Abstract B006: Mutant PPP2R1A induces the expression and secretion of IGFBP2 to promote uterine serous carcinoma metastasis

Abstract

Abstract Uterine serous carcinoma (USC) tumors demonstrate a unique aggressiveness suggesting that the primary tumor is intrinsically equipped to disseminate, metastasize and initiate tumor formation at secondary sites. Yet the drivers and pathways regulating dissemination and metastasis in USC remain incompletely understood. Previous work by our group and others identified a mutational hotspot within PPP2R1A, which encodes the Aa scaffolding subunit of protein phosphatase 2A (PP2A), a heterotrimeric serine/threonine phosphatase and known tumor suppressor. Two recurrent mutations, P179R and S256F, occur exclusively within high-grade subtypes of uterine cancer at a rate of 30-40%. We previously published that the P179R mutant drives USC tumorigenesis through the inactivation of PP2A, and genetic correction of this mutant resulted in decreased primary and metastatic tumor formation. The underlying mechanisms for these observations, however, remain unclear. To study the mechanistic basis for these observations, we generated isogenic patient-derived USC cell lines expressing the Aa – P179R and S256F mutants. Expression of these mutants enhanced the tumor-initiating capacity (TIC), a hybrid epithelial to mesenchymal (EM) plasticity profile, and the secretion of tumor-promoting factors in vitro and in vivo. Molecular analysis of these cell lines and tumors demonstrated that these mutants drove increased NF-kb phosphorylation resulting in the upregulation and secretion of the EM cytokine, IGFBP2. We found that the Aa mutant phenotype was dependent on the IGFBP2 cytokine function in vitro and in vivo. Future experiments will focus on identifying which PP2A B regulatory subunits are responsible for regulating the onset of the NF-kb transcriptional program. Cellular reprogramming through the IGFBP2-induced NF-kb signaling pathway mediated by recurrent Aa mutants may explain the intrinsically aggressive nature of USC, through enhanced dissemination and metastasis. Citation Format: Terrance James Haanen, Sophie Boock, Sarah Taylor, Caitlin O'Connor, Analisa DiFeo, Goutham Narla. Mutant PPP2R1A induces the expression and secretion of IGFBP2 to promote uterine serous carcinoma metastasis [abstract]. In: Proceedings of the AACR Special Conference on Endometrial Cancer: Transforming Care through Science; 2023 Nov 16-18; Boston, Massachusetts. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(5_Suppl):Abstract nr B006.