Translational Control by Human Pumilio Proteins

Project Summary The human RNA-binding proteins, PUM1 and PUM2, are essential for mammalian development and their dysfunction is linked to multiple human diseases including developmental defects, neurological disorders, infertility, cancers, and mitochondrial dysfunction. These important functions compel our overall objective to discover how PUM1&2 control the flow of genetic information from gene to mRNA to protein and to identify the full repertoire of genes that they regulate. PUM1&2 bind to thousands of mRNAs in human cells by recognizing an RNA sequence called the Pumilio Response Element (PRE). Previous research showed that PUM1&2 promote degradation of hundreds of these PRE-containing mRNAs by recruiting RNA decay enzymes. It is now clear, however, that this mechanism represents only one type of PUM-mediated regulatory outcome. Thousands of mRNAs are bound by PUM1&2 but are not degraded. Therefore, it is now necessary to determine how PUM1&2 control the fate of all target mRNAs. The resulting data will provide a comprehensive view of their regulatory roles in biology and pathogenesis. We propose that human PUM1&2 repress many target mRNAs by inhibiting the process of translation. This hypothesis is supported by multiple examples of genes that are repressed by PUM1&2 at the level of protein abundance in the absence of mRNA degradation. The mechanism and prevalence of this translational inhibition is unknown. In addition, our data indicate that for some genes PUM-mediated translational inhibition can synergize with RNA degradation to regulate gene expression to a larger extent than either process alone. RNA molecules form structures that influence their function and fate. While biochemical evidence indicates that RNA structure can modulate PUM-PRE interactions, its effect in vivo remains unknown. In fact, there is an overall lack of RNA structural information of mRNAs in human cells that limits our understanding of how that structure influences gene regulation by RNA-binding proteins like PUM1&2. The proposed research seeks to determine how PUM1&2 inhibit translation and to identify the translational regulatory factors that are necessary for PUM1&2 activity. The structure of human mRNAs will be determined and its effect on PUM-mRNA interactions and regulatory network will be analyzed. By integrating this new data with existing knowledge of which mRNAs are bound and degraded by PUM1&2, we will develop a comprehensive understanding of this key genetic regulatory network. Discovery of the full regulatory network of PUM1&2 will provide new insights into how they control gene expression to regulate normal biological processes. Moreover, this knowledge will help elucidate how their dysfunction leads to diseases such as neurodegeneration and cancer.