of the intestinal wall experience a myriad of physical forces including strain, shear, and villous motility during normal gut function. Pathologic conditions alter these forces, leading to changes in the biology of these cells. The responses of intestinal epithelial cells to forces vary with both the applied force and the extracellular matrix proteins with which the cells interact, with differing effects on proliferation, differentiation, and motility, and the regulation of these effects involves similar but distinctly different signal transduction mechanisms. Although normal epithelial cells respond to mechanical forces, malignant gastrointestinal epithelial cells also respond to forces, most notably by increased cell adhesion, a critical step in tumor metastasis. This review will focus on the phenomenon of mechanical forces influencing cell biology and the mechanisms by which the gut responds these forces in both the normal as well as pathophysiologic states when forces are altered. Although more is known about epithelial responses to force, information regarding mechanosensitivity of vascular, neural, and endocrine cells within the gut wall will also be discussed, as will, the mechanism by which forces can regulate epithelial tumor cell adhesion.

The effects of increased extracellular deformation, pressure, and integrin phosphorylation on fibroblast migration

Wound healing requires fibroblast migration. Increased pressure slows migration and ulcer healing. Pressure also induces beta1 integrin phosphorylation. We hypothesized that beta1 phosphorylation influences cell adhesion and migration. We compared the effects of increased pressure on the adhesion and motility of GD25 beta1-integrin null fibroblasts transfected with wild-type beta1A-integrin, S785A or TT788/9AA (phosphorylation-deficient), or T788D (constitutively phosphomimetic) mutants. GD25 beta1 null cells adhered less than wild type beta1A cells, suggesting adherence by non-integrin mechanisms. Preventing Ser-785 or Thr 788/789 phosphorylation reduced adhesion, suggesting that phosphorylation regulates adhesiveness. Substituting Asp for Thr788 stimulated adhesion on both substrates. Pressure decreased migration in all lines and on all matrixes, the most in wild type beta1A integrin cells and only slightly in beta1A TT788/9AA cells. In comparison, another physical force, repetitive deformation, increased migration in the beta1A integrin T788D, S785A, and wild type cells on fibronectin, and decreased migration on collagen. Deformation did not affect the migration of GD25 beta1-integrin null or TT788/9AA cells. Extracellular signal-regulated kinase (ERK) blockade neither altered basal migration nor prevented pressure inhibition, while the cellular deformation response on fibronectin was altered. beta1-Integrin phosphorylation regulates cellular adhesion and the deformation effects on motility. The pressure-induced motility response is independently regulated.

Biological impact of mechanical stimuli on tumor metastasis

Increasing evidence suggests tumor cell exposure to mechanical stimuli during the perioperative period as well as throughout the normal disease process may have a discernable impact on tumor metastasis and patient outcome. In vitro studies have demonstrated that transient exposure to increased extracellular pressure and shear forces modulates integrin binding affinity and stimulates cancer cell adhesion through a cytoskeleton- and focal adhesion complex-dependent signaling mechanism. More prolonged exposure to elevated pressures stimulates tumor cell proliferation by a distinct signaling pathway. Whether pressure effects on cell adhesion and proliferation pose biological ramifications in vivo remained unknown. We recently reported that pressure activation of malignant cells does indeed have a biological impact on surgical wound implantation, tumor development and tumor-free survival in a murine colon tumor model. Moreover, this effect can be disrupted by preoperative administration of colchicine. Taken together with previous work from our laboratory and others, these findings suggest that further elucidation of the mechanical signaling pathways governing pressure-stimulated tumor cell adhesion and proliferation may identify novel therapeutic targets for the treatment and prevention of tumor metastasis.

TGF-beta1 modulates focal adhesion kinase expression in rat intestinal epithelial IEC-6 cells via stimulatory and inhibitory Smad binding elements

TGF-beta and FAK modulate cell migration, differentiation, proliferation and apoptosis, and TGF-beta promotes FAK transcription in intestinal epithelial cells via Smad-dependent and independent pathways. We utilized a 1320 bp FAK promoter-luciferase construct to characterize basal and TGF-beta-mediated FAK gene transcription in IEC-6 cells. Inhibiting JNK or Akt negated TGF-beta-stimulated promoter activity; ERK inhibition did not block the TGF-beta effect but increased basal activity. Co-transfection with Co-Smad4 enhanced the TGF-beta response while the inhibitory Smad7 abolished it. Serial deletions sequentially removing the four Smad binding elements (SBE) in the 5' untranslated region of the promoter revealed that the two most distal SBE's are positive regulators while SBE3 exerts a negative influence. Mutational deletion of two upstream p53 sites enhanced basal but did not affect TGF-beta-stimulated increases in promoter activity. TGF-beta increased DNA binding of Smad4, phospho-Smad2/3 and Runx1/AML1a to the most distal 435 bp containing 3 SBE and 2 AML1a sites by ChIP assay. However, although point mutation of SBE1 ablated the TGF-beta-mediated rise in SV40-promoter activity, mutation of AML1a sites did not. TGF-beta regulation of FAK transcription reflects a complex interplay between positive and negative non-Smad signals and SBE's, the last independent of p53 or AML1a.

