PRLs (phosphatases of regenerating liver) are frequently overexpressed in human cancers and are prognostic markers of poor survival. Despite their potential as therapeutic targets, their mechanism of action is not understood in part due to their weak enzymatic activity. Previous studies revealed that PRLs interact with CNNM ion transporters and prevent CNNM4‐dependent Mg2+ transport, which is important for energy metabolism and tumor progression. Here, we report that PRL‐CNNM complex formation is regulated by the formation of phosphocysteine. We show that cysteine in the PRL catalytic site is endogenously phosphorylated as part of the catalytic cycle and that phosphocysteine levels change in response to Mg2+ levels. Phosphorylation blocks PRL binding to CNNM Mg2+ transporters, and mutations that block the PRL‐CNNM interaction prevent regulation of Mg2+ efflux in cultured cells. The crystal structure of the complex of PRL2 and the CBS‐pair domain of the Mg2+ transporter CNNM3 reveals the molecular basis for the interaction. The identification of phosphocysteine as a regulatory modification opens new perspectives for signaling by protein phosphatases.
The PRL‐CNNM pathway regulates Mg2+ homeostasis and tumor progression. This study shows that the formation of a catalytic phosphocysteine PRL intermediate regulates binding to CNNM magnesium transporters and Mg2+ efflux.
Phosphatases of regenerating liver (PRLs) bind to CNNM proteins to regulate membrane Mg2+ transport.
Binding is mediated by an aspartic acid on the CNNM CBS‐pair domain that acts as a substrate mimic.
Phosphorylation of the catalytic cysteine of PRLs during the catalytic cycle prevents CNNM binding.
Phosphorylation of PRLs in cultured cells changes in response to Mg2+ availability.
- Received September 22, 2016.
- Revision received October 7, 2016.
- Accepted October 13, 2016.
- © 2016 The Authors