Cathepsin V: Molecular characteristics and significance in health and disease

Human cysteine cathepsins form a family of eleven proteases (B, C, F, H, K, L, O, S, V, W, X/Z) that play important roles in a considerable number of biological and pathophysiological processes. Among them, cathepsin V, also known as cathepsin L2, is a lysosomal enzyme, which is mainly expressed in cornea, thymus, heart, brain, and skin. Cathepsin V is a multifunctional endopeptidase that is involved in both the release of antigenic peptides and the maturation of MHC class II molecules and participates in the turnover of elastin fibrils as well in the cleavage of intra- and extra-cellular substrates. Moreover, there is increasing evidence that cathepsin V may contribute to the progression of diverse diseases, due to the dysregulation of its expression and/or its activity. For instance, increased expression of cathepsin V is closely correlated with malignancies (breast cancer, squamous cell carcinoma, or colorectal cancer) as well vascular disorders (atherosclerosis, aortic aneurysm, hypertension) being the most prominent examples. This review aims to shed light on current knowledge on molecular aspects of cathepsin V (genomic organization, protein structure, substrate specificity), its regulation by protein and non-protein inhibitors as well to summarize its expression (tissue and cellular distribution). Then the core biological and pathophysiological roles of cathepsin V will be depicted, raising the question of its interest as a valuable target that can open up pioneering therapeutic avenues.

Crystal structure of Leishmania mexicana cysteine protease B in complex with a high-affinity azadipeptide nitrile inhibitor

Leishmania mexicana is an obligate intracellular protozoan parasite that causes the cutaneous form of leishmaniasis affecting South America and Mexico. The cysteine protease LmCPB is essential for the virulence of the parasite and therefore, it is an appealing target for antiparasitic therapy. A library of nitrile-based cysteine protease inhibitors was screened against LmCPB to develop a treatment of cutaneous leishmaniasis. Several compounds are sufficiently high-affinity LmCPB inhibitors to serve both as starting points for drug discovery projects and as probes for target validation. A 1.4 Å X ray crystal structure, the first to be reported for LmCPB, was determined for the complex of this enzyme covalently bound to an azadipeptide nitrile ligand. Mapping the structure-activity relationships for LmCPB inhibition revealed superadditive effects for two pairs of structural transformations. Therefore, this work advances our understanding of azadipeptidyl and dipeptidyl nitrile structure-activity relationships for LmCPB structure-based inhibitor design. We also tested the same series of inhibitors on related cysteine proteases cathepsin L and Trypanosoma cruzi cruzain. The modulation of these mammalian and protozoan proteases represents a new framework for targeting papain-like cysteine proteases.

Cathepsin S-Mediated Negative Regulation of Wnt5a/SC35 Activation Contributes to Ischemia-Induced Neovascularization in Aged Mice

BACKGROUND

Given that cathepsin S (CatS) gained attention due to its enzymatic and non-enzymatic functions in signaling, the role of CatS in ischemia-induced angiogenesis of aged mice was explored.

METHODS AND RESULTS

To study the role of CatS in the decline in aging-related vascular regeneration capacity, a hindlimb ischemia model was applied to aged wild-type (CatS+/+) and CatS-deficient (CatS-/-) mice. CatS-/-mice exhibited impaired blood flow recovery and capillary formation and increased levels of p-insulin receptor substrate-1, Wnt5a, and SC35 proteins and decreased levels of phospho-endothelial nitric oxide synthase (p-eNOS), p-mTOR, p-Akt, p-ERK1/2, p-glycogen synthase kinase-3α/β, and galatin-3 proteins, as well as decreased macrophage infiltration and matrix metalloproteinase-2/-9 activities in the ischemic muscles. In vitro, CatS knockdown altered the levels of these targeted essential molecules for angiogenesis. Together, the results suggested that CatS-/-leads to defective endothelial cell functions and that CatS-/-is associated with decreased circulating endothelial progenitor cell (EPC)-like CD31+/c-Kit+cells. This notion was reinforced by the study finding that pharmacological CatS inhibition led to a declined angiogenic capacity accompanied by increased Wnt5a and SC35 levels and decreased eNOS/Akt-ERK1/2 signaling in response to ischemia.

CONCLUSIONS

These findings demonstrated that the impairment of ischemia-induced neovascularization in aged CatS-/-mice is due, at least in part, to the attenuation of endothelial cell/EPC functions and/or mobilization associated with Wnt5a/SC35 activation in advanced age.

Corneal angiogenesis modulation by cysteine cathepsins: In vitro and in vivo studies

Corneal avascularization is essential for normal vision. Several antiangiogenic factors were identified in cornea such as endostatin and angiostatin. Cathepsin V, which is highly expressed in the cornea, can hydrolyze human plasminogen to release angiostatin fragments. Herein, we describe a detailed investigation of the expression profile of cathepsins B, L, S and V in the human cornea and the role of cysteine peptidases in modulating angiogenesis both in vitro and in vivo. We used various methodological tools for this purpose, including real-time PCR, SDS-PAGE, western blotting, catalytic activity assays, cellular assays and induction of corneal neovascularity in rabbit eyes. Human corneal enzymatic activity assays revealed the presence of cysteine proteases that were capable of processing endogenous corneal plasminogen to produce angiostatin-like fragments. Comparative real-time analysis of cathepsin B, L, S and V expression revealed that cathepsin V was the most highly expressed, followed by cathepsins L, B and S. However, cathepsin V depletion revealed that this enzyme is not the major cysteine protease responsible for plasminogen degradation under non-pathological conditions. Furthermore, western blotting analysis indicated that only cathepsins B and S were present in their enzymatically active forms. In vivo analysis of angiogenesis demonstrated that treatment with the cysteine peptidase inhibitor E64 caused a reduction in neovascularization. Taken together, our results show that human corneal cysteine proteases are critically involved in angiogenesis.

Proteomic identification of protease cleavage sites characterizes prime and non-prime specificity of cysteine cathepsins B, L, and S

Cysteine cathepsins mediate proteome homeostasis and have pivotal functions in diseases such as cancer. To better understand substrate recognition by cathepsins B, L, and S, we applied proteomic identification of protease cleavage sites (PICS) for simultaneous profiling of prime and non-prime specificity. PICS profiling of cathepsin B endopeptidase specificity highlights strong selectivity for glycine in P3' due to an occluding loop blocking access to the primed subsites. In P1', cathepsin B has a partial preference for phenylalanine, which is not found for cathepsins L and S. Occurrence of P1' phenylalanine often coincides with aromatic residues in P2. For cathepsin L, PICS identifies 845 cleavage sites, representing the most comprehensive PICS profile to date. Cathepsin L specificity is dominated by the canonical preference for aromatic residues in P2 with limited contribution of prime-site selectivity determinants. Profiling of cathepsins B and L with a shorter incubation time (4 h instead of 16 h) did not reveal time-dependency of individual specificity determinants. Cathepsin S specificity was profiled at pH 6.0 and 7.5. The PICS profiles at both pH values display a high degree of similarity. Cathepsin S specificity is primarily guided by aliphatic residues in P2 with limited importance of prime-site residues.