Methotrexate changes the testicular tyrosine phosphorylated protein expression and seminal vesicle epithelia of adult rats / El metotrexato cambia la expresión de la proteína testicular-tirosina fosforilada y el epitelio vesicular seminal en ratas adultas

Methotrexate (MTX) is commonly used as a chemotherapy agent and immune system suppressant but its adverse effect on male reproductive system is still limited. This study aimed to investigate the effect of MTX on structure and functional proteins of testis and seminal vesicle. Adult male rats were divided into control and MTX groups (n =12). In 30 experimental days, the treated animals were injected with MTX (tail i.v., 75 mg/KgBW) at days 8 and 15. Then, the reproductive parameters and histology of both groups were examined. Thickness of seminal seminal vesicle epithelia was analyzed. Also, the expressions of testicular tyrosine phosphorylated proteins and steroidogenic acute regulatory (StAR) protein were investigated. The results showed that MTX could significantly decrease epididymal sperm concentration. In addition, the germ cell degeneration, increased spaces of interstitial tissues, and low epididymal sperm mass density were observed in MTX group. The thickness of seminal vesicle epithelia in MTX group was significantly lower than that of control group. Moreover, the intensity of testicular phosphorylated proteins of 31, 32, 72, and 85 kDas was significantly increased while of 42 and 47 kDas in MTX group was decreased as compared to control. The expression of testicular StAR protein in MTX group was also significantly decreased as compared to the control. In conclusion, MTX affects testicular and seminal tissues and changes testicular functional proteins in adult rats.

El metotrexato (MTX) se usa comúnmente como agente de quimioterapia y supresor del sistema inmunitario, pero su efecto adverso en el sistema reproductor masculino sigue siendo limitado. Este estudio tuvo como objetivo investigar el efecto del MTX sobre la estructura y las proteínas funcionales del testículo y la vesícula seminal. Ratas macho adultas se dividieron en grupos control y grupo con MTX (n = 12). En 30 días experimentales, a los animales tratados se les inyectó MTX (cola i.v., 75 mg / KgBW) los días 8 y 15. Luego, se examinaron los parámetros reproductivos y la histología de ambos grupos. Se analizó el espesor del epitelio de la vesícula seminal. Además, se investigaron las expresiones de la proteína tirosina testicular fosforilada y de la proteína reguladora aguda esteroidogénica (StAR). Los resultados mostraron que el MTX podría disminuir significativamente la concentración de espermatozoides epididimarios. Además, se observó la degeneración de las células germinales, el aumento de los espacios de los tejidos intersticiales y la baja densidad de masa del espermatozoide epididimal en el grupo de MTX. El grosor del epitelio de la vesícula seminal en el grupo MTX fue significativamente menor que el del grupo control. Además, la intensidad de las proteínas testiculares fosforiladas de 31, 32, 72 y 85 kDas aumentó significativamente, mientras que la de 42 y 47 kDas en el grupo MTX disminuyó en comparación con el control. La expresión de la proteína StAR testicular en el grupo MTX también se redujo significativamente en comparación con el control. En conclusión, el MTX afecta los tejidos testiculares y seminales y cambia las proteínas funcionales testiculares en ratas adultas.

SH2 Domains Serve as Lipid-Binding Modules for pTyr-Signaling Proteins.

The Src-homology 2 (SH2) domain is a protein interaction domain that directs myriad phosphotyrosine (pY)-signaling pathways. Genome-wide screening of human SH2 domains reveals that ∼90% of SH2 domains bind plasma membrane lipids and many have high phosphoinositide specificity. They bind lipids using surface cationic patches separate from pY-binding pockets, thus binding lipids and the pY motif independently. The patches form grooves for specific lipid headgroup recognition or flat surfaces for non-specific membrane binding and both types of interaction are important for cellular function and regulation of SH2 domain-containing proteins. Cellular studies with ZAP70 showed that multiple lipids bind its C-terminal SH2 domain in a spatiotemporally specific manner and thereby exert exquisite spatiotemporal control over its protein binding and signaling activities in T cells. Collectively, this study reveals how lipids control SH2 domain-mediated cellular protein-protein interaction networks and suggest a new strategy for therapeutic modulation of pY-signaling pathways.

