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.