Plasma Membrane Proteomics Identifies Biomarkers Associated with T(4;14) Multiple Myeloma

Abstract 1314

Multiple myeloma (MM) is characterized by recurrent chromosomal translocations. Patients with t(4;14) have very poor prognosis. MMSET, identified by its fusion to the IgH locus in t(4;14) MM, is universally overexpressed in t(4;14) MM. In order to identify cell surface biomarkers associated with t(4;14) MM for small molecule or antibody based therapies, we knocked down MMSET expression with shRNA and generated a cell line pair from KMS11, a t(4;14) MM cell line. We used quantitative mass spectrometry based on stable isotope labelling by amino acids in cell culture (SILAC) to identify plasma membrane proteins associated with MMSET overexpression. Using this approach, 55 cell surface proteins were identified as differentially expressed between KMS11 and KMS11/shMMSET. Western blot and flow cytometry analysis indicated SLAMF7 was universally over-expressed in t(4;14) MM cell lines and down-regulated by MMSET shRNAs. Quantitative RT-PCR (qPCR) analysis indicated MMSET shRNAs resulted in significant reduction of SLAMF7 mRNA, suggesting MMSET might regulate the transcription level of SLAMF7. ChIP followed by qPCR analysis indicated MMSET protein binding was concentrated in an upstream region (near −1,500 bp) of SLAMF7 transcript start site. Furthermore, SLAMF7 shRNA could induce G1 arrest or apoptosis and reduce clonogenetic capacity in t(4;14) MM cells. SLAMF7 is a self-ligand receptor, and we found that SLAMF7 extracellular domain (ECD) could specifically recognize t(4;14) MM cells. Overall, these results illustrated SLAMF7 might be a novel cell surface protein associated with t(4;14) MM, and SLAMF7 ECD might be an alternative approach for targeting SLAMF7 on t(4;14) MM.