Cytoskeleton modification and cholesterol depletion affect membrane properties and caveolae positioning of CHO cells.

The formation of protrusions is necessary for numerous biological processes. It involves extension of the plasma membrane, and the force needed for this is provided by the actin cytoskeleton. Tether pulling with optical tweezers can mimic the formation of a protrusion, so we used this method to investigate the effects of modifying not only actin (with latrunculin A) but also microtubules (with nocodazole) and the plasma membrane itself (with methyl-β-cyclodextrin) on the Chinese hamster ovary cell membrane. After these modifications, the membrane reservoir was supposed to redistribute. Caveolae constitute a small part of the reservoir, so the redistribution of caveolar proteins such as caveolin-1 and cavin-1 that represents caveolae per se was assessed. The main findings concerning protrusion force and membrane reservoir availability were as follows: (1) they correlated inversely, (2) their values underwent the greatest change after microtubule disruption, and (3) membrane composition had a major influence on the parameters studied. F-actin disruption and cholesterol depletion decreased, and microtubule disruption increased the amount of the caveolar proteins (caveolae). Caveolae presented just an example of the membrane reservoir, and from our findings, we suppose that the perturbations caused were too large to be related to caveolae redistribution alone. The integrity of the cytoskeleton and plasma membrane composition are important factors in the formation of protrusions and in determining the availability and distribution of the membrane reservoir.