Functional Role of TET3 Enzyme in Breast Tumorigenesis M.Sc. Thesis رسالة ماجستير

Abstract

Carcinogenesis is a multistep process that involves altered gene expression because of both genetic and epigenetic alterations. One of the most studied epigenetic modifications is DNA methylation. Aberrant DNA methylation is linked to carcinogenesis in different cancer types. Progression of such tumors is associated with an imbalance in DNA methylation and demethylation. Previously, methylation was thought to be an irreversible event until the recent discovery of the TET family of enzymes that includes TET1, TET2 and TET3. While TET1 and TET2 roles in breast tumorigenesis were previously studied, little is known about TET3 role in breast tumorigenesis. In the present study, we tried to elucidate the behaviour of TET3 in breast tumorigenesis by overexpressing TET3 cDNA in breast cancer cells that exhibit low TET3 expression. Then, we tested the effect of TET3 overexpression on different cancer phenotypes. Our results showed that TET3 overexpression leads to an increase in cell proliferation as well as survival rate of infected cells when compared to normal cells. Additionally, infected cells showed a higher migration capacity than normal, noninfected cells. Moreover, we tested the expression level and localization of TET3 enzyme in breast cancer samples using IHC. We also tested the expression level of TET3 mRNA using relative qRT-PCR in different breast cancer cell lines under different contexts. We found that invasive breast cancer samples had higher levels of TET3 compared to normal or early stage samples. Additionally, we did qRT-PCR on some target genes that are related to the different cancer hallmarks that we tested in order to find any correlation between the genotype and phenotype and found that TET3 overexpressing cells upregulated some oncogenes while it had a slight or no seen effect on VIII other genes like tumor suppressor genes. Lastly, and to be able to correlate our findings with clinical cases, we used the Kaplan-Meier (KM) plotter in order to assess the association of TET3 on survival. The obtained results showed that high TET3 expression predicts poor prognosis in breast cancer patients. In conclusion, our results show for the first time that TET3 exhibits an oncogenic behavior