转化生长因子β激活性激酶在胶质细胞信号转导中的作用机制

丝裂原激活蛋白激酶（MAPK）和 NFκB介导了炎症细胞转录活性的信号转导过程.转化生长因子β激活性激酶（TGFβ-activated kinase 1,TAK1）是这些转导通路的上游激酶.通过在胶质细胞株中瞬时转染TAK1和它的结合蛋白因子（TAK1-binding protein1 TAB1）基因,或与iNOS(可诱导型氧化氮合酶基因)启动子报告基因（iNOS-Luc）质粒共转染,探讨中枢两类胶质细胞在炎症反应过程中TAK1诱导iNOS 和细胞因子表达的作用机制.结果显示,TAK1明显激活iNOS 和细胞因子（TNFα、IL-1、IL-6）的表达活性. 而且当使用它的下游激酶p38 MAPK、JNK和NFκB的抑制剂（SB203580、SP620125和CAPE）后,这些表达活性明显被抑制.用IκBα的磷酸化突变体质粒(IκBαM)共转染胶质细胞株,能完全抑制iNOS的表达活性.研究结果提示：在胶质细胞内的p38 MAPK、JNK和NFκB信号介导的iNOS和细胞因子的转录表达过程中,TAK1起着非常重要的调节作用.     

动脉粥样硬化中胆固醇外流的研究进展

三磷酸腺苷结合盒转运体A1(ABCA1)、三磷酸腺苷结合盒转运体G1(ABCG1)和B族Ⅰ型清道夫受体(SR-BⅠ)介导的胆固醇外流是巨噬细胞内3条主要的胆固醇外流途径,对维持细胞内胆固醇动态平衡至关重要,其中转运体的功能及其表达的调节、胞外接受体的数量和活性等对细胞内胆固醇外流效率有重要的决定作用．最新研究发现,动脉粥样硬化(As)病变中出现的脂类蓄积、炎症、氧化应激、缺氧和胰岛素抵抗等病理情况,显著影响胆固醇转运体的表达,进而影响胆固醇外流及As的发生发展．本文主要针对As病变细胞内各胆固醇外流途径的作用及常伴随的脂类蓄积、炎症、氧化应激、缺氧和胰岛素抵抗现象,对胆固醇转运体表达调节的最新进展做一综述,以期为As治疗提供新理论依据和药物靶点,推动As治疗方法的发展．     

经MAPK信号转导通路介导的糖皮质激素的作用机制

糖皮质激素(GC)通过膜受体快速激活细胞内信号传导通路的机制,主要涉及ERK,JNK/SAPK和P38等MAPK家族的重要成员.GC在许多细胞中对ERK起抑制作用,在不同的细胞中,GC能激活JNK或抑制其活性,即具有一定的细胞特异性.GC还直接或间接地激活P38途径.GC激活MAPK介导的信号传导通路,产生一系列生物学效应,如抑制细胞的生长的繁殖,介导细胞的凋亡等.     

BKca蛋白通过调节SR-B1的表达介导胆固醇转运

[目的]探讨BKca通道蛋白对B族Ⅰ型清道夫受体(SR-B1)表达和调控胆固醇转运的影响。[方法]人脐静脉内皮细胞(HUVEC)体外传代培养2~5代,分为对照组、过表达BKca组和基因干扰BKca组。实时荧光定量PCR和蛋白免疫印迹法分别检测BKca的α及β亚基、SR-B1 mRNA和蛋白表达水平及胆固醇检测试剂盒检测胆固醇流出水平。[结果]与对照组相比,BKca过表达后SR-B1 mRNA及蛋白表达水平明显升高和基因干扰BKca后SR-B1 mRNA及蛋白表达水平明显降低(均P0.05)。BKca过表达后胆固醇流出水平明显升高,而基因干扰BKca后的胆固醇流出水平明显下降(均P0.05)。[结论]BKca通道蛋白上调SR-B1的表达,促进细胞内胆固醇的流出。     

