PLC Gamma Research Articles

Polatuzumab-bendamustine-rituximab as bridge to CD19-directed CAR T cells in mantle cell lymphoma refractory to ibrutinib and venetoclax.

Polatuzumab-bendamustine-rituximab as bridge to CD19-directed CAR T cells in mantle cell lymphoma refractory to ibrutinib and venetoclax.

PLCG1 is required for AML1-ETO leukemia stem cell self-renewal

AbstractIn an effort to identify novel drugs targeting fusion-oncogene–induced acute myeloid leukemia (AML), we performed high-resolution proteomic analysis. In AML1-ETO (AE)-driven AML, we uncovered a deregulation of phospholipase C (PLC) signaling. We identified PLCgamma 1 (PLCG1) as a specific target of the AE fusion protein that is induced after AE binding to intergenic regulatory DNA elements. Genetic inactivation of PLCG1 in murine and human AML inhibited AML1-ETO dependent self-renewal programs, leukemic proliferation, and leukemia maintenance in vivo. In contrast, PLCG1 was dispensable for normal hematopoietic stem and progenitor cell function. These findings are extended to and confirmed by pharmacologic perturbation of Ca++-signaling in AML1-ETO AML cells, indicating that the PLCG1 pathway poses an important therapeutic target for AML1-ETO+ leukemic stem cells.

KI Intolerance Study: A Phase 2 Study to Assess the Safety and Efficacy of Umbralisib (TGR-1202) in Patients with Chronic Lymphocytic Leukemia (CLL) Who Are Intolerant to Prior BTK or PI3K-δ Inhibitor Therapy

KI Intolerance Study: A Phase 2 Study to Assess the Safety and Efficacy of Umbralisib (TGR-1202) in Patients with Chronic Lymphocytic Leukemia (CLL) Who Are Intolerant to Prior BTK or PI3K-δ Inhibitor Therapy

Reelin Amplifies Glycoprotein VI Activation and AlphaIIb Beta3 Integrin Outside-In Signaling via PLC Gamma 2 and Rho GTPases.

Reelin, a secreted glycoprotein, was originally identified in the central nervous system, where it plays an important role in brain development and maintenance. In the cardiovascular system, reelin plays a role in atherosclerosis by enhancing vascular inflammation and in arterial thrombosis by promoting platelet adhesion, activation, and thrombus formation via APP (amyloid precursor protein) and GP (glycoprotein) Ib. However, the role of reelin in hemostasis and arterial thrombosis is not fully understood to date. Approach and Results: In the present study, we analyzed the importance of reelin for cytoskeletal reorganization of platelets and thrombus formation in more detail. Platelets release reelin to amplify alphaIIb beta3 integrin outside-in signaling by promoting platelet adhesion, cytoskeletal reorganization, and clot retraction via activation of Rho GTPases RAC1 (Ras-related C3 botulinum toxin substrate) and RhoA (Ras homolog family member A). Reelin interacts with the collagen receptor GP (glycoprotein) VI with subnanomolar affinity, induces tyrosine phosphorylation in a GPVI-dependent manner, and supports platelet binding to collagen and GPVI-dependent RAC1 activation, PLC gamma 2 (1-phosphatidylinositol-4,5-bisphosphate phosphodiesterase gamma-2) phosphorylation, platelet activation, and aggregation. When GPVI was deleted from the platelet surface by antibody treatment in reelin-deficient mice, thrombus formation was completely abolished after injury of the carotid artery while being only reduced in either GPVI-depleted or reelin-deficient mice. Our study identified a novel signaling pathway that involves reelin-induced GPVI activation and alphaIIb beta3 integrin outside-in signaling in platelets. Loss of both, GPVI and reelin, completely prevents stable arterial thrombus formation in vivo suggesting that inhibiting reelin-platelet-interaction might represent a novel strategy to avoid arterial thrombosis in cardiovascular disease.

An In Silico Investigation of Potential EGFR Inhibitors for the Clinical Treatment of Colorectal Cancer.

