Calcium-dependent phospholipid scramblase activity of TMEM16 protein family members.

Abstract

Asymmetrical distribution of phospholipids between the inner and outer plasma membrane leaflets is disrupted in various biological processes. We recently identified TMEM16F, an eight-transmembrane protein, as a Ca2+-dependent phospholipid scramblase that exposes phosphatidylserine (PS) to the cell surface. In this study, we established a mouse lymphocyte cell line with a floxed allele in the TMEM16F gene. When TMEM16F was deleted, these cells failed to expose PS in response to Ca2+ ionophore, but PS exposure was elicited by Fas ligand treatment. We expressed other TMEM16 proteins in the TMEM16F−/− cells and found that not only TMEM16F, but also 16C, 16D, 16G, and 16J work as lipid scramblases with different preference to lipid substrates. On the other hand, a patch clamp analysis in 293T cells indicated that TMEM16A and 16B, but not other family members, acted as Ca2+-dependent Cl− channels. These results indicated that among 10 TMEM16 family members, 7 members could be divided into two subfamilies, Ca2+-dependent Cl− channels (16A and 16B) and Ca2+-dependent lipid scramblases (16C, 16D, 16F, 16G, and 16J).