Increased extracellular pressure enhances cancer cell integrin-binding affinity through phosphorylation of beta1-integrin at threonine 788/789

Increased extracellular pressure stimulates beta1-integrin-dependent cancer cell adhesion. We asked whether pressure-induced adhesion is mediated by changes in beta1-integrin binding affinity or avidity and whether these changes are phosphorylation dependent. We evaluated integrin affinity and clustering in human SW620 colon cancer cells by measuring differences in binding between soluble Arg-Gly-Asp (RGD)-Fc ligands and RGD-Fc-F(ab')2 multimeric complexes under ambient and 15-mmHg increased pressures. Phosphorylation of beta1-integrin S785 and T788/9 residues in SW620 and primary malignant colonocytes was assessed in parallel. We further used GD25-beta1-integrin-null murine fibroblasts stably transfected with either wild-type beta1A-integrin, S785A, TT788/9AA, or T788D mutants to investigate the role of beta1-integrin site-specific phosphorylation. SW620 binding of RGD-Fc-F(ab')2 multimeric complexes, but not soluble RGD-Fc ligands, was sensitive to integrin clustering. RGD-Fc ligand binding was significantly increased under elevated pressure, suggesting that pressure modulates beta1-integrin affinity. Pressure stimulated both beta1-integrin S785 and T788/9 phosphorylation. GD25-beta1A-integrin wild-type and S785A cells displayed an increase in adhesion to fibronectin under elevated pressure, an effect absent in beta1-integrin-null and TT788/9AA cells. T788D substitution significantly elevated basal cell adhesion but displayed no further increase under pressure. These results suggest pressure-induced cell adhesion is mediated by beta1-integrin T788/9 phosphorylation-dependent changes in integrin binding affinity.

Colchicine inhibits pressure-induced tumor cell implantation within surgical wounds and enhances tumor-free survival in mice

Iatrogenic tumor cell implantation within surgical wounds can compromise curative cancer surgery. Adhesion of cancer cells, in particular colon cancer cells, is stimulated by exposure to increased extracellular pressure through a cytoskeleton-dependent signaling mechanism requiring FAK, Src, Akt, and paxillin. Mechanical stimuli during tumor resection may therefore negatively impact patient outcome. We hypothesized that perioperative administration of colchicine, which prevents microtubule polymerization, could disrupt pressure-stimulated tumor cell adhesion to surgical wounds and enhance tumor-free survival. Ex vivo treatment of Co26 and Co51 colon cancer cells with colchicine inhibited pressure-stimulated cell adhesion to murine surgical wounds and blocked pressure-induced FAK and Akt phosphorylation. Surgical wound contamination with pressure-activated Co26 and Co51 cells significantly reduced tumor-free survival compared with contamination with tumor cells under ambient pressure. Mice treated with pressure-activated Co26 and Co51 cells from tumors preoperatively treated with colchicine in vivo displayed reduced surgical site implantation and significantly increased tumor-free survival compared with mice exposed to pressure-activated cells from tumors not pretreated with colchicine. Our data suggest that pressure activation of malignant cells promotes tumor development and impairs tumor-free survival and that perioperative colchicine administration or similar interventions may inhibit this effect.

Evolving management of colorectal cancer

This article reviews recent advances in surgical techniques and adjuvant therapies for colorectal cancer, including total mesorectal excision, the resection of liver and lung metastasis and advances in chemoradiation and foreshadows some interventions that may lie just beyond the frontier. In particular, little is known about the intracellular and extracellular cascades that may influence colorectal cancer cell adhesion and metastasis. Although the phosphorylation of focal adhesion kinases and focal adhesion associated proteins in response to integrin-mediated cell matrix binding (”outside in integrin signaling”) is well described, the stimulation of cell adhesion by intracellular signals activated by pressure prior to adhesion represents a different signal paradigm. However, several studies have suggested that increased pressure and shear stress activate cancer cell adhesion. Further studies of the pathways that regulate integrin-driven cancer cell adhesion may identify ways to disrupt these signals or block integrin-mediated adhesion so that adhesion and eventual metastasis can be prevented in the future.

