[Biologic mechanisms of mitotic abnormalities and chromosome number changes in malignant tumors]

Abstract

The main goal of this work was to study the effect of Aurora kinase expression on cell ploidy and tumorigenesis. Fifty invasive breast cancer, 50 diffuse large B-cell lymphoma and 10 reactive lymph node samples were recruited in the study. Because of the significant correlation with the overall cell proliferation rate, the overexpression of Aurora B could not be stated on the basis of kinase expressing tumor cell fractions alone. The relative expression of Aurora B kinase is better reflected by the AMI index which represents the Aurora B expression in relation to the whole proliferative fraction of the tumor. A higher relative Aurora B expression was associated with higher mitotic activity in B-cell lymphoma. FISH analysis of the AURKB locus did not show any gains or amplifications in the samples analyzed. On the other hand, we have observed the loss of the gene in breast carcinoma and lymphoma samples as well. A strong correlation was shown between AURKB and TP53 copy numbers: AURKB loss was associated with TP53 deletion in all samples. According to our results on breast carcinoma, losses at 17p13.1 and chromosome 17 aneusomy determined by FISH showed a statistically significant correlation. Our study presents the frequent occurrence of chromosome 17 aneusomy in breast carcinoma and B-cell lymphoma samples. Chromosome 17 aneusomy evaluated by FISH correlated with aneuploidy determined by flow cytometry. Direct correlation between kinase expression and ploidy could not be shown. The highest AMI values were seen in B-ALCL samples, and it was associated with high chromosome 17 copy numbers and mitotic activity. The damaged Aurora B kinase function results in regulatory deficiencies in the CPC complex leading to mitotic errors, while p53 deficiency helps malignant cells to survive due to insufficient activation of the intrinsic apoptotic pathways. The upregulation of Aurora kinase B function may cause error in an important mitotic checkpoint, thus resulting in induction of aneuploid cell populations. These parallel effects finally increase the complexity of mitotic abnormalities and generate aneuploid cell populations.