Magnesium-sensitive upstream ORF controls PRL phosphatase expression to mediate energy metabolism

The phosphatases of regenerative liver (PRL) have been shown to interact with the CNNM magnesium transport regulators. Through this protein complex, PRL controls the levels of intracellular magnesium. Our study uncovers a remarkable posttranscriptional feedback mechanism by which magnesium controls PRL expression in mammalian cells. Here we show that regulation of PRL mRNA translation by magnesium depends on a 5'UTR-located upstream ORF, which is conserved among all vertebrates, proposing an evolutionary molecular mechanism of action by a divalent ion. This magnesium-sensing mechanism, which also involves the key metabolic sensor AMPK, is thus central to maintain cellular homeostasis in mammalian cells.Phosphatases of regenerating liver (PRL-1, PRL-2, and PRL-3, also known as PTP4A1, PTP4A2, and PTP4A3) control magnesium homeostasis through an association with the CNNM magnesium transport regulators. Although high PRL levels have been linked to cancer progression, regulation of their expression is poorly understood. Here we show that modulating intracellular magnesium levels correlates with a rapid change of PRL expression by a mechanism involving its 5'UTR mRNA region. Mutations or CRISPR-Cas9 targeting of the conserved upstream ORF present in the mRNA leader derepress PRL protein synthesis and attenuate the translational response to magnesium levels. Mechanistically, magnesium depletion reduces intracellular ATP but up-regulates PRL protein expression via activation of the AMPK/mTORC2 pathway, which controls cellular energy status. Hence, altered PRL-2 expression leads to metabolic reprogramming of the cells. These findings uncover a magnesium-sensitive mechanism controlling PRL expression, which plays a role in cellular bioenergetics

Phosphatase of regenerative liver-2 mediates cellular metabolic reprogramming in breast cancer

The three Phosphatase of Regenerative Liver (PRL-1, -2, -3 or PTP4A1, 2, 3) enzymes represent a group of protein tyrosine phosphatases that has been implicated in a number of diseases, and largely studied in the context of cancer metastasis. However, little is known about their physiological function. We previously showed that PRL-2 plays a key role in breast cancer progression by regulating intracellular magnesium levels. Characterization of the PRL-2 knockout mouse indicates that PRL-2 expression is both gender and circadian rhythm dependent. PRL-2 modulation leads to altered magnesium homeostasis resulting in changes in energy metabolism. This is of interest since breast cancer cells undergo a metabolic switch to aerobic glycolysis, known as the Warburg effect. In addition, we have shown that ATP citrate lyase expression is decreased upon loss of PRL-2, suggesting a potential role of the PRLs in fatty acid synthesis. We are using an inducible shRNA model to knock down PRL members and study their role in breast cancer metabolism in vitro. Results show that loss of PRL-2 in breast cancer induces a metabolic stress, due to lower ATP levels within the cells caused by impaired glucose and glutamine metabolism. Furthermore, the fatty acid synthesis pathway is inhibited, and cholesterol accumulation is favoured upon PRL-2 loss. Defining the metabolic role of this phosphatase family would not only provide a greater understanding of the physiological processes governed by these unique PTPs but could also contribute insight into potential pathological mechanisms.Les trois Phosphatase of Regenerative Liver (PRL-1, -2, -3 ou PTP4A1, 2, 3) représentent un groupe de protéines tyrosine phosphatases impliquées dans un certain nombre de maladies et largement étudiées dans le contexte des métastases cancéreuses. Cependant, peu d’information est disponible sur leur fonction physiologique. Précédemment, notre groupe a démontré que PRL-2 joue un rôle clé dans la progression du cancer du sein en régulant les niveaux de magnésium intracellulaire. La caractérisation de la souris knock-out PRL-2 indique que l'expression de PRL-2 dépend à la fois du sexe et du rythme circadien. La modulation de PRL-2 entraîne une altération de l'homéostasie du magnésium causant des changements dans le métabolisme énergétique. Ceci est intéressant, car les cellules cancéreuses du sein subissent un changement métabolique vers la glycolyse aérobie, connu sous le nom d'effet Warburg. En outre, nous avons montré que l'expression de l'ATP citrate lyase est diminuée lors de la perte de PRL-2, suggérant un rôle potentiel des PRL dans la synthèse des acides gras. Nous utilisons un modèle d'ARNsh inductible pour abattre les membres du PRL et étudier leur rôle dans le métabolisme du cancer du sein in vitro. Les résultats démontrent que la perte de PRL-2 dans le cancer du sein induit un stress métabolique, en raison de la diminution des taux d'ATP dans les cellules causée par une altération du métabolisme du glucose et de la glutamine. En outre, la voie de synthèse des acides gras est inhibée, et l'accumulation de cholestérol est favorisée lors de la perte de PRL-2. La définition du rôle métabolique de cette famille de phosphatases permettrait non seulement de mieux comprendre les processus physiologiques régis par ces PTP uniques, mais pourrait également contribuer à la compréhension de mécanismes pathologiques potentiels