β3整合素在生长因子促血管平滑肌细胞粘附和迁移中的作用

目的:探讨血小板衍生生长因子(PDGF)对β₃整合素表达的影响及β₃整合素在PDGF促血管平滑肌细胞(VSMC)粘附、迁移和增殖中的作用。方法:用抗β₃整合素胞外域抗体封闭VSMCβ₃整合素后,通过-TdR掺入、细胞粘附、细胞迁移分析及RT-PCR等方法,检测PDGF对β₃整合素表达及对VSMC粘附、迁移和增殖的影响。结果:阻断β₃整合素与细胞外基质(ECM)蛋白相互作用后,可在一定程度上抑制PDGF刺激的VSMC增殖,使-TdR掺入率降低39%;在β₃整合素抗体浓度为10mg/L时,PDGF引发的细胞粘附和迁移受到显著抑制(P＜0.05);PDGF作用于VSMC6h,β₃整合素基因表达活性达到峰值,比对照细胞高87%。结论:PDGF可显著诱导β₃整合素在VSMC中表达;β₃整合素与ECM蛋白相互作用在PDGF促VSMC粘附、迁移方面发挥重要作用。     

bFGF促进内皮细胞β1整合素表达及其意义探讨

目的:观察碱性成纤维细胞生长因子对血管内皮细胞β₁整合素表达的影响。方法:采用WesternBlot法结合图像处理分析,检测bFGF作用前后培养血管内皮细胞β₁整合素的表达。结果:bFGF处理组和对照组平均灰度值分别为166.11±9.86和175.32±5.12,两组免疫酶显色有显著差异。结论:bFGF能够诱导内皮细胞膜表面β₁整合素合成增加。推测bFGF通过上调内皮细胞β₁整合素表达,可能在促进血管生成方面有重要作用。     

多种粘附分子基因在原发性肝癌的表达及其临床意义

目的:探讨多种粘附分子基因在原发性肝癌中的表达及其临床意义。方法:取64例用RT-PCR法半定量检测肝癌粘附分子的基因表达情况,分析其临床意义。结果:(1)原发性肝癌各粘附分子的表达率分别为:E-钙粘蛋白 90.62%、细胞间粘附分子-1 93.75%、粘附分子CD44 50.00%、粘附分子CD_44V 96.88%、整合素α₅ 100%、整合素β₁ 100%,CD44与其他粘附分子表达率的差异显著。(2)肝癌组织各粘附分子E-钙粘蛋白 、细胞间粘附分子-1 、粘附分子CD44、粘附分子CD_44V 、整合素α₅、整合素β₁ mRNA的表达量分别为:1.24±0.54、0.96±0.37、0.62±0.73、0.86±0.33、 0.97±0.49、1.41±0.24,其中粘附分子CD44与E-钙粘蛋白、整合素β₁的表达量差异显著。(3)肝癌分期与粘附分子基因mRNA表达量的关系显示:E-钙粘蛋白、粘附分子CD44的表达量随分期增高而下降,其中粘附分子CD44Ⅰ-Ⅱ期和Ⅳ期的表达量差别显著;细胞间粘附分子-1、粘附分子CD_44V,整合素α₅、整合素β₁的表达量随分期增高而增高,其中细胞间粘附分子-1Ⅰ-Ⅱ期和Ⅳ期的表达量差别显著。(4)肝癌粘附分子基因mRNA表达量与临床病理生理特点相关分析显示:肝癌粘附分子基因mRNA表达量与肿瘤大小、有无转移、有无包膜和结节数目有关,与AFP水平、肝硬化情况、肝功能状况无关。结论:肝癌粘附分子基因mRNA的表达存在明显的差异,粘附分子CD44表达缺失率高。肝癌粘附分子基因mRNA的表达与肿瘤大小、有无转移、结节数目、有无包膜相关。     

