腺病毒介导人FRNK基因对结肠癌细胞Colo320WT中p190RhoGAP磷酸化和RhoA活性的影响

目的利用腺病毒载体表达人FRNK基因,体外观察其对胃泌素干预下的结肠癌细胞Colo320WT中p190RhoGAP磷酸化和RhoA活性的影响。方法2005年10月至2006年9月,武汉大学人民医院消化内科在中国科学院,武汉病毒所病毒学国家重点实验室,利用AdEasyTM系统在大肠埃希菌内同源重组构建表达人FRNK基因的腺病毒载体pAdhFRNK。脂质体转染pCR3.1-GR质粒于结肠癌细胞Colo320中,G418抗生素筛选出稳定表达胆囊收缩素-2受体/胃泌素受体(CCK-2R)的阳性克隆,逆转录-聚合酶链反应(RT-PCR)鉴定。用10~8mol/L胃泌素干预Colo320WT细胞12 h和pAdhFRNK体外感染Colo320WT细胞2 d后,再用10~8 mol/L的胃泌素干预细胞12 h,然后用免疫沉淀方法检测磷酸化的p190RhoGAP的表达,pull-down测定RhoA的活性。结果在胃泌素干预12 h后的磷酸化的p190RhoGAP的表达量明显增加,RhoA活性降低,而用pAdhFRNK感染后胃泌素干预的细胞中磷酸化p190RhoGAP表达又降低,RhoA活性却增加。结论hFRNK基因可明显阻断外源性胃泌素引起Colo320WT细胞中p190RhoGAP磷酸化的表达和RhoA的活性。     

胃泌素对结肠癌细胞中粘着斑激酶通路下游E-钙粘蛋白/β-连环蛋白复合物的影响

目的探讨胃泌素对结肠癌细胞CoLo320WT中粘着斑激酶（FAK）通路下游E-钙粘蛋白／β-连环蛋白（E-cadherin／β-catenin）复合物分布的影响；方法脂质体转染表达胃泌索受体CCK-2R的pCR3．1／OR质粒于结肠癌细胞CoLo320中。G418筛选出稳定表达CCK-2R的阳性克隆，RT-PCR鉴定，转染成功命为CoLo320WT。应用10^-8mmol／L 胃泌素（G17）以时间梯度（0h、1h、6h、12h、24h、48h）干预CoLo320WT细胞，同时应用10^-6mmol／L胃泌素受体拮抗剂L365，260干预CoLo320WT细胞30min，再予10^-8mmol／L胃泌素干预。采用免疫印迹法检测磷酸化的FAK Tyr397和总FAK的表达。采用免疫共沉淀和免疫印迹法检测CoLo320WT中TX-100溶解和未溶部分中的E-钙粘蛋白和β-连环蛋白的表达。用免疫细胞化学法观察E-钙粘蛋白和β-连环蛋白的在胞膜、胞质和胞核的分布。结果随着胃泌素干预时间的延长，细胞中磷酸化的FAK Tyr397的表达量呈增加趋势，12h达最大值。胃泌素受体拮抗剂L365，260阻断后磷酸化的FAK Tyr397表达减少。而胃泌素对总FAK没有明显影响。TX-100可溶性部分中E-钙粘蛋白和酽连环蛋白的量在胃泌素干预后表达减少，拮抗剂L365，260阻断后又增加。而TX-100不溶解部分中表达却相反。免疫细胞化学观察到在胃泌素干预下CoLo320WT细胞中E-钙粘蛋白和β-连环蛋白的分布发生胞质和胞核转移。结论胃泌素与其受体CCK-2受体结合，磷酸化的FAK Tyr397、激活FAK通路进而影响结肠癌细胞中E-钙粘蛋白和β-连环蛋白的分布，促进结肠癌细胞侵袭和转移。     