A phosphotyrosine switch regulates organic cation transporters.

Membrane transporters are key determinants of therapeutic outcomes. They regulate systemic and cellular drug levels influencing efficacy as well as toxicities. Here we report a unique phosphorylation-dependent interaction between drug transporters and tyrosine kinase inhibitors (TKIs), which has uncovered widespread phosphotyrosine-mediated regulation of drug transporters. We initially found that organic cation transporters (OCTs), uptake carriers of metformin and oxaliplatin, were inhibited by several clinically used TKIs. Mechanistic studies showed that these TKIs inhibit the Src family kinase Yes1, which was found to be essential for OCT2 tyrosine phosphorylation and function. Yes1 inhibition in vivo diminished OCT2 activity, significantly mitigating oxaliplatin-induced acute sensory neuropathy. Along with OCT2, other SLC-family drug transporters are potentially part of an extensive 'transporter-phosphoproteome' with unique susceptibility to TKIs. On the basis of these findings we propose that TKIs, an important and rapidly expanding class of therapeutics, can functionally modulate pharmacologically important proteins by inhibiting protein kinases essential for their post-translational regulation.

Effects of seawater pollutants on protein tyrosine phosphorylation in mussel tissues.

Different exogenous compounds are known to stimulate tyrosine kinase signaling, and this could explain a wide spectrum of pollutant effects on different organisms. We studied the effects of various seawater contaminants on tyrosine phosphorylation levels in different tissues of the mussel (Mytilus edulis), by using Western immunoblotting. Mussels were exposed in aquarium for 3 weeks to North Sea oil alone or to a mixture of North Sea oil, alkyl phenols, and polycyclic aromatic hydrocarbons (PAH). In another experiment, mussels were exposed for 3 weeks to each of the following potential endocrine disruptors: bisphenol A, diallyl phthalate, or tetrabromodiphenylether-47. In a third experiment, mussels were caged at four sites along a copper field gradient. Use of antiphosphotyrosine antibody showed that treatments with oil alone, or with oil, alkyl phenols and PAH induced phosphorylation increases in the digestive gland, gills and mantle. Bisphenol A produced significant effects in the gills and mantle, while diallyl phthalate and tetrabromodiphenylether-47 had a slight effect only on the gill tissue. Mussels exposed to the copper field gradient showed phosphotyrosine increases in the gills and mantle at intermediate levels of contamination. This latter result was also confirmed by using phosphospecific p38 antibody. In summary, the strength of induction was: oil mixture>oil>bisphenol A> or =copper; while the degree of tissue responsiveness was: mantle>gill>digestive gland. Based on these data, the use of tyrosine phosphorylation levels as a biomarker of seawater pollution is proposed.

A preliminary investigation into the action of anagrelide: thrombopoietin-c-Mpl receptor interactions.

OBJECTIVE: Many studies have validated the clinical efficacy of anagrelide to reduce platelet counts in thrombocythemic conditions. With the ability to support human megakaryopoiesis in vitro using thrombopoietin (TPO), specific investigation of changes in platelet levels can be carried out in human systems. Using CD34(+) stem cells and murine BaF3 cells transfected with the human or murine TPO receptor, c-Mpl (BaF3mpl), the effect of anagrelide on cell differentiation, proliferation, and signaling was examined in the presence of TPO. METHODS: Inhibition of TPO-mediated cell differentiation by anagrelide was evaluated by fluorescein-activated cell sorting analysis. Cell proliferation was monitored by 3-(4,5-dimethylthiazol-2-yl)-5-3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assays. Effect of anagrelide on TPO-mediated phosphotyrosine (pTyr) activity was examined by Western analysis of whole cell lysates. RESULTS: In the presence of TPO, anagrelide reduced the number of CD41(+) cells without a reduction in the total mononuclear cell number in a dose-dependent manner. Growth inhibition was also observed in BaF3 cells transfected with human c-Mpl. Anagrelide also reduced TPO-specific pTyr activity in a species-specific manner. No inhibitory effect could be demonstrated with interleukin-3 stimulation. CONCLUSION: Parallel dose-response effects were found in both CD41(+) number and TPO-specific pTyr activity. These results suggest that anagrelide reduces TPO-mediated megakaryocyte proliferation of CD34(+) cells through a mechanism that leads to inhibition of intracellular signaling events. Furthermore, data also suggest that it is a species-specific effect, with no inhibitory activity against the murine receptor. Because there is a less than 10% difference in DNA sequence homology between human and murine receptors, the difference in sequence-specific activity must reside in these amino acid differences.

