A dual inhibitor of platelet-derived growth factor beta-receptor and Src kinase activity potently interferes with motogenic and mitogenic responses to PDGF in vascular smooth muscle cells. A novel candidate for prevention of vascular remodeling

Src family kinase targeting in head and neck tumor cells using SU6656, PP2 and dasatinib

BACKGROUND

We have recently shown a frequent upregulation of Src-family kinases (SFK) in head and neck squamous cell carcinoma (HNSCC). Here we tested, if SFK targeting is effective especially in HNSCC cells with upregulated SFK signaling.

METHODS

The impact of SFK inhibitors SU6656, PP2 and dasatinib on three HNSCC cell lines with different SFK activity levels was analyzed using proliferation and colony formation assays, Western blot and functional kinomics.

RESULTS

Proliferation was blocked by all inhibitors in a micro-molar range. With respect to cell kill, dasatinib was most effective, while SU6656 showed moderate and PP2 minor effects. Cellular signaling was affected differently, with PP2 having no effect on SFK signaling while dasatinib probably has non-SFK specific effects. Only SU6656 showed clear SFK specific effects on signaling.

CONCLUSION

The results demonstrate potential benefit of SFK inhibition in HNSCC but they also highlight challenges due to non-specificities of the different drugs.

Electroacupuncture attenuates ischemic injury after stroke and promotes angiogenesis via activation of EPO mediated Src and VEGF signaling pathways

Although electroacupuncture (EA) has been shown to be effective in the treatment of stroke, its mechanisms of action remain undefined. This study explored the therapeutic effects of EA in rats with cerebral ischemia-reperfusion injury (CIRI) and evaluated its possible mechanisms in promoting angiogenesis. To evaluate the effect of EA, we used 2, 3, 5-Triphenyl-2H-Tetrazolium Chloride (TTC) staining and behavior score to calculate the cerebral infarct volume and neurological deficit score after CIRI. Western blot (WB) analysis was employed to evaluate the expression of cluster of differentiation 34 (CD34), erythropoietin (EPO), vascular endothelial growth factor (VEGF) and phospho-Src (p-Src) in the brain of the rats with CIRI. On the other hand, we established an oxygen-glucose deprivation/reoxygenation (OGD/R) injury model using brain microvascular endothelial cells (BMECs), and analyzed cell viability and expression of VEGF or p-Src using cell counting kit-8 (CCK-8) and WB, respectively. Our data showed that EA at the GV26 acupoint could significantly promote the expression of CD34, EPO, VEGF and p-Src in CIRI rats. Our CCK-8 results demonstrated that intervention with recombinant EPO and VEGF proteins remarkably improved the viability of BMECs after OGD/R, while a Src inhibitor, PP1, reversed this phenotype. The WB results showed that the recombinant EPO protein increased the expression of VEGF and p-Src, which was significantly inhibited by PP1. Taken together, our findings showed that EA at the GV26 acupoint can significantly attenuate ischemic injury after stroke and promote angiogenesis via activation of EPO-mediated Src and VEGF signaling pathways. Besides, the upregulation of VEGF may also be associated with the activation of Src by EPO.

Gene expression profiles and signaling mechanisms in α2B-adrenoceptor-evoked proliferation of vascular smooth muscle cells

BACKGROUND

α2-adrenoceptors are important regulators of vascular tone and blood pressure. Regulation of cell proliferation is a less well investigated consequence of α2-adrenoceptor activation. We have previously shown that α2B-adrenoceptor activation stimulates proliferation of vascular smooth muscle cells (VSMCs). This may be important for blood vessel development and plasticity and for the pathology and therapeutics of cardiovascular disorders. The underlying cellular mechanisms have remained mostly unknown. This study explored pathways of regulation of gene expression and intracellular signaling related to α2B-adrenoceptor-evoked VSMC proliferation.

RESULTS

The cellular mechanisms and signaling pathways of α2B-adrenoceptor-evoked proliferation of VSMCs are complex and include redundancy. Functional enrichment analysis and pathway analysis identified differentially expressed genes associated with α2B-adrenoceptor-regulated VSMC proliferation. They included the upregulated genes Egr1, F3, Ptgs2 and Serpine1 and the downregulated genes Cx3cl1, Cav1, Rhoa, Nppb and Prrx1. The most highly upregulated gene, Lypd8, represents a novel finding in the VSMC context. Inhibitor library screening and kinase activity profiling were applied to identify kinases in the involved signaling pathways. Putative upstream kinases identified by two different screens included PKC, Raf-1, Src, the MAP kinases p38 and JNK and the receptor tyrosine kinases EGFR and HGF/HGFR. As a novel finding, the Src family kinase Lyn was also identified as a putative upstream kinase.

CONCLUSIONS

α2B-adrenoceptors may mediate their pro-proliferative effects in VSMCs by promoting the activity of bFGF and PDGF and the growth factor receptors EGFR, HGFR and VEGFR-1/2. The Src family kinase Lyn was also identified as a putative upstream kinase. Lyn is known to be expressed in VSMCs and has been identified as an important regulator of GPCR trafficking and GPCR effects on cell proliferation. Identified Ser/Thr kinases included several PKC isoforms and the β-adrenoceptor kinases 1 and 2. Cross-talk between the signaling mechanisms involved in α2B-adrenoceptor-evoked VSMC proliferation thus appears to involve PKC activation, subsequent changes in gene expression, transactivation of EGFR, and modulation of kinase activities and growth factor-mediated signaling. While many of the identified individual signals were relatively small in terms of effect size, many of them were validated by combining pathway analysis and our integrated screening approach.

Astrocyte-shed extracellular vesicles regulate the peripheral leukocyte response to inflammatory brain lesions

Brain injury induces a peripheral acute cytokine response that directs the transmigration of leukocytes into the brain. Because this brain-to-peripheral immune communication affects patient recovery, understanding its regulation is important. Using a mouse model of inflammatory brain injury, we set out to find a soluble mediator for this phenomenon. We found that extracellular vesicles (EVs) shed from astrocytes in response to intracerebral injection of interleukin-1β (IL-1β) rapidly entered into peripheral circulation and promoted the transmigration of leukocytes through modulation of the peripheral acute cytokine response. Bioinformatic analysis of the protein and microRNA cargo of EVs identified peroxisome proliferator-activated receptor α (PPARα) as a primary molecular target of astrocyte-shed EVs. We confirmed in mice that astrocytic EVs promoted the transmigration of leukocytes into the brain by inhibiting PPARα, resulting in the increase of nuclear factor κB (NF-κB) activity that triggered the production of cytokines in liver. These findings expand our understanding of the mechanisms regulating communication between the brain and peripheral immune system and identify astrocytic EVs as a molecular regulator of the immunological response to inflammatory brain damage.

RGS5 promotes arterial growth during arteriogenesis

Arteriogenesis—the growth of collateral arterioles—partially compensates for the progressive occlusion of large conductance arteries as it may occur as a consequence of coronary, cerebral or peripheral artery disease. Despite being clinically highly relevant, mechanisms driving this process remain elusive. In this context, our study revealed that abundance of regulator of G-protein signalling 5 (RGS5) is increased in vascular smooth muscle cells (SMCs) of remodelling collateral arterioles. RGS5 terminates G-protein-coupled signalling cascades which control contractile responses of SMCs. Consequently, overexpression of RGS5 blunted Gα_q/11-mediated mobilization of intracellular calcium, thereby facilitating Gα_12/13-mediated RhoA signalling which is crucial for arteriogenesis. Knockdown of RGS5 evoked opposite effects and thus strongly impaired collateral growth as evidenced by a blockade of RhoA activation, SMC proliferation and the inability of these cells to acquire an activated phenotype in RGS5-deficient mice after the onset of arteriogenesis. Collectively, these findings establish RGS5 as a novel determinant of arteriogenesis which shifts G-protein signalling from Gα_q/11-mediated calcium-dependent contraction towards Gα_12/13-mediated Rho kinase-dependent SMC activation.

