Xu Congfeng, Zhang Yanhui H, Thangavel Muthusamy, Richardson Mekel M, Liu Li, Zhou Bin, Zheng Yi, Ostrom Rennolds S, Zhang Xin A
Vascular Biology Center, University of Tennessee Health Science Center, Memphis, TN 38163, USA.
FASEB J. 2009 Oct;23(10):3273-88. doi: 10.1096/fj.08-123414. Epub 2009 Jun 4.
Tetraspanin CD82 suppresses cell migration, tumor invasion, and tumor metastasis. To determine the mechanism by which CD82 inhibits motility, most studies have focused on the cell surface CD82, which forms tetraspanin-enriched microdomains (TEMs) with other transmembrane proteins, such as integrins. In this study, we found that CD82 undergoes endocytosis and traffics to endosomes and lysosomes. To determine the endocytic mechanism of CD82, we demonstrated that dynamin and clathrin are not essential for CD82 internalization. Depletion or sequestration of sterol in the plasma membrane markedly inhibited the endocytosis of CD82. Despite the demand on Cdc42 activity, CD82 endocytosis is distinct from macropinocytosis and the documented dynamin-independent pinocytosis. As a TEM component, CD82 reorganizes TEMs and lipid rafts by redistributing cholesterol into these membrane microdomains. CD82-containing TEMs are characterized by the cholesterol-containing microdomains in the extreme light- and intermediate-density fractions. Moreover, the endocytosis of CD82 appears to alleviate CD82-mediated inhibition of cell migration. Taken together, our studies demonstrate that lipid-dependent endocytosis drives CD82 trafficking to late endosomes and lysosomes, and CD82 reorganizes TEMs and lipid rafts through redistribution of cholesterol.
四跨膜蛋白CD82可抑制细胞迁移、肿瘤侵袭和肿瘤转移。为了确定CD82抑制细胞运动的机制，大多数研究都集中在细胞表面的CD82上，它与其他跨膜蛋白（如整合素）形成富含四跨膜蛋白的微结构域（TEMs）。在本研究中，我们发现CD82会发生内吞作用，并运输至内体和溶酶体。为了确定CD82的内吞机制，我们证明发动蛋白和网格蛋白对CD82的内化并非必不可少。质膜中固醇的耗尽或隔离显著抑制了CD82的内吞作用。尽管需要Cdc42活性，但CD82的内吞作用不同于巨胞饮作用以及已报道的不依赖发动蛋白的胞饮作用。作为TEM的一个组成部分，CD82通过将胆固醇重新分布到这些膜微结构域中来重组TEM和脂筏。含有CD82的TEM的特征是在极轻和中等密度级分中含有胆固醇的微结构域。此外，CD82的内吞作用似乎减轻了CD82介导的对细胞迁移的抑制。综上所述，我们的研究表明脂质依赖性内吞作用驱动CD82运输至晚期内体和溶酶体，并且CD82通过胆固醇的重新分布来重组TEM和脂筏。
