Dysregulation of Protein Translation in Colon Cancer through eIF3H

• Applicants: Dr. Mario Brosch; Professor Dr. Jochen Hampe; Professor Dr. Clemens Schafmayer
• Subject Area: General Genetics and Functional Genome Biology ; Cell Biology
• Term: from 2013 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 249508859

With estimated 70,000 cases of colorectal cancer (CRC) diagnosed in Germany each, CRC is a common type of cancer and the second leading cause of cancer death. Genome-wide association studies (GWAS) have identified over 20 susceptibility loci for non-syndromatic CRC and systematic international resequencing projects are increasingly defining its somatic mutational landscape. However, both a functional understanding of germ line risk variants and an integration of germ line risk factors with the somatic mutational signature of CRC are as yet largely lacking. A common variant at 8q23, that has been shown to disturb a transcriptional repressor of eukaryotic translation initiation factor 3H (eIF3H) has been identified by GWAS. Further, somatic amplification of EIF3H in CRC cell lines and upregulation of the transcript in established colon cancer has been shown. Thus, overexpression of eIF3H both by means of germ line variants and by somatic evolution are a consistent observation in this tumor entity. Thus, given the function of eIF3H as a eukaryotic translation initiation factor, increased expression may have profound consequences on the regulation of translation, with a fundamental change of the proteomic landscape in tumor tissue. The main goal of the application is therefore a better elucidation of the biological effects of eIF3H dysregulation in colon cancer. Because eIF3H has been linked to reinitiation competence after uORF-translation, increased levels of eIF3H may abolish the regulatory control of oncogenes by allowing unregulated translation of protein product despite the presence of a regulatory uORF. Up until recently, systematic (transcriptome-wide) analyses of protein translation have not been possible. The recently developed ribosome profiling allows the analysis of ribosome binding with base pair resolution and has been employed by the applicants in the definition of more than 4000 novel uORFs. Thus, this project will employ ribosome profiling for the definition of specific translational targets under the hypothesis of increased translation of characteristic oncogenes and reduced translation of tumor suppressor genes caused by overexpression of eIF3H.First, translational targets of eIF3H will be identified in cell lines with abolished or increased eIF3H expression. Second, we will define the global translational dysregulation in CRC and help to identify eIF3H targets by surveying the translational landscape in matching tumor and normal tissue with varying degrees of eIF3H expression. Using the bioinformatic cross-section of the above agendas, specific genes that are regulated by eIF3H and of relevance to CRC biology shall be identified and then validated using targeted reporter assays and analysis in a large CRC tumor bank. In summary, this project shall provide both an in-depth understanding of a germ line and somatic risk locus for CRC and shed new light on the role of translational gene expression control in CRC.

• DFG Programme: Research Grants