Altered protein tyrosine phosphorylation in asthmatic bronchial epithelium.

A disease-related, corticosteroid-insensitive increase in the expression of epidermal growth factor (EGF) receptor (EGFR) tyrosine kinase in asthmatic bronchial epithelium has been shown previously by the current authors. To determine whether this is associated with enhanced intracellular signalling, the aim of this study was to evaluate epithelial tyrosine phosphorylation. Bronchial biopsies were analysed for the presence of phosphotyrosine by immunohistochemistry. Bronchial epithelial cells were exposed to EGF, hydrogen peroxide or tumour necrosis factor-alpha in vitro for measurement of tyrosine phosphorylated signalling intermediates and interleukin (IL)-8 release. Phosphotyrosine was increased significantly in the epithelium of severe asthmatics when compared with controls or mild asthmatics; however, in mild asthma, phosphotyrosine levels were significantly decreased when compared with controls. There was no significant difference between phosphotyrosine levels before or after 8 weeks of treatment with budesonide. Stimulation of bronchial epithelial cells resulted in tyrosine phosphorylation of several proteins, including EGFR, Shc and p42/p44 mitogen-activated protein kinase. In the presence of salbutamol, a transient partial suppression of EGFR phosphorylation occurred, whereas dexamethasone was without effect. Neither salbutamol nor dexamethasone inhibited EGF-stimulated IL-8 release. These data indicate that regulation of protein tyrosine kinase activity is abnormal in severe asthma. The epidermal growth factor receptor and/or other tyrosine kinase pathways may contribute to persistent, corticosteroid-unresponsive inflammation in severe asthma.

Singlet oxygen-induced attenuation of growth factor signaling: possible role of ceramides.

Singlet oxygen, an electronically excited form of molecular oxygen, is a primary mediator of the activation of stress-activated protein kinases elicited by ultraviolet A (UVA; 320-400 nm). Here, the effects of singlet oxygen (1O2) on the extracellular signal-regulated kinase (ERK) 1/2 and Akt/protein kinase B pathways were analyzed in human dermal fibroblasts. While basal ERK 1/2 phosphorylation was lowered in cells exposed to either 1O2, UVA or photodynamic treatment, Akt was moderately activated by photochemically generated 1O2 in a phosphoinositide 3-kinase (PI3K)-dependent fashion, resulting in the phosphorylation of glycogen synthase kinase-3 (GSK3). The activation of ERK 1/2 and Akt as induced by stimulation with epidermal growth factor (EGF) or platelet-derived growth factor (PDGF) was inhibited by 1O2 generated intracellularly upon photoexcitation of rose Bengal (RB). Photodynamic therapy (PDT)-induced apoptosis is known to be associated with increased formation of ceramides. Likewise, both 1O2 and UVA induced ceramide generation in human skin fibroblasts. The attenuation of EGF- and PDGF-induced activation of ERK 1/2 and Akt by 1O2 was mimicked by stimulation of fibroblasts with the cell-permeable C2-ceramide. Interestingly, EGF-induced tyrosine phosphorylation of the EGF receptor was strongly attenuated by 1O2 but unimpaired by C2-ceramide, implying that, although ceramide formation may mediate the above attenuation of ERK and Akt phosphorylation induced by 1O2, mechanisms beyond ceramide formation exist that mediate impairment of growth factor signaling by singlet oxygen. In summary, these data point to a novel mechanism of 1O2 toxicity: the known 1O2-induced activation of proapoptotic kinases such as JNK and p38 is paralleled by the prevention of activation of growth factor receptor-dependent signaling and of anti-apoptotic kinases, thus shifting the balance towards apoptosis.

