Histone deacetylase inhibitor NaB relieves repressing activities of RARα chimeric proteins and synergizes with ATRA in differentiation of APL cells. (A) Transcriptional activities of the wild-type and mutant RARs assayed in 293T cells. Cotransfections were performed with RARE2-tkluc reporter plasmid (200 ng), 50 ng of CMV-lacZ control, and a pSG5 expression vectors for the indicated proteins (50 ng each). ATRA (10−6 mol/L) was added alone or in combination with histone deacetylase inhibitor NaB (1 mmol/L). NaB synergizes with ATRA in alleviating the transcriptional inhibition of RARE2-tkluc reporter by PML-RARα and PLZF-RARα. ATRA alone, or together with NaB, had a considerably lower effect on transcriptional activation by PML-RARα, but not by the wild-type RARα (not shown), when an equal amount of the wild-type PLZF expression vector was cotransfected. All cell transfections were performed in 24-well plates (∼105 cells per well per transfection) using calcium phosphate precipitation. (B) NaB potentiated differentiating effects of ATRA on NB-4 cells. The Y-axis indicates the percentage of NBT-positive cells assayed 2 and 3 days after treatment with 500 nmol/L ATRA, no treatment, or treatment with 500 nmol/L ATRA followed by 1 mmol/L of NaB.
