A novel isoform of microphthalmia-associated transcription factor inhibits IL-8 gene expression in human cervical stromal cells.
Cervical ripening during pregnancy is a profound change in cervix structure and function characterized by increases in the proinflammatory cytokine IL-8 and dissolution of the cervical extracellular matrix. Relatively little is known about the molecular mechanisms that underlie these events. Here, we report identification of a novel isoform of micropthalmia-associated transcription factor in human cervical stromal cells (MiTF-CX) that is down-regulated 12-fold during cervical ripening and that represses expression of IL-8. Ectopic expression of MiTF-CX in human cervical stromal cells resulted in substantial suppression of endogenous IL-8 mRNA and protein expression, whereas expression of dominant negative MiTF-CX mutants with impaired DNA binding resulted in dramatic increases in IL-8 production. Gel shift, reporter gene, and chromatin immunoprecipitation assays revealed one strong binding site (E-box (-397) CACATG(-391)) in the human IL-8 promoter that was crucial for mediating transcriptional repression by MiTF-CX. Moreover, we show that MiTF-CX expression in the cervix was itself positively autoregulated via two E-box motifs within a 2.1-kb promoter fragment. We therefore propose that maintenance of cervical competency during pregnancy is an active process maintained through suppression of IL-8 by the transcription factor MiTF-CX. During cervical ripening, loss of MiTF-CX would result in significant up-regulation of IL-8 mRNA and protein synthesis, thereby leading to recruitment and activation of leukocytes within the cervix and dissolution of the extracellular matrix.
Li
Xiang-Hong
XH
Division of Reproductive Endocrinology and Urogynecology, Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9032, USA.
Kishore
A Hari
AH
Dao
Doan
D
Zheng
Weiming
W
Roman
Christopher A
CA
Word
R Ann
RA
D000818:Animals; D002478:Cells, Cultured; D002584:Cervix Uteri / Q000166:cytology*; D047369:Chromatin Immunoprecipitation; D024202:Electrophoretic Mobility Shift Assay; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism*; D051379:Mice; D051739:Microphthalmia-Associated Transcription Factor / Q000235:genetics / Q000378:metabolism*; D036801:Parturition / Q000235:genetics; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D017154:Stromal Cells / Q000378:metabolism*
D016209:Interleukin-8; D051739:Microphthalmia-Associated Transcription Factor; D020033:Protein Isoforms