Surface expression of TTYH2 is attenuated by direct interaction with β-COP.

TTYH2 is a calcium-activated, inwardly rectifying anion channel that has been shown to be related to renal cancer and colon cancer. Based on the topological prediction, TTYH2 protein has five transmembrane domains with the extracellular N-terminus and the cytoplasmic C-terminus. In the present study, we identified a vesicle transport protein, β-COP, as a novel specific binding partner of TTYH2 by yeast two-hybrid screening using a human brain cDNA library with the C-terminal region of TTYH2 (TTYH2-C) as a bait. Using in vitro and in vivo binding assays, we confirmed the protein-protein interactions between TTYH2 and β-COP. We also found that the surface expression and activity of TTYH2 were decreased by co-expression with β-COP in the heterologous expression system. In addition, β-COP associated with TTYH2 in a native condition at a human colon cancer cell line, LoVo cells. The over-expression of β-COP in the LoVo cells led to a dramatic decrease in the surface expression and activity of endogenous TTYH2. Collectively, these data suggested that β-COP plays a critical role in the trafficking of the TTYH2 channel to the plasma membrane.