SiRNA-mediated reduction of alpha-actinin-1 inhibits pressure-induced murine tumor cell wound implantation and enhances tumor-free survival

Viable cancer cells can commonly be recovered from surgical sites and venous blood during tumor resection. The adhesion of these cells to surrounding tissues may impact patient outcomes. Iatrogenic exposure to increased extracellular pressure modulates integrin binding affinity and stimulates colon cancer cell adhesion in vitro through an alpha-actinin-1-dependent signaling pathway. We hypothesized that preoperative small interfering RNA-mediated silencing of alpha-actinin-1 in tumor tissue could disrupt pressure-stimulated cancer cell adhesion to murine surgical wounds and thereby enhance subsequent tumor-free survival. Reducing alpha-actinin-1 in CT26 murine adenocarcinoma cells blocked cell adhesion to collagen in vitro and similarly inhibited pressure-induced CT26 implantation in murine surgical wounds in vivo. Surgical wound contamination with pressure-activated CT26 cells significantly reduced tumor-free survival compared to contamination with tumor cells maintained under ambient pressure. However, mice treated with pressure-activated CT26 cells preoperatively transfected with alpha-actinin-1-specific small interfering RNA displayed reduced surgical site implantation and increased tumor-free survival compared to mice exposed to pressure-activated cells expressing normal levels of alpha-actinin-1 protein. These results suggest that pressure activation of malignant cells promotes tumor development and impairs tumor-free survival. alpha-Actinin-1 may be an effective therapeutic target to inhibit perioperative pressure-stimulated tumor cell implantation.

An intracellular signal pathway that regulates cancer cell adhesion in response to extracellular forces

Increasing evidence suggests that tumor cells can regulate their own adhesion via intracellular signals that modulate integrin binding affinity. Although the full pathway has not yet been elucidated, the effects of pressure seem likely to require cytoskeletal mechanosensing, Src, phosphatidylinositol 3-kinase, focal adhesion kinase, and Akt-1 activation. Ultimately, activated focal adhesion kinase accumulates at the membrane in association with beta(1)-integrin heterodimers and may modulate integrin binding affinity. This pathway may be a promising target for manipulation to inhibit metastatic cancer cell adhesion.

Cytoskeletal signaling by way of alpha-actinin-1 mediates ERK1/2 activation by repetitive deformation in human Caco2 intestinal epithelial cells

BACKGROUND

Repetitive deformation stimulates proliferation in human Caco2 intestinal epithelial cells by way of an ERK1/2-dependent pathway. We examined the effects of cytoskeletal perturbation on deformation-induced signaling in Caco2 cells.

METHODS

The Caco2 cell cytoskeleton was disrupted with either cytochalasin D, phalloidin, colchicine, or paclitaxel. Levels of alpha-actinin-1 and -4 and paxillin were reduced by specific small interfering RNA. Cells on collagen I-precoated membranes were subjected to 10% repetitive deformation at 10 cycles/min. After 1 hour, cells were lysed for Western blot analysis.

RESULTS

Strain-activated ERK1/2, focal adhesion kinase, and Src phosphorylation in dimethyl sulfoxide- and/or nontargeting small interfering RNA-treated control cell populations. Cytochalasin D and paclitaxel, but not phalloidin and colchicine, blocked ERK1/2 phosphorylation. A decrease in alpha-actinin-1, but not in alpha-actinin-4 or paxillin, inhibited ERK1/2 and focal adhesion kinase phosphorylation, whereas Src activation appears to be independent of these effects.

CONCLUSIONS

The intestinal epithelial cell cytoskeleton may transduce mechanical signals by way of alpha-actinin-1 into the focal adhesion complex, culminating in ERK1/2 activation and proliferation.

Alpha-actinin-1 phosphorylation modulates pressure-induced colon cancer cell adhesion through regulation of focal adhesion kinase-Src interaction

