Family Kinases (family + kinase)

Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of Family Kinases

  • src family kinase


  • Selected Abstracts


    Combination of Clk family kinase and SRp75 modulates alternative splicing of Adenovirus E1A

    GENES TO CELLS, Issue 3 2008
    Jun-ichiro Yomoda
    SR proteins are non-snRNP splicing factors harbouring a domain rich in Arg-Ser repeats, which are extensively phosphorylated by several kinases. We performed a comparative study of different SR kinases, including SRPK, Clk, PRP4 and DYRK, and found that only Clks efficiently altered 5, splice site selection of Adenovirus E1A. The phosphorylation state of SR proteins was examined using a phospho-SR specific antibody mAb1H4 and a 75 kDa protein was most evidently hyperphosphorylated by Clks. Administration of TG003, a specific inhibitor for the Clk family members, specifically and rapidly induced dephosphorylation of 75 kDa SR protein. Imaging with mRFP-SRp75 in living cells revealed that its nuclear distribution was rapidly altered upon inhibition of the Clk activity by TG003. Co-transfection experiments demonstrated that HA-tagged SRp75 was hyperphosphorylated by Clk family members, but not by other SR kinases. These results indicate that Clks specifically hyperphosphorylate SRp75. Furthermore, SRp75 over-expression promoted the selection of 12S 5, splice site in E1A pre-mRNA, which is stimulated by co-expression of Clks. These results suggest that the specific combination of SR protein and SR kinase plays a distinct role in alternative splicing through dynamic balance of phosphorylation. [source]


    Human remyelination promoting antibody inhibits apoptotic signaling and differentiation through Lyn kinase in primary rat oligodendrocytes

    GLIA, Issue 15 2010
    J. Watzlawik
    Abstract Purpose: Human remyelination promoting IgM mAbs target oligodendrocytes (OLs) and function in animal models of multiple sclerosis (MS). However, their mechanism of action is unknown. This study seeks to identify the cellular mechanism of action of a recombinant human IgM on OL survival. Methods: Binding of rHIgM22 to the surface of rat OLs was studied by co-localization with various markers. RHIgM22-mediated effects on apoptotic signaling in OLs, differentiation markers, and signaling molecules were detected by Western blotting and immunoprecipitation. Results: RHIgM22 co-localized with integrin ,3 but not other integrin ,-chains in OLs. Downstream of integrin ,3 we identified Src family kinase (SFK) Lyn as a key player of rHIgM22-mediated actions in OLs. Lyn immunoprecipitated in a complex together with integrin ,v,3 and PDGF,R. Lyn expression was 9-fold up-regulated and Lyn activation was 3-fold higher inrHIgM22-treated OL cultures compared with controls. RHIgM22 inhibited apoptotic signaling by greater than 10-fold reduction of caspase-3 and capsase-9 cleavage and reduced by 4-fold expression of differentiation markers MBP and MOG in OLs. SFK inhibitors PP2 and SU6656 inhibited Lyn activity and restored caspase-cleavage in OLs. A human IgM that did not promote remyelination and medium wereused as controls. Conclusions: rHIgM22 prevented apoptotic signaling andinhibited OL differentiation by Lyn implying thatIgM-mediated remyelination is due toprotection of OPC and OLs rather than promotion of OPC differentiation. 2010 Wiley-Liss, Inc. [source]


    Lysophosphatidic acid induces ovarian cancer cell dispersal by activating Fyn kinase associated with p120-catenin

    INTERNATIONAL JOURNAL OF CANCER, Issue 4 2008
    Ruby Yun-Ju Huang
    Abstract Lysophosphatidic acid (LPA), known as the "ovarian cancer activating factor," is a natural phospholipid involved in important biological functions, such as cell proliferation, wound healing and neurite retraction. LPA causes colony dispersal in various carcinoma cell lines by inducing morphological changes, including membrane ruffling, lamellipodia formation, cell,cell dissociation and single cell migration. However, its effects on cell,cell dissociation and cell,cell adhesion of ovarian cancer cells have not been studied. In our study, we showed that LPA induced sequential events of intercellular junction dispersal and "half-junction" formation in ovarian cancer SKOV3 cells and that Src-family kinases were involved in both processes, since the effects were abolished by the selective tyrosine kinase inhibitor PP2. LPA induced rapid and transient activation of Src family kinases, which were recruited to cell,cell junctions by increasing the association with the adherens junction protein p120-catenin. We identified the Src family kinase, Fyn, as the key component associated with p120-catenin after LPA stimulation in SKOV3 cells. Our study provides evidence that LPA induces junction dispersal in ovarian cancer SKOV3 cells by activating the Src family kinase Fyn and increasing its association with p120-catenin at the cell,cell junction. 2008 Wiley-Liss, Inc. [source]


