Src family protein tyrosine kinases: cooperating with growth factor and adhesion signaling pathways

Arachidonic acid promotes FAK activation and migration in MDA-MB-231 breast cancer cells

Arachidonic acid (AA) is a common dietary n-6 polyunsaturated fatty acid that is present in an esterified form in cell membrane phospholipids, and it might be present in the extracellular microenvironment. In particular, AA promotes MAPK activation and mediates the adhesion of MDA-MB-435 breast cancer cells to type IV collagen. However, the signal transduction pathways mediated by AA have not been studied in detail. Our results demonstrate that stimulation of MDA-MB-231 breast cancer cells with AA promotes an increase in the phoshorylation of Src and FAK, as revealed by site-specific antibodies that recognized the phosphorylation state of Src at Tyr-418, and of FAK at tyrosine-397 and in vitro kinase assays. In addition, AA also induces an increase in the migration of MDA-MB-231 cells. In contrast, AA does not induce phosphorylation of FAK and an increase in cell migration of non-tumorigenic epithelial cells MCF10A. Inhibition of Gi/Go proteins, LOX and Src activity prevent FAK activation and cell migration. In conclusion, our results demonstrate, for the first time, that Gi/Go proteins, LOX and Src play an important role in FAK activation and cell migration induced by AA in MDA-MB-231 breast cancer cells.

Integrin stimulation-induced hypertrophy in neonatal rat cardiomyocytes is NO-dependent

Prolonged myocardial stretch typically leads to hypertrophy of cardiomyocytes. As integrins are cellular receptors of stretch, we hypothesize that integrin stimulation induces cardiomyocyte hypertrophy. Integrins of neonatal rat cardiomyocytes (NRCMs) were stimulated with a peptide containing the Arg-Gly-Asp (RGD) sequence for 24 h. For comparison, alpha(1)-adrenergic stimulation by phenylephrine (PE) for 24 h was applied. Saline-treated NRCMs were used as control. The hypertrophic response was quantified by measuring cell surface area (CSA). Phosphorylation of NO-synthase-1 (NOS1) was assessed by immunocytochemistry. CSA was increased by 38% (IQR 31-44%) with RGD and by 68% (IQR 64-84%) with PE versus control (both P < 0.001). NOS-1 phosphorylation was increased by 61% with RGD and by 21% with PE versus control (both P < 0.01). A general NOS-inhibitor (L-NAME) inhibited RGD-induced hypertrophy completely, but had no significant effect on PE-induced hypertrophy. Administration of NO-donor to NRCMs co-incubated with RGD + L-NAME partly restored hypertrophy (to 62% of the hypertrophic effect of RGD alone), but had no effect if incubated with PE + L-NAME. Ryanodine and BAPTA-AM inhibited RGD-induced hypertrophy completely but not that induced by PE. Integrin stimulation of NRCMs by RGD leads to hypertrophy, likely by activation of NOS-1. Abrogation of RGD-induced hypertrophic response upon NOS-inhibition and rescue of this hypertrophic effect by NO-donor suggest that integrin stimulation-induced hypertrophy of NRCMs is NO-dependent.

Combined inhibition of PLC{gamma}-1 and c-Src abrogates epidermal growth factor receptor-mediated head and neck squamous cell carcinoma invasion

PURPOSE

Mortality from head and neck squamous cell carcinoma (HNSCC) is usually associated with locoregional invasion of the tumor into vital organs, including the airway. Understanding the signaling mechanisms that abrogate HNSCC invasion may reveal novel therapeutic targets for intervention. The purpose of this study was to investigate the efficacy of combined inhibition of c-Src and PLCgamma-1 in the abrogation of HNSCC invasion.

EXPERIMENTAL DESIGN

PLCgamma-1 and c-Src inhibition was achieved by a combination of small molecule inhibitors and dominant negative approaches. The effect of inhibition of PLCgamma-1 and c-Src on invasion of HNSCC cells was assessed in an in vitro Matrigel-coated transwell invasion assay. In addition, the immunoprecipitation reactions and in silico database mining was used to examine the interactions between PLCgamma-1 and c-Src.

RESULTS

Here, we show that inhibition of PLCgamma-1 or c-Src with the PLC inhibitor U73122 or the Src family inhibitor AZD0530 or using dominant-negative constructs attenuated epidermal growth factor (EGF)-stimulated HNSCC invasion. Furthermore, EGF stimulation increased the association between PLCgamma-1 and c-Src in HNSCC cells. Combined inhibition of PLCgamma-1 and c-Src resulted in further attenuation of HNSCC cell invasion in vitro.

CONCLUSIONS

These cumulative results suggest that PLCgamma-1 and c-Src activation contribute to HNSCC invasion downstream of EGF receptor and that targeting these pathways may be a novel strategy to prevent tumor invasion in HNSCC.

Modulation of enzymatic activities by n-3 polyunsaturated fatty acids to support cardiovascular health

Epidemiological evidence from Greenland Eskimos and Japanese fishing villages suggests that eating fish oil and marine animals can prevent coronary heart disease. Dietary studies from various laboratories have similarly indicated that regular fish oil intake affects several humoral and cellular factors involved in atherogenesis and may prevent atherosclerosis, arrhythmia, thrombosis, cardiac hypertrophy and sudden cardiac death. The beneficial effects of fish oil are attributed to their n-3 polyunsaturated fatty acid (PUFA; also known as omega-3 fatty acids) content, particularly eicosapentaenoic acid (EPA; 20:5, n-3) and docosahexaenoic acid (DHA; 22:6, n-3). Dietary supplementation of DHA and EPA influences the fatty acid composition of plasma phospholipids that, in turn, may affect cardiac cell functions in vivo. Recent studies have demonstrated that long-chain omega-3 fatty acids may exert beneficial effects by affecting a wide variety of cellular signaling mechanisms. Pathways involved in calcium homeostasis in the heart may be of particular importance. L-type calcium channels, the Na+-Ca2+ exchanger and mobilization of calcium from intracellular stores are the most obvious key signaling pathways affecting the cardiovascular system; however, recent studies now suggest that other signaling pathways involving activation of phospholipases, synthesis of eicosanoids, regulation of receptor-associated enzymes and protein kinases also play very important roles in mediating n-3 PUFA effects on cardiovascular health. This review is therefore focused on the molecular targets and signaling pathways that are regulated by n-3 PUFAs in relation to their cardioprotective effects.

AFAP-110 is required for actin stress fiber formation and cell adhesion in MDA-MB-231 breast cancer cells

Regulation of actin organization and dynamics is a highly complex process that involves a number of actin-binding proteins, including capping, branching, severing, sequestering, and cross-linking proteins. The actin-binding and cross-linking protein AFAP-110 is expressed in normal myoepithelial cells. Screening of different breast epithelial cell lines revealed high expression levels of AFAP-110 in the human breast cancer cell lines MDA-MB-231 and MDA-MB-435. Knockdown of AFAP-110 expression in MDA-MB-231 cells does not result in any changes in cell proliferation but did result in a loss of actin stress fiber cross-linking and decreased adhesion to fibronectin. An inducible knockdown approach confirms that MDA-MB-231 breast cancer cells require AFAP-110 expression for stress fiber formation and adhesion. Thus, AFAP-110 may provide cytoskeletal tension through stress fiber formation, which is required for focal adhesion formation. Indeed, we could not detect any focal contacts or focal adhesions in AFAP-110 knockdown cells after adhesion to fibronectin. Although expression levels of crucial focal adhesion components were not influenced by AFAP-110 expression levels, treatment of AFAP-110 knockdown cells with LPA did not result in induction of actin stress fibers and focal adhesions. In summary, AFAP-110 plays an important role in MDA-MB-231 breast cancer cell adhesion possibly by regulating stress filament cross-linking which would promote focal adhesion formation.

