Molecular composition of type VI collagen. Evidence for chain heterogeneity in mammalian tissues and cultured cells

C. M. Kielty, R. P. Boot-Handford, S. Ayad, C. A. Shuttleworth, M. E. Grant

    Research output: Contribution to journalArticlepeer-review

    Abstract

    The chain composition and relative abundance of type VI collagen synthesized by cells cultured from foetal bovine nuchal ligament and skin were compared with those of the type VI collagen present in these foetal tissues. Immunoprecipitation of intact collagen VI from medium and cell layers of nuchal ligament fibroblasts and skin fibroblasts at confluence revealed collagen type VI molecules with a chain composition consistent with an [α1(VI)α2(VI)α3(VI)] monomeric assembly. Maintenance of cells in a post-confluent quiescent state promoted a marked phenotypic change in these ratios, with increased concentrations of assemblies composed of equimolar ratios of α1(VI) and α2(VI) chains detected in the medium of these cultures. Analysis of steady-state concentrations of mRNA for α1(VI) and α2(VI) chains revealed these species to be present in increased abundance at post-confluence in all the cultures, but no corresponding increase was observed in the α3(VI) mRNA. In order to assess the physiological significance of these observations, the chain composition of the collagen VI content of the corresponding foetal tissues was assessed by Western blotting after extraction in guanidinium isothiocyanate under reducing conditions. Extracts of nuchal ligament revealed a collagen VI chain composition consistent with a heterotrimeric chain assembly. In contrast, the skin extracts revealed an abundance of α1(VI) and α2(VI) chains with only traces of the α3(VI) chain detected. Increased equimolar concentrations of the α1(VI)-chain and α2(VI)-chain mRNAs in skin again reflected the increased concentrations of these polypeptide chains. Type VI collagen was present in greater abundance both in the nuchal ligament and in the corresponding nuchal-ligament fibroblast cultures. The results indicate that the chain composition of type VI collagen is subject to modulation at the level of transcription as a result of variations in the proliferative state of the cells, and demonstrate that different isoforms of collagen VI occur in foetal development.
    Original languageEnglish
    Pages (from-to)787-795
    Number of pages8
    JournalBiochemical Journal
    Volume272
    Issue number3
    Publication statusPublished - 1990

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