Abstract PR02: PMEPA1 has an oncogenic role in the context of TGF-β signaling in hepatocellular carcinoma

Background: Transforming growth factor β (TGFβ) has a dual role in cancer, including hepatocellular carcinoma (HCC). It acts as a tumor suppressor in early stages of hepatocarcinogenesis, but promotes epithelial-to-mesenchymal transition, angiogenesis and immunosuppression in advanced stages. PMEPA1 (prostate transmembrane protein androgen induced 1) negatively regulates TGFβ signaling by interacting with SMAD proteins, and has been shown to promote TGFβ oncogenic effects in other cancers. Thus, we aimed to explore the role of PMEPA1 in HCC pathogenesis. Methods: We analyzed transcriptomic, genomic, epigenomic and clinicopathological data of a discovery cohort comprising 228 HCCs and a validation cohort of 361 HCCs. PMEPA1 levels were quantified by qPCR in the discovery cohort. PMEPA1 overexpression was validated in 6 independent publicly available cohorts (n = 916) with either microarray or RNAseq data. We also evaluated PMEPA1 expression at the single-cell level using a publicly available single-cell RNA sequencing (scRNAseq) dataset comprising 22 HCC samples. Genetically engineered mouse models were generated by performing hydrodynamic tail-vein injection of equal amounts of plasmids overexpressing MYC and MYC+PMEPA1. Molecular and histopathological analyses of the murine tumors are currently ongoing. Results: PMEPA1 was overexpressed in 18% of human HCCs [FC > 2; n = 203/1144], a feature associated with TGFβ signaling (p < 0.05). Overexpression of PMEPA1 was associated with gene body hypermethylation (p < 0.0001). HCCs displaying both TGFβ signaling and high PMEPA1 levels (11% of cases) were significantly enriched in signatures of immune exhaustion, late TGFβ activation, tumor microenvironment (TME) response to TGFβ and active stroma (p < 0.05) when compared with HCCs with TGFβ signalling alone (8% of cases) or PMEPA1 overexpression alone (11% of cases). Analyses of PMEPA1 expression at the single-cell level revealed that this gene is not only expressed by tumoral cells but also by the TME cell populations, including endothelial cells, pericytes, fibroblasts, and dendritic cells. In vivo, overexpression of MYC+PMEPA1 led to HCC development in 9/16 mice and was associated with a significantly reduced survival when compared to mice overexpressing MYC alone (p = 0.014), which did not develop tumors. Compared to healthy liver controls, MYC+PMEPA1 tumors presented upregulation of AKT. Conclusion: PMEPA1 upregulation is linked to TGF-β activation and an aggressive phenotype in human HCC. Overexpression of PMEPA1 in combination with MYC in vivo led to HCC development, showing for the first time the oncogenic role of PMEPA1 in this cancer type. Citation Format: Marta Piqué-Gili, Carmen Andreu-Oller, Roser Pinyol, Roger Esteban, Marina Bárcena-Varela, Judit Peix, Jordi Abril-Fornaguera, Katherine E. Lindblad, Miguel Torres-Martin, Júlia Huguet-Pradell, Daniela Sia, Amaia Lujambio, Josep M Llovet. PMEPA1 has an oncogenic role in the context of TGF-β signaling in hepatocellular carcinoma [abstract]. In: Proceedings of the AACR Special Conference: Advances in the Pathogenesis and Molecular Therapies of Liver Cancer; 2022 May 5-8; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(17_Suppl):Abstract nr PR02.