We studied the regulation of fibronectin (FN) gene expression by cAMP and phorbol-12-myristate-13acetate (PMA) in HT-1080 human fibrosarcoma cells. Dibutyryl cAMP increased FN synthesis and mRNA levels, while PMA inhibited the cAMP-induced FN synthesis. In transient transfection assays, cAMP increased FN promoter activity, while PMA paradoxically enhanced the cAMP-induced promoter activity. Stable transfection experiments, however, showed that neither cAMP or PMA alone nor together affected FN

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... romoter activity. These results suggest that PMA antagonizes the cAMP-induced FN gene expression and that both the action of cAMP and the inhibition of its action by PMA may occur at the posttranscriptional level in HT-1080 cells. K e y w o r d s : c A M P, fibronectin, HT-1080, phorbol myristate acetate, protein kinase C Materials and Methods Cell cultures A human fibrosarcoma cell line HT-1080 (ATCC CCL 121) was obtained from the American Type Culture Collection. Cells were cultured in minimal essential medium (MEM) supplemented with 10% fetal bovine serum (Gibco/BRL), 100 U/ml of penicillin, 100 µg/ml of streptomycin, and 0.1% nonessential amino acids. Cells were incubated at 37˚C in a 5% CO 2 air environment. Enzyme-linked immunosorbent assay (ELISA) of FN Confluent cells in 24-well culture plates were incubated with serum-free MEM containing 1% bovine serum albumin Regulation of fibronectin gene expression by cyclic AMP and phorbol myristate acetate in HT-1080 human fibrosarcoma