The osterix transcription factor down-regulates interleukin-1α expression in mouse osteosarcoma cells

K7M2 mouse osteosarcoma cells form lytic tumors and are deficient in osterix (Osx), a zinc finger-containing transcription factor required for osteoblast differentiation and bone formation. Our previous studies showed that replacement of Osx suppresses lytic bone destruction. Cytokines, including interleukin (IL)-1α, IL-6, IL-11, and prostaglandin E2, have been shown to stimulate osteoclast activity. We showed that IL-1α production by K7M2 cells was significantly suppressed following Osx transfection through a transcription-mediated mechanism. Osx had no effect on IL-6, IL-11, or prostaglandin E2. Site-directed mutagenesis and chromatin immunoprecipitation indicated that Osx down-regulated IL-1α through an Sp1-binding site on the IL-1α promoter. Inhibiting Osx by small interfering RNA in two cell lines (Dunn and DLM8) that expressed high levels of Osx led to enhanced IL-1α promoter activity and protein production and altered the phenotype from blastic to lytic. These data suggest that Osx down-regulates IL-1α expression in mouse osteosarcoma cells via transcriptional repression of IL-1α and this may in turn affect the lytic activity of the tumor cells.