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

Christopher Bricogne,Ricardo Henriques,Michael Fine,Pedro M Pereira,Youxue Wang,Julia Sung,Mary K Collins,Donald W Hilgemann,Maha Tijani

doi:10.1038/s41598-018-37056-x

Abstract

TMEM16F is a Ca2+ -gated ion channel that is required for Ca2+ -activated phosphatidylserine exposure on the surface of many eukaryotic cells. TMEM16F is widely expressed and has roles in platelet activation during blood clotting, bone formation and T cell activation. By combining microscopy and patch clamp recording we demonstrate that activation of TMEM16F by Ca2+ ionophores in Jurkat T cells triggers large-scale surface membrane expansion in parallel with phospholipid scrambling. With continued ionophore application,TMEM16F-expressing cells then undergo extensive shedding of ectosomes. The T cell co-receptor PD-1 is selectively incorporated into ectosomes. This selectivity depends on its transmembrane sequence. Surprisingly, cells lacking TMEM16F not only fail to expand surface membrane in response to elevated cytoplasmic Ca2+, but instead undergo rapid massive endocytosis with PD-1 internalisation. These results establish a new role for TMEM16F as a regulator of Ca2+ activated membrane trafficking.

Highlights

TMEM16F is a Ca2+ -gated ion channel that is required for Ca2+ -activated phosphatidylserine exposure on the surface of many eukaryotic cells
In this paper we show that cytoplasmic Ca2+ elevations induced by ionomycin cause rapid plasma membrane expansion in parallel with PS exposure in Jurkat T cells
We further find that in Jurkat T cells, PD-1 is selectively shed in vesicles after TMEM16F activation, while it is selectively internalised in the absence of TMEM16F

Summary

Introduction

TMEM16F is a Ca2+ -gated ion channel that is required for Ca2+ -activated phosphatidylserine exposure on the surface of many eukaryotic cells. Cells lacking TMEM16F fail to expand surface membrane in response to elevated cytoplasmic Ca2+, but instead undergo rapid massive endocytosis with PD-1 internalisation. These results establish a new role for TMEM16F as a regulator of Ca2+ activated membrane trafficking. Ca2+-activated phospholipid scrambling is mediated by a transmembrane protein, TMEM16F ( known as anoctamin 6)[3,4], a widely expressed member of the TMEM16 family of ion channels[5]. The mechanism by which PD-1 expression on T lymphocytes is regulated by TMEM16F has not been explained

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Conclusion