Subject Categories Vascular Biology & Angiogenesis

β Integrins mediate FAK Y397 autophosphorylation of resistance arteries during eutrophic inward remodeling in hypertension

Human essential hypertension is characterized by eutrophic inward remodeling of the resistance arteries with little evidence of hypertrophy. Upregulation of αVβ3 integrin is crucial during this process. In order to investigate the role of focal adhesion kinase (FAK) activation in this process, the level of FAK Y397 autophosphorylation was studied in small blood vessels from young TGR(mRen2)27 animals as blood pressure rose and eutrophic inward remodeling took place. Between weeks 4 and 5, this process was completed and accompanied by a significant increase in FAK phosphorylation compared with normotensive control animals. Phosphorylated (p)FAK Y397 was coimmunoprecipitated with both β1- and β3-integrin-specific antibodies. In contrast, only a fraction (<10-fold) was coprecipitated with the β3 integrin subunit in control vessels. Inhibition of eutrophic remodeling by cRGDfV treatment of TGR(mRen2)27 rats resulted in the development of smooth-muscle-cell hypertrophy and a significant further enhancement of FAK Y397 phosphorylation, but this time with exclusive coassociation of pFAK Y397 with integrin β1. We established that phosphorylation of FAK Y397 with association with β1 and β3 integrins occurs with pressure-induced eutrophic remodeling. Inhibiting this process leads to an adaptive hypertrophic vascular response induced by a distinct β1-mediated FAK phosphorylation pattern.

Inhibitory Effects of Brazilin on the Vascular Smooth Muscle Cell Proliferation and Migration Induced by PDGF-BB

Abnormal vascular smooth muscle cell (VSMC) proliferation and migration contribute to the pathogenesis of vascular diseases including atherosclerosis and restenosis. Brazilin isolated from the heartwood of Caesalpinia sappan L. has been reported to exhibit various biological activities, such as anti-platelet aggregation, anti-inflammation, vasorelaxation and pro-apoptosis. However, the functional effects of Brazilin on VSMCs remain unexplored. The present study investigated the potential effects of Brazilin on platelet-derived growth factor (PDGF)-BB induced VSMC proliferation and migration as well as the underlying mechanism of action. VSMC proliferation and migration were measured by Crystal Violet Staining, wound-healing and Boyden chamber assays, respectively. Cell cycle was analyzed by flow cytometry. Enzymatic action of matrix metalloproteinase-9 (MMP-9) was carried out by gelatin zymography. Expression of adhesion molecules, cell cycle regulatory proteins, the phosphorylated levels of PDGF receptor β (PDGF-Rβ), Src, extracellular signal regulated kinase (ERK) and Akt were tested by immunoblotting. The present study demonstrated that pretreatment with Brazilin dose-dependently inhibited PDGF-BB stimulated VSMC proliferation and migration, which were associated with a cell-cycle arrest at G0/G1 phase, a reduction in the adhesion molecule expression and MMP-9 activation in VSMCs. Furthermore, the increase in PDGF-Rβ, Src, ERK1/2 and Akt phosphorylation induced by PDGF-BB were suppressed by Brazilin. These findings indicate that Brazilin inhibits PDGF-BB induced VSMC proliferation and migration, and the inhibitory effects of Brazilin may be associated with the blockade of PDGF-Rβ - ERK1/2 and Akt signaling pathways. In conclusion, the present study implicates that Brazilin may be useful as an anti-proliferative agent for the treatment of vascular diseases.

CB₁ cannabinoid receptors promote maximal FAK catalytic activity by stimulating cooperative signaling between receptor tyrosine kinases and integrins in neuronal cells

Tyrosine phosphorylation (Tyr-P) of focal adhesion kinase (FAK) regulates FAK activation. Phosphorylated FAK Tyr 397 binds Src family kinases (Src), which in turn directly phosphorylate FAK Tyr 576/577 to produce maximal FAK enzymatic activity. CB₁ cannabinoid receptors (CB₁) are abundantly expressed in the nervous system and influence FAK activation by presently unknown mechanisms. The current investigation determined that CB₁-stimulated maximal FAK catalytic activity is mediated by Gi/o proteins in N18TG2 neuronal cells, and that G12/13 regulation of Rac1 and RhoA occurs concomitantly. Immunoblotting analyses using antibodies against FAK phospho-Tyr 397 and phospho-Tyr 576/577 demonstrated that the time-course of CB₁-stimulated FAK 576/577 Tyr-P occurred in three phases: Phase I (0-2 min) maximal Tyr-P, Phase II (5-20 min) rapid decline in Tyr-P, and Phase III (>20 min) plateau in Tyr-P at submaximal levels. In contrast, FAK 397 Tyr-P was monophasic and significantly lower in magnitude. FAK 397 Tyr-P and Phase I FAK 576/577 Tyr-P involved protein tyrosine phosphatase (PTP1B and Shp1/Shp2)-mediated Src activation, Protein Kinase A (PKA) inhibition, and integrin activation. Phase I maximal FAK 576/577 Tyr-P also required cooperative signaling between receptor tyrosine kinases (RTKs) and integrins. The integrin antagonist RGDS peptide, Flk-1 vascular endothelial growth factor receptor (VEGFR) antagonist SU5416, and epidermal growth factor receptor (EGFR) antagonist AG 1478 blocked Phase I FAK 576/577 Tyr-P. CB₁ agonists failed to stimulate FAK Tyr-P in the absence of integrin activation upon suspension in serum-free culture media. In contrast, cells grown on the integrin ligands fibronectin and laminin displayed increased FAK 576/577 Tyr-P that was augmented by CB₁ agonists and blocked by the Src inhibitor PP2 and Flk-1 VEGFR antagonist SU5416. Taken together, these studies have identified a complex integrative pathway utilized by CB₁ to stimulate maximal FAK 576/577 Tyr-P in neuronal cells.

Gastrodin inhibits cell proliferation in vascular smooth muscle cells and attenuates neointima formation in vivo

Vascular smooth muscle cell (VSMC) proliferation plays a critical role in the development of vascular diseases. In the present study, we tested the efficacy and the mechanisms of action of gastrodin, a bioactive component of the Chinese herb Gastrodia elata Bl, in relation to platelet-derived growth factor-BB (PDGF-BB)-dependent cell proliferation and neointima formation after acute vascular injury. Cell experiments were performed with VSMCs isolated from rat aortas. WST and BrdU incorporation assays were used to evaluate VSMC proliferation. Eight-week-old C57BL/6 mice were used for the animal experiments. Gastrodin (150 mg/kg/day) was administered in the animal chow for 14 days, and the mice were subjected to wire injury of the left carotid artery. Our data demonstrated that gastrodin attenuated the VSMC proliferation induced by PDGF-BB, as assessed by WST assay and BrdU incorporation. Gastrodin influenced the S-phase entry of VSMCs and stabilised p27Kip1 expression. In addition, pre-incubation with sinomenine prior to PDGF-BB stimulation led to increased smooth muscle-specific gene expression, thereby inhibiting VSMC dedifferentiation. Gastrodin treatment also reduced the intimal area and the number of PCNA-positive cells. Furthermore, PDGF-BB-induced phosphorylation of ERK1/2, p38 MAPK, Akt and GSK3β was suppressed by gastrodin. Our results suggest that gastrodin can inhibit VSMC proliferation and attenuate neointimal hyperplasia in response to vascular injury. Furthermore, the ERK1/2, p38 MAPK and Akt/GSK3β signalling pathways were found to be involved in the effects of gastrodin.

Identification of SRC as a potent drug target for asthma, using an integrative approach of protein interactome analysis and in silico drug discovery

Network-biology inspired modeling of interactome data and computational chemistry have the potential to revolutionize drug discovery by complementing conventional methods. We consider asthma, a complex disease characterized by intricate molecular mechanisms, for our study. We aim to integrate prediction of potent drug targets using graph-theoretical methods and subsequent identification of small molecules capable of modulating activity of the best target. In this work, we construct the protein interactome underlying this disease: Asthma Protein Interactome (API). Using a strategy based on network analysis of the interactome, we identify a set of potential drug targets for asthma. Topologically and dynamically, v-src sarcoma (Schmidt-Ruppin A-2) viral oncogene homolog (SRC) emerges as the most central target in API. SRC is known to play an important role in promoting airway smooth muscle cell growth and facilitating migration in airway remodeling. From interactome analysis, and with the reported role in respiratory mechanisms, SRC emerges as a promising drug target for asthma. Further, we proceed to identify leads for SRC from a public database of small molecules. We predict two potential leads for SRC using ligand-based virtual screening methodology.

