C/EBPαp30 Plays Transcriptional Regulatory Roles Distinct From C/EBPαp42

CCAAT/enhancer binding proteinαis a transcriptional factor that inhibits cell proliferation with two peptides, C/EBPαp30 and C/EBPαp42. Expression profiling revealed that C/EBPαp30 specifically inhibited a unique set of genes, including MPP11, p84N5 and SMYD2, which were not affected by C/EBPαp42 in both QSG-7701 and QGY-7703 hepatoma cells. Semi-quantitative RT-PCR independently confirmed the results. Chromatin immunoprecipitation showed that C/EBPαp30 bound to the promoters of these genes more strongly than C/EBPαp42. In clinical hepatoma samples, all three C/EBPαp30-specific genes were up-regulated and C/EBPαwas down-regulated,. However, MPP11, p84N5 and SMYD2 genes might not directly be involved in the C/EBPαp30-mideated growth inhibition. Our data suggested that C/EBPαp30 had a distinct function and was more than a negative dominant regulator of C/EBPαp42.