Defining the regulation of repressive epigenetic marks by the ubiquitin-conjugating enzyme UBE2K and its impact on cell fate decisions and organismal aging

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The development and survival of an organism are linked to its ability to maintain the integrity of the cellular proteome. Human embryonic stem cells (hESCs) are immortal in culture. This capacity demands avoidance of any imbalance in protein homeostasis (proteostasis) that would otherwise compromise hESC identity. We have found that hESCs exhibit increase levels of UBE2K, an E2 enzyme that regulates protein ubiquitination. Notably, UBE2K is required for neuronal differentiation of hESCs. Interestingly, we found that UBE2K binds to histone H3.3 and regulates its ubiquitination. Moreover, loss of UBE2K changes the epigenetic landscape of hESCs by inducing trimethylation of H3K9. Although the histone code has a critical role in chromatin and gene regulation, the molecular mechanisms that modulate the unique chromatin pattern of hESCs remain largely unknown. Here we will seek to define how modulation of H3K9 trimethylation by UBE2K impinges upon neurogenesis of hESCs. Since cell reprogramming involves a marked reorganization of chromatin, we will examine whether changes in UBE2K levels alter the H3K9me3 landscape of somatic cells and facilitate cell reprogramming. Given the importance of histone modifications in cell function, we will define the molecular mechanisms by which UBE2K regulates H3K9 trimethylation. Epigenetic changes are not only a determinant of development but also a hallmark of aging. H3K9me3 epigenetic modifications are downregulated during the aging process. Most importantly, the epigenetic landscape can be modulated to extend lifespan in model organisms such as C. elegans. These findings highlight the role of epigenetic dysregulation as a driver of mammalian aging. Thus, defining novel modulators of age-associated epigenetic marks may provide further insights into aging research. Interestingly, we have observed that loss of UBE2K triggers H3K9me3 levels in C. elegans. We will examine whether modulation of UBE2K is sufficient to extend longevity and ameliorate the downregulation of H3K9me3 associated to biological aging. Finally, we will perform a RNAi screen to define how UBE2K modulates trimethylation of H3K9 in vivo. Thus, our experiments can define the interconnectedness between two tentative hallmarks of aging (i.e., loss of proteostasis, epigenetic changes) and uncover novel mechanisms to slow down the aging process. Taken together, our research proposal can have a big impact in several fields such as stem cell research, cell therapy, aging and age-related diseases.