Introduction: Myxoid Liposarcoma (MLS) is an aggressive soft tissue tumor, characterized by a high rate of local recurrence and development of distant metastases. Most MLS are driven by a specific reciprocal t(12;16) translocation, and the resulting chimeric FUS-DDIT3 fusion protein acts as an oncogenic transcription factor. Although MLS display a higher chemosensitivity than other liposarcoma subtypes, the substantial rate of recurrence and metastasis in MLS underlines the urgent need for novel, biology- guided therapeutic strategies. As the mechanisms of FUS-DDIT3 mediating MLS pathogenesis are incompletely understood, we here investigate the functional relevance of the transcription factor CREB in MLS cells in vitro and in vivo.

Experimental procedures: In a large cohort of MLS tissue specimens (n=92), CREB (S133) and transcriptional targets such as Rb, Cyclin D1, PCNA and Bcl-xL were analyzed by immunohistochemistry. The functional interplay between CREB and FUS-DDIT3 was analyzed by RNAi-mediated knockdown of the chimeric fusion protein in MLS cells and induced expression of FUS-DDIT3 in human mesenchymal stem cells. CREB-mediated transcriptional activity was modulated by CREB-specific siRNA and treatment with small molecule inhibitors (666-15, KG-501, NASTRp and Ro-318220). The biological effects on MLS cell proliferation were monitored by cell viability, apoptosis and immunoblotting assays. An established myxoid liposarcoma avian chorioallantoic membrane model was used for in vivo confirmation.

Results: Elevated CREB phosphorylation (S133) was demonstrated in 60% of MLS tissue specimens by immunohistochemistry. In MLS cells, RNAi-mediated knockdown of FUS-DDIT3 lead to decreased phosphorylation levels of CREB (S133), accompanied by reduced transcriptional activity. Induced expression of FUS-DDIT3 in human mesenchymal stem cells stimulated phosphorylation of CREB (S133) and CREB target gene expression. Phosphorylation of CREB (S133) was induced by IGF-II stimulation and reduced by RNAi-mediated knockdown of IGF-IR. MLS cell viability was significantly reduced by specific RNAi-mediated knockdown of CREB and treatment with small molecule inhibitors (666-15, KG-501, NASTRp and Ro-318220) in vitro and in vivo.

Conclusions: Our preclinical study demonstrates the essential role of CREB-mediated transcriptional activity in myxoid liposarcoma tumorigenesis and provides a molecularly based rationale for a novel targeted therapeutic approach.

Citation Format: Magdalene Cyra, Sebastian Huss, Miriam Schulte, Ilka Isfort, Susanne Hafner, Thomas Simmet, Thomas Kindler, Pierre Åman, Eva Wardelmann, Wolfgang Hartmann, Marcel Trautmann. The transcription factor CREB is essential in myxoid liposarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1257.