Tumor necrosis factor and immune interferon synergistically increase transcription of HLA class I heavy- and light-chain genes in vascular endothelium.

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Abstract
Tumor necrosis factor and immune interferon synergistically increase cell-surface expression of class I major histocompatibility complex molecules in cultured human endothelial cells. We report that tumor necrosis factor and interferon .gamma. each independently increase mRNa levels and together cause a greater-than-additive (i.e., synergistic) increase in steady-state mRNA levels and transcriptional rates of the class I heavy- and light-chain genes. HLA heavy-chain mRNA is equally stable in cytokine-treated and -untreated endothelial cells. Interferon .gamma. does not increase tumor necrosis factor receptor number or affinity on human endothelial cells. We conclude that the synergistic increase in class I major histocompatibility complex cell-surface expression results principally from the synergistic increase in transcriptional rates. We propose that this increase is caused by the cooperative binding of independently activated transcription factors to the promoter/enhancer sequences of class I genes.