高糖诱导肾小球系膜细胞表达TNFα-的机制探讨

目的:初步探讨高糖诱导肾小球系膜细胞表达肿瘤坏死因子α(TNFα-)的机制。方法:分别用p38丝裂原活化蛋白激酶(p38MAPK)特异性抑制剂SB203580、核因子-κB(NFκ-B)特异性抑制剂PDTC预刺激肾小球系膜细胞30 min,再以高糖(20 mmol/L)干预48 h后,分别采用RT-PCR法检测系膜细胞内TNFα-mRNA水平,Western blot法检测系膜细胞内磷酸化p38MAPK蛋白水平、细胞核及细胞浆NFκ-B p65蛋白水平。结果:与低糖对照组相比,高糖可促进肾小球系膜细胞内TNFα-mRNA表达,以及p38MAPK、NFκ-B蛋白活化;SB203580(10 mmol/L)、PDTC(10 mmol/L)预刺激肾小球系膜细胞均可抑制高糖诱导肾小球系膜细胞表达TNFα-,且SB203580可抑制高糖诱导系膜细胞内NFκ-B蛋白活化。结论:p38MAPK-NFκ-B信号途径参与介导高糖诱导肾小球系膜细胞表达TNFα-。     

ERR促进乳腺癌发生的作用机制

乳腺癌是发病率逐年增加、女性最常见的恶性肿瘤之一.ERR(雌激素受体相关受体)α,β和γ(NR3B1-3)是核受体超家族成员,也是配体依赖的转录因子.ERRs可通过线粒体、血管生成、脂肪生成等方式参与乳腺癌肿瘤细胞的代谢.ERRs的功能不受配体影响,但受特异性共调控子调节.这些调控子包括类固醇受体的共激活体(SRC)、PPARγ共激活体PGC-1α/β和共抑制体受体相互作用蛋白140(RIP140).对ERR的研究可为治疗乳腺癌提供新的途径.     

ERα的辅调节因子与乳腺癌关系的研究进展

雌激素受体α（estrogen receptorα,ERα）是配体依赖的转录因子,属于核受体超家族成员。ERα介导转录的经典途径是与雌激素结合后作用于靶基因启动子区的雌激素反应元件（estrogen response element,ERE）,进而诱导靶基因转录。ERα招募辅调节因子（共激活子和共抑制子）参与ERα介导的基因转录调控。辅调节因子主要通过乙酰化、磷酸化、甲基化等表观遗传机制参与转录调控,影响靶蛋白表达水平。ΕRα介导的基因转录调控在乳腺癌的增殖、分化、侵袭转移等过程中发挥重要作用。综述在ERα介导的基因转录调控中几类辅调节因子对乳腺癌发生发展的影响。     

高密度脂蛋白抗动脉粥样硬化作用

高密度脂蛋白通过清道夫受体BI(SR—BI)选择性的摄取外周组织细胞胆固酵,调节胆固酵逆转运过程;依赖对氧磷酶-1(PON1)的抗氧化作用及过氧化体增殖物激活型受体(PPAR-α)调节HDL代谢过程中5种蛋白质编码基因的表达等多种机制发挥其抗AS作用。     

蛋白激酶MSK在表观遗传学调控中的作用及其生物学意义

丝裂原和应激激活的蛋白激酶(MSK)是一类核内丝/苏氨酸蛋白激酶,参与丝裂原激活蛋白激酶(MAPK)信号通路介导的下游基因转录调控和表观遗传学调控.首先,MSK是MAPK通路的下游媒介分子.在丝裂原或应激刺激下,p38或ERK激酶通过级联磷酸化激活MSK蛋白.然后,活化的MSK介导转录因子磷酸化活化和组蛋白H3的10位丝氨酸磷酸化.MSK介导的组蛋白H3磷酸化,可引发组蛋白乙酰化和甲基化修饰的动态变化,相互协同或拮抗,开放染色质结构,利于诱导型基因的表达.除组蛋白H3外,MSK直接磷酸化的下游底物还包括CREB、NF-κB等转录因子以及多个非转录相关蛋白.因此,MSK能在多层次调控基因表达和细胞功能,广泛参与肿瘤转化、炎症反应、神经突触可塑性以及心肌肥大等生物学事件.本文将简要介绍MSK蛋白的研究进展,探讨其在转录调控、表观遗传学修饰等生物学事件中的作用.     