Role of Src tyrosine kinase in the atherogenic effects of the 12/15-lipoxygenase pathway in vascular smooth muscle cells

OBJECTIVE

The 12/15-Lipoxygenase (12/15-LO) and its metabolite 12(S)-Hydroxyeicosatetraenoic acid [12(S)-HETE] mediate proatherogenic responses in vascular smooth muscle cells (VSMCs). We examined the role of the nonreceptor tyrosine kinase Src in the signaling and epigenetic chromatin mechanisms involved in these processes.

METHODS AND RESULTS

Rat VSMCs (RVSMCs) were stimulated with 12(S)-HETE (0.1 micromol/L) in the presence or absence of the Src inhibitor PP2 (10 micromol/L). Src activation and downstream signaling events including inflammatory gene expression and chromatin histone H3-Lys-9/14 acetylation were examined by immunoblotting, RT-PCR, and chromatin immunoprecipitation assays, respectively. 12(S)-HETE significantly activated Src, focal adhesion kinase, Akt, p38MAPK, and CREB. Expression of monocyte chemoattractant protein-1 and interleukin-6 genes and histone H3-Lys-9/14 acetylation on their promoters were also increased by 12(S)-HETE. PP2 inhibited these responses as well as 12(S)-HETE-induced VSMC migration. Furthermore, dominant negative mutants of Src, CREB, and a histone acetyltransferase p300 significantly blocked 12(S)-HETE-induced inflammatory gene expression. In addition, growth factor induced Src signaling and downstream events including H3-Lys-9/14 acetylation and migration were significantly attenuated in VSMCs derived from 12/15-LO(-/-) mice relative to WT.

CONCLUSIONS

Src kinase signaling plays a central role in the proatherogenic responses mediated by 12/15-LO and its oxidized lipid metabolite 12(S)-HETE in VSMCs.

A substrate peptide for the FLT3 receptor tyrosine kinase

FLT3 (fms-like tyrosine kinase 3) is frequently activated by mutation in acute myeloid leukemia, and is therefore under study as a drug target. Testing and characterization of tyrosine kinase inhibitors is facilitated by the availability of efficient peptide substrates. Searching for FLT3 peptide substrates using phosphorylation experiments on peptide arrays and in solution revealed that the peptide F-T-D-R-L-Q-Q-Y(8)-I-S-T-R-G-L-G is efficiently phosphorylated (apparent Km 10 micromol/l), with Y8 as the phosphorylated site. This peptide presents a novel tool for identifying and characterizing FLT3 kinase inhibitors.

c-Src tyrosine kinase, a critical component for 5-HT2A receptor-mediated contraction in rat aorta

Serotonin (5-hydroxytryptamine, 5-HT) receptors (5-HTRs) play critical roles in brain and cardiovascular functions. In the vasculature, 5-HT induces potent vasoconstrictions, which in aorta are mainly mediated by activation of the 5-HT(2A)R subtype. We previously proposed that one signalling mechanism of 5-HT-induced vasoconstriction could be c-Src, a member of the Src tyrosine kinase family. We now provide evidence for a central role of c-Src in 5-HT(2A)R-mediated contraction. Inhibition of Src kinase activity with 10 mum 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) prior to contraction resulted in approximately 90-99% inhibition of contractions induced by 5-HT or by alpha-methyl-5-HT (5-HT(2)R agonist). In contrast, PP2 pretreatment only partly inhibited contractions induced by angiotensin II and the thromboxane A(2) mimetic, U46619, and had no significant action on phenylephrine-induced contractions. 5-Hydroxytryptamine increased Src kinase activity and PP2-sensitive tyrosine-phosphorylated proteins. As expected for c-Src identity, PP2 pretreatment inhibited 5-HT-induced contraction with an IC(50) of approximately 1 mum. Ketanserin (10 nm), a 5-HT(2A) antagonist, but not antagonists of 5-HT(2B)R (100 nm SB204741) or 5-HT(2C)R (20 nm RS102221), prevented 5-HT-induced contractions, mimicking PP2 and implicating 5-HT(2A)R as the major receptor subtype coupled to c-Src. In HEK 293T cells, c-Src and 5-HT(2A)R were reciprocally co-immunoprecipitated and co-localized at the cell periphery. Finally, 5-HT-induced Src activity was unaffected by inhibition of Rho kinase, supporting a role of c-Src upstream of Rho kinase. Together, the results highlight c-Src activation as one of the early and pivotal mechanisms in 5-HT(2A)R contractile signalling in aorta.

Tyrosine kinase signalling in embryonic stem cells

Pluripotent ES (embryonic stem) cells can be expanded in culture and induced to differentiate into a wide range of cell types. Self-renewal of ES cells involves proliferation with concomitant suppression of differentiation. Some critical and conserved pathways regulating self-renewal in both human and mouse ES cells have been identified, but there is also evidence suggesting significant species differences. Cytoplasmic and receptor tyrosine kinases play important roles in proliferation, survival, self-renewal and differentiation in stem, progenitor and adult cells. The present review focuses on the role of tyrosine kinase signalling for maintenance of the undifferentiated state, proliferation, survival and early differentiation of ES cells.

Phorbol 12-myristate 13-acetate-dependent protein kinase C delta-Tyr311 phosphorylation in cardiomyocyte caveolae

Protein kinase Cdelta (PKCdelta) activation is generally attributed to lipid cofactor-dependent allosteric activation mechanisms at membranes. However, recent studies indicate that PKCdelta also is dynamically regulated through tyrosine phosphorylation in H(2)O(2)- and phorbol 12-myristate 13-acetate (PMA)-treated cardiomyocytes. H(2)O(2) activates Src and related Src-family kinases (SFKs), which function as dual PKCdelta-Tyr(311) and -Tyr(332) kinases in vitro and contribute to H(2)O(2)-dependent PKCdelta-Tyr(311)/Tyr(332) phosphorylation in cardiomyocytes and in mouse embryo fibroblasts. H(2)O(2)-dependent PKCdelta-Tyr(311)/Tyr(332) phosphorylation is defective in SYF cells (deficient in SFKs) and restored by Src re-expression. PMA also promotes PKCdelta-Tyr(311) phosphorylation, but this is not associated with SFK activation or PKCdelta-Tyr(332) phosphorylation. Rather, PMA increases PKCdelta-Tyr(311) phosphorylation by delivering PKCdelta to SFK-enriched caveolae. Cyclodextrin treatment disrupts caveolae and blocks PMA-dependent PKCdelta-Tyr(311) phosphorylation, without blocking H(2)O(2)-dependent PKCdelta-Tyr(311) phosphorylation. The enzyme that acts as a PKCdelta-Tyr(311) kinase without increasing PKCdelta phosphorylation at Tyr(332) in PMA-treated cardiomyocytes is uncertain. Although in vitro kinase assays implicate c-Abl as a selective PKCdelta-Tyr(311) kinase, PMA-dependent PKCdelta-Tyr(311) phosphorylation persists in cardiomyocytes treated with the c-Abl inhibitor ST1571 and c-Abl is not detected in caveolae; these results effectively exclude a c-Abl-dependent process. Finally, we show that 1,2-dioleoyl-sn-glycerol mimics the effect of PMA to drive PKCdelta to caveolae and increase PKCdelta-Tyr(311) phosphorylation, whereas G protein-coupled receptor agonists such as norepinephrine and endothelin-1 do not. These results suggest that norepinephrine and endothelin-1 increase 1,2-dioleoyl-sn-glycerol accumulation and activate PKCdelta exclusively in non-caveolae membranes. Collectively, these results identify stimulus-specific PKCdelta localization and tyrosine phosphorylation mechanisms that could be targeted for therapeutic advantage.

c-Src couples PI 3 kinase/Akt and MAPK signaling to PDGF-induced DNA synthesis in mesangial cells

Platelet-derived growth factor BB (PDGF) and PDGF receptor-beta (PDGFR) play critical roles in mesangial cell proliferation during embryonic development and in mesangioproliferative glomerulonephritis. We have shown previously that phosphatidylinositol (PI) 3 kinase/Akt and Erk1/2 mitogen-activated protein kinase (MAPK) contribute to PDGF-dependent proliferation of mesangial cells, but the mechanism by which these two enzyme cascades are activated by PDGFR signaling is not precisely known. We examined the role of c-Src tyrosine kinase in this process. PDGF increased phosphorylation of c-Src in a time-dependent manner indicating its activation. A pharmacologic inhibitor of c-Src, PP1, blocked PDGF-induced DNA synthesis with concomitant inhibition of c-Src phosphorylation. Immune-complex kinase assays of c-Src and PDGFR demonstrated inhibition of c-Src tyrosine kinase activity by PP1, without an effect on PDGFR tyrosine phosphorylation. Both PP1 and expression of dominant negative c-Src inhibited PDGF-induced PI 3 kinase, resulting in attenuation of Akt kinase activity. Expression of constitutively active c-Src increased Akt activity to the same extent as with PDGF. Constitutively active c-Src augmented PDGF-induced Akt activity, thus contributing to Akt signaling. Inhibition of c-Src tyrosine kinase blocked PDGF-stimulated MAPK activity and resulted in attenuation of c-fos gene transcription with concomitant prevention of Elk-1 transactivation. Furthermore, inhibition of c-Src increased p27(Kip1) cyclin kinase inhibitor, and attenuated PDGF-induced pRb phosphorylation and CDK2 activity. These data provide the first evidence in mesangial cells that PDGF-activated c-Src tyrosine kinase relays signals to PI 3 kinase/Akt and MAPK. Furthermore our results demonstrate that c-Src integrates signals into the nucleus to activate CDK2, which is required for DNA synthesis.