Ca(2+)-sensitive tyrosine kinase Pyk2/CAK beta-dependent signaling is essential for G-protein-coupled receptor agonist-induced hypertrophy.

G-protein-coupled receptor agonists including endothelin-1 (ET-1) and phenylephrine (PE) induce hypertrophy in neonatal ventricular cardiomyocytes. Others and we previously reported that Rac1 signaling pathway plays an important role in this agonist-induced cardiomyocyte hypertrophy. In this study reported here, we found that a Ca(2+)-sensitive non-receptor tyrosine kinase, proline-rich tyrosine kinase 2 (Pyk2)/cell adhesion kinase beta (CAKbeta), is involved in ET-1- and PE-induced cardiomyocyte hypertrophy medicated through Rac1 activation. ET-1, PE or the Ca(2+) inophore, ionomycin, stimulated a rapid increase in tyrosine phosphorylation of Pyk2. The tyrosine phosphorylation of Pyk2 was suppressed by the Ca(2+) chelator, BAPTA. ET-1- or PE-induced increases in [(3)H]-leucine incorporation and expression of atrial natriuretic factor and the enhancement of sarcomere organization. Infection of cardiomyocytes with an adenovirus expressing a mutant Pyk2 which lacked its kinase domain or its ability to bind to c-Src, eliminated ET-1- and PE-induced hypertrophic responses. Inhibition of Pyk2 activation also suppressed Rac1 activation and reactive oxygen species (ROS) production. These findings suggest that the signal transduction pathway leading to hypertrophy involves Ca(2+)-induced Pyk2 activation followed by Rac1-dependent ROS production.

Nitric oxide-induced motility in aortic smooth muscle cells: role of protein tyrosine phosphatase SHP-2 and GTP-binding protein Rho.

We have previously reported that SHP-2 upregulation is necessary for NO-stimulated motility in differentiated rat aortic smooth muscle cells. We now test the hypothesis that upregulation of SHP-2 is necessary and sufficient to stimulate cell motility. Overexpression of SHP-2 via recombinant adenoviral vector stimulated motility to the same extent as NO, whereas the expression of C463S-SHP-2, the dominant-negative SHP-2 allele, blocked the motogenic effect of NO. On the basis of previous studies, we next tested the hypothesis that NO decreases RhoA activity and that this event is necessary and sufficient to explain NO-induced motogenesis. We found that NO decreased RhoA activity in a concentration-dependent manner. Moreover, a dominant-negative SHP-2 allele, DSH2, blocked the NO-induced inhibition of RhoA activity, indicating that upregulation of SHP-2 is necessary for this event. Expression of G14V-RhoA, the constitutively active RhoA allele, decreased cell motility and blocked the motogenic effect of NO, whereas the expression of T19N-RhoA, the dominant-negative RhoA allele, increased cell motility to an extent similar to that induced by NO. Dominant-negative RhoA reversed the effect of dominant-negative SHP-2, indicating that RhoA functions downstream from SHP-2. To investigate events downstream from RhoA, we treated cells with fasudil, a selective Rho kinase inhibitor, and found that it increased cell motility. These results indicate that upregulation of SHP-2, leading to downregulation of RhoA, which is followed by decreased Rho kinase activity, is a sequence of events necessary and sufficient to explain NO-induced cell motility in differentiated aortic smooth muscle cells. The results may be of relevance to in vivo events such as neointimal formation, angiogenesis, and vasculogenesis.

Inhibition of shear-stress-induced platelet aggregation and phosphotyrosine signaling by GPIIb-IIIa antagonists.

