Development of a Cre-Inducible Rabl6a Transgenic Mouse Model That Enhances Sarcoma Growth In Vivo.

Background: Malignant peripheral nerve sheath tumors (MPNSTs) are deadly sarcomas that arise from Schwann cells and lack effective therapies. RABL6A is an oncogenic Rab-like GTPase whose expression is associated with worse survival in many human cancers. It is required for human MPNST cell survival, and its expression is dramatically increased in patient MPNSTs compared to benign precursor lesions. Methods: To model elevated expression of RABL6A in vivo, we developed transgenic mice expressing Cre-inducible Rabl6a. These Rabl6a-tg mice express the murine Rabl6a cDNA with a 5' hemagglutinin [HA] epitope sequence downstream of a CMV enhancer and separated by a lox-stop-lox cassette. Double transgenic DhhCre; Rabl6a-tg mice were generated to achieve Schwann-cell specific Cre expression from the Desert hedgehog (Dhh) promoter. De novo MPNSTs were induced by CRISPR editing of Nf1, Ink4a, and Arf genes in the mouse sciatic nerve. Results: Cre-dependent expression of transgenic Rabl6a was verified at the mRNA and protein levels in Cre-positive mouse embryo fibroblasts and tissues. Increased Rabl6a expression in DhhCre; Rabl6a-tg mice had no effect on de novo MPNST initiation but significantly accelerated tumor progression relative to DhhCre control mice. The Rabl6a phenotype was associated with increased tumor angiogenesis but not proliferation. Interestingly, many MPNSTs in the DhhCre background exhibited varying levels of rhabdomyoblastic (RMB) features. That immature muscle cell phenotype is a hallmark of malignant Triton tumors, a rare histological variant of human MPNSTs associated with worse outcomes. Conclusions: These data provide direct evidence that Rabl6a is a functional driver of MPNSTs while establishing Rabl6a-tg mice as a suitable model for investigating Rabl6a's role in other lethal RABL6A-high tumors.