RHAMM expression and isoform balance predict aggressive disease and poor survival in multiple myeloma

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Abstract
Multiple myeloma (MM) plasma cells (PCs) express receptor for hyaluronan-mediated motility (RHAMM), a hyaluronan-binding, cytoskeleton and centrosome protein. The most abundant RHAMM isoforms in MM are full-length RHAMM (RHAMMFL) and the splice variant RHAMM-exon4. We separately examined the significance of RHAMM expression, and isoform balance, in 2 groups of MM patients. In oligonucleotide microarray experiments (n = 210, Arkansas), increasing RHAMM mRNA expression in MM PCs is strongly associated with osteolytic bone lesions (P < .001), and event-free (P = .05) and overall (P = .04) survival. Semiquantitative determination of RHAMM isoform expression (Alberta, Canada) used capillary electrophoretic detection and measurement of RHAMM-exon4/RHAMMFL reverse-transcriptase-polymerase chain reaction (RT-PCR) products. RHAMM isoforms are rarely expressed concurrently in single MM PCs; the pattern of isoform expression, at the single-cell level, is approximated in larger numbers of cells by the RHAMM-exon4/RHAMMFL ratio. Absolute RHAMM expression and the RHAMM-exon4/RHAMMFL ratio are only partially correlated in MM PCs; in cell lines, absolute RHAMM expression is elevated in mitosis, while RHAMM ratios remain stable. Temporal examination of MM patients9 peripheral blood reveals that the RHAMM-exon4/RHAMMFL ratio increases with disease burden. The RHAMM-exon4/RHAMMFL ratio in diagnostic bone marrow samples (n = 101, Alberta) is an independent prognostic factor. Thus, expression and splicing of RHAMM are important molecular determinants of disease severity in MM. (Blood. 2004;104:1151-1158)