纤维连接蛋白对人结肠癌细胞侵袭力的影响

目的研究纤维连接蛋白（fibronectin，FN）对人结肠癌细胞侵袭力的影响，并探讨其中的信号传导机制。方法以递增浓度的FN刺激结肠癌细胞株Colo320，以免疫沉淀和蛋白质印迹法检测结肠癌细胞内黏着斑激酶（focal adhesion kinase，FAK）第397位酪氨酸（tyr-397）磷酸化的状况．以改良Boyden小室法检测相应的细胞侵袭力变化。设计反义寡核苷酸阻断FAK蛋白质表达，再次观察接受FN刺激后．结肠癌细胞内FAK tyr-397磷酸化状况及细胞侵袭力的改变。结果FN能够促进Colo320 FAK tyr-397磷酸化，在一定范围内具有剂量依赖性。FN浓度达10nmol／L时．此作用最显著，继续增加FN浓度．FAK tyr-397磷酸化不再呈现继续增强趋势．当浓度达到100nmol／L时，磷酸化程度反而有所下降；FN可以增强细胞侵袭力，同样在一定范围内具有剂量依赖性；反义寡核苷酸干预后．结肠癌细胞内FAK tyr-397磷酸化及细胞侵袭力均有显著降低（P〈0.01）。结论FN可以有效增强结肠癌细胞的侵袭力，其作用是通过FN—FAK信号通路实现的，FAK的活性形式是其酪氨酸位点的磷酸化．阻断FAK的表达町以减弱FN促进细胞侵袭的作用。     

磷酸化黏着斑激酶在结肠癌中表达及意义

目的:观察磷酸化黏着斑激酶(phosphorylatedfocaladhesionkinase,phospho-FAK)在结肠癌组织和对应癌旁组织中的表达,探讨其在结肠癌发病的可能机制.方法:采用Westernbloting方法检测20例新鲜结肠癌及相对应的癌旁组织FAK表达水平,并在调平每对组织FAK的含量后再进行FAKTyr397磷酸化蛋白的检测.结果:20例结肠癌组织FAK阳性表达率为95%,对应癌旁组织FAK阳性表达率为60%(c2=5.16,P<0.05);癌组织表达平均值为0.482±0.150,癌旁表达平均值为0.269±0.015(t=6.39,P<0.01).20例结肠癌组织18例有FAKTyr397磷酸化蛋白表达,表达率为90%,而对应癌旁组织仅有4例有FAKTyr397磷酸化蛋白表达,表达率为20%(c2=17.1,P<0.01);癌组织表达平均值为0.385±0.021,癌旁表达平均值为0.110±0.005(t=54.23,P<0.01).结论:FAK特别是FAKTyr397磷酸化蛋白的表达水平增加在结肠癌的发生、发展中可能起重要作用.     

人结肠癌细胞胃泌素-黏着斑激酶通路的研究

目的研究胃泌素对人结肠癌细胞信号分子黏着斑激酶(FAK)酪氨酸磷酸化和蛋白质表达的影响。方法使用胆囊收缩素2受体(CCK2R)的真核表达载体pCR3.1/CCK2R,转染人结肠癌细胞株Colo320,上调胃泌素作用;使用胃泌素拮抗剂下调胃泌素作用。使用胃泌素按浓度和时间梯度刺激细胞,以免疫沉淀和蛋白质印迹法检测FAK酪氨酸磷酸化和蛋白质表达情况。结果胃泌素能够引起FAK酪氨酸磷酸化,具有时间和剂量依赖性;CCK2R表达上调可以增强此作用;胃泌素拮抗剂具有相反作用。结论FAK是胃泌素发挥效应的下游信号分子,以酪氨酸磷酸化的形式发挥作用。胃泌素CCKRFAK信号通路在胃泌素引起的肿瘤细胞增殖过程中发挥重要作用。     