重症烧伤休克大鼠白细胞表面beta-2整合素的表达

目的 :阐明烧伤休克时 beta-2整合素与白细胞 -内皮细胞粘附间的关系。方法 :将 16只 SD大鼠随机均分为对照组和烧伤休克组。应用流式细胞技术检测中性粒细胞及单细胞表面 beta-2整合素CD11a( LFA-1)和 CD11b( Mac-1)的表达量变化 ,同时比较观察二组动物肠系膜微循环中微静脉内白细胞与内皮细胞粘附数量变化。结果 :二组自身对照 (烫伤前与烫伤后 3 h或开腹前与开腹后 3 h)及相互对比结果显示 ,中性粒细胞及单核细胞表面 CD11a表达量均无显著差异 ( P>0 .0 5 ) ;在烧伤组 ,单核细胞 CD11b有显著降低( P<0 .0 5 ) ,而中性粒细胞 CD11b有显著升高 ( P<0 .0 5 )。微循环观察结果显示 ,休克组动物烫伤后随时程延长附壁滚动及紧密粘附的白细胞数量明显增多 ,而对照组则无明显变化。结论 :烧伤休克状态下 ,白细胞表面 CD11a数量无显著变化 ,而 CD11b数量则有所改变。白细胞 -内皮细胞粘附力的增强可能有 beta-2整合素功能活性上调参与。     

低强度超声联合微泡通过提高ROS水平促进甲状腺癌细胞自噬性死亡

目的:探讨低强度超声联合微泡造影剂对甲状腺癌细胞自噬性死亡的作用,并分析自噬的激活机制及其对细胞活力的影响。方法:采用频率20 k Hz、功率80 m W的低强度超声联合微泡造影剂处理人甲状腺癌TPC1细胞,处理细胞60、120和240 s后,采用Live/Dead实验和CCK-8实验分析细胞死亡和活力;Western blot分析微管相关蛋白1轻链3Ⅱ(microtubule-associated protein 1 light chain 3-Ⅱ,LC3-Ⅱ)、自噬相关蛋白5(autophagy-related protein 5,ATG5)和SQSTM1/P62的蛋白水平变化;单丹磺酰戊二胺(monodansylcadaverine,MDC)染色、绿色荧光蛋白(green fluorescent protein,GFP)-LC3转染和透射电镜观察细胞内自噬体的数量;2',7'-二氯二氢荧光素二乙酸脂(DCFDA)染色分析细胞活性氧簇(reactive oxygen species,ROS)的水平,用N-乙酰半胱氨酸(N-acetyl-L-cysteine,NAC)抑制氧化应激水平,分析ROS在自噬激活中的作用;ATG5 siRNA转染抑制自噬水平并分析自噬性死亡的作用。结果:低强度超声联合微泡显著促进TPC1细胞死亡,抑制TPC1细胞活力(P0.05),并与处理时间显著相关。相对于单纯低强度超声组和微泡组,超声联合微泡显著升高LC3-Ⅱ和ATG5蛋白水平,抑制P62蛋白水平(P0.05)。MDC染色、GFP-LC3转染和透射电镜观察发现,超声联合微泡明显增加TPC1细胞中自噬体的数量。超声联合微泡与单纯低强度超声组和微泡组相比,提高了细胞的ROS水平,而NAC显著降低超声联合微泡提高的LC3-Ⅱ蛋白水平(P0.05)。ATG5 siRNA抑制自噬并显著增加细胞活力(P0.05)。结论:本研究说明低强度超声联合微泡可能通过提高甲状腺癌细胞中的ROS水平促进细胞的自噬性死亡,从而引起甲状腺癌细胞死亡。     

整合素激活FAK介导的信号传导途径研究进展

整合素是一类重要的细胞表面受体家族,主要介导细胞与细胞外基质的粘附。整合素在胞内外信号传导中起重要作用。FAK是整合素信号传导途径中的关键酪氨酸激酶,整合素、FAK及细胞骨架蛋白共聚于焦点粘附物上,使FAK自身磷酸化而激活,FAK激活后,其磷酸化的Tyr397与Src家族激酶结合,通过形成FAK/Src复合物而引起Paxillin和Cas磷酸化,后二者通过接头蛋白Crk和Grb2激活Ras途径的下游激酶MAPK,通过MAPK改变细胞行为。本文综述了FAK在整合素信号传导中的生物学作用,即介导细胞在ECM上的粘附和迁移,调节细胞增殖和存活等。     

