A computational in silico approach to predict high-risk coding and non-coding SNPs of human PLCG1 gene

PLCG1 gene is responsible for many T-cell lymphoma subtypes, including peripheral T-cell lymphoma (PTCL), angioimmunoblastic T-cell lymphoma (AITL), cutaneous T-cell lymphoma (CTCL), adult T-cell leukemia/lymphoma along with other diseases. Missense mutations of this gene have already been found in patients of CTCL and AITL. The non-synonymous single nucleotide polymorphisms (nsSNPs) can alter the protein structure as well as its functions. In this study, probable deleterious and disease-related nsSNPs in PLCG1 were identified using SIFT, PROVEAN, PolyPhen-2, PhD-SNP, Pmut, and SNPS&GO tools. Further, their effect on protein stability was checked along with conservation and solvent accessibility analysis by I-mutant 2.0, MUpro, Consurf, and Netsurf 2.0 server. Some SNPs were finalized for structural analysis with PyMol and BIOVIA discovery studio visualizer. Out of the 16 nsSNPs which were found to be deleterious, ten nsSNPs had an effect on protein stability, and six mutations (L411P, R355C, G493D, R1158H, A401V and L455F) were predicted to be highly conserved. Among the six highly conserved mutations, four nsSNPs (R355C, A401V, L411P and L455F) were part of the catalytic domain. L411P, L455F and G493D made significant structural change in the protein structure. Two mutations-Y210C and R1158H had post-translational modification. In the 5' and 3' untranslated region, three SNPs, rs139043247, rs543804707, and rs62621919 showed possible miRNA target sites and DNA binding sites. This in silico analysis has provided a structured dataset of PLCG1 gene for further in vivo researches. With the limitation of computational study, it can still prove to be an asset for the identification and treatment of multiple diseases associated with the target gene.

Tryptophan Ameliorates Barrier Integrity and Alleviates the Inflammatory Response to Enterotoxigenic Escherichia coli K88 Through the CaSR/Rac1/PLC-γ1 Signaling Pathway in Porcine Intestinal Epithelial Cells

Background

Impaired intestinal barrier integrity plays a crucial role in the development of many diseases such as obesity, inflammatory bowel disease, and type 2 diabetes. Thus, protecting the intestinal barrier from pathological disruption is of great significance. Tryptophan can increase gut barrier integrity, enhance intestinal absorption, and decrease intestinal inflammation. However, the mechanism of tryptophan in decreasing intestinal barrier damage and inflammatory response remains largely unknown. The objective of this study was to test the hypothesis that tryptophan can enhance intestinal epithelial barrier integrity and decrease inflammatory response mediated by the calcium-sensing receptor (CaSR)/Ras-related C3 botulinum toxin substrate 1 (Rac1)/phospholipase Cγ1 (PLC-γ1) signaling pathway.

Methods

IPEC-J2 cells were treated with or without enterotoxigenic Escherichia coli (ETEC) K88 in the absence or presence of tryptophan, CaSR inhibitor (NPS-2143), wild-type CaSR overexpression (pcDNA3.1-CaSR-WT), Rac1-siRNA, and PLC-γ1-siRNA.

Results

The results showed that ETEC K88 decreased the protein concentration of occludin, zonula occludens-1 (ZO-1), claudin-1, CaSR, total Rac1, Rho family member 1 of porcine GTP-binding protein (GTP-rac1), phosphorylated phospholipase Cγ1 (p-PLC-γ1), and inositol triphosphate (IP3); suppressed the transepithelial electrical resistance (TEER); and enhanced the permeability of FITC-dextran compared with the control group. Compared with the control group, 0.7 mM tryptophan increased the protein concentration of CaSR, total Rac1, GTP-rac1, p-PLC-γ1, ZO-1, claudin-1, occludin, and IP3; elevated the TEER; and decreased the permeability of FITC-dextran and contents of interleukin-8 (IL-8) and TNF-α. However, 0.7 mM tryptophan+ETEC K88 reversed the effects induced by 0.7 mM tryptophan alone. Rac1-siRNA+tryptophan+ETEC K88 or PLC-γ1-siRNA+tryptophan+ETEC K88 reduced the TEER, increased the permeability of FITC-dextran, and improved the contents of IL-8 and TNF-α compared with tryptophan+ETEC K88. NPS2143+tryptophan+ETEC K88 decreased the TEER and the protein concentration of CaSR, total Rac1, GTP-rac1, p-PLC-γ1, ZO-1, claudin-1, occludin, and IP3; increased the permeability of FITC-dextran; and improved the contents of IL-8 and TNF-α compared with tryptophan+ETEC K88. pcDNA3.1-CaSR-WT+Rac1-siRNA+ETEC K88 and pcDNA3.1-CaSR-WT+PLC-γ1-siRNA+ETEC K88 decreased the TEER and enhanced the permeability in porcine intestine epithelial cells compared with pcDNA3.1-CaSR-WT+ETEC K88.

Conclusion

Tryptophan can improve intestinal epithelial barrier integrity and decrease inflammatory response through the CaSR/Rac1/PLC-γ1 signaling pathway.

Protection of the Crayfish Mechanoreceptor Neuron and Glial Cells from Photooxidative Injury by Modulators of Diverse Signal Transduction Pathways

Oxidative stress is the reason of diverse neuropathological processes. Photodynamic therapy (PDT), an effective inducer of oxidative stress, is used for cancer treatment, including brain tumors. We studied the role of various signaling pathways in photodynamic injury and protection of single neurons and satellite glial cells in the isolated crayfish mechanoreceptor. It was photosensitized with alumophthalocyanine Photosens in the presence of inhibitors or activators of various signaling proteins. PDT eliminated neuronal activity and killed neurons and glial cells. Inhibitory analysis showed the involvement of protein kinases Akt, glycogen synthase kinase-3β (GSK-3β), mammalian target of rapamycin (mTOR), mitogen-activated protein kinase kinases 1 and 2 (MEK1/2), calmodulin, calmodulin-dependent kinase II (CaMKII), adenylate cyclase, and nuclear factor NF-κB in PDT-induced necrosis of neurons. Nitric oxide (NO) and glial cell-derived neurotrophic factor (GDNF) reduced neuronal necrosis. In glial cells, protein kinases Akt, calmodulin, and CaMKII; protein kinases C and G, adenylate cyclase, and p38; and nuclear transcription factor NF-κB also mediated PDT-induced necrosis. In contrast, NO and neurotrophic factors nerve growth factor (NGF) and GDNF demonstrated anti-necrotic activity. Phospholipase Cγ, protein kinase C, GSK-3β, mTOR, NF-κB, mitochondrial permeability transition pores, and NO synthase mediated PDT-induced apoptosis of glial cells, whereas protein kinase A, tyrosine phosphatases, and neurotrophic factors NGF, GDNF, and neurturin were involved in protecting glial cells from photoinduced apoptosis. Signaling pathways that control cell survival and death differed in neurons and glia. Inhibitors or activators of some signaling pathways may be used as potential protectors of neurons and glia from photooxidative stress and following death.

Phosphoinositid signal pathway mediate neurite outgrowth in PC12 cells by staurosporine

OBJECTIVES

In previous studies, we showed that staurosporine uses intracellular calcium ions to affect cell death in PC12 cells. The bulk release of intracellular excessive Ca(2+) from intracellular sources into cytosol contributes to neuronal apoptotic events, which in turn results in neuronal cell death. However, the mechanisms of Ca(2+)-induced neuronal cell death or neurite elongation is still unclear. Therefore, we investigated the relation between phosphoinositid signal pathway, intracellular calcium, and reactive oxygen species on one hand, with staurosporine-induced neurite outgrowth in PC12 cells on the other.

RESULTS

The inhibition of phospholipase C or IP3 receptor antagonist or phosphoinositid signal transduction antagonist produced cell death and suppressed neurite outgrowth by staurosporine in PC12 cells. The inhibition of these enzymes and pathway results in an increase in intracellular Ca(2+) although subsequent hydroxyl radical (•OH) production began after inhibitors exposure. •OH production was significantly attenuated in inhibitor supplemented medium treatment, and it was dependent on the intracellular Ca(2+) concentration. These data indicate that staurosporine activates phosphoinositid signal pathway while endoplasmic Ca(2+), and subsequent •OH production are critical events in staurosporine-induced neurite outgrowth in PC12 cells.

