The central dogma of molecular biology describes the cellular processes that are involved in the replication of DNA and expression of genes within a genome. Once considered definitive, it has instead been continuously modified and refined, as new discoveries bring novel insights to our understanding of molecular and cellular biology. Recent studies show strong and convincing evidence that protein synthesis occurs in the nucleus;however, the functional significance of nuclear translation remains unknown. Unlike the compartmentalization of cytoplasmic functions into membrane-bound organelles, activities within the nucleus are contained in non- membranous assemblies, or nuclear bodies (NBs). Promyelocytic leukemia (PML) nuclear bodies have multiple proposed functions, but the precise role of PML bodies remains poorly characterized. Prior research suggests that PML bodies are involved in protein degradation, apoptosis, and the response to cellular stress. Additional evidence also indicates that PML bodies may play a role in protein synthesis. Several components of the translation machinery including ribosomal proteins, eIF3, eIF4E, and elongation factor 1 are found in PML bodies. Moreover, it is suggested that PML bodies require eIF4E for proper assembly. Based upon the overwhelming evidence that PML bodies contain translation machinery, we have tested and determined that there is indeed PML-mediated nuclear translation. This proposal will determine how PML-localized protein translation functions in the context of cellular stress and transformation, and will identify the proteins involved in translation at PML bodies.
Aim 1 will determine how PML-mediated nuclear translation is altered by cell stress and transformation and investigate the link between nuclear translation and aberrant cell growth or proliferation.
Aim 2 will identify the proteins present at translating PML bodies in normal, stressed, and transformed cells using immunoprecipitation and mass spectrometry. In tandem, the dynamic assembly of translating PML bodies will be interrogated to determine if proteins involved in translation can form PML bodies de novo.
Aim 3 will determine if experimental manipulation of PML expression alters nuclear translation and the transformation efficiency thus establishing a novel role for PML and nuclear translation in disease. The experiments described in this proposal are designed to test the novel hypothesis that nuclear translation occurs at PML bodies and is involved in the regulation of the stress response and cellular transformation. This study also takes a unique approach to examine the mechanism of tumor suppression by PML through addressing the role of PML mediated nuclear translation in cell fate choices. Overall, these experiments will contribute to the understanding o a new process, nuclear translation, and may uncover previously unknown therapeutic targets for multiple cancers.
Cellular transformation is a hallmark cancer and occurs when normal cells override cell cycle checkpoints and/or disrupt the action of tumor suppressors, proteins which regulate cell growth. Promyelocytic leukemia protein, PML, is a tumor suppressor protein localized to PML bodies;unique structures within the nucleus that participate in many cellular processes. The work described in this study suggests that PML bodies are involved in protein quality control within the nucleus which may function to regulate the transition of normal cells to a cancerous state.