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Cathepsins limit macrophage necroptosis through cleavage of Rip1 kinase.

Journal of immunology (Baltimore, Md. : 1950) (2014-05-07)
Scott McComb, Bojan Shutinoski, Susan Thurston, Erin Cessford, Kriti Kumar, Subash Sad

It has recently been shown that programmed necrosis, necroptosis, may play a key role in the development of inflammation. Deciphering the regulation of this pathway within immune cells may therefore have implications in pathology associated with inflammatory diseases. We show that treatment of macrophages with the pan caspase inhibitor (zVAD-FMK) results in both increased phosphorylation and decreased cleavage of receptor interacting protein kinase-1 (Rip1), leading to necroptosis that is dependent on autocrine TNF signaling. Stimulation of cells with TLR agonists such as LPS in the presence of zVAD-FMK also induced Rip1-phosphorylation via a TNFR-independent mechanism. Further examination of Rip1 expression under these stimulatory conditions revealed a regulatory cleavage of Rip1 in macrophages that is not apparently attributable to caspase-8. Instead, we provide novel evidence that cysteine family cathepsins, which are highly abundant in myeloid cells, can also cleave Rip1 kinase. Using small interfering RNA knockdown, specific cathepsin inhibitors, and cell-free cleavage assays, we demonstrate that cysteine cathepsins B and S can directly cleave Rip1. Finally, we demonstrate that only through combined inhibition of cathepsins and caspase-8 could a potent induction of macrophage necroptosis be achieved. These data reveal a novel mechanism of regulation of necroptosis by cathepsins within macrophage cells.

Product Number
Product Description

Propidium iodide, ≥94.0% (HPLC)
Phosphatase Inhibitor Cocktail 2, aqueous solution (dark coloration may develop upon storage, which does not affect the activity)
Thiazolyl Blue Tetrazolium Bromide, powder, BioReagent, suitable for cell culture, suitable for insect cell culture, ≥97.5% (HPLC)
Propidium iodide, ≥94% (HPLC)
Lipopolysaccharides from Escherichia coli O111:B4, purified by phenol extraction
Propidium iodide solution, solution (1.0 mg/ml in water)
Cathepsin S Active human, recombinant, expressed in FreeStyle 293-F cells, ≥90% (SDS-PAGE)