ORIGINAL ARTICLES
Early growth response transcription factor EGR‐1 regulates Gαq gene in megakaryocytic cells

https://doi.org/10.1111/j.1538-7836.2006.02229.xGet rights and content
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Summary

Background:Gαq (Gene GNAQ) plays a major role in platelet signal transduction but little is known regarding its transcriptional regulation. Objectives:We studied Gαq promoter activity using luciferase reporter gene assays in human erythroleukemia (HEL) cells treated with phorbol 12‐myristate 13‐acetate (PMA) for 24 h to induce megakaryocytic transformation. Methods and results:PMA‐treated HEL cells showed enhanced Gαq expression. Reporter (luciferase) gene studies on 5′ upstream construct (up to −116 bp from ATG) revealed a negative regulatory site at −238/−202 and two positive sites at −203/−138 and −1116/−731. The positive regulatory region −203/−138 contained overlapping Sp1/AP‐2/EGR‐1 consensus sites. Gel shift studies on Gαq oligonucleotides 1 (−203/−175) and 2 (−174/−152) using HEL cell extracts demonstrated protein binding that was due to early growth response factor EGR‐1 at two sites. Mutations in either EGR‐1 site markedly decreased the gene activity, indicating functional relevance. Mutation of consensus E‐Box motif (−185/−180) had no effect. Reduction in the expression of endogenous EGR‐1 with antisense oligonucleotide to EGR‐1 inhibited PMA‐induced Gαq transcription. Correspondingly, Egr‐1 deficient mouse platelets also showed ∼50% reduction in the Gαq expression relative to wild‐type platelets. Conclusions:These studies suggest that Gαq gene is regulated during PMA‐induced megakaryocytic differentiation by EGR‐1, an early growth response transcription factor that regulates a wide array of genes and plays a major role in diverse activities, including cell proliferation, differentiation and apoptosis, and in vascular response to injury and atherosclerosis.

Keywords

EGR‐1
Gαq
HEL cells
megakaryocytic differentiation
transcriptional regulation

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