转化生长因子-β族信号的转导

TGF-β族细胞因子通过各自信号转导产生多种生物学效应,其基本过程是：信号沿TGF-β族配体→受体→SMAD蛋白→转录因子→DNA表达的次序转导.在TGF-β族各因子刺激各自具有蛋白激酶活性的两型膜受体时,各因子先结合Ⅱ型受体,结合配体的Ⅱ型受体再激活Ⅰ型受体.活化的I型受体磷酸化通路特异性SMAD,后者与公用性SMAD结合后从胞浆移至核内,核内SMAD通过与转录因子结合和直接与DNA结合调节基因的表达.     

An involvement of SR-B1 mediated PI3K-Akt-eNOS signaling in HDL-induced cyclooxygenase 2 expression and prostacyclin production in endothelial cells

It is well-known that sphingosine-1-phosphate (S1P), the phospholipid content of HDL, binding to S1P receptors can raise COX-2 expression and PGI(2) release through p38MAPK/CREB pathway. In the present study we assess the action of SR-B1 initiated PI3K-Akt-eNOS signaling in the regulation of COX-2 expression and PGI(2) production in response to HDL. We found that apoA1 could increase PGI(2) release and COX-2 expression in ECV 304 endothelial cells. Furthermore, SR-B1 was found to be involved in HDL induced up-regulation of COX-2 and PGI(2). Over-expressed SR-B1 did not significantly increase the expression of COX-2 and the PGI(2) levels, but knock-down of SR-B1 by siRNA could significantly attenuate COX-2 expression and PGI(2) release together with p38MAPK and CREB phosphorylation. Consistently, the declines of p-p38MAPK, p-CREB, COX-2 and PGI(2) were also observed after incubation with LY294002 (25μmol/L; PI3K special inhibitor) or L-NAME (50μmol/L; eNOS special inhibitor). In addition, we demonstrated the increases of PGI(2) release, COX-2 expression and p38MAPK phosphorylation, when nitric oxide level was raised through the incubation of L-arginine (10 or 20nmol/L) in endothelial cells. Taking together, our data support that SR-B1 mediated PI3K-Akt-eNOS signaling was involved in HDL-induced COX-2 expression and PGI(2) release in endothelial cells.     

Chemerin induced by Treponema pallidum predicted membrane protein Tp0965 mediates the activation of endothelial cell via MAPK signaling pathway

Chemerin, a chemoattractant protein, is involved in endothelial dysfunction and vascular inflammation in pathological conditions. In a recent study, we observed the upregulation of chemerin in endothelial cells following in vitro treatment with Treponema pallidum. Here, we investigated the role of chemerin in endothelial cells activation induced by the T. pallidum predicted membrane protein Tp0965. Following stimulation of human umbilical vein endothelial cells (HUVECs) with Tp0965, chemerin and its receptor chemerin receptor 23 (ChemR23) were upregulated, companied with elevated expression of Toll-like receptor 2. Furthermore, chemerin from HUVECs activated endothelial cells via chemerin/ChemR23 signaling in an autocrine/paracrine manner, characterized by upregulated expression of intercellular adhesion molecule 1, E-selectin, and matrix metalloproteinase-2. Activation of endothelial cells depended on the mitogen-activated protein kinase signaling pathway. In addition, Tp0965-induced chemerin promoted THP-1-derived macrophages migration to endothelial cells, also via the chemerin/ChemR23 pathway. The RhoA/ROCK signaling pathway was also involved in THP-1-derived macrophages migration in response to chemerin/ChemR23. Our results highlight the role of Tp0965-induced chemerin in endothelial cells dysfunction, which contributes to the immunopathogenesis of vascular inflammation of syphilis.     

