Osterix inhibits bone destruction in osteosarcoma through transcriptional repression of Interleukin-1alpha expression

Osteosarcoma, a malignant bone tumor, rapidly destroys the cortical bone. We demonstrated that mouse K7M2 osteosarcoma cells were deficient in osterix (osx), a zinc finger-containing transcription factor required for osteoblasts differentiation and bone formation. These cells formed lytic tumors when injected into the tibia. The destruction of bone is mediated by osteoclasts in osteosarcoma. The less expression of osterix with osteolytic phenotype was also observed in more tumor cell lines. Replacement of osterix in K7M2 cells suppressed lytic bone destruction, inhibited tumor growth in vitro and in vivo, and suppressed lung metastasis in vivo and the migration of K7M2 to lung conditioned medium in vitro. By contrast, inhibiting osterix by vector-based small interfering RNA (siRNA) in two cell lines (Dunn and DLM8) that expressed high levels of osterix converted osteoblastic phenotype to lytic. Recognizing and binding of Receptor Activator of NF-κB (RANK) on osteoclast precursors by its ligand RANKL is the key osteoclastogenic event. Increased RANKL results in more osteoclast activity. We investigated whether K7M2-mediated bone destruction was secondary to an effect on RANKL. The conditioned medium from K7M2 could upregulate RANKL in normal osteoblast MC3T3, which might lead to more osteoclast formation. By contrast, the conditioned medium from K7M2 cells transfected with osx-expressing plasmid did not upregulate RANKL. Furthermore, Interleukin-1alpha (IL-1α) was significantly suppressed following osx transfection. IL-1α increased RANKL expression in MC3T3 cells, suggesting that osx may control RANKL via a mechanism involving IL-1α. Using a luciferase reporter assay, we demonstrated that osx downregulated IL-1α through a transcription-mediated mechanism. Following suppression of osterix in Dunn and DLM8 cells led to enhanced IL-1α promoter activity and protein production. Site-directed mutagenesis and Chromatin immunoprecipitation (ChIP) indicated that osterix downregulated IL-1α through a Sp1-binding site on the IL-1α promoter. These data suggest that osterix is involved in the lytic phenotype of osteosarcoma and that this is mediated via transcriptional repression of IL-1α. ^

Reconnaissance survey of Galveston Bay sediments for selective nonresidual trace metals

The nonresidual concentrations of five trace metals were determined for 322 sediments that were the product of a systematic sampling program of the entire Galveston Bay system. The nonresidual component of the trace metal concentration (e.g. that fraction of the metals that can be relatively easily removed from the sediments without complete destruction of the sediment particle) was considered to be more indicative of the anthropogenic metal pollution that has impacted the Galveston Bay ecosystem.^ For spatial analysis of the metal concentrations, the Galveston Bay system was divided into nine bay-areas, based on easily definable geological and geographical characteristics. Isopleth mapping analyses of these metal concentrations indicated a direct relationship with the $<$63$\mu$m fraction of the sediment (%FINE) in all of the bay areas. Covariate regression analyses indicated that position of the sediment within the Galveston Bay system (e.g. bay-area) was a better predictor of metal concentration than %FINE. Analysis of variance of the metals versus the bay-areas indicated that the five metals maintained a relatively constant order and magnitude of concentration for all the bay-areas.^ The major shipping channels of the Galveston Bay system, with their associated vessels and transported materials, are a likely source of metal pollution. However, these channels were not depositional corridors of high metal concentration. All metal concentration highs were found to be located away from the channels and associated with %FINE highs in the deeper portions of the bay-areas.^ Disturbance of the sediments, by the proposed widening and deepening of these channels, is not predicted to remobilize the trace metals. A more likely adverse effect on the health of the Galveston Bay ecosystem would come from the increase in turbidity of the water due to the dredging and in an extension of the salt water wedge farther north into the bay system. ^