Human ribosome biogenesis and the regulation of the tumour suppressor p53

PhD ThesisRibosome production is an energetically expensive and, therefore, highly regulated process. Defects in ribosome biogenesis lead to genetic diseases called Ribosomopathies, such as Dyskeratosis Congenita (DC), and mutations in ribosomal proteins and ribosome biogenesis factors are linked to multiple types of cancer. During ribosome biogenesis, the ribosomal RNAs (rRNAs) are processed and modified, and defects in ribosome biogenesis lead to the activation of p53. This project aimed to investigate the functions of Dyskerin, mutated in X-linked DC, in human ribosome biogenesis and p53 regulation, and to explore the link between ribosome production and p53 homeostasis. Dyskerin is an rRNA pseudouridine synthase and required for telomere maintenance. There is some debate as to whether DC is the result of telomere maintenance or ribosome biogenesis defects. It is shown here that human Dyskerin is required for the production of both LSU and SSU, and knockdown of Dyskerin leads to p53 activation via inhibition of MDM2 via the 5S RNP, an LSU assembly intermediate which accumulates after ribosome biogenesis defects. My data indicate that p53 activation, due to defects in ribosome biogenesis, may contribute to the clinical symptoms seen in patients suffering with DC. In addition, it is shown that defects in early or late stages of SSU or LSU biogenesis, result in activation of p53 via the 5S RNP-MDM2 pathway, and that p53 is induced in less than 12 hours after ribosome biogenesis defects. SSU defects do not cause any obvious defects in LSU production, but they result in inhibition of export of the pre-LSU in the cytoplasm, suggesting that p53 activation after SSU defects is probably due to defects in pre-LSU export. Finally, there are evidence that RPS27a or RPL40, two ribosomal proteins produced as ubiquitin-fusion precursors in the cell, might be novel regulators of the 5S RNP-MDM2 pathway. In conclusion, this work shows the importance of ribosome biogenesis in the regulation of p53 for the development of Ribosomopathies and cancer.BBSRC-DTP and the Diamond-Blackfan Anaemia Foundation, U.K

A puzzle of life: crafting ribosomal subunits

The biogenesis of eukaryotic ribosomes is a complicated process during which the transcription, modification, folding, and processing of the rRNA is coupled with the ordered assembly of ∼80 ribosomal proteins (r-proteins). Ribosome synthesis is catalyzed and coordinated by more than 200 biogenesis factors as the preribosomal subunits acquire maturity on their path from the nucleolus to the cytoplasm. Several biogenesis factors also interconnect the progression of ribosome assembly with quality control of important domains, ensuring that only functional subunits engage in translation. With the recent visualization of several assembly intermediates by cryoelectron microscopy (cryo-EM), a structural view of ribosome assembly begins to emerge. In this review we integrate these first structural insights into an updated overview of the consecutive ribosome assembly steps

Impact of Thermal Processing Methods on Polyphenols and Antioxidant Activity of Olive Oil Polar Fraction

Several health claims of olive oil are correlated with phenolic compounds. The objective of this study was to evaluate the effect of different thermal processing methods on phenolic composition and antioxidant properties of heated olive oils. In particular, the phenolic antioxidants of olive oils, which were subjected to frying, baking, boiling and microwave irradiation, were estimated using multi-spectrophotometric assays approach. Results showed that thermal processing methods affected significantly the phenolic content as well as the antioxidant potency of heated olive oils. The frying and boiling of olive oils caused the highest losses of phenolic compounds that reached up to 75%, whereas a slight decrease in polyphenols was monitored after microwave irradiation. Furthermore, the baked olive oils retained better phenolic antioxidants than olive oils that were subjected to frying and boiling. Overall, our findings suggest baking as the most appropriate thermal method to heat olive oils. Practical Applications: The present work investigated the influence of thermal processing methods on olive oil polyphenols and their antioxidant properties. Results showed that frying and boiling have to be avoided in heating olive oils, while microwave heating did not decrease statistically the amount of phenolic antioxidants. Based on phenolic content and antioxidant potency, baking of olive oil is preferred when heating of olive oil is required. This study recommended good practices for home-cooking in order to retain phenolic antioxidants through selecting thermal processing method. Taking into consideration that the food industry uses olive oil to replace meat fat or refined vegetable oils, this work is a useful guide to produce healthier and high added-value food products