The HMC-1 cell line represents the phenotype of immature mast cells. The HIF1A gene product HIF-1 alpha plays key roles in maintaining oxygen homeostasis in eukaryotic organisms and is involved in many processes, including immune response and hematopoiesis. In this study we investigated HIF1A expression in HMC-1 immature hematopoietic cells and CD34+ hematopoietic progenitors HMC-1 cells exhibited exceptionally low levels of HIF1A expression compared to other cell lines as determined by real-time PCR. and multipotent CD34+ hematopoietic progenitors in bone marrow exhibited significantly lower levels of HIF1A mRNA compared to mature blood cells in peripheral blood. We searched for the mechanisms responsible for suppression of HIF1A expression in HMC-1 cells and obtained evidence for a DNA methylation-dependent process. In vitro methylation of the HIF1A promoter resulted in a decrease in its transcriptional activity and the level of DNA methylation in the HIF1A promoter region in analyzed cell lines was negatively correlated with HIF1A expression Furthermore, the DNA demethylating agent 5'-azacytidine increased HIF1A expression, and MeCP2 protein was preferentially associated with the HIF1A promoter In vivo. In conclusion, we report that the HIF1A gene in HMC-1 immature hematopoietic cells IS Suppressed by a process dependent oil DNA methylation, and we present evidence indicating downregulation of HIF1A expression in multipotent CD34+ hematopoietic progenitors. (C) 2009 Elsevier Inc. All rights reserved.