IL-1 INDUCES EXPRESSION OF MONOCYTE CHEMOATTRACTANT JE IN CLONAL MOUSE OSTEOBLASTIC CELL-LINE MC3T3-E1

Recent studies demonstrated that platelet-derived growth factor-inducible JE is an inflammatory cytokine that directs chemotaxis of monocytes, and is a homolog of monocyte chemoattractant protein-1, which is a human monocyte chemotactic factor. Migration and accumulation of monocyte lineage cells in bone tissue sites are very important for the recruitment of multinucleate osteoclasts, because the origin of osteoclasts is derived from monocyte lineage cells in hemopoietic cells. Because IL-1 is a potent regulator in bone remodeling, we examined whether IL-1beta induces JE expression in a clonal mouse osteoblastic cell line, MC3T3-E1. Significant chemotactic activity for human monocytes was detected in conditioned medium of the cells at 6 h after initiation of IL-1beta treatment, and the chemotactic activity increased in both a culture time- and dose-dependent manner. The peak of the chemotactic activity in the conditioned medium was observed in fractions corresponding to a m.w. of 26 kDa when the conditioned medium was fractionated by gel filtration. The chemotactic activity in the peak fraction was completely neutralized by antiserum specific for JE protein. And the JE gene product in the conditioned medium was detected as a microheterogeneous protein with a m.w. of 21 to 33 kDa by immunoprecipitation with the specific antiserum. IL-1beta induced a maximal JE gene expression in the cells at 3 h after initiation of the cytokine treatment. This significant expression was observed when IL-1beta was used at a concentration of 10 U/ml, and the expression was dose dependent. The run-on assay showed that the cytokine-induced JE gene expression increased at the transcriptional level. IL-1beta and TNF-alpha acted synergistically to stimulate JE gene expression in the cells. Expression and product of the JE gene were also observed in an osteoblast-enriched cell population prepared from mouse calvariae. These results suggest the possibility that osteoblastic cells can participate in osteoclast recruitment via the JE gene product.