黏着斑激酶在结肠癌组织中的表达及意义

目的探讨黏着斑激酶（FAK）在结肠癌发生、发展中的作用。方法采用RT-PCR法检测30例新鲜结肠癌及与之相对应的癌旁组织的FAK mRNA表达；同时用Western印迹法检测20例新鲜结肠癌及相对应的癌旁组织FAK蛋白表达水平，调平每对组织FAK蛋白含量后再行FAK Tyr397磷酸化位点蛋白检测。结果30例结肠癌组织FAK mRNA阳性率为90．0％，其表达值为0．745±0．530，对应癌旁组织阳性率为43．3％，其表达值为0．241±0．131（P〈0．01）；20例结肠癌组织FAK蛋白阳性率为95．0％，表达值为0．482±0．150；对应癌旁组织阳性率为60．0％，表达值为0．269±0．015；P均〈0．01。20例结肠癌组织中FAK Tyr397磷酸化蛋白阳性率为90．0％（18／20），表达值为0．385±0．021；而对应癌旁组织阳性率为20％（4／20），表达值为0．110±0．005，P均〈0．01。结论FAK特别是FAK Tyr397磷酸化蛋白表达增加在结肠癌的发生、发展中可能起重要作用。     

黏着斑激酶对血小板源性生长因子刺激的血管平滑肌细胞迁移和黏附的调控

目的探讨黏着斑激酶(FAK)信号分子在雷帕霉素抑制血小板源性生长因子(PDGF)诱导血管平滑肌细胞(VSMC)迁移、黏附中的调控作用。方法将培养的大鼠VSMC分为对照组、PDGF组、雷帕霉素+PDGF组(雷帕霉素组)和FAK反义寡核苷酸+PDGF组(FAK组)。用PDGF诱导VSMC的迁移和黏附,计数贴壁细胞;采用Boyden检测细胞迁移;采用RT-PCR、Western blot、免疫沉淀方法分别检测FAK基因、蛋白及蛋白磷酸化表达量。将FAK反义寡核苷酸经脂质体转染VSMC,观察FAK mRNA及蛋白磷酸化、细胞迁移和黏附的变化。结果与对照组比较,PDGF组明显诱导细胞迁移和黏附,上调FAK mRNA的表达,提高FAK蛋白和磷酸化FAK表达,差异有统计学意义(P0.05),与PDGF组比较,FAK组和雷帕霉素组细胞迁移、黏附能力减弱,FAK mRNA、FAK蛋白和磷酸化FAK表达水平明显降低,差异有统计学意义(P0.05)。结论 PDGF诱导细胞迁移和黏附可能是FAK介导的,雷帕霉素可能是通过抑制FAK蛋白和磷酸化FAK来抑制VSMC的迁移和黏附。     

黏着斑激酶相关非激酶对肝星状细胞活化及迁移功能的影响

目的探讨黏着斑激酶相关非激酶(FRNK)对肝星状细胞(HSCs)活化及迁移功能的影响。方法2019年3—9月,收集贵州医科大学附属医院肝胆外科9例肝纤维化患者肝组织标本。人体肝组织分为健康对照组与纤维化组。C57BL/6实验小鼠分为野生型(WT)、FRNK基因敲除型(FRNK-/-)两组,以四氯化碳(CCl4)进行肝纤维化造模,完成后使用腺病毒载体构建FRNK基因过表达型(Ad-FRNK)。通过HE、Masson染色观察肝组织病理改变,Western蛋白印迹法检测磷酸化黏着斑激酶(PY397-FAK)与α平滑肌肌动蛋白(α-SMA)蛋白表达;提取小鼠原代HSCs,细胞划痕实验检测FRNK对HSCs迁移功能的影响,及对Rac、Rho活化的影响。结果肝纤维化人体肝组织PY397-FAK蛋白表达量显著高于健康对照组(0.88±0.09比0.73±0.09),FRNK低于健康对照组(0.68±0.09比0.79±0.11),P值均<0.01。CCl4造模后,FRNK-/-组小鼠肝纤维化[(153±13)%]较WT组(100%)程度更明显,PY397-FAK与α-SMA蛋白表达量高于WT组(2.50±0.23比0.75±0.09,1.46±0.20比0.92±0.10),P值均<0.01。在FRNK-/-组小鼠体内重新导入FRNK基因(100%)后,小鼠肝纤维化程度减轻[(74±6)%],PY397-FAK与α-SMA蛋白表达量减少(0.68±0.11比1.12±0.19,0.68±0.10比0.85±0.06),P值均<0.01。体外实验显示,FRNK可抑制HSCs的迁移功能[WT︰FRNK-/-︰Ad-FRNK为(339±49)%︰(580±53)%︰(259%±33)%],并抑制Rac和Rho蛋白的活化(Rac为0.54±0.07比0.91±0.10比0.77±0.12,Rho为0.45±0.05比0.64±0.06比0.53±0.07),P值均<0.01。结论FRNK可通过抑制HSCs的活化及迁移功能改善肝纤维化,其机制可能与下调PY397-FAK、抑制Rac和Rho的活化有关。     