Pyrazolo-pyrimidine-derived c-Src inhibitor reduces angiogenesis and survival of squamous carcinoma cells by suppressing vascular endothelial growth factor production and signaling

Src tyrosine kinase family cooperates with activated growth factor receptors to regulate growth, invasion and metastasis. The authors examined the influence of a novel c-Src inhibitor, 1l, derived from 4-amino-substituted-pyrazolo-pyrimidines, on tumor angiogenesis and on the angiogenic output of squamous carcinoma cells, A431 and SCC-4. The effect of 1l was assessed on growth and microvessel density in A431 tumors and its effect compared with the established c-Src inhibitor PP-1. The effects of c-Src inhibition were investigated on vascular endothelial growth factor (VEGF) expression and activity in tumor cells grown in vivo and in vitro, as well as on VEGF mediated signaling and on endothelial cell functions. Nanomolar concentrations of 1l decreased tumor volume promoted by A431 implanted in nude mice, without affecting in vitro cell tumor survival. This effect was related to 1l inhibition of VEGF production, and secondary to an effect on tumor microvessel density. The rabbit cornea assay confirmed that 1l markedly decreased neovessel growth induced by VEGF. In cultured endothelial cells, 1l inhibited the VEGF-induced phosphorylation on tyr416 of c-Src, resulting in a reduced cell proliferation and invasion. Consistently, 1l dowregulated endothelial nitric oxide synthase, MAPK-extracellular receptor kinase 1-2 (ERK1-2) activity and matrix metalloproteinases (MMP-2/MMP-9), while the tissue inhibitors of metalloproteinases (TIMP2/TIMP-1) were upregulated. These results demonstrate that nM concentrations of c-Src kinase inhibitors (1l and PP-1), by reducing the production of VEGF released by tumor cell and its endothelial cell responses, have a highly selective antiangiogenesis effect, which might be useful in combination therapies.

Differential regulation of blood–brain barrier permeability in brain trauma and pneumococcal meningitis—role of Src kinases

Increased vascular permeability causing vasogenic brain edema is characteristic for many acute neurological diseases such as stroke, brain trauma, and meningitis. Src family kinases, especially c-Src, play an important role in regulating blood-brain barrier permeability in response to VEGF, but also mediate leukocyte function and cytokine signalling. Here we demonstrate that pharmacological inhibition of Src or c-Src deficiency does not influence cerebrospinal fluid (CSF) pleocytosis, brain edema formation, and bacterial outgrowth during experimental pneumococcal meningitis despite the increased cerebral expression of inflammatory chemokines, such as IL-6, CCL-9, CXCL-1, CXCL-2 and G-CSF as determined by protein array analysis. In contrast, inhibition of Src significantly reduced brain edema formation, lesion volume, and clinical worsening in cold-induced brain injury without decreasing cytokine/chemokine expression. While brain trauma was associated with increased cerebral VEGF formation, VEGF levels significantly declined during pneumococcal meningitis. Therefore, we conclude that in brain trauma blood-brain barrier tightness is regulated by the VEGF/Src pathway whereas c-Src does not influence brain edema formation and leukocyte function during bacterial meningitis.

Inhibition of vascular remodelling in a porcine coronary injury model by herbal extract XS0601

Background

Arterial remodelling is a major pathologic change of restenosis after percutaneous coronary intervention (PCI). Our previous studies showed that XS0601 (consisting of Chuangxingol and paeoniflorin) had some effects on the prevention of restenosis after PCI. Therefore, the purpose of this study was to examine whether and how its mechanism was related to the regulation of the arterial remodelling after endothelial injury by balloon dilation.

Methods

Twenty Chinese mini-pigs were randomized into four groups: control, probucol, low-dose XS0601 and high-dose XS0601 group before oversized balloon injury of the left anterior descending coronary arteries. Starting from two days before balloon injury, the mini-pigs in the treated group were administered with probucol (2 g/day) and XS0601 (0.02 g/kg/day for low dose; 0.04 g/kg/day for high dose) for four weeks after balloon injury. The animals receiving balloon injury alone were used as control. Morphometric and angiographic analysis of the injured arteries were performed.

Results

The contribution of intimal hyperplasia and arterial remodelling to angiographic late lumen loss was 41% and 59% respectively. XS0601 markedly inhibited proliferation of smooth muscle cells (SMCs) and transformation of SMCs from contractile to synthetic phenotype in neointima, inhibited hyperplasia-related indices of morphometric analysis and reduce late angiographic lumen loss. The reduction of the late angiographic lumen loss resulting from vascular remodelling was greater after XS0601 treatment.

Conclusion

Both intimal hyperplasia and vascular remodelling are attributed to late lumen loss in this porcine coronary injury model. XS0601 markedly reduced angiographic late lumen loss resulting from intimal hyperplasia, vascular remodelling and XS0601 may be a potential agent to prevent restenosis after PCI.

Structure and chemical inhibition of the RET tyrosine kinase domain

The RET proto-oncogene encodes a receptor tyrosine kinase for the glial cell line-derived neurotrophic factor family of ligands. Loss-of-function mutations in RET are implicated in Hirschsprung disease, whereas activating mutations in RET are found in human cancers, including familial medullar thyroid carcinoma and multiple endocrine neoplasias 2A and 2B. We report here the biochemical characterization of the human RET tyrosine kinase domain and the structure determination of the non-phosphorylated and phosphorylated forms. Both structures adopt the same active kinase conformation competent to bind ATP and substrate and have a pre-organized activation loop conformation that is independent of phosphorylation status. In agreement with the structural data, enzyme kinetic data show that autophosphorylation produces only a modest increase in activity. Longer forms of RET containing the juxtamembrane domain and C-terminal tail exhibited similar kinetic behavior, implying that there is no cis-inhibitory mechanism within the RET intracellular domain. Our results suggest the existence of alternative inhibitory mechanisms, possibly in trans, for the autoregulation of RET kinase activity. We also present the structures of the RET tyrosine kinase domain bound to two inhibitors, the pyrazolopyrimidine PP1 and the clinically relevant 4-anilinoquinazoline ZD6474. These structures explain why certain multiple endocrine neoplasia 2-associated RET mutants found in patients are resistant to inhibition and form the basis for design of more effective inhibitors.

Src tyrosine kinase as a chemotherapeutic target: is there a clinical case?

Src tyrosine kinase was the first protooncogene described. It has been found to be overexpressed and activated in a large number of different cancers. Cellular Src has been shown to activate a number of different effectors that are involved in different aspects of cancer biology such as metastasis, cell cycle regulation and cell survival. Despite this, Src inhibitors have not entered the regular arsenal of chemotherapeutics. This article reviews some of the biology, rationale, in vitro and in vivo preclinical evidence, and some very early clinical trials demonstrating efficacy of Src inhibitors.

