Impact of early centrosome deregulation in malignant transformation

Abstract

Centrosome amplification (CA) is a hallmark of human cancers and is therefore a potential feature to explore for prognosis and therapy. However, the poor understanding of its origin and impact has limited its use in the clinic. Here, we used Barrett’s esophagus (BE) tumorigenesis as a human cancer model to test if CA has a contributory role in tumorigenesis and progression. Barrett’s esophagus is a premalignant condition and its neoplastic progression is a process with well-characterized and defined steps that go from metaplasia (premalignant condition - BE) to dysplasia (low- or high-grade intraepithelial neoplasia), adenocarcinoma (invasive neoplasia) and metastasis. Given that CA arises in BE metaplasia and that its incidence significantly increases from metaplasia to dysplasia, we posed the hypothesis that CA may play an important role in the acquisition of malignant properties. If this hypothesis is correct, then an increase of CA in metaplasia and/or a decrease of CA in dysplasia would be sufficient to respectively promote or reduce malignant properties such as invasiveness potential. To test these hypotheses, we first tested two different methods to reduce the CA levels in dysplasia cells: depletion of important molecules in the centrosome duplication cycle - PLK4, SAS6 and STIL - by siRNA, and inhibition of PLK4 activity using the specific chemical inhibitor centrinone-B. We then assessed changes in migration and invasive potential using 2D migration and invasion assays and 3D cell cultures. Both strategies were effective in reducing CA in dysplasia cells but as the treatment with the inhibitor acts directly on the protein's activity level, its effects were more quickly detected. Importantly, by providing the opportunity to reduce CA levels by affecting different molecules, the siRNA approach allowed us to confirm if the effects in the invasiveness properties of dysplasia cells is in fact a consequence of the reduction in the number of centrioles, and not just due to the dysfunction of specific molecules. Indeed, while results obtained with 2D migration and invasion assay were mostly inconclusive and further optimization is needed, we found that reduction of CA levels, with both approaches, reduced the invasiveness capacity of dysplasia cells in 3D cultures. Our findings therefore support a role for CA in promoting the invasiveness capacity in dysplasia, and provided important clues into their mechanisms that will be explored in the future. We then tested if an increase in CA is sufficient to induce invasion in metaplasia cells. To do this we first depleted p53 in metaplasia cells by siRNA, already known to increase CA in these cells, and then assessed their behavior using 3D cell cultures. Interestingly, our preliminary tests did not reveal any phenotypic differences in metaplasia cells with increased CA when compared to the controls. These findings indicate that increasing CA levels in metaplasia may not be sufficient, by itself, to induce an invasive capacity in metaplasia cells. In the future, testing different approaches to induce CA in these cells, as well as assessing their impact in cell migration and invasion using other assays, will be important to confirm this. By showing that CA contributes to the invasiveness potential in dysplasia, our results reveal the importance of CA in the acquisition of malignant properties in BE progression. These findings may contribute to new clinical tools, namely using CA as a biomarker of progression. Given widespread occurrence of CA in human tumors, our results may be extended to other cancers where CA is prevalent.