p130Cas对胃癌细胞AGS增殖和凋亡的影响

目的探讨p130Cas对胃癌恶性生物学表型的影响及可能的分子机制。方法构建p130Cas siRNA慢病毒载体、p130Cas过表达慢病毒载体和相应的对照载体,转染AGS细胞株,筛选获得稳定转染株;RT-PCR及Western印迹证实载体的有效性;采用四甲基偶氮唑蓝比色法(MTT)比较慢病毒载体转染后各组细胞增殖情况;运用Annexin V-PI流式细胞实验检测各组细胞凋亡情况。结果成功构建了p130Cas siRNA慢病毒载体及p130Cas过表达慢病毒载体,构建的慢病毒载体均能高效率的感染AGS细胞,感染慢病毒过表达载体后细胞p130Cas mRNA及蛋白表达水平明显升高,感染慢病毒干扰载体后p130Cas mRNA及蛋白表达水平显著降低。p130Cas高表达细胞株无外界刺激时p130Cas磷酸化水平未发现有明显增加(P0.05);p130Cas低表达细胞株p130Cas磷酸化水平明显下降(P0.05)。高表达p130Cas细胞的增殖和凋亡无明显影响(P0.05);低表达p130Cas组细胞增殖受到抑制,凋亡率明显升高(P0.05)。结论 p130Cas总蛋白及磷酸化表达水平降低可抑制胃癌细胞株AGS细胞增殖,并促进AGS细胞凋亡,但其总蛋白表达增高对AGS细胞的增殖和凋亡无明显影响。     

肝细胞生长因子对肝细胞癌细胞系SMMC-7721黏着斑激酶的影响

目的:探讨肝细胞生长因子(HGF)对黏着斑激酶(FAK)、Src表达及活性的影响以及PI3K在该过程中的作用.方法:LY294002预处理阻断PI3K的活性、HGF处理SMMC-7721后检测FAK和Src的表达、磷酸化及在细胞内的分布. 应用免疫印迹技术检测FAK、Src的表达及磷酸化, 免疫荧光技术检测FAK在SMMC-7721细胞中的分布.结果:HGF(50 μg/L)可以促进FAK Y397位点的磷酸化, 对FAK的表达没有影响. 应用PI3K抑制物LY294002处理后, FAK Y397的磷酸化水平显著降低. HGF处理后, FAK主要位于细胞边缘, 呈簇状分布, 应用PI3K抑制物, FAK在细胞内弥散分布. HGF处理后, Src激酶和SrcY416的磷酸化水平明显增加, 而经LY294002处理后, Src激酶与Src Y416的磷酸化水平明显降低.结论:肝细胞癌中, HGF以PI3K依赖性的方式促进FAK和Src的活化.     