Transient expression of protein tyrosine phosphatases encoded in Cotesia plutellae bracovirus inhibits insect cellular immune responses

Several immunosuppressive factors are associated with parasitism of an endoparasitoid wasp, Cotesia plutellae, on the diamondback moth, Plutella xylostella. C. plutellae bracovirus (CpBV) encodes a large number of putative protein tyrosine phosphatases (PTPs), which may play a role in inhibiting host cellular immunity. To address this inhibitory hypothesis of CpBV-PTPs, we performed transient expression of individual CpBV-PTPs in hemocytes of the beet armyworm, Spodoptera exigua, and analyzed their cellular immune responses. Two different forms of CpBV-PTPs were chosen and cloned into a eukaryotic expression vector under the control of the p10 promoter of baculovirus: one with the normal cysteine active site (CpBV-PTP1) and the other with a mutated active site (CpBV-PTP5). The hemocytes transfected with CpBV-PTP1 significantly increased in PTP activity compared to control hemocytes, but those with CpBV-PTP5 exhibited a significant decrease in the PTP activity. All transfected hemocytes exhibited a significant reduction in both cell spreading and encapsulation activities compared to control hemocytes. Co-transfection of CpBV-PTP1 together with its double-stranded RNA reduced the messenger RNA (mRNA) level of CpBV-PTP1 and resulted in recovery of both hemocyte behaviors. This is the first report demonstrating that the polydnaviral PTPs can manipulate PTP activity of the hemocytes to interrupt cellular immune responses.

Transforming growth factor-beta1 effects on endothelial monolayer permeability involve focal adhesion kinase/Src

Transforming growth factor (TGF)-beta1 activity has been shown to increase vascular endothelial barrier permeability, which is believed to precede several pathologic conditions, including pulmonary edema and vessel inflammation. In endothelial monolayers, TGF-beta1 increases permeability, and a number of studies have demonstrated the alteration of cell-cell contacts by TGF-beta1. We hypothesized that focal adhesion complexes also likely contribute to alterations in endothelial permeability. We examined early signal transduction events associated with rapid changes in monolayer permeability and the focal adhesion complex of bovine pulmonary artery endothelial cells. Western blotting revealed rapid tyrosine phosphorylation of focal adhesion kinase (FAK) and Src kinase in response to TGF-beta1; inhibition of both of these kinases using pp2 (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine), ameliorates TGF-beta1-induced monolayer permeability. Activation of FAK/Src requires activation of the epidermal growth factor receptor downstream of the TGF-beta receptors, and is blocked by the epidermal growth factor receptor inhibitor AG1478. Immunohistochemistry showed that actin and the focal adhesion proteins paxillin, vinculin, and hydrogen peroxide-inducible clone-5 (Hic-5) are rearranged in response to TGF-beta1; these proteins are released from focal adhesion complexes. Rearrangement of paxillin and vinculin by TGF-beta1 is not blocked by the FAK/Src inhibitor, pp2, or by SB431542 inhibition of the TGF-beta type I receptor, anaplastic lymphoma kinase 5; however, pp1 (4-Amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine), which inhibits both type I and type II TGF-beta receptors, does block paxillin and vinculin rearrangement. Hic-5 protein rearrangement requires FAK/Src activity. Together, these results suggest that TGF-beta1-induced monolayer permeability involves focal adhesion and cytoskeletal rearrangement through both FAK/Src-dependent and -independent pathways.

Dasatinib inhibits migration and invasion in diverse human sarcoma cell lines and induces apoptosis in bone sarcoma cells dependent on SRC kinase for survival

Sarcomas are rare malignant mesenchymal tumors for which there are limited treatment options. One potential molecular target for sarcoma treatment is the Src tyrosine kinase. Dasatinib (BMS-354825), a small-molecule inhibitor of Src kinase activity, is a promising cancer therapeutic agent with p.o. bioavailability. Dasatinib exhibits antitumor effects in cultured human cell lines derived from epithelial tumors, including prostate and lung carcinomas. However, the action of dasatinib in mesenchymally derived tumors has yet to be shown. Based on our previous findings of Src activation in human sarcomas, we evaluated the effects of dasatinib in 12 cultured human sarcoma cell lines derived from bone and soft tissue sarcomas. Dasatinib inhibited Src kinase activity at nanomolar concentrations in these sarcoma cell lines. Downstream components of Src signaling, including focal adhesion kinase and Crk-associated substrate (p130(CAS)), were also inhibited at similar concentrations. This inhibition of Src signaling was accompanied by blockade of cell migration and invasion. Moreover, apoptosis was induced in the osteosarcoma and Ewing's subset of bone sarcomas at nanomolar concentrations of dasatinib. Inhibition of Src protein expression by small interfering RNA also induced apoptosis, indicating that these bone sarcoma cell lines are dependent on Src activity for survival. These results show that dasatinib inhibits migration and invasion of diverse sarcoma cell types and selectively blocks the survival of bone sarcoma cells. Therefore, dasatinib may provide therapeutic benefit by preventing the growth and metastasis of sarcomas in patients.

Differential effect of FGF and PDGF on cell proliferation and migration in osteoblastic cells

It has been known that growth factors such as fibroblast growth factor (FGF) and platelet-derived growth factor (PDGF) can promote proliferation and migration in a variety of cell types including osteoblastic cells. However, the mechanism underlying their action has not been clearly defined. The present study was undertaken to examine the effect of FGF and PDGF on cell proliferation and migration and to determine the role of extracellular signal-regulated kinase (ERK) and Akt in action of FGF and PDGF in osteoblastic cells. FGF enhanced proliferation in a dose- and time-dependent manner, whereas it did not affect cell migration. FGF induced a transient activation of ERK, but not Akt, which was inhibited by an inhibitor of MEK, the upstream kinase of ERK, but not by inhibitors of PI3K/Akt (LY294002), epidermal growth factor receptor (EGFR, AG1478), and Src (PP2). FGF-induced proliferation was inhibited by inhibitors of MEK/ERK and Src pathways. Exposure of cells to FGF stimulated transition of cell cycle from the G1 phase to S phase and increased phosphorylation of Rb. FGF-induced phosphorylation of Rb was attenuated by inhibitors of MEK/ERK and Src pathways. Cell migration studies indicated that PDGF stimulated migration, but it had no effect on cell proliferation. PDGF induced activation of ERK and Akt. The ERK activatin was inhibited by the Src inhibitor and the Akt activation was inhibited by inhibitors of EGFR and Src. PDGF-induced migration was inhibited by inhibitors of MEK/ERK, PI3K/Akt, EGFR and Src pathways. Taken together, these findings suggest that the MEK/ERK and Src pathways play an important role in the FGF-induced proliferation and signaling pathways involving MEK/ERK, EGFR, Src and PI3K/Akt mediate the PDGF-induced migration. These data are of importance in understanding the roles of these growth factors in osteoblastic cell proliferation and migration.

Calreticulin affects fibronectin-based cell-substratum adhesion via the regulation of c-Src activity

Calreticulin is an endoplasmic reticulum Ca2+-storage protein, which influences gene expression and cell adhesion. In this study, we show that calreticulin induces fibronectin gene expression and matrix deposition, leading to differences in cell spreading and focal adhesion formation in cells differentially expressing calreticulin. We further show that these effects of calreticulin occur via a c-Src-regulated pathway and that c-Src activity is inversely related to calreticulin abundance. Since c-Src is an important regulator of focal contact turnover, we investigated the effect of c-Src inhibition on cells differentially expressing calreticulin. Inhibition of c-Src rescued the poorly adhesive phenotype of the calreticulin-underexpressing cells in that they became well spread, commenced formation of numerous focal contacts, and deposited a rich fibronectin matrix. Importantly, we show that c-Src activity is dependent on releasable Ca2+ from the endoplasmic reticulum, thus implicating Ca2+-sensitive pathways that are affected by calreticulin in cell-substratum adhesion. We propose that calreticulin affects fibronectin synthesis and matrix assembly via the regulation of fibronectin gene expression. In parallel, calcium-dependent effects of calreticulin on c-Src activity influence the formation and/or stability of focal contacts, which are instrumental in matrix assembly and remodeling.

