Loss of type VI collagen in experimental and most spontaneous human fibrosarcomas

Expression of type VI collagen, an adhesive protein of mesenchymal tissues, is significantly down-regulated upon viral transformation of fibroblasts. Likewise, most cell lines derived from spontaneous mesenchymal tumors, including fibrosarcomas, rhabdomyosarcomas, leiomyosarcomas, chondrosarcomas and liposarcomas, do not synthesize type VI collagen because they are not capable of expressing all 3 of the polypeptide chains required for the assembly of a functional heterotrimeric molecule. When injected into nude mice, neither fibrosarcoma cells (HT1080) nor rhabdomyosarcoma cells (A204) initiate the synthesis of type VI collagen, suggesting that the inhibition is not caused by deficiency of a paracrine factor. Immuno-histochemical studies further illustrate that 15 of 17 spontaneous adult fibrosarcomas lack type VI collagen in the tumor stroma. The absence of this important adhesion protein may contribute to tumorigenicity, invasiveness and/or metastasis of mesenchymal tumor cells.