Browsing by Subject "DNA Damage"

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Open Access
Doxorubicin induces prolonged DNA damage signal in cells overexpressing DEK isoform-2
(Public Library of Science, 2022-10-03) Özçelik, Emrah; Kalaycı, Ahmet; Çelik, Büşra; Avcı, Açelya; Akyol, Hasan; Kılıç, İrfan Baki; Güzel, Türkan; Çetin, Metin; Öztürk, Merve Tuzlakoğlu; Çalışkaner, Zihni Onur; Tombaz, Melike; Yoleri, Dilan; Konu, Özlen; Kandilci, Ayten
DEK has a short isoform (DEK isoform-2; DEK2) that lacks amino acid residues between 49–82. The full-length DEK (DEK isoform-1; DEK1) is ubiquitously expressed and plays a role in different cellular processes but whether DEK2 is involved in these processes remains elusive. We stably overexpressed DEK2 in human bone marrow stromal cell line HS-27A, in which endogenous DEKs were intact or suppressed via short hairpin RNA (sh-RNA). We have found that contrary to ectopic DEK1, DEK2 locates in the nucleus and nucleolus, causes persistent үH2AX signal upon doxorubicin treatment, and couldn’t functionally compensate for the loss of DEK1. In addition, DEK2 overexpressing cells were more sensitive to doxorubicin than DEK1-cells. Expressions of DEK1 and DEK2 in cell lines and primary tumors exhibit tissue specificity. DEK1 is upregulated in cancers of the colon, liver, and lung compared to normal tissues while both DEK1 and DEK2 are downregulated in subsets of kidney, prostate, and thyroid carcinomas. Interestingly, only DEK2 was downregulated in a subset of breast tumors suggesting that DEK2 can be modulated differently than DEK1 in specific cancers. In summary, our findings show distinct expression patterns and subcellular location and suggest non-overlapping functions between the two DEK isoforms. © 2022 Ozçelik et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Open Access
Effects of Cholinergic Receptor Nicotinic Alpha 5 (CHRNA5) RNAi on apoptosis, DNA damage response, drug sensitivity, and HSA-MIR-495-3P overexpression in breast cancer
(2018-12) Köker, Şahika Cıngır
Cholinergic Receptor Nicotinic Alpha 5 (CHRNA5) is associated with nicotine addiction and it has an important role in the prognosis of lung cancer. Despite its important cellular functions, its role in breast cancer remains to be elucidated. In this thesis, I aimed to identify the alterations in the important cancer signaling pathways occurring upon CHRNA5 depletion. Drug resistance is one of the major obstacles in breast cancer therapy. Heterogeneous nature of breast cancer necessitates identification of more biomarkers which aid in precise diagnosis and hence development of proper treatment options. In this study, by using more than one cell line which is representative of different subtypes of breast cancer, I showed the alterations occurred in cancer signaling pathways such as cell cycle and apoptosis upon CHRNA5 depletion, which could serve as a novel biomarker in breast cancer subtyping. Depending on mutation status of TP53, which is the gatekeeper protein during G1/S checkpoint, CHRNA5 depletion mostly exerted its effects over decreasing the levels of total CHEK1 and pCHEK1 (S345) which significantly altered the response of MCF7 cells to topoisomerase inhibitors in terms of enhanced drug sensitivity. Increases in apoptotic markers, such as BAX/BCL2 ratio along with increased FAS levels, further confirmed that this sensitization of MCF7 cells upon CHRNA5 depletion might have ended with apoptosis. So far in the literature, there is no study examining the regulation of CHRNA5 by small endogenous molecules such as miRNAs. Due to the predictive binding sites in 3’UTR of CHRNA5 and the importance of participating in tamoxifen resistance in breast cancer; I also examined the interplay between miR-15a family and CHRNA5 in MCF7 cells. I showed significant decrease in CHRNA5 levels upon using miR-15a mimic while demonstrating similar activity of miR-15a family mimics with CHRNA5 depletion using RT-qPCR. Another important implication of CHRNA5 depletion in MCF7 cells was the global change in miRNA expression prolife which was verified with independent microRNA arrays. Based on these in silico results, hsa-miR-495-3p appeared as the most downregulated miRNA which is known as a tumor suppressor miRNA. As stated in the literature, the role of miR-495 differs depending on the tumor type. Therefore, I tried to restore its expression by mimicking along with CHRNA5 depletion. The transcriptomic changes observed with CHRNA5 depletion was boosted with the restoration of miR-495 levels.