CUTL1 promotes tumor cell migration by decreasing proteasome-mediated Src degradation

Recently, we identified the homeodomain transcription factor CUTL1 as important mediator of cell migration and tumor invasion downstream of transforming growth factor beta (TGFbeta). The molecular mechanisms and effectors mediating the pro-migratory and pro-invasive phenotype induced by CUTL1 have not been elucidated so far. Therefore, the aim of this study was to identify signaling pathways downstream of CUTL1 which are responsible for its effects on tumor cell migration. We found that the reduced motility seen after knock down of CUTL1 by RNA interference is accompanied by a delay in tumor cell spreading. This spreading defect is paralleled by a marked reduction of Src protein levels. We show that CUTL1 leads to Src protein stabilization and activation of Src-regulated downstream signaling molecules such as RhoA, Rac1, Cdc42 and ROCK. In addition, we demonstrate that CUTL1 decreases proteasome-mediated Src protein degradation, possibly via transcriptionally upregulating C-terminal Src kinase (Csk). Based on experiments using Src knockout cells (SYF), we present evidence that Src plays a crucial role in CUTL1-induced tumor cell migration. In conclusion, our findings linking the pro-invasive transcription factor CUTL1 and the Src pathway provide important new insights in the molecular effector pathways mediating CUTL-induced migration and invasion.

Tau impacts on growth-factor-stimulated actin remodeling

The microtubule-associated protein tau interacts with the SH3 domain of non-receptor Src family protein tyrosine kinases. A potential consequence of the SH3 interaction is the upregulation of tyrosine kinase activity. Here we investigated the activation of Src or Fyn by tau, both in vitro and in vivo. Tau increased the kinase activity in in vitro assays and in transfected COS7 cells. In platelet-derived growth factor (PDGF)-stimulated fibroblasts, tau appeared to prime Src for activation following PDGF stimulation, as reflected by changes in Src-mediated actin rearrangements. In addition, while fibroblasts normally recovered actin stress fibers by 5-7 hours after PDGF stimulation, tau-expressing cells showed sustained actin breakdown. Microtubule association by tau was not required for the observed changes in actin morphology. Inhibition of Src kinases or a mutant deficient in Src interaction reduced the effects, implicating Src family protein tyrosine kinases as a mediator of the effects of tau on actin rearrangements. Our results provide evidence that the interaction of tau with Src upregulates tyrosine kinase activity and that this interaction allows tau to impact on growth-factor-induced actin remodeling.

Elevated Levels of Phosphorylated Fibrinogen-α-Isoforms and Differential Expression of Other Post-Translationally Modified Proteins in the Plasma of Ovarian Cancer Patients

We evaluated the differentially expressed proteins in the plasma of ovarian cancer (OVC) patients using 2-D SDS-polyacrylamide gel electrophoresis (SDS-PAGE) with post-translational modification (PTM) specific stains after the removal of six high-abundance proteins. The pooled plasma from patients with stage III or IV OVC was compared to a pooled postmenopausal age-matched control. Several proteins were identified as differentially expressed in the plasma of OVC patients. Among them, the phosphorylated fibrinogen-alpha-chain isoform (containing fibrinopeptide-A) was found to be up-regulated. Previously in our laboratory, phosphorylated fibrinopeptide-A was found to be up-regulated in the low molecular weight fraction of serum derived from OVC patients. We examined the levels of phosphorylated fibrinogen-alpha-chain in each patient that constituted the pooled plasma using Western blot, mass spectrometry (MS), and PTM specific stains. Phosphoprotein bands containing fibrinogen-alpha-chain fragments showed up-regulation in all OVC patients.

Regulation of c-Src activity by the expression of wild-type v-Src and its kinase-dead double Y416F-K295N mutant

Active, wild-type v-Src and its kinase-dead double Y416F-K295N mutant were expressed in hamster fibroblasts. Expression of the active v-Src induced activation of endogenous c-Src and increased general protein-tyrosine phosphorylation in the infected cells. Expression of the kinase-dead mutant induced hypophosphorylation of Tyr416 of the endogenous c-Src. The inactivation of c-Src was reversible, as confirmed by in vitro kinase activity of c-Src immunoprecipitated from the kinase-dead v-Src-expressing cells. Both activation and inactivation of c-Src may be explained by direct interaction of the v-Src and c-Src that may either facilitate transphosphorylation of the regulatory Tyr416 in the activation loop, or prevent it by formation of transient dead-end complexes of the Y416F-K295N mutant with c-Src. The interaction was also indicated by co-localization of v- and c-Src proteins in immunofluorescent images of the infected cells. These results suggest that dimerization of Src plays an important role in the regulation of Src tyrosine kinase activity.

Integrin engagement modulates the phosphorylation of focal adhesion kinase, phagocytosis, and cell spreading in molluscan defence cells

Integrins play a key role in cellular immune responses in a variety of organisms; however, knowledge of integrins and their effects on cell signalling and functional responses in molluscan defence reactions is poor. Using integrin-mediated cell adhesion kits, alphaVbeta3 and beta1 integrin-like subunits were identified on the surface of Lymnaea stagnalis haemocytes. Haemocyte binding via these integrins was found to be dependent on Ca2+/Mg2+. Western blotting with an anti-phospho (anti-active) focal adhesion kinase (FAK) antibody revealed a 120-125 kDa FAK-like protein in these cells; this protein was transiently phosphorylated upon haemocyte adhesion over 90 min, with maximal phosphorylation occurring after 30 min binding. Also, integrin engagement with the tetrapeptide Arg-Gly-Asp-Ser (RGDS) resulted in a rapid increase in phosphorylation of the FAK-like protein; however, RGDS did not affect the phosphorylation of extracellular signal-regulated kinase. Treatment of haemocytes with RGDS (2 mM) inhibited phagocytosis of E. coli bioparticles by 88%. Moreover, at this concentration, RGDS reduced cell spreading by 61%; stress fiber formation was also impaired. Taken together, these results demonstrate a role for integrins in L. stagnalis haemocyte adhesion and defence reactions and, for the first time, link integrin engagement to FAK activation in molluscs.

Herbal formulation, Yukmi-jihang-tang-Jahage, regulates bone resorption by inhibition of phosphorylation mediated by tyrosine kinase Src and cyclooxygenase expression

Anti-bone resorption properties of the Korean herbal medicine, Yukmi-jihang-tang (YJ), which is comprised of seven herbs such as Rehmannia glutinosa Libosch, Dioscorea japonica THUNB, Cornus officinalis SIEB et. ZUCC, Smilax glabra ROXB, Paeonia suffruticosa ANDR, Alisma platago-aquatica var. orientale SAMUELS and Hominis placenta, were investigated. Cyclooxygenase-2 (COX-2) and tyrosine kinase involve on prostaglandin E2 (PGE2) production in mouse calvarial osteoblasts stimulated by cytokine interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha) and/or interleukin-6 (IL-6). IL-1beta and IL-6 and to a lesser extent TNF-alpha, enhanced COX-2 mRNA levels in calvarial osteoblasts. TGF-beta, YJ (100microg/ml) and their combinations of YJ+TGF-beta reduced the COX-2 mRNA level, PGE2 biosynthesis and bone resorption induced by IL-1beta, TNF-alpha, IL-6 or their combination. Finally, YJ inhibits in vitro and in vivo bone resorption by inhibition of phosphorylation of peptide substrates. The parathyroid hormone-induced bone resorption in mouse fetal long bone cultures was inhibited with an IC(50) of 16microg/ml. YJ dose-dependently reduced the hypercalcemia induced in mice by IL-1beta and partly prevented bone loss and microarchitectural changes in young ovariectomized rats, showing that the protective effect on bone was exerted via the inhibition of bone resorption. These results indicate that the synergy between IL-beta, TNF-alpha, IL-6 on PGE2 production is due to an enhanced gene expression of COX-2 and that tyrosine kinase(s) are involved in the signal transduction of COX-2 in mouse calvarial osteoblasts. Thus, YJ as a possible Src family kinase inhibitor may be useful for the treatment of diseases associated with elevated bone loss. This result also suggested that the YJ extracts is effective for bone resorptive action in bone cells.

