SECRETION AND MATRIX ASSEMBLY OF RECOMBINANT TYPE-VI COLLAGEN

A monomer of type VI collagen is composed of three different chains of 140 (alpha 1), 130 (alpha 2), and 250-350 kDa (alpha 3). Monomers ass emble into dimers (6 chains) and tetramers (12 chains) that are stabil ized by disulfide bonds and, once associated one to another, give rise to a microfilamentous network in close apposition with cell surfaces and banded collagen fibers. We have derived murine NIH/3T3 cell lines that were transfected with the cDNAs for the three chains and that con stitutively expressed chicken type VI collagen. Cotransfection was eff icient because, in three out of six isolated cell lines, all chicken c hains were expressed. Southern blotting demonstrated that several copi es of each cDNA were integrated approximately in equal number. Express ion of the three polypeptide chains was consistent with the levels of the respective mRNAs. The three chicken chains assembled by disulfide bonding to form correctly folded triple helical aggregated composites with sizes corresponding to type VI collagen monomers, dimers, and tet ramers. These functional recombinant assemblies were secreted and beca me incorporated into the extracellular matrix, where they formed an ex tensive fibrillar network.