Human genes for complement components C1r and C1s in a close tail-to-tail arrangement.

Abstract

Complementary DNA clones for human Cls were isolated from cDNA libraries that were prepared with poly(A)+ RNAs of human liver and HepG2 cells. A clone with the largest cDNA insert of 2664 base pairs (bp) was analyzed for its complete nucleotide sequence. It contained 202 bp of a 5' untranslated region, 45 bp of coding for a signal peptide (15 amino acid residues), 2019 bp for complement component Cls zymogen (673 amino acid residues), 378 bp for a 3' untranslated region, a stop codon, and 17 bp of a poly(A) tail. The amino acid sequence of Cis was 40.5% identical to that of COr, with excellent matches of tentative disulfide bond locations conserving the overall domain structure of COr. DNA blotting and sequencing analyses of genomic DNA and of an isolated genomic DNA clone clearly showed that the human genes for COr and Cls are closely located in a "tail-to-tail" arrangement at a distance of about 9.5 kilobases. Furthermore, RNA blot analyses showed that both COr and Cis genes are primarily expressed in liver, whereas most other tissues expressed both COr and Cis genes at much lower levels (less than 10% of that in liver). Multiple molecular sizes of specific mRNAs were observed in the RNA blot analyses for both COr and Cis, indicating that alternative RNA processing(s), likely an alternative polyadenylylation, might take place for bith genes.The human complement system, which is composed of the classical and alternative pathways, involves about two dozen plasma proteins, including proteases and cofactors (1-3). These proteins are sequentially activated to form a lytic complex that attacks the foreign cell. Anaphylatoxic and vasoactive peptides are also generated during the course of this reaction (4). Clr and Cls are single-chain plasma glycoproteins of about 85 kDa. These proteins are highly homologous to each other, and both are subcomponents of the complement C1 complex in which two molecules of each Cir and Cls form a complex with one molecule of Clq, another subcomponent of C1, in the presence of calcium ions (2,3). Clq in the C1 complex binds to the antigen-antibody immune complex through the constant region of immunoglobulin heavy chains, resulting in autoactivation of Clr (5). The activated Clr then proteolytically activates Cls, which in turn activates C2 and C4 in the complement cascade reactions. Upon proteolytic activation, both Clr and Cls are converted to two-chain-form proteases comprised of a heavy chain (58 kDa) and a light chain (27 kDa) and are readily inhibited by C1 inhibitor, forming a stoichiometric complex.Recently, an isolation and characterization of Clr and its unique domain structures have been reported (6). In addition to the serine protease module contained in the light chain of Cir, the heavy chain of Clr contains five distinct structural domains. Domains I and III are homologous repeats, and domain II is an epidermal growth factor precursor-like sequence that is also found in many other proteins such as blood coagulation factors and low density lipoprotein receptors. Doma...

Change of complement C1s synthesis during development of hamster cartilage

“…In fact, activated C1s is immunostained arround vessels invading into cartilage (H. Sakiyama, unpublished work). Since C1s has widespread distribution in many tissues (Kusumoto et al 1988;Sakiyama et al 1991), it may have a specific function in each tissue.…”

Molecular Basis of a Selective C1s Deficiency Associated with Early Onset Multiple Autoimmune Diseases

“…Combined and partial C1s and C1r deficiency has also been reported in several patients including four siblings, two of whom developed discoid lupus and rheumatoid arthritis (18), and a 60-year-old woman with SLE (19). The genetic defect of combined C1r/C1s deficiency has not yet been elucidated but might be related to the close location of the two genes on chromosome 12 (12p13) (7). A few cases of selective C1r deficiency have also been reported, associated with lupus-like syndrome (20,21) or susceptibility to infection (22,23).…”

Coordinated change between complement C1s production and chondrocyte differentiation in vitro

“…The major synthesis site of serum C1s is the liver. However, C1s gene expression has been found in most other tissues, including brain, kidney, stomach, and muscle (Kusumoto et al 1988;Sakiyama et al 1991), and in several types of cultured cells, such as monocytes (Bensa et al 1983), endothelial cells (Morris et al 1978), and fibroblasts (Kats and Strunk 1989). By immunostaining (Sakiyama et al 1991 and in situ hybridization (Toyoguchi et al 1996), we have shown that C1s is also synthesized by chondrocytes and that the synthesis increases in accordance with chondrocyte hypertrophy.…”