Loss of RanBP9 cooperates with p53 deficiency to promote sarcomagenesis.

INTRODUCTION: Ubiquitination is a major regulatory process that is often dysregulated in carcinogenesis. The C-terminal to LisH (CTLH) complex is a multi-subunit E3 ubiquitin ligase that has been shown to exert tumor-promoting and tumor-suppressing functions. Its core scaffolding subunit, RanBP9, has been implicated in regulating oncogenic signaling, but it remains unclear whether RanBP9 loss promotes tumorigenesis in vivo. OBJECTIVES: This study aimed to evaluate the functional consequence of RanBP9 loss, alone or in combination with p53 deficiency, in mice. METHODS: Mice with single or combined germline deletion of Ranbp9 or Trp53, were generated and assessed for in vivo tumorigenesis. Tumors were characterized by histology and immunohistochemistry staining. Functional assays in mixed Ranbp9/Trp53 mouse embryonic fibroblasts (MEFs) were performed to evaluate proliferation and survival properties. Global label-free quantification (LFQ) proteomics was performed on MEFs to identify differentially expressed proteins. Genomic alterations of CTLH complex subunits were evaluated in sarcoma patients using the TCGA-SARC dataset. RESULTS: Biallelic deletion of Ranbp9 did not induce tumor development. In contrast, double heterozygous Ranbp9 and Trp53 (R9/p53DHet ) mice exhibited earlier tumor onset and increased soft tissue sarcoma development compared with Trp53 heterozygous (p53Het ) mice. Histopathological analysis revealed increased mitotic activity in R9/p53DHet sarcomas with high Ki-67 and phospho-ERK expression. Functional and proteomic characterization of R9/p53DHet MEFs demonstrated increased proliferative capacity and changes in proteomic landscape in proteins involved in DNA replication, cell cycle, and metabolism. Finally, TCGA-SARC analysis showed that that low mRNA expression of CTLH catalytic subunit RMND5B correlated significantly with reduced overall survival. DISCUSSION: Loss of RanBP9 induces deregulation of signaling cascades, and combined with p53 deficiency, further promotes sarcoma development in mice. This mouse model provides a valuable platform to further study pathways and candidates regulated by the CTLH complex in sarcoma biology.