小鼠早期完整胚胎诱导子宫内膜白血病抑制因子和整合素β3表达并提高子宫容受性

目的: 探讨小鼠早期胚胎诱导子宫内膜容受性改变的空间结构,确定胚胎各个部分能否引起子宫内膜容受性中白血病抑制因子(LIF)和整合素β₃改变。方法: 选用6~8周昆明雌鼠,体外实验分为子宫内膜培养前组、子宫内膜单纯培养组、子宫内膜全胚胎共培养组、子宫内膜卵裂球共培养组、子宫内膜透明带共培养组,各组培养2 d后收集子宫内膜行下一步检测;体内实验分为胚胎移植前组、单纯培养液移植组、全胚胎移植组、卵裂球移植组、透明带移植组及正常妊娠未干预组,移植后2 d收集子宫内膜行下一步检测。荧光定量PCR检测整合素β₃和LIF mRNA表达;免疫组织化学及Western blotting检测整合素β₃和LIF的蛋白表达部位及表达水平。结果: 体外实验子宫内膜全胚胎共培养组中子宫内膜的整合素β₃ 和LIF表达显著高于其它组,体内实验正常妊娠未干预组的整合素β₃ 和LIF表达显著高于其它组。结论: 完整胚胎可显著提升小鼠孕早期子宫内膜容受性因子整合素β₃ 和LIF的表达,而单纯透明带或卵裂球则不能明显增加整合素β₃ 和LIF的表达。早期胚胎诱导子宫内膜容受性可能需要完整胚胎结构的存在。     

细胞外基质促血管平滑肌细胞迁移及β3整合素和粘着斑激酶表达

目的:研究细胞外基质(ECM)蛋白促血管平滑肌细胞(VSMC)迁移与β₃整合素及粘着斑激酶(FAK)表达之间的关系。方法:应用细胞迁移实验观察骨桥蛋白(OPN)和纤连蛋白(FN)对VSMC迁移活性的影响,利用RT-PCR和Western印迹探讨β₃整合素、FAK和转录因子Gax表达与细胞迁移之间的关系。结果:VSMC经10、20mg/LOPN和20mg/LFN处理后,迁移活性分别达对照组的1.36、1.57和1.26倍(P＜0.05)。用相同浓度(20mg/L)OPN和FN刺激细胞,随着作用时间延长,VSMC迁移距离逐渐增加。Western印迹和RT-PCR结果证实,两种基质蛋白促进VSMC迁移与诱导β₃整合素和FAK基因表达及抑制转录因子Gax表达有关。结论:β₃整合素-FAK是介导OPN和FN促VSMC迁移的信号途径之一。     

选择素及其信号转导

选择素家族是表达于白细胞、内皮细胞和血小板表面的粘附分子。免疫和炎症反应时 ,选择素与其配体结合介导白细胞同内皮细胞和血小板的粘附作用。此外 ,选择素还可启动细胞内信号转导通路 ,如可引起细胞内第二信使Ca2 的增加、MAPK及 β2 整合素的活化等 ,进一步调节细胞在粘附时的功能反应。     

红景天苷促进培养乳鼠心肌细胞肌质网钙离子的释放

目的: 观察红景天苷对乳鼠心肌细胞胞浆Ca²⁺浓度的影响并分析其可能的作用机制。方法: 应用荧光指示剂Fluo-3/AM负载培养大鼠乳鼠的心肌细胞,用激光共聚焦显微镜动态观察胞内游离钙荧光信号强度的变化,检测不同浓度红景天苷对培养心肌细胞胞内游离钙离子浓度([Ca²⁺]_i)的影响。结果: 红景天苷浓度为15 mg/L、30 mg/L和60 mg/L时,细胞内的平均[Ca²⁺]_i升高,峰值分别为574.08±4.65、591.86±3.64和618.66±4.27(均P<0.01);有剂量依赖性而无时间依赖性。用维拉帕米阻断细胞膜外钙内流时,红景天苷同样引起细胞内[Ca²⁺]_i升高,峰值由357.74±3.13、387.17±2.37和391.43±1.34分别上升到480.86±3.98、496.70±3.08和522.18±3.19(均P<0.01)。结论: 红景天苷能升高乳鼠心肌细胞中[Ca²⁺]_i,其机制可能与其促进肌浆网钙离子释放有关。     