Receptor association and tyrosine phosphorylation of S6 kinases

Ribosomal protein S6 kinase (S6K) is activated by an array of mitogenic stimuli and is a key player in the regulation of cell growth. The activation process of S6 kinase involves a complex and sequential series of multiple Ser/Thr phosphorylations and is mainly mediated via phosphatidylinositol 3-kinase (PI3K)-3-phosphoinositide-dependent protein kinase-1 (PDK1) and mTor-dependent pathways. Upstream regulators of S6K, such as PDK1 and protein kinase B (PKB/Akt), are recruited to the membrane via their pleckstrin homology (PH) or protein-protein interaction domains. However, the mechanism of integration of S6K into a multi-enzyme complex around activated receptor tyrosine kinases is not clear. In the present study, we describe a specific interaction between S6K with receptor tyrosine kinases, such as platelet-derived growth factor receptor (PDGFR). The interaction with PDGFR is mediated via the kinase or the kinase extension domain of S6K. Complex formation is inducible by growth factors and leads to S6K tyrosine phosphorylation. Using PDGFR mutants, we have shown that the phosphorylation is exerted via a PDGFR-src pathway. Furthermore, src kinase phosphorylates and coimmunoprecipitates with S6K in vivo. Inhibitors towards tyrosine kinases, such as genistein and PP1, or src-specific SU6656, but not PI3K and mTor inhibitors, lead to a reduction in tyrosine phosphorylation of S6K. In addition, we mapped the sites of tyrosine phosphorylation in S6K1 and S6K2 to Y39 and Y45, respectively. Mutational and immunofluorescent analysis indicated that phosphorylation of S6Ks at these sites does not affect their activity or subcellular localization. Our data indicate that S6 kinase is recruited into a complex with RTKs and src and becomes phosphorylated on tyrosine/s in response to PDGF or serum.

Src family tyrosine kinases differentially modulate exocytosis from rat brain nerve terminals

We have studied the role of src family tyrosine kinases in regulating synaptic transmitter release from rat brain synaptosomes by using two assays that measure different aspects of synaptic vesicle exocytosis: glutamate release (that directly measures exocytosis of vesicle contents) and release of FM 2-10 styryl dye (that is proportional to the time the synaptic vesicle is fused to the plasma membrane). Depolarisation was induced by KCl (30 mM) or 4-aminopyridine (4AP: 0.3mM) to induce release by full fusion (FF) exocytosis, or by 1 mM 4AP to induce release by both FF and kiss-and-run (KR)-like exocytosis. The src family selective inhibitor, PP1 (10 microM), increased KCl and 0.3 mM 4AP-evoked Ca2+ -dependent release of glutamate, but had little effect upon exocytosis evoked by 1mM 4AP. PP1 did not affect the release of FM 2-10 under any of the depolarisation conditions used. PP1 also had no effect on overall intracellular calcium levels, as measured by FURA2, suggesting that the effects of the inhibitor are downstream of calcium entry. At the same concentration the inactive analogue of this compound, PP3, had no effect on any measure. Immunoblotting with an antibody to phosphotyrosine revealed that phosphorylation of many synaptosomal proteins was reduced by PP1. The immunoreactivity of three protein bands increased upon depolarisation and this increase was blocked by PP1. Phosphorylation of src at tyrosine-416 was reduced by PP1 but changes in its phosphorylation did not correlate with the effects of PP1 on release. These results suggest one or more members of the src family of tyrosine kinases is a negative regulator of the KR mode of exocytosis in synaptosomes, perhaps by tonically inhibiting KR under normal stimulation conditions.

Src Activation Is Not Necessary for Transforming Growth Factor (TGF)-β-mediated Epithelial to Mesenchymal Transitions (EMT) in Mammary Epithelial Cells

Epithelial to mesenchymal transitions (EMTs) are key events during embryonic development and cancer progression. It has been proposed that Src plays a major role in some EMT models, as shown by the overexpression of viral Src (v-Src) in epithelial cells. It is clear that Src family kinases can regulate the integrity of both adherens junctions and focal adhesions; however, their significance in EMT, especially in the physiological context, remains to be elucidated. Here we showed that Src is activated in transforming growth factor-beta1 (TGF-beta1)-mediated EMT in mammary epithelial cells and that the Src family kinase inhibitor, PP1, prevents EMT. However, neither a more specific Src family kinase inhibitor, SU6656, nor a dominant-negative Src inhibited TGF-beta1-mediated EMT, leading us to speculate that Src activation is not an essential component of TGF-beta1-mediated EMT. Unexpectedly, PP1 prevented Smad2/3 activation by TGF-beta1, whereas SU6656 did not. Most interestingly, an in vitro kinase assay showed that PP1 strongly inhibited the TGF-beta receptor type I, and to a lesser extent, the TGF-beta receptor type II. Taken together, our data indicated that PP1 interferes with TGF-beta1-mediated EMT not by inhibiting Src family kinases but by inhibiting the Smad pathway via a direct inhibition of TGF-beta receptor kinase activity.

Growth factors induce differential phosphorylation profiles of the Hrs-STAM complex: a common node in signalling networks with signal-specific properties

Hrs (hepatocyte growth factor-regulated tyrosine kinase substrate) and STAM (signal-transducing adaptor molecule) form a heterodimeric complex that associates with endosomal membranes and is tyrosine-phosphorylated in response to a variety of growth factors including EGF (epidermal growth factor), HGF (hepatocyte growth factor) and PDGF (platelet-derived growth factor). Phosphorylation of the Hrs-STAM complex requires receptor endocytosis. We show that an intact UIM (ubiquitin interaction motif) within Hrs is a conserved requirement for Hrs phosphorylation downstream of both EGF and HGF stimulations. Consistent with this, expression of a dominant-negative form of the E3 ubiquitin ligase, c-Cbl, inhibits EGF- and HGF-dependent Hrs phosphorylation. Despite this conservation, kinase inhibitor profiles using PP1 (4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine) and SU6656 indicate that distinct non-receptor tyrosine kinases couple EGF, HGF and PDGF stimulation with the tyrosine phosphorylation of the Hrs-STAM complex. Crucially, analysis with phospho-specific antibodies indicates that these kinases generate a signal-specific, combinatorial phosphorylation profile of the Hrs-STAM complex, with the potential of diversifying tyrosine kinase receptor signalling through a common element.

High glucose-induced apoptosis through store-operated calcium entry and calcineurin in human umbilical vein endothelial cells

Diabetes mellitus causes multiple cardiovascular complications. Previous studies have shown that prolonged exposure (96 h) of human umbilical vein endothelial cells (HUVECs) to hyperglycemia causes a significant increase in apoptosis. We report here that this increase in apoptosis is associated with an increase in Ca(2+) current (whole cell patch-clamp recorded) resulting from Ca(2+) entry mediated by store-operated channels (SOCs). The number of apoptotic cells after prolonged high glucose (HG, 30 mmol/L) exposure was significantly reduced in the presence of the SOC inhibitor 2-APB or of La(3+). A marked increase (approximately 80%) in Ca(2+)-dependent calcineurin (CN-A) phosphatase activity also occurred after prolonged HG exposure. Prolonged HG exposure-induced increase in CN-A activity was prevented by 2-APB, and selective CN-A phosphatase inhibition by FK506 or calmodulin inhibition by calmidazolium decreased HG-induced apoptosis. Blocking hydrogen peroxide production using catalase or inhibiting the tyrosine kinase pp60(src) during prolonged exposure to HG, resulted in a marked decrease in apoptosis and was further associated with a significant reduction in CN-A phosphatase activity. The results demonstrate a significant role for Ca(2+) entry in HG-induced apoptosis in HUVECs, and suggest that this role is mediated via H(2)O(2) generation and the action of the Ca(2+)-activated protein phosphatase calcineurin.

High Affinity Targets of Protein Kinase Inhibitors Have Similar Residues at the Positions Energetically Important for Binding

Inhibition of protein kinase activity is a focus of intense drug discovery efforts in several therapeutic areas. Major challenges facing the field include understanding of the factors determining the selectivity of kinase inhibitors and the development of compounds with the desired selectivity profile. Here, we report the analysis of sequence variability among high and low affinity targets of eight different small molecule kinase inhibitors (BIRB796, Tarceva, NU6102, Gleevec, SB203580, balanol, H89, PP1). It is observed that all high affinity targets of each inhibitor are found among a relatively small number of kinases, which have similar residues at the specific positions important for binding. The findings are highly statistically significant, and allow one to exclude the majority of kinases in a genome from a list of likely targets for an inhibitor. The findings have implications for the design of novel inhibitors with a desired selectivity profile (e.g. targeted at multiple kinases), the discovery of new targets for kinase inhibitor drugs, comparative analysis of different in vivo models, and the design of "a-la-carte" chemical libraries tailored for individual kinases.

