Nuclear pore complex (NPC) composition in hepatocarcinogenesis.

• Applicant: Professor Dr. Stephan Singer
• Subject Area: Pathology
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 267361865

Signalling cascades of most cancer-relevant pathways cross the nuclear envelope and thereby rely on transport events between the cytoplasm and the nucleus. Nucleocytoplasmic transport occurs exclusively through the nuclear pore complex (NPC) a multiprotein complex embedded in the nuclear envelope and composed of ~30 nucleoporins (Nups). Recent studies, predominantly conducted in S. cerevisiae and D. melanogaster, indicate that a subset of Nups is directly or indirectly linked to gene expression and involved in cell cycle regulation, stress response, and development. Given its central position and its multiple functions it seems most likely that the NPC may serve as an important modulator of oncogenic and/or tumorsuppressive pathways. So far NPC components have been linked to cancer mainly in the context of oncogenic Nup-containing fusion proteins resulting from chromosomal translocations mostly found in leukemia patients. However, the role of Nups in cancer biology independent of these oncogenic protein chimeras remains poorly understood. We could previously show that the nucleoporin Nup98 is connected to the p53 pathway in HCC and downregulated in a significant fraction of murine and human HCCs (Singer et al, 2012). Interestingly, own preliminary data indicate that Nup153, sharing structural and functional similarities with Nup98, is upregulated in a subset of HCCs. Here, we propose to investigate comprehensively Nup expression on mRNA and protein level in tumorous and non-tumorous liver tissues and cell lines to identify alterations of the overall NPC composition in hepatocarcinogenesis. Nup protein expression will be determined in collaboration with the Beck lab (EMBL, Heidelberg) that has developed targeted proteomic assays for all known human Nups. The results will be correlated with clinico-pathological data such as tumor grading, staging, and etiology to get insights how these parameters/factors may contribute to an altered Nup expression. To test if remodelling of the NPC is required to maintain a malignant phenotype we will perform RNAi screens in liver derived cancer cells by using different read-outs (e.g. cell viability, proliferation, and migration). Based on the resulting expression profiles and the phenotypic changes the most promising Nups will be studied more detailed. Genes/pathways regulated by these candidate Nups will be identified by performing genome-wide expression arrays upon knockdown or overexpression. Possible regulatory mechanisms to be analyzed will include Nup/chromatin interactions, import of transcription factors, export of gene products such as mRNAs, among others. In this project we aim to unveil tumor-specific and functional relevant alterations of the NPC composition in HCC. Interfering with such a remodeling process in a therapeutic approach could be the basis for future studies.

• DFG Programme: Research Grants