Auranofin promotes retinoic acid- or dihydroxyvitamin D ₃- mediated cell differentiation of promyelocytic leukaemia cells by increasing histone acetylation

Background and purpose: To investigate the molecular mechanism for the effect of auranofin on the induction of cell differentiation, the cellular events associated with differentiation were analysed in acute promyelocytic leukaemia (APL) cells. Experimental approach: The APL blasts from leukaemia patients and NB4 cells were cotreated with auroanofin and all-trans-retinoic acid (ATRA) at suboptimal concentration. The HL-60 cells were treated with auroanofin and a subeffective dose of 1α,25-dihydroxyvitamin D ₃ (1,25(OH) ₂ vit D ₃) in combination. The effect of auroanofin was investigated on histone acetylation at the promoter of differentiation-associated genes and expression of cell cycle regulators. Key results: Treatment with auroanofin and ATRA cooperatively induced granulocytic differentiation of fresh APL blasts isolated from patients and NB4 cells. The combined treatment also increased reorganization of nuclear PML bodies and histone acetylation at the promoter of the RARβ2 gene. Auroanofin also promoted monocytic differentiation of the HL-60 cells triggered by subeffective concentration of 1,25(OH) ₂ vit D ₃. The combined treatment of auroanofin and 1,25(OH) ₂ vit D ₃ stimulated histone acetylation at p21 promoters and increased the accumulation of cells in the G ₀/G ₁ phase. Consistent with this, the expressions of p21, p27 and PTEN were increased and the levels of cyclin A, Cdk2 and Cdk4 were decreased. Furthermore, the hypophosphorylated form of pRb was markedly increased in cotreated cells. Conclusions and implications: These findings indicate that auroanofin in combination with low doses of either ATRA or 1,25(OH) ₂ vit D ₃ promotes APL cell differentiation by enhancing histone acetylation and the expression of differentiation-associated genes.