Plasma membrane-associated annexin A6 reduces Ca2+ entry by stabilizing the cortical actin cytoskeleton.
The annexins are a family of Ca(2+)- and phospholipid-binding proteins, which interact with membranes upon increase of [Ca(2+)](i) or during cytoplasmic acidification. The transient nature of the membrane binding of annexins complicates the study of their influence on intracellular processes. To address the function of annexins at the plasma membrane (PM), we fused fluorescent protein-tagged annexins A6, A1, and A2 with H- and K-Ras membrane anchors. Stable PM localization of membrane-anchored annexin A6 significantly decreased the store-operated Ca(2+) entry (SOCE), but did not influence the rates of Ca(2+) extrusion. This attenuation was specific for annexin A6 because PM-anchored annexins A1 and A2 did not alter SOCE. Membrane association of annexin A6 was necessary for a measurable decrease of SOCE, because cytoplasmic annexin A6 had no effect on Ca(2+) entry as long as [Ca(2+)](i) was below the threshold of annexin A6-membrane translocation. However, when [Ca(2+)](i) reached the levels necessary for the Ca(2+)-dependent PM association of ectopically expressed wild-type annexin A6, SOCE was also inhibited. Conversely, knockdown of the endogenous annexin A6 in HEK293 cells resulted in an elevated Ca(2+) entry. Constitutive PM localization of annexin A6 caused a rearrangement and accumulation of F-actin at the PM, indicating a stabilized cortical cytoskeleton. Consistent with these findings, disruption of the actin cytoskeleton using latrunculin A abolished the inhibitory effect of PM-anchored annexin A6 on SOCE. In agreement with the inhibitory effect of annexin A6 on SOCE, constitutive PM localization of annexin A6 inhibited cell proliferation. Taken together, our results implicate annexin A6 in the actin-dependent regulation of Ca(2+) entry, with consequences for the rates of cell proliferation.
Monastyrskaya
Katia
K
From the Department of Cell Biology, Institute of Anatomy, University of Bern, 3000 Bern 9, Switzerland. Electronic address: monastyk@ana.unibe.ch.
Babiychuk
Eduard B
EB
From the Department of Cell Biology, Institute of Anatomy, University of Bern, 3000 Bern 9, Switzerland.
Hostettler
Andrea
A
From the Department of Cell Biology, Institute of Anatomy, University of Bern, 3000 Bern 9, Switzerland.
Wood
Peta
P
Faculty of Pharmacy, Department of Pharmaceutical Chemistry, University of Sydney, Sydney, New South Wales 2006, Australia.
Grewal
Thomas
T
Faculty of Pharmacy, Department of Pharmaceutical Chemistry, University of Sydney, Sydney, New South Wales 2006, Australia.
Draeger
Annette
A
From the Department of Cell Biology, Institute of Anatomy, University of Bern, 3000 Bern 9, Switzerland.
D000199:Actins / Q000378:metabolism*; D017305:Annexin A1 / Q000378:metabolism; D017306:Annexin A2 / Q000378:metabolism; D017317:Annexin A6 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D049109:Cell Proliferation; D003599:Cytoskeleton / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
D000199:Actins; D017305:Annexin A1; D017306:Annexin A2; D017317:Annexin A6; D015220:Calcium Channels; D017931:DNA Primers; D011993:Recombinant Fusion Proteins; D018631:ras Proteins