MOLECULAR AND FUNCTIONAL EVIDENCE FOR IN-VITRO CYTOKINE ENHANCEMENT OF HUMAN AND MURINE TARGET-CELL SENSITIVITY TO GLUCOCORTICOIDS - TNF-ALPHA PRIMING INCREASES GLUCOCORTICOID INHIBITION OF TNF-ALPHA-INDUCED CYTOTOXICITY APOPTOSIS/

Cytokine-induced glucocorticoid secretion and glucocorticoid inhibitio n of cytokine synthesis and pleiotropic actions act as important safeg uards in preventing cytokine overreaction. We found that TNF-alpha inc reased glucocorticoid-induced transcriptional activity of the glucocor ticoid receptor (GR) via the glucocorticoid response elements (GRE) in L-929 mouse fibroblasts transfected with a glucocorticoid-inducible r eporter plasmid. In addition, TNF-alpha also enhanced GR number. The T NF-alpha effect on transcriptional activity was absent in other cell l ines that express TNF-alpha receptors but not GRs, and became manifest when a GR expression vector was cotransfected, indicating that TNF-al pha, independent of any effect it may have on GR number, has a stimula tory effect on the glucocorticoid-induced transcriptional activity of the GR. Moreover, TNF-alpha increased GR binding to GRE. As a function al biological correlate of this mechanism, priming of L-929 cells with a low (noncytotoxic) dose of TNF-alpha significantly increased the se nsitivity to glucocorticoid inhibition of TNF-alpha-induced cytotoxici ty/apoptosis. TNF-alpha and IL-1 beta had the same stimulatory action on glucocorticoid-induced transcriptional activity of the GR via the G RE, in different types of cytokine/glucocorticoid target cells (glioma , pituitary, epithelioid). The phenomenon may therefore reflect a gene ral molecular mechanism whereby cytokines modulate the transcriptional activity of the GR, thus potentiating the counterregulation by glucoc orticoids at the level of their target cells.