Journal Article

Calcium-dependent phospholipid scrambling by TMEM16F

Umeda, Masato, Suzuki, Jun, Sims, Peter J., Nagata, Shigekazu

2010

Overview

Phospholipid scrambling The plasma membranes of eukaryotic cells have an asymmetrical distribution of phospholipids. Lipid asymmetry can be disrupted during biological processes such as apoptosis, when phosphatidylserine in the inner leaflet of the membrane is exposed on the outer membrane. It has been proposed that activation of a phospholipid scramblase catalyses bidirectional transbilayer movement of phospholipids, and now a protein corresponding to this activity has been identified as TMEM16F, a member of the TMEM16 family of transmembrane proteins. Furthermore, a patient with Scott syndrome, which results from a defect in phospholipid scrambling activity, was found to carry a mutation in the gene encoding TMEM16F. Lipid asymmetry can be disrupted during biological processes such as apoptosis, during which phosphatidylserine in the inner leaflet of the membrane is exposed on the outer membrane. It has been proposed that activation of a phospholipid scramblase catalyses bidirectional transbilayer movement of phospholipids, but the protein corresponding to this activity has not been identified. Here, the protein TMEM16F is identified, and is an essential component for the Ca 2+ -dependent exposure of phosphatidylserine on the plasma membrane. A patient with Scott syndrome, which results from a defect in phospholipid scrambling activity, was found to carry a mutation in the gene encoding TMEM16F. In all animal cells, phospholipids are asymmetrically distributed between the outer and inner leaflets of the plasma membrane 1 . This asymmetrical phospholipid distribution is disrupted in various biological systems. For example, when blood platelets are activated, they expose phosphatidylserine (PtdSer) to trigger the clotting system 2 , 3 . The PtdSer exposure is believed to be mediated by Ca 2+ -dependent phospholipid scramblases that transport phospholipids bidirectionally 1 , 4 , but its molecular mechanism is still unknown. Here we show that TMEM16F (transmembrane protein 16F) is an essential component for the Ca 2+ -dependent exposure of PtdSer on the cell surface. When a mouse B-cell line, Ba/F3, was treated with a Ca 2+ ionophore under low-Ca 2+ conditions, it reversibly exposed PtdSer. Using this property, we established a Ba/F3 subline that strongly exposed PtdSer by repetitive fluorescence-activated cell sorting. A complementary DNA library was constructed from the subline, and a cDNA that caused Ba/F3 to expose PtdSer spontaneously was identified by expression cloning. The cDNA encoded a constitutively active mutant of TMEM16F, a protein with eight transmembrane segments 5 . Wild-type TMEM16F was localized on the plasma membrane and conferred Ca 2+ -dependent scrambling of phospholipids. A patient with Scott syndrome 6 , 7 , which results from a defect in phospholipid scrambling activity 8 , 9 , was found to carry a mutation at a splice-acceptor site of the gene encoding TMEM16F, causing the premature termination of the protein.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 631/337 / 631/45/287/1194 / 631/80 / 692/699/1541 / Animals / Anoctamins / B-Lymphocytes - cytology / B-Lymphocytes - drug effects / Biological and medical sciences / Biological transport / Calcium / Calcium - antagonists & inhibitors / Calcium - metabolism / Calcium - pharmacology / Cell Line / Cell Membrane - drug effects / Cell Membrane - metabolism / Classical genetics, quantitative genetics, hybrids / Cloning / Cloning, Molecular / DNA, Complementary - genetics / Flow Cytometry / Fundamental and applied biological sciences. Psychology / Gene Library / Gene mutations / Genetic aspects / Genetics of eukaryotes. Biological and molecular evolution / Genomics / Hematologic and hematopoietic diseases / Human / Humanities and Social Sciences / Humans / Ionophores - pharmacology / letter / Lipids / Medical sciences / Mice / multidisciplinary / Mutant Proteins - chemistry / Mutant Proteins - genetics / Mutant Proteins - metabolism / Phosphatidylserines - metabolism / Phospholipid Transfer Proteins - chemistry / Phospholipid Transfer Proteins - genetics / Phospholipid Transfer Proteins - metabolism / Phospholipids / Phospholipids - metabolism / Physiological aspects / Platelet diseases and coagulopathies / Proteins / Reverse Transcriptase Polymerase Chain Reaction / RNA Splice Sites - genetics / Science / Science (multidisciplinary) / Syndrome