Expression of the transcriptional repressor Gfi-1 is regulated by C/EBPα and is involved in its proliferation and colony formation inhibitory effects in p210BCR/ABL-expressing cells

摘要

Ectopic expression of C/EBPα in p210BCR/ABL-expressing cells induces granulocytic differentiation, inhibits proliferation and suppresses leukemogenesis.To dissect the molecular mechanisms underlying these biological effects, C/EBPα-regulated genes were identified by microarray analysis in 32D-p210BCR/ABL cells. One of the genes whose expression was activated by C/EBPα in a DNA binding-dependent manner in BCR/ABL-expressing cells is the transcriptional repressor Gfi-1. We show here that C/EBPα interacts with a functional C/EBP binding site in the Gfi-1 5′ flanking region and enhances the promoter activity of Gfi-1. Moreover, in K562 cells, RNAi-mediated downregulation of Gfi-1 expression partially rescued the proliferation inhibitory but not the differentiation inducing effect of C/EBPα. Ectopic expression of wild type Gfi-1 but not of a transcriptional repressor mutant (Gfi-1P2A) inhibited proliferation and markedly suppressed colony formation but did not induce granulocytic differentiation of BCR/ABL-expressing cells. By contrast, Gfi-1 shRNA-tranduced CD34+ CML cells were markedly more clonogenic than the scramble-transduced counterpart.Together, these studies indicate that Gfi-1 is a direct target of C/EBPα required for its proliferation and survival inhibitory effects in BCR/ABL-expressing cells.