Gα(q)-coupled receptor stimulation was implied in the activation process of transient receptor potential canonical (TRPC)1/4 and TRPC1/5 heterotetrameric channels. The inactivation occurs due to phosphatidylinositol 4,5-biphosphate (PI(4,5)P₂) depletion. When PI(4,5)P₂ depletion was induced by muscarinic stimulation or inositol polyphosphate 5-phosphatase (Inp54p), however, the inactivation by muscarinic stimulation was greater compared to that by Inp54p. The aim of this study was to investigate the complete inactivation mechanism of the heteromeric channels upon Gα(q)-phospholipase C β (Gα(q)-PLCβ) activation. We evaluated the activity of heteromeric channels with electrophysiological recording in HEK293 cells expressing TRPC channels. TRPC1/4 and TRPC1/5 heteromers undergo further inhibition in PLCβ activation and calcium/protein kinase C (PKC) signaling. Nevertheless, the key factors differ. For TRPC1/4, the inactivation process was facilitated by Ca²⁺ release from the endoplasmic reticulum, and for TRPC1/5, activation of PKC was concerned mostly. We conclude that the subsequent increase in cytoplasmic Ca²⁺ due to Ca²⁺ release from the endoplasmic reticulum and activation of PKC resulted in a second phase of channel inhibition following PI(4,5)P₂ depletion.
Calcium ; Cytoplasm ; Endoplasmic Reticulum ; GTP-Binding Proteins ; HEK293 Cells ; Inositol ; Phosphatidylinositol 4,5-Diphosphate ; Phospholipases ; Phosphotransferases ; Protein Kinase C ; Transient Receptor Potential Channels ; Type C Phospholipases

Neurite outgrowth, a cell differentiation process involving membrane morphological changes, is critical for neuronal network and development. The membrane lipid, phosphatidylinositol (PI) 4,5-bisphosphate (PIP2), is a key regulator of many important cell surface events of membrane signaling, trafficking and dynamics. This lipid is produced mainly by the type I PI 4-phosphate 5-kinase (PIP5K) family members. In this study, we addressed whether PIP5Kalpha, an isoform of PIP5K, could have a role in neurite outgrowth induced by nerve growth factor (NGF). For this purpose, we knocked down PIP5Kalpha in PC12 rat pheochromocytoma cells by stable expression of PIP5Kalpha microRNA that significantly reduced PIP5Kalpha expression and PIP2 level. Interestingly, NGF-induced neurite outgrowth was more prominent in PIP5Kalpha-knockdown (KD) cells than in control cells. Conversely, add-back of PIP5Kalpha into PIP5Kalpha KD cells abrogated the effect of NGF on neurite outgrowth. NGF treatment activated PI 3-kinase (PI3K)/Akt pathway, which seemed to be associated with reactive oxygen species generation. Similar to the changes in neurite outgrowth, the PI3K/Akt activation by NGF was potentiated by PIP5Kalpha KD, but was attenuated by the reintroduction of PIP5Kalpha. Moreover, exogenously applied PIP2 to PIP5Kalpha KD cells also suppressed Akt activation by NGF. Together, our results suggest that PIP5Kalpha acts as a negative regulator of NGF-induced neurite outgrowth by inhibiting PI3K/Akt signaling pathway in PC12 cells.
Animals ; Enzyme Activation/drug effects ; Gene Knockdown Techniques ; Mice ; Nerve Growth Factor/*pharmacology ; Neurites/drug effects/*enzymology ; PC12 Cells ; Phosphatidylinositol 3-Kinases/metabolism ; Phosphatidylinositol 4,5-Diphosphate/metabolism ; Phosphorylation/drug effects ; Phosphotransferases (Alcohol Group Acceptor)/*metabolism ; Proto-Oncogene Proteins c-akt/metabolism ; Rats ; Reactive Oxygen Species/metabolism ; Signal Transduction/drug effects

