|
||
J. Cell Biol.,
Volume 144, Number 5, March 8, 1999 1069-1080
1 and BMP-2

* Washington University School of Medicine, Department of Orthopedic Surgery, St. Louis, Missouri 63110; Type II procollagen is expressed as two splice
forms. One form, type IIB, is synthesized by chondrocytes and is the major extracellular matrix component
of cartilage. The other form, type IIA, contains an additional 69 amino acid cysteine-rich domain in the NH2-propeptide and is synthesized by chondrogenic mesenchyme and perichondrium. We have hypothesized that
the additional protein domain of type IIA procollagen
plays a role in chondrogenesis. The present study was
designed to determine the localization of the type IIA
NH2-propeptide and its function during chondrogenesis. Immunofluorescence histochemistry using antibodies to three domains of the type IIA procollagen molecule was used to localize the NH2-propeptide, fibrillar
domain, and COOH-propeptides of the type IIA procollagen molecule during chondrogenesis in a developing human long bone (stage XXI). Before chondrogenesis, type IIA procollagen was synthesized by
chondroprogenitor cells and deposited in the extracellular matrix. Immunoelectron microscopy revealed
type IIA procollagen fibrils labeled with antibodies to
NH2-propeptide at ~70 nm interval suggesting that the
NH2-propeptide remains attached to the collagen molecule in the extracellular matrix. As differentiation proceeds, the cells switch synthesis from type IIA to IIB
procollagen, and the newly synthesized type IIB collagen displaces the type IIA procollagen into the interterritorial matrix. To initiate studies on the function of
type IIA procollagen, binding was tested between recombinant NH2-propeptide and various growth factors
known to be involved in chondrogenesis. A solid phase binding assay showed no reaction with bFGF or IGF-1,
however, binding was observed with TGF-
Department of
Pathology, University of Washington, Seattle, Washington 98195; and § Shriners Hospital for Children, Portland, Oregon 97201
1 and
BMP-2, both known to induce endochondral bone formation. BMP-2, but not IGF-1, coimmunoprecipitated with type IIA NH2-propeptide. Recombinant type IIA
NH2-propeptide and type IIA procollagen from media
coimmunoprecipitated with BMP-2 while recombinant
type IIB NH2-propeptide and all other forms of type II
procollagens and mature collagen did not react with
BMP-2. Taken together, these results suggest that the
NH2-propeptide of type IIA procollagen could function
in the extracellular matrix distribution of bone morphogenetic proteins in chondrogenic tissue.
This article has been cited by other articles:
|
|