An Intracellular Serpin Regulates Necrosis by Inhibiting the Induction and Sequelae of Lysosomal Injury

Abstract

Extracellular serpins such as antithrombin and alpha1-antitrypsin are the quintessential regulators of proteolytic pathways. In contrast, the biological functions of the intracellular serpins remain obscure. We now report that the C. elegans intracellular serpin, SRP-6, exhibits a prosurvival function by blocking necrosis. Minutes after hypotonic shock, srp-6 null animals underwent a catastrophic series of events culminating in lysosomal disruption, cytoplasmic proteolysis, and death. This newly defined hypo-osmotic stress lethal (Osl) phenotype was dependent upon calpains and lysosomal cysteine peptidases, two in vitro targets of SRP-6. By protecting against both the induction of and the lethal effects from lysosomal injury, SRP-6 also blocked death induced by heat shock, oxidative stress, hypoxia, and cation channel hyperactivity. These findings suggest that multiple noxious stimuli converge upon a peptidase-driven, core stress response pathway that, in the absence of serpin regulation, triggers a lysosomal-dependent necrotic cell death routine.

The Human Host Defense Peptide LL-37 Induces Apoptosis in a Calpain- and Apoptosis-Inducing Factor–Dependent Manner Involving Bax Activity

“…Bcl-2 proteins have been shown to contribute to this process, as Bax translocation to lysosomes followed by lysosomal permeabilization has recently been reported (59). Activated calpains have also been implicated in lysosomal permeabilization, leading to cathepsin release (60,61). Therefore, it is possible that LL-37 triggers lysosomal permeabilization through the activation of calpains, as indicated by the result that calpain inhibition blocks both Bax translocation to mitochondria and apoptosis (Fig.…”

NRA-2, a Nicalin Homolog, Regulates Neuronal Death by Controlling Surface Localization of Toxic Caenorhabditis elegans DEG/ENaC Channels

“…Large side-chain amino acid substitutions for a small amino acid near the pore domain (MEC-4(A713V), referred to here as MEC-4(d)) create a hyperactivated channel that is permeable to Na ϩ and Ca ϩ2 (6 -8). Calcium dysregulation in mec-4(d) neurons is amplified by calreticulin-dependent release of calcium from ER stores (7,9), which activates cytosolic calpain proteases (10) that ultimately influence deleterious lysosomal activity (11). That the mammalian neuronal DEG/ENaC channel subunit ASIC1 contributes to necrotic death in mouse ischemia models (12)(13)(14) supports that conserved mechanisms of neuronal DEG/ENaC hyperactivation toxicity are operative across phyla.…”

Lysosomal membrane permeabilization in cell death

“…Another member of the serpin family, hurpin, blocks CL but not CB and confers resistance to ultraviolet lightinduced apoptosis in human keratinocytes (Welss et al, 2003). Recently, an intracellular serpin from C. elegans, SRP-6, has been shown to protect against cell death induced by hypotonic shock, hypoxia, heat shock and paraquat, which are all stimuli that reportedly induce lysosomal rupture and cysteine protease-dependent cell death in worms (Abraham and Shaham, 2007;Luke et al, 2007). Thus, serpins act as physiologically relevant inhibitors of LMP-mediated cell death.…”