The role of Src kinase in insulin-like growth factor-dependent mitogenic signaling in vascular smooth muscle cells

Activation of the MAPK pathway mediates insulin-like growth factor-I (IGF-I)-dependent proliferation in vascular smooth muscle cells (SMC). Our previous studies have shown that IGF-I-induced Shc phosphorylation is necessary for sustained activation of MAPK and increased cell proliferation of SMCs, and both Shc and the tyrosine phosphatase SHP-2 must be recruited to the membrane protein SHPS-1 in order for Shc to be phosphorylated. These studies were undertaken to determine whether Src kinase activity is required to phosphorylate Shc in response to IGF-I in SMC and because SHP-2 binds to Src whether their interaction was also required for IGF-I-stimulated mitogenesis. Our results show that IGF-I induces activation of Src kinase and that is required for Shc phosphorylation and for optimal MAPK activation. We tested whether Shc is a substrate of c-Src in SMC by disrupting Src/Shc association using a peptide containing a YXXL (Tyr328) motif sequence derived from Src. The peptide blocked the binding of Src and Shc in vitro and in vivo. Cells expressing a mutant Src (Src-FF) that had Tyr328/Tyr358 substituted with phenylalanines (Src-FF) showed defective Src/Shc binding, impaired IGF-I-dependent Shc phorylation, and impaired mitogenesis. This supports the conclusion that Src phosphorylates Shc. IGF-I induced both Src/SHP-2 and Src/SHPS-1 association. SMCs expressing an SHP-2 mutant that had the polyproline-rich region of SH2 deleted (SHP-2Delta10) had disrupted SHP-2/Src association, impaired IGF-I-dependent Shc phosphorylation, and an attenuated mitogenic response. IGF-I-induced association of Src and SHPS-1 was also impaired in SHP-2Delata10-expressing cells, although SHP-2/SHPS-1 association was unaffected. Upon IGF-I stimulation, a complex assembles on SHPS-1 that contains SHP-2, c-Src, and Shc wherein Src phosphorylates Shc, a signaling step that is necessary for an optimal mitogenic response.

Absence of SPARC in lens epithelial cells results in altered adhesion and extracellular matrix production in vitro

The matricellular protein SPARC (also known as osteonectin and BM-40) is expressed abundantly in lens epithelium. That SPARC-null mice exhibit early cataractogenesis, indicates a role for SPARC in the maintenance of lens transparency. Comparison of cultured wild-type and SPARC-null lens epithelial cells revealed significant changes in adhesion to different substrates. SPARC-null lens cells displayed enhanced attachment and spreading, focal adhesion formation, and resistance to trypsin detachment in comparison to wild-type cells. In the absence of SPARC, there was increased deposition of the ECM protein laminin-1 (LN-1). Proteins associated with focal adhesions were increased in SPARC-null versus wild-type lens cells: levels of alpha6-integrin heterodimers, talin, and paxillin phosphorylated on tyrosine were enhanced significantly, as was the association of beta1-integrin with talin and paxillin. Restoration of the wild-type phenotype in SPARC-null cultures was accomplished through genetic rescue by stable transfection of SPARC cDNA. Our findings indicate that SPARC is counter-adhesive for murine lens epithelial cells and demonstrate that multiple factors contribute to this activity. We also identify SPARC as a modulator of LN-1 secretion and deposition by these cells, an activity important in epithelial cell-ECM interactions in the ocular lens.

Modulation of response to tumor therapies by the extracellular matrix

The composition of the extracellular matrix in tumors is vastly different from that found in the normal tissue counterparts. As the extracellular matrix can signal to cells via integrin binding and activation, which is known to modulate cell proliferation, survival and migration, it may influence the response of both tumor and endothelial cells to anticancer therapies. Certain tumor-associated extracellular matrix proteins have been shown to confer resistance to chemotherapeutic drugs, radiation and anti-angiogenic factors. The current literature regarding this phenomenon and the potential therapeutic modalities to overcome extracellular matrix-induced resistance will be discussed.

Key role of Src kinase in S100B-induced activation of the receptor for advanced glycation end products in vascular smooth muscle cells

The receptor for advanced glycation end products (RAGE) and its ligands have been implicated in the activation of oxidant stress and inflammatory pathways in vascular smooth muscle cells (VSMCs) leading to the initiation and augmentation of atherosclerosis. Here we report that non-receptor Src tyrosine kinase and the membrane protein caveolin-1 (Cav-1) play a key role in the activation of RAGE by S100B in VSMCs. S100B increased the activation of Src kinase and tyrosine phosphorylation of caveolin-1 in VSMCs. A RAGE-specific antibody blocked both these effects. An inhibitor of Src kinase, PP2, significantly blocked S100B-induced activation of Src kinase, mitogen-activated protein kinases, transcription factors NF-kappaB and STAT3, superoxide production, tyrosine phosphorylation of Cav-1, VSMC migration, and expression of the pro-inflammatory genes monocyte chemotactic protein-1 and interleukin-6. Cholesterol depletion also inhibited S100B-induced effects indicating the requirement for intact caveolae in RAGE-specific signaling. Nucleofection of either a Src dominant negative mutant, or a Cav-1 mutant lacking the scaffolding domain, or Cav-1 short hairpin RNA significantly reduced S100B-induced inflammatory gene expression in VSMCs. Furthermore, VSMCs derived from insulin-resistant and diabetic db/db mice displayed increased RAGE expression, Src activation, and migration compared with those from control db/+ mice. The RAGE antibody blocked enhanced migration in db/db cells. These studies demonstrate for the first time that, in VSMCs, Src kinase and Cav-1 play important roles in RAGE-mediated inflammatory gene expression and migration, key events associated with diabetic vascular complications.

Ultrasound Stimulates Cyclooxygenase-2 Expression and Increases Bone Formation through Integrin, Focal Adhesion Kinase, Phosphatidylinositol 3-Kinase, and Akt Pathway in Osteoblasts

It has been shown that ultrasound (US) stimulation accelerates fracture healing in animal models and in clinical studies. Here we found that US stimulation transiently increased the surface expression of alpha2, alpha5, beta1, and beta3 integrins in cultured osteoblasts, as shown by flow cytometric analysis and immunofluorescence staining. US stimulation increased prostaglandin E(2) formation and the protein and mRNA levels of cyclooxygenase-2 (COX-2). At the mechanistic level, anti-integrin alpha5beta1 and alphavbeta3 antibodies or rhodostomin, a snake venom disintegrin, attenuated the US-induced COX-2 expression. Phosphatidylinositol 3-kinase (PI3K) inhibitors 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride (LY294002) and wortmannin also inhibited the potentiating action of US. US stimulation increased the phosphorylation of focal adhesion kinase (FAK), extracellular signal-regulated kinases (ERK), p85 subunit of PI3K, and serine 473 of Akt. COX-2 promoter activity was enhanced by US stimulation in cells transfected with pCOX2-Luc. Cotransfection with dominant-negative mutant of FAK(Y397F), p85(Deltap85), Akt(K179A), or ERK2(K52R) inhibited the potentiating action of US on COX-2 promoter activity. Expression of mineralized nodule was lower in dominant-negative mutants of FAK, p85, and Akt-transfected clones than in vector-transfected control cells. Taken together, our results provide evidence that US stimulation increases COX-2 expression and promotes bone formation in osteoblasts via the integrin/FAK/PI3K/Akt and ERK signaling pathway.

