Abstract
Cells can expand their plasma membrane laterally by unfolding membrane undulations and by exocytosis. Here, we describe a third mechanism involving invaginations held shut by the membrane adapter, dynamin. Compartments open when Ca activates the lipid scramblase, TMEM16F, anionic phospholipids escape from the cytoplasmic monolayer in exchange for neutral lipids, and dynamins relax. Deletion of TMEM16F or dynamins blocks expansion, with loss of dynamin expression generating a maximally expanded basal plasma membrane state. Re-expression of dynamin2 or its GTPase-inactivated mutant, but not a lipid binding mutant, regenerates reserve compartments and rescues expansion. Dynamin2-GFP fusion proteins form punctae that rapidly dissipate from these compartments during TMEM16F activation. Newly exposed compartments extend deeply into the cytoplasm, lack numerous organellar markers, and remain closure-competent for many seconds. Without Ca, compartments open slowly when dynamins are sequestered by cytoplasmic dynamin antibodies or when scrambling is mimicked by neutralizing anionic phospholipids and supplementing neutral lipids. Activation of Ca-permeable mechanosensitive channels via cell swelling or channel agonists opens the compartments in parallel with phospholipid scrambling. Thus, dynamins and TMEM16F control large plasma membrane reserves that open in response to lateral membrane stress and Ca influx.
Highlights
Cells can expand their plasma membrane laterally by unfolding membrane undulations and by exocytosis
The results demonstrate that PIEZO1 can initiate local Ca transients and PL scrambling that would physiologically activate plasma membrane (PM) expansion during mechanoperturbation
This study delineates a molecular pathway in which PL scrambling by TMEM16F initiates large-scale PM expansion in diverse cell types
Summary
Cells can expand their plasma membrane laterally by unfolding membrane undulations and by exocytosis. Compartments open when Ca activates the lipid scramblase, TMEM16F, anionic phospholipids escape from the cytoplasmic monolayer in exchange for neutral lipids, and dynamins relax. Dynamins and TMEM16F control large plasma membrane reserves that open in response to lateral membrane stress and Ca influx. Most cells expand their plasma membrane (PM) laterally to prevent tears during mechanical perturbation, cell swelling and spreading, and macropinocytosis and phagocytosis[1,2,3,4]. During lateral PM stress, Ca influx by mechanosensitive channels activates the PL scramblase, TMEM16F12, resulting in the exchange of cytoplasmic anionic PLs for neutral PLs, followed by dynamin relaxation and opening of the reserve PM compartments. We show that cells activate this process during both cell swelling and activation of Ca-permeable mechanosensitive channels[26], revealing a previously undescribed cellular mechanism in the regulation and relief of lateral PM stress
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