Effects of gastrin 17 on β-catenin/Tcf-4 pathway in Colo320WT colon cancer cells

AIM: To explore the effect of gastrin 17 (G17) on beta-catenin/T cell factor-4 (Tcf-4) signaling in colonic cancer cell line Colo320WT. METHODS: The pCR3.1/GR plasmid, which expresses gastrin receptor, cholecystokinin-2 receptor (CCK-2R), was transfected into a colonic cancer cell line Colo320 by Lipofectamine (TM)2000 and the stably expressing CCK-2R clones were screened by G418. The expression levels of gastrin receptor in the Colo320 and the transfected Colo320WT cell line were assayed by RT-PCR. Colo320WT cells were treated with G17 in a time-dependent manner (0, 1, 6, 12, 24 and 48 h), then with L365,260 (Gastrin(17) receptor blocker) for 30 min, and with G17 again for 12 h or L365,260 for 12 h. Expression levels of beta-catenin in a TX-100 soluble fraction and TX-100 insoluble fraction of Colo320WT cells treated with G17 were detected by co-immuniprecipation and Western blot. Immunocytochemistry was used to examine the distribution of beta-catenin in CoLoWT320 cells. Expression levels of c-myc and cyclin D1 in Colo320WT cells treated with G17 were assayed by Western blot. RESULTS: Expression levels of beta-catenin in the TX-100 solution fraction decreased apparently in a time-dependent fashion and reached the highest level after G17 treatment for 12 h, while expression levels of beta-catenin in the TX-100 insoluble fraction were just on the contrary. Immunocytochemistry showed that beta-catenin was translocated from the cell membranes into the cytoplasm and nucleus under G17 treatment. Expression levels of c-myc and cyclin D1 in the G17-treated Colo320WT cells were markedly higher compared to the untreated Colo320WT cells. In addition, the aforementioned G17-stimulated responses were blocked by L365,260. CONCLUSION: Gastrin17 activates beta-catenin/Tcf-4 signaling in Colo320WT cells, thereby leading to over-expression of c-myc and cyclin D1.     

Effects of gastrin 17 on β-catenin/Tcf-4 pathway in Colo320WT colon cancer cells

AIM: To explore the effect of gastrin 17 (G17) on β-catenin/T cell factor-4 (Tcf-4) signaling in colonic cancer cell line Colo320WT.METHODS: The pCR3.1/GR plasmid, which expresses gastrin receptor, cholecystokinin-2 receptor (CCK-2R),was transfected into a colonic cancer cell line Colo320 by Lipofectamine TM2000 and the stably expressing CCK-2R clones were screened by G418. The expression levels of gastrin receptor in the Colo320 and the transfected Colo320WT cell line were assayed by RTPCR. Colo320WT cells were treated with G17 in a timedependent manner (0, 1, 6, 12, 24 and 48 h), then with L365,260 (Gastrin17 receptor blocker) for 30 min, and with G17 again for 12 h or L365,260 for 12 h. Expression levels of β-catenin in a TX-100 soluble fraction and TX-100 insoluble fraction of Colo320WT cells treated with G17 were detected by co-immuniprecipation and Western blot. Immunocytochemistry was used to examine the distribution of β-catenin in CoLoWT320 cells. Expression levels of c-myc and cyclin D1 in Colo320WT cells treated with G17 were assayed by Western blot.RESULTS: Expression levels of β-catenin in the TX-100 solution fraction decreased apparently in a timedependent fashion and reached the highest level after G17 treatment for 12 h, while expression levels of β-catenin in the TX-100 insoluble fraction were just on the contrary. Immunocytochemistry showed that β-catenin was translocated from the cell membranes into the cytoplasm and nucleus under G17 treatment.Expression levels of c-myc and cyclin D1 in the G17-treated Colo320WT cells were markedly higher compared to the untreated Colo320WT cells. In addition, the aforementioned G17-stimulated responses were blocked by L365,260.CONCLUSION: Gastrin17 activates β-catenin/Tcf-4 signaling in Colo320WT cells, thereby leading to overexpression of c-myc and cyclin D1.     

Gastrin suppresses growth of CCK2 receptor expressing colon cancer cells by inducing apoptosis in vitro and in vivo