Absence of Fyn and Src causes a reeler-like phenotype

Nonreceptor protein tyrosine kinases of the Src family regulate the survival, proliferation, differentiation, and motility of many cell types, but their roles in brain development are unclear. Biochemical and in vitro experiments implicate Src and Fyn in the Reelin-dependent tyrosine phosphorylation of Dab1, which controls the positioning of radially migrating neurons in many brain regions. However, genetic evidence that either Src or Fyn mediates Reelin-dependent migrations in vivo has been lacking. Here, we report that, although Src is dispensable and although the absence of Fyn causes an intermediate phenotype, the combined absence of Src and Fyn almost abolishes tyrosine phosphorylation of Dab1 and causes defects in the fetal cortex and cerebellum very similar to those of dab1 mutants of the same age. Neurogenesis is not detectably affected, but the layering of neurons in the cortex is inverted, and the formation of the Purkinje plate is impaired. This implies that Src and Fyn are needed for Reelin-dependent events during brain development.

The role of Src in solid and hematologic malignancies

c-Src was the first protooncogene described and was among the first molecules in which tyrosine kinase activity was documented. c-Src has been defined as a common modular structure that participates in much of the crosstalk between the cytoplasmic protein tyrosine kinases and tyrosine kinase receptors. Understanding the structure and function of this important class of protein kinases and elucidating the molecular signaling events mediated by c-Src are important not only for identifying the critical pathways but also for designing new strategies to block or inhibit the action of these kinases. Despite the large amount of information available on c-Src, its precise functions in cancer remain to be elucidated. Recently, there has been renewed interest in c-Src as a molecular target for cancer therapy, and multiple c-Src inhibitors are entering clinical trials. In this review, the authors describe the function and expression of c-Src in human malignancies and the novel c-Src inhibitors and their potential applications for cancer treatment.

Type IV collagen induces STAT5 activation in MCF7 human breast cancer cells

A rapid increase in the tyrosine phosphorylation of signal transducer and activators of transcription (STAT) proteins has been extensively documented in cells stimulated with cytokines and growth factors, but virtually nothing is known about the regulation of STAT5 activation in breast cancer cells stimulated with basement membrane (BM) components. Stimulation of MCF7 cells with type IV collagen (Col-IV) promoted a striking increase in the phosphorylation of STAT5 at Tyr-694, as revealed by site-specific antibodies that recognized the phosphorylated state of this residue. In addition, Col-IV also stimulated STAT5 nuclear translocation and an increased in STAT5 DNA binding activity. Treatment with the selective Src family inhibitor pyrazolopyrimidine PP-2 prevented STAT5 phosphorylation at Tyr-694, nuclear translocation of STAT5 and the STAT5-DNA complex formation. Our results demonstrate, for the first time, that stimulation with Col-IV induces STAT5 phosphorylation of endogenous STAT5 at Tyr-694, nuclear translocation of STAT5 and increases in STAT5 DNA binding activity via a Src-dependent pathway in MCF7 cells.

Targeting STAT3 affects melanoma on multiple fronts

As a point of convergence for numerous oncogenic signaling pathways, STAT3 is constitutively-activated at 50 to 90% frequency in diverse human cancers, including melanoma. A critical role of STAT3 in tumor cell survival, proliferation, angiogenesis, metastasis and immune evasion has been recently demonstrated. STAT3 contributes to tumor cell growth by regulating the expression of genes that are involved in cell survival and proliferation. STAT3 promotes metastasis and angiogenesis by inducing expression of the metastatic gene, MMP-2, and the potent angiogenic gene, VEGF. STAT3 participates in the regulation of tumor immune evasion by inhibiting expression of proinflammatory mediators while promoting expression of immune-suppressing factors, which in turn activates STAT3 signaling in dendritic cells leading to immune tolerance. Thus, targeting STAT3 for therapy assaults cancer on multiple fronts. Many of the studies that defined STAT3's role in oncogenesis were carried out in melanoma cells and tumor models. In this review, we summarize the key role of STAT3 in cancer in general and melanoma in particular. With the emergence of small-molecule drugs that directly inhibit STAT3 or the oncogenic signaling pathways upstream of STAT3 in melanoma, a promising novel approach for melanoma therapy is emerging.

Src Family Kinase Activity Is Required for Murine Embryonic Stem Cell Growth and Differentiation

Self-renewal and differentiation of embryonic stem (ES) cells are regulated by cytokines and growth factors through tyrosine kinase-dependent signaling pathways. In murine ES cells, signals for self-renewal are generated by the leukemia inhibitory factor (LIF). LIF and other growth factors are linked to the activation of the Src family of cytoplasmic protein-tyrosine kinases (SFKs), which consists of eight members having shared structural architecture. In this article, we show that murine ES cells express seven SFKs, three of which (Hck, Src, and Fyn) exhibit constitutive activity in self-renewing ES cells. Differentiation of ES cells to embryoid bodies was associated with rapid transcriptional silencing of Hck and Lck and with the loss of the corresponding kinase proteins. The expression of other family members remained relatively constant, although some loss of Fgr and Lyn proteins was observed during differentiation. Like ES cells, embryoid bodies maintained constitutive Src and Fyn kinase activity. Partial inhibition of endogenous SFK activity with the ATP-competitive inhibitors 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine or Src kinase inhibitor-1 induced differentiation of ES cells in the presence of LIF. In contrast, suppression of all SFK activity with higher concentrations of these inhibitors, or with the more potent compound A-419259 (Bioorg Med Chem Lett 12:1683-1686, 2002) blocked differentiation in response to LIF withdrawal. It is surprising that these inhibitor-treated cells remained pluripotent despite the absence of LIF. Our results implicate individual members of the Src kinase family in distinct ES cell renewal and differentiation pathways and show that small-molecule SFK inhibitors can control ES cell fate.

PKC-δ-dependent pathways contribute to PDGF-stimulated ERK1/2 activation in vascular smooth muscle

Platelet-derived growth factor (PDGF) is an important regulator of vascular smooth muscle (VSM) cell growth and migration and has been identified as a key mediator of neointima formation resulting from vascular injury. PDGF exerts its effects, in part, through activation of ERK1/2. Previously, we reported that PKC-δ, specifically compared with PKC-α, mediated phorbol ester- and ATP-dependent activation of ERK1/2 in VSM cells. The purpose of this study was to determine whether PKC-δ was involved in PDGF-dependent activation of ERK1/2 in VSM cells. The addition of PDGF resulted in the activation, and Src family kinase-dependent tyrosine phosphorylation, of PKC-δ. Treatment with rottlerin (0.1–10 μM), a selective PKC-δ inhibitor, or adenoviral overexpression of kinase-negative PKC-δ significantly attenuated PDGF-induced activation of ERK1/2. The effects of the PKC-δ inhibitors decreased with increasing concentrations of activator PDGF. Interestingly, treatment with Gö6976 (0.1–3 μM), a selective inhibitor of cPKCs, or adenoviral overexpression of kinase-negative PKC-α also inhibited PDGF-stimulated ERK1/2. Furthermore, inhibition of cPKC activity with Gö6976 or overexpression of kinase-negative PKC-α attenuated PKC-δ activation and tyrosine phosphorylation in response to PDGF. These studies indicate involvement of both PKC-δ and PKC-α isozymes in PDGF-stimulated signaling in VSM and suggest an unexpected role for PKC-α in the regulation of PKC-δ activity.