Colorectal cancer possesses the third highest diagnostic rate and is the second leading cause of cancer death in the USA as reported by NIH. Epidermal Growth Factor Receptor (EGFR), a transmembrane protein, participates in PLC gamma-1, RAS-RAF-MEK-MAPKs, phosphatidylinositol-3 kinase, Akt pathways and plays a key role in normal functioning of cell division, cell differentiation, apoptosis and migration. This protein is found to be overexpressed in more than 60% of the colorectal cancers. Overexpressed EGFR advances the tumorigenic properties through cell cycle dysregulation and activates signaling pathways linked to cancer such as WNT/β-catenin, transforming growth factor β (TGF-β) and phosphoinositide-3-kinase (PI3K). Inhibiting the overexpressed EGFR protein has been proposed for the treatment and many inhibitors have been reported suppressing the activity of EGFR. However, patients in malignant state of cancer show resistance to those inhibitors, which open a wide space to research for the discovery of novel inhibitors. The present study employed Molecular Docking and Virtual Screening to find novel inhibitors with high affinity against EGFR. Molecular docking of existing inhibitors resulted in the compound titled as BGB-283 (PubChem CID-89670174) having the highest score, which was subjected to similarity search to retrieve the drugs with similar structure. The virtual screening concluded a compound SCHEMBL18435602 (PubChem CID-126517400) which revealed a better affinity with the target protein. A comparative study of both the compounds showed equivalent pharmacokinetic properties. These identified drugs have a high potential to act as EGFR inhibitors and can show promising results in the research of colorectal cancer.

3133Hyperlipidaemia associated oxidised phospholipids induce sustained platelet hyperactivity by CD36 and PLC gamma 2 dependent ROS production

3133Hyperlipidaemia associated oxidised phospholipids induce sustained platelet hyperactivity by CD36 and PLC gamma 2 dependent ROS production

Hypoxia induced CCL28 promotes angiogenesis in lung adenocarcinoma by targeting CCR3 on endothelial cells.

Tumor hypoxia is one of the important features of lung adenocarcinoma. Chemokines might mediate the effects caused by tumor hypoxia. As confirmed in tumor tissue and serum of patients, CC chemokine 28 (CCL28) was the only hypoxia induced chemokine in lung adenocarcinoma cells. CCL28 could promote tube formation, migration and proliferation of endothelial cells. In addition, angiogenesis was promoted by CCL28 in the chick chorioallantoic membrane and matrigel implanted in dorsal back of athymic nude mice (CByJ.Cg-Foxn1nu/J). Tumors formed by lung adenocarcinoma cells with high expression of CCL28 grew faster and had a higher vascular density, whereas tumor formation rate of lung adenocarcinoma cells with CCL28 expression knockdown was quite low and had a lower vascular density. CCR3, receptor of CCL28, was highly expressed in vascular endothelial cells in lung adenocarcinoma when examining by immunohistochemistry. Further signaling pathways in endothelial cells, modulated by CCL28, were analyzed by Phosphorylation Antibody Array. CCL28/CCR3 signaling pathway could bypass that of VEGF/VEGFR on the levels of PI3K-Akt, p38 MAPK and PLC gamma. The effects could be neutralized by antibody against CCR3. In conclusion, CCL28, as a chemokine induced by tumor hypoxia, could promote angiogenesis in lung adenocarcinoma through targeting CCR3 on microvascular endothelial cells.

Abstract 40: Prothrombotic Role of Platelet Tlr2 in Hyperlipidemia

A prothrombotic state and increased platelet reactivity are common in hyperlipidemia and oxidative stress. Lipid peroxidation, a major consequence of oxidative stress, generates highly reactive products including hydroxy-w-oxoalkenoic acids that modify autologous proteins generating biologically active derivatives. Phosphatidylethanolamine, the second most abundant eukaryotic phospholipid can also be modified by hydroxy-w-oxoalkenoic acids. However, the conditions leading to accumulation of such derivatives in circulation and their biological activities remain poorly understood. We now show that carboxyalkylpyrrole-phosphatidylethanolamine derivatives (CAP-PE) accumulate in plasma of hyperlipidemic ApoE -/- mice. CAP-PE directly bind to TLR2 and induce platelet integrin alpha 2b beta 3 activation and P-selectin expression in TLR2 dependent manner. Platelet activation by CAP-PE includes assembly of TLR2/TLR1 receptor complex, induction of downstream signaling via MyD88/TIRAP, phosphorylation of IRAK4, and subsequent activation of TRAF6. This in turn activates the Src family kinases, Syk and PLC gamma 2 and platelet integrins. By intravital thrombosis studies we have demonstrated that CAP-PE accelerate thrombosis in TLR2 dependent manner. Furthermore, we demonstrate that TLR2 deficient mice are protected from accelerated thrombosis induced by hyperlipidemia. Taken together, our studies demonstrate a cross-talk between innate immunity and integrin activation signaling pathways in platelets and reveal that TLR2 plays a key role in platelet hyperreactivity and prothrombotic state in hyperlipidemia.

