PRL3 pseudophosphatase activity is necessary and sufficient to promote metastatic growth

Abstract

Phosphatases of regenerating liver (PRLs) are markers of cancer and promote tumor growth. They have been implicated in a variety of biochemical pathways but the physiologically relevant target of phosphatase activity has eluded 20 years of investigation. Here, we show that PRL3 catalytic activity is not required in a mouse model of metastasis. PRL3 binds and inhibits CNNM4, a membrane protein associated with magnesium transport. Analysis of PRL3 mutants specifically defective in either CNNM-binding or phosphatase activity demonstrate that CNNM-binding is necessary and sufficient to promote tumor metastasis. As PRLs do have phosphatase activity, they are in fact pseudo-pseudophosphatases. Phosphatase activity leads to formation of phosphocysteine, which blocks CNNM-binding and may play a regulatory role. We show levels of PRL cysteine phosphorylation vary in response to culture conditions and in different tissues. Examination of related protein phosphatases shows the stability of phosphocysteine is a unique and evolutionarily conserved property of PRLs. The demonstration that PRL3 functions as a pseudophosphatase has important ramifications for the design of PRL inhibitors for cancer.

Phosphatase of regenerating liver‐3 regulates cancer cell metabolism in multiple myeloma

“…26,62 In the interaction between the PRLs and the magnesium-regulatory proteins of the CNNM family, PRLs acts as pseudophosphatases. 16,63 In the present study, the phosphatase-dead C104S mutant PRL-3 was as potent as WT PRL-3 in most of the experiments. As an example, phosphatase-dead PRL-3stimulated aerobic glycolysis to the same extent as WT PRL-3.…”

Crystal structure of a bacterial CNNM magnesium transporter

“…In animals, PRL phosphatases provide an additional level of regulation. PRL binding to CNNMs is regulated by PRL phosphorylation in response to Mg 2+ levels (Gulerez et al, 2016; Kozlov et al, 2020). PRLs are highly oncogenic and promote cancer metastasis through their suppression of CNNM proteins (Funato et al, 2014; Yamazaki et al, 2019).…”

“…CNNMs are also implicated in cancer through binding of PRLs, highly oncogenic protein phosphatases involved in metastasis (Funato et al, 2014; Hardy et al, 2015). PRL binding inhibits CNNM-associated Mg 2+ efflux and is in turn is regulated by magnesium levels (Gulerez et al, 2016; Hirata et al, 2014; Kozlov et al, 2020). In bacteria and yeast, mutations in CNNMs confer resistance to toxic metals and sensitivity to elevated levels of Mg 2+ .…”

“…The CBS-pair domains of CNNMs have been characterized structurally and shown to undergo large conformational changes upon Mg 2+ -ATP binding (Chen et al, 2020; Corral-Rodriguez et al, 2014). The domains are the site of PRL binding that regulates the activity of CNNM proteins in humans (Gulerez et al, 2016; Kozlov et al, 2020).…”

“…CBS-pair domains are composed of tandem CBS motifs and found in a wide variety of proteins, including the bacterial Mg 2+ transporter MgtE, where they mediate dimerization and Mg 2+ -ATP binding (Ereno-Orbea et al, 2013). The CBS-pair domains of CNNMs have been characterized structurally and shown to undergo large conformational changes upon Mg 2+ -ATP binding (Chen et al, 2020;Corral-Rodriguez et al, 2014). The domains are the site of PRL binding that regulates the activity of CNNM proteins in humans (Gulerez et al, 2016;Kozlov et al, 2020).…”