Functional interaction of transcriptional coactivator ASC-2 and C/EBP alpha in granulocyte differentiation of HL-60 promyelocytic cell

HL-60 promyelocytic eels were treated with retinoic acid (RA) to stimulate granulocyte differentiation. CCAAT/enhancer binding protein alpha (C/EBP al pha) is known to be the molecular switch during early hematopoietic develop mental events that direct cells to the granulocytic pathway. Here we show t hat the coactivator activating signal cointegrator-2 (ASC-2) plays an impor tant role in differentiation of HL-60 cells into granulocytes by mediating C/EBP alpha -induced gene transcription. The differentiation inducer RA inc reased mRNA and protein expression of ASC-S. The protein-protein interactio n of C/EBP alpha and ASC-2 was detected by coimmunoprecipitation during gra nulocyte differentiation. Subsequently, GST-pull-down assay revealed that t he N-terminal transactivation domain of C/EBPa could interact with ASC-2. T his functional interaction of ASC-2 with C/EBPa drove a synergistic enhance ment of C/EBP alpha -dependent transactivation and overexpression of the N- terminal C/EBP alpha protein in HL-60 cells inhibited ASC-2 responsiveness for C/EBP alpha activity in granulocyte differentiation, indicating C/EBP a lpha dependency of ASC-2 activity. Taken together, these results suggest th at the differentiation-dependent expressed ASC-S protein physically and fun ctionally interacts with G/EBP alpha and increases its transactivation acti vity, regulating specific gene transcription for granulocyte differentiatio n. (C) 2001 Academic Press.