Retinoid X receptor agonists impair arterial mononuclear cell recruitment through peroxisome proliferator-activated receptor-γ activation

Mononuclear cell migration into the vascular subendothelium constitutes an early event of the atherogenic process. Because the effect of retinoid X receptor (RXR)α on arterial mononuclear leukocyte recruitment is poorly understood, this study investigated whether RXR agonists can affect this response and the underlying mechanisms involved. Decreased RXRα expression was detected after 4 h stimulation of human umbilical arterial endothelial cells with TNF-α. Interestingly, under physiological flow conditions, TNF-α-induced endothelial adhesion of human mononuclear cells was concentration-dependently inhibited by preincubation of the human umbilical arterial endothelial cells with RXR agonists such as bexarotene or 9-cis-retinoid acid. RXR agonists also prevented TNF-α-induced VCAM-1 and ICAM-1 expression, as well as endothelial growth-related oncogene-α and MCP-1 release. Suppression of RXRα expression with a small interfering RNA abrogated these responses. Furthermore, inhibition of MAPKs and NF-κB pathways were involved in these events. RXR agonist-induced antileukocyte adhesive effects seemed to be mediated via RXRα/peroxisome proliferator-activated receptor (PPAR)γ interaction, since endothelial PPARγ silencing abolished their inhibitory responses. Furthermore, RXR agonists increased RXR/PPARγ interaction, and combinations of suboptimal concentrations of both nuclear receptor ligands inhibited TNF-α-induced mononuclear leukocyte arrest by 60-65%. In vivo, bexarotene dose-dependently inhibited TNF-α-induced leukocyte adhesion to the murine cremasteric arterioles and decreased VCAM-1 and ICAM-1 expression. Therefore, these results reveal that RXR agonists can inhibit the initial inflammatory response that precedes the atherogenic process by targeting different steps of the mononuclear recruitment cascade. Thus, RXR agonists may constitute a new therapeutic tool in the control of the inflammatory process associated with cardiovascular disease.     

Heterodimerization of human apelin and bradykinin 1 receptors: Novel signal transduction characteristics

Apelin receptor (APJ) and bradykinin 1 receptor (B1R) are involved in a variety of important physiological processes, which share many similar characteristics in distribution and functions in the cardiovascular system. This study explored the possibility of heterodimerization between APJ and B1R, and investigated the impact of heterodimer on the signal transduction characteristics and the physiological functions in human endothelial cells after stimulation with their agonists. We first identified the endogenous expression of APJ and B1R in HUVECs and their co-localization on HEK293 membrane. The constitutive heterodimerization between the APJ and B1R was then demonstrated by BRET and FRET assays. Stimulation with Apelin-13 and des -Arg⁹-BK enhanced the phosphorylation of eNOS in HUVECs, which could be dampened by the knockdown of APJ or B1R, indicating the co-existence of APJ and B1R is critical for eNOS phosphorylation in HUVECs. Furthermore, APJ/B1R heterodimers were found to enhance the activity of PKC signaling pathway and increase intracellular Ca^2 + concentration in HEK293 cells, which might be the mechanism of APJ/B1R heterodimers promoting the phosphorylation of eNOS and leads to increased Gαq, PKC signal pathway activities and a significant increase in cell proliferation. The results provide a new theoretical and experimental base for revealed intracellular molecular mechanisms of physiological function involved in the APJ and B1R and provide potential new targets for the development of drugs and treating cardiovascular disease.     

Glutathione peroxidase-1 deficiency augments proinflammatory cytokine-induced redox signaling and human endothelial cell activation

Glutathione peroxidase-1 (GPx-1) is a crucial antioxidant enzyme, the deficiency of which promotes atherogenesis. Accordingly, we examined the mechanisms by which GPx-1 deficiency enhances endothelial cell activation and inflammation. In human microvascular endothelial cells, we found that GPx-1 deficiency augments intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression by redox-dependent mechanisms that involve NFκB. Suppression of GPx-1 enhanced TNF-α-induced ROS production and ICAM-1 expression, whereas overexpression of GPx-1 attenuated these TNF-α-mediated responses. GPx-1 deficiency prolonged TNF-α-induced IκBα degradation and activation of ERK1/2 and JNK. JNK or NFκB inhibition attenuated TNF-α induction of ICAM-1 and VCAM-1 expression in GPx-1-deficient and control cells, whereas ERK1/2 inhibition attenuated only VCAM-1 expression. To analyze further signaling pathways involved in GPx-1-mediated protection from TNF-α-induced ROS, we performed microarray analysis of human microvascular endothelial cells treated with TNF-α in the presence and absence of GPx-1. Among the genes whose expression changed significantly, dual specificity phosphatase 4 (DUSP4), encoding an antagonist of MAPK signaling, was down-regulated by GPx-1 suppression. Targeted DUSP4 knockdown enhanced TNF-α-mediated ERK1/2 pathway activation and resulted in increased adhesion molecule expression, indicating that GPx-1 deficiency may augment TNF-α-mediated events, in part, by regulating DUSP4.     