BACKGROUND & AIMS: The role of amidated gastrin17 (G17) and the gastrin/CCKB/CCK2 receptor in colorectal carcinogenesis is still a controversial issue. Here, we investigated the effect of G17 on proliferation and apoptosis of CCK2 receptor-expressing human colon cancer cell lines in vitro and in vivo. METHODS: Proliferation was determined by cell counting and cell cycle analysis. Apoptosis was analyzed by annexin V staining, TUNEL staining, caspase-3/7 assay, and JC1 (delta psi) assay. Signal-transduction pathways were analyzed by Western blotting and gel-shift and luciferase assays. An in vivo tumor model with subcutaneously inoculated colon cancer cells in SCID mice was used, and systemic hypergastrinemia was induced by omeprazole. RESULTS: In Colo320 cells stably transfected with the wild-type CCK2 receptor (Colo320wt) or in Lovo cells endogenously expressing CCK2 receptors, G17 treatment inhibited proliferation along with a G2/M cell cycle arrest. Furthermore, the administration of G17 significantly augmented apoptosis of CCK2 receptor-expressing cells. In contrast, G17 had no effect on proliferation and apoptosis in Colo320 cells stably transfected with a tumor-derived CCK2 receptor mutant (Colo320mut) or in cells lacking CCK2 receptor expression. Systemic hypergastrinemia in severe combined immunodeficiency (SCID) mice suppressed the growth of Colo320wt tumors accompanied by enhanced apoptosis as compared with untreated tumors. In contrast, omeprazole did not affect Colo320mut tumors reflecting a loss-of-function state of the CCK2(mut) receptor. This is supported by the observation that, in Colo320wt cells, but not in Colo320mut cells, G17 treatment induced the MAPK/ERK/AP-1 pathway and inhibited the activity of NF-kappaB. CONCLUSIONS: G17 exerts an antiproliferative and proapoptotic effect on human colon cancer cells expressing the wild-type CCK2 receptor. This supports the view that amidated gastrin prevents rather than promotes colorectal carcinogenesis.     

Dysregulation of MicroRNA-34a Expression in Colorectal Cancer Inhibits the Phosphorylation of FAK Via VEGF

Background

MicroRNAs (miRs) are small non-coding RNAs that play important roles in cancer development where they can act as oncogenes or as tumor-suppressors. MiR-34a is a tumor suppressor that is frequently downregulated in a number of tumor types. However, little is known about the role of miR-34a in colorectal cancer (CRC).

Aim

This study aims to show the dysregulation of miR-34a in CRC and to characterize the function and mechanism of miR-34a in CRC cell lines.

Methods

The expression of miR-34a was detected using real-time PCR on CRC tissues and adjacent non-tumorous tissues. The ELISA was used to assess vascular endothelial growth factor (VEGF). The focal adhesion kinase (FAK) and phosphorylated FAK Y397 (pY397FAK) were measured by Western blot. The functions of miR-34a in vivo were measured by migration, invasion, CCK-8 assay and flow cytometry.

Results

MiR-34a was significantly downregulated and pY397FAK was upregulated in CRC cancer tissues. It plays an important role in inhibiting migration and invasion and in increasing apoptosis of CRC cells. Bioinformatic analysis suggested that VEGF may be a target of miR-34a, and this hypothesis was proved by ELISA and RT-PCR. The level of pY397FAK that could be activated by VEGF was downregulated in miR-34a overexpression CRC cell lines. The phosphorylation of FAK at 397 sites in miR-34a-stable cell lines was completely rescued by extra VEGF treatment.

Conclusion

MiR-34a is frequently downregulated in CRC and modulates the phosphorylation of FAK by negatively regulating VEGF.     

Affinity maturation of antibodies assisted by in silico modeling

Rational engineering methods can be applied with reasonable success to optimize physicochemical characteristics of proteins, in particular, antibodies. Here, we describe a combined CDR3 walking randomization and rational design-based approach to enhance the affinity of the human anti-gastrin TA4 scFv. The application of this methodology to TA4 scFv, displaying only a weak overall affinity for gastrin17 (K(D) = 6 microM), resulted in a set of nine affinity-matured scFv variants with near-nanomolar affinity (K(D) = 13.2 nM for scFv TA4.112). First, CDR-H3 and CDR-L3 randomization resulted in three scFvs with an overall affinity improvement of 15- to 35-fold over the parental. Then, the modeling of two scFv constructs selected from the previous step (TA4.11 and TA4.13) was followed by a combination of manual and molecular dynamics-based docking of gastrin17 into the respective binding sites, analysis of apparent packing defects, and selection of residues for mutagenesis through phage display. Nine scFv mutants were obtained from the second maturation step. A final 454-fold improvement in affinity compared with TA4 was obtained. These scFvs showed an enhanced potency to inhibit gastrin-induced proliferation in Colo 320 WT and BxPc3 tumoral cells. In conclusion, we propose a structure-based rational method to accelerate the development of affinity-matured antibody constructs with enhanced potential for therapeutic use.     

