We previously reported that v-Fos transformation effector (Fte-1) is a novel CD2 binding protein identified by yeast two hybrid system. In the present study, we further characterize the molecular properties and biological activity of the Fte-1. In vitro interaction analysis by an IAsys Resonant Mirror Biosensor further demonstrated that Fte-1 interacts with CD2 specifically, and the dissociation constant (Kd) of Fte-1-CD2 is 10(7 mol. The molecular section analysis showed that protein kinase C (PKC) phosphorylation site at Ser238 of Fte-1, as confirmed by in vitro phosphorylation, is essential for the specific interaction with CD2. Jurkat T cells transfected with expression vector encoding for EGFP-Fte-1 fusion protein showed that Fte-1 displays a clustering distribution in the cells. Upon stimulation by CD2 monoclonal antibody T11, Fte-1 lost the character of clustering distribution and translocation to the plasma membrane, which were disrupted by mutation of Fte-1 (Ser238Gly), suggesting that Fte-1 could be co-localized with CD2 on the membrane, and Fte-1 phosphorylation at Ser238 is a crucial factor in CD2-mediated interaction with Fte-1. Suppression of Fte-1 expression by small interference RNA (siRNA) diminished the susceptibility of Jurkat T cells to apoptosis triggered by phorbol 12-myristate 13-ace- tate (PMA) and ionomycin, indicating that the biological function of Fte-1 may be involved in the regulation of activation and apoptosis of T cells. These results provide further evidence that Fte-1 is a novel binding protein of CD2, and may function as a downstream molecule in the CD2-mediated events.