Knockdown of PLC-gamma-2 and calmodulin 1 genes sensitizes human cervical adenocarcinoma cells to doxorubicin and paclitaxel

BackgroundRNA interference (RNAi) is a powerful approach in functional genomics to selectively silence messenger mRNA (mRNA) expression and can be employed to rapidly develop potential novel drugs against a complex disease like cancer. However, naked siRNA being anionic is unable to cross the anionic cell membrane through passive diffusion and therefore, delivery of siRNA remains a major hurdle to overcome before the potential of siRNA technology can fully be exploited in cancer. pH-sensitive carbonate apatite has recently been developed as an efficient tool to deliver siRNA into the mammalian cells by virtue of its high affinity interaction with the siRNA and the desirable size distribution of the resulting siRNA-apatite complex for effective cellular endocytosis. Moreover, internalized siRNA was found to escape from the endosomes in a time-dependent manner and efficiently silence gene expression.ResultsHere we show that carbonate apatite-mediated delivery of siRNA against PLC-gamma-2 (PLCG2) and calmodulin 1 (CALM1) genes has led to the sensitization of a human cervical cancer cell line to doxorubicin- and paclitaxel depending on the dosage of the individual drug whereas no such enhancement in cell death was observed with cisplatin irrespective of the dosage following intracellular delivery of the siRNAs.ConclusionThus, PLCG2 and CALM1 genes are two potential targets for gene knockdown in doxorubicin and paclitaxel-based chemotherapy of cervical cancer.

Grb14 inhibits FGF receptor signaling through the regulation of PLCγ recruitment and activation

To decipher the mechanism involved in Grb14 binding to the activated fibroblast growth factor receptor (FGFR), we used the bioluminescence resonance energy transfer (BRET) technique and the Xenopus oocyte model. We showed that Grb14 was recruited to FGFR1 into a trimeric complex containing also phospholipase C gamma (PLCγ). The presence of Grb14 altered FGF-induced PLCγ phosphorylation and activation. Grb14-FGFR interaction involved the Grb14-SH2 domain and the FGFR pY766 residue, which is the PLCγ binding site. Our data led to a molecular model whereby Grb14 binding to the phosphorylated FGFR induces a conformational change that unmasks a PLCγ binding motif on Grb14, allowing trapping and inactivation of PLCγ. Structured summary MINT- 8019680: Grb14 (uniprotkb: O88900) physically interacts (MI: 0915) with FGFR1 (uniprotkb: P11362) by anti tag coimmunoprecipitation (MI: 0007) MINT- 8019693, MINT- 8019727: Grb14 (uniprotkb: O88900) physically interacts (MI: 0915) with FGFR1 (uniprotkb: P11362) by bioluminescence resonance energy transfer (MI: 0012) MINT- 8019714, MINT- 8019746: PLC gamma1 (uniprotkb: P19174) physically interacts (MI: 0915) with FGFR1 (uniprotkb: P11362) by bioluminescence resonance energy transfer (MI: 0012)

Abstract 3124: Platelet-derived growth factor receptor α cooperates with loss of p16/INK4a and p19/ARF to enhance tumorigenesis through the PI3K- and SHP-2-mediated signaling in the brain

