Cathepsin S (CTSS), one of the lysosomal proteinases, has many important physiological functions in the nervous system, especially in process of extracellular matrix degradation and endocellular antigen presentation. CTSS is synthesized as inactive precursor of 331 amino acids consisting of a 15-aa signal peptide, a propeptide of 99 aa, and a mature polypeptide of 217 aa. It is activated in the lysosomes by a proteolytic cleavage of the propeptide. Cathepsin S is expressed in the lysosome of antigen presenting cells, primarily dendritic cells, B-cells and macrophages. Compared with other lysosomal cysteine proteases, cathepsin S has displayed some unique characteristics. Cathepsin S is most well known for its critical function in the proteolytic digestion of the invariant chain chaperone molecules, thus controlling antigen presentation to CD4+ T-cells by major histocompatibility complex (MHC) class II molecules or to NK1.1+ T-cells via CD1 molecules. Cathepsin S also appears to participate in direct processing of exogenous antigens for presentation by MHC class II to CD4+ T-cells, or in cross-presentation by MHC class I molecules to CD8+ T-cells. In addition, although direct evidence is still lacking, in its secreted form cathepsin S is implicated in degradation of the extracellular matrix, which may contribute to the pathology of a number of diseases, including arthritis, atherosclerosis, neurological diseases and chronic obstructive pulmonary disease.
Cathepsin Z (CTSZ); also known as Cathepsin X or CATX; belongs to the C1 family of lysosomal cysteine proteases. Its gene structure and activity properties show several unique features that distinguish it clearly from other human cysteine proteases. It has a very short pro-region that shows no similarity to those of other cathepsins and a three-residue insertion motif that forms a characteristic ‘mini loop’. Cathepsin Z exhibits mono- and di-peptidase activity at its C-terminus; and in contrast to cathepsin B; it does not act as an endopeptidase. It is restricted to the cells of theimmune system; predominantly monocytes; macrophages and dendritic cells. Cathepsin Z is widely expressed in human tissues; suggesting that this enzyme could be involved in the normal intracellular protein degradation taking place in all cell types. It is capable to cleave regulatory motifs at C-terminus affecting the function of targeted molecules. Cathepsin X may regulate also the maturation of dendritic cells; a process; which is crucial in the initiation of adaptive immunity. Furthermore; higher levels of Cathepsin Z are also found in tumour and immune cells of prostate and gastric carcinomas and inmacrophages of gastric mucosa; especially after infection by Helicobacter pylori. Cathepsin Z is also ubiquitously distributed in cancer cell lines and in primary tumors from different sources; suggesting that this enzyme may participate in tumor progression.
Cathepsin Z is a lysosomal cysteine proteinase and belongs to the peptidase C1 family. Human Cathepsin Z contains a singnal sequence; a propeptide and a mature chain. It exhibits bothcarboxy-monopeptidase and carboxy-dipeptidase activities. In contrast to cathepsin B; it does not act as an endopeptidase. Cathepsin Z is restricted to the cells of theimmune system; predominantly monocytes; macrophages and dendritic cells. It is expressed ubiquitously in cancer cell lines and primary tumors. Like other members of this family; Cathepsin Z may be involved in tumorigenesis.
The protein encoded by this gene is a major component of the inner surface of caveolae, small invaginations of the plasma membrane, and is involved in essential cellular functions, including signal transduction, lipid metabolism, cellular growth control and apoptosis. This protein may function as a tumor suppressor. This gene and related family member (CAV1) are located next to each other on chromosome 7, and express colocalizing proteins that form a stable hetero-oligomeric complex. Alternatively spliced transcript variants encoding different isoforms have been identified for this gene. Additional isoforms resulting from the use of alternate in-frame translation initiation codons have also been described, and shown to have preferential localization in the cell (PMID:11238462). [provided by RefSeq, May 2011]
CBL proteins, such as Cbl-c, are phosphorylated upon activation of a variety of receptors that signal via protein tyrosine kinases. Through interactions with proteins containing SRC homology-2 (SH2) and SH3 domains, CBL proteins modulate downstream cell signaling. Cbl-c is a member of the Cbl family of E3 ubiquitin ligases. Expression of Cbl-c gene may be restricted to epithelial cells, and alternatively spliced transcript variants encoding multiple isoforms have been observed for Cbl-c gene.
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