Regulation of caveolae through cholesterol-depletion dependent tubulation by PACSIN2/Syndapin II
The membrane shaping ability of PACSIN2 via its FCH-BAR (F-BAR) domain has been shown to be essential for caveolar morphogenesis, presumably through the shaping of the caveolar neck. Caveolar membrane contains abundant levels of cholesterol. However, the role of cholesterol in PACSIN2-mediated membrane deformation remains unclear. We show that the binding of PACSIN2 to the membrane could be negatively regulated by the amount of cholesterol in the membrane. We prepared a reconstituted membrane based on the lipid composition of caveolae. The reconstituted membrane with cholesterol had a weaker affinity to the F-BAR domain of PACSIN2 than the membrane without cholesterol, presumably due to a decrease in electrostatic charge density. Consistently, the acute depletion of cholesterol from the plasma membrane resulted in the appearance of PACSIN2-localized tubules with caveolin-1 at their tips, suggesting that the presence of cholesterol inhibited the prominent membrane tubulation by PACSIN2. The tubules induced by PACSIN2 were suggested to be an intermediate of caveolae endocytosis. Consistently, the removal of caveolae from the plasma membrane upon cholesterol depletion was diminished in the cells deficient in PACSIN2. These data suggested that PACSIN2 mediated the caveolae internalization dependently on the amount of cholesterol at the plasma membrane, providing a possible mechanism for the cholesterol-dependent regulation of caveolae.