CDDO increases the expression of p42/p30 CEBPA protein isoforms at a posttranscriptional level. (A) CEBPA protein expression after 24 hours in untreated, DMSO-treated, and CDDO-treated HL60 cells is shown by Western blotting using a polyclonal rabbit anti-CEBPA antibody that recognizes the C-terminal part of CEBPA (top panel). P42 and p30 designate the 2 prominent isoforms of CEBPA, and beta-tubulin served as a loading control. (B) Time course of HL60 cells cultured in the presence or absence of 0.01% DMSO or 1 μM CDDO. Protein lysates were obtained at the indicated time points, and Western blotting for CEBPA was performed. Beta-tubulin served as a loading control. (C) The ratio of p42/p30 as determined by densitometry is shown in the panel on the right. *P < .05 versus untreated control. (D) HL60 cells were cultured for 24 hours without treatment or treated with 0.01% DMSO-treated or CDDO at the indicated doses, RNA was extracted, and Northern blotting performed. CEBPA mRNA expression was detected using a probe against the 3′UTR of human CEBPA. GAPDH mRNA served as a loading control. (E) Real-time RT-PCR analysis of RNA extracted from HL60 cells that were treated or not treated with different doses of CDDO for 24 hours (left panel) or 0.8 μM CDDO for different periods of time (right panel), as indicated. Human CEBPA mRNA expression is shown as the percentage of 18S RNA.