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

A. Kmit, R. van Kruchten, J. Ousingsawat, N. J. A. Mattheij, B. Senden-Gijsbers, J. W. M. Heemskerk, R. Schreiber, E. M. Bevers, K. Kunzelmann*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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 Ca2+ -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 Ca2+ dependent, and whether Ca2+ -independent scrambling during intrinsic and extrinsic apoptosis is controlled by Ano6. Ca2+ 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 Ca2+, 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, Ca2+ -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 Ca2+, or Ca2+ -independent by stimulation of Fas receptors; (ii) Ca2+ -dependent PS induced by Ano6 does not require Cl- currents; (iii) Ca2+ -independent PS does not require Ano6; (iv) Ano6 is necessary for Ca2+ -dependent PS, but not by increasing intracellular Ca2+. Cell Death and Disease ( 2013) 4, e611; doi:10.1038/cddis.2013.135; published online 25 April 2013
Original languageEnglish
Article numbere611
JournalCell Death & Disease
Volume4
DOIs
Publication statusPublished - Apr 2013

Keywords

  • TMEM16F
  • anoctamin 6
  • Ano6
  • Ca2+ -activated Cl- channels
  • phospholipid scrambling

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