Tailored Protection against Plasmalemmal Injury by Annexins with Different Ca2+ Sensitivities

Abstract

The annexins, a family of Ca 2؉ -and lipid-binding proteins, are involved in a range of intracellular processes. Recent findings have implicated annexin A1 in the resealing of plasmalemmal injuries. Here, we demonstrate that another member of the annexin protein family, annexin A6, is also involved in the repair of plasmalemmal lesions induced by a bacterial pore-forming toxin, streptolysin O. An injury-induced elevation in the intra- 2؉ -sensitivities provide a cell with the means to react promptly to a limited injury in its early stages and, at the same time, to withstand a sustained injury accompanied by the continuous formation of plasmalemmal lesions.The annexins are a family of Ca 2ϩ -binding proteins expressed in most phyla and species (1-4). Twelve annexins are present in vertebrates (A1-A11 and A13) with different splice variants (1). Annexins share a common folding motif, the "annexin core," which harbors the Ca 2ϩ -and membrane-binding sites (2-4). In their Ca 2ϩ -bound form, the annexins translocate from the cytoplasm to the plasma membrane and associate with negatively charged phospholipids (2-4). The N-terminal region precedes the conserved core and is unique for a given member of the annexin family. It mediates interactions with protein ligands and regulates the annexin-membrane association (2-4). Different annexins have been shown to orchestrate a variety of intracellular processes, ranging from the regulation of membrane dynamics to cell migration, proliferation, and apoptosis (2-12). However, the intriguing question why the majority of cells express several annexins, which differ only slightly in their biochemical properties, remains unanswered.Recent findings have implicated annexin A1 in the resealing of plasmalemmal lesions following cell injury (13,14). An injury-induced rise in the local concentration of intracellular Ca 2ϩ (15) is sensed by annexin A1 and triggers its binding to the plasma membrane at the site of the injury (13,14). Subsequently, annexin A1 promotes fusion of the damaged membrane around the pore, forming sealed, lesion-containing structures: large, cytosol-containing blebs (14) or smaller, cytosol-free microvesicles (16). The microvesicles subsequently can be shed by the cell (16, 17).Here, we show that, similar to annexin A1, annexin A6 is directly involved in the repair of plasmalemmal lesions induced by streptolysin O (SLO).2 The shedding of microvesicles appears to be predominant in the elimination of pores by annexin A6-dependent repair. Annexin A6 requires lower [Ca 2ϩ ] i for its plasmalemmal binding and, thus, responds faster to an injury than annexin A1. Correspondingly, a plasmalemmal lesion can be repaired by annexin A6 even without involvement of annexin A1; however, the concerted action of both annexins is instrumental for the efficient repair of multiple, simultaneously occurring plasmalemmal lesions. EXPERIMENTAL PROCEDURESReagents-Monoclonal anti-annexin A6 and anti-annexin A1 antibodies were from BD Biosciences; an antiserum against SLO was from Bioacad...

Annexin A6 is an organizer of membrane microdomains to regulate receptor localization and signalling

“…Annexins like AnxA1 (68) and AnxA2 (69) have previously been implicated in membrane repair and recent studies have provided more evidence of how annexins might fulfil their task of protecting cells from injuries of the plasma membrane caused by radiation (70) or bacterial toxins (14). In this context, AnxA6 appears to act in concert with AnxA1 to close up lesions in the plasma membrane.…”

“…Although it is still unclear if the two isoforms generally fulfil different functions, recent studies indicate different localization and regulation of AnxA6 isoforms in the endosomal compartment of Balb/3T3 fibroblasts (11) and different involvement in catecholamine secretion and calcium homeostasis of PC12 cells (12). Ca 21 -activated AnxA6 preferably binds to phospholipids found in the inner leaflet of the plasma membrane, for example phosphatidylserine (PS), phosphatidylinositol, phosphatidic acid (7), and phosphatidylethanolamine (13), which points to its supposed involvement in membrane organization and recently discovered role in membrane repair (14). Apart from membrane phospholipids (7), AnxA6 has affinity for arachidonic acid (13).…”

S100 and annexin proteins identify cell membrane damage as the Achilles heel of metastatic cancer cells

“…Here, ANXA6 was shown to be activated and recruited to the site of injury at lower Ca 2C concentration as compared to ANXA1 suggesting a potential for sequential recruitment of annexins to facilitate PMR. 55 Enhanced PMR is Needed for Tumor metastasis -Role of Annexin and S100 Proteins Cellular membranes of cancer cells are known to be destabilized -we have previously shown lysosomal membrane of tumor cells are more fragile 56,57 and that death induced by lysosomal membrane pemebilization is prominent in cancer cells. 56 This fragility has been harnessed for the development of novel therapeutics.…”

Annexins in Translational Research: HIDDEN Treasures to Be Found

“…Because a similar function for forces. In line with their proposed function as part of the repair machinery that kicks in when a high Ca 2+ influx is sensed [20,148], several annexins are involved in repairing the PM lesions caused by SLO [149,150]. This annexin-mediated resealing, blebbing, and subsequent shedding of the affected PM domains as pore-containing microvesicles is cell-protective and thus might constitute a vital part of the host cell innate immune response.…”