He Bo, Liu Li, Cook George A, Grgurevich Svetozar, Jennings Lisa K, Zhang Xin A
Vascular Biology Center and Department of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA.
J Biol Chem. 2005 Feb 4;280(5):3346-54. doi: 10.1074/jbc.M406680200. Epub 2004 Nov 19.
Tetraspanin CD82 has been implicated in integrin-mediated functions such as cell motility and invasiveness. Although tetraspanins associate with integrins, it is unknown if and how CD82 regulates the functionality of integrins. In this study, we found that Du145 prostate cancer cells underwent morphogenesis on the reconstituted basement membrane Matrigel to form an anastomosing network of multicellular structures. This process entirely depends on integrin alpha6, a receptor for laminin. After CD82 is expressed in Du145 cells, this cellular morphogenesis was abolished, indicating a functional cross-talk between CD82 and alpha6 integrins. Interestingly, antibodies against other tetraspanins expressed in Du145 cells such as CD9, CD81, and CD151 did not block this integrin alpha6-dependent morphogenesis. We further found that CD82 significantly inhibited cell adhesion on laminin 1. Notably, the level of alpha6 integrins on the cell surface was down-regulated upon CD82 expression, although total cellular alpha6 protein levels remained unchanged in CD82-expressing cells. This down-regulation indicates that the diminished cell adhesiveness of CD82-expressing Du145 cells on laminin likely resulted from less cell surface expression of alpha6 integrins. As expected, CD82 physically associated with the integrin alpha6 in Du145-CD82 transfectant cells, suggesting that the formation of the CD82-integrin alpha6 complex reduces alpha6 integrin cell surface expression. Finally, the internalization of cell surface integrin alpha6 is significantly enhanced upon CD82 expression. In conclusion, our results indicate that 1) CD82 attenuates integrin alpha6 signaling during a cellular morphogenic process; 2) the decreased surface expression of alpha6 integrins in CD82-expressing cells is likely responsible for the diminished adhesiveness on laminin and, subsequently, results in the attenuation of alpha6 integrin-mediated cellular morphogenesis; and 3) the accelerated internalization of integrin alpha6 upon CD82 expression correlates with the down-regulation of cell surface integrin alpha6.
四跨膜蛋白CD82与整合素介导的功能有关，如细胞运动和侵袭。尽管四跨膜蛋白与整合素相关联，但CD82是否以及如何调节整合素的功能尚不清楚。在本研究中，我们发现Du145前列腺癌细胞在重组基底膜基质胶上发生形态发生，形成多细胞结构的吻合网络。这个过程完全依赖于整合素α6，层粘连蛋白的一种受体。在Du145细胞中表达CD82后，这种细胞形态发生被消除，表明CD82与α6整合素之间存在功能性相互作用。有趣的是，针对Du145细胞中表达的其他四跨膜蛋白（如CD9、CD81和CD151）的抗体并未阻断这种整合素α6依赖性形态发生。我们进一步发现，CD82显著抑制细胞在层粘连蛋白1上的黏附。值得注意的是，尽管在表达CD82的细胞中总细胞α6蛋白水平保持不变，但CD82表达后细胞表面α6整合素水平下调。这种下调表明，表达CD82的Du145细胞在层粘连蛋白上黏附性降低可能是由于α6整合素在细胞表面表达减少所致。正如预期的那样，在Du145-CD82转染细胞中，CD82与整合素α6发生物理关联，表明CD82-整合素α6复合物的形成减少了α6整合素在细胞表面的表达。最后，CD82表达后细胞表面整合素α6的内化显著增强。总之，我们的结果表明：1）CD82在细胞形态发生过程中减弱整合素α6信号；2）表达CD82的细胞中α6整合素表面表达的降低可能是其在层粘连蛋白上黏附性降低的原因，进而导致α6整合素介导的细胞形态发生减弱；3）CD82表达后整合素α6内化加速与细胞表面整合素α6的下调相关。