Abstract Glioblastomas are the most common and lethal cancer in the central nervous system. Comprehensive genetic studies showed that in high-grade gliomas, overexpression of platelet-derived growth factor receptor alpha (PDGFRα) ranks third among top amplified genes and frequently co-occurs with loss of tumor suppressor genes, p16/INK4a and p14/ARF (p19/ARF in mice), in these high-grade glioblastomas. However, the biological consequences of PDGFRα overexpression in INK4a/ARF-deficient glial cells and glioma cells remain elusive. Here we show that activation of PDGFRα signaling by overexpressing PDGFRα and/or PDGF-A transformed Ink4a/Arf-deficient mouse astrocytes in vitro and rendered these cells highly tumorigenic in the brain of mice. Consistently, in INK4a/ARF null but not wild-type human glioma cell lines that express endogenous PDGFRα, overexpression of PDGF-A significantly enhances glioma formation in the brain. Re-introduction of p16/INK4a into Ink4a/Arf-null astrocytes suppressed PDGFRα-induced cell transformation in vitro and glioma formation in the brain. Conversely, cellular depletion of endogenous p16/INK4a by RNA interference in human glioma cells markedly enhances colony formation in vitro when compared to the controls. Mechanistically, abrogation of intrinsic tyrosine kinase activity of PDGFRα or interruptions of signaling modules at PDGFRα (Y to F mutations at specific tyrosine residues) that lost binding capacity for PI3K or Shp-2, but not PLC gamma or c-Src, significantly diminished PDGFRα-induced glioma formation in the brain. In vitro, specific YF mutations or inhibitors of PI3K or Shp-2 attenuated Akt activation and PDGFRα-induced colony formation. Furthermore, inhibition of Shp-2 by its inhibitors and siRNAs disrupts the interaction of PI3K with PDGFRα that is critical for gliomagenesis of Ink4a/Arf null cells. In summary, our data suggests that activation of PDGFRα signaling, particularly through the PI3K and Shp-2 pathways, in INK4a/ARF deficient astrocytes and glioma cells induce gliomagenesis in the brain. Our findings provide critical insights into interactions of genetic lesions frequently found in clinical glioma specimens and will be useful for identification of new therapeutic targets for treatments of patients with malignant gliomas. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3124.

The adaptor 3BP2 activates CD244-mediated cytotoxicity in PKC- and SAP-dependent mechanisms

Natural killer (NK) cell cytotoxicity requires triggering of activation receptors over inhibitory receptors. CD244, a member of CD150 receptor family, positively regulates NK-mediated lyses by activating an intracellular multiproteic signaling network that involves the adaptors X-linked lymphoproliferative gene product SAP and 3BP2. However, the exact mechanisms used by 3BP2 to enhance CD244-mediated cytotoxicity are still not fully understood. Here using the human NK cell line YT-overexpressing 3BP2, we found that the adaptor increases CD244, PI3K, and Vav phosphorylation upon CD244 engagement. The use of enzymatic inhibitors revealed that 3BP2-dependent cytolysis enhancement was PKC-dependent and PI3K-ERK independent. Furthermore, 3BP2 overexpression enhanced PKC delta phosphorylation. SAP knockdown expression inhibited PKC delta activation, indicating that the activating role played by 3BP2 depends upon the presence of SAP. In conclusion, our data show that 3BP2 acts downstream of SAP, increases CD244 phosphorylation and links the receptor with PI3K, Vav, PLC gamma, and PKC downstream events in order to achieve maximum NK killing function.

Is the c‐Cbl Proto‐Oncogene Involved in Chronic Lymphocytic Leukemia?

Chronic lymphocytic leukemia (CLL) is characterized by survival advantage and accumulation of CD5+ mature B lymphocytes. Expression of zeta-chain-associated protein-70 (ZAP-70), normally present in T lymphocytes or immature B cells, is associated with disease aggressiveness, as IgVH mutational status, and some proteins implicated in survival signal pathways are found to be constitutively activated in CLL cells. ZAP-70 signaling is regulated through molecular adaptors, such as the proto-oncogene product c-Casitas B lineage lymphoma (c-Cbl). The aim of this study was to determine the implication of this proto-oncogene product in CLL in survival signals. It appeared that expression of c-Cbl was increased in CLL and not correlated to that of B cell linker protein or ZAP-70. Furthermore, c-Cbl was significantly hypophosphorylated in progressive disease, so that hypophosphorylated form of c-Cbl (c-Cbl.P) along with ZAP-70, set a cutoff ratio distributing patients with stable situation below 1, and those with progressive disease equal or above 1. Given that phospholipase gamma 2 (PLC gamma 2) function is also influenced by c-Cbl hypophosphorylation, the ratio of PLC gamma 2 to c-Cbl.P was measured in CLL B cells and consistently found to be >or= 1 in Binet stage B CLL patients, as opposed to stage A CLL patients. These findings invite analysis of the role of c-Cbl in CLL.

