Abstract

Hypoxia is a condition always present in tumor environment owing to the fast growth of tumor cells not supported by adequate blood supply.

There is increasing evidence that hypoxia plays an important role in cancer dormancy and cancer metabolism, increasing stemness activity and bringing about cancer initiation and progression.

This condition may influence the production of hypoxia inducible factor (HIF) a helix transcription factor which is involved in carcinogenesis and tumor growth through the regulation of genes involved in angiogenesis, glycolytic metabolism and other biological mechanisms.

In normoxia condition HIF is inactivated by prolyl hydroxylase enzymes (EGLN 1–3, also known as PHD 1–3) using oxygen as a substrate. Once hydroxilated it binds to a protein called Von Hippel Lindau protein (VHL) for its degradation, whereas in hypoxia condition stabilization and nuclear translocation occur, leading to oncogenes activation. It has got three isoforms HIF-1 HIF-2 and HIF-3. The most studied factor is HIF-1 which is a heterodimer consisting of two forms, the form α is expressed in manner oxygen dependent, the form β is expressed constitutively.

Its presence in tumor microenvironment could foster among other the expression of VEGF, HGF, Met protoncogene which induces degradation of the extracellular matrix and TWIST gene, which is in turn involved in a mechanism of cancer cell metastasis called epithelial-mesenchimal transition(EMT). In this review, we summarize the most important findings in HIF action in different types of cancer focusing on its properties to induce tumor cell growth and highlighting its poor prognostic value in different cancers sites.

Keywords: HIF-1, metastases, tumor progression, hypoxia, microenvironment, metabolic pathways.