Characterization of oligodendrocyte transcription factor 2 as a putative regulator of eosinophil-specific genes

Abstract

Eosinophils arise from hematopoietic CD34+ stem cells in the bone marrow through a network of cooperative and antagonistic interactions of transcription factors GATA-1, CCAAT enhancer-binding protein (C/EBP), and PU.1. Eosinophils are armed with abundant specific cytoplasmic granules with their structural packaging of cationic proteins, including major basic protein (MBP), and exert their effector functions largely by releasing these proteins. Although eosinophil lineage determination and regulation of eosinophil-specific genes are dictated by these transcription factors, whether additional factors exist and/or are required to regulate eosinophil development and expression eosinophil-specific genes is not known. In the present study, we screened and characterized a putative gene, called oligodendrocyte transcription factor 2, Olig2 that might regulate eosinophil development/differentiation using a microarray analysis and a battery of molecular biology technologies. Olig2 was upregulated during cord blood-derived eosinophil differentiation and also highly expressed in peripheral blood eosinophils. Ectopic expression of Olig2 dose-dependently repressed MBP promoter activity both in the presence and absence of C/EBP??, which is known to be a critical activator for eosinophil development and MBP transcription. However, neither Olig2 did interact with C/EBP?? nor bind to its putative binding sites, E-box, in the proximal MBP promoter. To find putative Olig2-binding sites in the proximal MBP promoter, we made a series of deletion constructs, and mapped a region between -92 and -137 of the promoter that is responsible for Olig2-mediated suppression of MBP transcription. Furthermore, introduction of Olig2 siRNA reversed the repressed effect of Olig2 as much as the effect by Olig2AQ, a dominant negative form of Olig2. Collectively, although these results do not provide a decisive evidence for the Olig2 as a regulator of eosinophil development, they ignite active investigation of Olig2…s role in eosinophil development/differentiation.