Structural and functional characterization of the CXXC-type zinc finger protein 5 (CXXC5)

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Tezin Türü: Doktora

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Edebiyat Fakültesi, Biyolojik Bilimler Bölümü, Türkiye

Tezin Onay Tarihi: 2018

Öğrenci: GAMZE AYAZ ŞEN

Danışman: MESUT MUYAN

Özet:

Estrogen hormones, particularly 17β-estradiol (E2), are involved in the regulation of physiological and pathophysiological functions of many organs and tissues including breast tissue. The expression of CXXC type zinc finger protein 5 (CXXC5) gene is regulated by E2 through estrogen receptor α. Due to a highly conserved zinc-finger CXXC domain (ZF-CXXC), CXXC5 is considered to be a member of ZF-CXXC family, which binds to non-methylated CpG dinucleotides of transcriptionally active DNA regions. This binding is thought to play critical roles in epigenetic modulation of transcription through the prevention of cytosine methylation and the recruitment of DNA modifying enzymes. The structure and function of CXXC5 and its role in cellular events are yet unclear. However, accumulating evidence is suggesting that CXXC5 is involved in transcriptions as a transcription factor, co-regulator and/or epigenetic factor. In this PhD thesis, I successfully expressed and purified the full-length CXXC5 protein, with which I showed that CXXC5 is a non-methylated CpG DNA binding protein and that the ZF-CXXC domain is indeed responsible for the ability of the protein to interact with DNA. Since proteins exert their functions in the context of dynamically changing interacting protein network, I envisioned that identification of interacting protein partners of CXXC5 would be a critical step in the elucidation of cellular function of the protein. To address this issue, I performed proximity dependent biotinylation assay (BioID) in a cell line model derived from breast adenocarcinoma. Of the identified proteins by Liquid chromatography-tandem mass spectrometry (LC-MS/MS), I validated that CXXC5 protein interacts with MeCP2 (MethylCpG binding protein 2), MAZ (Myc-associated Zinc Finger Protein) and EMD (Emerin) proteins by co-immunoprecipitation assay. I found that the zinc finger domain of CXXC5 is necessary for protein interaction as well. The findings of this study could provide important insights into the mechanism of CXXC5 actions in E2- mediated cellular events.