Cylindroma overexpresses collagen VII, the major anchoring fibril protein

The cell clusters of the human adnexal tumor, cylindroma, are surrounded by an unusual, thick, unorganized basement membrane-like zone in vivo. Ultrastructural analysis of this electron-dense zone revealed recesses that contained numerous anchoring fibrils. Indirect immunofluorescence staining with antibodies to collagen VII, the major structural component of the anchoring fibrils, showed strong fluorescence of this zone. Collagen VII could be isolated from tumor tissue by limited pepsin digestion or by extraction with chaotropic agents. Cylindroma cells were cultured from the tumor and passaged several times. The cells exhibited a strong expression of collagen VII in vitro, when assayed with immunofluorescence staining or immunoblotting of culture extracts. These results suggest that cylindroma can be used as an abundant source to produce collagen VII in vitro to study the biosynthesis and regulation of collagen VII and the formation of the anchoring fibrils, as other culture systems have failed to produce ample amounts of this anchoring fibril protein.