Cathepsin S Signals via PAR2 and Generates a Novel Tethered Ligand Receptor Agonist

Abstract

Protease-activated receptor-2 is widely expressed in mammalian epithelial, immune and neural tissues. Cleavage of PAR2 by serine proteases leads to self-activation of the receptor by the tethered ligand SLIGRL. The contribution of other classes of proteases to PAR activation has not been studied in detail. Cathepsin S is a widely expressed cysteine protease that is upregulated in inflammatory conditions. It has been suggested that cathepsin S activates PAR2. However, cathepsin S activation of PAR2 has not been demonstrated directly nor has the potential mechanism of activation been identified. We show that cathepsin S cleaves near the N-terminus of PAR2 to expose a novel tethered ligand, KVDGTS. The hexapeptide KVDGTS generates downstream signaling events specific to PAR2 but is weaker than SLIGRL. Mutation of the cathepsin S cleavage site prevents receptor activation by the protease while KVDGTS retains activity. In conclusion, the range of actions previously ascribed to cysteine cathepsins in general, and cathepsin S in particular, should be expanded to include molecular signaling. Such signaling may link together observations that had been attributed previously to PAR2 or cathepsin S individually. These interactions may contribute to inflammation.

Cathepsin S Causes Inflammatory Pain via Biased Agonism of PAR2 and TRPV4

“…to reveals a the tethered ligand 42 KVDGTS, which, like the trypsin-exposed AP SLIGRL, stimulates Ca 2ϩ signaling in HeLa cells, albeit with reduced potency (58). However, we found no evidence that Cat-S induced mobilization of intracellular Ca 2ϩ in KNRK or HEK cells expressing PAR 2 , but instead observed that Cat-S stimulates a TRPV4-dependent influx of extracellular Ca 2ϩ ions in nociceptive neurons.…”

“…Thus, the selectivity with which Cat-S cleaves PAR 2 probably relies on a series of mutual interactions from numerous sites, which requires future study. In addition to the E 56 2T 57 site, Cat-S can also cleave PAR 2 more proximally at G 41 2K 42 (58). However, this study did not assess whether Cat-S cleaves PAR 2 at the site that we have identified.…”

Cathepsin S Cleavage of Protease-Activated Receptor-2 on Endothelial Cells Promotes Microvascular Diabetes Complications

“…9,31,32 Cat-S consistently induced ED in vitro and in vivo through PAR2, which is in line with a recent report on Cat-S cleavage of the extracellular domain of PAR2 required for activation. 16 Madhusudhan et al 33 reported human kidney to stain positive for PAR2 in podocytes. We got similar results with several different antibodies in mouse kidney, but PAR2-deficient kidney sections unraveled this staining as unspecific (data not shown).…”

“…15 So far, the functional role of Cat-S has been related to its elastolytic protease activity in macrovascular diseases, [7][8][9][10][11] but Cat-S was also recognized as a protease-activated receptor-2 (PAR2) agonist. 16 Hence, we speculated on functional roles of Cat-S also on microvascular disease. Our data confirm this hypothesis and identify Cat-S as a circulating trigger of ED by activating PAR2 on endothelial cells, a process promoting microvascular complications in diabetes (e.g., DN and diabetic retinopathy [DR]).…”

Neutrophil Elastase Activates Protease-activated Receptor-2 (PAR2) and Transient Receptor Potential Vanilloid 4 (TRPV4) to Cause Inflammation and Pain

“…biased agonism). Such proteases include cathepsin S, which cleaves at Gly 41 2Lys 42 (30) (32). However, the precise molecular mechanisms and the physiological consequences of biased protease signaling are poorly defined.…”