Labile proteins play a dual role in the control of endothelial leukocyte adhesion molecule-1 (ELAM-1) gene regulation.

Endothelial leukocyte adhesion molecule-1 (ELAM-1) is a membrane protein exclusively expressed on endothelial cells, where it plays a key role in the inflammatory response by adhering to a subset of leukocytes. The expression of the ELAM-1 gene is very tightly regulated. ELAM-1 is undetectable in uninduced cells, and it is transiently expressed following cytokine induction. Treatment of resting endothelial cells with three different protein synthesis inhibitors, cycloheximide (CHX), anisomycin, and emetine, caused an increase in the steady-state level of ELAM-1 mRNA above that observed with IL (interleukin)-1 alone. Furthermore, ELAM-1 mRNA was found in the presence of all three protein synthesis inhibitors without IL-1 treatment. Analysis of the mRNA half-life indicated that the protein synthesis inhibitors act, in part, by stabilizing ELAM-1 mRNA. In addition, protein synthesis inhibitors potentiate the effect of IL-1 beta at the level of transcription initiation as shown by nuclear run-on experiments. The NF kappa B-like binding activity to the ELAM-1 promoter sequence induced by IL-1 beta is augmented by inhibitors of protein synthesis. The NF kappa B binding sequence was found to be necessary and sufficient for superinduction of the ELAM-1 gene by CHX. These results show that regulation at the level of protein synthesis is implicated in the overall regulation of ELAM-1 gene expression. Mechanisms which could explain these effects are discussed.