CONCLUSION

We conclude that the fact that staurosporine mobilizes Ca2+, probably via activating the subcellular compartment, is responsible for staurosporine-induced (Ca2+]i increase during neurite outgrowth in PC12 cells (Fig. 7, Ref. 30).

von Willebrand factor mutation promotes thrombocytopathy by inhibiting integrin αIIbβ3

von Willebrand disease type 2B (vWD-type 2B) is characterized by gain-of-function mutations in von Willebrand factor (vWF) that enhance its binding to the glycoprotein Ib-IX-V complex on platelets. Patients with vWD-type 2B have a bleeding tendency that is linked to loss of vWF multimers and/or thrombocytopenia. In this study, we uncovered evidence that platelet dysfunction is a third possible mechanism for bleeding tendency. We found that platelet aggregation, secretion, and spreading were diminished due to inhibition of integrin αIIbβ3 in platelets from mice expressing a vWD-type 2B-associated vWF (vWF/p.V1316M), platelets from a patient with the same mutation, and control platelets pretreated with recombinant vWF/p.V1316M. Impaired platelet function coincided with reduced thrombus growth. Further, αIIbβ3 activation and activation of the small GTPase Rap1 were impaired by vWF/p.V1316M following exposure to platelet agonists (thrombin, ADP, or convulxin). Conversely, thrombin- or ADP-induced Ca2+ store release, which is required for αIIbβ3 activation, was normal, indicating that vWF/p.V1316M acts downstream of Ca2+ release and upstream of Rap1. We found normal Syk phosphorylation and PLCγ2 activation following collagen receptor signaling, further implying that vWF/p.V1316M acts directly on or downstream of Ca2+ release. These data indicate that the vWD-type 2B mutation p.V1316M is associated with severe thrombocytopathy, which likely contributes to the bleeding tendency in vWD-type 2B.

Inactivation of Ras GTPase-activating proteins promotes unrestrained activity of wild-type Ras in human liver cancer

BACKGROUND & AIMS

Aberrant activation of the RAS pathway is ubiquitous in human hepatocarcinogenesis, but the molecular mechanisms leading to RAS induction in the absence of RAS mutations remain under-investigated. We defined the role of Ras GTPase activating proteins (GAPs) in the constitutive activity of Ras signaling during human hepatocarcinogenesis.

METHODS

The mutation status of RAS genes and RAS effectors was assessed in a collection of human hepatocellular carcinomas (HCC). Levels of RAS GAPs (RASA1-4, RASAL1, nGAP, SYNGAP1, DAB2IP, and NF1) and the RASAL1 upstream inducer PITX1 were determined by real-time RT-PCR and immunoblotting. The promoter and genomic status of RASAL1, DAB2IP, NF1, and PITX1 were assessed by methylation assays and microsatellite analysis. Effects of RASAL1, DAB2IP, and PITX1 on HCC growth were evaluated by transfection and siRNA analyses of HCC cell lines.

RESULTS

In the absence of Ras mutations, downregulation of at least one RAS GAP (RASAL1, DAB2IP, or NF1) was found in all HCC samples. Low levels of DAB2IP and PITX1 were detected mostly in a HCC subclass from patients with poor survival, indicating that these proteins control tumor aggressiveness. In HCC cells, reactivation of RASAL1, DAB2IP, and PITX1 inhibited proliferation and induced apoptosis, whereas their silencing increased proliferation and resistance to apoptosis.

CONCLUSIONS

Selective suppression of RASAL1, DAB2IP, or NF1 RAS GAPs results in unrestrained activation of Ras signaling in the presence of wild-type RAS in HCC.

Release of intracellular calcium stores facilitates coxsackievirus entry into polarized endothelial cells

Group B coxsackieviruses (CVB) are associated with viral-induced heart disease and are among the leading causes of aseptic meningitis worldwide. Here we show that CVB entry into polarized brain microvasculature and aortic endothelial cells triggers a depletion of intracellular calcium stores initiated through viral attachment to the apical attachment factor decay-accelerating factor. Calcium release was dependent upon a signaling cascade that required the activity of the Src family of tyrosine kinases, phospholipase C, and the inositol 1,4,5-trisphosphate receptor isoform 3. CVB-mediated calcium release was required for the activation of calpain-2, a calcium-dependent cysteine protease, which controlled the vesicular trafficking of internalized CVB particles. These data point to a specific role for calcium signaling in CVB entry into polarized endothelial monolayers and highlight the unique signaling mechanisms used by these viruses to cross endothelial barriers.

Enteroviruses are associated with a number of diverse syndromes such as myocarditis, febrile illness, and are the main causative agents of aseptic meningitis. No effective therapeutics exist to combat non-poliovirus enterovirus infections. A better understanding of the mechanisms by which these viruses infect host cells could lead to the design of effective therapeutic interventions. In this study, we found that intracellular calcium stores in polarized endothelial monolayers are depleted upon exposure to coxsackievirus B (CVB) and that this release is mediated by viral attachment to its receptor decay-accelerating factor. We also discovered that the calcium release requires the activation of signaling molecules involved in calcium signaling such as Src tyrosine kinases, phospholipase C, and the inositol 1,4,5-trisphosphate receptor isoform 3 on the ER membrane. Furthermore, we found that a calcium-activated cystein protease, calpain-2, was activated and necessary for proper viral trafficking inside the cell. Interestingly, we found that this signaling cascade was critical for CVB internalization into the endothelium, but was not involved in CVB entry into the epithelium. This is an important advance in our understanding of how enteroviruses hijack host endothelial cell signaling mechanisms in order to facilitate their entry and eventual spread.

Phospholipase Cgamma2 mediates RANKL-stimulated lymph node organogenesis and osteoclastogenesis

Phospholipase Cgamma2 (PLCgamma2) is an important signaling effector of multiple receptors in the immune system. Here we show that PLCgamma2-deficient mice displayed impaired lymph node organogenesis but normal splenic structure and Peyer's patches. Receptor activator of NF-kappaB ligand (RANKL) is a tumor necrosis factor family cytokine and is essential for lymph node organogenesis. Importantly, PLCgamma2 deficiency severely impaired RANKL signaling, resulting in marked reduction of RANKL-induced activation of MAPKs, p38 and JNK, but not ERK. The lack of PLCgamma2 markedly diminished RANKL-induced activation of NF-kappaB, AP-1, and NFATc1. Moreover, PLCgamma2 deficiency impaired RANKL-mediated biological function, leading to failure of the PLCgamma2-deficient bone marrow macrophage precursors to differentiate into osteoclasts after RANKL stimulation. Re-introduction of PLCgamma2 but not PLCgamma1 restores RANKL-mediated osteoclast differentiation of PLCgamma2-deficient bone marrow-derived monocyte/macrophage. Taken together, PLCgamma2 is essential for RANK signaling, and its deficiency leads to defective lymph node organogenesis and osteoclast differentiation.

Phospholipase-C gamma-1 (PLCgamma-1) is critical in hepatocyte growth factor induced in vitro invasion and migration without affecting the growth of prostate cancer cells

BACKGROUND

Phospholipase C gamma-1 (PLCgamma-1) is an intracellular signalling molecule regulating a number of biological processes including transporter mechanisms, transcription factors, and scaffolding proteins mediating cytoskeleton and membrane trafficking. Hepatocyte growth factor (HGF) is a pleiotrophic factor and a mediator of metastatic spread. This study sought to determine the effect of HGF on the invasive and migratory potential of prostate cancer cells targeted by a ribozyme transgene to PLCgamma-1.

METHODS

A ribozyme transgene consisting of hammerhead ribozyme and antisense specific to PLCgamma-1 was cloned into a PEF6 expression vector and transfected into PC-3 cells. RT-PCR and Western blotting confirmed knock down of PLCgamma-1. In vitro invasion and a cytodex-2 bead motility assays with in vitro and in vivo growth models were used to assess the impact of PLCgamma-1 manipulation.

