Pressure activates colon cancer cell adhesion by inside-out focal adhesion complex and actin cytoskeletal signaling

Pressure activates colon cancer cell adhesion via paxillin phosphorylation, Crk, Cas, and Rac1

Physical forces can activate colon cancer cell adhesion, critical for metastasis. Paxillin is phosphorylated by FAK and required for pressure-stimulated adhesion. However, whether paxillin acts as an inert scaffolding protein or whether paxillin phosphorylation is required is unknown. Transfection with paxillin point-phosphorylation mutants demonstrated that phosphorylation at tyrosines 31 and 118 together is necessary for pressure-stimulated adhesion. We further evaluated potential paxillin partners. Reducing the adaptor protein Crk or the focal adhesion protein p130Cas blocked pressure-stimulated adhesion. Furthermore, Crk and p130Cas both displayed increased co-immunoprecipitation with paxillin in response to increased pressure, except in cells transfected with a Y31Y118 paxillin mutant. Inhibiting the small GTPase Rac1 also abolished pressure-stimulated adhesion, and reducing paxillin by siRNA blocked Rac1 phosphorylation by pressure. Thus, paxillin phosphorylation at tyrosines 31 and 118 together is necessary for pressure-induced adhesion. Paxillin, Crk and Cas form a trimeric complex that activates Rac1 and mediates this effect.

Repetitive deformation activates Src-independent FAK-dependent ERK motogenic signals in human Caco-2 intestinal epithelial cells

Repetitive deformation due to villous motility or peristalsis may support the intestinal mucosa, stimulating intestinal epithelial proliferation under normal circumstances and restitution in injured and inflamed mucosa rich in tissue fibronectin. Cyclic strain enhances Caco-2 and IEC-6 intestinal epithelial cell migration across fibronectin via ERK. However, the upstream mediators of ERK activation are unknown. We investigated whether Src and FAK mediate strain-induced ERK phosphorylation and migration in human Caco-2 intestinal epithelial cells on fibronectin. Monolayers on tissue fibronectin-precoated membranes were subjected to an average 10% repetitive deformation at 10 cycles/min. Phosphorylation of Src-Tyr 418, FAK-Tyr 397-Tyr 576-Tyr 925, and ERK were significantly increased by deformation. The stimulation of wound closure by strain was prevented by Src blockade with PP2 (10 micromol/l) or specific short interfering (si)RNA. Src inhibition also prevented strain-induced FAK phosphorylation at Tyr 397 and Tyr 576 but not FAK-Tyr 925 or ERK phosphorylation. Reducing FAK by siRNA inhibited strain-induced ERK phosphorylation. Transfection of NH2-terminal tyrosine phosphorylation-deficient FAK mutants Y397F, Y576F-Y577F, and Y397F-Y576F-Y577F did not prevent the activation of ERK2 by cyclic strain, but a FAK mutant at the COOH terminal (Y925F) prevented the strain-induced activation of ERK2. Although the Y397F-Y576F-Y577F FAK construct exhibited less basal FAK-Tyr 925 phosphorylation under static conditions, it nevertheless exhibited increased FAK-Tyr 925 phosphorylation in response to strain. These results suggest that repetitive deformation stimulates intestinal epithelial motility across fibronectin in a manner that requires both Src activation and a novel Src-independent FAK-Tyr 925-dependent pathway that activates ERK. This pathway may be an important target for interventions to promote mucosal healing in settings of intestinal ileus or fasting.

Akt2, but not Akt1 or Akt3 mediates pressure-stimulated serum-opsonized latex bead phagocytosis through activating mTOR and p70 S6 kinase

Monocytes and macrophages play critical roles in innate host defense and are sensitive to mechanical stimuli. Tissue pressure is often altered in association with inflammation or infection. Low pressure (20 mmHg), equivalent to normal tissue pressure, increases phagocytosis by primary monocytes and PMA-differentiated THP-1 macrophages, in part by FAK and ERK inhibition and p38 activation. PI-3K is required for macrophage phagocytosis, but whether PI-3K mediates pressure-stimulated phagocytosis is not known. Furthermore, little is known about the role played by the PI-3K downstream Kinases, Akt, and p70 S6 kinase (p70S6K) in modulating macrophage phagocytosis. Thus, we studied the contribution of PI-3K, Akt, and p70S6K to pressure-increased serum-opsonized bead phagocytosis. Pressure-induced p85 PI-3K translocation from cytosolic to membrane fractions and increased Akt activation by 36.1 +/- 12.0% in THP-1 macrophages. LY294002 or Akt inhibitor IV abrogated pressure-stimulated but not basal phagocytosis. Basal Akt activation was inhibited 90% by LY294002 and 70% by Akt inhibitor IV. Each inhibitor prevented Akt activation by pressure. SiRNA targeted to Akt1, Akt2, or Akt3 reduced Akt1, Akt2, and Akt3 expression by 50%, 45%, and 40%, respectively. However, only Akt2SiRNA abrogated the pressure-stimulated phagocytosis without affecting basal. Pressure also activated mTOR and p70S6K. mTORSiRNA and p70S6K inhibition by rapamycin or p70S6KSiRNA blocked pressure-induced, but not basal, phagocytosis. Changes in tissue pressure during inflammation may regulate macrophage phagocytosis by activation of PI-3K, which activates Akt2, mTOR, and p70S6K.

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.