Shear-stress-mediated platelet thrombus formation has been implicated in the pathophysiology of cardiovascular diseases such as acute myocardial infarction and unstable angina. Although previous studies have established that fluid shear forces cause platelet aggregation, a direct comparison of GPIIb-IIIa antagonists used in the treatment of acute coronary syndromes on shear-induced platelet activation has not been reported. Therefore, the objective of the present study was to characterize the effects of the platelet antagonists abciximab, eptifibatide, and tirofiban on shear-mediated platelet activation and aggregation using flow cytometric and Western blotting techniques. Flow cytometric analyses indicated that all three platelet antagonists, when used at concentrations that saturated all GPIIb-IIIa receptors, significantly inhibited platelet aggregate formation and expression of the platelet activation marker p-selectin. None of the antagonists caused increased expression of GPIbalpha or GPIIb-IIIa on the platelet surface compared to untreated controls. Additionally, Western blotting demonstrated that a 72 kDa protein tentatively identified as Syk became phosphorylated in response to shear stress and that its phosphorylation was inhibited by each antagonist. The findings of this study indicate that abciximab, eptifibatide, and tirofiban, though possessing distinct biochemical and pharmacological properties, effectively and equivalently inhibit platelet aggregation, p-selectin expression, and intracellular tyrosine phosphorylation events induced by fluid shear stress.

Angiotensin II type 2 receptor inhibits epidermal growth factor receptor transactivation by increasing association of SHP-1 tyrosine phosphatase.

Angiotensin (Ang) II has 2 major receptor isoforms, Ang type 1 (AT(1)) and Ang type (AT(2)). AT(1) transphosphorylates epidermal growth factor receptor (EGFR) to activate extracellular signal-regulated kinase (ERK). Although AT(2) was shown to inactivate ERK, the action of AT(2) on EGFR activation remains undefined. Using AT(2)-overexpressing vascular smooth muscle cells from AT(2) transgenic mice, we studied these undefined actions of AT(2). Maximal ERK activity induced by Ang II was increased 1.9- and 2.2-fold by AT(2) inhibition, which was abolished by orthovanadate but not okadaic acid or pertussis toxin. AT(2) inhibited AT(1)-mediated EGFR tyrosine phosphorylation by 63%. The activity of SHP-1 tyrosine phosphatase was significantly upregulated 1 minute after AT(2) stimulation and association of SHP-1 with EGFR was increased, whereas AT(2) failed to tyrosine phosphorylate SHP-1. Stable overexpression of SHP-1-dominant negative mutant completely abolished AT(2)-mediated inhibition of EGFR and ERK activation. AT(1)-mediated c-fos mRNA accumulation was attenuated by 48% by AT(2) stimulation. Induction of fibronectin gene containing an AP-1 responsive element in its 5'-flanking region was decreased by 37% after AT(2) stimulation, corresponding to the results of gel mobility assay with the AP-1 sequence of fibronectin as a probe. These findings suggested that AT(2) inhibits ERK activity by inducing SHP-1 activity, leading to decreases in AP-1 activity and AP-1-regulated gene expression, in which EGFR dephosphorylation plays an important role via association of SHP-1.

Interleukin-6-induced tyrosine phosphorylation of phospholipase C-gamma1 in PC12 cells.

Phospholipase C (PLC)-gamma1 plays a pivotal role in the signal transduction pathway mediated by growth factors. In this study, we found that neurite outgrowth of pheochromocytoma (PC12) cells was significantly induced by interleukin-6 (IL-6). Stimulation of PC12 cells with IL-6 led to tyrosine phosphorylation of PLC-gamma1 in a dose- and time-dependent manner. IL-6 stimulation also increased the hydrolysis of phosphatidylinositol 4,5-bisphosphate. Accumulation of total inositol phosphate as well as tyrosine phosphorylation of PLC-gamma1 was inhibited by the pretreatment of protein kinase inhibitors such as genistein and staurosporine. These results suggest that PLC-gamma1 may be involved in the signal transduction pathway of IL-6-induced PC12 cell differentiation.

Tyrosine phosphorylation: a critical component in the formation of hemidesmosomes.