大鼠触须毛囊干细胞的分离培养和鉴定

背景：毛囊干细胞在体内膀胱及周围组织环境作用下有可能向尿路上皮细胞和平滑肌细胞分化,成为目前研究较新的干细胞之一。 目的：建立一种高效简单的分离培养和鉴定毛囊干细胞的方法。 方法：取大鼠触须部皮肤组织,体式显微镜下分离出毛囊组织,中性蛋白酶Ⅱ与胰蛋白酶和乙二胺四乙酸混合液“两步酶法”消化;所得细胞悬液中添加含体积分数10%胎牛血清的角质细胞无血清培养基,Ⅳ型胶原差速贴壁法筛选毛囊干细胞,20 min以内贴壁的细胞作为实验组,未贴壁的细胞作为对照组;待筛选后的细胞生长至70%~80%汇合后,进行传代培养。 结果与结论：筛选后的细胞形态均匀一致,折光性强,呈典型的“铺路石状”。透射电镜显示细胞处于原始状态。流式细胞仪检测实验组CD34和β1整合素的表达分别为(39.52±19.57)%和(93.46±4.73)%,对照组相应为(19.20±11.53)%和(63.57± 14.42)%,两组间差异有显著性意义(P < 0.05)。结果表明联用显微分离技术、二步酶法及差速贴壁法筛选可以获得纯度较高的毛囊干细胞。CD34和β1整合素表达是较理想的鉴定方法。     

低氧时肺癌细胞侵润和迁移特性的变化及分子基础

目的:探讨低氧对肺癌细胞侵润、迁移特性的影响及其机制。方法:将肺癌细胞株置常氧(空气、5%CO₂)、低氧(5%O₂、5%CO₂、90%N₂)、无氧(95%N₂、5%CO₂)的不同氧环境中培养48 h后,用划痕法测定各组细胞的迁移能力,用羊膜内皮细胞模型测定各组细胞的侵润能力。同时将处理的细胞接种于裸鼠背部皮下,观察其生长情况及转移特点。同时分析上皮钙粘附素、β1-整合素的表达量。结果:低氧组细胞迁移能力、侵润能力显著高于常氧组。无氧组成瘤率和肺转移率显著低于常氧组和低氧组。低氧组上皮钙粘附素表达显著低于常氧组而β1-整合素表达量显著高于常氧组,无氧组两者均显著低于常氧组。结论:适度低氧可以下调肺癌细胞上皮钙粘附素表达,增加β1-整合素表达,增强癌细胞迁移力和侵润力。但是严重低氧使癌细胞粘附分子表达下降,生长增殖能力、迁移力和侵润力下降。     

P-selectin mediates adhesion of leukocytes, platelets, and cancer cells in inflammation, thrombosis, and cancer growth and metastasis

Stimulated endothelial cells and activated platelets express P-selectin (CD62P), a member of the selectin family of cell adhesion molecules, which interacts with P-selectin glycoprotein ligand-1 (PSGL-1, CD162) for leukocyte rolling on stimulated endothelial cells and heterotypic aggregation of activated platelets onto leukocytes. Cross-linking of PSGL-1 by P-selectin also primes leukocytes intracellularly for cytokine and chemoattractant-induced β₂-integrin activation for firm adhesion of leukocytes. Furthermore, P-selectin mediates heterotypic aggregation of activated platelets to cancer cells and adhesion of cancer cells to stimulated endothelial cells. Here we provide a comprehensive summary of the functional roles and the biological importance of P-selectin-mediated cell adhesive interactions in the pathogeneses of inflammation, thrombosis, and the growth and metastasis of cancers.     

Differential expression of VLA-4 integrin by resident and peripheral blood B lymphocytes. Acquisition of functionally active α4β1-fibronectin receptors upon B cell activation

Very-late antigen (VLA)-4 (CD49d/CD29) constitutes the only member of the β1 integrin family that plays a role in the interaction of lymphoid cells with both extracellular matrix and endothelial cells through two identified ligands: fibronectin (FN) and VCAM-1, respectively. The expression and functional activity of VLA-4 has been studied in different maturation and activation stages of B cells from several cellular compartments. Resident B lymphocytes of different lymphoid organs were almost negative for VLA-4 as detected by both immunoperoxidase staining and flow cytometry analysis. However, a high expression of both chains of this heterodimer was observed when tonsillar B cells were activated in vitro with different stimuli, such as phorbol esters or Staphylococcus aureus Cowan I (SAC). Both nonactivated and in vitro activated B cells from peripheral blood constitutively expressed high levels of this surface antigen. The induced expression of VLA-4 after activation of tonsillar B lymphocytes was accompanied by the acquisition of the capacity to bind to a 38-kDa proteolytic fragment, containing the connecting segment I domain, of FN. Interestingly, nonactivated peripheral blood B cells were unable to attach to this FN fragment, in spite of their constitutive expression of VLA-4, and only acquired this functional capacity after cell activation with phorbol esters and SAC. This FN-binding acquisition was not affected by preincubation with inhibitors of protein and RNA synthesis. These results underline that the FN-binding activity of VLA-4 is dependent on processes affecting cellular activation as described for other members of the integrin family. By contrast, VLA-4-mediated homotypic aggregation of peripheral blood B cells could be triggered by anti-α4 monoclonal antibodies independently of the cell activation state.     

