Abstract
BackgroundGenetic instability is a hallmark of tumours and preneoplastic lesions. The predominant form of genome instability in human cancer is chromosome instability (CIN). CIN is characterized by chromosomal aberrations, gains or losses of whole chromosomes (aneuploidy), and it is often associated with centrosome amplification. Centrosomes control cell division by forming a bipolar mitotic spindle and play an essential role in the maintenance of chromosomal stability.However, whether centrosome amplification could directly cause aneuploidy is not fully established. Also, alterations in genes required for mitotic progression could be involved in CIN.A major candidate is represented by Aurora-A/STK15 that associates with centrosomes and is overexpressed in several types of human tumour.MethodsCentrosome amplification were induced by hydroxyurea treatment and visualized by immunofluorescence microscopy. Aurora-A/STK15 ectopic expression was achieved by retroviral infection and puromycin selection in HCT116 tumour cells. Effects of Aurora-A/STK15 depletion on centrosome status and ploidy were determined by Aurora-A/STK15 transcriptional silencing by RNA interference. Changes in the expression levels of some mitotic genes were determined by Real time RT-PCR.ResultsWe investigated whether amplification of centrosomes and overexpression of Aurora-A/STK15 induce CIN using as a model system a colon carcinoma cell line (HCT116). We found that in HCT116 cells, chromosomally stable and near diploid cells harbouring a MIN phenotype, centrosome amplification induced by hydroxyurea treatment is neither maintained nor induces aneuploidy. On the contrary, ectopic overexpression of Aurora-A/STK15 induced supernumerary centrosomes and aneuploidy. Aurora-A/STK15 transcriptional silencing by RNA interference in cells ectopically overexpressing this kinase promptly decreased cell numbers with supernumerary centrosomes and aneuploidy.ConclusionOur results show that centrosome amplification alone is not sufficient to induce chromosomal instability in colon cancer cells with a MIN phenotype. Alternatively, centrosome amplification has to be associated with alterations in genes regulating mitosis progression such as Aurora-A/STK15 to trigger CIN.
Highlights
Genetic instability is a hallmark of tumours and preneoplastic lesions
We investigated whether amplification of centrosomes and overexpression of Aurora-A/STK15 induce chromosomal instability (CIN) using as a model system a colon carcinoma cell line (HCT116)
We found that in HCT116 cells, chromosomally stable and near diploid cells harbouring a microsatellite instability (MIN) phenotype, centrosome amplification induced by hydroxyurea treatment is neither maintained nor induces aneuploidy
Summary
Genetic instability is a hallmark of tumours and preneoplastic lesions. The predominant form of genome instability in human cancer is chromosome instability (CIN). The presence of mutations of the mitotic checkpoint regulators BUB1 and BUBR1 and amplification of Aurora-A/STK15 ( known as BTAK, Aurora 2, and AIK1) in a subset of human colon cancers have suggested that CIN results primarily from deregulation of DNA replication and mitotic-spindle checkpoints [3]. Overexpression of the Aurora-A/ STK15 gene is often associated with centrosome amplification, chromosomal instability, aneuploidy, and transformation. The loss of genomic stability appears to be a key molecular and pathogenetic step occurring early in tumourigenesis creating a permissive environment for the occurrence of alterations in tumour suppressor genes and oncogenes [3] Another protein involved in these processes is the tumour suppressors p53, important regulator of the cell cycle and apoptosis that is frequently inactivated in human cancers. Aurora-A/STK15 transcriptional silencing by RNAi decreases both cells with supernumerary centrosomes and aneuploidy in HCT116 cells ectopically expressing Aurora-A/STK15
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