Our goal was to evaluate the role of tyrosine phosphorylation in the complete formation of hemidesmosomes that occurs during development or during remodeling after injury. A corneal organ culture system was used to study hemidesmosome formation as it would occur in an intact tissue. Phosphorylation of the integrin subunit beta 4 and bullous pemphigoid antigen-1 (BPAG-1) was examined, as these proteins are known to play a role in linking the electron-dense plaques along the basal surface with the intermediate filaments to complete the formation of hemidesmosomes. Corneal epithelial sheets were placed on substrata that contained an intact basal lamina or basal laminae that had been either modified or removed. These constructs were incubated for up to 18 h, and hemidesmosome formation was evaluated by using transmission electron microscopy. When epithelial sheets were placed on intact basal laminae and incubated in the presence of the tyrosine kinase inhibitor genistein (200 microM), hemidesmosome formation was impaired. The formation of electron-dense regions was delayed, and no association of intermediate filaments was detected. Results were confirmed by biochemical studies. When the epithelium and underlying proteins were extracted and immunoprecipitated with beta 4 or BPAG-1, tyrosine phosphorylation decreased in the presence of genistein. In addition, the phosphorylation of beta 4 decreased when epithelial sheets were incubated on substrata from which the basal lamina had been removed or altered. Thus, a reduction in phosphorylation of tyrosine residues impairs the formation of mature hemidesmosomes, and substrata that fail to support hemidesmosome formation also demonstrate decreased phosphorylation of tyrosine residues.

In vivo and in vitro correlation of pulmonary MAP kinase activation following metallic exposure.

Residual oil fly ash (ROFA) is a particulate pollutant produced in the combustion of fuel oil. Exposure to ROFA is associated with adverse respiratory effects in humans, induces lung inflammation in animals, and induces inflammatory mediator expression in cultured human airway epithelial cells (HAEC). ROFA has a high content of transition metals, including vanadium, a potent tyrosine phosphatase inhibitor that we have previously shown to disregulate phosphotyrosine metabolism and activate mitogen-activated protein kinase (MAPK) signaling cascades in HAEC. In order to study MAPK activation in response to in vivo metal exposure, we used immunohistochemical methods to detect levels of phosphorylated protein tyrosines (P-Tyr) and the MAPKs ERK1/2, JNK, and P38 in lung sections from rats intratracheally exposed to ROFA. After a 1-h exposure to 500 microg ROFA, rat lungs showed no histological changes and no significant increases in immunostaining for either P-Tyr or phospho-(P-) MAPKs compared to saline-instilled controls. At 4 h of exposure, there was mild and variable inflammation in the lung, which was accompanied by an increase in specific immunostaining for P-Tyr and P-MAPKs in airway and alveolar epithelial cells and resident macrophages. By 24 h of exposure, there was a pronounced inflammatory response to ROFA instillation and a marked increase in levels of P-Tyr and P-MAPKs present within the alveolar epithelium and in the inflammatory cells, while the airway epithelium showed a continued increase in the expression of P-ERK1/2. By comparison, HAEC cultures exposed to 100 microg/ml ROFA for 20 min resulted in marked increases in P-Tyr and P-MAPKs, which persisted after 24 h of exposure. P-Tyr levels continued to accumulate for up to 24 h in HAEC exposed to ROFA. These results demonstrate in vivo activation in cell signaling pathways in response to pulmonary exposure to particulate matter, and support the relevance of in vitro studies in the identification of mechanisms of lung injury induced by pollutant inhalation.

Activation of NF-kappaB p50/p65 is regulated in the developing mammary gland and inhibits STAT5-mediated beta-casein gene expression.