Phosphoinositide-specific phospholipase C-gamma1 (PLC-gamma1) has two pleckstrin homology (PH) domains: an amino-terminal domain (PH1) and a split PH domain (PH2). Here, we show that overlay assay of bovine brain tubulin pool with glutathione-S-transferase (GST)-PLC-gamma1 PH domain fusion proteins, followed by matrix-assisted laser-desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), identified 68-kDa neurofilament light chain (NF-L) as a binding protein of amino-terminal PH domain of PLC-gamma1. NF-L is known as a component of neuronal intermediate filaments, which are responsible for supporting the structure of myelinated axons in neuron. PLC-gamma1 and NF-L colocalized in the neurite in PC12 cells upon nerve growth factor stimulation. In vitro binding assay and immunoprecipitation analysis also showed a specific interaction of both proteins in differentiated PC12 cells. The phosphatidylinositol 4, 5-bisphosphate [PI(4,5)P2] hydrolyzing activity of PLC-gamma1 was slightly decreased in the presence of purified NF-L in vitro, suggesting that NF-L inhibits PLC-gamma1. Our results suggest that PLC-gamma1-associated NF-L sequesters the phospholipid from the PH domain of PLC-gamma1.
Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization ; Rats ; Protein Interaction Mapping ; Protein Biosynthesis/drug effects ; Protein Binding/drug effects ; Phosphoproteins/chemistry/*metabolism ; Phospholipase C gamma/antagonists & inhibitors/chemistry/*metabolism ; Phosphatidylinositol 4,5-Diphosphate/metabolism ; Peptides/chemistry/metabolism ; PC12 Cells ; Neurofilament Proteins/chemistry/*metabolism ; Nerve Growth Factor/pharmacology ; Molecular Weight ; Molecular Sequence Data ; Microtubules/metabolism ; Microscopy, Fluorescence ; Isoenzymes/metabolism/pharmacology/physiology ; Glutathione Transferase/metabolism ; Blotting, Far-Western ; Blood Proteins/chemistry/*metabolism ; Binding Sites ; Animals ; Amino Acid Sequence

OBJECTIVETo test whether tanshinone II A (Tan II A), a highly valued herb derivative to treat vascular diseases in Chinese medicine, could protect endothelial cells from bacterial endotoxin (lipopolysaccharides, LPS)-induced endothelial injury.

METHODSEndothelial cell injury was induced by treating human umbilical vein endothelial cells (HUVECs) with 0.2 μg/mL LPS for 24 h. Y27632 and valsartan were used as positive controls. The effects of tanshinone II A on the LPS-induced cell viability and apoptosis rate of HUVECs were tested by flow cytometry, cell migration by transwell, adhesion by a 96-well plate pre-coated with vitronectin and cytoskeleton reorganization by immunofluorescence assay. Rho/Rho kinase (ROCK) pathway-associated gene and protein expression were examined by microarray assay; quantitative real-time polymerase chain reaction and Western blotting were used to confirm the changes observed by microarray.

RESULTSTan II A improved cell viability, suppressed apoptosis and protected cells from LPS-induced reductions in cell migration and adhesion at a comparable magnitude to that of Y27632 and valsartan. Tan II A, Y27632 and valsartan also normalized LPS-induced actomyosin contraction and vinculin protein aggregation. A microarray assay revealed increased levels of fibronectin, integrin A5 (ITG A5), Ras homolog gene family member A (RhoA), myosin light chain phosphatase, phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K, or PIP2 in Western blotting), focal adhesion kinase, vascular endothelial growth factor and vascular endothelial growth factor receptor 2 in the damaged HUVECs, which were attenuated to different degrees by Tan II A, Y27632 and valsartan.

CONCLUSIONTan II A exerted a strong protective effect on HUVECs, and the mechanism was caused, at least in part, by a blockade in the Rho/ROCK pathway, presumably through the down-regulation of ITG A5.

Apoptosis ; drug effects ; Cell Adhesion ; drug effects ; Cell Movement ; drug effects ; Cell Shape ; drug effects ; Cell Survival ; drug effects ; Cytoprotection ; drug effects ; Cytoskeleton ; drug effects ; metabolism ; Diterpenes, Abietane ; chemistry ; pharmacology ; Down-Regulation ; drug effects ; genetics ; Human Umbilical Vein Endothelial Cells ; drug effects ; enzymology ; pathology ; Humans ; Integrin alphaV ; metabolism ; Lipopolysaccharides ; Myosin Light Chains ; metabolism ; Oligonucleotide Array Sequence Analysis ; Phosphatidylinositol 4,5-Diphosphate ; metabolism ; Protective Agents ; pharmacology ; Signal Transduction ; drug effects ; Up-Regulation ; drug effects ; genetics ; Vinculin ; metabolism ; rho GTP-Binding Proteins ; metabolism ; rho-Associated Kinases ; metabolism