It is the long-term objective of this project to elucidate the mechanism whereby retinoids act as anti-carcinogens. The particular models to be used will be promoted mouse skin, mouse skin papillomas, mouse epidermal cells (JB-6) and mouse and human fibroblasts in culture. We have previously determined (1) that tumor promoter causes the loss of the cell-surface glycoprotein fibronectin (FN) both from promoted mouse skin in short-term culture, and from mouse fibroblasts, and that this detachment can be reversed by retinoids; (2) that in mouse skin papillomas retinoids stimulate FN synthesis. We have studied the release kinetics of FN from the surface of human lung fibroblasts and are doing the same with promoter-sensitive and promoter-resistant JB-6 cells. We found that tumor promoter TPA peels off pre-existing cell-surface FN with-cells. We found that tumor promoter TPA peels off pre-existing cell-surface FN without affecting FN synthesis or the structure of newly-synthesized FN. We studied the kinetics of retinoic acid (RA) inhibition of the TPA action. We now plan to denude cells of FN by TPA and study kinetics of re-attachment of FN, to determine whether the TPA has affected cell-surface binding sites or a pericellular-matrix component or the structure of FN itself, and to find out whether and how RA affects re-attachment. We also plan to study cell attachment to substratum--bound FN with a new cell-attachment assay, to determine how TPA and RA affect cell attachment, and how factors such as cell-surface binding sites and pericellular matrix components may affect this attachment. The results of these studies should reveal whether retinoids directly protect the FN-binding sites from TPA action and how the destruction of the FN-binding sites by TPA is reversed by retinoids. The results should also reveal information about FN-binding sites and how they are affected (on a molecular basis) by TPA and by retinoids. In parallel, we intend to study the release of FN from promoted (or initiated and promoted) mouse skin at various stages of promotion and its reversal by retinoids, as well as the stimulation of FN synthesis in skin and papillomas; also the level of FN in papillomas and how regressing papillomas, as a result of retinoid treatment, increase their FN synthesis and FN attachment.
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| Zerlauth, G; Wolf, G (1985) Studies on the tumour promoter-induced release of fibronectin from human lung fibroblasts, and its counteraction by retinoic acid. Carcinogenesis 6:531-4 |
