The biological effects of C/EBPalpha in K562 cells depend on the potency of the N-terminal regulatory region, not on specificity of the DNA binding domain.

The transcription factor C/EBP\u3b1 is more potent than C/EBP\u3b2 in inducing granulocitic differentiation and inhibiting BCR/ABL-expressing cells. We took a \u201cdomain swapping\u201d approach to assess biological effects, modulation of gene expression, and binding to C/EBP\u3b1-regulated promoters by wild-type and chimeric C/EBP\u3b1/C/EBP\u3b2 proteins. Wild-type and N-C/EBP\u3b1+ C/EBP\u3b2-DBD induced transcription of the granulocyte-colony stimulating factor receptor (G-CSFR) gene, promoted differentiation, and suppressed proliferation of K562 cells vigorously; instead, wild-type C/EBP\u3b2 and N-C/EBP\u3b2+C/EBP\u3b1-DBD had modest effects, although they bound the G-CSFR promoter like wild-type C/EBP\u3b1 and N-C/EBP\u3b1+C/EBP\u3b2-DBD. Chimeric proteins consisting of the TAD of VP16 and the DBD of C/EBP\u3b1 or C/EBP\u3b2 inhibited proliferation and induced differentiation of K562 cells as effectively as wild-type C/EBP\u3b1. Gene expression profiles induced by C/EBP\u3b1 resembled those modulated by N-C/EBP\u3b1+C/EBP\u3b2-DBD, whereas C/EBP\u3b2 induced a pattern similar to that of N-C/EBP\u3b2+C/EBP\u3b1-DBD. C/EBP\u3b1 activation induced changes in the expression of more cell cycle- and apoptosis-related genes than the other proteins and enhanced Imatinib-induced apoptosis of K562 cells. Expression of FOXO3a, a novel C/EBP\u3b1-regulated gene, was required for apoptosis but not for differentiation induction or proliferation inhibition of K562 cells