    Structural characterization of Lyn-SH3 domain in complex with a herpesviral protein reveals an extended recognition motif that enhances binding affinity

    PROTEIN SCIENCE, Issue 10 2005
    Finn Bauer
    Abstract The Src homology 3 (SH3) domain of the Src family kinase Lyn binds to the herpesviral tyrosine kinase interacting protein (Tip) more than one order of magnitude stronger than other closely related members of the Src family. In order to identify the molecular basis for high-affinity binding, the structure of free and Tip-bound Lyn-SH3 was determined by NMR spectroscopy. Tip forms additional contacts outside its classical proline-rich recognition motif and, in particular, a strictly conserved leucine (L186) of the C-terminally adjacent sequence stretch packs into a hydrophobic pocket on the Lyn surface. Although the existence of this pocket is no unique property of Lyn-SH3, Lyn is the only Src family kinase that contains an additional aromatic residue (H41) in the n-Src loop as part of this pocket. H41 covers L186 of Tip by forming tight hydrophobic contacts, and model calculations suggest that the increase in binding affinity compared with other SH3 domains can mainly be attributed to these additional interactions. These findings indicate that this pocket can mediate specificity even between otherwise closely related SH3 domains. [source]


    GDNF hyperalgesia is mediated by PLC,, MAPK/ERK, PI3K, CDK5 and Src family kinase signaling and dependent on the IB4-binding protein versican

    EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2008
    Oliver Bogen
    Abstract The function of the isolectin B4 (IB4+)-binding and GDNF-dependent Ret (Ret+)-expressing non-peptidergic subpopulation of nociceptors remain poorly understood. We demonstrate that acute administration of GDNF sensitizes nociceptors and produces mechanical hyperalgesia in the rat. Intrathecal IB4,saporin, a selective toxin for IB4+/Ret+ -nociceptors, attenuates GDNF but not NGF hyperalgesia. Conversely, intrathecal antisense to Trk A attenuated NGF but not GDNF hyperalgesia. Intrathecal administration of antisense oligodeoxynucleotides targeting mRNA for versican, the molecule that renders the Ret-expressing nociceptors IB4-positive (+), also attenuated GDNF but not NGF hyperalgesia, as did ADAMTS-4, a matrix metalloprotease known to degrade versican. Finally, inhibitors for all five signaling pathways known to be activated by GDNF at GFR,1/Ret: PLC,, CDK5, PI3K, MAPK/ERK and Src family kinases, attenuated GDNF hyperalgesia. Our results demonstrate a role of the non-peptidergic nociceptors in pain produced by the neurotrophin GDNF and suggest that the IB4-binding protein versican functions in the expression of this phenotype. [source]


    Regulation of NMDA receptor trafficking and function by striatal-enriched tyrosine phosphatase (STEP)

    EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2006
    Steven P. Braithwaite
    Abstract Regulation of N -methyl- d -aspartate (NMDA) receptors is critical for the normal functioning of the central nervous system. There must be precise mechanisms to allow for changes in receptor function required for learning and normal synaptic transmission, but within tight constraints to prevent pathology. Tyrosine phosphorylation is a major means by which NMDA receptors are regulated through the equilibrium between activity of Src family kinases and tyrosine phosphatases. Identification of NMDA receptor phosphatases has been difficult, the best candidate being striatal-enriched tyrosine phosphatase (STEP). Here we demonstrate that STEP is a critical regulator of NMDA receptors and reveal that the action of this tyrosine phosphatase controls the constitutive trafficking of NMDA receptors and leads to changes in NMDA receptor activity at the neuronal surface. We show that STEP binds directly to NMDA receptors in the absence of other synaptic proteins. The activity of STEP selectively affects the expression of NMDA receptors at the neuronal plasma membrane. The result of STEP's action upon the NMDA receptor affects the functional properties of the receptor and its downstream signaling. These effects are evident when STEP levels are chronically reduced, indicating that there is no redundancy amongst phosphatases to compensate for altered STEP function in the CNS. STEP may have evolved specifically to fill a pivotal role as the NMDA receptor phosphatase, having a distinct and restricted localization and compartmentalization, and unique activity towards the NMDA receptor and its signaling pathway. [source]