Physical forces including pressure, strain, and shear can be converted into intracellular signals that regulate diverse aspects of cell biology. Exposure to increased extracellular pressure stimulates colon cancer cell adhesion by a beta(1)-integrin-dependent mechanism that requires an intact cytoskeleton and activation of focal adhesion kinase (FAK) and Src. alpha-Actinin facilitates focal adhesion formation and physically links integrin-associated focal adhesion complexes with the cytoskeleton. We therefore hypothesized that alpha-actinin may be necessary for the mechanical response pathway that mediates pressure-stimulated cell adhesion. We reduced alpha-actinin-1 and alpha-actinin-4 expression with isoform-specific small interfering (si)RNA. Silencing of alpha-actinin-1, but not alpha-actinin-4, blocked pressure-stimulated cell adhesion in human SW620, HT-29, and Caco-2 colon cancer cell lines. Cell exposure to increased extracellular pressure stimulated alpha-actinin-1 tyrosine phosphorylation and alpha-actinin-1 interaction with FAK and/or Src, and enhanced FAK phosphorylation at residues Y397 and Y576. The requirement for alpha-actinin-1 phosphorylation in the pressure response was investigated by expressing the alpha-actinin-1 tyrosine phosphorylation mutant Y12F in the colon cancer cells. Expression of Y12F blocked pressure-mediated adhesion and inhibited the pressure-induced association of alpha-actinin-1 with FAK and Src, as well as FAK activation. Furthermore, siRNA-mediated reduction of alpha-actinin-1 eliminated the pressure-induced association of alpha-actinin-1 and Src with beta(1)-integrin receptor, as well as FAK-Src complex formation. These results suggest that alpha-actinin-1 phosphorylation at Y12 plays a crucial role in pressure-activated cell adhesion and mechanotransduction by facilitating Src recruitment to beta(1)-integrin, and consequently the association of FAK with Src, to enhance FAK phosphorylation.

Identification of functional domains in AKT responsible for distinct roles of AKT isoforms in pressure-stimulated cancer cell adhesion

Cell adhesion is a critical step in cancer metastasis, activated by extracellular forces such as pressure and shear. Reducing AKT1, but not AKT2, ablates the increase in cancer cell adhesion associated with 15 mm Hg increased extracellular pressure. To identify the determinants of this AKT isoform specificity, we exchanged the pleckstrin homology (PH) domains and/or hinge regions of AKT1 and AKT2. Wild type isoforms or these chimeras were overexpressed in Caco-2 cells in the absence or presence of isoform-specific siRNA to suppress endogenous AKT1. Pressure-induced AKT translocation and phosphorylation to the membrane were compared, along with the stimulation of cell adhesion by pressure. Pressure stimulated translocation of AKT1, but not AKT2 to the plasma membrane. Among our chimeras, only the chimeric AKT2 (chimera2), in which both the AKT2 PH domain and hinge region had been replaced by those of AKT1, translocated to the membrane in response to pressure. Similarly, only chimera2 rescued the function of AKT1 in mediating pressure-stimulated adhesion after endogenous AKT1 had been reduced. Pressure also promoted phosphorylation of AKT1 but not AKT2, and expression of a nonphosphorylatable double point mutant prevented pressure-stimulated adhesion. Among the chimeras, pressure promoted only chimera2 phosphorylation. These results identify the AKT1 PH domain and hinge region as functional domains which jointly permit AKT1 translocation and phosphorylation in response to extracellular pressure and distinguish determine the specificity of AKT1 in mediating the effects of extracellular pressure on cancer cell adhesion. These may be useful targets for interventions to inhibit metastasis.

FAK association with multiple signal proteins mediates pressure-induced colon cancer cell adhesion via a Src-dependent PI3K/Akt pathway

Cancer cell adhesion is traditionally viewed as random, occurring if the cell's receptors match the substrate. Cancer cells are subjected to pressure and shear during growth against a constraining stroma, surgical manipulation, and passage through the venous and lymphatic system. Cells shed into a cavity such as the abdomen postoperatively also experience increased pressure from postoperative edema. Increased extracellular pressure stimulates integrin-mediated cancer cell adhesion via FAK and Src. PI 3-kinase (PI3K) inhibitors (LY294002 or wortmannin), Akt inhibitors, or Akt1 siRNA blocked adhesion stimulated by 15 mmHg pressure in SW620 or primary human malignant colonocytes. Pressure activated PI3K, tyrosine-phosphorylated and membrane-translocated the p85 subunit, and phosphorylated Akt. PI3K inhibitor (LY294002) prevented pressure-stimulated Akt Ser473 and FAK Tyr397, but not FAK576 or Src416 phosphorylation. PP2 inhibited PI3K activity and Akt phosphorylation. FAK siRNA did not affect pressure-induced PI3K activation but blocked Akt phosphorylation. Pressure also stimulated FAK or FAKY397F mutant translocation to the membrane. Akt inhibitor IV blocked pressure-induced Akt and FAK translocation. Pressure activated Src- and PI3K-dependently induced p85 interaction with FAK, and FAK with beta1 integrin. These results delineate a novel force-activated inside-out Src/PI3K/FAK/Akt pathway by which cancer cells regulate their own adhesion. These signals may be potential targets for inhibition of metastatic adhesion.

