Hypermethylated PODN represses the progression of osteosarcoma by inactivating the TGF-β/Smad2/3 pathway

Background: PODN is reported to be an promising biomarker for prognosis of osteosarcoma (OS), while the specific function of PODN has not been explored in OS. This study is designed to explore the function and underlying mechanism of PODN in OS. Methods: The mRNA expression of PODN was determined using qRT-PCR. Protein levels of PODN, DNMT1, DNMT3A, DNMT3B, TGF-beta 1, Smad2/3 and p-Smad2/3 were detected using western blot. The methylation of PODN was determined with methylation-specific PCR. Moreover, CCK-8 assay and colony formation assay were used for assessing the proliferation of OS cells. Transwell assay was used to evaluate migration and invasion abilities of OS cells. Immunohistochemical staining was performed to determine the protein expression of Ki67 and PODN in tumor tissues. For constructing a xenograft tumor model, MG-63 cells were introduced into the right side of the mouse back via subcutaneous injection. Results: PODN was lowly expressed and was hypermethylated in OS tissues and cells. PODN overexpression prevented OS cells from proliferating, migrating and invading, and inhibited tumorigenesis in xenograft mice. After PODN overexpression, protein levels of TGF-beta 1 and p-Smad2/3 were decreased in OS cells. Meantime, the suppressive effects of PODN overexpression on proliferation, migration and invasion of OS cells as well as mouse tumorigenesis were partly counteracted by TGF-beta 1 overexpression. Conclusions: PODN overexpression inactivated the TGF-beta/Smad2/3 pathway to suppress OS development in vitro and in vivo.