    Functional dissection of transformation by c-Src and v-Src

    GENES TO CELLS, Issue 1 2008
    Chitose Oneyama
    The c-src proto-oncogene product, c-Src, is frequently over-expressed and activated in various human malignant cancers, implicating a role for c-Src in cancer progression. To verify the role of c-Src, we analyzed the transforming ability of c-Src in mouse embryonic fibroblasts that lack Csk, a negative regulator of Src family kinases. Although Csk deficiency is not sufficient for cell transformation, c-Src over-expression induced characteristic transformed phenotypes including anchorage-independent growth and tumorigenecity. These phenotypes were dose-dependently inhibited by the re-expression of Csk, indicating that there is a certain threshold for c-Src transformation, which is determined by the c-Src : Csk ratio. In contrast to v-Src, c-Src induced the phosphorylation of a limited number of cellular proteins and elicited a restricted change in gene expression profiles. The activation of some critical targets for v-Src transformation, such as STAT3, was not significantly induced by c-Src transformation. Several genes that are involved in cancer progression, that is, cyclin D1 and HIF-1,, were induced by v-Src, but not by c-Src. Furthermore, v-Src tumors exhibited aggressive growth and extensive angiogenesis, while c-Src tumors grew more slowly accompanied by the induction of hematomas. These findings demonstrate that c-Src has the potential to induce cell transformation, but it requires coordination with an additional pathway(s) to promote tumor progression in vivo. [source]


    The Versatility of Helicobacter pylori CagA Effector Protein Functions: The Master Key Hypothesis

    HELICOBACTER, Issue 3 2010
    Steffen Backert
    Abstract Several bacterial pathogens inject virulence proteins into host target cells that are substrates of eukaryotic tyrosine kinases. One of the key examples is the Helicobacter pylori CagA effector protein which is translocated by a type-IV secretion system. Injected CagA becomes tyrosine-phosphorylated on EPIYA sequence motifs by Src and Abl family kinases. CagA then binds to and activates/inactivates multiple signaling proteins in a phosphorylation-dependent and phosphorylation-independent manner. A recent proteomic screen systematically identified eukaryotic binding partners of the EPIYA phosphorylation sites of CagA and similar sites in other bacterial effectors by high-resolution mass spectrometry. Individual phosphorylation sites recruited a surprisingly high number of interaction partners suggesting that each phosphorylation site can interfere with many downstream pathways. We now count 20 reported cellular binding partners of CagA, which represents the highest quantitiy among all yet known virulence-associated effector proteins in the microbial world. This complexity generates a highly remarkable and puzzling scenario. In addition, the first crystal structure of CagA provided us with new information on the function of this important virulence determinant. Here we review the recent advances in characterizing the multiple binding signaling activities of CagA. Injected CagA can act as a ,master key' that evolved the ability to highjack multiple host cell signalling cascades, which include the induction of membrane dynamics, actin-cytoskeletal rearrangements and the disruption of cell-to-cell junctions as well as proliferative, pro-inflammatory and anti-apoptotic nuclear responses. The discovery that different pathogens use this common strategy to subvert host cell functions suggests that more examples will emerge soon. [source]


    T-cell receptor proximal signaling via the Src-family kinases, Lck and Fyn, influences T-cell activation, differentiation, and tolerance

    IMMUNOLOGICAL REVIEWS, Issue 1 2009
    Robert J. Salmond
    Summary:, T-cell development in the thymus and activation of mature T cells in secondary lymphoid organs requires the ability of cells to respond appropriately to environmental signals at multiple stages of their development. The process of thymocyte selection insures a functional T-cell repertoire, while activation of naive peripheral T cells induces proliferation, gain of effector function, and, ultimately, long-lived T-cell memory. The T-cell immune response is initiated upon engagement of the T-cell receptor (TCR) and coreceptor, CD4 or CD8, by cognate antigen/major histocompatibility complexes presented by antigen-presenting cells. TCR/coreceptor engagement induces the activation of biochemical signaling pathways that, in combination with signals from costimulator molecules and cytokine receptors, direct the outcome of the response. Activation of the src- family kinases p56lck (Lck) and p59fyn (Fyn) is central to the initiation of TCR signaling pathways. This review focuses on our current understanding of the mechanisms by which these two proteins orchestrate T-cell function. [source]


