Realgar transforming solution-induced differentiation of NB4 cell by the degradation of PML/RARα partially through the ubiquitin–proteasome pathway

PML/retinoic acid receptor alpha (RARα), as a hallmark of acute promyeloid leukemia (APL), is directly related to the outcome of clinical APL remedy. It is reported that arsenicals can effectively degrade PML/RARα, such as arsenic trioxide and realgar. However, the high toxicity or insolubility have hampered their clinical applications. Realgar transforming solution (RTS) was produced from realgar by bioleaching process in our lab. Previous studies demonstrated that RTS had a significant anti-cancer ability on chronic myeloid leukemia through oncoprotein degradation. The capacity of RTS on treating APL is what is focused on in this study. The results showed that RTS had a noticeable sensitivity in NB4 cell, and RTS remarkably down-regulated PML/RARα expression and induced cell differentiation. Further, RTS could accumulate PML/RARα into the nuclear bodies and then execute degradation, which could be reversed by proteasome inhibitor MG132. The results also exhibited that the reduction of RTS-induced PML/RARα expression accompanied by the elevation of ubiquitin and SUMO-1 protein expression. Finally, PML and SUMO-1 had been demonstrated to be co-localized after RTS treatment by immunofluorescence co-localization assay and immunoprecipitation assay. In conclusion, these results suggested that RTS-induced cell differentiation may attribute to the PML/RARα degradation partially through the ubiquitin–proteasome pathway.