RESULTS

PC-3 cells stably transfected with PLCgamma-1 ribozyme transgene (PC-3(DeltaPLC)gamma) manifested a reduction of PLCgamma-1 expression at mRNA/protein levels. HGF/SF increased invasiveness (P < 0.01) and motility (P < 0.0001) of PC-3(WT) and PC-3(PEF6) cells. In contrast, PLCgamma-1 knock down PC-3(DeltaPLC)gamma cells had reduced invasiveness (P < 0.05) and motility (P < 0.01) compared with PC-3(WT) and PC-3(PEF6) cells. Although there was a marginal change of cell growth in vitro, there was no difference in the rate of growth between PC-3(DeltaPLC)gamma, PC-3(WT), and PC-3(PEF6) cells.

CONCLUSION

Targeting PLCgamma-1 by way of a hammerhead ribozyme to PLCgamma-1 is an effective method in reducing invasive phenotype of prostate cancer. PLCgamma-1 is a signalling intermediate that has prime influence on HGF induced cellular invasion and migration without affecting the growth of the cells.

The role of phospholipase C gamma 1 in primitive hematopoiesis during zebrafish development

OBJECTIVES

Phospholipase C (PLC) gamma 1 has been shown to mediate signal transduction of tyrosine kinases and affect function of hematopoietic cells. However, its role in hematopoiesis during embryonic development is currently unclear. In this study, we examined this issue using morpholino (MO) gene knockdown in zebrafish embryos

METHODS

MO targeting at the exon-1-intron-1 junction of zebrafish PLC-gamma1 was injected into embryos at the one- to four-cell stage (referred herein zPLC-gamma1(MO) embryos). Primitive hematopoiesis was examined quantitatively by flow cytometry in Tg(gata1:GFP) embryos and by real-time quantitative polymerase chain reaction at 18 hours-post-fertilization (hpf), before the onset of circulation. The embryos were also treated with receptor inhibitors of vascular endothelial growth factor, fibroblast growth factor, and platelet-derived growth factor at 25, 1, and 30 micromol/L, respectively, from one cell until 48 hpf.

RESULTS

Erythropoiesis was reduced in zPLC-gamma1(MO) embryos, as shown by the reduction in gata1(+) cells (wild-type: 4.32% +/- 0.10% vs zPLC-gamma1(MO): 2.38% +/- 0.11%, p = 0.021) and gata1 and alpha-embryonic hemoglobin expression [0.47 +/- 0.06-fold (p = 0.013) and 0.46 +/- 0.04-fold (p = 0.013)]. Expression of scl, lmo-2 (early hematopoietic progenitors), pu.1, and l-plastin (myelomonocytic lineages) as well as fli1 (vascular progenitors) were unaffected. Fli1(+) cells in Tg(fli1:GFP) embryos were also unaffected by zPLC-gamma1(MO). When embryos were incubated with receptor inhibitors of vascular endothelial growth factor (VEGFRTKI), fibroblast growth factor (SU5402), or platelet-derived growth factor (AG1296), only VEGFRTKI reduced erythropoiesis [VEGFRTKI: 2.10% +/- 0.07% (p = 0.021) vs SU5402: 4.08% +/- 0.12% (p = 0.248) vs AG1296: 4.12% +/- 0.14% (p = 0.149)].

CONCLUSION

PLC-gamma1 is involved in the regulation of primitive hematopoiesis in zebrafish embryos, which is distinct from its later effect on vascular formation.

Phospholipase C-gamma1 is required for the activation of store-operated Ca2+ channels in liver cells

Repetitive hormone-induced changes in concentration of free cytoplasmic Ca2+ in hepatocytes require Ca2+ entry through receptor-activated Ca2+ channels and SOCs (store-operated Ca2+ channels). SOCs are activated by a decrease in Ca2+ concentration in the intracellular Ca2+ stores, but the molecular components and mechanisms are not well understood. Some studies with other cell types suggest that PLC-gamma (phospholipase C-gamma) is involved in the activation of receptor-activated Ca2+ channels and/or SOCs, independently of PLC-gamma-mediated generation of IP3 (inositol 1,4,5-trisphosphate). The nature of the Ca2+ channels regulated by PLC-gamma has not been defined clearly. The aim of the present study was to determine if PLC-gamma is required for the activation of SOCs in liver cells. Transfection of H4IIE cells derived from rat hepatocytes with siRNA (short interfering RNA) targeted to PLC-gamma1 caused a reduction (by approx. 70%) in the PLC-gamma1 protein expression, with maximal effect at 72-96 h. This was associated with a decrease (by approx. 60%) in the amplitude of the I(SOC) (store-operated Ca2+ current) developed in response to intracellular perfusion with either IP(3) or thapsigargin. Knockdown of STIM1 (stromal interaction molecule type 1) by siRNA also resulted in a significant reduction (approx. 80% at 72 h post-transfection) of the I(SOC) amplitude. Immunoprecipitation of PLC-gamma1 and STIM1, however, suggested that under the experimental conditions these proteins do not interact with each other. It is concluded that the PLC-gamma1 protein, independently of IP3 generation and STIM1, is required to couple endoplasmic reticulum Ca2+ release to the activation of SOCs in the plasma membrane of H4IIE liver cells.

Minimal regulation of platelet activity by PECAM-1

PECAM-1 is a member of the superfamily of immunoglobulins (Ig) and is expressed on platelets at moderate level. PECAM-1 has been reported to have contrasting effects on platelet activation by the collagen receptor GPVI and the integrin, alphaIIbbeta3, even though both receptors signal through Src-kinase regulation of PLCgamma2. The present study compares the role of PECAM-1 on platelet activation by these two receptors and by the lectin receptor, CLEC-2, which also signals via PLCgamma2. Studies using PECAM-1 knockout-mice and cross-linking of PECAM-1 using specific antibodies demonstrated a minor inhibitory role on platelet responses to the above three receptors and also under some conditions to the G-protein agonist thrombin. The degree of inhibition was considerably less than that produced by PGI2, which elevates cAMP. There was no significant difference in thrombus formation on collagen in PECAM-1-/- platelets relative to litter-matched controls. The very weak inhibitory effect of PECAM-1 on platelet activation relative to that of PGI2 indicate that the Ig-receptor is not a major regulator of platelet activation. PECAM-1 has been reported to have contrasting effects on platelet activation. The present study demonstrates a very mild or negligible effect on platelet activation in response to stimulation by a variety of agonists, thereby questioning the physiological role of the immunoglobulin receptor as a major regulator of platelet activation.

A discourse on cancer cell chemotaxis: where to from here?

The study of cancer cell chemotaxis on two-dimensional surfaces in vitro has relevance to the diverse migratory behaviours exhibited in vivo that involve a directed path. These may include translocation along collagen fibres, invasion into the basement membrane and across stroma, intravasation and extravasation to arrive at a secondary destination designated for cancer cell colonization. Chemotaxis invariably denotes the ability of cells to sense gradients, polarize, adhere and deadhere to substrate, and translocate in the right direction. Amongst these, the sensing function is perhaps the unifying aspect of different migration styles, permitting the cells to resolve its orientation and path. This review examines the decision-making processes that take place during chemotaxis and illustrates that a universal mechanism is involved. In various cell types from Dictyostelium to neutrophils, there are some unifying principles that dictate sensing and how the putative leading edge and trailing end of cells are determined. Some of these principles have recently been applied in the study of cancer cell chemotaxis albeit different pathways are substituted. In amoeboid-like cancer cells, local excitation of the EGFR/PLCgamma/cofilin pathway and parallel, global inhibition of cofilin by LIMK occur to promote the asymmetric distribution and amplification of these internal signals in response to an external EGF gradient.

Btk and phospholipase C gamma 2 can function independently during B cell development

The pre-BCR and the BCR regulate B cell development via a signalosome nucleated by the adaptor protein B cell linker protein (BLNK). Formation of this complex facilitates activation of phospholipase C (PLC) gamma2 by Bruton's tyrosine kinase (Btk). To determine whether Btk and PLCgamma2 also have separate functions, we generated Btk(-/-)PLCgamma2(-/-) mice. They demonstrated a block in development at the pre-B stage and increased pre-BCR surface expression. This phenotype was more severe than that of Btk(-/-) or PLCgamma2(-/-) mice. Although both Btk and PLCgamma2 were required for proliferation of splenic B cells in response to BCR cross-linking, they contributed differently to anti-IgM-induced phosphorylation of ERK. Btk(-/-) and PLCgamma2(-/-) mice each had a reduced frequency of Iglambda-expressing B cells and impaired migration of pre-B cells towards stromal cell-derived factor 1. However, the increase in pre-B cell malignancy that occurs in BLNK(-/-) mice in the absence of Btk was not observed in the absence of PLCgamma2. Thus, Btk and PLCgamma2 act both in concert and independently throughout B cell development.

