Chromosomal instability in aging and cancer

Among the central themes in human genetics are chromosomal copy number changes and genetic instability, which both are associated with the occurrence of disease and aging. At present, a cancer genetics dogma states that hematological malignancies arise as the result of defined chromosomal translocations, whereas mutations underlie epithelial solid tumors. However, beside mutations chromosomal changes have recently been shown to be also causatively involved in the initiation of epithelial tumors. For example, the continuous erosion of chromosome ends, the telomeres, may increase the risk for chromosomal aberrations, which in turn may result in genetic instability and cancer. As telomere attrition is associated with aging, this mechanism is attractive as it yields a rational explanation for the increasing incidence of cancer with aging. Another mechanism is characterized by an increased rate of chromosomal gains or losses and is commonly referred to as chromosomal instability (CIN). CIN typically results in a high number of aneuploid cells. CIN causing mutations were identified in genes such as BUB1, MAD2, securin, or CDC4. However, mutations in these genes are found only in a minority of tumors so that these mutations are at best responsible for a small fraction of the total cases. Furthermore, it seems unlikely that mutations in these genes could provide a rational and unifying explanation for age-associated increase in epithelial cancers. Therefore at present, both the impact during early tumorigenesis and origin of CIN in human cancers are unclear. At the same time, it has been known for several decades that aging is also associated with an increasing number of aneuploid cells. Thus, the analysis of mechanisms resulting in age dependent aneuploidy and the analysis of its possible impact in the initiation of cancer should be especially rewarding. This project aims at elucidating factors involved in CIN and age-dependent aneuploidy. We want to address the hypothesis whether CIN occurs early during tumorigenesis. Furthermore, we ask whether CIN is caused by chromosome segregation errors resulting in whole chromosome aneuploidies or by other mechanisms more prone to result in segmental aneuploidies. The project consists of three different steps: In a first, mainly descriptive step, we will employ latest 3D-multicolor FISH imaging techniques directly on tissue sections or on single cell suspensions to identify CIN/aneuploid regions in biological material. In a second step, we will apply to these CIN/aneuploid regions our unbiased whole genome amplification strategies for subsequent array-CGH. This strategy will yield a high-resolution analysis of the genome of the respective cells. Furthermore, this analysis will clarify whether in early lesions whole-chromosome or segmental-chromosome aneuploidies are more common. This distinction will allow drawing conclusion about the origin of early chromosomal changes. The third, functional step addresses the expression of selected genes in cells with chromosomal aberrations and involves RNAi for gene knockdown to verify that reduced function of these genes has indeed an impact on chromosomal stability. Thus, this project combines both descriptive approaches applied to biological material and functional in vitro technologies.

Among the central themes in human genetics are chromosomal copy number changes and genetic instability, which both are associated with the occurrence of disease and aging. At present, a cancer genetics dogma states that hematological malignancies arise as the result of defined chromosomal translocations, whereas mutations underlie epithelial solid tumors. However, beside mutations chromosomal changes have recently been shown to be also causatively involved in the initiation of epithelial tumors. For example, the continuous erosion of chromosome ends, the telomeres, may increase the risk for chromosomal aberrations, which in turn may result in genetic instability and cancer. As telomere attrition is associated with aging, this mechanism is attractive as it yields a rational explanation for the increasing incidence of cancer with aging. Another mechanism is characterized by an increased rate of chromosomal gains or losses and is commonly referred to as chromosomal instability (CIN). CIN typically results in a high number of aneuploid cells. CIN causing mutations were identified in genes such as BUB1, MAD2, securin, or CDC4. However, mutations in these genes are found only in a minority of tumors so that these mutations are at best responsible for a small fraction of the total cases. Furthermore, it seems unlikely that mutations in these genes could provide a rational and unifying explanation for age-associated increase in epithelial cancers. Therefore at present, both the impact during early tumorigenesis and origin of CIN in human cancers are unclear. At the same time, it has been known for several decades that aging is also associated with an increasing number of aneuploid cells. Thus, the analysis of mechanisms resulting in age dependent aneuploidy and the analysis of its possible impact in the initiation of cancer should be especially rewarding. This project aims at elucidating factors involved in CIN and age-dependent aneuploidy. We want to address the hypothesis whether CIN occurs early during tumorigenesis. Furthermore, we ask whether CIN is caused by chromosome segregation errors resulting in whole chromosome aneuploidies or by other mechanisms more prone to result in segmental aneuploidies. The project consists of three different steps: In a first, mainly descriptive step, we will employ latest 3D-multicolor FISH imaging techniques directly on tissue sections or on single cell suspensions to identify CIN/aneuploid regions in biological material. In a second step, we will apply to these CIN/aneuploid regions our unbiased whole genome amplification strategies for subsequent array-CGH. This strategy will yield a high-resolution analysis of the genome of the respective cells. Furthermore, this analysis will clarify whether in early lesions whole-chromosome or segmental-chromosome aneuploidies are more common. This distinction will allow drawing conclusion about the origin of early chromosomal changes. The third, functional step addresses the expression of selected genes in cells with chromosomal aberrations and involves RNAi for gene knockdown to verify that reduced function of these genes has indeed an impact on chromosomal stability. Thus, this project combines both descriptive approaches applied to biological material and functional in vitro technologies.