E3B1, a human homologue of the mouse gene product Abi-1, sensitizes activation of Rap1 in response to epidermal growth factor

E3B1, a human homologue of the mouse gene product Abi-1, has been implicated in growth-factor-mediated regulation of the small GTPases p21Ras and Rac. E3b1 is a regulator of Rac because it can form a complex with Sos-1 and eps8, and such a Sos-1-e3B1-eps8 complex serves as a guanine nucleotide exchange factor for Rac. In the present study, we found that overexpression of e3B1 in NIH3T3/EGFR cells sensitized EGF-induced activation of Rac1, whereas it had no impact on EGF-induced activation of p21Ras. Remarkably, we found that EGF-induced activation of the p21Ras-related GTPase Rap1 was also sensitized in NIH3T3/EGFR-e3B1 cells. Thus, in NIH3T3/EGFR-e3B1 cells, maximal EGF-induced activation of Rap1 occurs with a dose of EGF much lower than in NIH3T3/EGFR cells. We also report that overexpression of e3B1 in NIH3T3/EGFR cells renders EGF-induced activation of Rap1 completely dependent on Src tyrosine kinases but not on c-Abl. However, EGF-induced tyrosine phosphorylation of the Rap GEF C3G occurred regardless of whether e3B1 was overexpressed or not, and this did not involve Src tyrosine kinases. Accordingly, we propose that overexpression of e3B1 in NIH3T3/EGFR cells leads to mobilization of Src tyrosine kinases that participate in EGF-induced activation of Rap1 and inhibition of cell proliferation.

Focal adhesion kinase signaling regulates cardiogenesis of embryonic stem cells

The signaling steps that induce cardiac differentiation in embryonic stem (ES) cells are incompletely understood. We examined the effect of adhesion signaling including Src and focal adhesion kinase (FAK) on cardiogenesis in mouse ES cells using alpha-myosin heavy chain promoter-driven enhanced green fluorescent protein or luciferase as reporters. Cardiac transcription factors including Nkx2.5 and Tbx5 mRNA were first expressed at day 4 in hanging drop embryoid bodies, and adhesion of embryoid bodies to surfaces at or before that day strongly inhibited differentiation of ES cells to cardiomyocytes. Since adhesion signaling could suppress cardiogenesis through Src kinases, embryoid bodies were exposed to the small molecule PP2, known as a Src family kinase inhibitor. PP2 during embryoid body adhesion dramatically increased cardiomyocyte differentiation and decreased mRNA expression of neuronal cellular adhesion molecule and alpha-fetoprotein, neuroectodermal, and endodermal markers, respectively. Surprisingly, although there was an interaction between Src and FAK in cardiogenesis, the procardiogenic effect of PP2 appeared incompletely explained by Src kinase inhibition, since another Src family kinase inhibitor, SU6656, failed to induce cardiogenesis. Instead, PP2 specifically inhibited adhesion-induced FAK phosphorylation. In ES cells stably expressing FAK-related nonkinase, which functions as a dominant negative FAK, cell migration from embryoid bodies was inhibited, whereas alpha-myosin heavy chain expression and myosin-stained cardiomyocytes were increased, suggesting that reducing cell motility may contribute to cardiogenesis. These data indicate that FAK is a key regulator of cardiogenesis in mouse ES cells and that FAK signaling within embryoid bodies can direct stem cell lineage commitment.

Redox regulation of platelet-derived-growth-factor-receptor: Role of NADPH-oxidase and c-Src tyrosine kinase

This study identifies some early events contributing to the redox regulation of platelet-derived growth factor receptor (PDGFr) activation and its signalling in NIH3T3 fibroblasts. We demonstrate for the first time that the redox regulation of PDGFr tyrosine autophosphorylation and its signalling are related to NADPH oxidase activity through protein kinase C (PKC) and phosphoinositide-3-kinase (PI3K) activation and H2O2 production. This event is also essential for complete PDGF-induced activation of c-Src kinase by Tyr416 phosphorylation, and the involvement of c-Src kinase on H2O2-induced PDGFr tyrosine phosphorylation is demonstrated, suggesting a role of this kinase on the redox regulation of PDGFr activation. Finally, it has been determined that not only PI3K activity, but also PKC activity, are related to NADPH oxidase activation due to PDGF stimulation in NIH3T3 cells, as it occurs in non-phagocyte cells. Therefore, we suggest a redox circuit whereby, upon PDGF stimulation, PKC, PI3K and NADPH oxidase activity contribute to complete c-Src kinase activation, thus promoting maximal phosphorylation and activation of PDGFr tyrosine phosphorylation.

Divergent roles of c-Src in controlling platelet-derived growth factor-dependent signaling in fibroblasts

The vast complexity of platelet-derived growth factor (PDGF)-induced downstream signaling pathways is well known, but the precise roles of critical players still elude us due to our lack of specific and temporal control over their activities. Accordingly, although Src family members are some of the better characterized effectors of PDGFbeta signaling, considerable controversy still surrounds their precise functions. To address these questions and limitations, we applied a chemical-genetic approach to study the role of c-Src at the cellular level, in defined signaling cascades; we also uncovered novel phosphorylation targets and defined its influence on transcriptional events. The spectacular control of c-Src on actin reorganization and chemotaxis was delineated by global substrate labeling and transcriptional analysis, revealing multiple cytoskeletal proteins and chemotaxis promoting genes to be under c-Src control. Additionally, this tool revealed the contrasting roles of c-Src in controlling DNA synthesis, where it transmits conflicting inputs via the phosphatidylinositol 3 kinase and Ras pathways. Finally, this study reveals a mechanism by which Src family kinases may control PDGF-mediated responses both at transcriptional and translational levels.

Modulation of cell adhesion molecules in various epithelial cell lines after treatment with PP2

Regulation and expression of E-cadherin and other adhesion molecules were evaluated after exposure to a selective inhibitor of the Src family of tyrosine kinases and inducer of E-cadherin, PP2. E-cadherin is located within the intercellular junction, and it is involved in the management of paracellular permeability of various epithelial barriers in the body. Epithelial cell lines HCT-116, HT29, Caco-2, LS174T, and ARPE-19 were examined for morphological, functional, protein, and mRNA changes following 20 microM PP2 treatment. PP2 treatment caused cell clustering in Caco-2, HT29, and HCT-116 cells. E-cadherin also redistributed to the points of cell contact in Caco-2 cells. These changes suggest increased E-cadherin-dependent cell adhesion. Studies evaluating transepithelial electrical resistance, an established measurement of paracellular permeability, displayed increases in resistance for the Caco-2 cells following PP2 treatment, which correlates with our microscopy data. In addition, E-cadherin protein levels increased for all cells except HCT-116. ARPE-19 cells did not express E-cadherin at the protein or mRNA level. Expression of adhesion molecules varied for the cell lines, and only Claudin 3 mRNA expression was significantly increased in the three intestinal cell lines treated with PP2. Overall, our data suggest that E-cadherin is positively regulated by inhibition of Src tyrosine kinases at the functional and protein expression levels within these epithelial cell lines.

Ca2+-independent activation of Bruton's tyrosine kinase is required for store-mediated Ca2+ entry in human platelets

Store-mediated Ca(2+) entry (SMCE), which is rapidly activated by depletion of the intracellular Ca(2+) stores, is a major mechanism for Ca(2+) influx. Several studies have involved tyrosine kinases in the activation of SMCE, such as pp60(src), although at present those involved in the early activation steps are unknown. Here we report the involvement of Bruton's tyrosine kinase (Btk) in the early stages of SMCE in human platelets. Cell treatment with thrombin or thapsigargin (TG) plus ionomycin (Iono) results in rapid activation of Btk, which was independent of rise in intracellular Ca(2+) concentration ([Ca(2+)](i)) but dependent on H(2)O(2) generation. Platelet treatment with Btk inhibitors, LFM-A13 or terreic acid, significantly reduced TG+Iono- and thrombin-evoked SMCE. Btk was rapidly activated by addition of low concentrations of H(2)O(2), whose effect on Ca(2+) entry was prevented by Btk inhibitors. Our results indicate that pp60(src) and Btk co-immunoprecipitate after platelet stimulation with TG+Iono, thrombin or H(2)O(2). In addition, we have found that LFM-A13 impaired actin filament reorganization after store depletion and agonist-induced activation of pp60(src), while the inhibitor of pp60(src), a protein that requires actin reorganization for its activation, did not modify Btk activation, suggesting that Btk is upstream of pp60(src). We propose a role for Btk in the early steps of activation of SMCE in human platelets.

