ΔNp63α enhances the oncogenic phenotype of osteosarcoma cells by inducing the expression of GLI2.

BACKGROUND: ΔNp63, a splice variant of p63, is overexpressed and exhibits oncogenic activity in many cancers including pancreatic and breast cancer and promotes cell survival by inhibiting apoptosis. Despite its role in tumorigenesis, mechanistic activity of ΔNp63 mediated oncogenic function in osteosarcoma is poorly understood. METHODS: The expression levels of p63 isoforms in osteosarcoma cell lines were identified using quantitative techniques. Expression profiling using microarray, siRNA mediated loss-of-function, and chromatin immunoprecipitation assays were employed to identify novel ΔNp63α targets in p63-null osteosarcoma SaOS-2 cells that were engineered to express ΔNp63α. The phenotype of SaOS-2-ΔNp63α cells was assessed using wound-healing, colony formation, and proliferation assays. RESULTS: The comparative expression analyses identified ΔNp63α as the predominant p63 isoform expressed by invasive OS cell lines. Phenotypic analyses of SaOS-2-ΔNp63α cells in vitro indicate that ΔNp63α imparted tumorigenic attributes upon tumor cells. Further, we show that in osteosarcoma cells ΔNp63α directly regulated the transcription factor GLI2, which is a component of the hedgehog signaling pathway, and that functional interactions between ΔNp63α and GLI2 confer oncogenic properties upon OS cells. CONCLUSIONS: Here, we report that GLI2 is the novel target gene of ΔNp63α and that ΔNp63α-GLI2 crosstalk in osteosarcoma cells is a necessary event in osteosarcoma progression. Defining the exact mechanisms involved in this interaction that mediate the pathogenesis of osteosarcoma promises to identify targets for drug therapy.

Primary stability and stiffness in ankle arthrodes-crossed screws versus anterior plating.

BACKGROUND: Ankle arthrodesis is commonly used for the treatment of osteoarthritis or failed arthroplasty. Screw fixation is the predominant technique to perform ankle arthrodesis. Due to a considerable frequency of failures research suggests the use of an anatomically shaped anterior double plate system as a reliable method for isolated tibiotalar arthrodesis. The purpose of the present biomechanical study was to compare two groups of ankle fusion constructs - three screw fixation and an anterior double plate system - in terms of primary stability and stiffness. METHODS: Six matched-pairs human cadaveric lower legs (Thiel fixated) were used in this study. One specimen from each pair was randomly assigned to be stabilized with the anterior double plate system and the other with the three-screw technique. The different arthrodesis methods were tested by dorsiflexing the foot until failure of the system, defined as rotation of the talus relative to the tibia in the sagittal plane. Experiments were performed on a universal materials testing machine. The force required to make arthrodesis fail was documented. For calculation of the stiffness, a linear regression was fitted to the force-displacement curve in the linear portion of the curve and its slope taken as the stiffness. RESULTS: For the anatomically shaped double-plate system a mean load of 967N was needed (range from 570N to 1400N) to make arthrodesis fail. The three-screw fixation method resisted a mean load of 190N (range from 100N to 280N) (p=0.005). In terms of stiffness a mean of 56N/mm (range from 35N/mm to 79N/mm) was achieved for the anatomically shaped double-plate system whereas a mean of 10N/mm (range from 6N/mm to 18N/mm) was achieved for the three-screw fixation method (p=0.004). CONCLUSIONS: Our biomechanical data demonstrates that the anterior double-plate system is significantly superior to the three-screw fixation technique for ankle arthrodesis in terms of primary stability and stiffness.