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© The Rockefeller University Press, 0021-9525/1999//1069 $5.00
The Journal of Cell Biology, Volume 144, Number 5, , 1999 1069-1080


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Type IIA Procollagen Containing the Cysteine-rich Amino Propeptide Is Deposited in the Extracellular Matrix of Prechondrogenic Tissue and Binds to TGF-β1 and BMP-2



Yong Zhu*, Anush Oganesian{ddagger}, Douglas R. Keene§, and Linda J. Sandell*

* Washington University School of Medicine, Department of Orthopedic Surgery, St. Louis, Missouri 63110; {ddagger} Department of Pathology, University of Washington, Seattle, Washington 98195; and § Shriners Hospital for Children, Portland, Oregon 97201

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-β1 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.

Key Words: type IIA procollagen • bone morphogenetic proteins • chondrogenesis • collagen NH2-propeptide • skeletal patterning



Abbreviations used in this paper: BMPs, bone morphogenetic proteins; C, chondrocytes; CP, chondroprogenitor cells; ECM, extracellular matrix; RT-PCR, reverse transcription-polymerase chain reaction; sog, short gastrulation gene.

The study was supported in part by the National Institutes of Health research grant R01AR36994, the Department of Veterans Affairs, the Department of Orthopedics, University of Washington, and the Shriners Hospital for Children (Portland, OR).



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