Lateral hypothalamic signaling mechanisms underlying feeding stimulation: differential contributions of Src family tyrosine kinases to feeding triggered either by NMDA injection or by food deprivation

In rats, feeding can be triggered experimentally using many approaches. Included among these are (1) food deprivation and (2) acute microinjection of the neurotransmitter l-glutamate (Glu) or its receptor agonist NMDA into the lateral hypothalamic area (LHA). Under both paradigms, the NMDA receptor (NMDA-R) within the LHA appears critically involved in transferring signals encoded by Glu to stimulate feeding. However, the intracellular mechanisms underlying this signal transfer are unknown. Because protein-tyrosine kinases (PTKs) participate in NMDA-R signaling mechanisms, we determined PTK involvement in LHA mechanisms underlying both types of feeding stimulation through food intake and biochemical measurements. LHA injections of PTK inhibitors significantly suppressed feeding elicited by LHA NMDA injection (up to 69%) but only mildly suppressed deprivation feeding (24%), suggesting that PTKs may be less critical for signals underlying this feeding behavior. Conversely, food deprivation but not NMDA injection produced marked increases in apparent activity for Src PTKs and in the expression of Pyk2, an Src-activating PTK. When considered together, the behavioral and biochemical results demonstrate that, although it is easier to suppress NMDA-elicited feeding by PTK inhibitors, food deprivation readily drives PTK activity in vivo. The latter result may reflect greater PTK recruitment by neurotransmitter receptors, distinct from the NMDA-R, that are activated during deprivation-elicited but not NMDA-elicited feeding. These results also demonstrate how the use of only one feeding stimulation paradigm may fail to reveal the true contributions of signaling molecules to pathways underlying feeding behavior in vivo.

Characterization of a conserved structural determinant controlling protein kinase sensitivity to selective inhibitors

Some protein kinases are known to acquire resistance to selective small molecule inhibitors upon mutation of a conserved threonine at the ATP binding site to a larger residue. Here, we performed a comprehensive mutational analysis of this structural element and determined the cellular sensitivities of several disease-relevant tyrosine kinases against various inhibitors. Mutant kinases possessing a larger side chain at the critical site showed resistance to most compounds tested, such as ZD1839, PP1, AG1296, STI571, and a pyrido[2,3-d]pyrimidine inhibitor. In contrast, indolinones affected both wild-type and mutant kinases with similar potencies. Resistant mutants were established for pharmacological analysis of betaPDGF receptor-mediated signaling and allowed the generation of a drug-inducible system of cellular Src kinase activity. Our data establish a conserved structural determinant of protein kinase sensitivity relevant for both signal transduction research and drug development.

Identifying the binding mode of a molecular scaffold

We describe a method for docking of a scaffold-based series and present its advantages over docking of individual ligands, for determining the binding mode of a molecular scaffold in a binding site. The method has been applied to eight different scaffolds of protein kinase inhibitors (PKI). A single analog of each of these eight scaffolds was previously crystallized with different protein kinases. We have used FlexX to dock a set of molecules that share the same scaffold, rather than docking a single molecule. The main mode of binding is determined by the mode of binding of the largest cluster among the docked molecules that share a scaffold. Clustering is based on our 'nearest single neighbor' method [J. Chem. Inf. Comput. Sci., 43 (2003) 208-217]. Additional criteria are applied in those cases in which more than one significant binding mode is found. Using the proposed method, most of the crystallographic binding modes of these scaffolds were reconstructed. Alternative modes, that have not been detected yet by experiments, could also be identified. The method was applied to predict the binding mode of an additional molecular scaffold that was not yet reported and the predicted binding mode has been found to be very similar to experimental results for a closely related scaffold. We suggest that this approach be used as a virtual screening tool for scaffold-based design processes.

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.

Human bronchial smooth muscle cell proliferation via thromboxane A2 receptor

Thromboxane A2 receptor (TP) mediates bronchial smooth muscle cell (BSMC) contraction, airway hyperresponsiveness, and airway inflammation in patients with asthma. In the present study, a pathogenic role of TP activation in airway remodeling was examined using primary cultures of human BSMC. A TP agonist, I-BOP, concentration-dependently enhanced not only bromodeoxyuridine (BrdU) uptake but also cell proliferation of BSMC. A TP-selective antagonist, AA-2414, blocked the effects of I-BOP on both BrdU uptake and cell proliferation. I-BOP-induced BrdU uptake was significantly blocked by two non-selective tyrosine kinase inhibitors, genistein and herbimycin A, or a Src family tyrosine kinase inhibitor, PP2, but not by an inhibitor of epidermal growth factor (EGF) receptor-associated tyrosine kinase, AG1478. In conclusion, TP receptor activation causes DNA synthesis and cell proliferation of human BSMC by activating tyrosine kinases including Src, but not by EGF receptor transactivation.

Molecular interdiction of Src-family kinase signaling in hematopoietic cells

The ability of Src-family kinases (SFKs) to mediate signaling from cell surface receptors in hematopoietic cells is a function of their catalytic activity, location and binding partners. Kinase activity is regulated in the cell by kinases and phosphatases that alter the state of phosphorylation of key tyrosine residues and by protein binding partners that stabilize the kinase in active or inactive conformations or localize the enzyme to specific subcellular or submembrane domains. Kinase activity and function can be modulated experimentally through the use of small molecule inhibitors designed to directly target catalytic or binding domains or regulate the location of the protein by altering its state of acylation.

Activation of diacylglycerol kinase α is required for VEGF-induced angiogenic signaling in vitro

Vascular endothelial growth factor-A (VEGF-A) promotes angiogenesis by stimulating migration, proliferation and organization of endothelium, through the activation of signaling pathways involving Src tyrosine kinase. As we had previously shown that Src-mediated activation of diacylglycerol kinase-alpha (Dgk-alpha) is required for hepatocytes growth factor-stimulated cell migration, we asked whether Dgk-alpha is involved in the transduction of angiogenic signaling. In PAE-KDR cells, an endothelial-derived cell line expressing VEGFR-2, VEGF-A165, stimulates the enzymatic activity of Dgk-alpha: activation is inhibited by R59949, an isoform-specific Dgk inhibitor, and is dependent on Src tyrosine kinase, with which Dgk-alpha forms a complex. Conversely in HUVEC, VEGF-A165-induced activation of Dgk is only partially sensitive to R59949, suggesting that also other isoforms may be activated, albeit still dependent on Src tyrosine kinase. Specific inhibition of Dgk-alpha, obtained in both cells by R59949 and in PAE-KDR by expression of Dgk-alpha dominant-negative mutant, impairs VEGF-A165-dependent chemotaxis, proliferation and in vitro angiogenesis. In addition, in HUVEC, specific downregulation of Dgk-alpha by siRNA impairs in vitro angiogenesis on matrigel, further suggesting the requirement for Dgk-alpha in angiogenic signaling in HUVEC. Thus, we propose that activation of Dgk-alpha generates a signal essential for both proliferative and migratory response to VEGF-A165, suggesting that it may constitute a novel pharmacological target for angiogenesis control.

Pervanadate-induced reverse translocation and tyrosine phosphorylation of phorbol ester-stimulated protein kinase C betaII are mediated by Src-family tyrosine kinases in porcine neutrophils

Protein kinase C (PKC), upon activation, translocates from the cytosol to the plasma membrane. Phorbol 12-myristate 13-acetate (PMA), a potent PKC activator, is known to induce irreversible translocation of PKC to the plasma membrane, in contrast to the reversible translocation resulting from physiological stimuli and subsequent rapid return to the cytosol (reverse translocation). However, we have previously shown that tyrosine phosphatase (PTPase) inhibitors induce reverse translocation of PMA-stimulated PKCbetaII in porcine polymorphonuclear leukocytes (PMNs). In the present study, we showed that pervanadate, a potent PTPase inhibitor, also induces tyrosine phosphorylation of PMA-stimulated PKCbetaII in porcine PMNs. Furthermore, PP2, a specific inhibitor of Src-family tyrosine kinases (PTKs), was found to inhibit both pervanadate-induced reverse translocation and tyrosine phosphorylation of PMA-stimulated PKCbetaII, suggesting that these two pervanadate-induced responses are mediated by Src-family PTKs. Our findings provide novel insight into the relationship between the subcellular localization and tyrosine phosphorylation of PKC.

