Glucocorticoid Inhibition of Transcription from Adenovirus Major Late Promoter

Abstract

Glucocorticoids inhibit proliferation of lymphosarcoma P1798 cells in culture. This is accompanied by inhibition of expression of class I as well as some class II genes. We have used the technique of transcription in vitro and the adenovirus major late promoter (AdMLP) to investigate molecular mechanisms of glucocorticoid inhibition of transcription of class II genes. Nuclear extracts from exponentially growing P1798 cells support faithful transcription from AdMLP. However, treatment of P1798 cells with 10(-7) M dexamethasone (a synthetic glucocorticoid) for 24 h impairs the ability of nuclear extracts prepared from such cells to support faithful transcription from AdMLP. Transcription from the human histone H4 gene promoter is unaffected by dexamethasone treatment. Gel mobility shift assays using synthetic oligonucleotide probe indicate no difference in the CAAT box binding activity of control and dexamethasone-treated cell extracts. Similarly, dexamethasone treatment does not affect the upstream stimulatory factor activity of P1798 cells. Furthermore, up-stream stimulatory factor purified from control cell extracts is unable to reconstitute the glucocorticoid-treated cell extracts for transcription from AdMLP. Fractionation of the control cell extracts on Sepharose S yields two protein fractions, neither of which supports transcription from AdMLP. However, one of these fractions, S-II, confers upon glucocorticoid-treated cell extracts the ability to support faithful transcription from AdMLP. We conclude that glucocorticoids regulate the transcription from AdMLP by regulating the activity of a trans-acting transcription factor which copurifies with fraction S-II.