• Open Access

The role of HIF prolyl hydroxylases in tumour growth

Authors

  • Terhi Jokilehto,

    1. Turku Centre for Biotechnology, University of Turku and Åbo Akademi University, Turku, Finland
    2. Turku Graduate School for Biomedical Sciences (TuBS), University of Turku, Turku, Finland
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  • Panu M. Jaakkola

    Corresponding author
    1. Turku Centre for Biotechnology, University of Turku and Åbo Akademi University, Turku, Finland
    2. Department of Oncology and Radiotherapy, Turku University Hospital, Turku, Finland
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Correspondence to: Panu M. JAAKKOLA, Turku Centre for Biotechnology, Tykistökatu 6B, FIN-20520, Turku, Finland.
Tel.: +358 44 5483806
Fax: +358 2 3338000
E-mail: panjaa@utu.fi

Abstract

  • • Hypoxia in tumours
  • • Overview of the oxygen-sensing mechanisms
  • • The family of HIF hydroxylases
  • • Expression of PHDs in normal tissues
  • • Regulation of PHDs
  • • PHDs in cell growth and differentiation
  • • Expression of PHDs in cancer
  • • Function of the PHDs in cancer
  • • Other dioxygenase targets in cancer and future directions

Tumour hypoxia is a well-known microenvironmental factor that causes cancer progression and resistance to cancer treatment. This involves multiple mechanisms of which the best-understood ones are mediated through transcriptional gene activation by the hypoxia-inducible factors (HIFs). HIFs in turn are regulated in response to oxygen availability by a family of iron- and 2-oxoglutarate-dependent dioxygenases, the HIF prolyl hydroxylases (PHDs). PHDs inactivate HIFs in normoxia by activating degradation of the HIF-α subunit but release HIF activation in poorly oxygenated conditions. The function of HIF in tumours is fairly well characterized but our understanding on the outcome of PHDs in tumours is much more limited. Here we review the function of PHDs on the HIF system, the expression of PHDs in human tumours as well as their putative function in cancer. The PHDs may have either tumour promoting or suppressing activity. Their outcome in cancer depends on the cell and cancer type-specific expression and on the availability of diverse natural PHD inhibitors in tumours. Moreover, besides the action of PHDs on HIF, recent data suggest PHD function in non-HIF signalling. Together the data illustrate a complex operation of the oxygen sensors in cancer.

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