Inhibitors of JAKs/STATs and the kinases: a possible new cluster of drugs

JAK(s)/STAT(s) relay cytokine signals through tyrosine site-specific phosphorylation of the proteins involved in cellular responses for the activation and proliferation of bone marrow-derived cells. In recent years, the constitutive or elevated expression of JAK/STAT has been found in cancer cells and oncogene transfected cells, and has been shown to be involved in the immune rejection of allografts and the inflammatory processes of autoimmune diseases. This review discusses the strategies for screening and rational design of selective, potent JAK/STAT and kinase inhibitors that are either ATP-competitive or non-ATP competitive, naturally derived or synthetic, as well as other unique inhibitors and analogues for different therapeutic indications.

Imatinib-mesylate blocks recombinant T-type calcium channels expressed in human embryonic kidney-293 cells by a protein tyrosine kinase-independent mechanism

The 2-phenylaminopyrimidine derivative imatinib-mesylate, a powerful protein tyrosine kinase (PTK) inhibitor that targets abl, c-kit, and the platelet-derived growth factor receptors, is rapidly gaining a relevant role in the treatment of several types of neoplasms. Because first generation PTK inhibitors affect the activity of a large number of voltage-dependent ion channels, the present study explored the possibility that imatinib-mesylate could interfere with the activity of T-type channels, a class of voltage-dependent Ca2+ channels that take part in the chain of events elicited by PTK activation. The effect of the drug on T-type channel activity was examined using the whole-cell patch-clamp technique with Ba2+ (10 mM) as the permeant ion in human embryonic kidney-293 cells, stably expressing the rat Ca(V)3.3 channels. Imatinib-mesylate concentrations, ranging from 30 to 300 microM, reversibly decreased Ca(V)3.3 current amplitude with an IC(50) value of 56.9 microM. By contrast, when imatinib-mesylate (500 microM) was intracellularly dialyzed with the pipette solution, no reduction in Ba2+ current density was observed. The 2-phenylaminopyrimidine derivative modified neither the voltage dependence of activation nor the steady-state inactivation of Ca(V)3.3 channels. The decrease in extracellular Ba2+ concentration from 10 to 2 mM and the substitution of Ca2+ for Ba2+ increased the extent of 30 microM imatinib-mesylate-induced percentage of channel blockade from 25.9 +/- 2.4 to 36.3 +/- 0.9% in 2 mM Ba2+ and 44.2 +/- 2.3% in 2 mM Ca2+. In conclusion, imatinib-mesylate blocked the cloned Ca(V)3.3 channels by a PTK-independent mechanism. Specifically, the drug did not affect the activation or the inactivation of the channel but interfered with the ion permeation process.

Hydrogen Peroxide Generation Induces pp60 Activation in Human Platelets

Reactive oxygen species, such as H2O2, have been recognized as intracellular messengers involved in several cell functions. Here we report the activation of the tyrosine kinase pp60(src) by H2O2, a mechanism required for the activation of store-mediated Ca2+ entry (SMCE) in human platelets. Treatment of platelets with H2O2 resulted in a time- and concentration-dependent activation of pp60(src). Incubation with GF 109203X, a protein kinase C (PKC) inhibitor, prevented H2O2-induced pp60(src) activation. In contrast, dimethyl-BAPTA loading did not affect this response, suggesting that activation of pp60(src) by H2O2 is independent of increases in [Ca2+](i). Cytochalasin D, an inhibitor of actin polymerization, significantly reduced H2O2-induced pp60(src) activation. We found that platelet stimulation with thapsigargin (TG) plus ionomycin (Iono) or thrombin induced rapid H2O2 production, a mechanism independent of elevations in [Ca2+](i). Treatment of platelets with catalase attenuated TG plus Iono- and thrombin-induced activation of pp60(src). In addition, catalase as well as the pp60(src) inhibitor, PP1, reduced both the activation of SMCE and the coupling between the hTrp1 and the IP(3)R type II without having any effect on the maintenance of SMCE. Consistent with the role of PKC in the activation of pp60(src) by H2O2, the PKC inhibitors GF 109202X and Ro-31-8220 were found to reduced SMCE in platelets. This study suggests that platelet activation with TG plus Iono or thrombin is associated with H2O2 production, which acts as a second messenger by stimulating pp60(src) by a PKC-dependent pathway and is involved in the activation of SMCE in these cells.

Pyrazolo Pyrimidine-Type Inhibitors of Src Family Tyrosine Kinases Promote Ovarian Steroid-Induced Differentiation of Human Endometrial Stromal Cells In Vitro1

Reversible protein tyrosine phosphorylation, coordinately controlled by protein tyrosine kinases and phosphatases, is a critical element in signal transduction pathways regulating a wide variety of biological processes, including cell growth, differentiation, and tumorigenesis. We have previously reported that c-Src belonging to the Src family tyrosine kinase (SFK) becomes dephosphorylated at tyrosine 530 (Y530) and thereby activated during progestin-induced differentiation of human endometrial stromal cells (i.e., decidualization). In this study, to elucidate the role of decidual c-Src activation, we examined whether 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1) and 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), both potent and selective SFK inhibitors, affected the ovarian steroid-induced decidualization in vitro. Unexpectedly, PP1 paradoxically increased the kinase activity of decidual c-Src together with dephosphorylation of Y530 in the presence of ovarian steroids. Concomitantly, PP1 enhanced morphological and functional decidualization, as determined by induction of decidualization markers, such as insulin-like growth factor binding protein-1 and prolactin. PP2 also advanced decidualization along with up-regulation of the active form of c-Src whose Y-530 was dephosphorylated. In contrast to PP1 and PP2, herbimycin A, a tyrosine kinase inhibitor with less specificity for SFKs, showed little enhancing effect on the expression of both IGFBP-1 and active c-Src. These results suggest that SFKs, including c-Src, may play a significant role in stromal cell differentiation, providing a clue for a possible therapeutic strategy to modulate endometrial function by targeting signaling pathway(s) involving SFKs.

Fibroblast growth factor receptor‐1 interacts with the T‐cell receptor signalling pathway

Fibroblast growth factor receptors are expressed by some T cells, and provide costimulation for these cells. Such receptors allow T cells to respond to fibroblast growth factors expressed in response to injury and inflammation and may provide a mechanism for 'context-dependent' responses to antigens within the local microenvironment. The mechanisms by which fibroblast growth factor receptors might interact with the TCR signalling pathway are not defined. Here we show that the TCR and fibroblast growth factor receptors co-localize during combined stimulation. Signalling via fibroblast growth factor receptors alone results in phosphorylation of Lck and induces nuclear translocation of nuclear factors of activated T cells. Combined stimulation via fibroblast growth factor receptors and the TCR synergistically enhances the activation of nuclear factors of activated T cells. The results suggest that peptide growth factors produced at sites of injury and inflammation can contribute to the outcome of T-cell encounters with antigen.

Reconstitution of Src-dependent phospholipase Cgamma phosphorylation and transient calcium release by using membrane rafts and cell-free extracts from Xenopus eggs

We reported previously that egg membrane rafts serve as a subcellular microdomain for sperm-dependent tyrosine kinase signaling in Xenopus fertilization. Moreover, we demonstrated that raft-associated Src tyrosine kinase was activated by sperm in vitro. Here we show that egg rafts incubated with sperm or hydrogen peroxide (H2O2) can promote Src-dependent phosphorylation of phospholipase Cgamma (PLCgamma) and transient calcium release in the extracts of unfertilized Xenopus eggs. In vivo egg activation by sperm or H2O2 also promotes tyrosine phosphorylation and raft-translocalization of PLCgamma. Immunodepletion of PLCgamma from the egg extracts inhibits the raft-dependent calcium release. Rafts prepared from H2O2-activated eggs also promote Src-dependent dephosphorylation of p42 mitogen-activated protein kinase and cell cycle transition from metaphase II to interphase in egg extracts. PLCgamma phosphorylation and calcium release in egg extracts can be promoted by rafts prepared from COS-7 cells expressing the Xenopus Src gene. These results demonstrate that the signaling events elicited by fertilization in Xenopus eggs can be reconstituted in vitro. The development of such experimental platforms will allow us to dissect the molecular mechanism of sperm-dependent activation of raft-associated Src and subsequent up-regulation of PLCgamma and egg activation machinery in Xenopus eggs.