Date Approved


Document Type


Degree Name

PhD in Cell & Molecular Biology


Cell Biology and Neuroscience


Graduate School of Biomedical Sciences

First Advisor

Dimitri Pestov, PhD

Committee Member 1

William McAllister, PhD

Committee Member 2

Michael Law, PhD

Committee Member 3

Eric Moss, PhD

Committee Member 4

Venkateswar Venkataraman, PhD


Ribosomal Proteins, RNA Precursors, Cell Proliferation, Aminacrine, Aminoacridines, Cytostatic Agents


Amino Acids, Peptides, and Proteins | Biological Phenomena, Cell Phenomena, and Immunity | Cancer Biology | Cell Biology | Laboratory and Basic Science Research | Medical Cell Biology | Medical Molecular Biology | Medicinal Chemistry and Pharmaceutics | Medicine and Health Sciences | Molecular Biology | Molecular Genetics | Neoplasms


In order to maintain the ability to generate proteins, proliferating cells must continuously generate ribosomes, designating up to 80% of their energy to ribosome biogenesis (RBG). RBG involves transcription of rDNA by RNA polymerases I (Pol I) and III (Pol III), expression of approximately 80 ribosomal proteins, and assembly of these components in a process referred to as ribosome maturation. During maturation, the Pol I transcribed 47S pre-rRNA undergoes a number of processing events, while simultaneously interacting with processing factors and ribosomal proteins that drive pre-ribosome assembly. Inhibition of RBG has become one of the pursued targets for cancer therapy in the past 15 years (Drygin et al., 2010; Hannan et al., 2013), prompted by the observation that cancer cells upregulate RBG (Brighenti et al 2015).

This project was aimed to determine whether RBG inhibition can induce reversible cell cycle arrest, a key feature in a cancer fighting strategy known as cyclotherapy (van Leeuwen, 2012). Cyclotherapy aims to halt proliferation of healthy host cells prior to treatment with chemotherapeutic agents that target dividing cells. This approach ensures selective targeting of deregulated cells that continue to proliferate, while the arrested healthy host cells are protected. To test this approach, I inhibited RBG by knocking down expression of ribosomal proteins and by 9-aminoacridine (9-AA) treatment. I demonstrated that in addition to inhibiting Pol I transcription, 9-AA also impedes pre-rRNA processing in a dose-dependent manner. Further, I found that the association between pre-ribosomes and snoRNAs required for rRNA

maturation is disrupted due to 9-AA treatment. This finding suggested a mechanism by which 9-AA may inhibit pre-rRNA processing. Significantly, this work demonstrated that RBG inhibition can cause a stress response that selectively protects p53 positive cells during treatment with cytotoxic agents targeting proliferating cells.

Finally, I initiated characterization of two previously unknown potential factors of RBG, PSMA3 and Nol7. These proteins are required for a pre-rRNA processing step, however the molecular mechanisms of their function in RBG are not known. PSMA3 and Nol7 may present themselves as exploitable targets for RBG inhibition.