Mechanism and Regulatory Function of CpG Signaling via Scavenger Receptor B1 in Primary B Cells

It is well established that CpG promotes pro-inflammatory cytokine and antibody production by B cells via the Toll-like receptor 9 (TLR9)-dependent pathway. However, scavenger receptors (SRs) are also capable of binding such pathogen-derived molecules, yet their contribution to CpG-induced signaling events has not yet been evaluated. Here we identified a novel TLR9-independent mechanism of CpG-induced signaling and immune function that is mediated by the scavenger B1 receptor (SR-B1). Specifically, we show that CpG/SR-B1 triggers calcium entry into primary B lymphocytes via phospholipase Cγ-1-mediated activation of TRPC3 channels and also B cell adhesion to vascular cell adhesion molecule-1. CpG-induced calcium signals and vascular cell adhesion molecule-1 adhesion are TLR9-independent and are mediated exclusively by SR-B1. Although pro-inflammatory cytokine and Ig production induced by CpG require TLR9 expression, we also found that SR-B1 negatively regulates TLR9-dependent production of interleukin-6, interleukin-10, and IgM. Thus, our results provide a novel perspective on the complexity of CpG signaling within B cells by demonstrating that SR-B1 is an alternative pathway for nucleic acid-induced signaling that provides feedback inhibition on specific TLR9-dependent responses of B cells. Consequently, these results have wide implications for understanding the mechanisms regulating immune tolerance to nucleic acids and pathogen-associated molecules.Stimulus-induced dynamic changes in the concentration of cytoplasmic calcium are primary determinants of the activation, immunological function, and developmental fate of lymphocytes. Calcium signaling through the B cell antigen receptor (BCR)² complex is initiated by the activation of proximal tyrosine kinases Lyn and Syk, which phosphorylate the adaptor BLNK to facilitate its association with and activation of PLCγ-2. PLCγ2 hydrolyzes phosphatidylinositol 4,5-bisphosphate into diacylglycerol and 1,4,5-inositol trisphosphate (IP₃) (for review see Ref. 1), which activates IP₃ receptor/channels that mediate Ca²⁺ release from endoplasmic reticulum into the cytosol (2) (for review see Refs. 3, 4). Ca²⁺ release from endoplasmic reticulum stores and the resulting depletion of Ca²⁺ (not an increase in cytoplasmic [Ca²⁺]) are the central and prerequisite events required to activate plasma membrane “store-operated” calcium release-activated calcium (CRAC) channels.CRAC channels are responsible for antigen receptor-triggered calcium entry; however, a growing body of evidence suggests that CRAC channels do not underlie all the diverse calcium-regulated responses of lymphocytes, particularly those triggered by innate stimuli. For example, we previously identified several calcium-permeant non-selective cation channels (NSCCs) that are uniquely activated by distinct arachidonic acid-derived (eicosanoid) inflammatory mediators and by mechanical stimuli (5–7). Thus, multiple calcium-permeant channels with distinct activation mechanisms may underlie stimulus-specific calcium-dependent B cell functions in vivo. Surprisingly, a number of pathogen-associated Toll-like receptor agonists are known to be strong B cell mitogens, yet the potential for calcium-dependent signaling functions by these polyclonal B cell mitogens has not yet been fully evaluated.Studies detailed in this report focus on the mechanism of calcium signaling elicited by unmethylated CpG DNA in primary B cells. Unmethylated CpG DNA is typically considered a pathogen-derived molecule that triggers polyclonal B cell activation, cytokine production, and immunoglobulin production via Toll-like receptor 9 (TLR9) engagement (8, 9). Because CpG induces a subset of the B cell responses normally elicited by cognate antigen binding to the BCR complex, we asked whether CpG stimulation mobilizes calcium. We found that while CpG stimulation and BCR engagement both elicit similar biphasic calcium signals, CpG-mediated calcium entry is regulated by TRPC3, a calcium-permeant NSCC of the canonical transient receptor potential (TRPC) channel family (10) and that, unlike the BCR, which couples to calcium entry via PLCγ-2, TRPC3 activation involves an adaptor like function of PLCγ-1.We also report that CpG-mediated calcium signals are initiated by the scavenger receptor B1 (SR-B1) independently of TLR9. To our knowledge, this is the first demonstration of SR-B1 function in B lymphocytes; although scavenger receptors have been implicated in the responses of other immune cells. For example, bacterial pathogens and byproducts of apoptotic cells contribute to the pathogenesis of immune-mediated diseases, including lupus in part via MARCO and CD36 expressed by marginal zone macrophages (11). In naïve B cells, CD36 expression is largely restricted to marginal zone cells. Notably, CD36 cooperates with TLR2 to produce antibodies against phosphocholine, which is an endogenous antigen (13). Given our finding that CpG elicits calcium signals via SR-B1 on lymphocytes, we asked whether SR-B1 might also act cooperatively, in this case with TLR9, to trigger inflammatory responses of B cells. In fact, our results indicate that SR-B1 negatively regulates CpG/TLR9-mediated production of specific immunoglobulins (IgM) and pro-inflammatory cytokines (IL-6 and IL-10) by B cells. These findings have important implications for understanding how calcium is regulated in B cells, but also point to novel mechanisms by which pathogen-associated molecules regulate B cell activation.     