Antitumour effects on human colorectal carcinomas cells by stable silencing of phospholipase C-gamma 1 with lentivirus-delivered siRNA

BACKGROUND

In most colorectal carcinomas, the level of phospholipase C (PLC)-gamma 1 expression is greatly elevated. Increased expression of PLC-gamma 1 may play an important role in colon carcinogenesis, but the mechanism is not well known. The aim of this study was to evaluate the role of PLC-gamma 1 in colon carcinogenesis by using recombinant lentivirus that stably suppressed the PLC-gamma 1 expression in human colorectal carcinoma LoVo cells.

METHODS

Recombinant lentivirus producing PLC-gamma 1 siRNA were prepared. After LoVo cells were transduced by each lentivirus, stably transduced cells were selected by Blasticidin. The protein and mRNA expression of PLC-gamma 1 were examined by Western-blot and reverse transcription-polymerase chain reaction (RT-PCR) analysis, and the effects of the lentivirus on the cell adhesion, migration and apoptosis were analyzed.

RESULTS

Stable LoVo cell line deficient in PLC-gamma 1, was established. Notably, PLC-gamma 1 was silenced without affecting the levels of other subtypes of PLC so that the role of PLC-gamma 1 in colon carcinogenesis could be examined. Silencing of endogenous PLC-gamma 1 resulted in efficient inhibition of the adhesion and migration of LoVo cells in vitro and a great increase of 5-fluorouracil induced apoptosis (30%-40%) of LoVo cells.

CONCLUSIONS

PLC-gamma 1 may play an important role in metastasis and anti-apoptosis in human colorectal carcinomas.

The Role of the Calcium Sensing Receptor in Regulating Intracellular Calcium Handling in Human Epidermal Keratinocytes

Calcium is critical for controlling the balance of proliferation and differentiation in epidermal keratinocytes. We previously reported that the calcium sensing receptor (CaR) is required for mediating Ca2+ signaling and extracellular Ca2+ (Ca2+(o))-induced differentiation. In this study, we investigated the mechanism by which CaR regulates intracellular Ca2+ (Ca2+(i)) and its role in differentiation. Membrane fractionation, fluorescence immunolocalization, and co-immunoprecipitation studies were performed to assess potential interactions between CaR and other regulators of Ca2+ stores and channels. We found that the glycosylated form of CaR forms a complex with phospholipase C gamma1, IP3 receptor (IP3R), and the Golgi Ca2+-ATPase, secretory pathway Ca2+-ATPase 1, in the trans-Golgi. Inactivation of the endogenous CaR gene by adenoviral expression of a CaR antisense cDNA inhibited Ca2+(i) response to Ca2+(o), decreased Ca2+(i) stores, decreased Ca2+(o)-induced differentiation, but augmented store-operated channel activity and Ca2+ uptake by intracellular organelles. Our results indicate that CaR regulates keratinocyte differentiation in part by modulating Ca2+(i) stores via interactions with Ca2+ pumps and channels that regulate those stores.

A Remote Substrate Docking Mechanism for the Tec Family Tyrosine Kinases

During T cell signaling, Itk selectively phosphorylates a tyrosine within its own SH3 domain and a tyrosine within PLCgamma1. We find that the remote SH2 domain in each of these substrates is required to achieve efficient tyrosine phosphorylation by Itk and extend this observation to two other Tec family kinases, Btk and Tec. Additionally, we detect a stable interaction between the substrate SH2 domains and the kinase domain of Itk and find that addition of specific, exogenous SH2 domains to the in vitro kinase assay competes directly with substrate phosphorylation. On the basis of these results, we show that the kinetic parameters of a generic peptide substrate of Itk are significantly improved via fusion of the peptide substrate to the SH2 domain of PLCgamma1. This work is the first characterization of a substrate docking mechanism for the Tec kinases and provides evidence of a novel, phosphotyrosine-independent regulatory role for the ubiquitous SH2 domain.

Antineutrophil Cytoplasm Antibody–Stimulated Neutrophil Adhesion Depends on Diacylglycerol Kinase–Catalyzed Phosphatidic Acid Formation

Patients with certain forms of systematic vasculitis, such as Wegener's granulomatosis, have circulating antineutrophil cytoplasmic antibodies (ANCA). These inappropriately stimulate circulating neutrophils adhere to and thereby obstruct small vessels. This, together with ANCA-induced degranulation and an oxidative burst, leads to local tissue damage. The signaling pathways that are activated by ANCA IgG are distinct from those that are involved in normal neutrophil activation. This study shows that diacylglycerol kinase is selectively activated by ANCA and that the generated phosphatidic acid is responsible for promoting neutrophil adhesion, in part through integrin activation. The data presented point to diacylglycerol kinase alpha as a novel but selective target for the development of drugs to treat this potentially fatal disorder.

Inositide-dependent phospholipase C signaling mimics insulin in skeletal muscle differentiation by affecting specific regions of the cyclin D3 promoter

Our main goal in this study was to investigate the role of phospholipase C (PLC) beta(1) and PLCgamma(1) in skeletal muscle differentiation and the existence of potential downstream targets of their signaling activity. To examine whether PLC signaling can modulate the expression of cyclin D3, a target of PLCbeta(1) in erythroleukemia cells, we transfected C2C12 cells with expression vectors containing PLCbeta(1) or PLCgamma(1) cDNA and with small interfering RNAs from regions of the PLCbeta(1) or PLCgamma(1) gene and followed myogenic differentiation in this well-established cell system. Intriguingly, overexpressed PLCbeta(1) and PLCgamma(1) were able to mimic insulin induction of both cyclin D3 and muscle differentiation. By knocking down PLCbeta(1) or PLCgamma(1) expression, C2C12 cells almost completely lost the increase in cyclin D3, and the differentiation program was down-regulated. To explore the induction of the cyclin D3 gene promoter during this process, we used a series of 5'-deletions of the 1.68-kb promoter linked to a reporter gene and noted a 5-fold augmentation of promoter activity upon insulin stimulation. These constructs were also cotransfected with PLCbeta(1) or PLCgamma(1) cDNAs and small interfering RNAs, respectively. Our data indicate that PLCbeta(1) or PLCgamma(1) signaling is capable of acting like insulin in regard to both the myogenic differentiation program and cyclin D3 up-regulation. Taken together, this is the first study that hints at cyclin D3 as a target of PLCbeta(1) and PLCgamma(1) during myogenic differentiation in vitro and implies that up-regulation of these enzymes is sufficient to mimic the actions of insulin in this process.

Phospholipase C gamma negatively regulates Rac/Cdc42 activation in antigen-stimulated mast cells

The Rho GTPases Rac and Cdc42 play a central role in the regulation of secretory and cytoskeletal responses in antigen-stimulated mast cells. In this study, we examine the kinetics and mechanism of Rac and Cdc42 activation in the rat basophilic leukemia RBL-2H3 cells. The activation kinetics of both Rac and Cdc42 show a biphasic profile, consisting of an early transient peak at 1 min and a late sustained activation phase at 20-40 min. The inhibition of phospholipase C (PLC)gamma causes a twofold increase in Rac and Cdc42 activation that coincides with a dramatic production of atypical filopodia-like structures. Inhibition of protein kinase C using bisindolylmaleimide mimics the effect of PLCgamma inhibition on Rac activation, but not on Cdc42 activation. In contrast, depletion of intracellular calcium leads to a complete inhibition of the early activation peak of both Rac and Cdc42, without significant effects on the late sustained activation. These data suggest that PLCgamma is involved in a negative feedback loop that leads to the inhibition of Rac and Cdc42. They also suggest that the presence of intracellular calcium is a prerequisite for both Rac and Cdc42 activation.