Morphological instability and cancer invasion: a 'splashing water drop' analogy

Background

Tissue invasion, one of the hallmarks of cancer, is a major clinical problem. Recent studies suggest that the process of invasion is driven at least in part by a set of physical forces that may be susceptible to mathematical modelling which could have practical clinical value.

Model and conclusion

We present an analogy between two unrelated instabilities. One is caused by the impact of a drop of water on a solid surface while the other concerns a tumor that develops invasive cellular branches into the surrounding host tissue. In spite of the apparent abstractness of the idea, it yields a very practical result, i.e. an index that predicts tumor invasion based on a few measurable parameters. We discuss its application in the context of experimental data and suggest potential clinical implications.

Src and focal adhesion kinase mediate mechanical strain-induced proliferation and ERK1/2 phosphorylation in human H441 pulmonary epithelial cells

Pulmonary epithelial cells are exposed to repetitive deformation during physiological breathing and mechanical ventilation. Such deformation may influence pulmonary growth, development, and barotrauma. Although deformation stimulates proliferation and activates extracellular signal-regulated kinases (ERK1/2) in human pulmonary epithelial H441 cells, the upstream mechanosensors that induce ERK activation are poorly understood. We investigated whether c-Src or focal adhesion kinase (FAK) mediates cyclic mechanical strain-induced ERK1/2 activation and proliferation in human pulmonary epithelial (NCI-H441) cells. The H441 and A549 cells were grown on collagen I-precoated membranes and were subjected to an average 10% cyclic mechanical strain at 20 cycles/min. Cyclic strain activated Src within 2 min by increasing phosphorylation at Tyr(418), followed by rapid phosphorylation of FAK at Tyr(397) and Tyr(576) and ERK1/2 at Thr(202)/Tyr(204) (n = 5, P < 0.05). Twenty-four (A549 cells) and 24-72 h (H441 cells) of cyclic mechanical strain increased cell numbers compared with static culture. Twenty-four hours of cyclic strain also increased H441 FAK, Src, and ERK phosphorylation without affecting total FAK, Src, or ERK protein. The mitogenic effect was blocked by Src (10 micromol/l PP2 or short interfering RNA targeted to Src) or MEK (50 micromol/l PD-98059) inhibition. PP2 also blocked strain-induced phosphorylation of FAK-Tyr(576) and ERK-Thr(202)/Tyr(204) but not FAK-Tyr(397). Reducing FAK by FAK-targeted short interfering RNA blocked mechanical strain-induced mitogenicity and significantly attenuated strain-induced ERK activation but not strain-induced Src phosphorylation. Together, these results suggest that repetitive mechanical deformation induced by ventilation supports pulmonary epithelial proliferation by a pathway involving Src, FAK, and then ERK signaling.

Differential FAK phosphorylation at Ser-910, Ser-843 and Tyr-397 induced by angiotensin II, LPA and EGF in intestinal epithelial cells

A rapid increase in the tyrosine phosphorylation of the non-receptor tyrosine kinase FAK is a prominent early event in fibroblasts stimulated by a variety of signaling molecules. However, a variety of epithelial cells, including intestinal epithelial cells, show a high basal level of tyrosine phosphorylated FAK that is only slightly further increased by addition of G protein-coupled receptor (GPCR) agonists or growth factors. In this study, we determined whether these stimuli could elicit FAK phosphorylation at serine residues, including Ser-910 and Ser-843. Our results show that multiple agonists including angiotensin II (ANGII), lysophosphatidic acid (LPA), phorbol esters and EGF induced a striking stimulation of FAK phosphorylation at Ser-910 in rat intestinal epithelial IEC-18 cells via an ERK-dependent pathway. In striking contrast, none of these stimuli promoted a significant further increase in FAK phosphorylation at Tyr-397 in these cells. These results were extended using cultures of polarized human colonic epithelial T84 cells. We found that either carbachol or EGF promoted a striking ERK-dependent phosphorylation of FAK at Ser-910, but these agonists caused only slight stimulation of FAK at Tyr-397 in T84 cells. In addition, we demonstrated that GPCR agonists also induced a dramatic increase of FAK phosphorylation at Ser-843 in either IEC-18 or T84 cells. Our results indicate that Ser-910 and Ser-843, rather than Tyr-397, are prominent sites differentially phosphorylated in response to neurotransmitters, bioactive lipids, tumor promoters and growth factors in intestinal epithelial cells.