Focal adhesion kinase: a promising target for anticancer therapy

Focal adhesion kinase (FAK) is a protein tyrosine kinase acting as an early modulator of the integrin signalling cascade, thus regulating various basic cellular functions. In transformed cells, upregulation of FAK protein expression and uncontroled signalling were held responsible for the promotion of malignant phenotypic characteristics, as well as resistance to chemotherapy and radiotherapy. Direct FAK targeting resulted in the inhibition of the malignant phenotype of cancer cells, whereas increased apoptotic rates of cancer cells, either used alone or in combination with conventional chemotherapeutic agents, radiotherapy or hormonal therapy. Furthermore, drugs used in cancer chemotherapy, besides their basic mode of action, were also shown to act through altering FAK signalling. Finally, positive results were noted by the transfection of cancer cells with fak mutants or genes that suppress FAK expression or activity, such as phosphatase and tensin homolog deleted on chromosome Ten (PTEN), ribonucleotide reductase M1 polypeptide (RRM1) and melanoma differentiation-associated gene-7 (mda-7). The purpose of this article is a comprehensive review of the existing data on the possible use of FAK targeting in anticancer therapy.

Focal adhesion kinase mediates defects in the force-dependent reinforcement of initial integrin-cytoskeleton linkages in metastatic colon cancer cell lines

Micro-environmental clues, including the biophysical interpretation of the extracellular matrix, are critical to proliferation, apoptosis and migration. Here, we show that metastatic human colon cancer cell lines display altered matrix interaction. Interaction of colon cancer cells with collagen I depends on integrins (mainly alpha(1)/beta(1)) but metastatic cells display delayed spreading and reduced extension of lamellipodia. In addition, cells show defective strengthening of integrin-cytoskeleton linkages upon mechanical stimulation, as determined by laser trapping experiments and binding of large beads to the cell surface. However, adhesion to pliable surfaces is ameliorated in metastatic variants. These changes are caused by constitutive activation of focal adhesion kinase (FAK) and can be modulated by changing expression and/or activity of FAK via RNA-interference or expression of inhibitory constructs, respectively. In addition, consistent with defective strengthening of integrin-cytoskeleton linkages, metastatic cell lines show reduced random motility. Taken together these data suggest that constitutive activation of FAK causes defects in spreading, reinforcement of integrin-cytoskeleton linkages and migration and at the same time could ameliorate the adhesion of metastatic cells to suboptimal surfaces.

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.

p75 Neurotrophin Receptor Inhibits Invasion and Metastasis of Gastric Cancer

The p75 neurotrophin receptor (p75NTR) is a focus for study at present. However, its function in gastric cancer was not elucidated. Here, we investigated its relation with metastasis of gastric cancer. By immunohistochemistry, we found that the positive rate of p75NTR expression in metastatic gastric cancer was 15.09% (16 of 106), which was lower compared with nonmetastatic gastric cancer (64.15%; 68 of 106). The average staining score in nonmetastatic gastric cancer was significantly higher than in metastatic gastric cancer (1.21 +/- 0.35 versus 0.23 +/- 0.18; P<0.01). p75NTR protein level was also lowly expressed in the highly liver-metastatic gastric cancer cell line XGC9811-L compared with other gastric cancer cell lines by Western blotting. It could also significantly inhibit the in vitro adhesive, invasive, and migratory and in vivo metastatic abilities of gastric cancer cell lines SGC7901 and MKN45 by reducing urokinase-type plasminogen activator (uPA) and matrix metalloproteinase (MMP)-9 proteins and by increasing tissue inhibitor of matrix metalloproteinase (TIMP)-1 protein. Further studies showed that p75NTR could suppress the nuclear factor-kappaB (NF-kappaB) signal. SN50, a specific inhibitor of NF-kappaB, which could inhibit in vitro invasive and migratory abilities of gastric cancer cells, reduced expression of uPA and MMP9 proteins and increased expression of TIMP1 protein. Taken together, p75NTR had the function of inhibiting the invasive and metastatic abilities of gastric cancer cells, which was mediated, at least partially, by down-regulation of uPA and MMP9 proteins and up-regulation of TIMP1 protein via the NF-kappaB signal transduction pathway. Our studies suggested that p75NTR may be used as a new potential therapeutic target in metastatic gastric cancer.

Osteopontin promotes integrin activation through outside-in and inside-out mechanisms: OPN-CD44V interaction enhances survival in gastrointestinal cancer cells

Osteopontin (OPN) and splice variants of CD44 (CD44(V)) have independently been identified as markers for tumor progression. In this study, we show that both OPN and CD44(V) are frequently overexpressed in human gastric cancer and that OPN-engaged CD44(V) ligation confers cells an increased survival mediated through integrin activation. First, we show that OPN treatment confers cells an increased resistance to UV-induced apoptosis. The OPN-mediated antiapoptosis is dependent on the expression of the variant exon 6 (V6)- or V7-containing CD44 as shown by overexpression of individual CD44(V) in gastric AZ521 cells that express no or very low level of endogenous CD44 and by knockdown of the constitutively expressed V6-containing CD44 isoforms in colon HT29 cells. Although OPN also interacts with RGD integrins, OPN-RGD sequence is dispensable for OPN-mediated antiapoptosis. OPN-induced antiapoptosis is mainly attributed to the engagement of CD44(V) isoforms and the relay of an inside-out signaling via Src activity, leading to robust integrin activation. Furthermore, OPN-elicited antiapoptosis was observed when cells were plated on fibronectin but not on poly-D-lysin, and preincubation of cells with anti-integrin beta(1) antibody to block integrin-extracellular matrix (ECM) interaction or ectopic expression of the dominant-negative forms of focal adhesion kinase to block ECM-derived signal abolished OPN-induced survival, suggesting that OPN-elicited antiapoptotic function is propagated from matrix transduced by integrin. Taken together, we showed that OPN-CD44(V) interaction promotes ECM-derived survival signal mediated through integrin activation, which may play an important role in the pathogenic development and progression of gastric cancer.