Transient forebrain ischemia effects interaction of Src, FAK, and PYK2 with the NR2B subunit of N-methyl-d-aspartate receptor in gerbil hippocampus

Two different models of brain ischemia were used to examine the evoked changes in the tyrosine phosphorylation of NMDA receptor subunits 2A and 2B (NR2A and NR2B), as well as their interactions with non-receptor tyrosine kinases (NRTKs: FAK, PYK2 Src), and PSD-95 protein. Only short-term 5 min ischemia followed by 3 h reperfusion resulted in the elevated tyrosine phosphorylation of both investigated NMDA receptor subunits, but in contrast to previously published data, more pronounced in the case of NR2B. Concomitantly, an increased association of NR2B with FAK, PYK2, Src and PSD-95 has been observed. This sharp early reaction to brief ischemia was markedly attenuated during prolonged recovery (72 h) with almost complete return to control values. The initial recruitment of tyrosine kinases to NMDA receptor during the first 3 h of reperfusion is generally consistent with an active postischemic remodeling of PSD and may participate in the induction of the postischemic signal transduction pathway in gerbil hippocampus. In contrast, ischemia of longer duration (up to 30 min) caused an immediate decrease in the protein levels as well as tyrosine phosphorylation of both NR2A and NR2B subunits which was accompanied by the marked attenuation of the association with their investigated molecular partners--PSD-95 and NRTKs. This effect may be mimicked in vitro by Ca2+-dependent activation of endogenous calpains in purified PSD preparation suggesting irreversible deterioration of the synaptic signaling machinery during irreversible long-term ischemia.

Molecular partitioning during host cell penetration by Toxoplasma gondii

During invasion by Toxoplasma gondii, host cell transmembrane proteins are excluded from the forming parasitophorous vacuole membrane (PVM) by the tight apposition of host and parasite cellular membranes. Previous studies suggested that the basis for the selective partitioning of membrane constituents may be a preference for membrane microdomains, and this hypothesis was herein tested. The partitioning of a diverse group of molecular reporters for raft and nonraft membrane subdomains was monitored during parasite invasion by time-lapse video or confocal microscopy. Unexpectedly, both raft and nonraft lipid probes, as well as both raft and nonraft cytosolic leaflet proteins, flowed unhindered past the host-parasite junction into the PVM. Moreover, neither a raft-associated type 1 transmembrane protein nor its raft-dissociated counterpart accessed the PVM, while a multispanning membrane raft protein readily did so. Considered together with previous data, these studies demonstrate that selective partitioning at the host-parasite interface is a highly complex process, in which raft association favors, but is neither necessary nor sufficient for, inclusion into the T. gondii PVM.

(alpha)v(beta)3 integrins and Pyk2 mediate insulin-like growth factor I activation of Src and mitogen-activated protein kinase in 3T3-L1 cells

IGF-I stimulates cell growth through interaction of the IGF receptor with multiprotein signaling complexes. However, the mechanisms of IGF-I receptor-mediated signaling are not completely understood. We have previously shown that IGF-I-stimulated 3T3-L1 cell proliferation is dependent on Src activation of the ERK-1/2 MAPK pathway. We hypothesized that IGF-I activation of the MAPK pathway is mediated through integrin activation of Src-containing signaling complexes. The disintegrin echistatin decreased IGF-I phosphorylation of Src and MAPK, and blocking antibodies to (alpha)v and beta3 integrin subunits inhibited IGF-I activation of MAPK, suggesting that (alpha)v(beta)3 integrins mediate IGF-I mitogenic signaling. IGF-I increased ligand binding to (alpha)v(beta)3 as detected by immunofluorescent staining of ligand-induced binding site antibody and stimulated phosphorylation of the beta3 subunit, consistent with inside-out activation of (alpha)v(beta)3 integrins. IGF-I increased tyrosine phosphorylation of the focal adhesion kinase (FAK) Pyk2 (calcium-dependent proline-rich tyrosine kinase-2) to a much greater extent than FAK, and increased association of Src with Pyk2 but not FAK. The intracellular calcium chelator BAPTA prevented IGF-I phosphorylation of Pyk2, Src, and MAPK, suggesting that IGF-I activation of Pyk2 is calcium dependent. Transient transfection with a dominant-negative Pyk2, which lacks the autophosphorylation and Src binding site, decreased IGF-I activation of MAPK, but no inhibition was seen with transfected wild-type Pyk2. These results indicate that IGF-I signaling to MAPK is dependent on inside-out activation of (alpha)v(beta)3 integrins and integrin-facilitated multiprotein complex formation involving Pyk2 activation and association with Src.

Integrins and angiogenesis

The growth of new blood vessels is a dynamic yet highly regulated process that depends on coordinated signaling by growth factor and cell adhesion receptors. As part of the molecular program regulating angiogenesis, endothelial cells acquire a proliferative and invasive phenotype but also show increased susceptibility to apoptotic stimuli. Integrins are the principle adhesion receptors used by endothelial cells to interact with their extracellular microenvironment, and integrin-mediated interactions play a critical role in regulating cell proliferation, migration, and survival. Alterations in the repertoire and?or activity of integrins, as well as the availability and structural property of their ligands, regulate the vascular cell during the growth or repair of blood vessels.

Regulation by ultrasound treatment on the integrin expression and differentiation of osteoblasts

It has been shown that ultrasound (US) stimulation accelerates fracture healing in the animal models and in clinical studies. However, the mechanism by which US achieves these outcomes is not clear. Here we investigated the effect of US stimulation on the differentiation of osteoblasts and osteoclastogenesis. The effect of different intensities of US stimulation (1 MHz, continuous wave) on the osteoblastic cell line MC3T3-E1 or primary cultured osteoblasts was examined. Flow cytometry showed that US stimulation at 125 mW/cm2 for 10 min transiently increased the surface expression of alpha2, alpha5, and beta1 integrins in both MC3T3-E1 and primary osteoblasts. Fluorocytochemistry showed that the actin cytoskeleton also reorganized in response to US stimulation. When the MC3T3-E1 cells were cultured in differentiation medium containing vitamin C and beta-glycerophosphate, long-term US stimulation (10 min/day for 11 days) increased mineralized nodule formation, collagen content, and alkaline phosphatase activity. The intensity at 125 mW/cm2 exerts the most prominent action. Effect of long-term US stimulation on the osteoclastogenesis was also examined. US stimulation at a power of 62.5 or 125 mW/cm2 markedly inhibited RANKL plus M-CSF-induced osteoclastic differentiation from bone marrow stromal cells. These findings suggest that US has a regulatory effect on the integrin expression and the differentiation of osteoblasts and osteoclastogenesis, which may contribute to the beneficial effects of US on the fracture repair.

Src-dependent ezrin phosphorylation in adhesion-mediated signaling

In addition to providing a regulated linkage between the membrane and the actin cytoskeleton, ezrin participates in signal transduction pathways. Here we describe that expression of the ezrin Y145F mutant delays epithelial cell spreading on fibronectin by inhibiting events leading to FAK activation. The defect in spreading was rescued by the overexpression of catalytically functional Src. We demonstrate that ezrin Y145 is phosphorylated in A431 cells stimulated with epidermal growth factor (EGF) and in v-Src-transformed cells. Moreover in cells devoid of Src, SYF-/- fibroblasts, ezrin Y145 phosphorylation could only be detected upon the introduction of an active form of Src. The phosphorylation of ezrin at Y145 required prior binding of the Src SH2 domain to ezrin. Our results further show that Src activity influences its binding to ezrin and a positive feedback mechanism for Src-mediated Y145 phosphorylation is implied. Interestingly, cells expressing ezrin Y145F did not proliferate when cultured in a 3D collagen gel. Collectively, our results demonstrate a key signaling input of Src-dependent ezrin phosphorylation in adhesion-mediated events in epithelial cells.

Src family kinases, key regulators of signal transduction

The Src family of protein tyrosine kinases (SFKs) plays key roles in regulating signal transduction by a diverse set of cell surface receptors in the context of a variety of cellular environments. SFKs have evolved many ingenious molecular strategies to couple receptors with the cytoplasmic signaling machinery. The contributions to this issue of ONCOGENE describe how this machinery regulates fundamental cellular processes, including cell growth, differentiation, cell shape, migration and survival, and specialized cell signals. The pleiotropic functions of Src and Src family members underscore the importance of these kinases and explain why many of the members of this family have been identified as cellular oncogenes. In this volume, we have attempted to provide the reader with an overview of the current understanding of the function of Src family kinases in the regulation of selected cellular signaling pathways.

