Maintenance of proteostasis in human aneuploid cell lines

• Applicant: Professorin Dr. Zuzana Storchova
• Subject Area: General Genetics and Functional Genome Biology ; Biochemistry ; Cell Biology
• Term: from 2012 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 209937551

Abnormal chromosome numbers, or aneuploidy, affects physiology in nearly all eukaryotic organisms and is particularly detrimental in non-transformed human cells. The physiological changes triggered by aneuploidy are not fully clarified, but it has been well documented that imbalanced protein expression due to an extra chromosome copy is necessary for the observed phenotypes. Aneuploidy is also prevalent in cancer, where nearly 70% of cancers show karyotypes differing from diploidy. Therefore, aneuploidy might serve as a novel target for cancer therapy. The main aim of our research is to dissect the molecular mechanisms that underlie the consequences of aneuploidy in human cells. To facilitate our efforts, we have established a series of human cell lines where a single chromosome is added to normal, diploid cells (Stingele et al, 2012). By comparing the quantitative genome, transcriptome and proteome changes in aneuploid cells with their diploid controls, we found that the genes on the extra chromosome are transcribed and translated, yet the protein levels often do not scale linearly with the gene and mRNA copy number changes (Stingele et al, 2012). We identified pathways that were differentially regulated in response to aneuploidy. This so called Aneuploidy Response Pattern does not depend on the specific chromosome composition and resembles the changes observed in cells suffering from proteotoxic stress (Durrbaum et al, 2014). Additionally, aneuploid cells accumulate ubiqutin-positive protein agreggates and activate selective autophagy mediated by SQSTM1/p62 (Stingele et al, 2012; Stingele et al, 2013). Most recently we found that the HSP90 and HSF1 functions and, hence, protein folding are impaired by aneuploidy (Donnelly et al, 2014). Thus, we propose that aneuploidy and subsequent abnormal protein expression leads to altered proteostasis, which in turn affect the cell physiology (Donnelly et Storchova, 2014). In the continuation of our project we will further elucidate the changes in maintenance of protein homeostasis caused by aneuploidy and the underlying molecular mechanisms. Firstly, by detailed analysis of the changes in regulation of HSF1 function, such as posttranslation modifications and binding of HSF1 to the promoter regions, we will identify the mechanisms underlying the HSF1 deficiency in human cells. We will also test the possibility that HSF1 is inactivated due to its sequestration to cytoplasmic protein aggregates or by degradation via autophagy that is highly active in aneuploid cells. Secondly, we will disect the mechanisms by which aneuploid cells activate autophagy. We will also analyze whether the defect in protein folding is causally linked with the autophagy activation. Finally, we will determine what are the consequences of the changes in maintenance of protein homeostasis for physiology of aneuploid cells and whether the protein folding defect is the primary cause of phenotypes observed in aneuploid cells.

• DFG Programme: Research Grants