Collagen formation in extracellular matrix of transplants of human transformed keratinocyte cell lines.

Background, Materials And Methods: The role of epithelial cell growth and neoplastic transformation on collagen formation and deposition in the extracellular matrix (ECM) was analyzed by culturing immortalized human epidermal cell lines and Ras-transformed benign and malignant clones on collagen gels as transplants. The lesions were analyzed for extent of growth and morphology of epithelial and mesenchymal components as well as synthesis and deposition of different collagens.

Results: Immortalized cell lines required up to 5 weeks of growth for a well-organized mesenchyme to develop; transplants of Ras-transformed benign clones needed 3 weeks and transplants of highly malignant clones only 2 weeks to form an organized stroma. In transplants of immortalized cells after 2 weeks of growth newly-synthesized collagen type I and type III were deposited in the mesenchyme adjacent to the muscle, forming a mature ECM, while ECM was absent adjacent to growing, differentiated, immortalized cells. In transplants of Ras-transformed benign clones the subepithelial ECM was immature at day 14, but it was forming fibers at the same time in transplants of malignant clones. These were seen as thin irregular fibers in immunohistochemistry, ultimately organized into fibrillar structures in similar locations to active synthesis detected by in situ hybridization. Depositions of crosslinked mature type I collagen occurred later in similar locations. Type III collagen synthesis and deposition was most prominent in transplants of malignant cell clones, with degradation and destruction of the extracellular matrix around invading islets of malignant cells.

Conclusion: The development of mesenchyme was directly related to duration of growth of transplants and degree of malignancy; mesenchyme organization was inversely related to differentiation of the epithelial cells. The results showed the usefulness of the transplant model in studies on cell and tissue growth and organization.