Expressions of epidermal growth factor receptor signaling substances in gastric mucosal cells influenced by serum derived from rats treated with electroacupuncture at stomach meridian acupoints

To study the effects of serum derived from rats treated with electroacupuncture at stomach meridian acupoints on the expressions of epidermal growth factor receptor (EGFR) signaling substances phospholipase C gamma-1 (PLC gamma-1), protein kinase C (PKC) and c-myc in gastric mucosal cells. Sixty rats were randomly divided into normal group, stomach meridian group, gallbladder meridian group, stomach meridian plus PD153035 group and gallbladder meridian plus PD153035 group. Water-immersion and restrained stress methods were adopted for inducing gastric mucosal injury in the rats. Gastric mucosal cells were separated by using pronase digestion method, and incubated by PD153035, a EGFR inhibitor, and 100 ml/L serum. The expression of PLC gamma-1 in the gastric mucosal cells was tested by enzyme linked-immunosorbent assay (ELISA), while the expression of PKC by isotope incorporate assay and the expression of c-myc by reverse transcription polymerase chain reaction assay (RT-PCR). In gastric mucosal cells, weak expressions of PLC gamma-1, PKC and c-myc were seen in the normal group, and relatively strong expressions of PLC gamma-1, PKC and c-myc were seen in the stomach meridian group and the gallbladder meridian group, among which, the expressions of PLC gamma-1, PKC and c-myc in the stomach meridian group were the strongest, and there was a significant difference between the stomach meridian group and the gallbladder meridian group (P<0.01). Relative weak expressions of PLC gamma-1, PKC and c-myc were seen in the stomach meridian plus PD153035 group and the gallbladder meridian plus PD153035 group, and there was a significant difference between the stomach meridian group and the stomach meridian plus PD153035 group (P<0.01). The serum derived from the rats treated with electroacupuncture at stomach meridian acupoints can activate the EGFR singling pathway, and this provides an evidence for the theory of "relative particularity between meridians and viscera" in traditional Chinese medicine.

Combination of PP1/PP2 and LY294002 Induce Apoptosis Efficiently to TEL-FGFR3 Transfected Ba/F3 Cells.

We previously reported that TEL-FGFR3 in a patient with peripheral T-cell lymphoma and AML conferred IL-3 independency to Ba/F3 cells and activates MAPKs, p38, PI3K, Stat3 and Stat5 through its constitutive tyrosine kinase (TK) activity in TEL-FGFR3 transfected Ba/F3 cells (TF-V5). Both FGFR3 TK specific inhibitor SU5402 and PI3K inhibitor LY294002 inhibited cell growth of TF-V5 in a dose dependent manner (IC50=5μM, 10μM respectively). SU5402(25μM) resulted in G1 arrest (90%) and induced 80% of apoptosis to TF-V5 after 24hr. LY294002(50μM) decreased expression of c-Myc, Cyclin D3 and CDK4 in TF-V5 and induced G1 arrest (90%) and apoptosis about 20% to TF-V5 after 24hr. SU5402 completely suppressed expression of Bcl-xL and Bcl-2 after 24hr. LY294002 partially suppressed these expressions. As LY294002 did not affect the phosphorylation of STAT5 and STAT3, we hypothesized that these distinct apoptosis inducing abilities between SU5402 and LY294002 might be caused by the difference of Bcl-xL and Bcl-2 expression levels. Recent report suggests that FGFR3 activates Stat5 through recruitment of Pyk2 (proline-rich tyrosine kinase 2)-Src to its juxta-membrane (JM) domain. Therefore, we examined whether PP1/PP2 which are known as Src kinase inhibitors inhibit TF-V5 cell growth. PP1 and PP2 inhibited TEL-FGFR3 induced cell proliferation in a dose dependent manner (IC50=15μM, 15μM respectively). In contrast, growth of mock with IL-3 was not inhibited at a high concentration of PP1or PP2(30μM). PP1/PP2 did not affect auto-phosphorylation of TEL-FGFR3. Interestingly, PP1/PP2 inhibit Tyr phosphorylation of Pyk2 except Tyr402 and markedly suppressed activation of Stat3, Stat5 without affecting MAPKs and PLC gamma activation. PP1/PP2 suppressed expression of Bcl-xL and Bcl-2 partially but not of Bax and induced apoptosis 20% and 30% respectively. PP1/PP2 partially blocks cell cycle at G1 phase. When TF-V5 was co-treated with PP1(30μM)+LY294002(50μM) or PP2(30μM)+LY294002(50μM), apoptosis was induced in 60–70% of TF-V5 cells which remained at G1 phase after 24hr. Although PP1+LY294002 or PP2+LY294002 did not suppress Bcl-xL and Bcl-2 completely like SU5402, PP1/PP2 induced N-terminal cleavage form of Bax.Conclusion: PP1/PP2 induces apoptosis in TF-V5 by activating Bax and by Pyk2-Src kinase inactivation that leads to the change of Bax/Bcl-2 or Bax/Bcl-XL ratio. Combination of PP1/PP2 and LY294002 induce high rate of apoptosis under G1 arrest in TF-V5 and may represent a novel approach against TEL-FGFR3 associated hematopoietic malignancies.