Epothilone B Inhibits Neointimal Formation after Rat Carotid Injury through the Regulation of Cell Cycle-Related Proteins

The abnormal proliferation of vascular smooth muscle cells (VSMCs) in arterial walls is an important pathogenetic factor of vascular disorders such as atherosclerosis and restenosis after angioplasty. Epothilone B, a novel potential antitumor compound, has a potent effect on preventing postangioplasty restenosis. Therefore, we established an in vivo rat carotid injury model and examined the potential effects of epothilone B on cardiovascular disease. We found that epothilone B potently prevented neointimal formation and in vivo VSMCs proliferation. In addition, we also showed that epothilone B significantly inhibited 5% fetal bovine serum (FBS)- and 50 ng/ml platelet-derived growth factor (PDGF)-BB-induced proliferation and cell cycle progression in rat aortic VSMCs. Furthermore, FBS and PDGF-BB induced the activations of extracellular signal-regulated kinases 1 and 2, Akt, phospholipase C gamma 1, and PDGF-receptor beta chain tyrosine kinase were not changed by epothilone B. However, epothilone B treatment caused a significant decrease in the level of cyclin-dependent protein kinase (CDK) 2, whereas it caused no change in the levels of cyclin E and down-regulated the phosphorylation of retinoblastoma, which plays a critical role in cell cycle regulation. Furthermore, levels of p27, an inhibitor of cyclin E/CDK2 complex, were significantly increased in VSMCs treated with epothilone B, indicating that this might be a major molecular mechanism for the inhibitory effects of epothilone B on the proliferation and cell cycle of VSMCs. These findings suggest that epothilone B can inhibit neointimal formation via the cell cycle arrest by the regulation of the cell cycle-related proteins in VSMCs.

Differential and nonredundant roles of phospholipase Cgamma2 and phospholipase Cgamma1 in the terminal maturation of NK cells

NK cells play a central role in mediating innate immune responses. Activation of NK cells results in cytotoxicity, cytokine, and chemokine secretions. In this study, we show that in mice with targeted deletion of phospholipase Cgamma (PLCgamma)2, one of the key signal transducers, there are profound effects on the development and terminal maturation of NK cells. Lack of PLCgamma2 significantly impaired the ability of lineage-committed NK precursor cells to acquire subset-specific Ly49 receptors and thereby terminal maturation of NK cells. Overexpression of isozyme, PLCgamma1, in PLCgamma2-deficient NK cells resulted in the successful Ly49 acquisition and terminal maturation of the NK cells; however, it could only partially rescue NKG2D-mediated cytotoxicity with no cytokine production. Furthermore, PLCgamma2-deficient NK cells failed to mediate antitumor cytotoxicity and inflammatory cytokine production, displaying a generalized hyporesponsiveness. Our results strongly demonstrate that PLCgamma1 and PLCgamma2 play nonredundant and obligatory roles in NK cell ontogeny and in its effector functions.

The role of phospholipase Cgamma1 tyrosine phosphorylation during phasic myometrial contractions

OBJECTIVE

Phospholipase Cgamma1 (PLCgamma1) is expressed in myometrium and is activated by tyrosine phosphorylation. These studies sought to determine the association between PLCgamma1 tyrosine phosphorylation and spontaneous uterine contractions.

STUDY DESIGN

In vitro contraction studies were performed with spontaneously contracting rat uterine strips along with strips that were treated with potassium bisperoxo(1,10 phenanthroline)oxovanadate (bpV(phen), a protein tyrosine phosphatase inhibitor. Additional studies were performed with phenylarsine oxide (a PLCgamma inhibitor) and other inhibitors. Western blots were performed to determine the phosphotyrosine PLCgamma1 levels.

RESULTS

Spontaneous contractile activity and tyrosine phosphorylation of PLCgamma1 (but not PLCgamma2) were increased significantly in response to bpV(phen); in contrast, oxytocin and thrombin produced comparable contractile activity but did not alter phosphotyrosine-PLCgamma1. Phenylarsine oxide and neomycin significantly decrease bpV(phen)-stimulated contractions and PLCgamma1 tyrosine phosphorylation; other inhibitors only suppressed contractions.

CONCLUSION

These studies support the hypothesis that spontaneous myometrial contractions are associated with tyrosine phosphorylation of PLCgamma1; both of which are further enhanced by the inhibition of protein tyrosine phosphatase activity.

Angiotensin II-induced delayed stimulation of phospholipase C gamma1 requires activation of both phosphatidylinositol 3-kinase gamma and tyrosine kinase in vascular myocytes

In vascular smooth muscles, angiotensin II (AII) has been reported to activate phospholipase C (PLC) and phosphatidylinositol 3-kinase (PI3K). We investigated the time-dependent effects of AII on both phosphatidylinositol 3,4,5-trisphosphate (PtdInsP3) and inositol phosphates (InsPs) accumulation in permeabilized microsomes from rat portal vein smooth muscle in comparison with those of noradrenaline (NA). AII stimulated an early production of PtdInsP3 (within 30 s) followed by a delayed production of InsPs (within 3-5 min), in contrast to NA which activated only a fast production of InsPs. The use of pharmacological inhibitors and antibodies raised against the PI3K and PLC isoforms expressed in portal vein smooth muscle showed that AII specifically activated PI3Kδ and that this isoform was involved in the AII-induced stimulation of InsPs accumulation. NA-induced InsPs accumulation depended on PLCβ1 activation whereas AII-induced InsPs accumulation depended on PLCγ1 activation. AII-induced PLCδ1 activation required both tyrosine kinase and PI3Kδ since genistein and tyrphostin B48 (inhibitors of tyrosine kinase), LY294002 and wortmannin (inhibitors of PI3K) and anti-PI3Kδ antibody abolished AII-induced stimulation of InsPs accumulation. Increased tyrosine phosphorylation of PLCβ1 was only detected for long-lasting applications of AII and was suppressed by genistein. These data indicate that activation of both PI3Kβ and tyrosine kinase is a prerequisite for AII-induced stimulation of PLCβ1 in vascular smooth muscle and suggest that the sequential activation of the three enzymes may be responsible for the slow and long-lasting contraction induced by AII.

Phospholipase Cgamma1 stimulates transcriptional activation of the matrix metalloproteinase-3 gene via the protein kinase C/Raf/ERK cascade

The phospholipid hydrolase phospholipase Cgamma1 (PLCgamma1) plays a major role in regulation of cell proliferation, development, and cell motility. Overexpression of PLCgamma1 is associated with tumor development, and it is overexpressed in some tumors. Matrix metalloproteinase-3 (MMP-3) is a protein involved in tumor invasion and metastasis. Here, we demonstrate that overexpression of PLCgamma1 stimulates MMP-3 expression at the transcriptional level via the PKC-mediated Raf/MEK1/ERK signaling cascade. We propose that modulation of PLCgamma1 activity might be of value in controlling the activity of MMPs, which are important regulators of invasion and metastasis in malignant tumors.

Cordycepin (3'-deoxyadenosine) inhibits human platelet aggregation in a cyclic AMP- and cyclic GMP-dependent manner

Cordycepin (3'-deoxyadenosine) is isolated from Cordyceps militaris, a species of the fungal genus Cordyceps. Cordycepin is an ingredient used in traditional Chinese medicine and is prescribed for various diseases, such as cancer and chronic inflammation. In this study, we investigated the novel effect of cordycepin (3'-deoxyadenosine) on collagen-induced human platelet aggregation. Cordycepin inhibited dose-dependently collagen-induced platelet aggregation in the presence of various concentrations of exogenous CaCl(2). Of two aggregation-inducing molecules, cytosolic free Ca(2+) ([Ca(2+)](i)) and thromboxane A(2) (TXA(2)), cordycepin (500 microM) blocked the up-regulation of [Ca(2+)](i), by up to 74%, but suppressed TXA(2) production by 46%. Subsequently, Ca(2+)-dependent phosphorylation of both 47-kDa and 20-kDa proteins in collagen-treated platelets was potently diminished by cordycepin. However, upstream pathways for producing these two inducers, such as the activation of phospholipase C-gamma2 (PLC-gamma2) (assessed by the phosphotyrosine level) and the formation of inositol 1,4,5-trisphosphate (IP(3)), were not altered by cordycepin. Cordycepin increased the level of second messengers adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) in collagen-stimulated platelets. Whereas the NO-sensitive guanylyl cyclase inhibitor ODQ did not alter the cordycepin-induced up-regulation of cGMP, the adenylyl cyclase inhibitor SQ22536 completely blocked the cAMP enhancement mediated by cordycepin, indicating that cordycepin had different modes of action. Therefore, our data suggest that the inhibitory effect of cordycepin on platelet aggregation might be associated with the down-regulation of [Ca(2+)](i) and the elevation of cAMP/cGMP production.

