SMAR1 attenuates the stemness of osteosarcoma cells via through suppressing ABCG2 transcriptional activity

The promoting roles of the transcriptional regulator SMAR1 have been revealed in several tumors, such as colorectal and breast cancer, however, its roles in osteosarcoma (OS) progression are still confusing. Here, we find that SMAR1 expression is positively correlated with the overall survival of OS patients and negatively correlated with the expression of stemness markers by analyzing the online datasets. Through analyzing different Gene Expression Omnibus (GEO) datasets, SMAR1 is found to be lowly expressed in OS tissues relative to that in adjacent tissues. Functional experiments indicate that SMAR1 overexpression attenuates the stemness of OS cells, characterized as the decrease of stemness marker expression, sphere-formation ability and ALDH activity. Mechanistically, it is shown that SMAR1 increases the deacetylation level of the drug efflux pump ABCG2 via recruiting HDAC2 to the promoter of the gene coding ABCG2, and thus decreases ABCG2 transcriptional activity. Additionally, overexpression of ABCG2 rescues the inhibition of SMAR1 overexpression on the stemness of OS cells. Moreover, this SMAR1/ABCG2 axis positively regulates the chemotherapeutic sensitivity of OS cells. This work indicates that SMAR1 is a critical suppressor for OS progression through transcriptionally regulating ABCG2 expression.