N-MYC regulates focal adhesion kinase expression in human neuroblastoma

N-MYC is a transcription factor that plays an important role in cellular survival in neuroblastoma, and amplification of the N-MYC oncogene is the primary adverse prognostic indicator for neuroblastoma. Focal adhesion kinase (FAK) is a survival factor that has been shown to be overexpressed in many types of human cancers. In this study, we investigated the role of N-MYC regulation of FAK expression in neuroblastoma. We first found a correlation between N-MYC and FAK expression in neuroblastoma. Real time quantitative PCR demonstrated an increase in FAK mRNA abundance in the N-MYC-amplified IMR-32 compared with the nonamplified SK-N-AS neuroblastoma cell lines. FAK protein expression also correlated positively with N-MYC expression in the N-MYC-amplified IMR-32 versus nonamplified SK-N-AS neuroblastoma cell lines. The same results were seen with the isogenic N-MYC(+) (Tet(-)) and N-MYC(-) (Tet(+)) neuroblastoma cell lines. Promoter-reporter assays showed that activity of the FAK promoter was increased in the N-MYC-amplified IMR-32 cell line, in the N-MYC-transfected SK-N-AS nonamplified cell line, and in the isogenic N-MYC(+) (Tet(-)) neuroblastoma cell lines compared with the nonamplified and N-MYC-nonexpressing cell lines. We also identified two N-MYC binding sites in the FAK promoter sequence and showed binding of N-MYC transcription factor to the FAK promoter through electrophoretic mobility shift, chromatin immunoprecipitation, and dual luciferase assays. Finally down-regulation of FAK expression in N-MYC-inducible neuroblastoma cell lines with FAK small interfering RNA or a dominant-negative FAK inhibitor (AdFAK-CD) significantly decreased viability and increased apoptosis in the N-MYC(+) (Tet(-)) cells compared with the isogenic N-MYC(-) (Tet(+)) cells, demonstrating the biological significance of FAK overexpression in the N-MYC-expressing cell lines. This is the first report linking N-MYC and FAK in neuroblastoma, and it clearly demonstrates that N-MYC induces FAK expression. The results indicate that N-MYC regulation of FAK expression can control cellular functions in isogenic N-MYC(-/+) (Tet(+/-)) neuroblastoma cell lines.

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.

Paxillin modulates squamous cancer cell adhesion and is important in pressure-augmented adhesion

Paxillin is an adapter protein regulating signaling and focal adhesion assembly that has been linked to malignant potential in many malignancies. Overexpression of paxillin has been noted in aggressive tumors. Integrin-mediated binding through the focal adhesion complex is important in metastatic adhesion and is upregulated by extracellular pressure in malignant colonocytes through FAK and Src activation. Neither head and neck cancers nor paxillin have been studied in this regard. We hypothesized that paxillin would play a role in modulating squamous cancer adhesion both at baseline and under conditions of increased extracellular pressure. Using SCC25 tongue squamous cancer cells stably transfected with either an empty selection vector or paxillin expression and selection vectors, we studied adhesion to collagen, paxillin, FAK, and Src expression and phosphorylation in cells maintained for 30 min under ambient or 15 mmHg increased pressure conditions. Paxillin-overexpressing cells exhibited adhesion 121 +/- 2.9% of that observed in vector-only cells (n = 6, P < 0.001) under ambient pressure. Paxillin-overexpression reduced FAK phosphorylation. Pressure stimulated adhesion to 118 +/- 2.3% (n = 6, P < 0.001) of baseline in vector-only cells, similar to its effect in the parental line, and induced paxillin, FAK, and Src phosphorylation. However, increased pressure did not stimulate adhesion or phosphorylate paxillin, FAK, or Src further in paxillin-overexpressing cells. Metastasizing squamous cancer cell adhesiveness may be increased by paxillin-overexpression or by paxillin activation by extracellular pressure during surgical manipulation or growth within a constraining compartment. Targeting paxillin in patients with malignancy and minimal tumor manipulation during surgical resection may be important therapeutic adjuncts.

Deoxycholic acid differentially regulates focal adhesion kinase phosphorylation: role of tyrosine phosphatase ShP2

Environmental factors, including dietary fats, are implicated in colonic carcinogenesis. Dietary fats modulate secondary bile acids including deoxycholic acid (DCA) concentrations in the colon, which are thought to contribute to the nutritional-related component of colon cancer risk. Here we demonstrate, for the first time, that DCA differentially regulated the site-specific phosphorylation of focal adhesion kinase (FAK). DCA decreased adhesion of HCA-7 cells to the substratum and induced dephosphorylation of FAK at tyrosine-576/577 (Tyr-576/577) and Tyr-925. Tyrosine phosphorylation of FAK at Tyr-397 remained unaffected by DCA stimulation. Interestingly, we found that c-Src was constitutively associated with FAK and DCA actually activated Src, despite no change in FAK-397 and an inhibition of FAK-576 phosphorylation. DCA concomitantly and significantly increased association of tyrosine phosphatase ShP2 with FAK. Incubation of immunoprecipitated FAK, in vitro, with glutathione-S-transferase-ShP2 fusion protein resulted in tyrosine dephosphorylation of FAK in a concentration-dependent manner. Antisense oligodeoxynucleotides directed against ShP2 decreased ShP2 protein levels and attenuated DCA-induced FAK dephosphorylation. Inhibition of FAK by adenoviral-mediated overexpression of FAK-related nonkinase and gene silencing of Shp2 both abolished DCA's effect on cell adhesion, thus providing a possible mechanism for inside-out signaling by DCA in colon cancer cells. Our results suggest that DCA differentially regulates focal adhesion complexes and that tyrosine phosphatase ShP2 has a role in DCA signaling.

