Okamoto I, Kawano Y, Tsuiki H, Sasaki J, Nakao M, Matsumoto M, Suga M, Ando M, Nakajima M, Saya H
Department of Tumor Genetics and Biology, Kumamoto University School of Medicine, Japan.
Oncogene. 1999 Feb 18;18(7):1435-46. doi: 10.1038/sj.onc.1202447.
CD44 is a cell surface receptor for hyaluronate, a component of the extracellular matrix (ECM). Although CD44 has been implicated in tumor invasion and metastasis, the molecular mechanisms remain to be elucidated. Here we find that CD44 expressed in cancer cells is cleaved at the membrane-proximal region of the ectodomain and the membrane-bound cleavage product can be detected using an antibody against the cytoplasmic domain of CD44. Furthermore, we report that CD44 cleavage is mediated by a membrane-associated metalloprotease expressed in cancer cells. A tissue inhibitor of metalloproteases-1 (TIMP-1), as well as metalloprotease inhibitors, inhibit CD44 cleavage in the cell-free assay. Contrary, serine protease inhibitors enhance CD44 cleavage, and the enhancement can be prevented by pretreatment with a metalloprotease inhibitor. Thus, CD44 cleavage is regulated by an intricate balance between some proteases and their inhibitors. Interestingly, treatment with the metalloprotease blocker 1,10-phenanthroline, which strongly prevent the CD44 cleavage, suppressed RERF-LC-OK lung cancer cell migration on a hyaluronate substrate, but not on several other substrates. These results suggest that CD44 cleavage plays a critical role in an efficient cell-detachment from a hyaluronate substrate during the cell migration and consequently promotes CD44-mediated cancer cell migration. Our present data indicate that CD44, not only ECM per se, is one of the targets of pericellular proteolysis involved in tumor invasion and metastasis.
CD44是一种细胞表面受体，可与透明质酸结合，透明质酸是细胞外基质（ECM）的一个组成部分。尽管CD44与肿瘤侵袭和转移有关，但其分子机制仍有待阐明。在此我们发现，癌细胞中表达的CD44在胞外域的膜近端区域被切割，并且可以使用抗CD44胞质域的抗体检测到膜结合的切割产物。此外，我们报告CD44切割是由癌细胞中表达的一种膜相关金属蛋白酶介导的。金属蛋白酶组织抑制剂-1（TIMP-1）以及金属蛋白酶抑制剂在无细胞试验中可抑制CD44切割。相反，丝氨酸蛋白酶抑制剂可增强CD44切割，并且这种增强可通过用金属蛋白酶抑制剂预处理来阻止。因此，CD44切割受一些蛋白酶及其抑制剂之间复杂平衡的调节。有趣的是，用金属蛋白酶阻滞剂1,10-菲咯啉处理可强烈阻止CD44切割，抑制RERF-LC-OK肺癌细胞在透明质酸底物上的迁移，但在其他几种底物上则不然。这些结果表明，CD44切割在细胞迁移过程中从透明质酸底物上有效脱离细胞的过程中起关键作用，从而促进CD44介导的癌细胞迁移。我们目前的数据表明，CD44不仅是细胞外基质本身，还是参与肿瘤侵袭和转移的细胞周围蛋白水解的靶点之一。
