Document Details
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Document Type |
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Thesis |
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Document Title |
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Exploring potential specific inhibitors of the epigenetic reader UHRF1 as a new strategy of cancer treatment استكشاف مثبطات نوعية محتملة للقارئ وفق الوراثي UHRF1 كاستراتيجية جديدة لمعالجة السرطان |
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Subject |
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Faculty of Science |
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Document Language |
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Arabic |
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Abstract |
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Cancer is considered one of the prominent reasons of death among mankind. cancer is categorized as a multi-factor disorder initiated by the dysregulation of different genes in the human body, which raise the demand to find specific medications that function by pointing definite signaling mechanisms. Various mechanisms, including genetic alterations, epigenetic alterations, and ubiquitination, can lead to the progression of carcinogenesis. Epigenetic mechanisms such as DNA methylation, post-translational histone changes, and non-coding RNA. Epigenetic silencing of tumor suppressor genes (TSGs) is thought to be one of the main pathways of the mechanism for stimulating tumor initiation and progression. Because of their reversibility, epigenetic modifications have attracted attention as interesting targets in cancer prevention and treatment. The epigenetic reader UHRF1 (ubiquitin-like containing plant homeodomain (PHD) and an interesting new gene (RING), finger domains 1) is highly expressed in various types of cancer and involved in the activity of epigenetic silencing of many TSGs via different pathways like; histone deacetylation and DNA methylation which encourage cell proliferation and suppress apoptosis.
UHRF1 has five function domains that enable it to bind to several other epigenetic players such as DNMT1 (DNA methyltransferase 1), HDAC1 (histone deacetylase 1), Tip60 (histone acetyltransferase), the histone methyltransferase G9a and HAUSP (herpes virus-associated ubiquitin-specific protease). UHRF1 can connect DNA methylation to histone epigenetic marks and accordingly ensure transferring them to the next generation throughout cell division. On the other hand, UHRF1 has been shown to be regulated by several pathways including tumor suppressor gene p73 and the deubiquitinase HAUSP. Indeed, low expression levels of p73 and overexpression of HAUSP are considered as main causes of the high expression levels of UHRF1. p73 expression is downregulated in various malignant tumors with p53 mutations by multiple mechanisms including the ubiquitination pathway. Therefore, studying and understanding the ubiquitin-proteasome signaling pathway in p73 regulation will help to identify this signaling pathway and find a talented new therapeutic strategy to fight cancer. A panel of E3 ubiquitin ligase enzymes is involved in the regulation of p73 expression in cancer cells with p53 mutation, such as the human promyelocytic leukemia (HL60) cells, human acute lymphoblastic leukemia Jurkat cells, and the human triple-negative breast cancer (MDA-MB-468) cells. The herpes virus-associated ubiquitin-specific protease (HAUSP) known as USP7 was shown to protect several RING-finger E3-ubiquitin ligases, such as Mdm2, ICP0, Chfr, and UHRF1, from autoubiquitination. Indeed, HAUSP belongs to the Epigenetic Code Replication Machinery ‘ECREM’ complex that also contains numerous epigenetic participants, such as UHRF1, HDAC1, DNMT1, G9a as well as TIP60. Because of its deubiquitinase specialty and capability to bind directly to the other epigenetic regulators in the ECREM complex, HAUSP allocates itself at the top of the regulatory list.
My study aimed to understand the regulatory mechanisms involved in the regulation of both the tumor suppressor gene p73 and the deubiquitinase HAUSP and to find new inhibitors able to target specifically these two signaling pathways and by the consequence of UHRF1. Thymoquinone (TQ), is the main active ingredient found in black seed oil sourced from Nigella Sativa. TQ was shown to downregulate UHRF1 in leukemia cells through an unknown mechanism involving the upregulation of p73 and the downregulation of HAUSP.
RNA-seq data showed that several E3 ubiquitin-ligase enzymes, to be involved in the degradation of p73 including Itch, Pirh2, E3s Pin2, Mdm2, TRIM32, and SCFFBXO45 were downregulated in Jurkat cells in response to TQ. Among the target genes, Itch was significantly downregulated in TQ-treated Jurkat cells as compared with control cells. TQ-induced Itch downregulation was confirmed by real-time RT-PCR in Jurkat cells, MDA-MB-468 cells, and HL60. Treating Jurkat cells with either TQ or the proteasome inhibitor MG132 induced upregulation of p73 indicating that TQ could be a promising inhibitor of the E3-ubiquitin ligase Itch leading to the upregulation of tumor suppressor p73 in cancers expressing mutant p53.
The data from RNA sequencing showed that TQ induced an important decrease in the illustration of HAUSP. UHRF1 was initiated by TQ to go through a fast ubiquitination process as an initial phase of UHRF1degredation, followed by suppressing the cell proliferation. It’s noticed that UHRF1 ubiquitination induced by TQ is accompanied by the downregulation of HAUSP.
Our findings also showed that the anticancer drug doxorubicin provoked a similar effect of TQ dose- and time-dependent, where doxorubicin decreased the expression of UHRF1 in cancer cells, but UHRF1 did not go through ubiquitination as noticed in response to treatment with TQ. Moreover, the expression of the oncogene Bcl-2 is reduced by the effect of TQ, but without triggering its ubiquitination, like UHRF1. Together, these findings indicate that a UHRF1 undergoes fast ubiquitination in response to TQ treatment, which is a vital event for its degradation, where it’s not the same response to doxorubicin treatment. It seems like TQ is initiating UHRF1 ubiquitination, but not the Bcl-2 oncogene, thus recognizing UHRF1 as a specific target of TQ in fighting cancer.
Keywords: Cancer mechanisms; UHRF1; p73; ubiquitination; E3 ubiquitin-ligase enzymes; Itch; HAUSP; Thymoquinone. |
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Supervisor |
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Dr. Mahmoud Alhosin (PI) |
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Thesis Type |
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Doctorate Thesis |
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Publishing Year |
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1444 AH
2022 AD |
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Co-Supervisor |
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Prof. Fahad A. Al-Abbasi (Co-PI) |
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Added Date |
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Sunday, February 19, 2023 |
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Researchers
| أسعد إبراهيم الخليل | Kayali, Asaad Ibrahim | Researcher | Doctorate | |
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