Overexpression of transcripts originating from the MMSET locus characterizes all t(4;14)(p16;q32)-positive multiple myeloma patients.
Multiple myeloma (MM) is a B-lineage malignancy characterized by diverse genetic subtypes and clinical outcomes. The recurrent immunoglobulin heavy chain (IgH) switch translocation, t(4;14)(p16;q32), is associated with poor outcome, though the mechanism is unclear. Quantitative reverse-transcription-polymerase chain reaction (RT-PCR) for proposed target genes on a panel of myeloma cell lines and purified plasma cells showed that only transcripts originating from the WHSC1/MMSET/NSD2 gene are uniformly dysregulated in all t(4;14)POS patients. The different transcripts detected, multiple myeloma SET domain containing protein (MMSET I), MMSET II, Exon 4a/MMSET III, and response element II binding protein (RE-IIBP), are produced by alternative splicing and alternative transcription initiation events. Translation of the various transcripts, including those from major breakpoint region 4-2 (MB4-2) and MB4-3 breakpoint variants, was confirmed by transient transfection and immunoblotting. Green fluorescent protein (GFP)-tagged MMSET I and II, corresponding to proteins expressed in MB4-1 patients, localized to the nucleus but not nucleoli, whereas the MB4-2 and MB4-3 proteins concentrate in nucleoli. Cloning and localization of the Exon 4a/MMSET III splice variant, which contains the protein segment lost in the MB4-2 variant, identified a novel protein domain that prevents nucleolar localization. Kinetic studies using photobleaching suggest that the breakpoint variants are functionally distinct from wild-type proteins. In contrast, RE-IIBP is universally dysregulated and also potentially functional in all t(4;14)POS patients irrespective of fibroblast growth factor receptor 3 (FGFR3) expression or breakpoint type.
Keats
Jonathan J
JJ
Department of Oncology, University of Alberta & Cross Cancer Institute, 11560 University Ave, Edmonton, AB, T6G 1Z2, Canada.
Maxwell
Christopher A
CA
Taylor
Brian J
BJ
Hendzel
Michael J
MJ
Chesi
Marta
M
Bergsagel
P Leif
PL
Larratt
Loree M
LM
Mant
Michael J
MJ
Reiman
Tony
T
Belch
Andrew R
AR
Pilarski
Linda M
LM
D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D002883:Chromosomes, Human, Pair 14 / Q000235:genetics*; D002894:Chromosomes, Human, Pair 4 / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D011495:Histone-Lysine N-Methyltransferase; D006801:Humans; D007700:Kinetics; D009101:Multiple Myeloma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D015996:Survival Rate; D014158:Transcription, Genetic / Q000235:genetics*; D014178:Translocation, Genetic / Q000235:genetics*; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D012097:Repressor Proteins; D011495:Histone-Lysine N-Methyltransferase; C419586:NSD2 protein, human