Abstract
Type XV collagen has a widespread distribution in human tissues, but a nearly restricted localization in basement membrane zones. The alpha1(XV) chain contains a highly interrupted collagenous region of 577 residues, and noncollagenous amino- and carboxyl-terminal domains of 530 and 256 residues, respectively. Cysteines are present in each domain and consensus sequences for O-linked glycosaminoglycans are situated in the amino terminus and in two large, noncollagenous interruptions. We now report that type XV collagen is a chondroitin sulfate proteoglycan in human tissues and cultured cells, and that the alpha chains are covalently linked by interchain disulfide bonds only between the two cysteines in the collagenous region. Western blotting of tissue extracts revealed a diffuse smear with a mean size >/=400 kDa, which after chondroitinase digestion resolved into a 250-kDa band in umbilical cord, and 250- and 225-kDa bands in placenta, lung, colon, and skeletal muscle. The latter two bands were also directly visualized by alcian blue/silver staining of a purified placenta extract. In a human rhabdomyosarcoma cell line, almost all of the newly synthesized type XV collagen was secreted into the medium and upon chondroitinase digestion just the 250-kDa alpha chain was generated. Chondroitinase plus collagenase digestion of tissue and medium proteins followed by Western blotting using domain-specific antibodies revealed a 135-kDa amino-terminal fragment containing glycosaminoglycan chains and a 27-kDa fragment representing the intact carboxyl terminus. However, a truncated carboxyl peptide of approximately 8-kDa was also evident in tissue extracts containing the 225-kDa form. Our data suggest that the 225-kDa form arises from differential carboxyl cleavage of the 250-kDa form, and could explain the approximately 19-kDa endostatin-related fragments (John, H., Preissner, K. T., Forssmann, W.-G., and Ständker, L. (1999) Biochemistry 38, 10217-10224), which may be liberated from the alpha1(XV) chain.
Highlights
¶ To whom correspondence should be addressed: Dept. of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, 805 Stellar Chance Laboratories, 422 Curie Blvd., Philadelphia, PA 191046059
We report that type XV collagen is a chondroitin sulfate proteoglycan in human tissues and cultured cells, and that the ␣ chains are covalently linked by interchain disulfide bonds only between the two cysteines in the collagenous region
The carboxyl-terminal domain of type XVIII collagen has become a focal point in tumor biology upon finding that the terminal 20-kDa fragment is identical to the potent anti-angiogenic factor, endostatin [17]
Summary
¶ To whom correspondence should be addressed: Dept. of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, 805 Stellar Chance Laboratories, 422 Curie Blvd., Philadelphia, PA 191046059. Comparison of domain arrangement, restricted sequence homology, as well as intron/exon organization indicated that ␣1(XV) and ␣1(XVIII) evolved from a common ancestral gene [4, 13,14,15,16] Both collagens, but especially type XV, contain extensive interruptions in their collagenous regions such that the majority of the residues in each chain are found within the amino- and carboxyl-terminal noncollagenous domains. The carboxyl-terminal domain of type XVIII collagen has become a focal point in tumor biology upon finding that the terminal 20-kDa fragment is identical to the potent anti-angiogenic factor, endostatin [17] Pursuant to this discovery is more current research in which the analogous peptide of type XV collagen, displaying by far the highest degree of sequence conservation with type XVIII, is being investigated for related properties [18, 19]. Subsequent use of antibodies from both sources, revealed a similar pattern of BMZ localization [9, 10]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
