Chen Yih-Wen, Tekle Christina, Fodstad Oystein
Mitchell Cancer Institute, University of South Alabama, Mobile, AL 36688, USA.
Curr Cancer Drug Targets. 2008 Aug;8(5):404-13. doi: 10.2174/156800908785133141.
The monoclonal antibody (mAb) 376.96 has been used for detection of micrometastatic tumor cells due to its high binding specificity for a wide range of tumor cells, but the identity and function of its target antigen have not been known. Here, using immunoprecipitation and siRNA technology, we demonstrate that the antigen is the human 4Ig-B7H3 (4Ig-hB7H3) protein, previously known as an immunoregulatory protein in immune cells. Immunoblots of whole cell lysates, subcellular fractionation and tunicamycin treatment of human tumor cells indicated that 4Ig-hB7H3 is a approximately 100-kDa N-linked glycosylated membrane protein. The tumor promoter phorbol 12-myristate 13-acetate (PMA) enhanced the expression of 4Ig-hB7H3 in FEMX-I (melanoma), MA11 (breast cancer), and OHS (osteosarcoma) cells, suggesting that 4Ig-hB7H3 may be implicated in tumorigenesis. Most importantly, siRNA-downregulation of hB7H3 reduced cell adhesion to fibronectin of melanoma and breast cancer cells by up to 50 %, and migration and matrigel-invasion by more than 70 %, but surprisingly had no apparent impact on cell proliferation. In conclusion, our data present 4Ig-hB7H3 as a tumor-associated antigen and suggests a novel biological role of 4Ig-hB7H3 in tumor progression and metastasis.
单克隆抗体（mAb）376.96因其对多种肿瘤细胞具有高结合特异性，已被用于检测微转移肿瘤细胞，但其靶抗原的身份和功能尚不清楚。在此，我们利用免疫沉淀和小干扰RNA（siRNA）技术证明，该抗原是人类4Ig-B7H3（4Ig-hB7H3）蛋白，此前已知其为免疫细胞中的一种免疫调节蛋白。对人类肿瘤细胞的全细胞裂解物进行免疫印迹、亚细胞分级分离和衣霉素处理表明，4Ig-hB7H3是一种约100 kDa的N-连接糖基化膜蛋白。肿瘤启动子佛波醇12-肉豆蔻酸酯13-乙酸酯（PMA）增强了4Ig-hB7H3在FEMX-I（黑色素瘤）、MA11（乳腺癌）和OHS（骨肉瘤）细胞中的表达，提示4Ig-hB7H3可能与肿瘤发生有关。最重要的是，hB7H3的siRNA下调使黑色素瘤和乳腺癌细胞与纤连蛋白的黏附减少高达50%，迁移和基质胶侵袭减少超过70%，但令人惊讶的是对细胞增殖没有明显影响。总之，我们的数据表明4Ig-hB7H3是一种肿瘤相关抗原，并提示4Ig-hB7H3在肿瘤进展和转移中具有新的生物学作用。
