Numerous studies highlight the fact that concerted proteolysis is essential for skin morphology and function. The cysteine protease cathepsin L (Ctsl) has been implicated in epidermal proliferation and desquamation, as well as in hair cycle regulation. In stark contrast, mice deficient in cathepsin B (Ctsb) do not display an overt skin phenotype. To understand the systematic consequences of deleting Ctsb or Ctsl, we determined the protein abundances of >1300 proteins and proteolytic cleavage events in skin samples of wild-type, Ctsb ؊/؊ , and Ctsl ؊/؊ mice via mass-spectrometry-based proteomics. Both protease deficiencies revealed distinct quantitative changes in proteome composition. Ctsl Cathepsins B and L are ubiquitously expressed papain-like cysteine proteases belonging to the C1a papain family (clan CA), with 11 members in humans (1) and 18 members in mice (2). Most cysteine cathepsins like cathepsin L are endopeptidases, whereas cathepsin B shows both endopeptidase and carboxydipeptidase activity (3). Mainly localized in the endosomal/lysosomal compartment, cathepsins have traditionally been thought to play important roles in lysosomal protein turnover. Additional specific functions have been postulated that link cathepsins to different physiological and pathological processes.Studies using cathepsin L (Ctsl)-gene-deficient mice 1 revealed an important role of Ctsl in cardiac homeostasis (4 -6) and a contribution of Ctsl to MHC II-mediated antigen presentation (7, 8) and prohormone processing (9, 10). In a mouse model of pancreatic neuroendocrine cancer, Ctsl promoted tumor growth and invasiveness (11,12). In stark contrast, Ctsl was found to attenuate tumor progression in mouse models of skin cancer, highlighting the context-specific function of this protease (13,14).The most prominent phenotype of Ctsl-deficient mice is periodic hair loss together with epidermal hyperplasia, acanthosis, and hyperkeratosis (15). These alterations in skin morphology are assumed to be keratinocyte specific, as controlled re-expression of Ctsl under a keratin 14 promoter Research

Cysteine cathepsins are endolysosomal cysteine proteases highly expressed in macrophages; however, their individual contributions to the elimination of bacteria and bacteria-induced cytokine production by macrophages are unknown. We assessed the contribution of cysteine cathepsins to macrophage defense pathways against Staphylococcus aureus by using chemical inhibitors and by infecting primary bone marrow-derived macrophages deficient in 1 of 7 major macrophage-expressed endolysosomal cysteine proteases. We show that cysteine cathepsins are involved in the phagocytosis and killing of S. aureus. Cathepsin L was identified as an executor of nonoxidative killing. Moreover, microarray data revealed cysteine cathepsins to be important for the maximal induction of certain proinflammatory genes, such as IL6, in response to S. aureus. Cysteine cathepsin's contribution to IL6 production was dependent on phagocytosis, and cathepsin K was identified to be a critical protease in this process. Analysis of macrophages with impaired trafficking of endolysosomal Toll-like receptors (TLRs) to the acidic compartment revealed that they were not involved in cathepsin-dependent IL6 induction. Because IL6 production was completely dependent on the TLR-adaptor protein myeloid differentiation primary response gene 88 (MyD88), it appears that other TLRs are involved. In summary, lysosomal cysteine proteases are functionally linked to the complex bactericidal and inflammatory activities of macrophages.

Endolysosomal cysteine cathepsins functionally cooperate. Cathepsin B (Ctsb) and L (Ctsl) double-knockout mice die 4 weeks after birth accompanied by (autophago-) lysosomal accumulations within neurons. Such accumulations are also observed in mouse embryonic fibroblasts (MEFs) deficient for Ctsb and Ctsl. Previous studies showed a strong impact of Ctsl on the MEF secretome. Here we show that Ctsb alone has only a mild influence on extracellular proteome composition. Protease cleavage sites dependent on Ctsb were identified by terminal amine isotopic labeling of substrates (TAILS), revealing a prominent yet mostly indirect impact on the extracellular proteolytic cleavages. To investigate the cooperation of Ctsb and Ctsl, we performed a quantitative secretome comparison of wild-type MEFs and Ctsb (-/-) Ctsl (-/-) MEFs. Deletion of both cathepsins led to drastic alterations in secretome composition, highlighting cooperative functionality. While many protein levels were decreased, immunodetection corroborated increased levels of matrix metalloproteinase (MMP)-2. Re-expression of Ctsl rescues MMP-2 abundance. Ctsl and to a much lesser extent Ctsb are able to degrade MMP-2 at acidic and neutral pH. Addition of active MMP-2 to the MEF secretome degrades proteins whose levels were also decreased by Ctsb and Ctsl double deficiency. These results suggest a degradative Ctsl-MMP-2 axis, resulting in increased MMP-2 levels upon cathepsin deficiency with subsequent degradation of secreted proteins such as collagen α-1 (I).

No abstract