Regulation of ribosome biogenesis during the cell cycle, stress and cellular transformation

Lead Research Organisation: Newcastle University
Department Name: Inst for Cell and Molecular Biosciences

Abstract

One basic feature of cells is their ability to grow and divide. The production of proteins, essential cell components that represent a significant proportion of the cell mass, is essential for cell growth. The ribosome is a molecular factory in the cell responsible for the synthesis of proteins. The cell regulates protein production by changing the activity and/or the levels of ribosomes. In cell transformation, the initial stage in the generation of tumours, the basic regulation of cell growth and division is lost allowing the cell to continue growing unchecked. It has recently been shown that many proteins that either cause or regulate cancer are also linked to the regulation of protein synthesis in the cell. This often involves the regulation of the synthesis of new ribosomes in a specific compartment in the cell known as the nucleolus. The production of the ribosome is a highly complicated process that is at present poorly understood. The cell has natural tumour suppressive agents such as the protein p53. The activation of this protein inhibits cell growth and division and is linked to the function of the nucleolus. We have found that chemical inhibitors that activate p53 also block the production of ribosomes. We propose to investigate the mechanisms by which these inhibitors block to production of ribosomes. The information gained from this approach will provide important information on how the cell activates the tumour suppressor p53. This research will provide important information on how the cell regulates cell growth and division and should provide new targets for anti-cancer therapeutics.

Technical Summary

The average HeLa cell produces 7500 ribosomes each minute in a process that involves ~150 small nucleolar RNAs (snoRNAs), 80 ribosomal proteins, and 150 additional trans-acting factors in the nucleolus. As a major consumer of the cell?s resources ribosome biogenesis is linked to cell growth and proliferation and upregulated in the majority of transformed cells and cancers. Furthermore, the nucleolus is a stress sensor and its disruption, which is likely caused by the impairment of ribosome biogenesis, results in the stabilisation of the tumour suppressor p53, which leads to cell cycle arrest or apoptosis. However, a major unanswered question is how the cell responds to the various stimuli to bring about the block in nucleolar function, which then leads to nucleolar disruption. The 18S rRNA is processed from a larger precrusor transcript by the small subunit (SSU) processome, a large multiprotein complex that contains the U3 snoRNA. During pre-rRNA processing the U3 snoRNA base-pairs with the pre-rRNA and functions as a chaperone in the folding and processing of the 18S rRNA. These essential interactions are proposed to be mediated by the Mpp10 complex, a SSU processome subcomplex, which is comprised of the M-phase phosphoprotein Mpp10 and the RNA annealing factors Imp3 and Imp4. Our preliminary data show that multiple agents that cause nucleolar disruption, such as actinomycin D, DRB, roscovitine, all result in a significant change in the composition of the SSU processome and lead to the spatial separation of the Mpp10 complex and the SSU processome within the nucleolus. Our hypothesis is that these agents function by inhibiting a U3 snoRNA association with the pre-rRNA resulting in accumulation of an inactive, pre-ribosome. We therefore propose to define the changes in composition of the SSU processome and the localisation of its various components induced by the addition of nucleolar segregation agents. In addition, phosphorylation is likely key to this regulation and we will investigate the modification of two key phosphoproteins in the SSU processome, namely nucleolin and Mpp10, in response to these agents. Defining the molecular mechanism by which these agents affect the SSU processome and pre-rRNA processing will significantly enhance our understanding of nucleolar segregation and the activation of the p53 response. It is hoped that using these approaches we will be able to identify nucleolar proteins that can be used as targets for anti-cancer therapeutic agents.

Publications

10 25 50
 
Title Anti-SSU processome antibodies 
Description Antibodies were generated against key ribosome biogenesis factors 
Type Of Material Technology assay or reagent 
Year Produced 2007 
Provided To Others? Yes  
Impact The material was key to the published paper (PubMed ID: 19332556) and all other research on the project 
URL http://europepmc.org/abstract/MED/19332556
 
Description Brian McStay 
Organisation National University of Ireland, Galway
Department Department of Biochemistry
Country Ireland 
Sector Academic/University 
PI Contribution This was a collaboration with Dr Brian McStay (now at NUI Galway). The collaboration focused around an exchange of resources and information.
Collaborator Contribution Provided materials, support and ideas.
Impact The collaboration is ongoing and highly fruitful. The collaboration was key to the current publication derived from the grant (PUBMED ID: 19332556).
Start Year 2006
 
Description University open day 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact I talk to prospective students and their parents about the research we do.

NA
Year(s) Of Engagement Activity 2007,2008