    Lysophosphatidic acid induces ovarian cancer cell dispersal by activating Fyn kinase associated with p120-catenin

    INTERNATIONAL JOURNAL OF CANCER, Issue 4 2008
    Ruby Yun-Ju Huang
    Abstract Lysophosphatidic acid (LPA), known as the "ovarian cancer activating factor," is a natural phospholipid involved in important biological functions, such as cell proliferation, wound healing and neurite retraction. LPA causes colony dispersal in various carcinoma cell lines by inducing morphological changes, including membrane ruffling, lamellipodia formation, cell,cell dissociation and single cell migration. However, its effects on cell,cell dissociation and cell,cell adhesion of ovarian cancer cells have not been studied. In our study, we showed that LPA induced sequential events of intercellular junction dispersal and "half-junction" formation in ovarian cancer SKOV3 cells and that Src-family kinases were involved in both processes, since the effects were abolished by the selective tyrosine kinase inhibitor PP2. LPA induced rapid and transient activation of Src family kinases, which were recruited to cell,cell junctions by increasing the association with the adherens junction protein p120-catenin. We identified the Src family kinase, Fyn, as the key component associated with p120-catenin after LPA stimulation in SKOV3 cells. Our study provides evidence that LPA induces junction dispersal in ovarian cancer SKOV3 cells by activating the Src family kinase Fyn and increasing its association with p120-catenin at the cell,cell junction. 2008 Wiley-Liss, Inc. [source]


    Src and FAK mediate cell,matrix adhesion-dependent activation of met during transformation of breast epithelial cells

    JOURNAL OF CELLULAR BIOCHEMISTRY, Issue 6 2009
    Angela Y. Hui
    Abstract Cell,matrix adhesion has been shown to promote activation of the hepatocyte growth factor receptor, Met, in a ligand-independent manner. This process has been linked to transformation and tumorigenesis in a variety of cancer types. In the present report, we describe a key role of integrin signaling via the Src/FAK axis in the activation of Met in breast epithelial and carcinoma cells. Expression of an activated Src mutant in non-neoplastic breast epithelial cells or in carcinoma cells was found to increase phosphorylation of Met at regulatory tyrosines in the auto-activation loop domain, correlating with increased cell spreading and filopodia extensions. Furthermore, phosphorylated Met is complexed with ,1 integrins and is co-localized with vinculin and FAK at focal adhesions in epithelial cells expressing activated Src. Conversely, genetic or pharmacological inhibition of Src abrogates constitutive Met phosphorylation in carcinoma cells or epithelial cells expressing activated Src, and inhibits filopodia formation. Interestingly, Src-dependent phosphorylation of Met requires cell,matrix adhesion, as well as actin stress fiber assembly. Phosphorylation of FAK by Src is also required for Src-induced Met phosphorylation, emphasizing the importance of the Src/FAK signaling pathway. However, stimulation of Met phosphorylation by addition of exogenous HGF in epithelial cells is refractory to inhibition of Src family kinases, indicating that HGF-dependent and Src/integrin-dependent Met activation occur via distinct mechanisms. Together these findings demonstrate a novel mechanism by which the Src/FAK axis links signals from the integrin adhesion complex to promote Met activation in breast epithelial cells. J. Cell. Biochem. 107: 1168,1181, 2009. 2009 Wiley-Liss, Inc. [source]


    Bradykinin-induced p42/p44 MAPK phosphorylation and cell proliferation via Src, EGF receptors, and PI3-K/Akt in vascular smooth muscle cells

    JOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2005
    Chuen-Mao Yang
    In our previous study, bradykinin (BK) exerts its mitogenic effect through Ras/Raf/MEK/MAPK pathway in vascular smooth muscle cells (VSMCs). In addition to this pathway, the non-receptor tyrosine kinases (Src), EGF receptor (EGFR), and phosphatidylinositol 3-kinase (PI3-K) have been implicated in linking a variety of G-protein coupled receptors to MAPK cascades. Here, we investigated whether these different mechanisms participating in BK-induced activation of p42/p44 MAPK and cell proliferation in VSMCs. We initially observed that BK- and EGF-dependent activation of Src, EGFR, Akt, and p42/p44 MAPK and [3H]thymidine incorporation were mediated by Src and EGFR, because the Src inhibitor PP1 and EGFR kinase inhibitor AG1478 abrogated BK- and EGF-dependent effects. Inhibition of PI3-K by LY294002 attenuated BK-induced Akt and p42/p44 MAPK phosphorylation and [3H]thymidine incorporation, but had no effect on EGFR phosphorylation, suggesting that EGFR may be an upstream component of PI3-K/Akt and MAPK in these responses. This hypothesis was supported by the tranfection with dominant negative plasmids of p85 and Akt which significantly attenuated BK-induced Akt and p42/p44 MAPK phosphorylation. Pretreatment with U0126 (a MEK1/2 inhibitor) attenuated the p42/p44 MAPK phosphorylation and [3H]thymidine incorporation stimulated by BK, but had no effect on Akt activation. Moreover, BK-induced transactivation of EGFR and cell proliferation was blocked by matrix metalloproteinase inhibitor GM6001. These results suggest that, in VSMCs, the mechanism of BK-stimulated activation of p42/p44 MAPK and cell proliferation was mediated, at least in part, through activation of Src family kinases, EGFR transactivation, and PI3-K/Akt. Copyright 2004 Wiley-Liss, Inc. [source]


