Maspin acts at the cell membrane to inhibit invasion and motility of mammary and prostatic cancer cells.

Maspin, a novel serine protease inhibitor (serpin), inhibits tumor invasion and metastasis of mammary carcinoma. We show here that recombinant maspin protein blocks the motility of these carcinoma cells in culture over 12 h, as demonstrated by time-lapse video microscopy. Lamellopodia are withdrawn but ruffling continues. Both exogenous recombinant maspin and maspin expressed by tumor transfectants exhibit inhibitory effects on cell motility and cell invasion as shown in modified Boyden chamber assays. In addition, three prostatic cancer cell lines treated with recombinant maspin exhibited similar inhibition of both invasion and motility, suggesting a similar mode of maspin action in these two glandular epithelial cancers. When mammary carcinoma cells were treated with recombinant maspin, the protein was shown by immunostaining to bind specifically to the cell surface, suggesting that maspin activity is membrane associated. When pretreated with antimaspin antibody, maspin loses its inhibitory effects on both invasion and motility. However, when maspin is added to these cells preceding antibody treatment, the activity of maspin is no longer inhibited by subsequent addition of the antibody. It is concluded therefore that the inhibition of invasion and motility by maspin is initially localized to the cell surface. IMAGES:

Maspin是一种新型丝氨酸蛋白酶抑制剂（serine protease inhibitor，serpin），可抑制乳腺癌的肿瘤侵袭与转移。本研究通过延时视频显微镜术证实，重组maspin蛋白可在12小时以上的培养周期中抑制此类癌细胞的运动能力。癌细胞的板状伪足发生回缩，但膜皱褶仍持续存在。通过改良型博伊登室分析法（Boyden chamber assay）验证，外源性重组maspin以及肿瘤转染细胞表达的maspin均对细胞运动与细胞侵袭具有抑制作用。此外，经重组maspin处理的三株前列腺癌细胞系同样表现出侵袭与运动能力的抑制效果，提示maspin在这两种腺上皮癌中具有相似的作用机制。对乳腺癌细胞施加重组maspin处理后，经免疫染色（immunostaining）检测发现，该蛋白可特异性结合于细胞表面，提示maspin的活性与细胞膜相关联。若先用抗maspin抗体（antimaspin antibody）预处理，maspin将丧失其对侵袭与运动能力的抑制作用。但如果先向细胞中加入maspin，再进行抗体处理，则后续添加抗体将无法抑制maspin的活性。综上，maspin对癌细胞侵袭与运动能力的抑制作用最初定位于细胞表面。图片：