We previously shown that LES contraction depends on M3 receptors linked to PTX insensitive Gq protein and activation of PLC. This results in production of IP3, which mediates calcium release, and contraction through a CaM dependent pathway. In the esophagus ACh activates M2 receptors linked to PTX sensitive Gi3 protein, resulting in activation of PLD, presumably, production of DAG. We investigated the role of PLC isozymes which can be activated by Gq or Gbeta protein on ACh-induced contraction in LES and esophagus. Immunoblot analysis showed the presence of 3 types of PLC isozymes, PLC-beta1, PLC-beta3, and PLC-gamma1, but not PLC-beta2, PLC-beta4, PLC-gamma2, PLC-delta1, and PLC-delta2 from both LES and esophageal muscle. ACh produced contraction in a dose dependent manner in LES and esophageal muscle cells obtained by enzymatic digestion with collagenase. PLC-beta1 or PLC-beta3 antibody incubation reduced contraction in response to ACh in LES but not in esophageal permeabilized cells, but PLC-gamma1 antibody incubation did not have an inhibitory effect. The inhibition by PLC-beta1 or PLC-beta3 antibody on Ach-induced contraction was antibody concentration dependent. The combination with PLC-beta1 and PLC-beta3 antibody completely abolished the contraction, suggesting that PLC-beta1 and PLC-beta3 have a synergism to inhibit the contraction in LES. PLC-beta1, -beta3 or -gamma1 antibody did not reduce the contraction of LES cells in response to DAG (10 (-6) M), suggesting that this isozyme of PLC may not activate PKC. When Gq/11 antibody was incubated, the inhibitory effect of the incubation of PLC beta3, but not of PLC beta1 was additive (Fig. 6). In contrast, when Gbeta antibody was incubated, the inhibitory effect of the incubation of PLC beta1, but not of PLC beta3 was additive. This data suggest that Gq/11 or Gbeta may activate cooperatively different PLC isozyme, PLCbeta1 or PLCbeta3 respectively.
Animals ; Calcium ; Cats* ; Collagenases ; Digestion ; Esophageal Sphincter, Lower* ; Esophagus ; GTP-Binding Protein alpha Subunits, Gq-G11* ; Isoenzymes ; Muscle Cells ; Phospholipase C beta ; Type C Phospholipases

More than 85% of patients with uveal melanoma (UM) carry a GNAQ or GNA11 mutation at a hotspot codon (Q209) that encodes G protein α subunit q/11 polypeptides (Gα_q/11). GNAQ/11 relies on palmitoylation for membrane association and signal transduction. Despite the palmitoylation of GNAQ/11 was discovered long before, its implication in UM remains unclear. Here, results of palmitoylation-targeted mutagenesis and chemical interference approaches revealed that the loss of GNAQ/11 palmitoylation substantially affected tumor cell proliferation and survival in UM cells. Palmitoylation inhibition through the mutation of palmitoylation sites suppressed GNAQ/11^Q209L-induced malignant transformation in NIH3T3 cells. Importantly, the palmitoylation-deficient oncogenic GNAQ/11 failed to rescue the cell death initiated by the knock down of endogenous GNAQ/11 oncogenes in UM cells, which are much more dependent on Gα_q/11 signaling for cell survival and proliferation than other melanoma cells without GNAQ/11 mutations. Furthermore, the palmitoylation inhibitor, 2-bromopalmitate, also specifically disrupted Gα_q/11 downstream signaling by interfering with the MAPK pathway and BCL2 survival pathway in GNAQ/11-mutant UM cells and showed a notable synergistic effect when applied in combination with the BCL2 inhibitor, ABT-199, in vitro. The findings validate that GNAQ/11 palmitoylation plays a critical role in UM and may serve as a promising therapeutic target for GNAQ/11-driven UM.
Humans ; Mice ; Animals ; Lipoylation ; NIH 3T3 Cells ; Uveal Neoplasms/genetics* ; Melanoma/genetics* ; Cell Proliferation ; Proto-Oncogene Proteins c-bcl-2 ; GTP-Binding Protein alpha Subunits, Gq-G11/genetics*

BACKGROUNDThe role of the G alpha q/11-mediated signal transduction pathway in angiotensin II (AngII) induced cardiac hypertrophy remains unclear. This study was to investigate the role of the G alpha q/11 signal transduction pathway in the development of cardiac hypertrophy in 2K1C hypertensive rats and in cultured neonatal rat ventricular myocytes (NRVMs) and to elucidate the effects of the pathway on AngII induced cardiac hypertrophy.