    Quinolinic acid modulates the activity of src family kinases in rat striatum: in vivo and in vitro studies

    JOURNAL OF NEUROCHEMISTRY, Issue 5 2006
    Alessio Metere
    Abstract Quinolinic acid (QA) has been shown to evoke neurotoxic events via NMDA receptor (NMDAR) overactivation and oxidative stress. NMDARs are particularly vulnerable to free radicals, which can modulate protein tyrosine kinase (PTK) and phosphotyrosine phosphatase (PTP) activities. The src family of tyrosine kinases are associated with the NMDAR complex and regulate NMDA channel function. Because QA is an NMDAR agonist as well as a pro-oxidant agent, we investigated whether it may affect the activity of PTKs and PTPs in vivo and in vitro. In synaptosomes prepared from striata dissected 15 min, 30 min or 15 days after bilateral injection of QA we observed modulation of the phosphotyrosine pattern; a significant decrease in PTP activity; and a sustained increase in c-src and lyn activity at 15 and 30 min after treatment with QA, followed by a decrease 2 weeks later. Striatal synaptosomes treated in vitro with QA showed time- and dose-dependent modulation of c-src and lyn kinase activities. Moreover, the nitric oxide synthase inhibitor NG -nitro- l -arginine-methyl ester, the NMDAR antagonist d -2-amino-5-phosphonovaleric acid and pyruvate suppressed the QA-induced modulation of c-src activity. These findings suggest a novel feature of QA in regulating src kinase activity through the formation of reactive radical species and/or NMDAR overactivation. [source]


    L -NAME reverses quinolinic acid-induced toxicity in rat corticostriatal slices: Involvement of src family kinases

    JOURNAL OF NEUROSCIENCE RESEARCH, Issue 12 2007
    Cinzia Mallozzi
    Abstract Quinolinic acid (QA) is an endogenous excitotoxin acting on N -methyl- d -aspartate receptors (NMDARs) that leads to the pathologic and neurochemical features similar to those observed in Huntington's disease (HD). The mechanism of QA toxicity also involves free radicals formation and oxidative stress. NMDARs are particularly vulnerable to the action of reactive oxygen species (ROS) and reactive nitrogen species (RNS) that can act as modulators of the activity of protein tyrosine kinases (PTKs) and phosphotyrosine phosphatases (PTPs). Because QA is able to activate neuronal nitric oxide synthase (nNOS) as well as to stimulate the NMDARs, we evaluated the effect of N,-Nitro- l -arginine-methyl ester (l -NAME), a selective nNOS inhibitor, on QA-induced neurotoxicity in rat corticostriatal slices. In electrophysiologic experiments we observed that slice perfusion with QA induced a strong reduction of field potential (FP) amplitude, followed by a partial recovery at the end of the QA washout. In the presence of l -NAME the recovery of FP amplitude was significantly increased with respect to QA alone. In synaptosomes, prepared from corticostriatal slices after the electrophysiologic recordings, we observed that l -NAME pre-incubation reversed the QA-mediated inhibitory effects on protein tyrosine phosphorylation pattern, c-src, lyn, and fyn kinase activities and tyrosine phosphorylation of NMDAR subunit NR2B, whereas the PTP activity was not recovered in the presence of l -NAME. These findings suggest that NO plays a key role in the molecular mechanisms of QA-mediated excitotoxicity in experimental model of HD. 2007 Wiley-Liss, Inc. [source]


    von Willebrand factor activates endothelial nitric oxide synthase in blood platelets by a glycoprotein Ib-dependent mechanism

    JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 12 2006
    R. RIBA
    Summary.,Background: The molecular regulation of endothelial nitric oxide synthase (eNOS) in blood platelets and the signalling events induced by platelet-derived NO are poorly defined. In particular, the ability of von Willebrand factor (VWF) to stimulate cyclic guanosine monophosphate (cGMP) formation in platelets has produced conflicting data. Objectives: To determine the mechanisms leading to eNOS activation and clarify the downstream signaling pathways activated by platelet-derived NO in response to VWF. Methods: We used three independent markers of NO signaling, [3H] l -citrulline production, cGMP accrual and immunoblotting of vasodilator,stimulated phosphoprotein (VASP) to examine the NO signaling cascade in response to VWF. Results: VWF increased NO synthesis and bioavailability, as evidenced by increased [3H] l -citrulline production and cGMP accrual, respectively. VWF-induced eNOS activation was GPIb-IX-dependent and independent of integrin ,IIb,3. cGMP formation in response to VWF required Ca2+ mobilization, Src family kinases, phosphatidylinositol 3-kinase and phospholipase C, but not protein kinase C. This suggests that a cross-talk between the signaling mechanisms regulates platelet activation and NO synthesis. VWF-induced cGMP accrual was completely blocked by apyrase and indomethacin, demonstrating an essential role for platelet-derived ADP and thromboxane A2 (TxA2). Elevated cGMP levels led to increased VASP phosphorylation at serine239 that was both protein kinase G (PKG)- and protein kinase A (PKA)-dependent. Conclusions: We demonstrate that VWF activates eNOS through a specific Ca2+ -dependent GPIb receptor-signaling cascade that relies on the generation of platelet-derived ADP and TxA2. Furthermore, we provide the first evidence to suggest that platelet derived-NO/cGMP activates PKA in addition to PKG. [source]


    Flow cytometric determination of Src phosphorylation in pediatric patients treated with dasatinib,

    PEDIATRIC BLOOD & CANCER, Issue 6 2009
    Bella S. Guerrouahen MS
    Abstract Tyrosine kinase inhibitors, such as imatinib, have dramatically improved the outcomes for patients with selected cancers. For imatinib, western blotting of phospho-CrkL was an insensitive, indirect, and descriptive method to determine drug efficacy. Greater use of targeted therapies should involve more quantitative evaluation of the target's dose-inhibition. The Src/Abl kinase inhibitor dasatinib has recently been approved for use in Ph+ leukemias after failure with imatinib. Src family kinases (SFK) also play a critical role in nonhematologic cancers. We have developed a flow cytometric assay to measure SFK autophosphorylation levels in blood mononuclear cells and observed a direct correlation between its inhibition and patient dosage. This method provides a sensitive, quick, and quantitative tool to assess drug efficacy. Pediatr Blood Cancer 2009;53:1132,1135. 2009 Wiley-Liss, Inc. [source]


    Activation of T Cells by Cross-Linking Qa-2, the Ped Gene Product, Requires Fyn

    AMERICAN JOURNAL OF REPRODUCTIVE IMMUNOLOGY, Issue 4 2007
    Sally R. De Fazio
    Problem Qa-2, the product of the Ped (preimplantation development) gene, regulates the rate of cell division of preimplantation mouse embryos by an unknown mechanism. Due to the limited availability of preimplantation embryos, T cells were used as a model system to assess the possible roles of Fyn and Lck, and two downstream effectors, PI-3 kinase and Akt, in Qa-2 induced cell proliferation. Method of study Resting T cells were stimulated to proliferate by treating with mouse anti-Qa-2 antibody, cross-linking with anti-mouse immunoglobulin, and adding PMA. The effects of kinase inhibitors on this proliferation were studied. Co-immunoprecipitates of T-cell lysates were analyzed for possible associations between Qa-2 and Fyn or Lck. Fyn knockout mice (Fyn,/,) were used to determine whether Fyn is required for T-cell activation induced by cross-linking Qa-2. Results An inhibitor of Src family kinases and inhibitors of PI-3 kinase and Akt suppressed proliferation of resting T cells induced by cross-linking Qa-2. Fyn, but not Lck, co-immunoprecipitated with Qa-2. Fyn,/, T cells failed to proliferate in response to Qa-2 cross-linking. Conclusion Fyn, PI-3 kinase, and Akt are required for the activation of T cells by cross-linking Qa-2. [source]