Altered microtubule plus end assembly during mitosis as a key trigger for chromosomal instability in human cancer cells

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The perpetual gain or loss of whole chromosomes during mitotic cell division is known as chromosomal instability (CIN) and represents a major hallmark of human cancer. CIN results in evolving aneuploidy, which is thought to provide rapid adaptation capabilities and thereby might support tumorigenesis and tumor progression. Despite the importance of this highly prevalent cancer phenotype the molecular mechanisms underlying CIN remained elusive. Our most recent work now revealed a key and wide-spread trigger for CIN in human cancer cells. In fact, increased microtubule plus end dynamics within mitotic spindles can trigger transient mitotic spindle abnormalities leading to erroneous microtubule-kinetochore attachments and chromosome missegregation. We identified the oncogenic Aurora-A kinase as a key inducer of this phenotype and the tumor suppressor genes CHK2 and BRCA1 as negative regulators of Aurora-A. However, it is not clear how the CHK2-BRCA1 tumor suppressor pathway can restrain the activity of Aurora-A and how the hyper-activity of the Aurora-A kinase at mitotic centrosomes can lead to increased microtubule plus end assembly and chromosome missegregation. Given the fact that increased microtubule plus end assembly underlies chromosomal instability in human cancer cells it is pivotal to understand the molecular mechanisms ensuring proper microtubule dynamics during mitosis and to reveal how an increase in microtubule plus end assembly can drive chromosome missegregation and CIN. These questions will be in focus of our research proposal. In particular, we will address the question how the CHK2-BRCA1 tumor suppressor pathway can restrain Aurora-A activity at mitotic centrosomes and and we will analyze how an increase in centrosomal Aurora-A activity is causing spindle assembly and positioning defects that subsequently might facilitate the generation of hyper-stable and erroneous microtubule-kinetochore attachments. Moreover, we aim to systematically identify novel regulators of microtubule plus end assembly that might be altered in human cancer and thus, might represent novel CIN genes in cancer. For this, we will use large-scale siRNA screens based on a new phenotypic assay that we recently developed in our lab to robustly identify microtubule assembly factors. Newly identified genes that mediate an increase in microtubule assembly rates and chromosomal instability will be subject to detailed characterization for their role during mitosis and for their alteration in human cancer. Thus, our research plan aims to characterize the phenotype of increased microtubule plus end assembly as a key mechanism for CIN at a molecular level and to identify genes that contribute to this intriguing phenotype in human cancer cells. Those CIN genes might represent attractive targets for anti-cancer therapy to suppress the tumor promoting CIN phenotype.