Induction of a feed forward pro-apoptotic mechanistic loop by nitric oxide in a human breast cancer model

Gasotransmitters in the tumor microenvironment: Impacts on cancer chemotherapy (Review)

Nitric oxide, carbon monoxide and hydrogen sulfide are three endogenous gasotransmitters that serve a role in regulating normal and pathological cellular activities. They can stimulate or inhibit cancer cell proliferation and invasion, as well as interfere with cancer cell responses to drug treatments. Understanding the molecular pathways governing the interactions between these gases and the tumor microenvironment can be utilized for the identification of a novel technique to disrupt cancer cell interactions and may contribute to the conception of effective and safe cancer therapy strategies. The present review discusses the effects of these gases in modulating the action of chemotherapies, as well as prospective pharmacological and therapeutic interfering approaches. A deeper knowledge of the mechanisms that underpin the cellular and pharmacological effects, as well as interactions, of each of the three gases could pave the way for therapeutic treatments and translational research.

A HIF-1α-driven feed-forward loop augments HIF signalling in Hep3B cells by upregulation of ARNT

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-1β and HIF-2β, 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-1α-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.