Pressure stimulates breast cancer cell adhesion independently of cell cycle and apoptosis regulatory protein (CARP)-1 regulation of focal adhesion kinase

BACKGROUND

Pressure stimulates colon cancer adhesion via focal adhesion kinase (FAK). Extracellular pressures reaching 29 mm Hg have been reported in rapidly growing breast cancers, and tumors experience pressure during surgical manipulation. We hypothesized that pressure stimulates breast cancer adhesion and that CARP-1, which influences cancer biology, inhibits FAK, and modulates pressure effects.

METHODS

We compared MDA-MB-468 breast cancer cells under ambient or 15-mm Hg increased pressure. We studied FAK-397 autophosphorylation, which parallels activation, after CARP-1 overexpression, and investigated whether CARP-1 stable overexpression or reduction alters pressure-stimulated adhesion.

RESULTS

Pressure increased MDA-MB-468 adhesion 25% (n = 30, P < .05). CARP-1 overexpression inhibited FAK-397 phosphorylation. However, pressure stimulated adhesion equivalently in CARP-1-overexpressing and CARP-1-reduced lines (n = 6, P < .05).

CONCLUSIONS

Pressure within proliferative tumors or during manipulation may activate breast cancer cells. Thus, inhibiting pressure signaling in rapidly growing breast tumors may be beneficial. CARP-1 does regulate FAK, but CARP-1 modulation does not alter pressure-stimulated adhesion. Targeting CARP-1 is unlikely to manipulate this pathway.

Repetitive deformation activates focal adhesion kinase and ERK mitogenic signals in human Caco-2 intestinal epithelial cells through Src and Rac1

Intestinal epithelial cells are subject to repetitive deformation during peristalsis and villous motility, whereas the mucosa atrophies during sepsis or ileus when such stimuli are abnormal. Such repetitive deformation stimulates intestinal epithelial proliferation via focal adhesion kinase (FAK) and extracellular signal-regulated kinases (ERK). However, the upstream mediators of these effects are unknown. We investigated whether Src and Rac1 mediate deformation-induced FAK and ERK phosphorylation and proliferation in human Caco-2 and rat IEC-6 intestinal epithelial cells. Cells cultured on collagen-I were subjected to an average 10% cyclic strain at 10 cycles/min. Cyclic strain activated Rac1 and induced Rac1 translocation to cell membranes. Mechanical strain also induced rapid sustained phosphorylation of c-Src at Tyr(418), Rac1 at Ser(71), FAK at Tyr(397) and Tyr(576), and ERK1/2 at Thr(202)/Tyr(204). The mitogenic effect of cyclic strain was blocked by inhibition of Src (PP2 or short interfering RNA) or Rac1 (NSC23766). Src or Rac1 inhibition also prevented strain-induced FAK phosphorylation at Tyr(576) and ERK phosphorylation but not FAK phosphorylation at Tyr(397). Reducing FAK using short interfering RNA blocked strain-induced mitogenicity and attenuated ERK phosphorylation but not Src or Rac1 phosphorylation. Src inhibition blocked strain-induced Rac1 phosphorylation, but Rac inhibition did not alter Src phosphorylation. Transfection of a two-tyrosine phosphorylation-deficient FAK mutant Y576F/Y577F prevented activation of cotransfected myc-ERK2 by cyclic strain. Repetitive deformation induced by peristalsis or villus motility may support the gut mucosa by a pathway involving Src, Rac1, FAK, and ERK. This pathway may present important targets for interventions to prevent mucosal atrophy during prolonged ileus or fasting.

Focal adhesion kinase protein levels in gut epithelial motility

Mucosal healing requires migration and proliferation. Most studies of focal adhesion kinase (FAK), a protein that regulates motility, proliferation, and apoptosis, have focused on rapid phosphorylation. We reported lower FAK protein levels in motile Caco-2 colon cancer cells and postulated that this reduction in FAK available for activation might impact cell migration and mucosal healing. Therefore, total and active FAK (FAK(397)) immunoreactivity was assessed at the migrating fronts of human Caco-2 and rat IEC-6 intestinal epithelial cells. Caco-2 and IEC-6 motility, quantitated as migration into linear or circular wounds, was examined following FAK protein inhibition by small interfering RNA (siRNA). FAK protein stability and mRNA expression were ascertained by cycloheximide decay, RT-PCR, and in situ hybridization in static and migrating Caco-2 cells. Cells at the migrating front of Caco-2 and IEC-6 monolayers exhibited lower immunostaining for both total and activated FAK than cells immediately behind the front. Western blot analysis also demonstrated diminished FAK protein levels in motile cells by >/=30% in both the differential density seeding and multiple scrape models. siRNA FAK protein inhibition enhanced motility in both the linear scrape (20% in Caco-2) and circular wound (16% in Caco-2 and 19% in IEC-6 cells) models. FAK protein degradation did not differ in motile and static Caco-2 cells and was unaffected by FAK(397) phosphorylation, but FAK mRNA was lower in migrating Caco-2 cells. Thus FAK protein abundance appears regulated at the mRNA level during gut epithelial cell motility and may influence epithelial cell migration coordinately with signals that modify FAK phosphorylation.

