The highly recurrent PP2A Aα-subunit mutation P179R alters protein structure and impairs PP2A enzyme function to promote endometrial tumorigenesis

Somatic mutation of the PP2A Aα-subunit gene PPP2R1A is highly prevalent in high-grade endometrial carcinoma (EMCA). The structural, molecular, and biological basis by which the most recurrent EMCA-specific mutation site P179 facilitates features of EMCA malignancy have yet to be fully determined. Here we used a series of structural, biochemical, and biological approaches to investigate the impact of the P179R missense mutation on PP2A function. Enhanced sampling molecular dynamics simulations showed that arginine-to-proline substitution at the P179 residue changes the protein9s stable conformation profile. A crystal structure of the tumor-derived PP2A mutant revealed marked changes in A-subunit conformation. Binding to the PP2A catalytic subunit was significantly impaired, disrupting holoenzyme formation and enzymatic activity. Cancer cells were dependent on PP2A disruption for sustained tumorigenic potential, and restoration of wildtype Aα in a patient-derived P179R mutant cell line restored enzyme function and significantly attenuated tumorigenesis and metastasis in vivo. Furthermore, small molecule-mediated therapeutic reactivation of PP2A significantly inhibited tumorigenicity in vivo. These outcomes implicate PP2A functional inactivation as a critical component of high-grade EMCA disease pathogenesis. Moreover, they highlight PP2A reactivation as a potential therapeutic strategy for patients who harbor P179R PPP2R1A mutations.