Positive regulation of additional sex comb-like 1 gene expression by the pluripotency factor SOX2

Additional sex comb-like 1 (ASXL1) has been suggested to be an enhancer of trithorax and polycomb proteins, and functions as a dual co-regulator of retinoid acid (RA) signaling. However, the mechanism by which ASXL1 gene expression is regulated remains unresolved. Concomitant downregulation of both SOX2 and ASXL1 during the RA-induced differentiation of P19 cells prompted us to investigate the role of SOX2 in the regulation of ASXL1. Knockdown of SOX2 in SOX2-rich NT2 cells resulted in the reduction of ASXL1 expression, whereas SOX2 overexpression in SOX2-deficient H1299 cells increased ASXL1 expression. Using a cloned ASXL1-luciferase reporter, we demonstrated that SOX2 directly transactivates the ASXL1 promoter. Serial deletion and mutation studies mapped the SOX2 response element region in the ASXL1 promoter to -1600 to -1400 bp. We showed by chromatin immunoprecipitation assay that SOX2 directly binds to the ASXL1 promoter region. Finally, formation of embryonic bodies by ASXL1-depleted murine E14TG2a embryonic stem cells was significantly impaired, similar to SOX2-knockdown cells. From these results, we suggest that ASXL1 may be a direct target of SOX2 and may play a role in maintaining the pluripotency of stem cells.