Oncogenic H-Ras Reprograms Madin-Darby Canine Kidney (MDCK) Cell-derived Midbody Remnant Proteins Following Epithelial-Mesenchymal Transition

Epithelial-mesenchymal transition (EMT) is a highly conserved morphogenic process that allows highly polarized, immotile epithelial cells to transform into motile mesenchymal cells: it is a fundamental cellular process involved in embryonic development, tumour cell metastasis, organ fibrosis and tissue regeneration. To assess the contribution of secreted midbody remnants (MBRs) - a new class of membranous extracellular vesicle (EV) molecularly distinct from exosomes/small EVs - to the EMT process, we conducted a proteomic analysis of MBRs released from Madin-Darby canine kidney (MDCK) cells, and MDCK cells transformed with oncogenic H-Ras (21D1 cells). MBRs were harvested from cell culture media in milligram quantities using a continuous culture bioreactor device and purified using sequential centrifugation and buoyant density gradient centrifugation (OptiPrep). Gel-MS/MS protein profiling showed MDCK cell-MBRs reflect their epithelial origin (e.g., enriched CDH1, DSP, THBS1, OLCN, EPCAM proteins) and 21D1 cell-MBRs their mesenchymal phenotype (e.g., HRAS, VIM, MMP14, CDH2, WNT5A and enriched invasive and cell motility proteins). Prominent findings were the unique expression of the immune checkpoint protein NT5E/CD73 (ecto-5'-nucleotidase), and ser/thr kinases LIMK1/K2 in 21D1-MBRs (not present in MDCK cell-MBRs), and enrichment in Wnt signalling network proteins. Collectively, our findings suggest MBRs might play a previously unrecognized role in the EMT process. SignificanceO_LIEpithelial-to-mesenchymal transition (EMT) is a critical cell biological process that occurs during normal embryonic development and cancer progression. Our study describes, for the first time, the large-scale sequential purification of secreted midbody remnants (MBRs) and exosomes/sEVs from the in vitro cell line EMT model Madin-Darby canine kidney (MDCK) cells and MDCK cells transformed with oncogenic H-Ras (21D1 cells): GeLC-MS/MS protein profiling identified the repertoire of enriched MDCK-MBR proteins following EMT. C_LIO_LIMBRs display a proteome profile distinct from sEVs that is enriched with factors of the centralspindlin complex (KIF23.1, KIF4A, INCENP, CEP55, PLK1) and further include components of the mitochondrial network, cytokinesis, microtubule movement, and intercellular connection. C_LIO_LIIn the context of EMT, our data reveal simultaneous activation of EMT signalling pathways in MBRs including signalling receptor binding, regulation of cell differentiation, and Wnt, VEGF and PDGF signalling. C_LIO_LIWe identify several mesenchymal enriched networks in MBRs associated with focal adhesion, cell matrix, kinase activity, and cell shape/organisation, while epithelial derived MBRs are show enriched networks predominately associated with mitochondrial (processing/transport), midbody, and plasma membrane annotation. C_LIO_LIOur study sheds light on the signalling architecture of MBRs following oncogenic H- Ras-induced EMT: collectively, our data informs ongoing efforts to delineate oncogenic drivers of cancer initiation, progression, and metastasis. C_LI