Serotonin inhibits Na +/H + exchange activity via 5-HT4 receptors and activation of PKCα in human intestinal epithelial cells

Increased serotonin levels have been implicated in the pathophysiology of diarrhea associated with celiac and inflammatory diseases. However, the effects of serotonin on Na+ /H+ exchange (NHE) activity in the human intestine have not been investigated fully. The present studies examined the acute effects of 5-hydroxytryptamine (5-HT) on NHE activity using Caco-2 cells as an in vitro model. Caco-2 cells were treated with 5-HT (.1 micromol/L, 1 h) and NHE activity was measured as ethyl-isopropyl-amiloride (EIPA)-sensitive 22Na uptake. The effect of 5-HT receptor-specific agonists and antagonists was examined. The role of signaling intermediates in 5-HT-mediated effects on NHE activity was elucidated using pharmacologic inhibitors and immunoblotting. NHE activity was inhibited significantly (approximately 50%-75%, P < .05) by .1 micromol/L 5-HT via inhibition of maximal velocity (Vmax) without any changes in apparent affinity (Km) for the substrate Na+ . NHE inhibition involved a decrease of both NHE2 and NHE3 activities. Studies using specific inhibitors and agonists showed that the effects of 5-HT were mediated by 5-HT4 receptors. 5-HT-mediated inhibition of NHE activity was dependent on phosphorylation of phospholipase C gamma 1 (PLC gamma 1) via activation of src-kinases. Signaling pathways downstream of PLC gamma 1 involved increase of intracellular Ca 2+ levels and subsequent activation of protein kinase C alpha (PKC alpha). The effects of 5-HT on NHE activity were not cell-line specific because T84 cells also showed NHE inhibition. A better understanding of the regulation of Na+ absorption by 5-HT offers the potential for providing insights into molecular and cellular mechanisms involved in various diarrheal and inflammatory disorders.

Phospholipase Cγ in distinct regions of the ventral tegmental area differentially regulates morphine‐induced locomotor activity

Neurotrophic factors and the signaling pathways they activate play a role in mediating long-term molecular, cellular, and behavioral adaptations associated with drug addiction. Here we mimicked the biological response of phospholipase C-gamma (PLC gamma) induction in the ventral tegmental area (VTA) observed after chronic morphine using viral-mediated gene transfer. Using a behavioral sensitization paradigm, we demonstrate that microinjections of PLC gamma 1 into distinct (rostral vs. caudal) regions of the VTA result in differential locomotor responses to morphine.

