Transcriptional repression of c-Myb and GATA-2 is involved in the effects of C/EBPα in p210 BCR/ABL-expressing cells

Levels of C/EBPα are low in myeloid blast crisis (BC) of chronic myelogenous leukemia (CML) and its expression in p210BCR/ABL-expressing hematopoietic cells induces granulocytic differentiation, inhibits proliferation and suppresses leukemogenesis. To assess the mechanisms involved in these effects, C/EBPα targets were identified by microarray analyses. Upon C/EBPα activation, expression of c-Myb and GATA-2 was repressed in 32D-BCR/ABL, K562 and CML-BC primary cells but only c-Myb levels decreased slightly in CD34+ normal progenitors. The role of these two genes for the biological effects of C/EBPα was assessed by perturbing their expression in K562 cells. Expression of c-Myb blocked the proliferation inhibition and differentiation-inducing effects of C/EBPα while c-Myb siRNA treatment enhanced C/EBPα-mediated proliferation inhibition and induced changes in gene expression indicative of monocytic differentiation. GATA-2 expression suppressed the proliferation inhibitory effect of C/EBPα but blocked in part the effect on differentiation; GATA-2 siRNA treatment had no effects on C/EBPα induction of differentiation but inhibited proliferation of K562 cells, alone or upon C/EBPα activation. In summary, the effects of C/EBPα in p210BCR/ABL -expressing cells depend, in part, on transcriptional repression of c-Myb and GATA-2. Since perturbation of c-Myb and GATA-2 expression has non identical consequences for proliferation and differentiation of K562 cells, the effects of C/EBPα appear to involve different transcription-regulated targets. 48 samples total. 4-HT-treated 32D-BCR/ABL cells transduced with the MigRI empty vector, MigRI WT C/EBPα-ER , MigRI K298E C/EBPα-ER (a DNA binding-deficient mutant) or MigRI-delta(177-191) C/EBPα-ER (a mutant deficient in CDK2/CDK4 interaction). Total RNA was extracted at 0, 6, 9 and 12h post-4-HT treatment in triplicate and hybridized onto the Affymetrix MOE430 _2 array.