PLCγ contributes to metastasis of in situ-occurring mammary and prostate tumors

Phospholipase C-gamma (PLCgamma) has been implicated in tumor cell motility required for invasiveness and metastasis. Diminished tumor dissemination has been demonstrated in xenograft models, but studies in naturally-occurring tumors are lacking, having been limited by the timing of the interventions. Therefore, we generated mice that express a doxycycline (DOX)-inducible dominant-negative fragment of PLCgamma, PLCz; this approach avoids the in utero lethality caused by the absence of PLCgamma. As we targeted two de novo-occurring carcinomas of the mammary (MMTV-driven polyoma middle T antigen model, PyVmT) and prostate (TRAMP model) glands, we limited expression to these epithelial cells by driving DOX transactivator from the prostatein C3 promoter. This avoids the confounding variable of potentially abrogating motility in stromal and endothelial cells. These mice developed normally in the presence of DOX, except for limited mammary development if treated before 6 weeks and immaturity of the prostate gland if treated before 2 weeks of age. DOX-mediated induction of PLCz from age 8 to 16 weeks in PyVmT mice decreased the number of lung metastases by >10-fold (P<0.06) without a detectable effect on in situ tumor cell proliferation or tumor size. Lung metastases were also significantly decreased in the TRAMP model in which the mice expressed the PLCz fragment (P<0.05). DOX treatment itself had no effect on tumor size or metastasis in control mice, nor did it affect tumor dissemination in nontransgenic littermates. In conclusion, abrogation of the PLCgamma signaling pathway can limit the metastatic potential of carcinomas.

Distinct but critical roles for integrin ?IIb?3in platelet lamellipodia formation on fibrinogen, collagen-related peptide and thrombin

Integrins are the major receptor type known to facilitate cell adhesion and lamellipodia formation on extracellular matrix proteins. However, collagen-related peptide and thrombin have recently been shown to mediate platelet lamellipodia formation when presented as immobilized surfaces. The aims of this study were to establish if there exists a role for the platelet integrin alpha(IIb)beta(3) in this response; and if so, whether signalling from the integrin is required for lamellipodia formation on these surfaces. Real-time analysis was used to compare platelet morphological changes on surfaces of fibrinogen, collagen-related peptide or thrombin in the presence of various pharmacological inhibitors and platelets from 'knockout' mice. We demonstrate that collagen-related peptide and thrombin stimulate distinct patterns of platelet lamellipodia formation and elevation of intracellular Ca(2+) to that induced by the integrin alpha(IIb)beta(3) ligand, fibrinogen. Nevertheless, lamellipodia formation on collagen-related peptide and thrombin is dependent upon engagement of alpha(IIb)beta(3), consistent with release of alpha(IIb)beta(3) ligand(s) from platelet granules. However, the requirement for signalling by the integrin on fibrinogen can be bypassed by the addition of thrombin to the solution. These observations reveal a critical role for alpha(IIb)beta(3) in forming lamellipodia on collagen-related peptide and thrombin which is dependent on its ability to function as an adhesive receptor but not necessarily on its ability to signal. These results suggest that integrins may play an important role in lamellipodia formation triggered by nonintegrin ligands in platelets and possibly in other cell types.

A PI3K pathway mediates hair cell survival and opposes gentamicin toxicity in neonatal rat organ of Corti

Gentamicin is well known to promote hair cell death in inner ear, but it also appears to activate opposing pathways that promote hair cell survival. In combination with others, our previous work has indicated that a K-Ras/Rac/JNK pathway is important for hair cell death and an H-Ras/Raf/MEK/Erk pathway is involved in promoting hair cell survival (Battaglia et al., Neuroscience 122(4):1025-1035, 2003). However, these data also suggested that a Ras-independent survival pathway for activation of MEK might be stimulated by gentamicin. To investigate alternatives to the Ras/Raf/MEK/Erk pathway in promoting hair cell survival, cochlear explants were exposed to gentamicin combined with several inhibitors of alternative pathways (LY294002, calphostin C, SH-6, U73122). When exposed to gentamicin with the PI3K inhibitor LY294002 (10, 50 microM), the protein kinase C (PKC) inhibitor calphostin C (50, 100 nM) or the PKB/Akt inhibitor SH-6 (5, 10 microM), hair cell damage was significantly increased compared to gentamicin alone. By Western blotting, strong PKB/Akt activation was observed in the organ of Corti following exposure to 50 microM gentamicin for 6 h. In addition, PKC activation by 12-O-tetradecanoylphorbol-13-acetate protected outer hair cells from gentamicin induced cell death. In contrast, the phospholipase C-gamma (PLCgamma) inhibitor U73122 (2, 5 microM) did not affect hair cell damage when combined with gentamicin. Also, phosphorylation of PLCgamma was not increased in the organ of Corti following gentamicin treatment, as evaluated by Western blot. The results indicate that PI3K promotes hair cell survival via its downstream targets, PKC and PKB/Akt. This suggests that both Ras-dependent and Ras-independent survival pathways are involved during gentamicin exposure. In contrast, PLCgamma activation of PKC does not appear to play a role.

Essential role of phospholipase C gamma 2 in early B-cell development and Myc-mediated lymphomagenesis

Phospholipase Cgamma2 (PLCgamma2) is a critical signaling effector of the B-cell receptor (BCR). Here we show that PLCgamma2 deficiency impedes early B-cell development, resulting in an increase of B220+ CD43+ BP-1+ CD24hi pre-BCR+ large pre-B cells. PLCgamma2 deficiency impairs pre-BCR-mediated functions, leading to enhanced interleukin-7 (IL-7) signaling and elevated levels of RAGs in the selected large pre-B cells. Consequently, PLCgamma2 deficiency renders large pre-B cells susceptible to transformation, resulting in dramatic acceleration of Myc-induced lymphomagenesis. PLCgamma2(-/-) Emu-Myc transgenic mice mainly develop lymphomas of B220+ CD43+ BP-1+ CD24hi pre-BCR+ large pre-B-cell origin, which are uncommon in wild-type Emu-Myc transgenics. Furthermore, lymphomas from PLCgamma2(-/-) Emu-Myc transgenic mice exhibited a loss of p27Kip1 and often displayed alterations in Arf or p53. Thus, PLCgamma2 plays an important role in pre-BCR-mediated early B-cell development, and its deficiency leads to markedly increased pools of the most at-risk large pre-B cells, which display hyperresponsiveness to IL-7 and express high levels of RAGs, making them prone to secondary mutations and Myc-induced malignancy.

Interaction of phospholipase C-gamma1 with villin regulates epithelial cell migration

Tyrosine-phosphorylated villin regulates actin dynamics, cell morphology, and cell migration. Previously, we identified four tyrosine phosphorylation sites in the amino-terminal domain of villin. In this study we report six new sites in the carboxyl-terminal region of the villin core. With this study we document all phosphorylatable tyrosine residues in villin and map them to functions of villin. In this study, we identify for the first time the functional relevance of the carboxyl-terminal domains of the villin core. Expression of the carboxyl-terminal phosphorylation site mutant, as well as the villin truncation mutant S1-S3, inhibited cell migration in HeLa and Madin-Darby canine kidney Tet-Off cells, confirming the role of the carboxyl-terminal phosphorylation sites in villin-induced cell migration. The carboxyl-terminal phosphorylation sites were found to be critical for the interaction of villin with its ligand phospholipase C-gamma1 and for its localization to the developing lamellipodia in a motile cell. The results presented here elucidate the molecular basis for tyrosine-phosphorylated villin-induced changes in cell motility.

