J. Biol. Chem., Vol. 262, Issue 30, 14461-14466, 10, 1987
Biosynthesis of chick type VI collagen. II. Processing and secretion in fibroblasts and smooth muscle cells
A Colombatti and P Bonaldo
Division of Experimental Oncology 2, Oncology Reference Center, Aviano, Italy.
The biosynthesis of type VI collagen was studied in "matrix-free" chick
embryo smooth muscle cells and fibroblasts. Omission of ascorbate from the
culture affected to a great extent the secretion in fibroblasts but had a
very minor effect on smooth muscle cells. Quantitative analysis of the
secretion process in continuous time course and in pulse-chase experiments
confirmed that fibroblasts and smooth muscle cells secreted type VI
collagen with the same chain composition but with different kinetics: after
4 h of chase more than 60% of the labeled type VI collagen was present in
the culture medium of fibroblasts, whereas at the same time interval less
than 25% was secreted by smooth muscle cells. The different kinetics
depends on intrinsic properties of the cells, since it was detected also in
adherent cells. However, even in fibroblasts, secretion of type VI collagen
was much slower than secretion of fibronectin, of which more than 50% was
already in the cell medium after 1 h of chase. Treatment of the cells with
inhibitors of hydroxylation and glycosylation caused a shift in mobility
that revealed a size heterogeneity in the Mr = 260,000 subunit. No evidence
of processing was observed in chick cells for any of the subunits that were
synthesized and secreted uncleaved. In addition, after several days of
chase the Mr of the subunits of type VI collagen isolated from the matrix
remained unchanged, thus excluding that in the chick even a partial or
incomplete processing takes place.
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