Proteomic Profiling Identifies Co-Regulated Expression of Splicing Factors as a Characteristic Feature of Intravenous Leiomyomatosis

SIMPLE SUMMARY: Intravenous leiomyomatosis is a rare form of smooth muscle tumour that has unique and distinct clinical features including growth within the uterine and pelvic veins. Here we use proteomics by mass spectrometry to show that this disease is distinct from uterine leiomyomas and other benign smooth muscle tumours due to the enrichment of components of the spliceosome machinery. In particular, we find that intravenous leiomyomatosis tumours harbour co-regulated expression of multiple splicing factors that are associated with biological processes including cell signalling. Our study demonstrates that intravenous leiomyomatosis is a distinct disease from other smooth muscle tumours and indicates a possible functional role for alternative splicing in disease initiation and progression. ABSTRACT: Intravenous leiomyomatosis (IVLM) is a rare benign smooth muscle tumour that is characterised by intravenous growth in the uterine and pelvic veins. Previous DNA copy number and transcriptomic studies have shown that IVLM harbors unique genomic and transcriptomic alterations when compared to uterine leiomyoma (uLM), which may account for their distinct clinical behaviour. Here we undertake the first comparative proteomic analysis of IVLM and other smooth muscle tumours (comprising uLM, soft tissue leiomyoma and benign metastasizing leiomyoma) utilising data-independent acquisition mass spectrometry. We show that, at the protein level, IVLM is defined by the unique co-regulated expression of splicing factors. In particular, IVLM is enriched in two clusters composed of co-regulated proteins from the hnRNP, LSm, SR and Sm classes of the spliceosome complex. One of these clusters (Cluster 3) is associated with key biological processes including nascent protein translocation and cell signalling by small GTPases. Taken together, our study provides evidence of co-regulated expression of splicing factors in IVLM compared to other smooth muscle tumours, which suggests a possible role for alternative splicing in the pathogenesis of IVLM.