A new twist on plasma membrane repair.

Cells in multicellular organisms are under constant mechanical stress, and often the plasma membrane (PM) is compromised. Fortunately, there is a vigorous repair mechanism that rapidly (within seconds) reseals the wound site by fusion with an internal membrane patch. Downstream events, remodeling of the injury site and forming replacement PM, must be carried out quickly (within minutes) if a cell is to survive multiple sequential injuries.

A plasma membrane wound proteome: reversible externalization of intracellular proteins following reparable mechanical damage.

Cells in mechanically active tissues undergo constant plasma membrane damage that must be repaired to allow survival. To identify wound-associated proteins, a cell-impermeant, thiol-reactive biotinylation reagent was used to label and subsequently isolate intracellular proteins that become exposed on the surface of cultured cells after plasma membrane damage induced by scraping from substratum or crushing with glass beads. Scrape-damaged cells survived injury and were capable of forming viable colonies.

Calcium-dependent plasma membrane repair requires m- or mu-calpain, but not calpain-3, the proteasome, or caspases.

Mechanically damaged plasma membrane undergoes rapid calcium-dependent resealing that appears to depend, at least in part, on calpain-mediated cortical cytoskeletal remodeling. Cells null for Capns1, the non-catalytic small subunit present in both m- and mu-calpains, do not undergo calcium-mediated resealing. However, it is not known which of these calpains is needed for repair, or whether other major cytosolic proteinases may participate.

Fetuin A stabilizes m-calpain and facilitates plasma membrane repair.

Yeast two-hybrid experiments identified alpha(2)-Heremans-Schmid glycoprotein (human fetuin A) as a binding partner for calpain domain III (DIII). The tandem DIIIs of calpain-10 interacted under the most selective culture conditions, but DIIIs of m-calpain, calpain-3, and calpain-5 also interacted under less stringent selection. DIIIs of mu-calpain, calpain-6, and the tandem DIII-like domains of the Dictyostelium Cpl protein did not interact with alpha(2)-Heremans-Schmid glycoprotein in the yeast two-hybrid system.