The interplay between Src family kinases and receptor tyrosine kinases

Src family tyrosine kinases (SFKs) are involved in a diverse array of physiological processes, as highlighted in this review. An overview of how SFKs interact with, and participate in signaling from, receptor tyrosine kinases (RTKs) is discussed. And also, how SFKs are activated by RTKs, and how SFKs, in turn, can activate RTKs, as well as how SFKs can promote signaling from growth factor receptors in a number of ways including participation in signaling pathways required for DNA synthesis, control of receptor turnover, actin cytoskeleton rearrangements and motility, and survival are discussed.

New pyrazolo[3,4-d]pyrimidines endowed with A431 antiproliferative activity and inhibitory properties of Src phosphorylation

New 4-aminopyrazolo[3,4-d]pyrimidines bearing various substituents at the position 1 and 6, were synthesized. The new compounds showed antiproliferative activity toward A431 cells, were found to be inhibitors of Src phosphorylation, and induced apoptotic cell death. In particular, 2h was a better inhibitor of Src phosphorylation than the reference compound PP2.

Src is necessary and sufficient for human airway smooth muscle cell proliferation and migration

Airway smooth muscle (ASM) hypertrophy and hyperplasia, important pathological features in chronic severe asthma, likely contribute to irreversible airflow obstruction. Despite considerable research effort, the precise cellular mechanisms that modulate ASM growth remain unknown. Src, a nonreceptor tyrosine kinase proto-oncogene, reportedly modulates cell proliferative responses to growth factors, contractile agonists, and inflammatory mediators. Here, we show that Src activation is required for human ASM mitogenesis and motility. Platelet-derived growth factor (PDGF), epidermal growth factor (EGF), and thrombin induce rapid activation of Src, and inhibition of Src induces a concentration-dependent abrogation of PDGF-, EGF-, and thrombin-induced ASM cell proliferation. Src immunoprecipitates had associated phosphatidylinositol 3-kinase, or PI3K, activation in response to PDGF and thrombin but not EGF. Further, Src activation is both necessary and sufficient for the stimulation of DNA synthesis as demonstrated by dominant negative Src inhibition of PDGF-, EGF-, and thrombin-induced DNA synthesis. Human ASM cell migration was also attenuated by transfection of cells with dominant negative Src. Further, expression of constitutively active Src promoted cell migration. Collectively, these data demonstrate that Src modulates human ASM cell proliferation and migration, suggesting that Src may play an important role in promoting ASM cell growth and migration that occur in airway remodeling found in asthma and chronic obstructive pulmonary disease, or COPD.

Focal adhesion regulation of cell behavior

Focal adhesions lie at the convergence of integrin adhesion, signaling and the actin cytoskeleton. Cells modify focal adhesions in response to changes in the molecular composition, two-dimensional (2D) vs. three-dimensional (3D) structure, and physical forces present in their extracellular matrix environment. We consider here how cells use focal adhesions to regulate signaling complexes and integrin function. Furthermore, we examine how this regulation controls complex cellular behaviors in response to matrices of diverse physical and biochemical properties. One event regulated by the physical structure of the ECM is phosphorylation of focal adhesion kinase (FAK) at Y397, which couples FAK to several signaling pathways that regulate cell proliferation, survival, migration, and invasion.

Mitogen-activated protein kinases and the evolution of Alzheimer's: a revolutionary neurogenetic axis for therapeutic intervention?

Alzheimer's disease (AD) is a neurogenetic condition that affects the processes via which the brain functions. Major observable hallmarks of AD are accumulated clusters of proteins in the brain. These clusters, termed neurofibrillary tangles (NFT), resemble pairs of threads wound around each other in a helix fashion accumulating within neurons. These tangles consist of a protein called Tau, which binds to tubulin, thus forming microtubules. Unlike NFTs, deposits of amyloid precursor protein (beta-APP) gather in the spaces between nerve cells. The nearby neurons often look swollen and deformed, and the clusters of protein are usually accompanied by reactive inflammatory cells, microglia, which are part of the brain's immune system responsible for degrading and removing damaged neurons or plaques. Since phosphorylation/dephosphorylation mechanisms are crucial in the regulation of Tau and beta-APP, a superfamily of mitogen-activated protein kinases (MAPKs) has recently emerged as key regulators of the formation of plagues, eventually leading to dementia and AD. The complex molecular interactions between MAPKs and proteins (plagues) associated with the evolution of AD form a cornerstone in the knowledge of a still burgeoning field of neurodegenerative diseases and ageing. This review overviews current understanding of the molecular pathways related to MAPKs and their role in the development of AD and, possibly, dementia. MAPKs, therefore, may constitute a neurogenetic, therapeutic target for the diagnosis and evolution of a preventative medical strategy for early detection, and likely treatment, of Alzheimer's.

Prostaglandin E2 activates Src signaling in lung adenocarcinoma cell via EP3

Accumulating evidence suggests that overproduction of prostaglandin (PG) E2 attributable to induction of cyclooxygenase-2 plays an important role in the development of lung adenocarcinoma. Recently, we have reported that a PGE2 receptor, EP3 is involved in appearance of malignant phenotype of a lung adenocarcinoma cell (A549 cell). In line with our previous study, here we investigated if Src signaling could be involved in PGE2-stimulated growth of A549 cells via EP3. PGE2-dependent cell growth in A549 cell positively related to the activation of Src. A specific antagonist against EP3 abrogated the cell growth and Src activation in the cells stimulated with PGE2. Also, the inhibition of Src activity suppressed its downstream signaling related to cell growth as well as the cell growth in the cells treated with PGE2. These results indicate that PGE2-dependent activation of Src signaling via EP3 plays an important role in growth of A549 cells.

Integrin signalling during tumour progression

During progression from tumour growth to metastasis, specific integrin signals enable cancer cells to detach from neighbouring cells, re-orientate their polarity during migration, and survive and proliferate in foreign microenvironments. There is increasing evidence that certain integrins associate with receptor tyrosine kinases (RTKs) to activate signalling pathways that are necessary for tumour invasion and metastasis. The effect of these integrins might be especially important in cancer cells that have activating mutations, or amplifications, of the genes that encode these RTKs.

Sertoli-Sertoli and Sertoli-germ cell interactions and their significance in germ cell movement in the seminiferous epithelium during spermatogenesis

Spermatogenesis is the process by which a single spermatogonium develops into 256 spermatozoa, one of which will fertilize the ovum. Since the 1950s when the stages of the epithelial cycle were first described, reproductive biologists have been in pursuit of one question: How can a spermatogonium traverse the epithelium, while at the same time differentiating into elongate spermatids that remain attached to the Sertoli cell throughout their development? Although it was generally agreed upon that junction restructuring was involved, at that time the types of junctions present in the testis were not even discerned. Today, it is known that tight, anchoring, and gap junctions are found in the testis. The testis also has two unique anchoring junction types, the ectoplasmic specialization and tubulobulbar complex. However, attention has recently shifted on identifying the regulatory molecules that "open" and "close" junctions, because this information will be useful in elucidating the mechanism of germ cell movement. For instance, cytokines have been shown to induce Sertoli cell tight junction disassembly by shutting down the production of tight junction proteins. Other factors such as proteases, protease inhibitors, GTPases, kinases, and phosphatases also come into play. In this review, we focus on this cellular phenomenon, recapping recent developments in the field.

