FKLF, a Novel Krüppel-Like Factor That Activates Human Embryonic and Fetal β-Like Globin Genes

Abstract

A cDNA encoding a novel Krüppel-type zinc finger protein, FKLF, was cloned from fetal globin-expressing human fetal erythroid cells. The deduced polypeptide sequence composed of 512 amino acids revealed that, like Sp1 and EKLF, FKLF has three contiguous zinc fingers at the near carboxyl-terminal end. A long amino-terminal domain is characterized by the presence of two acidic and two proline-rich regions. Reverse transcription (RT)-PCR assays using various cell lines demonstrated that the FKLF mRNA is expressed predominantly in erythroid cells. FKLF message is detectable by RT-PCR in fetal liver but not in adult bone marrow cells. As predicted from its structural features, FKLF is a transcriptional activator. In luciferase assays FKLF activated the γ- and ɛ-globin gene promoters, and, to a much lower degree, the β-globin promoter. Studies of HS2-γ gene reporter constructs carrying CACCC box deletions revealed that the CACCC box sequence of the γ gene promoter mediates the activation of the γ gene by FKLF. Other erythroid promoters (GATA-1, glycophorin B, ferrochelatase, porphobilinogen deaminase, and 5-aminolevulinate synthase) containing CACCC elements or GC-rich potential Sp1-binding sites were activated minimally, if at all, by FKLF, indicating that FKLF is not a general activator of genes carrying the CACCC motifs. Transfection of K562 cells with FKLF cDNA enhanced the expression of the endogenous ɛ- and γ-globin genes, suggesting an in vivo role of FKLF in fetal and embryonic globin gene expression. Our results indicate that the protein potentially encoded by the FKLF cDNA acts as a transcriptional activator of embryonic and fetal β-like globin genes.

ACKNOWLEDGMENTS

This study was supported by grants from the National Institute of Diabetes Digestive and Kidney Diseases and the National Heart, Lung, and Blood Institute, National Institutes of Health.