Vav1 and Vav3 Have Critical but Redundant Roles in Mediating Platelet Activation by Collagen

Vav family proteins are guanine nucleotide exchange factors for the Rho/Rac family of small GTP-binding proteins. In addition, they have domains that mediate protein-protein interactions, including one Src homology 2 (SH2) and two Src homology 3 (SH3) domains. Vav1, Vav2, and Vav3 play a crucial role in the regulation of phospholipase C gamma (PLC gamma) isoforms by immuno-tyrosine-based activation motif (ITAM)-coupled receptors, including the T- and B-cell antigen receptors. We have reported in platelets, however, that Vav1 and Vav2 are not required for activation of PLC gamma 2 in response to stimulation of the ITAM-coupled collagen receptor glycoprotein VI (GPVI). Here we report that Vav3 is tyrosinephosphorylated upon activation of GPVI but that Vav3-deficient platelets also exhibit a normal response upon activation of the ITAM receptor. In sharp contrast, platelets deficient in both Vav1 and Vav3 show a marked inhibition of aggregation and spreading upon activation of GPVI, which is associated with a reduction in tyrosine phosphorylation of PLC gamma 2. The phenotype of Vav1/2/3 triple-deficient platelets is similar to that of Vav1/3 double-deficient cells. These results demonstrate that Vav3 and Vav1 play crucial but redundant roles in the activation of PLC gamma 2 by GPVI. This is the first time that absolute redundancy between two protein isoforms has been observed with respect to the regulation of PLC gamma 2 in platelets.

Transformation potency of ErbB heterodimer signaling is determined by B-Raf kinase.

Cellular transformation occurs only in cells that express both ErbB1 and ErbB4 receptors, but not in cells expressing only one or the other of these receptors. However, when both receptors are coexpressed and ligand-stimulated, they interact with virtually the same adaptor/effector proteins as when expressed singly. To reveal the underlying regulatory mechanism of the kinase/phosphatase network in ErbB homo- and heterodimer receptor signaling, extracellular signal-regulated kinase (ERK) and Akt activities were evaluated in the presence of several enzyme inhibitors in ligand-induced cells expressing ErbB1 (E1), ErbB4 (E4), and ErbB1/ErbB4 (E1/4) receptor. The PP2A inhibitor okadaic acid showed receptor-specific inhibitory profiles for ERK and Akt activities. Moreover, B-Raf isolated only from E1/4 cells could induce in vitro phosphorylation for MEK; this B-Raf kinase activity was abolished by pretreatment of the cells with okadaic acid. Our study further showed that the E1/4 cell-specific B-Raf activity was stimulated by PLC gamma and subsequent Rap1 activation. The present study suggests that B-Raf kinase, which was specifically activated in the cells coexpressing ErbB1 and ErbB4 receptors, elevates total ERK activity within the cell and, therefore, can induce cellular transformation.

The receptor tyrosine kinase MerTK activates phospholipase C gamma2 during recognition of apoptotic thymocytes by murine macrophages.

Apoptotic leukocytes must be cleared efficiently by macrophages (Mø). Apoptotic cell phagocytosis by Mø requires the receptor tyrosine kinase (RTK) MerTK (also known as c-Mer and Tyro12), the phosphatidylserine receptor (PS-R), and the classical protein kinase C (PKC) isoform betaII, which translocates to Mø membrane and cytoskeletal fractions in a PS-R-dependent manner. How these molecules cooperate to induce phagocytosis is unknown. As the phosphatidylinositol-specific phospholipase (PI-PLC) gamma2 is downstream of RTKs in some cell types and can activate classical PKCs, we hypothesized that MerTK signals via PLC gamma2. To test this hypothesis, we examined the interaction of MerTK and PLC gamma2 in resident, murine peritoneal (P)Mø and in the murine Mø cell line J774A.1 (J774) following exposure to apoptotic thymocytes. We found that as with PMø, J774 phagocytosis of apoptotic thymocytes was inhibited by antibody against MerTK. Western blotting and immunoprecipitation showed that exposure to apoptotic cells produced three time-dependent changes in PMø and J774: tyrosine phosphorylation of MerTK; association of PLC gamma2 with MerTK; and tyrosine phosphorylation of PLC gamma2. Cross-linking MerTK using antibody also induced phosphorylation of PLC gamma2 and its association with MerTK. A PI-PLC appears to be required for phagocytosis of apoptotic cells, as the PI-PLC inhibitor Et-18-OCH3 and the PLC inhibitor U73122, but not the inactive control U73343, blocked phagocytosis without impairing adhesion. On apoptotic cell adhesion to Mø, MerTK signals at least in part via PLC gamma2.