TMEM16F activation by Ca2+triggers plasmalemma expansion and directs PD-1 trafficking

TMEM16F, an ion channel gated by high cytoplasmic Ca2+, is required for cell surface phosphatidylserine exposure during platelet aggregation and T cell activation. Here we demonstrate in Jurkat T cells and HEK293 cells that TMEM16F activation triggers large-scale surface membrane expansion in parallel with lipid scrambling. Following TMEM16F mediated scrambling and surface expansion, cells undergo extensive membrane shedding. The membrane compartment that expands the cell surface does not recycle, nor does it involve endoplasmic reticulum or acidified lysosomes. Surprisingly, T cells lacking TMEM16F expression not only fail to scramble lipid and expand surface membrane, but instead undergo a rapid membrane internalization known as massive endocytosis (MEND) in response to the same Ca2+ stimulus as their parental cells. TMEM16F dependent membrane shedding and MEND traffic similar sets of membrane receptors from the cell surface. The selective participation of the T cell co-receptor PD-1 in this trafficking is determined by its single transmembrane domain, establishing a fundamental role for TMEM16F as a regulator of Ca2+-activated membrane trafficking.