EPO induces a transient reduction in the level of GATA-1 mRNA followed by downregulation of EPOR mRNA in UT-7 cells. The effect of EPO on the expression of both EPOR, GATA-1, and GATA-2 mRNAs in UT-7 cells was examined by RNA blot hybridization analysis. Logarithmically growing cells were deprived of growth factors for 16 hours in IMDM containing 10% FBS and then stimulated with 10U EPO/mL (time 0). (A) Northern blot analysis. The total cellular RNA was isolated from the cells at the time points indicated. The RNAs (20 μg/lane) were electrophoresed on a formaldehyde/agarose gel. RNAs were then transferred to a nylon membrane and hybridized to ³²P-labeled probes. The amount of RNA loaded in each lane was assessed by the intensity of the 28S ribosomal RNA bands. (B) Densitometric analysis of the data presented in (A). The amounts of the mRNAs were quantitated and normalized to 28S ribosomal RNA levels.