The t(4;14) chromosomal translocation occurs in approximately 20% of mutiple myeloma (MM) patients, leading to the deregulated expression of two genes located on 4pl6.3: the fibroblast growth factor receptor 3 (FGFR3) and the putative transcription factor MMSET. Interestingly, FGFR3 point mutations known to be associated with autosomal dominant human skeletal disorders have been found in some MM cell lines with the t(4;14) (the Y373C and K650E mutations in KMS-11 and OPM-2 cell lines, respectively) but their pathogenetic role in MM is still controversial. We have characterized the t(4;14) from the recently established MM cell line KMS-18 and found that the FCFR3 is highly expressed as isoform Illb and mutated at codon 384 within the transmembrane domain. This novel mutation leads to the G384D aminoacid substitution within a highly conserved pentameric sequence thought to play an important role in receptor dimerization. We investigated the functional activity of FGFR3 mutants in KMS-18, KMS-11 and OPM-2 cell lines. In particular, we found that KMS-11 and OPM-2 cell lines express phosphorylated FGFR3 at appreciable levels even in the absen:e of the aFGF ligand, indicating a constitutive activation of the mutated receptors. However, the addition of aFGF is capable to increase further the receptor phosphorilation in a dosedependent manner. Conversely, G384D mutant in KMS-18 cells is phosphorylated only in the presence of the ligand. In all of the cell lines, mutated FGFR3 receptors activate the MAP kinase signaling pathway. We also examined the transforming activity of the three FGFR3 mutants by focus formation assay in NIH-3T3 cells and found that Y373C aid K650E (albeit at different levels) but not G384D, are able to induce transformed foci. Our data suggest that FGFR3 mutations found in MM cell lines may result in different levels of receptor activation and support the hypothesis of their possible role in myelomagenesis.
|Issue number||11 PART I|
|Publication status||Published - 2000|
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