No Significant Association between PIK3CA Mutation and Survival of Esophageal Squamous Cell Carcinoma: A Meta-analysis / 华中科技大学学报（医学）（英德文版）

The prognostic value of phosphatidylinositol-4,5-bisphosphate 3-kinase,catalytic subunit alpha (PIK3CA) in patients with esophageal squamous cell carcinoma (ESCC) is controversial.We aimed to investigate the prognostic significance of PIK3CA mutation in patients with ESCC.EMBASE,PubMed,and Web of Science databases were systematically searched from inception through Oct.3,2016.The hazard ratios (HRs) and 95％ confidence intervals (CI) were calculated using a random effects model for overall survival (OS) and disease-free survival (DFS).Seven studies enrolling 1505 patients were eligible for inclusion of the current meta-analysis.Results revealed that PIK3CA mutation was not significantly associated with OS (HR:0.90,95％ CI:0.63-1.30,P=0.591),with a significant heterogeneity (I2=65.7％,P=0.012).Additionally,subgroup analyses were further conducted according to various variables,such as types of specimen,the sample size,technique and statistical methodology.All results suggested that no significant relationship was found between PIK3CA mutation and OS in patients with ESCC.For DFS,there was no significant association between PIK3CA mutation and DFS in patients with ESCC (HR:1.00,95％ CI=0.47-2.11,P=0.993,I2=73.7％).Publication bias was not present and the results of sensitivity analysis were very stable in the current meta-analysis.Our findings suggest that PIK3CA mutation has no significant effects on OS and DFS in ESCC patients.More well-designed prospective studies with better methodology for PIK3CA assessment are required to clarify the prognostic significance of PIK3CA mutation in ESCC patients.

Phosphatidylinositol 4-phosphate 5-kinase alpha negatively regulates nerve growth factor-induced neurite outgrowth in PC12 cells

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.

Phosphatidylinositol 4-phosphate 5-kinase alpha is induced in ganglioside-stimulated brain astrocytes and contributes to inflammatory responses

In brain tissue, astrocytes play defensive roles in central nervous system integrity by mediating immune responses against pathological conditions. Type I phosphatidylinositol 4-phosphate 5-kinase alpha (PIP5Kalpha) that is responsible for production of phosphatidylinositol 4,5-bisphosphate (PI[4,5]P2) regulates many important cell functions at the cell surface. Here, we have examined whether PIP5Kalpha is associated with astrocyte inflammatory responses. Gangliosides are releasable from damaged cell membranes of neurons and capable of inducing inflammatory responses. We found that treatment of primary cultured astrocytes with gangliosides significantly enhanced PIP5Kalpha mRNA and protein expression levels. PI(4,5)P2 imaging using a fluorescent tubby (R332H) expression as a PI(4,5)P2-specific probe showed that ganglioside treatment increased PI(4,5)P2 level. Interestingly, microRNA-based PIP5Kalpha knockdown strongly reduced ganglioside-induced transcription of proinflammatory cytokines IL-1beta and TNFalpha. PIP5Kalpha knockdown also suppressed ganglioside-induced phosphorylation and nuclear translocation of NF-kappaB and the degradation of IkappaB-alpha, indicating that PIP5Kalpha knockdown interfered with the ganglioside-activated NF-kappaB signaling. Together, these results suggest that PIP5Kalpha is a novel inflammatory mediator that undergoes upregulation and contributes to immune responses by facilitating NF-kappaB activation in ganglioside-stimulated astrocytes.

A double point mutation in PCL-gamma1 (Y509A/F510A) enhances Y783 phosphorylation and inositol phospholipid-hydrolyzing activity upon EGF stimulation

Growth factor stimulation induces Y783 phosphorylation of phosphoinositide-specific PLC-gamma1, and the subsequent activation of this enzyme in a cellular signaling cascade. Previously, we showed that a double point mutation, Y509A/F510A, of PLC-gamma1, abolished interactions with translational elongation factor 1-alpha. Here, we report that the Y509A/F510A mutant PLC-gamma1 displayed extremely high levels of Y783 phosphorylation and enhanced catalytic activity, compared to wild-type PLC-gamma1, upon treatment of COS7 cells with EGF. In quiescent COS7 cells, the Y509A/F510A mutant PLC-gamma1 exhibited a constitutive hydrolytic activity, whereas the wild-type counterpart displayed a basal level of activity. Upon treatment of COS7 cells with EGF, the Y783F mutation in Y509A/F510A PLC-gamma1 (Y509A/F510A/Y783F triple mutant) cells also led to an enhanced catalytic activity, whereas Y783F mutation alone displayed a basal level of activity. Our results collectively suggest that the Y509A/F510A mutant is more susceptible to receptor tyrosine kinase-induced Y783 phosphorylation than is wild-type PLC-gamma1, but no longer requires Y783 phosphorylation step for the Y509A/F510A mutant PLC-gamma1 activation in vivo.

Modulation mechanism of PKC upon inwardly rectifying potassium channels / 第二军医大学学报

Inwardly rectifying potassium (Kir) channels are widely distributed in many tissues and play important roles in physiological processes such as maintaining K+ homeostasis, regulating cell excitability and insulin secretion. The activity of Kir channels is regulated by a number of modulators,such as K+, Mg2+, pH, ATP, GPCR, PIP2, PKA, PKC, AA (arachidonic acid), etc. Study of the regulating mechanisms of Kir channel is a key step in understanding the physiology and physiopathology of these channels. Because many extra molecular signals regulate Kir channels via PKC pathway, much effort has been made over the past decade to understand role of PKC in regulating Kir channels. This paper summarizes the molecular basis of PKC modulation of Kir channels and the recent progression on the area.

Regulatory role of phosphatidylinositol 4,5-bisphosphate in transient receptor potential channel / 第二军医大学学报

Transient receptor potential(TRP) superfamily includes seven subfamilies and TRP channels are regulated by a wide variety of physical and chemical factors. Recently, several members of the TRP channel family have been reported to be regulated by phosphatidylinositol 4,5-bisphosphate(PIP2). The regulation is complex and it can be activation or inhibition, involving multiple mechanisms and factors. This review summarizes the PIP2 regulation of several TRP channels of different superfamilies and the related pathophysiological significance.

Pleckstrin homology domain of phospholipase C-gamma1 directly binds to 68-kDa neurofilament light chain

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.