CD86 stimulation on a B cell activates the phosphatidylinositol 3-kinase/Akt and phospholipase C gamma 2/protein kinase C alpha beta signaling pathways

Stimulation of CD86 on a CD40L/IL-4-activated murine B cell increases the rate of mature IgG1 transcription by increasing the level of NF-kappaB activation, as well as Oct-2 expression and binding to the 3'-IgH enhancer. The signal transduction pathway activated by CD86 proximal to NF-kappaB activation is unknown. In this study, we show that CD86 stimulation on an activated B cell increases the activity of PI3K and the phosphorylation of phosphoinositide-dependent kinase 1, Akt, and IkappaB kinase alphabeta. In addition, CD86 stimulation induces an increase in the phosphorylation of phospholipase Cgamma2 and protein kinase C alphabeta. CD86-mediated activation of these two signaling pathways leads to increased Oct-2 expression, increased gene activity mediated by NF-kappaB and 3'-IgH enhancer increased activity. These results identify a previously unknown signaling pathway induced by CD86 to regulate the level of B cell gene expression and activity.

Quantitative analysis of phosphotyrosine signaling networks triggered by CD3 and CD28 costimulation in Jurkat cells

The mechanism by which stimulation of coreceptors such as CD28 contributes to full activation of TCR signaling pathways has been intensively studied, yet quantitative measurement of costimulation effects on functional TCR signaling networks has been lacking. In this study, phosphotyrosine networks triggered by CD3, CD28, or CD3 and CD28 costimulation were analyzed by site-specific quantitative phosphoproteomics, resulting in identification of 101 tyrosine and 3 threonine phosphorylation sites and quantification of 87 sites across four cell states. As expected, CD3 stimulation induced phosphorylation of CD3 chains and upstream components of TCR pathways such as Zap70, while CD28 stimulation induced phosphorylation of CD28, Vav-1, and other adaptor proteins including downstream of tyrosine kinase 1, Grb2-associated protein 2 (Grap2), and Wiskott-Aldrich syndrome protein. CD3 and CD28 costimulation induced a complex response including decreased threonine phosphorylation in the ERK1 and ERK2 activation loops and increased phosphorylation of selected tyrosine sites on ERK1/2, p38, phospholipase C-gamma, Src homology 2 domain-containing transforming protein 1, Grap2, and Vav-1, potentiating T cell activation. Hierarchical clustering and self-organizing maps were used to identify modules of coregulated phosphorylation sites within the network. Quantitative information in our study suggests quantitative and qualitative contribution by costimulation of CD28 on CD3-stimulated TCR signaling networks via enhanced phosphorylation of phospholipase C-gamma/Src homology 2 domain-containing transforming protein 1/Grap2/Vav-1 and their effects on downstream components including MAPKs.

Signal transduction at fertilization: The Ca2+ release pathway in echinoderms and other invertebrate deuterostomes

Gamete interaction and fusion triggers a number of events that lead to egg activation and development of a new organism. A key event at fertilization is the rise in intracellular calcium. In deuterostomes, this calcium is released from the egg's endoplasmic reticulum and is necessary for proper activation. This article reviews recent data regarding how gamete interaction triggers the initial calcium release, focusing on the echinoderms (invertebrate deuterostomes) as model systems. In eggs of these animals, Src-type kinases and phospholipase C-gamma are required components of the initial calcium trigger pathway in eggs.

The transcription factor AP-2beta causes cell enlargement and insulin resistance in 3T3-L1 adipocytes

We have reported the association of variations in the activating protein-2beta (AP-2beta) transcription factor gene with type 2 diabetes. This gene was preferentially expressed in 3T3-L1 adipocytes in a differentiation stage-dependent manner, and preliminary experiments showed that subjects with the disease-susceptible allele showed stronger expression in adipose tissue than those without the susceptible allele. Thus, we overexpressed the AP-2beta gene in 3T3-L1 adipocytes to clarify whether AP-2beta might play a crucial role in the pathogenesis of type 2 diabetes through dysregulation of adipocyte function. In cells overexpressing AP-2beta, cells increased in size by accumulation of triglycerides accompanied by enhanced glucose uptake. On the contrary, suppression of AP-2beta expression by small interfering RNA inhibited glucose uptake. Enhancement of glucose uptake by AP-2beta overexpression was attenuated by inhibitors of phospholipase C (PLC) and atypical protein kinase Czeta/lambda (PKCzeta/lambda), but not by a phosphatidylinositol 3-kinase (PI3-K) inhibitor. Consistently, we found activation of PLC and atypical PKC, but not PI3-K, by AP-2beta expression. Furthermore, overexpression of PLCgamma enhanced glucose uptake, and this activation was inhibited by an atypical PKC inhibitor, suggesting that the enhanced glucose uptake may be mediated through PLC and atypical PKCzeta/lambda, but not PI3-K. Moreover, we observed the increased tyrosine phosphorylation of Grb2-associated binder-1 (Gab1) and its association with PLCgamma, indicating that Gab1 may be involved in AP-2beta-induced PLCgamma activation. Finally, AP-2beta overexpression was found to relate to the impaired insulin signaling. We propose that AP-2beta is a candidate gene for producing adipocyte hypertrophy and may relate to the abnormal characteristics of adipocytes observed in obesity.

Distinct roles of phosphoinositide-3 kinase and phospholipase Cgamma2 in B-cell receptor-mediated signal transduction

During B-cell receptor (BCR) signaling, phosphoinositide-3 kinase (PI3K) is thought to function upstream of phospholipase Cgamma2 (PLCgamma2). PLCgamma2 deficiency specifically impedes transitional type 2 (T2) to follicular (FO) mature B-cell transition. Here, we demonstrate that PI3K deficiency specifically impaired T2-to-FO mature B-cell transition and marginal zone B-cell development. Furthermore, we investigated the functional relationship between PI3K and PLCgamma2 using PI3K-/-, PLCgamma2-/-, and PI3K-/- PLCgamma2-/- B cells. Interestingly, PLCgamma2 deficiency had no effect on BCR-mediated PI3K activation, whereas PI3K deficiency only partially blocked activation of PLCgamma2. Moreover, whereas PI3K-/- PLCgamma2-/- double deficiency did not affect hematopoiesis, it resulted in embryonic lethality. PI3K-/- PLCgamma2-/- fetal liver cells transplanted into B-cell null JAK3-/- mice failed to restore development of peripheral B cells and failed to progress through early B-cell development at the pro-B- to pre-B-cell transition, a more severe phenotype than was observed with either PI3K or PLCgamma2 single-deficiency B cells. Consistent with this finding, BCR signaling was more severely impaired in the absence of both PI3K and PLCgamma2 genes than in the absence of either one alone. Taken together, these results demonstrate that whereas PI3K functions upstream of PLCgamma2, activation of PLCgamma2 can occur independently of PI3K and that PI3K and PLCgamma2 also have distinct functions in BCR signal transduction.

A cyclic adenosine 3',5'-monophosphate stimulates phospholipase Cgamma1-calcium signaling via the activation of tyrosine kinase in boar spermatozoa

The aim of this study was to reveal a downstream part of the intracellular signaling that is mediated by cyclic adenosine monophosphate (cAMP)-dependent tyrosine kinases, including spleen tyrosine (Y) kinase (SYK), in boar spermatozoa. Ejaculated spermatozoa were incubated with cBiMPS (a cell-permeable cAMP analog; 0.1 mM) at 38.5 degrees C for 180 minutes and then used for Western blot and indirect immunofluorescence. Incubation of spermatozoa with cBiMPS induced tyrosine phosphorylation at the linker region of SYK (which was essential to binding to phospholipase C [PLC]gamma1) in the connecting and principal pieces, but the tyrosine phosphorylation was abolished by the addition of H-89 (a protein kinase A [PKA] inhibitor; 0.01-0.1 mM). Moreover, the cAMP-dependent tyrosine phosphorylation was also induced at the key regulatory residue of PLCgamma1 in the same segments of spermatozoa, but it was inhibited by the addition of herbimycin A (a tyrosine kinase inhibitor; 5 microM). These results suggest that the sperm cAMP-dependent tyrosine kinases, including SYK, are linked to the activation of PLCgamma1. Indirect immunofluorescence clearly detected both inositol 1,4,5-trisphosphate (IP(3)) receptor and calreticulin in the connecting piece, indicating the presence of internal calcium store. Cell imaging with fluo-3/AM (a cell-permeable Ca(2+) indicator) showed that incubation of spermatozoa with cBiMPS increased intracellular free calcium in the middle piece, but that it was reduced by the addition of U-73122 (a PLC inhibitor; 0.02 mM). Based on our findings, we conclude that the connecting piece of boar spermatozoa possesses the PLCgamma1-IP(3) receptor-calcium signaling that is triggered by cAMP and mediated by PKA and herbimycin A-sensitive tyrosine kinases, including SYK.

