Research ArticleBiochemistry

Structural analysis of the PTEN:P-Rex2 signaling complex reveals how cancer-associated mutations coordinate to hyperactivate Rac1

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Science Signaling  04 May 2021:
Vol. 14, Issue 681, eabc4078
DOI: 10.1126/scisignal.abc4078

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Ramping up Rac1 for metastasis

The phosphatase and tumor suppressor PTEN hydrolyzes the lipid second messenger PI(3,4,5)P3, thereby suppressing cellular proliferation mediated by the PI3K-Akt pathway. The protein P-Rex2 activates Rac members of the Rho GTPase family to promote cell migration, invasion, and metastasis. Because PTEN and P-Rex2 bind to each other to form a coinhibitory complex, D’Andrea et al. used cross-linking mass spectrometry and functional studies to characterize the regions within each protein that were necessary for complex formation. The authors found that cancer-associated mutations in both proteins combined to enhance the activation of Rac1. Together, these findings enhance our understanding of the dysregulation of the PTEN:P-Rex2 complex that occurs in metastasis.

Abstract

The dual-specificity phosphatase PTEN functions as a tumor suppressor by hydrolyzing PI(3,4,5)P3 to PI(4,5)P2 to inhibit PI3K-AKT signaling and cellular proliferation. P-Rex2 is a guanine nucleotide exchange factor for Rho GTPases and can be activated by Gβγ subunits downstream of G protein–coupled receptor signaling and by PI(3,4,5)P3 downstream of receptor tyrosine kinases. The PTEN:P-Rex2 complex is a commonly mutated signaling node in metastatic cancer. Assembly of the PTEN:P-Rex2 complex inhibits the activity of both proteins, and its dysregulation can drive PI3K-AKT signaling and cellular proliferation. Here, using cross-linking mass spectrometry and functional studies, we gained mechanistic insights into PTEN:P-Rex2 complex assembly and coinhibition. We found that PTEN was anchored to P-Rex2 by interactions between the PDZ-interacting motif in the PTEN C-terminal tail and the second PDZ domain of P-Rex2. This interaction bridged PTEN across the P-Rex2 surface, preventing PI(3,4,5)P3 hydrolysis. Conversely, PTEN both allosterically promoted an autoinhibited conformation of P-Rex2 and blocked its binding to Gβγ. In addition, we observed that the PTEN-deactivating mutations and P-Rex2 truncations combined to drive Rac1 activation to a greater extent than did either single variant alone. These insights enabled us to propose a class of gain-of-function, cancer-associated mutations within the PTEN:P-Rex2 interface that uncouple PTEN from the inhibition of Rac1 signaling.

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