Sirt1 modulates H3 phosphorylation and facilitates osteosarcoma cell autophagy

Abnormal histone modifications have been recognized as an important contributing factor to the initiation and progression of osteosarcoma. Sirtuin 1 (Sirt1) up-regulation has been discovered in osteosarcoma cells. This study tested the influence of Sirt1 on histone H3 phosphorylation at threonine 3 (H3^T3ph) in osteosarcoma cells, along with Sirt1-H3^T3ph axis on osteosarcoma cell autophagy. Plasmids or si-RNAs transfection was carried out to alter Sirt1 or H3^T3ph expressions. Co-immunoprecipitation analysis and GST pull-down assay were done to probe the relationship between Sirt1 and H3^T3ph. Phosphoryltransferase activity of Sirt1 was tested by in vitro kinase activity assay. Cell autophagy was measured by a number of autophagosome, conversion of LC3-I to LC3-II, degradation of long-lived protein and ATG protein expressions. We found that Sirt1 directly interacted with H3 and phosphorylate H3^T3 at threonine 3 in osteosarcoma cells. Moreover, Sirt1 facilitated osteosarcoma cell autophagy under starvation condition. H3^T3ph took part in the Sirt1-facilitated osteosarcoma cell autophagy under starvation condition. Besides, Sirt1-H3^T3ph axis facilitated osteosarcoma cell autophagy might be achieved through transcriptional activation of ATG genes. Sirt1 promoted osteosarcoma initiation and progression might be via phosphorylate H3^T3 and then facilitate osteosarcoma cell autophagy through activating ATG genes transcription under starvation condition.