INDUCTION OF EARLY GROWTH RESPONSE-1 GENE BY INTERLEUKIN-1-BETA AND TUMOR-NECROSIS-FACTOR-ALPHA IN NORMAL HUMAN BONE-MARROW STROMAL AND OSTEOBLASTIC CELLS - REGULATION BY A PROTEIN-KINASE-C INHIBITOR

The early growth response-1 (Egr-1) gene has been identified as a nucl ear transcriptional factor and implicated in the regulation of growth and differentiation of osteoblastic cells. In the present study, we in vestigated whether Egr-1 mRNA is expressed and induced by interleukin- 1 beta, (IL-beta) and tumor necrosis factor-alpha (TNF-alpha) in norma l human bone marrow stromal (HEMS) and osteoblastic (HOB) cells. Resul ts demonstrate a very low basal expression of Egr-1 mRNA which is indu ced by IL-1 beta, and TNF-alpha in a time- and dose-dependent manner. Egr-1 mRNA induction was detectable within 15 min, reached maximal by 60 min and thereafter declined to basal levels by 120 min. Induction o f Egr-1 mRNA by IL-1 beta and TNF-alpha was completely inhibited by H- 7 suggesting the mediation of protein kinase C. The induction by IL-1 beta, and TNF-alpha of Egr-1 mRNA was independent of de novo protein s ynthesis since this induction was also observed in the presence of pro tein synthesis inhibitor cycloheximide. Fetal bovine serum and cyclohe ximide also independently induced the Egr-1 mRNA. Actinomycin D experi ments demonstrated that Egr-1 mRNA is degraded very rapidly with a hal f-life of 30 min. Our results demonstrate the expression of Egr-1 gene and its induction by IL-1 beta, and TNF-alpha in normal human bone ma rrow stromal (osteoprogenitor) and osteoblastic cells in primary cultu res. Data also reveal that the expression of Egr-1 gene is inhibited b y protein kinase C inhibitor H-7 suggesting that the activation of pro tein kinase C or other protein kinases resulting in the phosphorylatio n of specific transcription factor(s) is the first immediate early ste p in the induction of immediate-early Egr-1 gene by IL-1 beta, and TNF -alpha. Results also suggest that Egr-1 is an important mediator of IL -1 beta and TNF-alpha action in normal human osteoblastic cells.