Open AccessA HIF-1α-driven feed-forward loop augments HIF signalling in Hep3B cells by upregulation of ARNT
Author(s) -
Markus Mandl,
Lieberum Mk,
Reinhard Depping
Publication year - 2016
Publication title -
cell death and disease
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.482
H-Index - 111
ISSN - 2041-4889
DOI - 10.1038/cddis.2016.187
Subject(s) - aryl hydrocarbon receptor nuclear translocator , downregulation and upregulation , transcription factor , hypoxia inducible factors , biology , gene silencing , hif1a , microbiology and biotechnology , reporter gene , hypoxia (environmental) , gene expression , angiogenesis , cancer research , chemistry , gene , aryl hydrocarbon receptor , biochemistry , oxygen , organic chemistry
Oxygen-deprived (hypoxic) areas are commonly found within neoplasms caused by excessive cell proliferation. The transcription factor Aryl hydrocarbon receptor nuclear translocator (ARNT) is part of the hypoxia-inducible factor (HIF) pathway, which mediates adaptive responses to ensure cellular survival under hypoxic conditions. HIF signalling leads to metabolic alterations, invasion/metastasis and the induction of angiogenesis in addition to radio-chemoresistance of tumour cells. Activation of the HIF pathway is based on the abundance of HIF- α subunits, which are regulated in an oxygen-dependent manner and form transcriptional active complexes with ARNT or ARNT2 (also referred as HIF-1 β and HIF-2 β, respectively). ARNT is considered to be unaffected by hypoxia but certain cell lines, including Hep3B cells, are capable to elevate this transcription factor in response to oxygen deprivation, which implies an advantage. Therefore, the aim of this study was to elucidate the mechanism of hypoxia-dependent ARNT upregulation and to determine implications on HIF signalling. Gene silencing and overexpression techniques were used to alter the expression pattern of HIF transcription factors under normoxic and hypoxic conditions. qRT-PCR and western blotting were performed to measure gene and protein expression, respectively. HIF activity was determined by reporter gene assays. The results revealed a HIF-1 α -dependent mechanism leading to ARNT upregulation in hypoxia. Forced expression of ARNT increased reporter activity under normoxic and hypoxic conditions. In conclusion, these findings indicate a novel feed-forward loop and suggest that ARNT might be a limiting factor. Augmented HIF signalling in terms of elevated target gene expression might be advantageous for tumour cells.