Aurora-A Polymorphisms in Multiple Myeloma: Implications On Chromosomal Instability

Abstract 3982

Aurora-A kinase (AURKA) is a member of the serine/threonine kinase family and has been implicated in regulating centrosome function, spindle assembly, and mitosis progression. The AURKA gene is frequently amplified in many cancers associated with aneuploidy and supernumerary centrosomes. In multiple myeloma (MM), a highly aneuploid hematologic malignancy, AURKA is frequently overexpressed and associated with poor prognosis. Several single nucleotide polymorphisms (SNPs) of the AURKA gene have been shown to be associated with certain types of cancer. One of the best characterized allelic variants is 57Val>Ile. We have analyzed this SNP in the data set of the genome-wide association study (GWAS) from 1014 German MM patients and correlated the allelic distribution with cytogenetic abnormalities assessed by interphase fluorescence in-situ hybridization (iFiSH). 728 (72%) samples were homozygous for 57Val, 286 (28%) homozygous for 57Ile or heterozygous. Of all analyzed cytogenetic aberrations, only del17p21 was significantly unequally distributed between the two isoforms. Specifically, samples homozygous for 57Ile or heterozygous (Val57Ile) harbored del17p21 less frequently than samples that were homozygous for 57Val (p<0.05). We were able to confirm these data by direct sequencing of 294 randomly selected samples from the same cohort. Therefore, we went on to analyze the differential effects of the 57Val>Ile SNP of AURKA on a chromosomally stable, Val57Ile heterozygous cell line, U2OS. Clones conditionally expressing either AURKA-57Ile (n=8) or -57Val (n=8) were generated. While no significant differences could be detected between levels of kinase activities of the two isoforms, growth of U2OS-57Val clones was significantly reduced compared to U2OS-57Ile cells (p<0.05). Furthermore, AURKA-57Val conferred a marked increase in centrosomal amplification (p<0.02) associated with a significantly higher frequency of polyploid cells and cells displaying micronuclei as a marker of chromosome missegregation upon conditional expression of AURKA-57Val (p<0.02). Interestingly, given the striking low frequency of del17p21 in MM samples homozygous for 57Ile or heterozygous (Val57Ile), we were able to show that only AURKA-57Val triggers p53/p21 activation in respective cells. Flowcytometry and live cell imaging revealed a significantly shorter duration of mitosis in AURKA-57Val compared with -57Ile expressing cells.

In summary, we show that the AURKA allelic variant 57Val is associated with del17p21 in a large cohort of MM samples, and that conditional expression of AURKA-57Val versus -57Ile leads to increased centrosome amplification levels, polyploidization, and chromosomal instability, resulting in an overall growth delay. These results suggest that AURKA-57Val might be involved in malignant transformation and clonal evolution of multiple myeloma by induction of chromosomal instability.