The NF-kappaB family of transcription factors regulates diverse cellular functions such as immune response and cell growth and development, and has been reported to be constitutively active in a variety of mammary carcinoma cell lines. However, its role in normal mammary gland development has not been addressed. In our study, we detected developmentally regulated NF-kappaB activity in the mammary gland of mice. During pregnancy, DNA binding activity of NF-kappaB p50/p65 increased until day 16 postcoitum and decreased with the onset of lactation, most likely due to reduced p50 and p65 protein levels in the nucleus. Cotransfection experiments performed with 293 cells revealed an inhibition of the prolactin receptor/JAK2/STAT5 pathway by NF-kappaB. In HC11 cells, NF-kappaB p50/p65 activity was inversely correlated with prolactin-induced STAT5 tyrosine phosphorylation, expression of endogenous beta-casein gene, and of a transfected beta-casein gene promoter reporter construct. This indicates a negative cross talk between NF-kappaB and the prolactin receptor/JAK2/STAT5 activation pathway, which occurs at the level of STAT5 tyrosine phosphorylation. Our results provide evidence for a role of NF-kappaB in normal mammary gland development, and indicate its function as a negative regulator of beta-casein gene expression during pregnancy by interfering with STAT5 tyrosine phosphorylation.

Motogenic activity of IGD-containing synthetic peptides.

Although the IGD amino acid motif (iso-gly-asp) is a highly conserved feature of the fibronectin type I module, no biological activity has as yet been ascribed to it. We have previously reported that the gelatin-binding domain of fibronectin stimulates the migration of human skin fibroblasts into native, but not denatured, type I collagen substrata. Two IGD-containing type I modules are present within the gelatin-binding domain. The object of this study was to ascertain whether soluble synthetic peptides containing the IGD motif stimulate fibroblast migration. We found that IGD peptides stimulated fibroblast migration in the following order of activity: IGDS (as present in the ninth type I module) > IGDQ (as present in the seventh type I module) > IGD. The scrambled SDGI peptide and the well-characterised RGDS peptide were devoid of motogenic activity. The migratory response of fibroblasts to IGD-containing peptides consisted of two distinct phases: an initial period of peptide-mediated cell activation and a subsequent period of enhanced migration manifest in the absence of further IGD peptide. Cell activation was substratum-independent (occurring equally well on both native and denatured type I collagen substrata), whilst the manifestation of enhanced migration was persistent and substratum-dependent (being evident only by cells adherent to a native collagen substratum). Our data further indicated that cell activation (1) is elicited by a signal transduction cascade occurring within minutes of cell exposure to IGD-containing peptides, (2) is dependent upon integrin alphavbeta3 functionality, (3) involves the tyrosine phosphorylation of focal adhesion kinase (ppFAK125) and (4) is inhibited by signalling mediated through integrin alpha5beta1. The expression of migration stimulating activity by soluble IGD-containing peptides clearly distinguishes them from their RGD counterparts. This is the first identified biological activity of the highly conserved IGD motif and provides a rational platform for the development of a novel family of therapeutic compounds designed to stimulate cell migration in relevant clinical situations, such as impaired wound healing.

Phosphotyrosine signalling as a regulator of neural crest cell adhesion and motility.

We demonstrate that neural crest cell-cell adhesion, cell-substrate adhesion, and ultimately cell motility, are highly dependent on the balanced action of tyrosine kinases and tyrosine phosphatases. Neural crest cell migration on fibronectin is diminished in the presence of the tyrosine phosphatase inhibitor vanadate or tyrosine kinase inhibitor herbimycin A, while cadherin-rich cell-cell adhesions are significantly increased. In contrast, cells treated with the kinase inhibitor genistein have decreased motility, rearrange rapidly and reversibly into a pavement-like monolayer, but have no increase in cadherin interactions. Genistein-sensitive tyrosine kinases may therefore abrogate a latent sensitivity of neural crest cells to contact-mediated inhibition of movement. Furthermore, we show that the activity of herbimycin A-sensitive kinases is necessary for focal adhesion formation in these cells. Moreover, the size and distribution of these adhesions are acutely sensitive to the actions of tyrosine phosphatases and genistein-sensitive kinases. We propose that in migrating neural crest cells there is a balance in phosphotyrosine signalling which minimises both cell-cell adhesion and contact inhibition of movement, while enhancing dynamic cell-substrate interactions and thus the conditions for motility.