Calpain is required for the rapid, calcium-dependent repair of wounded plasma membrane

Mammalian cells require extracellular calcium ion to undergo rapid plasma membrane repair seconds after mechanical damage. Utilizing transformed fibroblasts from calpain small subunit knock-out (Capns1^-/-) mouse embryos, we now show that the heterodimeric, typical subclass of calpains is required for calcium-mediated survival after plasma membrane damage caused by scraping a cell monolayer. Survival of scrape-damaged Capns1^-/- cells was unaffected by calcium in the scraping medium, whereas more Capns1 ^+/+ cells survived when calcium was present. Calcium-mediated survival was increased when Capns1^-/- cells were scraped in the presence of purified m- or μ-calpain. Survival rates of scraped Capns1 ^+/+, HFL-1, or Chinese hamster ovary cells were decreased by the calpain inhibitor, calpeptin, or the highly specific calpain inhibitor protein, calpastatin. Capns1^-/- cells failed to reseal following laser-induced membrane disruption, demonstrating that their decreased survival after scraping resulted, at least in part, from failed membrane repair. Proteomic and immunologic analyses demonstrated that the known calpain substrates talin and vimentin were exposed at the cell surface and processed by calpain following cell scraping. Autoproteolytic activation of calpain at the scrape site was evident at the earliest time point analyzed and appeared to precede proteolysis of talin and vimentin. The results indicate that conventional calpains are required for calcium-facilitated survival after plasma membrane damage and may act by localized remodeling of the cortical cytoskeleton at the injury site.