The human gamma-globin TATA and CACCC elements have key, distinct roles in suppressing beta-globin gene expression in embryonic/fetal development.

Thanh Giang Sargent,Joyce A Lloyd

doi:10.1074/jbc.m103073200

Thanh Giang Sargent, Joyce A Lloyd

Open Access

https://doi.org/10.1074/jbc.m103073200

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Abstract

The competition model of globin gene regulation states that the gamma-globin gene precludes expression of the beta-globin gene in early development by competing for the enhancing activity of the locus control region. The gamma-globin gene with a -161 promoter is sufficient for suppressing beta-globin gene expression, and the gamma-globin TATA and CACCC elements are necessary for this effect. In this work, stable transfection and transgenic mouse assays have been performed with constructs containing HS3 and HS2 from the locus control region, the gamma-globin gene with promoter mutation(s), and the beta-globin gene. The data indicate that the gamma-globin TATA and CACCC elements together have at least an additive effect on the beta/gamma-globin mRNA ratio in early erythroid cells, suggesting that the elements work coordinately to suppress beta-globin gene expression. The TATA and CACCC are the major gamma-globin promoter elements responsible for this effect. Transgenic mouse experiments indicate that the gamma-globin TATA element plays a role in gamma-globin expression and beta-globin suppression in the embryo and fetus; in contrast, the CACCC element has a stage-specific effect in the fetus. The results suggest that, as is true for the erythroid Krüppel-like factor (EKLF) and the beta-globin promoter CACCC, a protein(s) binds to the gamma-globin CACCC element to coordinate stage-specific gene expression.

Highlights

The major human ␤-like globin genes are the embryonic ⑀-globin, the two fetal ␥-globin, and the adult ␤-globin genes
Using stable transfection assays of constructs containing HS3, HS2, and the ␥- and ␤-globin genes in human erythroleukemia (HEL) and K562 cells, we have shown that the ␥-globin CACCC and TATA elements, but not the stage-selector element, are important in suppressing ␤-globin expression in erythroid cells with an early developmental program [25]
The TATA and CACCC Elements Are the Major Elements in the ␥-Globin Promoter Involved in Competitive Inhibition—We have previously shown that the ␥-globin TATA and CACCC elements, but not the stage-selector element, are important in competitive inhibition of ␤-globin gene expression using constructs containing HS3 and HS2 from the locus control region (LCR) in stable transfections of HEL cells [25], which express the ⑀- and ␥- but not the ␤-globin genes

Summary

Introduction

The major human ␤-like globin genes are the embryonic ⑀-globin, the two fetal ␥-globin, and the adult ␤-globin genes (see Fig. 1A). Competition with the ␥-globin gene for the enhancing activity of the LCR, appears to be at least one mechanism by which ␤-globin expression is inhibited in early development Further support for this competition model comes from experiments in which in situ hybridization of nascent globin transcripts demonstrate that only one ␤-like globin gene is generally transcribed at a time at each ␤-globin locus, suggesting that the genes are competing for a shared enhancer [16, 17]. Using stable transfection assays of constructs containing HS3, HS2, and the ␥- and ␤-globin genes in human erythroleukemia (HEL) and K562 cells, we have shown that the ␥-globin CACCC and TATA elements, but not the stage-selector element, are important in suppressing ␤-globin expression in erythroid cells with an early developmental program [25]

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