Alternate Splicing Is a Frequent Event and Impacts Clinical Outcome in Myeloma: A High-Density Exon Array Analysis of Uniformly Treated Newly-Diagnosed Myeloma Patients

Alternate splicing is an important post translational change that alters specificity of gene function. Misregulation of alternative splicing has been implicated in number of disease processes including cancer. We have here analyzed alternate splicing in myeloma using high throughput exon array analysis. The GeneChip Human Exon 1.0 ST Arrays used in this investigation not only provides information on expression levels for genes, but as the probe sets are spread evenly over each exon, the array data also provides information on presence of each exon and identify recurrent alternately spliced genes. We conducted a study in series of 170 newly-diagnosed patients with multiple myeloma treated homogeneously in tandem transplantation IFM trials. RNA isolated from CD138 purified MM cells collected at the time of diagnosis were analyzed using the GeneChip Human Exon 1.0 ST Arrays. The dChip software was modified to analyze exon array data. We first normalized gene-level expression values across samples, and then identified differentially expressed exons between two sample groups. These exons are candidates for alternatively splicing events. We observed over 100 genes with candidate alternate splicing events, which have up or down-regulation of an exon relative to the baseline group in more than 20% patients. Dividing the group based on response, 52 alternately spliced exons were identified as influencing response to therapy. The genes and their exons with highest frequency of alternate splicing were CD79A exon 5 and 6, EDNRB exon 2, RASSF1 exon 8, CD1d exon9, TGFBetaRII exon 1, Calmin exon2, CEACAM1 exon 7, MADH1 exon 7, TBX5 exon 2, Amyloid beta exon 14, Nit protein 2 exon 10, Thymidylate synthetase exon 7. Amongst these genes, 32 genes had the most influence on response with over 50% differential frequency in patients achieving CR. Similarly we have identified 85 alternately spliced genes as influencing overall survival between groups divided by less than or more than 48 month survival. The genes with highest frequency of alternate splicing were NOTCH2 exon 18, CXCL3 exon 8, CD9 exon 3 Calmin exon 2, TIMELESS exon 12, SPOUTY homolog 1 exon 4, Amyloid beta exon 14, Nit protein 2 exon 10, Cyclin A2 exon7, lymphocyte antigen 6 exon 7. Forty-nine genes within this group had the most influence on overall survival. Number of spliced variants were shared between both response and survival groups suggesting their biological and functional significance. Further validation of these alternate splicing is under investigations. This study highlights significant frequency of alternate splicing and points to the need for evaluation of not only the expression level of genes but also post translational modifications. The genes identified here are important target for therapy as well as possible immune modulation.