Disease relevance of EG317677

• FUT-175 also inhibited complement-mediated hemolysis, including both classical and alternative pathways, sites of inhibition being on C1r and C1s as evidenced by the intermediate-cell technique [1].
• Hamster complement C1s cDNA was inserted into expression plasmid BCMGSNeo, and transfected to SEA7 cells, A31 mouse fibroblasts transformed by polyoma virus [2].

High impact information on EG317677

• We found that a C4 mutant carrying only the 3-residue deletion is not cleaved by C1s and has essentially no hemolytic activity, whereas a mutant carrying only the six replacement changes is cleaved by C1s and has normal hemolytic activity [3].
• Slp is nonfunctional at least in part because it is not cleaved by the activated form of complement protease C1s (C1s), which proteolytically activates C4 in the classical complement pathway [3].
• In the present studies, we used site-directed mutagenesis of C4 and expression of the mutant proteins in cultured cells to identify the amino acid substitutions in Slp that are responsible for resistance to C1s cleavage [3].
• However, substitution of both the upstream and downstream segments gave a hybrid C5 protein, designated ASC4, which was cleaved by C1s [4].
• Previous studies showed that simply inserting or substituting a few amino acid residues immediately downstream of the proteolytic activation site in C component C3 renders that site susceptible to the C4-specific C1s protease [4].

Biological context of EG317677

• Substrate specificities of murine C1s [5].
• Those earlier studies used human, not murine, C1-s, however; a recent report has suggested that Slp is an essential component of a novel complement activation pathway and that the previous failure to observe cleavage of Slp is probably the result of a species incompatibility between Slp and the heterologous human C1-s (hC1-s) [5].
• The C1r and C1s loci also provide useful polymorphic DNA markers for the short arm of chromosome 12 [6].
• Recent comparisons indicate a significant degree of sequence similarity between C1r and C1s and support the hypothesis that they are related by gene duplication [6].
• Proteolysis of the heavy chain of major histocompatibility complex class I antigens by complement component C1s [7].

Anatomical context of EG317677

• We have previously shown that activated C1s complement and activated T cells cleave beta2-microglobulin (beta2m) in vitro leading to the formation of desLys58 beta2m [8].
• C1-esterase inhibitor blocks T lymphocyte proliferation and cytotoxic T lymphocyte generation in vitro [8].
• Thus the C1s activity can be modulated inside the C1 molecular complex upon binding of C1q to a lymphocyte product [9].
• BALB/c mouse fibroblast A31 cells, which do not produce C1s, were transfected with BCMGSNeoHACS and the transfectants were selected with G418 [10].

Associations of EG317677 with chemical compounds

• An early step in the initiation of the classical C pathway is the proteolytic activation of component C4 by subcomponent C1-s. We have examined the substrate specificity of murine C1-s (mC1-s) by measuring its proteolytic activity on human and murine C4, and on the murine C4 isotype designated sex-limited protein (Slp) [5].
• C1r and C1s are distinct, but structurally and functionally similar, serine protease zymogens responsible for the enzymatic activity of the first component of complement (C1) [6].
• C1r and C1s are the serine proteases that form the catalytic unit of the C1 complex, the first component of complement [11].
• Although the C2 cleaving activity of C1s was partially inhibited by M81, no blocking was observed with M365 [12].
• Transfectants of these mutated C1s cDNA did not form tumors in nude mice, To distinguish between active and inactive C1s in situ, we have developed novel antibodies, one directed to the NH2-terminal neoepitope of the L chain and the other specific for uncleaved inactive C1s [13].

Analytical, diagnostic and therapeutic context of EG317677

• In situ hybridization analyses were consistent with these assignments, showing in addition that both C1r and C1s are located on the short arm of the chromosome in the region p13 [6].
• In agreement with this observation, Western blotting demonstrated good binding to unreduced C1s, but no binding to the alpha or gamma-B domains [14].
• Anti-human C1s monoclonal antibody H1532, a mouse gamma-1-immunoglobulin elicited by a C1r2C1s2 immunogen, appeared to bind to the beta-domain of C1s by electron microscopy [14].
• C1s was purified to a homogeneity from the culture medium of the transfectant by DEAE-Sephadex, Dymatrex orange A and size-exclusion HPLC [2].

References