The role of TWIST1 in multiple myeloma

Abstract

Multiple myeloma (MM) is an incurable haematological malignancy characterised by the uncontrolled proliferation of clonal plasma cells (PCs) in the bone marrow (BM). MM disease progression relies on the continuous trafficking of MM PCs to distant BM sites leading to multiple focal tumours throughout the skeleton at diagnosis. While metastasis is not a concept generally applied to haematological malignancies, increasing evidence suggests that like solid tumours, an epithelial-to-mesenchymal (EMT)-like process is activated in MM PCs in order to disseminate. However, an association between high-risk MM subtypes, patient prognosis and the expression of an EMT-like gene expression signature in MM PCs had not been reported. The chromosomal translocation t(4;14), characterised by overexpression of MMSET and FGFR3, is associated with poor prognosis and aggressive tumour dissemination. This project sought to determine whether the highly aggressive phenotype observed in t(4;14) is mediated by activation of EMT-like process. Using previously published microarray data from large cohorts of newly diagnosed MM patients and RNA-sequencing data from human MM cell lines, an EMT-like expression signature in t(4;14) MM was comprehensively evaluated. Among the mesenchymal genes identified, TWIST1 was consistently upregulated in approximately 50% of the t(4;14) MM cases and was positively correlated with expression of MMSET. Using RNA-sequencing technology, the transcriptome-wide effects of TWIST1 overexpression in MM PCs were determined. Furthermore, ectopic expression of TWIST1 was found to enhance MM PC migration in vitro, consistent with the enrichment of genes involved in cell motility from Gene Ontology (GO) analysis. To evaluate the role of TWIST1 overexpression in vivo, the 5TGM1/KaLwRij murine model of myeloma was utilised. TWIST1 overexpression in 5TGM1 cells increased total tumour burden and extramedullary growth of tumour in the spleens of recipient mice. Transcriptome analysis demonstrated that TWIST1 overexpression in 5TGM1 cells led to overexpression of genes involved in cytokine production, regulation of cell death and cell motility. These studies highlight that TWIST1, downstream of MMSET promotes MM PC motility, which, in part contributes to the aggressive phenotype of t(4;14) MM patients. Taken together, this research reveals the role of TWIST1 in MM pathogenesis and adds to the current knowledge of mechanism underlying aggressive disease progression in t(4;14) patients.