Abstract: Objective To study cortactin function in cancer cell endocytosis. Methods We applied cortactin siRNA interference to MDA-Mb-231, a human breast adenocarcinoma cell line, in which cortactin is over-expressed, and introduced anti-cortactin immunoreagents into the cells using the BioPorter system to interfere with cortactin function in vivo. Capture -ELISA assay was used to measure transferrin uptake, immunoblot assay to assess the effect of cortactin knock-down, and immunoflurescence microscopy to examine the effect of cortactin down-regulation on transferrin uptake. Results Interference of cortactin function in cells led to the impairment of transferrin endocytosis. Transferrin fluorescent intensity in cytoplasm in cortactin siRNA treated-cells was apparently reduced in comparison to mock-treated cells. Less than 50% of cells subjected to cortactin siRNA treatment had normal transferrin uptake. Endocytosis in MDA-Mb-231 cells introduced with cortactin antibodies was impaired as well, showing a 30 ~ 60% reduction in transferrin uptake. Conclusions This study implies that cortactin, an actin-binding protein, plays an essential role in cell endocytosis

Key words: Cortactin, Cancer cell, Endocytosis, siRNA Interference