Diminished binding of hypophospharylated RARα to RARE leads to transactivation of RA-target genes in RA-sensitive and RA-resistant cells. A) ChIP analysis of S77A-hp21RARE or S77A-hβRARE interaction in HL60 and HL60R cells. C-terminal anti-RARα antibodies that did not recognize the endogenous mutant RARα in HL60R cells were used for ChIP assay. α-RARα, c-terminal anti-RARα antibodies. B, C) Densitometry quantification of RARα-bound DNA in HL60 cells (B) and HL60R cells (C) in panel A. Data represent 3 independent experiments with similar results, normalized against levels of input DNA. D) RT-PCR analysis of RARβ and p21 expression in HL60 and HL60R cells. E, F) Densitometry quantification of mRNA levels in HL60 cells (E; *P<0.005, **P=0.000) and HL60R cells (F; *P<0.05 vs. vector or RARα) in panel D. Data represent 3 independent experiments with similar results, normalized against actin expression.