Targeting Itch/p73 pathway by thymoquinone as a novel therapeutic strategy for cancers with p53 mutation

Abstract

The tumor suppressor p73 is a member of p53 family and has a high degree of similarity with p53 function and structure. Like p53, p73 can also induce the expression of several genes involved in cell cycle and apoptosis. p73 expression is downregulated in many tumors by several mechanisms including the ubiquitination pathway. Thus, understanding the ubiquitin-proteasome pathway in p73 regulation will help in targeting this later and develop a new promising therapeutic strategy for cancer with p53 mutations. The aim of this study was to evaluate the effect of Thymoquinone (TQ), the major biologically active compound of the black seed oil on the expression of several E3 ubiquitin ligase enzymes known to be regulators of p73 and the related events in cancer cells with p53 mutation, such as the human acute lymphoblastic leukemia Jurkat cells, the human triple-negative breast cancer (MDA-MB-468 cells) and human promyelocytic leukemia HL60 cells. RNA-seq data showed that several E3 ubiquitin-ligase enzymes, well documented to be involved in the degradation of p73 including Itch, Pirh2, E3s Pin2, Mdm2, TRIM32 and SCFFBXO45 were downregulated in Jurkat cells. 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 an upregulation of p73. The present study indicates 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.

Thymoquinone in Ocular Neurodegeneration: Modulation of Pathological Mechanisms via Multiple Pathways

“…This inhibition is due to compromised 20S proteosomes complex functionality and not to downregulation of its synthesis as observed through western blotting and 20S proteosomes activity analysis. In addition, E3 ubiquitin ligase was also downregulated with thymoquinone treatment in acute leukemia model ( Alghamdi et al, 2020 ). Based on this evidence in cancer subject and with the importance of autophagy in the eye, study on thymoquinone in proteosome might provide a novel mechanism of thymoquinone in ocular disease application.…”

Targeting Post-Translational Modifications of the p73 Protein: A Promising Therapeutic Strategy for Tumors

“…Itch E3 ubiquitin-protein ligase (Itch) has been reported to be highly expressed in several tumors, including lung cancer, breast cancer, pancreatic cancer, skin cancer, and neuroblastoma, and its inhibition leads to the induction of apoptosis and the inhibition of cell proliferation [ 38 , 59 , 62 , 63 , 64 ]. Itch selectively binds and ubiquitinates p73α via the PY motif (Met 452–Ala 489) but not p53, thereby leading to a proteasome-dependent p73 degradation [ 43 ].…”

“…We and others have shown that thymoquinone (TQ), the bioactive compound of black seed oil, has inhibitory effects on several cancers through the targeting of several signaling pathways [ 151 , 152 , 153 , 154 , 155 , 156 , 157 , 158 , 159 ], including the reactivation of the p73 protein in p53-mutated tumors [ 136 , 160 , 161 ]. Recently, TQ was proposed to increase the expression of the p73 protein in a p53-mutant acute lymphoblastic leukemia cell line (Jurkat cells) by targeting the expression of various E3 ubiquitin ligases for p73, including Itch, Mdm2, FBXO45, and TRIM32 [ 62 ]. TQ increased the expression of the p73 protein in Jurkat cells, and this effect was associated with a significant decrease in the expression of Itch in those cells, as well as in human promyelocytic leukemia HL60 cells and human triple-negative MDA-MB-468 breast cancer cells that also bear mutant p53 [ 62 ].…”

“…Recently, TQ was proposed to increase the expression of the p73 protein in a p53-mutant acute lymphoblastic leukemia cell line (Jurkat cells) by targeting the expression of various E3 ubiquitin ligases for p73, including Itch, Mdm2, FBXO45, and TRIM32 [ 62 ]. TQ increased the expression of the p73 protein in Jurkat cells, and this effect was associated with a significant decrease in the expression of Itch in those cells, as well as in human promyelocytic leukemia HL60 cells and human triple-negative MDA-MB-468 breast cancer cells that also bear mutant p53 [ 62 ].…”

“…Decrease in the expression levels of various E3 ubiquitin ligases for p73 including Itch, Mdm2, FBXO45, and TRIM32 [ 62 ].…”