Date of Award

January 2014

Document Type

Open Access Thesis

Degree Name

Master of Public Health (MPH)

Department

School of Public Health

First Advisor

Yong Zhu

Abstract

The control of gene expression is pivotal in the context of molecular pathogenesis of a number of diseases, and thus is of critical relevance to public health. An array of cellular tools exist in controlling gene expression, including epigenetic effects, non-coding RNAs, and RNA-binding proteins. These tools are critical to the modern study of public health, and are used in tandem with population-based studies. This work focuses on specific examples of non-coding RNAs and RNA-binding proteins, describing the effects of microRNA-618, a non-coding RNA, and MEX3D, a post-transcriptional regulator, in cancer.

MicroRNAs (miRNAs) form a class of highly conserved endogenous RNAs that inhibit gene expression and may act as oncogenes or as tumor suppressors, regulating extensive cancer-related gene networks. Here, we show the association between a single miRNA, miR-618, and cancer-related pathways in HeLa cells. MiR-618 was identified as a potentially oncogenic microRNA, controlling a number of cancer-related gene networks and pathways. Gain-of-function analysis reveals differential expression of 110 transcripts following miRNA-618 transfection. Notably, three upregulated genes are well-studied oncogenes--KIT, JUN, and FOSB--and three downregulated genes are well-known tumor suppressors--PTPRO, STK11/LKB1, and IGFBP5. Interestingly, investigation using the Ingenuity Pathway Analysis software tool reveals alterations in multiple cancer-related and cell cycle-related networks, including upregulated oncogenes in the top identified network "Post-translational modification, cellular development, cellular growth and proliferation" following miR-618 transfection. Further, miR-618 expression analysis shows overexpression in HeLa cells compared to normal cervical cells. Our findings present evidence for a novel oncogenic miRNA, miR-618, that is involved in cancer-related gene networks and is overexpressed in cancer.

This work also examined the role of a novel post-transcriptional regulator, MEX3D, in cancer. The Oncomine online database reveals that MEX3D is overexpressed in a number of solid tumors, notably in glioma. MEX3D is 3.01-fold overexpressed in glioma cells compared to non-cancerous, normal tissue. Kaplan-Meier survival analysis reveals that higher expression of MEX3D leads to poorer overall survival in overall glioma patients. Lastly, in a pilot case-control study of twelve glioma biopsies, we examined the effects of methylation in CpG sites in the MEX3D gene. The results were unclear, as we found a 3'UTR site that was 9.5% hypermethylated compared to normal tissue, a site in the body of the gene that was 24.8% hypermethylated, and second site in the body that was 15.4% hypomethylated compared to normal tissue.

Phenotypic studies reveal that MEX3D is responsible for two cancer phenotypes. Knockdown of MEX3D leads to increased cell proliferation and decreased cell invasion, suggesting that overexpression of MEX3D is responsible for increased cell proliferation and decreased cell invasion.

This study is the first to describe the effects of miR-618 and of MEX3D in cancer. The findings presented in this work lay the foundation for further mechanistic studies of miR-618 and MEX3D. More work is needed to identify the mechanisms of oncogenesis controlled by these molecules. Our study indicates that miR-618 may be a biomarker for several types of cancer and warrants further investigation.

Comments

This is an Open Access Thesis.

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