Calcium-activated and apoptotic phospholipid scrambling induced by Ano6 can occur independently of Ano6 ion currents

Cell Death Dis. 2013 Apr 25;4(4):e611. doi: 10.1038/cddis.2013.135.

Abstract

Immune cells and platelets maintain plasma membrane phospholipid asymmetry. Upon activation, this asymmetry is disrupted by phospholipid scrambling (PS), which is a major step during activation of immune cells, hemostasis and apoptosis. Anoctamin 6 (Ano6; TMEM16F) causes chloride (Cl(-)) and cation currents and is required for Ca(2+)-dependent PS. It is defective in blood cells from patients with Scott syndrome, a rare bleeding disorder. We examined if Cl(-) currents and PS are related, whether both processes are Ca(2+) dependent, and whether Ca(2+)-independent scrambling during intrinsic and extrinsic apoptosis is controlled by Ano6. Ca(2+) increase by ionomycin activated Ano6 Cl(-) currents and PS in normal lymphocytes, but not in B-lymphocytes from two different patients with Scott syndrome. Fas ligand (FasL) did not increase intracellular Ca(2+), but activated Cl(-) currents in normal but not in Scott lymphocytes. Whole-cell currents were inhibited by Cl(-) channel blockers and by siRNA knockdown of Ano6. In contrast, intrinsic mitochondrial apoptosis by ABT-737 did not induce Cl(-) currents in lymphocytes. PS was not inhibited by blockers of Ano6 or removal of Cl(-) ions. Remarkably, Ca(2+)-independent scrambling due to extrinsic (FasL) or intrinsic (ABT-737) apoptosis was unchanged in Scott cells. We conclude that: (i) Ano6 Cl(-) currents are activated by increase in cytosolic Ca(2+), or Ca(2+) independent by stimulation of Fas receptors; (ii) Ca(2+)-dependent PS induced by Ano6 does not require Cl(-) currents; (iii) Ca(2+)-independent PS does not require Ano6; (iv) Ano6 is necessary for Ca(2+)-dependent PS, but not by increasing intracellular Ca(2+).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anoctamins
  • Apoptosis / drug effects
  • B-Lymphocytes / immunology
  • B-Lymphocytes / physiology
  • Biphenyl Compounds / pharmacology
  • Blood Coagulation Disorders / physiopathology
  • Calcium / metabolism*
  • Calcium Ionophores / pharmacology
  • Chloride Channels / antagonists & inhibitors
  • Chloride Channels / metabolism
  • Fas Ligand Protein / pharmacology
  • HEK293 Cells
  • Humans
  • Ion Transport / drug effects
  • Ionomycin / pharmacology
  • Jurkat Cells
  • Nitrophenols / pharmacology
  • Patch-Clamp Techniques
  • Phospholipid Transfer Proteins / antagonists & inhibitors
  • Phospholipid Transfer Proteins / genetics
  • Phospholipid Transfer Proteins / metabolism*
  • Phospholipids / metabolism*
  • Piperazines / pharmacology
  • RNA Interference
  • RNA, Small Interfering / metabolism
  • Sulfonamides / pharmacology

Substances

  • ABT-737
  • ANO6 protein, human
  • Anoctamins
  • Biphenyl Compounds
  • Calcium Ionophores
  • Chloride Channels
  • Fas Ligand Protein
  • Nitrophenols
  • Phospholipid Transfer Proteins
  • Phospholipids
  • Piperazines
  • RNA, Small Interfering
  • Sulfonamides
  • Ionomycin
  • Calcium

Supplementary concepts

  • Scott Syndrome