解热醒神注射液对内毒素性发热家兔下丘脑cAMP、IL-1β含量的影响

目的:观察解热醒神(JRXS)注射液对内毒素(ET)性发热1h家兔体温、下丘脑cAMP、IL-1_β含量的影响。方法:复制家兔ET性发热模型,用放免法检测下丘脑及脑脊液cAMP、下丘脑IL-1_β的含量。结果:ET组的ΔT[(0.40±0.11)℃]、TRI₁(1.78±0.79)、下丘脑cAMP含量[(2.90±0.40)nmol/g]、脑脊液cAMP含量[(32.10±4.51)nmol/L]、下丘脑IL-1_β含量[(6.08±0.79)ng/g]显著高于生理盐水(NS)组及JRXS+ET组(P＜0.01)。JRXS+ET组ΔT[(0.10±0.10)℃]、TRI₁(0.36±0.64)、下丘脑cAMP含量[(1.37±0.27)nmol/g]、脑脊液cAMP含量[(14.40±3.69)nmol/L)]、下丘脑IL-1_β含量[(2.90±0.37)ng/g]接近NS组,但与ET组比较有非常显著差异(P＜0.01);4组下丘脑及脑脊液cAMP含量、下丘脑IL-1_β含量变化与体温变化呈正相关。结论:JRXS能明显抑制ET引起的发热反应,其抑制效应的机制与降低ET引起的下丘脑cAMP、IL-1_β含量增多有关。     

白蛋白微泡促进报告基因在细胞表达的实验研究

目的: 探讨白蛋白微泡作为非病毒载体在基因传输中的作用。方法:6孔板培养脐静脉内皮细胞(EC)和血管平滑肌细胞(VSMC),每孔加pcDNA3.1/His/LacZ质粒20 μg,加不同浓度微泡或不加微泡,超声条件为连续波,频率2MHz,机械指数1.8,照射时间1 min,48 h后计算蓝染细胞百分率和β-半乳糖苷酶活性。另以不同浓度微泡及超声照射时间处理细胞,测定细胞增殖情况。结果:与单纯超声质粒组相比,含微泡组蓝染细胞率增加约10-15倍(其中内皮细胞组11.6倍,平滑肌细胞组15.2倍),报告基因表达定量增加近8倍。微泡浓度为10％时细胞转染效率最高。超声照射对细胞增殖无影响,微泡浓度为50％时有明显的细胞毒作用。结论:白蛋白微泡在超声作用下能明显增加基因的传输效率,有可能成为一种安全有效的基因治疗的载体。     

Rapid killing of monocytes in vitro by Candida albicans yeast cells.

To study the interaction between Candida albicans blastoconidia and human phagocytes, we incubated peripheral leukocytes with fungi for 1 h at 37 degrees C and stained the cells with fluorescent vital stains ethidium bromide (EB) and fluorescein diacetate. Fungi that had been phagocytosed showed little staining; however, some leukocytes containing blastoconidia exhibited nuclear staining with EB, even though their cell membranes showed no signs of penetration by fungi. The number of EB-positive leukocytes was related to viability of the yeast cells and the temperature at which they were maintained before use. Because efforts to quantitate EB-positive leukocytes microscopically were frustrated by cell aggregation, we labeled the leukocytes with 51Cr and measured isotope release. We determined that leukocytes incubated with viable fungi released significantly more isotope than cells incubated alone or with killed blastoconidia. Furthermore, 51Cr release correlated directly with concentration of fungi in the assay, time of incubation, and temperature at which fungi were maintained before use. Using a number of isolates of C. albicans and several other species of Candida, we found that all exhibited cytotoxic activity against leukocytes, but the level of activity varied among organisms. Finally, we depleted or enriched peripheral leukocytes for specific cell populations and determined that only monocytes released more 51Cr after incubation with viable blastoconidia. Blastoconidia can lyse phagocytic cells through germination and penetration of cell membranes within 1 to 2 h, but the cytotoxic phenomenon we describe occurs within 15 to 30 min after yeast cells have been phagocytosed. Therefore, this capacity may represent a more immediate response by blastoconidia against phagocytosis and killing by monocytes.     