Decreased H3K9 acetylation level of LXRα mediated dexamethasone-induced placental cholesterol transport dysfunction

Due to the insufficient fetal cholesterol synthesis, maternal cholesterol transport through the placenta becomes an important source of fetal cholesterol pool, which is essential for fetal growth and development. This study aimed to investigate the effects of dexamethasone on fetal cholesterol levels, and explore its placental mechanism. Pregnant Wistar rats were injected subcutaneously with dexamethasone (0.8 mg/kg·d) from gestational day 9 to 20. Results showed that dexamethasone increased maternal serum total cholesterol (TC), high-density lipoprotein-cholesterol (HDL-C), low-density lipoprotein-cholesterol (LDL-C) levels, as well as placental cholesterol synthesis and TC concentration, while reduced fetal birth weight, and serum TC, HDL-C and LDL-C levels. Meanwhile, the expression of placental cholesterol transporters, including low-density lipoprotein receptor (LDLR), scavenger receptor class B type I (SR-B1) and ATP-binding cassette transporter A1 and G1 (ABCA1 and ABCG1) were decreased by dexamethasone. Furthermore, the expression of glucocorticoid receptor (GR) and histone deacetylase 3 (HDAC3) were increased, while the H3K9ac and expression levels of liver X receptor α (LXRα) promoter were reduced. In human trophoblast cell line (BeWo), dexamethasone concentration-dependently decreased the expression levels of LDLR, SR-B1, ABCA1, ABCG1 as well as LXRα. Dexamethasone (2500 nM) induced GR translocation into nucleus and recruited HDAC3. Furthermore, LXRα agonist and GR inhibitor reversed respectively dexamethasone-induced the expression inhibitions of cholesterol transporter and LXRα, and HDAC3 siRNA reversed the H3K9ac level of LXRα promoter and its expression. Together, dexamethasone impaired placental cholesterol transport and eventually decreased fetal cholesterol levels, which is related to the down-regulation of LXRα mediated by GR/HDAC3/H3K9ac signaling.     

Macrophage/microglia-specific protein Iba1 enhances membrane ruffling and Rac activation via phospholipase C-gamma -dependent pathway

