Thymoquinone challenges UHRF1 to commit auto-ubiquitination: a key event for apoptosis induction in cancer cells

// Abdulkhaleg Ibrahim 1, 2, * , Mahmoud Alhosin 3, 4, * , Christophe Papin 1 , Khalid Ouararhni 1 , Ziad Omran 5 , Mazin A. Zamzami 3, 4 , Abdulrahman Labeed Al-Malki 3 , Hani Choudhry 3, 4 , Yves Mély 6 , Ali Hamiche 1 , Marc Mousli 6 and Christian Bronner 1 1 Institut De Génétique Et De Biologie Moléculaire Et Cellulaire (IGBMC), INSERM U1258 CNRS UMR 7104, Université de Strasbourg, Illkirch, France 2 BioTechnology Research Center (BTRC), Tripoli, Lybia 3 Department of Biochemistry, Cancer Metabolism and Epigenetic Unit, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia 4 Cancer and Mutagenesis Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah, Saudi Arabia 5 College of Pharmacy, Umm Al-Qura University, Makkah, Saudi Arabia 6 CNRS UMR 7021 Laboratoire de Bioimagerie et Pathologies, Université de Strasbourg, Faculté de Pharmacie, Illkirch, France * These authors contributed equally to this work Correspondence to: Mahmoud Alhosin, email: malhaseen@kau.edu.sa Christian Bronner, email: bronnerc@igbmc.fr Keywords: apoptosis; thymoquinone; tumor suppressor genes; ubiquitination; UHRF1 Received: November 30, 2017      Accepted: May 19, 2018      Published: June 19, 2018 ABSTRACT Down-regulation of UHRF1 (Ubiquitin-like containing PHD and Ring Finger 1) in Jurkat cells, induced by natural anticancer compounds such as thymoquinone, allows re-expression of tumor suppressor genes such as p73 and p16 INK4A . In order to decipher the mechanisms of UHRF1 down-regulation, we investigated the kinetic of expression of HAUSP (herpes virus-associated ubiquitin-specific protease), UHRF1, cleaved caspase-3 and p73 in Jurkat cells treated with thymoquinone. We found that thymoquinone induced degradation of UHRF1, correlated with a sharp decrease in HAUSP and an increase in cleaved caspase-3 and p73. UHRF1 concomitantly underwent a rapid ubiquitination in response to thymoquinone and this effect was not observed in the cells expressing mutant UHRF1 RING domain, suggesting that UHRF1 commits an auto-ubiquitination through its RING domain in response to thymoquinone treatment. Exposure of cells to Z-DEVD, an inhibitor of caspase-3 markedly reduced the thymoquinone-induced down-regulation of UHRF1, while proteosomal inhibitor MG132 had no such effect. The present findings indicate that thymoquinone induces in cancer cells a fast UHRF1 auto-ubiquitination through its RING domain associated with HAUSP down-regulation. They further suggest that thymoquinone-induced UHRF1 auto-ubiquitination followed by its degradation is a key event in inducing apoptosis through a proteasome-independent mechanism.