K644E/M FGFR3 mutants activate Erk1/2 from the endoplasmic reticulum through FRS2 alpha and PLC gamma-independent pathways

Fibroblast growth factor receptors 3 (FGFR3) with K644M/E substitutions are associated to the severe skeletal dysplasias: severe achondroplasia with developmental delay and achanthosis nigricans(SADDAN) and thanatophoric dysplasia(TDII). The high levels of kinase activity of the FGFR3-mutants cause uncompleted biosynthesis that results in the accumulation of the immature/mannose-rich, phosphorylated receptors in the endoplasmic reticulum (ER) and STATs activation. Here we report that FGFR3 mutants activate Erk1/2 from the ER through an FRS2-independent pathway: instead, a multimeric complex by directly recruiting PLCgamma, Pyk2 and JAK1 is formed. The Erk1/2 activation from the ER however, is PLCgamma-independent, since preventing the PLCgamma/FGFR3 interaction by the Y754F substitution does not inhibit Erks. Furthermore, Erk1/2 activation is abrogated upon treatment with the Src inhibitor PP2, suggesting a role played by a Src family member in the pathway from the ER. Finally we show that the intrinsic kinase activity by mutant receptors is required to allow signaling from the ER. Overall these results highlight how activated FGFR3 exhibits signaling activity in the early phase of its biosynthesis and how segregation in a sub-cellular compartment can affect the FGFR3 multi-faceted capacity to recruit specific substrates.

Contrasting role of phospholipase C-gamma1 in the expression of immediate early genes induced by epidermal or platelet-derived growth factors

While significant progress has been achieved in identifying the signal transduction elements that operate downstream of activated receptor tyrosine kinases, it remains unclear how different receptors utilize these signaling elements to achieve a common response. This study compares the capacity of epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) to elicit the induction of immediate early gene (IEG) mRNAs in the presence or absence of phospholipase C-gamma1 (PLC-gamma1). The results show that while PDGF induction of nearly all IEG mRNAs is abrogated in plcg1 null cells, EGF induction of the same genes is variable in the null cells and exhibits three distinct responses. Five IEG mRNAs (Nup475, Cyr61, TF, Gly, TS7) are completely inducible by EGF in the presence or absence of PLC-gamma1, while three others (JE, KC, FIC) exhibit a stringent requirement for the presence of PLC-gamma1. The third type of response is exhibited by c-fos and COX-2. While these mRNAs are completely induced by EGF in the absence of PLC-gamma1, the time course of their accumulation is significantly delayed. No IEG was identified as completely inducible by EGF and PDGF in the absence of PLC-gamma1. Electrophoretic mobility shift assays (EMSA) demonstrate that PLC-gamma1 is necessary for nuclear extracts from PDGF-treated cells, but not EGF-treated cells, to interact with probes for AP-1 or NF-kappaB.

Targeting of protein kinase C-epsilon during Fcgamma receptor-dependent phagocytosis requires the epsilonC1B domain and phospholipase C-gamma1

Protein kinase C-epsilon (PKC-epsilon) translocates to phagosomes and promotes uptake of IgG-opsonized targets. To identify the regions responsible for this concentration, green fluorescent protein (GFP)-protein kinase C-epsilon mutants were tracked during phagocytosis and in response to exogenous lipids. Deletion of the diacylglycerol (DAG)-binding epsilonC1 and epsilonC1B domains, or the epsilonC1B point mutant epsilonC259G, decreased accumulation at phagosomes and membrane translocation in response to exogenous DAG. Quantitation of GFP revealed that epsilonC259G, epsilonC1, and epsilonC1B accumulation at phagosomes was significantly less than that of intact PKC-epsilon. Also, the DAG antagonist 1-hexadecyl-2-acetyl glycerol (EI-150) blocked PKC-epsilon translocation. Thus, DAG binding to epsilonC1B is necessary for PKC-epsilon translocation. The role of phospholipase D (PLD), phosphatidylinositol-specific phospholipase C (PI-PLC)-gamma1, and PI-PLC-gamma2 in PKC-epsilon accumulation was assessed. Although GFP-PLD2 localized to phagosomes and enhanced phagocytosis, PLD inhibition did not alter target ingestion or PKC-epsilon localization. In contrast, the PI-PLC inhibitor U73122 decreased both phagocytosis and PKC-epsilon accumulation. Although expression of PI-PLC-gamma2 is higher than that of PI-PLC-gamma1, PI-PLC-gamma1 but not PI-PLC-gamma2 consistently concentrated at phagosomes. Macrophages from PI-PLC-gamma2-/- mice were similar to wild-type macrophages in their rate and extent of phagocytosis, their accumulation of PKC-epsilon at the phagosome, and their sensitivity to U73122. This implicates PI-PLC-gamma1 as the enzyme that supports PKC-epsilon localization and phagocytosis. That PI-PLC-gamma1 was transiently tyrosine phosphorylated in nascent phagosomes is consistent with this conclusion. Together, these results support a model in which PI-PLC-gamma1 provides DAG that binds to epsilonC1B, facilitating PKC-epsilon localization to phagosomes for efficient IgG-mediated phagocytosis.

Early phosphorylation kinetics of proteins involved in proximal TCR-mediated signaling pathways

Activation of T cells via the stimulation of the TCR plays a central role in the adaptive immunological response. Although much is known about TCR-stimulated signaling pathways, there are still gaps in our knowledge about the kinetics and sequence of events during early activation and about the in vivo specificity of kinases involved in these proximal signaling pathways. This information is important not only for understanding the activation of signaling pathways important for T cell function but also for the development of drug targets and computer-based molecular models. In this study, phospho-specific Abs directed toward individual sites on signaling proteins were used to investigate the early phosphorylation kinetics of proteins involved in proximal TCR-induced pathways. These studies indicate that linker for activation of T cells' tyrosines have substantially different phosphorylation kinetics and that Src homology 2 domain-containing leukocyte protein of 76 kDa has rapid, transient phosphorylation kinetics compared to other proteins. In additions, we provide evidence that ZAP-70 is the primary in vivo kinase for LAT tyrosine 191 and that Itk plays a role in the phosphorylation of tyrosine 783 on phospholipase C-gamma1. In total, these studies give new insight into the sequence, kinetics and specificity of early TCR-mediated signaling events that are vital for T cell activation.

A novel Syk-dependent mechanism of platelet activation by the C-type lectin receptor CLEC-2

The snake venom rhodocytin has been reported to bind to integrin alpha2beta1 and glycoprotein (GP) Ibalpha on platelets, but it is also able to induce activation independent of the 2 receptors and of GPVI. Using rhodocytin affinity chromatography, we have identified a novel C-type lectin receptor, CLEC-2, in platelets that confers signaling responses to rhodocytin when expressed in a cell line. CLEC-2 has a single tyrosine residue in a YXXL motif in its cytosolic tail, which undergoes tyrosine phosphorylation upon platelet activation by rhodocytin or an antibody to CLEC-2, but not to collagen, thrombin receptor agonist peptide (TRAP), or convulxin. Tyrosine phosphorylation of CLEC-2 and other signaling proteins by rhodocytin is inhibited by the Src family kinase inhibitor PP2. Further, activation of murine platelets by rhodocytin is abolished in the absence of Syk and PLCgamma2, and partially reduced in the absence of LAT, SLP-76, and Vav1/Vav3. These findings define a novel signaling pathway in platelets whereby activation of CLEC-2 by rhodocytin leads to tyrosine phosphorylation of its cytosolic tail, binding of Syk and initiation of downstream tyrosine phosphorylation events, and activation of PLCgamma2. CLEC-2 is the first C-type lectin receptor to be found on platelets which signals through this novel pathway.