Characterization of the human type XVIII collagen gene and proteolytic processing and tissue location of the variant containing a frizzled motif

• Published in: Matrix biology 2003-09, Vol.22 (5), p.427-442
• Main Authors: Elamaa, Harri, Snellman, Anne, Rehn, Marko, Autio-Harmainen, Helena, Pihlajaniemi, Taina
• Format: Article
• Language: English
• Subjects: Alternative Splicing; Amino Acid Motifs; Amino Acid Sequence; Animals; Cell Line; Cloning, Molecular; Collagen gene; Collagen Type XVIII - chemistry; Collagen Type XVIII - genetics; Cysteine - chemistry; DNA, Complementary - metabolism; Exons; Genetic Variation; Human type XVII; Humans; Immunohistochemistry; Introns; Mice; Models, Genetic; Molecular Sequence Data; Peptides - chemistry; Precipitin Tests; Promoter Regions, Genetic; Protein Structure, Tertiary; Proteolytic processing; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - metabolism; Sequence Homology, Amino Acid; Tissue Distribution
• ISSN: 0945-053X; 1569-1802
• DOI: 10.1016/S0945-053X(03)00073-8

Human type XVIII collagen was found to be expressed as three variants, termed NC1-303, NC1-493 and NC1-728, differing in their N-terminal non-collagenous domains (NC1). The corresponding gene was found to be ∼105 kb in size and contain 43 exons. The short variant is derived from utilization of an upstream promoter associated with the first two exons of the gene. The two other variants are derived from a downstream promoter and alternative splicing of exon 3, resulting in 192 residues of shared sequences characterized by a putative ∼30 residue conserved coiled–coil motif and 235 residues of sequences specific to NC1-728. The NC1-728 variant has a conserved cysteine-rich domain homologous with the ligand-binding part of the frizzled proteins. A polyclonal antibody specific to the NC1-728 variant was generated, and immunostaining of fetal tissues revealed staining in lung and skeletal muscle. Human serum contained 173- and 144-kDa α1(XVIII) chains corresponding to the NC1-728 and NC1-493 variants, respectively. A 200-kDa polypeptide was detected in cells transfected with a cDNA construct corresponding to the full-length NC1-728 variant, and EBNA-293 cells endogenously synthesizing low amounts of type XVIII collagen had a 45-kDa fragment in their culture medium that corresponded to most of the NC1 domain of the NC1-728 variant, suggesting processing of the N-terminal frizzled-containing domain.