Diamond Michelle E, Sun Limin, Ottaviano Adam J, Joseph Mathew J, Munshi Hidayatullah G
Division of Hematology/Oncology, Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.
J Cell Sci. 2008 Jul 1;121(Pt 13):2197-207. doi: 10.1242/jcs.021782. Epub 2008 Jun 10.
Aberrant expression of N-cadherin is associated with tumor progression in squamous cell carcinomas (SCCs). Consequently, we examined the regulation of N-cadherin by TGFbeta1, an important mediator of keratinocyte and SCC function. N-cadherin expression was increased in oral SCC (OSCC) cell lines, regulating motility and correlating with TGFbeta1 production. Moreover, in normal keratinocytes TGFbeta1 increased expression of N-cadherin to regulate motility. TGFbeta1-mediated N-cadherin expression in the oral keratinocytes was blocked using siRNA targeting Smads. Unexpectedly, we found that EGF blocked TGFbeta1-mediated N-cadherin expression in oral keratinocytes and not in OSCC cells. Mechanistically, EGF enhanced Smad phosphorylation in the linker region, and attenuated TGFbeta1-mediated phosphorylation of Smad at the C-terminus, localization of Smad to the nucleus as well as Smad-driven promoter activity exclusively in oral keratinocytes but not in OSCC cells. The effect of EGF on TGFbeta1-mediated Smad-driven promoter activity and N-cadherin expression was reversed when activation of ERK1/2 was blocked. Although EGF and TGFbeta1 independently promoted migration of both oral keratinocytes and OSCC cells, EGF decreased TGFbeta1-mediated migration of oral keratinocytes but enhanced migration of OSCC cells. Together, these data support a model wherein EGF signaling has an important negative regulatory role on TGFbeta1-mediated N-cadherin expression and motility in normal oral keratinocytes, and in which loss of this regulatory mechanism accompanies malignant transformation of the oral epithelium.
N-钙黏蛋白的异常表达与鳞状细胞癌（SCC）的肿瘤进展相关。因此，我们研究了转化生长因子β1（TGFβ1）对N-钙黏蛋白的调控作用，TGFβ1是角质形成细胞和SCC功能的重要调节因子。在口腔SCC（OSCC）细胞系中，N-钙黏蛋白表达增加，调节细胞运动，并与TGFβ1的产生相关。此外，在正常角质形成细胞中，TGFβ1增加N-钙黏蛋白的表达以调节细胞运动。使用靶向Smads的小干扰RNA（siRNA）可阻断TGFβ1介导的口腔角质形成细胞中N-钙黏蛋白的表达。出乎意料的是，我们发现表皮生长因子（EGF）可阻断TGFβ1介导的口腔角质形成细胞而非OSCC细胞中N-钙黏蛋白的表达。从机制上讲，EGF增强了连接区Smad的磷酸化，并减弱了TGFβ1介导的Smad在C末端的磷酸化、Smad向细胞核的定位以及Smad驱动的启动子活性，且这种作用仅发生在口腔角质形成细胞而非OSCC细胞中。当细胞外信号调节激酶1/2（ERK1/2）的激活被阻断时，EGF对TGFβ1介导的Smad驱动的启动子活性和N-钙黏蛋白表达的影响被逆转。尽管EGF和TGFβ1均可独立促进口腔角质形成细胞和OSCC细胞的迁移，但EGF可降低TGFβ1介导的口腔角质形成细胞的迁移，却增强了OSCC细胞的迁移。总之，这些数据支持了一种模型，即EGF信号通路对TGFβ1介导的正常口腔角质形成细胞中N-钙黏蛋白的表达和运动具有重要的负调控作用，并且这种调控机制的丧失伴随着口腔上皮的恶性转化。
