Abstract LB-172: Role of post-translational modification of the RUNX2 transcription factor in osteosarcoma

Abstract

Abstract Background-Several transcription factors or co-factors have recently been reported to be methylated at certain arginine residues, a post-translational modification mediated by two classes of protein arginine methyltransferases (PRMT). Moreover, some PRMTs have been shown to be key regulators of mesenchymal differentiation, and one of the PRMTs is involved in the epigenetic programming of early embryo development. RUNX2 is major transcription factor in osteoblast differentiation but little is known about its activity or function in osteosarcoma (OS). RUNX1, another member of RUNT family, is known to methylated at R206/R210, within the Runt domain, a region that has considerable homology with RUNX2. Here, we examined the possible role of PRMTs in OS in relation to the post-translational modification of RUNX2 and its possible impact on cell proliferation and differentiation. Method-We generated arginine methylation-specific antibodies to RUNX2. The specificity of this antibody was confirmed by detecting immunoprecipitated RUNX2 from Saos2 cells by Western blot. We also confirmed the expression of RUNX2 and arginine methylated RUNX2 in Saos2 cell by immunofluorescence. We also examined the frequency of arginine methylation of RUNX2 in OS patient samples, compared to total RUNX2, by Western blot. Finally, we examined the influence of arginine methylation on the transcriptional activity of RUNX2 by luciferase assay using osteocalcin promoter plasmid. Results-We found that PRMTs can methylate the arginine residue in the Runt domain of RUNX2. This arginine methylation of RUNX2 alters its transcriptional activity at the osteocalcin promoter. Immunofluorescence with arginine methylation-specific antibody showed weak nuclear positivity in the SAOS-2 cell line. Patient tumor samples also show the expression of arginine methylated RUNX2, as well as total RUNX2. Conclusion- Our results confirm that arginine methylation of RUNX2 affects its function as a transcription factor. Further study of the possible role of arginine methylation of RUNX2 in regulating its effect on osteosarcoma proliferation and differentiation could be of translational interest, given the therapeutic potential of PRMT inhibitors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-172. doi:10.1158/1538-7445.AM2011-LB-172