17β-雌二醇对骨髓基质细胞骨形态发生蛋白受体ⅠA、B mRNA表达的影响

目的:研究骨髓基质细胞在向成骨细胞分化的介质中,17β-雌二醇(E₂)对其骨形态发生蛋白受体(BMPR)ⅠA,ⅠBmRNA表达的影响,探讨雌二醇对成骨细胞生成的作用。方法:用1,25(OH)₂D₃和地塞米松(DEX)诱导大鼠骨髓基质细胞向成骨细胞分化,应用半定量RT-PCR技术,观察不同浓度E₂对骨髓基质细胞分化过程中BMPR-ⅠA,ⅠBmRNA表达的影响,以α-磷酸奈酚为底物测定细胞碱性磷酸酶的活性,VanGieson染色法显示Ⅰ型胶原的含量。结果:E₂能明显抑制骨髓基质细胞分化过程中BMPR-ⅠAmRNA的表达,且呈剂量依赖性,随E₂浓度增加,BMPR-ⅠAmRNA从(23.7±1.7)%降至(16.3±1.5)%(P<0.05)和(8.3±1.2)%(P<0.01);BMPR-ⅠBmRNA随E₂浓度增加而增加,从(1.3±0.6)%增至(5.7±2.0)%(P<0.05)和(15.3±3.0)%(P<0.01)。ALP活性随E₂浓度增加而降低,从(42.6±2.5)U·L^-1·g^-1protein降至(10.8±1.5)U·L^-1·g^-1protein和(3.6±1.7)U·L^-1·g^-1protein(P<0.01);细胞Ⅰ型胶原的含量随E₂浓度增加而减少。结论:E₂能明显抑制体外培养的骨髓基质细胞分化过程中BMPR-ⅠAmRNA的表达,降低成骨细胞生成。     

A surrogate method for assessment of β2-integrin-dependent adhesion of human eosinophils to ICAM-1

We have developed and validated an inexpensive and equivalent method for measuring eosinophil adhesion by β₂-integrin to endothelial ICAM-1 using bovine serum albumin (BSA) as a surrogate for the immunoglobulin supergene. The number of adherent eosinophils on BSA or ICAM-1 coated microplates was quantified by residual eosinophil peroxidase activity. Non-stimulated eosinophils did not adhere to either BSA or ICAM-1. However, after IL-5 stimulation, either BSA or ICAM-1 caused comparable and concentration-dependent adhesion of eosinophils. Eosinophil adhesion was rapid and occurred within 15 to 30 min of incubation for either BSA or ICAM-1. Preincubation of cells with CD11b or CD18 antibody specifically decreased adhesion to either BSA or ICAM-1. IL-5, PAF and fMLP all induced adhesion of eosinophils to either BSA or ICAM-1 in a concentration-dependent manner, and the optimal IL-5, fMLP and PAF concentrations for adhesion to BSA were the same as for adhesion to ICAM-1. BSA-binding was specific for β₂-integrin; neither α-CD49d mAb directed against the α₄-chain or α-CD29 directed against the common β₁-chain of VLA-4 blocked adhesion to BSA or ICAM-1 controls. The protein tyrosine kinase inhibitor, genistein, the phosphatidylinositol 3-kinase (PI-3 kinase) inhibitor, wortmanin, and mitogen-activated protein kinase kinase (MEK) inhibitor, U0126, all inhibited IL-5-induced eosinophil adhesion to either BSA or ICAM-1 comparably. These results indicate that BSA is a reliable and economical surrogate ligand for ICAM-1 adhesion to β₂-integrin-dependent adhesion to ICAM-1. Ligation characteristics of BSA are identical to those for soluble ICAM-1, and the assay is suitable for assessment of signal transduction pathways mediating adhesion.