Cellular prion protein promotes invasion and metastasis of gastric cancer

Cellular prion protein (PrPc) is a glycosylphosphatidylinositol (GPI) -anchored membrane protein that is highly conserved in mammalian species. PrPc has the characteristics of adhesive molecules and is thought to play a role in cell adhesion and membrane signaling. Here we investigated the possible role of PrPc in the process of invasiveness and metastasis in gastric cancers. PrPc was found to be highly expressed in metastatic gastric cancers compared to nonmetastatic ones by immunohistochemical staining. PrPc significantly promoted the adhesive, invasive, and in vivo metastatic abilities of gastric cancer cell lines SGC7901 and MKN45. PrPc also increased promoter activity and the expression of MMP11 by activating phosphorylated ErK1/2 in gastric cancer cells. MEK inhibitor PD98059 and MMP11 antibody (Ab) significantly inhibited in vitro invasive and in vivo metastatic abilities induced by PrPc. N-terminal fragment (amino acid 24-90) was suggested to be an indispensable region for signal transduction and invasion-promoting function of PrPc. Taken together, the present work revealed a novel function of PrPc that the existence of N-terminal region of PrPc could promote the invasive and metastatic abilities of gastric cancer cells at least partially through activation of MEK/ERK pathway and consequent transactivation of MMP11.

Integrin alpha2-mediated ERK and calpain activation play a critical role in cell adhesion and motility via focal adhesion kinase signaling: identification of a novel signaling pathway

Higher levels of focal adhesion kinase (FAK) are expressed in colon metastatic carcinomas. However, the signaling pathways and their mechanisms that control cell adhesion and motility, important components of cancer metastasis, are not well understood. We sought to identify the integrin-mediated mechanism of FAK cleavage and downstream signaling as well as its role in motility in human colon cancer GEO cells. Our results demonstrate that phosphorylated FAK (tyrosine 397) is cleaved at distinct sites by integrin signaling when cells attach to collagen IV. Specific blocking antibodies (clone P1E6) to integrin alpha2 inhibited FAK activation and cell motility (micromotion). Ectopic expression of the FAK C-terminal domain FRNK attenuated FAK and ERK phosphorylation and micromotion. Calpain inhibitor N-acetyl-leucyl-leucyl-norleucinal blocked FAK cleavage, cell adhesion, and micromotion. Antisense approaches established an important role for mu-calpain in cell motility. Expression of wild type mu-calpain increased cell micromotion, whereas its point mutant reversed the effect. Further, cytochalasin D inhibited FAK phosphorylation and cleavage, cell adhesion, locomotion, and ERK phosphorylation, thus showing FAK activation downstream of actin assembly. We also found a pivotal role for FAK Tyr(861) phosphorylation in cell motility and ERK activation. Our results reveal a novel functional connection between integrin alpha2 engagement, FAK, ERK, and mu-calpain activation in cell motility and a direct link between FAK cleavage and enhanced cell motility. The data suggest that blocking the integrin alpha2/FAK/ERK/mu-calpain pathway may be an important strategy to reduce cancer progression.

Divalent cations influence colon cancer cell adhesion in a murine transplantable tumor model

BACKGROUND

Cancer cells adhere principally by integrins, matrix receptors that may be influenced by divalent cations. Surgical wound fluid is high in Mg2+ and low in Ca2+. We hypothesized that Mg+ and Mn2+ promote perioperative adhesion of shed cancer cells to surgical sites and that washing surgical wounds with Ca2+ inhibits implantation.

METHODS

We tested our hypothesis in a murine colon 26 adenocarcinoma model. We added 10 mmol/L CaCl2, 0.25 mmol/L MgCl2, or 0.5 mmol/L MnCl2 to suspended murine colon 26 cancer cells and placed these suspensions into wounds in anesthetized mice. After 30 minutes, we washed away nonadherent cells. In some studies, we 51Cr-labeled the cells and assayed tumor adhesion by wound radioactivity. In parallel studies, we closed the wounds and observed the mice for 90 days.

RESULTS

Mg2+ increased adhesion to 188% +/- 15% of control (n = 10, P < .001) and Mn2+ to 130% +/- 6% (n = 7, P < .001). However, Ca2+ inhibited adhesion to 61% +/- 12% (n = 7, P = .006) of control. Seventy-two percent of survival controls developed tumors during follow-up. Mg2+ and Mn2+ stimulated tumor formation to 96% and 92%, respectively, but adding Ca2+ to the wounds reduced subsequent tumor formation to 56% without altering serum Ca2+. The survival curves each differed significantly by log-rank test (P < .01 each). All pair-wise multiple comparisons were significant (Holm-Sidak, P < .05 each).

CONCLUSION

Thus, the high Mg2+ in endogenous wound fluid may potentiate tumor cell adhesion. However, 10 micromol/L Ca2+ inhibits cancer cell adhesion to murine wounds and subsequent tumor development. Irrigating with dilute CaCl2 could decrease local tumor recurrence by inhibiting the adhesion of shed tumor cells.

Pressure and endothelial coculture upregulate myocytic Fas-FasL pathway and induce apoptosis by way of direct and paracrine mechanisms

BACKGROUND

Pressurized endothelial cell (EC)-smooth muscle cell (SMCs) coculture significantly increases the apoptosis of SMCs. Our current hypothesis was that in EC-SMC coculture, pressure upregulates SMC apoptosis SMCs through EC-derived paracrine factors and that SMC apoptosis is induced through Fas-Fas ligand (FasL) activation.

METHODS

Conditioned media (CM) from ECs and SMCs exposed to ambient or high pressure was transferred to recipient SMCs. SMCs were stained with terminal deoxynucleotide transferase-mediated deoxy uridine triphosphate nick-end labeling. Fas and FasL expression was assessed in SMC grown in monoculture, coculture with EC, pressurized monoculture, and pressurized coculture with EC.

RESULTS

CM from pressurized ECs caused a 30% increase in SMC apoptosis compared with CM from control ECs (P < .05). Pressure increased Fas and FasL expression in monocultured and cocultured SMCs (1.6-fold and 2.3-fold for Fas [P < .05] and 1.65-fold and 1.7-fold for FasL [P < or = .05]). Coculture had synergistic effect on Fas expression and no effect on FasL expression.