Iba1 is a macrophage/microglia-specific calcium-binding protein that is involved in RacGTPase-dependent membrane ruffling and phagocytosis. In this study, we introduced Iba1 into Swiss 3T3 fibroblasts and demonstrated the enhancement of platelet-derived growth factor (PDGF)-induced membrane ruffling and chemotaxis. Wortmannin treatment did not completely suppressed this enhanced membrane ruffling in Iba1-expressing cells, whereas it did in Iba1-nonexpressing cells, suggesting that the enhancement is mediated through a phosphatidylinositol 3-kinase (PI3K)-independent signaling pathway. Porcine aorta endothelial cells transfected with expression constructs of Iba1 and PDGF receptor add-back mutants were used to analyze the signaling pathway responsible for the Iba1-induced enhancement of membrane ruffling. In the absence of Iba1 expression, PDGF did not induced membrane ruffling in cells expressing the Tyr-1021 receptor mutant, which is capable of activating phospholipase C-gamma (PLC-gamma) but not PI3K. In contrast, in the presence of Iba1 expression, membrane ruffling was formed in cells expressing the Tyr-1021 mutant. In addition, Rac was shown to be activated during membrane ruffling in cells expressing Iba1 and the Tyr-1021 mutant. Furthermore, dominant negative forms of PLC-gamma completely suppressed PDGF-induced Iba1-dependent membrane ruffling and Rac activation. These results indicate the existence of a novel signaling pathway where PLC-gamma activates Rac in a manner dependent on Iba1.     

ApoA-I/SR-BI modulates S1P/S1PR2-mediated inflammation through the PI3K/Akt signaling pathway in HUVECs

Endothelial dysfunction plays a vital role during the initial stage of atherosclerosis. Oxidized low-density lipoprotein (ox-LDL) induces vascular endothelial injury and vessel wall inflammation. Sphingosine-1-phosphate (S1P) exerts numerous vasoprotective effects by binding to diverse S1P receptors (S1PRs; S1PR1-5). A number of studies have shown that in endothelial cells (ECs), S1PR2 acts as a pro-atherosclerotic mediator by stimulating vessel wall inflammation through the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. Scavenger receptor class B member I (SR-BI), a high-affinity receptor for apolipoprotein A-I (apoA-I)/high-density lipoprotein (HDL), inhibits nuclear factor-κB (NF-κB) translocation and decreases the plasma levels of inflammatory mediators via the PI3K/Akt pathway. We hypothesized that the inflammatory effects of S1P/S1PR2 on ECs may be regulated by apoA-I/SR-BI. The results showed that ox-LDL, a pro-inflammatory factor, augmented the S1PR2 level in human umbilical vein endothelial cells (HUVECs) in a dose- and time-dependent manner. In addition, S1P/S1PR2 signaling influenced the levels of inflammatory factors, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-10, aggravating inflammation in HUVECs. Moreover, the pro-inflammatory effects induced by S1P/S1PR2 were attenuated by SR-BI overexpression and enhanced by an SR-BI inhibitor, BLT-1. Further experiments showed that the PI3K/Akt signaling pathway was involved in this process. Taken together, these results demonstrate that apoA-I/SR-BI negatively regulates S1P/S1PR2-mediated inflammation in HUVECs by activating the PI3K/Akt signaling pathway.     

Cholesterol trafficking and raft-like membrane domain composition mediate scavenger receptor class B type 1-dependent lipid sensing in intestinal epithelial cells

Scavenger receptor Class B type 1 (SR-B1) is a lipid transporter and sensor. In intestinal epithelial cells, SR-B1-dependent lipid sensing is associated with SR-B1 recruitment in raft-like/ detergent-resistant membrane domains and interaction of its C-terminal transmembrane domain with plasma membrane cholesterol. To clarify the initiating events occurring during lipid sensing by SR-B1, we analyzed cholesterol trafficking and raft-like domain composition in intestinal epithelial cells expressing wild-type SR-B1 or the mutated form SR-B1-Q445A, defective in membrane cholesterol binding and signal initiation. These features of SR-B1 were found to influence both apical cholesterol efflux and intracellular cholesterol trafficking from plasma membrane to lipid droplets, and the lipid composition of raft-like domains. Lipidomic analysis revealed likely participation of d18:0/16:0 sphingomyelin and 16:0/0:0 lysophosphatidylethanolamine in lipid sensing by SR-B1. Proteomic analysis identified proteins, whose abundance changed in raft-like domains during lipid sensing, and these included molecules linked to lipid raft dynamics and signal transduction. These findings provide new insights into the role of SR-B1 in cellular cholesterol homeostasis and suggest molecular links between SR-B1-dependent lipid sensing and cell cholesterol and lipid droplet dynamics.