Role of Ribosomal RNA Methyltransferase NSUN5 in Glioblastoma
Creators: Zhou,Jiesi
Publisher: name: University of Alberta Library
Year: 2022

<p>Background:<br>
Glioblastoma is the most common and aggressive malignant primary brain tumor. Despite aggressive standard treatment including surgery, radiation and chemotherapy, the median overall survival for patients with glioblastoma is only about 14 to 16 months. Using a glioblastoma TCGA dataset from 2013, we found that high NSUN5 mRNA expression is strongly associated with poor survival in glioblastoma patients. NSUN5 is a member of the Nol1/Nop2/Sun (NSUN) family of methyltransferases. It was first characterized in yeast where it was found to methylate 25S ribosomal RNA (rRNA). Moreover, NSUN5 functions to modulate protein synthesis in yeast, as its deletion leads to alterations in the rRNA structure, consequently leading to the favoured translation of oxidative response mRNAs. However, the function of NSUN5 in humans, as well as its role in cancer remains obscure. Since protein synthesis is a major mechanism by which cancer cells adapt to their environment and enhance their proliferation and survival, elevated NSUN5 expression and the consequent rRNA methylation could alter the structure and/or activity of ribosomes to modulate the proteome and to drive tumorigenic phenotypes in glioblastoma.</p>

<p>Hypothesis and objectives:<br>
Our hypothesis is that elevated NSUN5 alters the structure and/or activity of ribosomes by regulating the pattern of rRNA methylation, which leads to pro-tumorigenic translational reprogramming thereby promoting glioblastoma progression. We will address our hypothesis by: (1) investigating whether NSUN5 methylates rRNAs, (2) determining whether NSUN5 regulates protein synthesis in glioblastoma cells, (3) determining the functional role of NSUN5 in glioblastoma, and (4) characterizing the NSUN5-regulated proteome in glioblastoma cells.<br>
Results:<br>
In this study, we demonstrate that: (1) NSUN5 indeed methylates cytosine 3782 of human 28S rRNA; (2) NSUN5 regulates protein synthesis in glioblastoma cells; and (3) NSUN5 promotes the tumorigenic phenotypes of glioblastoma in vitro and in vivo. In Chapter 3, we demonstrate that NSUN5 is expressed in glioblastoma cells and patient tissues and that NSUN5 methylates cytosine 3782 of human 28S rRNA. Furthermore, we identify cysteines 308 and 359 as the key cysteines required for RNA methyltransferase activity of NSUN5. In Chapter 4, we show that NSUN5 promotes proliferation, sphere formation, resistance to temozolomide, and tumor formation/progression of glioblastoma cells in mice. In Chapter 5, we demonstrate that NSUN5 promotes protein synthesis and regulates the proteome of glioblastoma cells, modulating the expression of STAT3 and NSUN2.</p>

<p>Significance:<br>
In this study, we determine that NSUN5 plays a pro-tumorigenic role in glioblastoma. Since RNA methyltransferases have been shown to be readily targetable, our study suggests that NSUN5 is a potential novel therapeutic target for glioblastoma. Moreover, this project will help us to determine whether rRNA cytosine modification regulates translation, and whether it favors the translation of cancer-associated genes in glioblastoma.</p>