Beschreibung:
<jats:title>SUMMARY</jats:title><jats:p>Transformation of murine NIH3T3 fibroblasts with retroviral vectors carrying the mos, myc and the Ha‐ras oncogene, respectively, was associated with a strong reduction of <jats:italic>H2</jats:italic> antigen expression in the cell membrane. Analysis of <jats:italic>H‐2K</jats:italic> and β<jats:sub>2</jats:sub>‐microglobulin promoter‐driven CAT activity in these oncogenic transformants and normal NIH3T3 fibroblasts revealed unchanged promoter activity, suggesting post‐transcriptional control of MHC class I expression by these oncogenes. Treatment with IFN‐gamma and TNF‐alpha caused 2‐ to 3‐fold enhancement of <jats:italic>H‐2K</jats:italic> and β<jats:sub>2</jats:sub>‐microglobulin promoter activity, as well as a normalization (TNF‐alpha treatment) or enhancement (IFN‐gamma treatment) of <jats:italic>H2</jats:italic> membrane expression. These data suggest that IFN‐gamma as well as TNF‐alpha can counteract downregulation of <jats:italic>H‐2</jats:italic> genes by interference with an oncogene‐induced, post‐transcriptional block as well as by a direct enhancement of <jats:italic>H‐2</jats:italic> gene transcription.</jats:p>