Spontaneous and cytokine regulated c-fos gene expression in rheumatoid synovial cells: resistance to cytokine stimulation when the c-fos gene is overexpressed

Objective-To study the effect of cytokines on the transactivation of the c- fos gene in relation to the contribution of overexpression of c-fos/AP-1 in rheumatoid joint destruction. Methods-The promoter region (-447 to +109) of the human c-fos gene was inte grated upstream of the chloramphenicol acetyltransferase (CAT) reporter gen e, and the effect of cytokines on the expression of the c-fos gene was stud ied in the rheumatoid synovial cells of early (3-4) or late (14-18) passage s, in the presence or absence of cytokines, by the transient transfection a ssay. Results-Expression of c-fos gene was enhanced by tumour necrosis factor alp ha (TNF alpha) and interleukin 6 (IL6) in the synovial cells of early passa ge, whereas it was not enhanced in the synovial cells of late passage. The c-fos gene expression was also enhanced by 13-O-tetradecanoyl phorbol-13-ac etate (TPA) in early passage but was somewhat suppressed in the late passag e. It was found that the c-fos gene and c-Fos protein were both increased i n the synovial cells of late passage. Similarly, c-fos gene expression was also not increased by TPA or cytokine stimulation in the stable c-fos trans formants (fos-pH8) or H-ras transformed NIH3T3 cells (NIH H-ras cells) that constitutively expressed c-fos genes. Conclusions-Although TNF alpha and IL6 augmented c-fos gene expression of r heumatoid synovial cells, transactivation of c-fos gene became resistant ag ainst cytokine stimulation under prolonged expression of c-fos gene, which may impart a tumour-like characteristic to rheumatoid synovial cells.