title: Physical and functional interactions between homeodomain NKX2.1 and winged helix/forkhead FOXA1 in lung epithelial cells.
abstract: NKX2.1 is a homeodomain transcription factor that controls development of the brain, lung, and thyroid. In the lung, Nkx2.1 is expressed in a proximo-distal gradient and activates specific genes in phenotypically distinct epithelial cells located along this axis. The mechanisms by which NKX2.1 controls its target genes may involve interactions with other transcription factors. We examined whether NKX2.1 interacts with members of the winged-helix/forkhead family of FOXA transcription factors to regulate two spatially and cell type-specific genes, SpC and Ccsp. The results show that NKX2.1 interacts physically and functionally with FOXA1. The nature of the interaction is inhibitory and occurs through the NKX2.1 homeodomain in a DNA-independent manner. On SpC, which lacks a FOXA1 binding site, FOXA1 attenuates NKX2.1-dependent transcription. Inhibition of FOXA1 by small interfering RNA increased SpC mRNA, demonstrating the in vivo relevance of this finding. In contrast, FOXA1 and NKX2.1 additively activate transcription from Ccsp, which includes both NKX2.1 and FOXA1 binding sites. In electrophoretic mobility shift assays, the GST-FOXA1 fusion protein interferes with the formation of NKX2.1 transcriptional complexes by potentially masking the latter's homeodomain DNA binding function. These findings suggest a novel mode of selective gene regulation by proximo-distal gradient distribution of and functional interactions between forkhead and homeodomain transcription factors.
authors.affiliation: Department of Pediatrics, University of Southern California Keck School of Medicine, Los Angeles, CA 90033, USA. minoo@usc.edu
authors.forename: Parviz
authors.initials: P
authors.lastname: Minoo
authors.forename: Lingyan
authors.initials: L
authors.lastname: Hu
authors.forename: Yiming
authors.initials: Y
authors.lastname: Xing
authors.forename: Nian Ling
authors.initials: NL
authors.lastname: Zhu
authors.forename: Hongyan
authors.initials: H
authors.lastname: Chen
authors.forename: Min
authors.initials: M
authors.lastname: Li
authors.forename: Zea
authors.initials: Z
authors.lastname: Borok
authors.forename: Changgong
authors.initials: C
authors.lastname: Li
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D002460:Cell Line; D004247:DNA / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D051541:Hepatocyte Nuclear Factor 3-alpha / Q000235:genetics / Q000378:metabolism*; D051542:Hepatocyte Nuclear Factor 3-beta / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008168:Lung / Q000378:metabolism*; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: C496500:Foxa1 protein, mouse; C496501:Foxa1 protein, rat; C496504:Foxa2 protein, rat; D051541:Hepatocyte Nuclear Factor 3-alpha; C000614414:Nkx2-1 protein, mouse; C000614416:Nkx2-1 protein, rat; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors; D051542:Hepatocyte Nuclear Factor 3-beta; D004247:DNA