Src-dependent phosphorylation of the EGF receptor Tyr-845 mediates Stat-p21waf1 pathway in A431 cells

BACKGROUND

Cell surface receptor for the epidermal growth factor (EGFR) and cytoplasmic tyrosine kinase c-Src co-operate in several cellular functions such as proliferation and apoptosis. Our previous studies have shown that ectopic expression of the adaptor protein p52shc or p66shc, but not p46shc, and EGF stimulation lead to the activation of c-Src that is accompanied by phosphorylation of signal transducers and activators of transcription (Stat) in A431 cells.

RESULTS

Here, we show that by using A431 cells as a model system, expression of p52shc, or cell stimulation with EGF or H2O2 leads to phosphorylation of EGFR on Tyr 845 that is located to the activation segment of the catalytic domain. The phosphorylation of Tyr 845 can be inhibited by PP2, but not by AG1478, and is associated with Src activation and Stat 3/5 phosphorylation, but not with MAP (mitogen-activated protein) kinase phosphorylation. Phosphorylation of Stat 3/5 in response to p52shc expression, EGF or H2O2 could also be inhibited by introduction into cells of phospho-Tyr 845-specific antibody or by expression of dominant-negative version of c-Src. Co-incubation of purified c-Src and EGFR results in phosphorylation of Tyr 845 in vitro, indicating that c-Src can directly phosphorylate EGFR on Tyr 845.

CONCLUSION

These results indicate that multiple signals for c-Src activation can promote Stat 3/5 phosphorylations through Src-dependent phosphorylation of EGFR on Tyr 845.

Tobacco smoke control of mucin production in lung cells requires oxygen radicals AP-1 and JNK

In smokers' lungs, excessive mucus clogs small airways, impairing respiration and promoting recurrent infection. A breakthrough in understanding this pathology was the realization that smoke could directly stimulate mucin synthesis in lung epithelial cells and that this phenomenon was dependent on the cell surface receptor for epidermal growth factor, EGFR. Distal steps in the smoke-triggered pathway have not yet been determined. We report here that the predominant airway mucin (MUC5AC) undergoes transcriptional up-regulation in response to tobacco smoke; this is mediated by an AP-1-containing response element, which binds JunD and Fra-2. These transcription factors require phosphorylation by upstream kinases JNK and ERK, respectively. Whereas ERK activation results from the upstream activation of EGFR, JNK activation is chiefly EGFR-independent. Our experiments demonstrated that smoke activates JNK via a Src-dependent, EGFR-independent signaling cascade initiated by smoke-induced reactive oxygen species. Taken together with our earlier results, these data indicate that the induction of mucin by smoke is the combined effect of mutually independent, reactive oxygen species activation of both EGFR and JNK.

The Raman detection of peptide tyrosine phosphorylation

Drop-coating-deposition-Raman (DCDR) is used to detect spectral changes induced by phosphorylation of tyrosine amino acid residues in peptides. Four peptides are investigated, with sequences derived from the human protein-tyrosine kinase, p60c-src, with Y-216, Y-419, and Y-530 phosphorylation sites. Although the spectra of the four peptides are quite different, tyrosine phosphorylation is found to invariably induce the collapse of a doublet at 820-850cm(-1) and the attenuation of a peak around 1205cm(-1). Moreover, amide III band shifts suggest that tyrosine phosphorylation may promote beta sheet formation, particularly in peptides that lack phenylalanine residues. The degree of tyrosine phosphorylation in peptide mixtures is determined using DCDR combined with partial least squares multivariate calibration with a 2% root mean standard error of prediction.

Regulation of cell motility by tyrosine phosphorylated villin

Temporal and spatial regulation of the actin cytoskeleton is vital for cell migration. Here, we show that an epithelial cell actin-binding protein, villin, plays a crucial role in this process. Overexpression of villin in doxycyline-regulated HeLa cells enhanced cell migration. Villin-induced cell migration was modestly augmented by growth factors. In contrast, tyrosine phosphorylation of villin and villin-induced cell migration was significantly inhibited by the src kinase inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) as well as by overexpression of a dominant negative mutant of c-src. These data suggest that phosphorylation of villin by c-src is involved in the actin cytoskeleton remodeling necessary for cell migration. We have previously shown that villin is tyrosine phosphorylated at four major sites. To further investigate the role of tyrosine phosphorylated villin in cell migration, we used phosphorylation site mutants (tyrosine to phenylalanine or tyrosine to glutamic acid) in HeLa cells. We determined that tyrosine phosphorylation at residues 60, 81, and 256 of human villin played an essential role in cell migration as well as in the reorganization of the actin cytoskeleton. Collectively, these studies define how biophysical events such as cell migration are actuated by biochemical signaling pathways involving tyrosine phosphorylation of actin binding proteins, in this case villin.

Hyperosmotic stress induces rapid focal adhesion kinase phosphorylation at tyrosines 397 and 577. Role of Src family kinases and Rho family GTPases

Hyperosmotic stress induced by treatment of Swiss 3T3 cells with the non-permeant solutes sucrose or sorbitol, rapidly and robustly stimulated endogenous focal adhesion kinase (FAK) phosphorylation at Tyr-397, the major autophosphorylation site, and at Tyr-577, within the kinase activation loop. Hyperosmotic stress-stimulated FAK phosphorylation at Tyr-397 occurred via a Src-independent pathway, whereas Tyr-577 phosphorylation was completely blocked by exposure to the Src family kinase inhibitor PP-2. Inhibition of p38 MAP kinase or phosphatidylinositol 3-kinases did not prevent FAK phosphorylation stimulated by hyperosmotic stress. Overexpression of N17 RhoA did not reduce hyperosmotic stress-mediated localization of phosphorylated FAK to focal contacts and treatment with the Rho-associated kinase inhibitor Y-27632 did not prevent FAK translocation and tyrosine phosphorylation in response to hyperosmotic stress. Overexpression of N17 Rac only slightly altered the hyperosmotic stress-mediated localization of phosphorylated FAK to focal contacts. In contrast, overexpression of the N17 mutant of Cdc42 disrupted hyperosmotic stress-stimulated FAK Tyr-397 localization to focal contacts. Additionally, treatment of cells with Clostridium difficile toxin B potently inhibited hyperosmotic stress-induced FAK tyrosine phosphorylation. Furthermore, FAK null fibroblasts compared with their FAK containing controls show markedly increased sensitivity, manifest by subsequent apoptosis, to sustained hyperosmotic stress. Our results indicate that FAK plays a fundamental role in protecting cells from hyperosmotic stress, and that the pathway(s) that mediates FAK autophosphorylation at Tyr-397 in response to osmotic stress can be distinguished from the pathways utilized by many other stimuli, including neuropeptides and bioactive lipids (Rho- and Rho-associated kinase-dependent), tyrosine kinase receptor agonists (phosphatidylinositol 3-kinase-dependent), and integrins (Src-dependent).

CEACAM6 cross-linking induces caveolin-1-dependent, Src-mediated focal adhesion kinase phosphorylation in BxPC3 pancreatic adenocarcinoma cells

Despite lacking transmembrane or intracellular domains, glycosylphosphatidylinositol-anchored proteins can modulate intracellular signaling events, in many cases through aggregation within membrane "lipid raft" microdomains. CEACAM6 is a glycosylphosphatidylinositol-linked cell surface protein of importance in the anchorage-independent survival and metastasis of pancreatic adenocarcinoma cells. We examined the effects of antibody-mediated cross-linking of CEACAM6 on intracellular signaling events and anchorage-independent survival of the CEACAM6-overexpressing pancreatic ductal adenocarcinoma cell line, BxPC3. CEACAM6 cross-linking increased c-Src activation and induced tyrosine phosphorylation of p125(FAK) focal adhesion kinase. Focal adhesion kinase phosphorylation was dependent on c-Src kinase activation, for which caveolin-1 was required. CEACAM6 cross-linking induced a significant increase in cellular resistance to anoikis. These observations represent the first characterization of the mechanism through which this important cell surface oncoprotein influences intracellular signaling events and hence malignant cellular behavior.