Abstract: To investigate the role of cortactin, a protein encoded by oncogene EMS1, in the endocytosis of colon cancer cells. Methods The distribution of cortactin with Rab5/11 and internalized transferrin in human colon cancer cell HT29 was observed by confocal microscopy. Plasmids inserted full length cortactin or its mutants gene were transfected into HT29 cells by virus infection, and then the effect of these plasmids on cell endocytosis was detected. Furthermore, the relation between the cortactin phosphorylation and transferrin uptake in the process of endocytosis was analyzed by Werstern blot and immunofluorescence assay. ResultsCortactin was observed co-localized with Rab5/11 and transferrin in HT29 cells. Transferrin uptake in cells overexpressed N-terminal deletion cortactin or C-terminal deletion cortactin was significant attenuated, while no apparent change was seen in cells overexpressed full length cortactin or vector. The level of cortactin phosphorylation was depended on transferrin uptake in a time-and dose-dependent manner. ConclusionCortactin plays an important role in the endocytosis of colon cancer cell HT29. And its function maybe depend on the N- terminal and C-terminal domains. In addition, the cortactin phosphorylation is involved in the endocytosis of colon cancer cells.