p27^Kip1 protein accumulation with no change in transcription in response to RARα-mediated granulocytic differentiation. The regulation of p27^Kip1 during RARα-induced granulocytic differentiation was analyzed in the MPRO cells. (A) p27^Kip1 transcript does not increase following RARα-induced granulocytic differentiation (AGN195183; 10^–6 M). Total RNA (10 μg) was separated on a denaturing gel and transferred to a nylon membrane that was then probed for p27^Kip1 and GAPDH. (B) p27^Kip1 is not a direct transcriptional target of RARα. MPRO cells were treated with AGN195183, AGN195183, and cycloheximide (CHX; 10 μg/mL) or CHX alone for the indicated time points then RNA prepared and analyzed for p27^Kip1 expression. (C) A significant accumulation of p27^Kip1 protein occurs following differentiation through RARα. Cells were treated with AGN19183 and prepared as described, then probed for expression of p27^Kip1 protein and α-tubulin as loading control.