Genomic Organization of ht eGene for Human Mig Chemokine

Lee, Hwang Ho; Park, Kang Seo

Abstract

"Mig is a gamma interferon-inducible T cell chemoattractant that is a member of the chemokine family of cytokines. In order to gain a better understanding of the molecular mechanisms that regulate expression of the Mig gene, we have characterized the Mig gene and compared its structure and regulatory sequences with that of its ciosest IP10 gene. The genomic organization of the Mig gene reveals three introns that interrupt the transcribed sequence into four functional domains with a single ""CAT""- and ""TATA""-like structure. Primer extension analysis was used to identify the transcriptional initiation site that is located 50 bp upstream to the methionine codon that begins the long open reading frame. Comparison of the intron-exon structure of this gene to the gene for IP10 establishes that both genes are interrupted in precisely the same positions within homologous codons. The similarity of the intron-exon structure of the Mig and IP10 genes further support the hypothesis that Mig and IP10 genes have evolved from a common ancestral gene by gene duplication. The 5'-flanking region of Mig gene shows no overall sequence similarity with that from its closest IP10 gene whose production is also affected by gamma interferon. However, there are regions including a sequence with similarity to the NFxB binding site, AP-1 binding site, and ISRE. The r-RF-1 binding site is well conserved from -204 to -194 from the transcription start site in the Mig gene. Given the importance of IFN-r for effective immunity in tuberculosis and induction of Mig and IP10 genes in macrophages by IFN-r, we demonstrated induction of the genes Mig and IP10 with different message levels in the THP-1 human monocytic cell lines stimulated with whole M. tuberculosis. Despite the very similarity in genomic organization and the overlap in biological activities between MIG and IP10, our data described herein further support the suggestion that these chemokines rnay role nonredundantly in vivo. Moreover, our studies done on the Mig gene should provide the structural framework for future studies and begin to dissect cis-acting DNA sequences that are critical for gene regulation mediated by cell surface receptors."