The Codependent Expression of the Essential Mammalian RNA Polymerase I PAF49/PAF53 Heterodimer.

Ribosome biogenesis (RB) is a complex process that plays a central role in maintaining cellular homeostasis and supporting cell growth. Therefore, dysregulation of RB contributes to pathologies such as cancer, ribosomopathies, neurodegenerative diseases, and aging. Our lab studies transcription of ribosomal RNA by RNA polymerase I (Pol I), the rate-limiting step in ribosome biogenesis. Many studies have demonstrated that inhibiting Pol I transcription in cancer cells causes cell death while untransformed cells arrest, thereby making the Pol I apparatus a target for chemotherapeutic agents. This study focuses on two mammalian polymerase associated factors of the Pol I transcription apparatus, PAF49 and PAF53. The PAFs form a heterodimeric complex and are required for rDNA transcription and cell proliferation. The goal of this study is to determine the role(s) of PAF49 and PAF53 in rDNA transcription and understand how these two proteins are regulated. To rapidly knock down (KD) either PAF49 or 53 in HEK293 cells, a novel system that utilizes CRISPR/Cas 9 and an auxin inducible degron was used. Currently, we are using this system to determine if KD of PAF49 effects the expression of PAF53 and vice versa. Our data demonstrates that KD of PAF49 causes the rapid depletion of PAF53 protein levels while KD of PAF53 has no effect on PAF49. Additionally, we have found that the dimerization domain of PAF49 is not sufficient to stabilize PAF53. Rescue of PAF53 protein levels requires PAF49 to dimerize and bind to the polymerase. Dimerization to PAF53 and binding to the polymerase is also necessary to support cell proliferation and rDNA transcription. Further, KD of PAF49 or PAF53 has no effect on the protein levels of the core subunits of Pol I. These findings are significant because they aid in further understanding the process of rDNA transcription by Pol I. Additionally, they will contribute to the discovery of novel drug targets that could be utilized in effective cancer treatments. For example, disrupting the interaction between PAF49 and Pol I should inhibit Pol I transcription and cause cell death in cancer cells. © FASEB.

Citation

Rachel McNamar, Bruce Knutson, Lawrence Rothblum. The Codependent Expression of the Essential Mammalian RNA Polymerase I PAF49/PAF53 Heterodimer. FASEB journal : official publication of the Federation of American Societies for Experimental Biology. 2022 May;36 Suppl 1

PMID: 35554006

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