The mTOR and PP2A Pathways Regulate PHD2 Phosphorylation to Fine-Tune HIF1α Levels and Colorectal Cancer Cell Survival under Hypoxia

• Published in: Cell reports (Cambridge) 2017-02, Vol.18 (7), p.1699-1712
• Main Authors: Di Conza, Giusy, Trusso Cafarello, Sarah, Loroch, Stefan, Mennerich, Daniela, Deschoemaeker, Sofie, Di Matteo, Mario, Ehling, Manuel, Gevaert, Kris, Prenen, Hans, Zahedi, Rene Peiman, Sickmann, Albert, Kietzmann, Thomas, Moretti, Fabiola, Mazzone, Massimiliano
• Format: Article
• Language: English
• Subjects: Cell Hypoxia - physiology; Cell Line; Cell Line, Tumor; Cell Proliferation - physiology; Cell Survival - physiology; Colorectal Neoplasms - metabolism; HEK293 Cells; HT29 Cells; Humans; Hypoxia-Inducible Factor 1, alpha Subunit - metabolism; Hypoxia-Inducible Factor-Proline Dioxygenases - metabolism; Phosphorylation - physiology; Protein Phosphatase 2 - metabolism; Ribosomal Protein S6 Kinases, 70-kDa - metabolism; Signal Transduction - physiology; TOR Serine-Threonine Kinases - metabolism
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2017.01.051

Oxygen-dependent HIF1α hydroxylation and degradation are strictly controlled by PHD2. In hypoxia, HIF1α partly escapes degradation because of low oxygen availability. Here, we show that PHD2 is phosphorylated on serine 125 (S125) by the mechanistic target of rapamycin (mTOR) downstream kinase P70S6K and that this phosphorylation increases its ability to degrade HIF1α. mTOR blockade in hypoxia by REDD1 restrains P70S6K and unleashes PP2A phosphatase activity. Through its regulatory subunit B55α, PP2A directly dephosphorylates PHD2 on S125, resulting in a further reduction of PHD2 activity that ultimately boosts HIF1α accumulation. These events promote autophagy-mediated cell survival in colorectal cancer (CRC) cells. B55α knockdown blocks neoplastic growth of CRC cells in vitro and in vivo in a PHD2-dependent manner. In patients, CRC tissue expresses higher levels of REDD1, B55α, and HIF1α but has lower phospho-S125 PHD2 compared with a healthy colon. Our data disclose a mechanism of PHD2 regulation that involves the mTOR and PP2A pathways and controls tumor growth. [Display omitted] •PHD2 is phosphorylated at Ser125 by P70S6K and dephosphorylated by PP2A/B55α•PHD2 dephosphorylation impairs its function, resulting in increased HIF1α accumulation•HIF1α promotes CRC survival in hypoxia via autophagy in a PHD2/B55α-dependent fashion•B55α silencing blocks CRC tumor growth in vitro and in vivo; this is PHD2 dependent Di Conza et al. find that PP2A/B55α dephosphorylates and partly inactivates PHD2, leading to augmented HIF1α and CRC cell survival in hypoxia through autophagy. Dephosphorylated PHD2 and B55α accumulate in CRC human specimens versus normal colon, and B55α targeting impairs CRC neoplastic growth in vitro and in mice.