Globin gene switching may be mediated by proteins expressed during different 
stages of development. Their identification may clarify the mechanisms of the 
conversion from fetal to adult globin production and lead to new approaches to 
reversing or retarding the gamma- to beta-globin gene switch. To explore this 
hypothesis, K562 erythroleukemia cells were induced to differentiate with 1.25, 
2.5, and 5 mM sodium butyrate and gene expression was studied after 24, 48, and 
72 h. Erythroid differentiation was verified by benzidine staining and by 
measuring the activity of a transduced A gamma-globin gene promoter linked to a 
luciferase reporter gene. Using differential display polymerase chain reaction 
(PCR), total mRNA extracted from induced cells at each time point of induction 
was reverse transcribed in the presence of A, G, and C anchored primers and 16 
arbitrary primers, calculated to amplify approximately 50% of expressed genes. 
Amplified mRNAs from induced and uninduced cells were separated in 
polyacrylamide gels and compared. More than 110 cDNA fragments which appeared to 
represent either up- or downregulated mRNA species in induced K562 cells were 
identified. Sixty-four of these fragments had more than 95% homology to known 
GenBank sequences. Seventeen fragments with characteristics of transcription 
factors were cloned. These include differentiation-related gene-1 (drg-1), PAX 
3/forkhead transcription factor, HZF2 which is a Kruppel-related zinc finger 
protein, three helix-loop-helix proteins (heir-1, Id3, and GOS8), alpha-NAC 
transcriptional coactivator, LIM domain protein, and trophoblast hypoxia 
regulating factor. Differential expression of all 17 fragments over 72 h was 
confirmed by reverse Northern dot blot analysis, semiquantitative PCR using 
nested primers, and Northern analysis. Erythroid maturation in induced K562 
cells is associated with differential expression of numerous genes. Some encode 
transcription factors that could effect the initiation of HbF synthesis. Almost 
half of the differentially expressed clones contained cDNAs of unidentified open 
reading frames and these are the object of continued study.