Mutant PP2A Induces IGFBP2 Secretion to Promote Development of High-Grade Uterine Cancer.

Uterine serous carcinoma (USC) and uterine carcinosarcoma (UCS) tumors are uniquely aggressive, suggesting that the primary tumor is intrinsically equipped to disseminate and metastasize. Previous work identified mutational hotspots within PPP2R1A, which encodes the Aα scaffolding subunit of protein phosphatase 2A (PP2A), a heterotrimeric serine/threonine phosphatase. Two recurrent heterozygous PPP2R1A mutations, P179R and S256F, occur exclusively within high-grade subtypes of uterine cancer and can drive tumorigenesis and metastasis. Elucidation of the mechanisms by which PP2A-Aα mutants promote tumor development and progression could help identify therapeutic opportunities. Here, we showed that expression of these mutants in USC/UCS cell-lines enhanced tumor-initiating capacity, drove a hybrid epithelial-to-mesenchymal (EM) plasticity phenotype, and elevated secretion of the tumorigenic cytokine IGFBP2. Therapeutic targeting of the IGFBP2/IGF1R signaling axis using small molecules and genetic approaches resulted in marked tumor growth inhibition. Mechanistically, PP2A regulated IGFBP2 expression through the transcription factor, NF-κB, which harbors a B56 recognition motif. Collectively, these results identify a role for PP2A in regulating paracrine cancer cell signaling that can be targeted to block the initiation and metastasis of high-grade uterine cancer.