METHODSRenal hypertension was induced in 2K1C hypertensive rats by placing a silver clip around the left renal artery. At 8 weeks after operation, the systolic blood pressure, the ratio of left ventricular weight to body weight (LV/BW), and the concentration of AngII in the heart were measured. The protein levels of G alpha q/11 and extracellular signal-regulated kinase 1/2 (ERK1/2) were assayed by Western blot analysis, and the activity of phospholipase C (PLC) in the myocardium was detected using [(3)H]-PIP2 as a substrate. Changes in [(3)H]-leucine incorporation and in the protein levels of the signal molecules G alpha q/11, PLC beta 3, and ERK1/2 were measured after NRVMs were stimulated with 10(-7) mol/L AngII.

RESULTSThe protein levels of G alpha q/11 and ERK1/2 in the hearts of 2K1C rats increased by 35.8% and 31.9%, respectively, compared with the sham group. The PLC activity in the 2K1C group was also significantly increased (P < 0.05). The levels of G alpha q/11, PLC beta 3, and ERK1/2 increased significantly after NRVMs were stimulated by AngII. The upregulation of G alpha q/11, PLC beta 3 and ERK1/2 in NRVMs occurred prior to [(3)H]-leucine incorporation increases, and could be inhibited with losartan.

CONCLUSIONAngII can initiate cardiac hypertrophy and upregulate signal molecules in the G alpha q/11-mediated signal transduction pathway, such as G alpha q/11, PLC beta 3 and ERK1/2, at both tissue and cellular levels.

Angiotensin II ; physiology ; Animals ; Cardiomegaly ; etiology ; Cells, Cultured ; GTP-Binding Protein alpha Subunits, Gq-G11 ; physiology ; Hypertension ; complications ; Isoenzymes ; physiology ; Male ; Mitogen-Activated Protein Kinase 3 ; Mitogen-Activated Protein Kinases ; physiology ; Myocytes, Cardiac ; metabolism ; Phospholipase C beta ; Rats ; Rats, Wistar ; Receptor, Angiotensin, Type 1 ; physiology ; Signal Transduction ; physiology ; Type C Phospholipases ; physiology ; Up-Regulation

BACKGROUNDAngiotensin II (AngII) and platelet-derived growth factor (PDGF)-BB can induce hypertrophy in the cultured rat cardiomyocytes through different signal transduction pathways. AngII stimulates growth through G protein coupled receptor (GPCR), while PDGF-BB acts via receptor tyrosine kinase (RTK). Although there has been much development on the individual AngII and PDGF-BB mediated signal pathways, little is known about the interactions between these two factors. Therefore, the crosstalk between AngII and PDGF-BB mediated signal pathways in the rat cardiomyocytes was investigated in this study.

METHODSPrimary culture of neonatal rat ventricular myocytes was prepared. The amount of tyrosine-phosphorylated and non-phosphorylated PDGF-beta receptor, G(alphaq/11), and phospholipase C (PLC) beta(3) were measured by immunoblotting analysis. The statistical analysis was done by one-way ANOVA.

RESULTSTyrosine-phosphorylated PDGF-beta receptor was increased by 120.60% at 1 minute and recovered to the control level at 10 minutes after AngII stimulation. Phosphorylation of PDGF-beta receptor triggered by AngII was blocked by losartan, a specific antagonist of AT1 receptor. PLC inhibitor U73122, protein kinase C (PKC) inhibitor staurosporine (STS) and mitogen-activated ERK activating kinase (MEK) inhibitor PD98059 also inhibited the AngII-induced phosphorylation of PDGF-beta receptor. PDGF-BB slightly increased the expression of G(alphaq/11) protein.

CONCLUSIONAngII transactivates PDGF-beta receptor via AT(1) receptor-G(alphaq/11)-PLC-PKC pathway in the rat cardiomyocytes. ERK also participates in the transactivation of PDGF-beta receptor triggered by AngII.

Angiotensin II ; pharmacology ; Animals ; Cells, Cultured ; GTP-Binding Protein alpha Subunits, Gq-G11 ; metabolism ; Myocytes, Cardiac ; metabolism ; Phosphorylation ; Platelet-Derived Growth Factor ; pharmacology ; Proto-Oncogene Proteins c-sis ; Rats ; Rats, Wistar ; Receptor, Platelet-Derived Growth Factor beta ; metabolism ; Signal Transduction ; physiology ; Type C Phospholipases ; physiology