Introduction: Myxoid liposarcoma (MLS) represents the second most common subtype of liposarcoma. MLS is characterized by a chromosomal translocation t(12;16)(q13;p11) encoding a chimeric FUS-DDIT3 fusion gene. The resulting FUS-DDIT3 oncoprotein acts as a transcriptional dysregulator that was recently shown to mediate (i) IGF-IR/PI3K/AKT signaling and (ii) aberrant activation of the Hippo pathway effector YAP1 in MLS. This study was performed to analyze the functional interplay between IGF-IR/PI3K/AKT signals and aberrant YAP1 activity in MLS, aiming at a better functional understanding of MLS and the identification of specific molecular vulnerabilities.

Experimental procedures: Immunohistochemical stainings of IGF-IR, IGF-II and YAP1 were performed in a cohort of MLS specimens (n=45). To study FUS-DDIT3-dependency in vitro, SCP-1 mesenchymal stem cells stably expressing FUS-DDIT3, and MLS cell lines expressing a doxycycline-inducible shRNA against FUS-DDIT3 were employed. Interactions between the IGF-IR/PI3K/AKT and Hippo/YAP1 pathways were investigated using RNAi approaches as well as the small molecule compounds BMS-754807 and BKM120; effects were analyzed by immunoblotting and TEAD luciferase reporter assays. To determine the impact of YAP1 in FUS-DDIT3-mediated oncogenic effects, qPCR analysis and adipogenic differentiation assays were performed.

Results: Immunohistochemical analysis of human MLS tissue specimens demonstrated that expression of IGF-II and IGF-IR is associated with concomitant nuclear expression of YAP1 in a significant subset of MLS. Both, IGF-IR-dependent signals and YAP1 expression were shown to be functionally dependent on FUS-DDIT3. In MLS cell lines, inhibition of the IGF-IR/PI3K/AKT signaling cascade promoted downregulation of YAP1, accompanied by reduced TEAD transcriptional activity. Employing qPCR analyses, YAP1 was shown to co-regulate FUS-DDIT3 transcriptional targets and to be functionally involved in FUS-DDIT3-driven disruption of normal adipocytic differentiation.

Conclusions: Our study provides evidence of a complex regulatory interplay in MLS with FUS-DDIT3-driven IGF-IR/PI3K/AKT signals acting as activators of nuclear YAP1 expression. Conversely, YAP1 contributes to shape FUS-DDIT3 effects on the MLS transcriptional landscape and functionally adds to an immature non-lipogenic phenotype. Our data contribute to the understanding of MLS biology and reveal specific molecular liabilities to be considered in therapeutic approaches of MLS.

Citation Format: Ruth Berthold, Ilka Isfort, Jonas Breuer, Lorena Heinst, Thomas Kindler, Pierre Åman, Inga Grünewald, Eva Wardelmann, Thomas G. Grünewald, Florencia Cidre-Aranaz, Claudia Scholl, Stefan Fröhling, Marcel Trautmann, Wolfgang Hartmann. Oncogenic interplay of FUS-DDIT3 and YAP1 in myxoid liposarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2003.