CONCLUSIONS

Pressure plays significant role in EC-SMC interaction, SMC apoptosis, and vascular remodeling.

Differential regulation of monocyte/macrophage cytokine production by pressure

BACKGROUND

Cytokine production by macrophages is essential for the inflammatory response. Normal human interstitial tissue pressure is 20 to 30 mm Hg, but generally decreases in acute inflammation.

METHODS

We compared the effect of 20 mm Hg increased pressure (approximating normal interstitial tissue pressure) with that of ambient pressure (resembling pressure in inflamed tissues) on tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta production by undifferentiated (monocytic) and PMA (phorbol 12-, myristate 13-acetate)-differentiated (macrophage-like) THP-1 cells with or without lipopolysaccharide (LPS) (10 ng/mL).

RESULTS

Pressure stimulated spontaneous macrophage TNF-alpha secretion (30.5 +/- 6.3 vs. 49.1 +/- 2.8 pg/mL, P <.02), but not monocyte TNF-alpha secretion. Pressure did not stimulate IL-1beta release. As expected, LPS increased basal cytokine release. After LPS stimulation, pressure still tended to stimulate macrophage TNF-alpha, but inhibited monocyte TNF-alpha secretion (P <.05). In contrast, pressure inhibited IL-1beta release by both LPS-treated monocytes (986 +/- 134 vs. 595 +/- 226 pg/mL, P <.02) and macrophages (3,112 +/- 229 vs. 979 +/- 61 pg/mL, P <.01).

CONCLUSIONS

Extracellular pressure may regulate TNF-alpha and IL-1beta secretion differentially by monocytes and macrophages.

Modulation of angiogenesis with siRNA inhibitors for novel therapeutics

Cancer and many other serious diseases are characterized by the uncontrolled growth of new blood vessels. Recently, RNA interference (RNAi) has reinvigorated the therapeutic prospects for inhibiting gene expression and promises many advantages over binding inhibitors, including high specificity, which is essential for targeted therapeutics. This article describes the latest developments using small-interfering RNA (siRNA) inhibitors to downregulate various angiogenic and tumor-associated factors, both in cell-culture assays and in animal disease models. The majority of research efforts are currently focused on understanding gene function, as well as proof-of-concept for siRNA-mediated anti-angiogenesis. The prospects for siRNA therapeutics, both advantages and looming hurdles, are evaluated.

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

Increased extracellular pressure stimulates colon cancer cell adhesion by activating focal adhesion kinase (FAK) and Src. We investigated the role of the cytoskeleton in pressure-induced inside-out FAK and Src phosphorylation and pressure-stimulated adhesion. We perturbed actin polymerization with phalloidin, cytochalasin D and latrunculin B, and microtubule organization with colchicine and paclitaxol. We compared the effects of these agents on pressure-induced SW620 and human primary colon cancer cell adhesion and inside-out FAK/Src activation with outside-in adhesion-dependent FAK/Src activation. Cells pretreated with cytoskeletal inhibitors were subjected to 15 mmHg increased pressure and allowed to adhere to collagen I coated plates or prevented from adhesion to pacificated plates for 30 min. Phalloidin, cytochalasin D, latrunculin B and colchicine pretreatment completely prevented pressure-stimulated and significantly inhibited basal SW620 cell adhesion. Taxol did not inhibit pressure-induced colon cancer cell adhesion, but significantly lowered basal adhesion. Cytochalasin D and colchicine had similar effects in pressure-stimulated primary human malignant colonocytes. Phalloidin, cytochalasin D, latrunculin B and colchicine prevented pressure-induced SW620 FAK phosphorylation but not Src phosphorylation. FAK phosphorylation in response to collagen I adhesion was significantly attenuated but not completely prevented by these inhibitors. Although Src phosphorylation was not increased on adhesion, the cytoskeleton disrupting agents significantly lowered basal Src phosphorylation in adherent cells. These results suggest that both cytoskeleton-dependent FAK activation and cytoskeleton-independent Src activation may be required for extracellular pressure to stimulate colon cancer cell adhesion. Furthermore, the cytoskeleton plays a different role in pressure-activated FAK and Src signaling than in FAK and Src activation in adherent cells. We, therefore, hypothesize that cytoskeletal interactions with focal adhesion signals mediate the effects of extracellular pressure on colon cancer cell adhesion.

Molecular regulation of mechanotransduction

There is a common mechanism for mechanotransduction in cells, regardless of the cell type. Integrins, interacting with their matrix/environment, mediate increases in intracellular Ca2+ levels and activate MAP kinase cascades to cause ERK1/2 phosphorylation. Phosphorylated ERK1/2 causes the activation of the AP-1 family of transcription factors that are necessary for the pro-growth response. The pro-bone growth response involves upregulation of the genes c-fos, IGF-1, cyclooxygenase, and osteocalcin. In osteocytes, increases in intracellular Ca2+ levels may additionally occur by extracellular Ca2+ influx through a stretch-activated ion channel. Each bone cell appears fine-tuned for the type of stimulus, with accessory mechanotransduction signaling pathways, such as calcineurin-mediated activation of the tissue-specific transcription factor NF-AT, adjusting the outcome of signaling in each case.

Extracellular pressure stimulates colon cancer cell proliferation via a mechanism requiring PKC and tyrosine kinase signals

Pressure in colonic tumours may increase during constipation, obstruction or peri-operatively. Pressure enhances colonocyte adhesion by a c-Src- and actin-cytoskeleton-dependent PKC-independent pathway. We hypothesized that pressure activates mitogenic signals.

