Abstract 840: PMEPA1 is an oncogene linked to TGF-β signaling in hepatocellular carcinoma

Abstract 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), a direct target gene of the TGFβ pathway that negatively regulates TGFβ signaling by interacting with SMAD proteins, has been shown to promote TGFβ oncogenic effects in other cancers and we decided to explore its role in HCC pathogenesis. Methods: We analyzed transcriptomic, genomic, epigenomic and clinicopathological data of a discovery cohort of 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 cohorts (n = 916) using microarray and RNAseq data. Genetically engineered mouse models were generated through hydrodynamic tail-vein injection. Equal amounts of plasmids overexpressing PMEPA1, TGFB1 and MYC were injected in mice to evaluate survival. 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, TME response to TGFβ and active stroma (p < 0.05) compared to HCCs with TGFβ signalling alone (8% of cases) or PMEPA1 high levels alone (11% of cases). In vivo, overexpression of MYC+PMEPA1 led to HCC development in 9/16 mice and showed a lower survival when compared to the control arm, overexpression of MYC alone (p = 0.014). On the contrary, only 1/12 mice in the MYC+PMEPA1+TGFβ1 condition developed HCC and none of the MYC+TGFβ1 mice. Conclusion: PMEPA1 upregulation is linked to TGF-β activation and an aggressive phenotype in human HCC. Overexpression PMEPA1 in combination with MYC in vivo led to HCC development, showing for the first time the oncogenic role of PMEPA1 in this cancer. Citation Format: Marta Piqué-Gili, Carmen Andreu-Oller, Roser Pinyol, Marina Bárcena-Varela, Roger Esteban-Fabró, Judit Peix, Jordi Abril-Fornaguera, Katherine E. Lindblad, Miguel Torres-Martin, Daniela Sia, Amaia Lujambio, Josep M. Llovet. PMEPA1 is an oncogene linked to TGF-β signaling in hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 840.