Hypoxia-inducible factor-1alpha induces Twist expression in tubular epithelial cells subjected to hypoxia, leading to epithelial-to-mesenchymal transition.
Epithelial-to-mesenchymal transition (EMT) induced by chronic hypoxia is one of the critical causes of renal fibrosis. Twist, a basic helix-loop-helix transcription factor, is believed to be important in promoting EMT. We found that the expression of Twist was increased in human tubule cell lines (HK-2 and HKC) grown under hypoxic conditions. This was accompanied by reduced expression of the epithelial markers E-cadherin and ZO-1 and enhanced expression of the mesenchymal markers vimentin and alpha-smooth muscle actin. When Twist was overexpressed in these cells it induced a mesenchymal phenotype, whereas its knockdown by short interfering RNA (siRNA) effectively reversed hypoxia-induced EMT. We showed that transfection with siRNA to hypoxia-inducible factor-1alpha (HIF-1alpha), another basic helix-loop-helix transcription factor, reduced Twist expression. Twist promoters contain HIF1-alpha-binding sites and transfection of reporter constructs using the promoter showed increased transcription in cells subjected to hypoxia. Electrophoretic mobility shift and chromatin immunoprecipitation assays identified the presence of a functional HIF-1alpha-binding site within the proximal Twist gene promoter. In an in vivo assay using the rat remnant kidney we found that both Twist and HIF-1alpha were overexpressed in tubular epithelial cells showing EMT. These studies suggest that HIF-1alpha induces Twist expression in hypoxic tubular cells and that this plays a role in EMT during renal fibrogenesis.
Sun
Shiren
S
Department of Nephrology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China.
Ning
Xiaoxuan
X
State Key Laboratory of Cancer Biology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China; Department of Geriatrics, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China.
Zhang
Yanqi
Y
State Key Laboratory of Cancer Biology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China.
Lu
Yuanyuan
Y
State Key Laboratory of Cancer Biology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China.
Nie
Yongzhan
Y
State Key Laboratory of Cancer Biology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China.
Han
Shuang
S
State Key Laboratory of Cancer Biology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China.
Liu
Lili
L
State Key Laboratory of Cancer Biology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China.
Du
Rui
R
State Key Laboratory of Cancer Biology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China.
Xia
Lin
L
State Key Laboratory of Cancer Biology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China.
He
Lijie
L
State Key Laboratory of Cancer Biology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China.
Fan
Daiming
D
State Key Laboratory of Cancer Biology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China. Electronic address: fandaim@fmmu.edu.cn.
D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004848:Epithelium / Q000473:pathology; D015870:Gene Expression; D006801:Humans; D000860:Hypoxia / Q000378:metabolism / Q000473:pathology; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D007684:Kidney Tubules / Q000378:metabolism* / Q000473:pathology*; D008297:Male; D008648:Mesoderm / Q000473:pathology; D010641:Phenotype; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D015533:Transcriptional Activation; D051879:Twist-Related Protein 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D034741:RNA, Small Interfering; D051879:Twist-Related Protein 1; D004247:DNA