Overexpression of bHLH domain of HIF-1 failed to inhibit the HIF-1 transcriptional activity in hypoxia

Biological research: BR

article

Sadeghi, Fatemeh¹  Kardar, Gholam Ali³  Bolouri, Mohammad Reza¹  Nasri, Farzad¹  Sadri, Maryam¹  Falak, Reza¹ 

[1] Immunology Research Center, Iran University of Medical Sciences;Department of Immunology, School of Medicine, Iran University of Medical Sciences;Immunology Asthma & Allergy Research Institute, Children’s Medical Center, Tehran University of Medical Sciences

关键词: Cancer;    Hypoxia;    HIF-1;    Arnt;    bHLH;    PAS;    Gene therapy;    Hypoxia inducible factor;    Basic helix-loop helix;    DNA binding;   

DOI  :  10.1186/s40659-020-00293-4

来源: BioMed Central

【 摘 要 】

Hypoxia inducible factor-1 (HIF-1) is considered as the most activated transcriptional factor in response to low oxygen level or hypoxia. HIF-1 binds the hypoxia response element (HRE) sequence in the promoter of different genes, mainly through the bHLH domain and activates the transcription of genes, especially those involved in angiogenesis and EMT. Considering the critical role of bHLH in binding HIF-1 to the HRE sequence, we hypothesized that bHLH could be a promising candidate to be targeted in hypoxia condition. We inserted an inhibitory bHLH (ibHLH) domain in a pIRES2-EGFP vector and transfected HEK293T cells with either the control vector or the designed construct. The ibHLH domain consisted of bHLH domains of both HIF-1a and Arnt, capable of competing with HIF-1 in binding to HRE sequences. The transfected cells were then treated with 200 µM of cobalt chloride (CoCl2) for 48 h to induce hypoxia. Real-time PCR and western blot were performed to evaluate the effect of ibHLH on the genes and proteins involved in angiogenesis and EMT. Hypoxia was successfully induced in the HEK293T cell line as the gene expression of VEGF, vimentin, and β-catenin were significantly increased after treatment of untransfected HEK293T cells with 200 µM CoCl2. The gene expression of VEGF, vimentin, and β-catenin and protein level of β-catenin were significantly decreased in the cells transfected with either control or ibHLH vectors in hypoxia. However, ibHLH failed to be effective on these genes and the protein level of β-catenin, when compared to the control vector. We also observed that overexpression of ibHLH had more inhibitory effect on gene and protein expression of N-cadherin compared to the control vector. However, it was not statistically significant. bHLH has been reported to be an important domain involved in the DNA binding activity of HIF. However, we found that targeting this domain is not sufficient to inhibit the endogenous HIF-1 transcriptional activity. Further studies about the function of critical domains of HIF-1 are necessary for developing a specific HIF-1 inhibitor.

【 授权许可】

Unknown