METHODS

Malignant colonocytes on a collagen I matrix were subjected to 15 mmHg pressure. ERK, p38, c-Src and Akt phosphorylation and PKCalpha redistribution were assessed by western blot after 30 min and PKC activation by ELISA. Cells were counted after 24 h and after inhibition of each signal, tyrosine phosphorylation or actin depolymerization.

RESULTS

Pressure time-dependently increased SW620 and HCT-116 cell counts on collagen or fibronectin (P < 0.01). Pressure increased the SW620 S-phase fraction from 28 +/- 1 to 47 +/- 1% (P = 0.0002). Pressure activated p38, ERK, and c-Src (P < 0.05 each) but not Akt/PKB. Pressure decreased cytosolic PKC activity, and translocated PKCalpha to a membrane fraction. Blockade of p38, ERK, c-Src or PI-3-K or actin depolymerization did not inhibit pressure-stimulated proliferation. However, global tyrosine kinase blockade (genistein) and PKC blockade (calphostin C) negated pressure-induced proliferation.

CONCLUSIONS

Extracellular pressure stimulates cell proliferation and activates several signals. However, the mitogenic effect of pressure requires only tyrosine kinase and PKCalpha activation. Pressure may modulate colon cancer growth and implantation by two distinct pathways, one stimulating proliferation and the other promoting adhesion.

Activation of p38 MAPKalpha by extracellular pressure mediates the stimulation of macrophage phagocytosis by pressure

We have previously demonstrated that constant 20 mmHg extracellular pressure increases serum-opsonized latex bead phagocytosis by phorbol 12-myristate 13-acetate (PMA)- differentiated THP-1 macrophages in part by inhibiting focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK). Because p38 MAPK is activated by physical forces in other cells, we hypothesized that modulation of p38 MAPK might also contribute to the stimulation of macrophage phagocytosis by pressure. We studied phagocytosis in PMA-differentiated THP-1 macrophages, primary human monocytes, and human monocyte-derived macrophages (MDM). p38 MAPK activation was inhibited using SB-203580 or by p38 MAPKalpha small interfering RNA (siRNA). Pressure increased phagocytosis in primary monocytes and MDM as in THP-1 cells. Increased extracellular pressure for 30 min increased phosphorylated p38 MAPK by 46.4 +/- 20.5% in DMSO-treated THP-1 macrophages and by 20.9 +/- 9% in primary monocytes (P < 0.05 each). SB-203580 (20 microM) reduced basal p38 MAPK phosphorylation by 34.7 +/- 2.1% in THP-1 macrophages and prevented pressure activation of p38. p38 MAPKalpha siRNA reduced total p38 MAPK protein by 50-60%. Neither SB-203580 in THP-1 cells and peripheral monocytes nor p38 MAPK siRNA in THP-1 cells affected basal phagocytosis, but each abolished pressure-stimulated phagocytosis. SB-203580 did not affect basal or pressure-reduced FAK activation in THP-1 macrophages, but significantly attenuated the reduction in ERK phosphorylation associated with pressure. p38 MAPKalpha siRNA reduced total FAK protein by 40-50%, and total ERK by 10-15%, but increased phosphorylated ERK 1.4 +/- 0.1-fold. p38 MAPKalpha siRNA transfection did not affect the inhibition of FAK-Y397 phosphorylation by pressure but prevented inhibition of ERK phosphorylation. Changes in extracellular pressure during infection or inflammation regulate macrophage phagocytosis by a FAK-dependent inverse effect on p38 MAPKalpha that might subsequently downregulate ERK.

Extracellular pressure stimulates colon cancer cell adhesion in vitro and to surgical wounds by Src (sarcoma protein) activation

BACKGROUND

We hypothesized that pressure stimulates colon cancer cell adhesion to surgical wounds.

METHODS

We quantitated adhesion of murine 26/51 transplantable colon cancer cells by cell counting or chromium 51-labeling. Tumor cells were added to murine surgical wounds after 30 minutes preincubation under ambient or 15 mm Hg increased pressure. Src activation was assayed by immunoblotting for phosphorylated Src and inhibited by 4-amino-5-(4chlorophenyl)-7-(t-butyl)pyrazolo-[3-4-d]pyrimidine (PP2).

RESULTS

Pressure stimulated colon 26/51 cell adhesion to murine wounds by 43% to 52% (n = 9, P <0.05 each). Pressure stimulated Src phosphorylation by 39% +/- 4% (n = 5, P = 0.004) in colon 26 cells. The Src inhibitor PP2 (20 mumol/L) did not inhibit Src phosphorylation at ambient pressure but prevented pressure stimulation of Src phosphorylation. Src blockade by PP2 did not affect basal adhesion of either tumor to murine wounds but completely blocked pressure stimulation of adhesion (n = 4, P <0.001 each).

CONCLUSIONS

Increased pressure may activate cancer adhesion to surgical wounds via Src. Src antagonists might inhibit this process.

Pressure alters endothelial effects upon vascular smooth muscle cells by decreasing smooth muscle cell proliferation and increasing smooth muscle cell apoptosis

BACKGROUND

Although de-endothelialization after vascular intervention is associated with intimal hyperplasia, endothelial cells (ECs) increase smooth muscle cell (SMC) numbers in conventional cocultures. In previously published work, SMCs cocultured with ECs in a chronic high-pressure environment exhibited significantly decreased cell counts compared to monocultured SMCs in the same high pressure. This finding contrasted with SMCs cocultured with ECs in ambient pressure, which exhibited significantly higher cell counts than the monocultured SMCs in ambient pressure. We now hypothesize that extracellular pressure decreases SMC number during coculture with ECs by decreasing SMC proliferation through nuclear protein regulation and by increasing SMC apoptosis. Furthermore, this effect depends on the EC response to pressure.