Focal adhesion kinase-Tyr407 and -Tyr397 exhibit antagonistic effects on blood-testis barrier dynamics in the rat

Focal adhesion kinase (FAK), a nonreceptor protein tyrosine kinase, displays phosphorylation-dependent localization in the seminiferous epithelium of adult rat testes. FAK is an integrated component of the blood-testis barrier (BTB) involved in regulating Sertoli cell adhesion via its effects on the occludin-zonula occludens-1 complex. Herein, we report that p-FAK-Tyr(407) and p-FAK-Tyr(397) display restricted spatiotemporal and almost mutually exclusive localization in the epithelium, affecting BTB dynamics antagonistically, with the former promoting and the latter disrupting the Sertoli cell tight junction-permeability barrier function. Using primary cultured Sertoli cells as an in vitro model that mimics the BTB in vivo both functionally and ultrastructurally, effects of FAK phosphorylation on BTB function were studied by expressing nonphosphorylatable and phosphomimetic mutants, with tyrosine replaced by phenylalanine (F) and glutamate (E), respectively. Compared with WT FAK, Y407E and Y397F mutations each promoted barrier function, and the promoting effect of the Y407E mutant was abolished in the Y397E-Y407E double mutant, demonstrating antagonism between Tyr(407) and Tyr(397). Furthermore, Y407E mutation induced the recruitment of actin-related protein 3 to the Sertoli cell-cell interface, where it became more tightly associated with neuronal Wiskott-Aldrich syndrome protein, promoting actin-related protein 2/3 complex activity. Conversely, Y407F mutation reduced the rate of actin polymerization at the Sertoli cell BTB. In summary, FAK-Tyr(407) phosphorylation promotes BTB integrity by strengthening the actin filament-based cytoskeleton. FAK serves as a bifunctional molecular "switch" to direct the cyclical disassembly and reassembly of the BTB during the epithelial cycle of spermatogenesis, depending on its phosphorylation status, to facilitate the transit of preleptotene spermatocytes across the BTB.     

Characterization of gastrin-cholecystokinin 2 receptor interaction in relation to c-fos induction

The interaction of gastrin with the cholecystokinin 2 (CCK2)/gastrin receptor has been studied extensively in relation to gastric acid secretion. However, not much is known about the contribution of individual amino acids of gastrin interacting with the CCK2 receptor, when gastrin is acting as a tumor growth factor. The purpose of the present study was to determine the significance of each individual amino acid residue of human gastrin-17 with respect to CCK2 receptor-mediated cell proliferation. Activation of this receptor was assessed using an in vitro bioassay based on gastrin-induced expression of a c-fos-luciferase reporter, transfected in AR42JB13 and Colo 320 cells, a rat pancreatic and human colorectal cell line respectively. Gastrin-17 dose dependently increased c-fos induction in both cancer cell lines. L365,260, a known CCK2 receptor antagonist, completely blocked the gastrin signal, demonstrating the specificity of this assay. We demonstrated for the first time that four carboxy-terminal amino acids of gastrin-17 are essential for activation of the CCK2 receptor with respect to c-fos induction. Also other residues of gastrin-17, notably glycine-2 for the rat CCK2 receptor and glutamic acid 8-10 and tyrosine-12 for the human receptor, were found to be important, although to a lesser extent. Alanine-substitution variants of each of the four carboxy-terminal amino acids of gastrin-17 showed strongly reduced receptor activation but did not act as competitive inhibitors of gastrin-17. Identification of the essential role of the carboxy-terminal tetrapeptide of gastrin-17 in CCK2 receptor-mediated c-fos induction indicates that gastrin inhibitory therapeutic strategies should mainly be targeted toward this region of gastrin.