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Total Proteome Analysis Identifies Migration Defects as a Major Pathogenetic Factor in Immunoglobulin Heavy Chain Variable Region (IGHV)-unmutated Chronic Lymphocytic Leukemia*[S]

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The mutational status of the immunoglobulin heavy chain variable region defines two clinically distinct forms of chronic lymphocytic leukemia (CLL) known as mutated (M-CLL) and unmutated (UM-CLL). To elucidate the molecular mechanisms underlying the adverse clinical outcome associated with UM-CLL, total proteomes from nine UM-CLL and nine M-CLL samples were analyzed by isobaric tags for relative and absolute quantification (iTRAQ)-based mass spectrometry. Based on the expression of 3521 identified proteins, principal component analysis separated CLL samples into two groups corresponding to immunoglobulin heavy chain variable region mutational status. Computational analysis showed that 43 cell migration/adhesion pathways were significantly enriched by 39 differentially expressed proteins, 35 of which were expressed at significantly lower levels in UM-CLL samples. Furthermore, UM-CLL cells underexpressed proteins associated with cytoskeletal remodeling and overexpressed proteins associated with transcriptional and translational activity. Taken together, our findings indicate that UM-CLL cells are less migratory and more adhesive than M-CLL cells, resulting in their retention in lymph nodes, where they are exposed to proliferative stimuli. In keeping with this hypothesis, analysis of an extended cohort of 120 CLL patients revealed a strong and specific association between UM-CLL and lymphadenopathy. Our study illustrates the potential of total proteome analysis to elucidate pathogenetic mechanisms in cancer.

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Author contributions: J.Z., N.R.K., and A.R.P. designed research; G.L.E. performed research; G.L.E., J.Z., P.V.J., N.R.K., and A.R.P. analyzed data; G.L.E., J.Z., R.E.J., K.J.T., P.V.J., N.R.K., and A.R.P. wrote the paper; R.E.J. generated MS data; K.J.T. generated migration assay data; K.L. and G.G.J. characterized clinical features of patient samples; M.O. provided patient samples and clinical data; K.P. contributed to the generation of MS data.

*

This work was supported by the North West Cancer Research (UK), Leukaemia & Lymphoma Research (UK) and the Liverpool Cancer Research UK Centre Research Development Fund.

[S]

This article contains supplemental Tables S1–S3, supplemental Figs. S1–S5, and supplemental data.

Both authors contributed equally to this work.

‡‡

Present address: Translational Molecular Diagnostic Centre, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom.