The NLRP3 inflammasome is cytosolic multi-protein complex that induces inflammation and pyroptotic cell death in response to both pathogen (PAMPs) and endogenous activators (DAMPs). Recognition of PAMPs or DAMPs leads to formation of the inflammasome complex, which results in activation of caspase-1, followed by cleavage and release of pro-inflammatory cytokines. Excessive activation of NLRP3 inflammasome can contribute to development of inflammatory diseases and cancer. Autophagy is vital intracellular process for recycling and removal of damaged proteins and organelles, as well as destruction of intracellular pathogens. Cytosolic components are sequestered in a double-membrane vesicle—autophagosome, which then fuses with lysosome resulting in degradation of the cargo. The autophagy dysfunction can lead to diseases with hyperinflammation and excessive activation of NLRP3 inflammasome and thus acts as a major regulator of inflammasomes. Autophagic removal of NLRP3 inflammasome activators, such as intracellular DAMPs, NLRP3 inflammasome components, and cytokines can reduce inflammasome activation and inflammatory response. Likewise, inflammasome signaling pathways can regulate autophagic process necessary for balance between required host defense inflammatory response and prevention of excessive and detrimental inflammation. Autophagy has a protective role in some inflammatory diseases associated with NLRP3 inflammasome, including gouty arthritis, familial Mediterranean fever (FMF), and sepsis. Understanding the interregulation between these two essential biological processes is necessary to comprehend the biological mechanisms and designing possible treatments for multiple inflammatory diseases.
We report here that a number of commonly used small peptide caspase inhibitors consisting of a caspase recognition sequence linked to chloromethylketone, fluoromethylketone or aldehyde reactive group efficiently inhibit other cysteine proteases than caspases. The in vitro studies included cathepsins B, H, L, S, K, F, V, X and C, papain and legumain. Z-DEVD-cmk was shown to be the preferred irreversible inhibitor of most of the cathepsins in vitro, followed by Z-DEVD-fmk, Ac-YVAD-cmk, Z-YVAD-fmk and Z-VAD-fmk. Inactivation of legumain by all the inhibitors investigated was moderate, whereas cathepsins H and C were poorly inhibited or not inhibited at all. Inhibition by aldehydes was not very potent. All the three fluoromethylketones efficiently inhibited cathepsins in Jurkat and human embryonic kidney 293 cells at concentrations of 100 lM. Furthermore, they completely inhibited cathepsins B and X activity in tissue extracts at concentrations as low as 1 lM. These results suggest that data based on the use of these inhibitors should be taken with caution and that other proteases may be implicated in the processes previously ascribed solely to caspases.
Inflammation is an essential physiological process, which enables survival during infection and maintains tissue homeostasis. Interferons (IFNs) and pro- and anti-inflammatory cytokines are crucial for appropriate response to pathogens, damaged cells, or irritants in inflammatory response. The inflammasom is multiprotein complex, which initiates cleavage of pro-inflammatory cytokines IL-1β and IL-18 into active forms. In addition, inflammasomes initiate pyroptotic cell death. In the present review, I summarize and analyze recent findings regarding the cross talk of IFNs and inflammasomes.
The cystatins constitute a large group of evolutionary related proteins with diverse biological activities. Initially, they were characterized as inhibitors of lysosomal cysteine proteases -cathepsins. Cathepsins are involved in processing and presentation of antigens, as well as several pathological conditions such as inflammation and cancer. Recently, alternative functions of cystatins have been proposed: they also induce tumour necrosis factor and interleukin 10 synthesis and stimulate nitric oxide production. The aim of the present review was the analysis of data on cystatins from NCBI GEO database and the literature, and obtained in microarray and serial analysis of gene expression (SAGE) experiments. The expression of cystatins A, B, C, and F in macrophages, dendritic cells and natural killer cells of the immune system, during differentiation and activation is discussed.
Cysteine cathepsins are involved in protein degradation (1) and the development and function of the immune system (2). Cathepsin L is an endopeptidase that is able to perform limited proteolysis in the endosomes and lysosomes of specific cell types. Besides its role in hair formation and skin metabolism, it is involved in T-cell selection and NKT cell development (3). It participates in processing the major histocompatibility complex II invariant chain in thymic cortex epithelial cells (4), encephalin in chromaffin granules of neuroendocrine cells (5), and in the degradation and recycling of growth factors and their receptors in epidermal keratinocytes (6). Cathepsin L is also associated with an endosomal processing step during invasion of cells by Ebola virus (7), severe acute respiratory syndrome (SARS) coronavirus (8), and murine hepatitis coronavirus (9). As the result of gene duplication, the human genome encodes for two cathepsin L-like proteases, namely the human cathepsin L and cathepsin V (cathepsin L2), whereas in mouse only cathepsin L is present (10). At the protein level, mouse cathepsin L displays a higher sequence homology to human cathepsin V than to human cathepsin L (11). Cathepsin V shares 80% protein sequence identity with cathepsin L, but in contrast to the ubiquitously expressed cathepsin L, its expression is restricted to thymus and testis (11,12).Recently, the otherwise endosomal proteinase cathepsin L has been reported to be active in the nucleus. It cleaves the CUX1 transcription factor and as a result accelerates progression into the S phase of the cell cycle (13). Cathepsin L deficiency was shown to cause a global rearrangement of chromatin structure and redistribution of specifically modified histones (14). In addition, cathepsin L was found to cleave histone H3.2 in the nucleus during mouse embryonic stem cell differentiation (15).Cathepsin L is inhibited in vitro by a number of proteins as follows: cystatins (16), thyropins (17), and some of the serpins (18,19). Type 1 cystatins, or stefins, are mainly intracellular, whereas type 2 cystatins are predominantly secreted (20,21). Stefin B is localized in the cytosol and nucleus of proliferating cells (22). Loss-of-function mutations in the cystatin B (CTSB, stefin B) gene are found in patients with Unverricht-Lundborg disease (EPM1), but its physiological implication in the pathogenesis of the disease has yet to be defined (23-26). EPM1 is an autosomal recessive inherited disease in which patients suffer from myoclonic jerks, tonic-clonic epileptic seizures, and progressive decline in cognition (26). Histopathological examination of the brain has shown neural degeneration in several areas of the central nervous system, with cerebellar damage and serious alterations of Purkinje cells (27). The most common mutation in EPM1 patients is a dodecamer repeat expansion in the stefin B (CSTB) gene promoter region that leads to reduced mRNA and protein levels (23,25). In addition, four mutations in the coding region were reported in EPM1 (23,28...
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