Sequencing the Multiple Myeloma Kinome: Absence of Mutation in Known Malignancy-Associated Kinases.

In approximately 50% of Multiple Myeloma (MM), translocation of non random genes into the IgH locus is believed to be the seminal event in the pathogenesis of the disease. Another 50% of cases are hyperdiploid and trisomic to certain autosomes, but do not harbor any translocation and thus are believed to have genetic alterations in unidentified loci. These observations, together with the finding of somatic mutations in FGFR3, N- and K-RAS, MYC, TP53 and CDKN2C/p18^INK4C during the later stages of MM indicate that defective signaling pathways likely play a role in the progression of this malignancy. Of relevance then, in recent years recurrent mutations in kinases have frequently been implicated in malignancies including notably colon cancer and melanoma. We have therefore begun a comprehensive effort to sequence the tyrosine kinome for mutations and genetic polymorphisms in MM. Of particular interest are 90 receptor tyrosine kinases, 43 receptor tyrosine kinase-like, 5 receptor guanylate cyclase, and a lipid kinase. We report here results from our pilot high throughput exon scanning in 32 human MM cell lines which initially focused on 13 kinases known to be somatically mutated in human cancers. To date we have expanded this effort to assess 30 genes with sequence obtained which currently spans 80% coverage of the kinase domains of these genes. A total of 1.9 million bp have been sequenced across 235 exons. No recurrent mutations have been identified in the kinase domains of the cancer-associated genes: SRC, ILK1, KIT, GUCY2F, PDGFRA; in the genetic disorder-associated kinases: BTK, EPHA4, LAMA2, EPHB6, ACVR2; and in the mutation hot spots of frequently mutated cancer gene PIK3CA. A novel missense mutation is however identified upstream of the kinase domain of FGFR3 changing a Ser residue to Arg at codon 433. This residue, which is conserved across species and in FGFR1 and FGFR2, has not been reported in myeloma and in thanatophoric dysplasia, but the biological significance of this mutation is unknown. Several single nucleotide polymorphisms were identified in the coding regions of some of these kinases. Notably, synonymous polymorphisms in the kinase domains of EPHA4, PDGFRA3, KIT, MLK1, ILK1, NTRK3, FLT3, ABL1, FES, MLK4, and EGFR1 were identified that changed a codon but not the amino acid. More importantly, we identified non-synonymous amino acid variations in the kinase domains of EPHA4, GUCY2F, PTK2, and PIK3CA genes that are more likely to effect variability in the activity of these kinases. In summary, no recurrent kinase mutations of significance in Myeloma development or progression have yet been identified. Sequencing of the known cancer associated kinases in MGUS and hyperdiploid MM patients is now underway and our data set is being expanded to include all 139 kinases.