METHODS

Rat aortic SMCs were cultured independently (SMC/0) or cocultured with EC (SMC/EC) under either atmospheric or increased pressure (130-135 mmHg over ambient, SMC/0-P and SMC/EC-P) for 5 days. We assessed SMC proliferative potential by determining c-myc expression (by protein analysis), apoptosis (by cell counting, staining with acridine orange or TUNEL technique), and topoisomerase IIalpha levels. Parallel studies measured the effects of conditioned media from monocultured EC and SMC exposed for 5 days to control or increased pressure on recipient SMC growing in conventional culture.

RESULTS

In high-pressure conditions, SMC/EC-P exhibited 42% less c-myc expression than SMC/0s (P = .00028). Significantly increased apoptotic activity (22 +/- 1.8%) in SMC/EC-Ps compared to SMC/0s was coupled with significantly lower topoisomerase IIalpha levels. Interestingly, pressure (SMC/0-P) and EC coculture (SMC/EC) each separately raised myocyte apoptotic activity to 15 +/- 1.3% and 17 +/- 2.0%, respectively. Conditioned media from pressurized ECs caused a 20% decrease in cell counts in target SMC compared to conditioned media from ECs in atmospheric pressure. Media from pressurized SMCs did not affect target SMCs.

CONCLUSIONS

In a model designed to study SMC/EC interactions in a dynamic environment, EC exposure to pressure alters the growth characteristics and apoptotic activity of SMCs via a secreted factor. Extracellular pressure may alter EC regulation of SMC behavior and regulate intimal hyperplasia.

Extracellular pressure stimulates macrophage phagocytosis by inhibiting a pathway involving FAK and ERK

We hypothesized that changes in extracellular pressure during inflammation or infection regulate macrophage phagocytosis through modulating the focal adhesion kinase (FAK)-ERK pathway. Undifferentiated (monocyte-like) or PMA-differentiated (macrophage-like) THP-1 cells were incubated at 37 degrees C with serum-opsonized latex beads under ambient or 20-mmHg increased pressure. Pressure did not affect monocyte phagocytosis but significantly increased macrophage phagocytosis (29.9 +/- 1.8 vs. 42.0 +/- 1.6%, n = 9, P < 0.001). THP-1 macrophages constitutively expressed activated FAK, ERK, and Src. Exposure of macrophages to pressure decreased ERK and FAK-Y397 phosphorylation (77.6 +/- 7.9%, n = 7, P < 0.05) but did not alter FAK-Y576 or Src phosphorylation. FAK small interfering RNA (SiRNA) reduced FAK expression by >75% and the basal amount of phosphorylated FAK by 25% and significantly increased basal macrophage phagocytosis (P < 0.05). Pressure inhibited FAK-Y397 phosphorylation in mock-transfected or scrambled SiRNA-transfected macrophages, but phosphorylated FAK was not significantly reduced further by pressure in cells transfected with FAK SiRNA. Pressure increased phagocytosis in all three groups. However, FAK-SiRNA-transfected cells exhibited only 40% of the pressure effect on phagocytosis observed in scrambled SiRNA-transfected cells so that phagocytosis inversely paralleled FAK activation. PD-98059 (50 microM), an ERK activation inhibitor, increased basal phagocytosis (26.9 +/- 1.8 vs. 31.7 +/- 1.1%, n = 15, P < 0.05), but pressure did not further increase phagocytosis in PD-98059-treated cells. Pressure also inhibited ERK activation after mock transfection or transfection with scrambled SiRNA, but transfection of FAK SiRNA abolished ERK inhibition by pressure. Pressure did not increase phagocytosis in MonoMac-1 cells that do not express FAK. Increased extracellular pressure during infection or inflammation enhances macrophage phagocytosis by inhibiting FAK and, consequently, decreasing ERK activation.

Colon cancer cell adhesion in response to Src kinase activation and actin-cytoskeleton by non-laminar shear stress

Malignant cells shed from tumors during surgical resection or spontaneous metastasis experience physical forces such as shear stress and turbulence within the peritoneal cavity during irrigation, laparoscopic air insufflation, or surgical manipulation, and within the venous or lymphatic system. Since physical forces can activate intracellular signals that modulate the biology of various cell types in vitro, we hypothesized that shear stress and turbulence might increase colon cancer cell adhesion to extracellular matrix, potentiating metastatic implantation. Primary human malignant colon cancer cells isolated from resected tumors and SW620 were subjected to shear stress and turbulence by stirring cells in suspension at 600 rpm for 10 min. Shear stress for 10 min increased subsequent SW620 colon cancer cell adhesion by 40.0 +/- 3.0% (n = 3; P < 0.001) and primary cancer cells by 41.0 +/- 3.0% to collagen I when compared to control cells. In vitro kinase assay (1.5 +/- 0.13 fold) and Western analysis (1.34 +/- 0.04 fold) demonstrated a significant increase in Src kinase activity in cells exposed shear stress. Src kinase inhibitors PP1 (0.1 microM), PP2 (20 microM), and actin-cytoskeleton stabilizer phalloidin (10 microM) prevented the shear stress stimulated cell adhesion to collagen I. Furthermore, PP2 inhibited basal (50.0 +/- 2.8%) and prevented shear stress induced src activation but phalloidin pretreatment did not. These results raise the possibility that shear stress and turbulence may stimulate the adhesion of malignant cells shed from colon cancers by a mechanism that requires both actin-cytoskeletal reorganization an independent physical force activation of Src kinase. Blocking this pathway might reduce tumor metastasis during surgical resection.