Abstract
Downregulation of the ubiquitin-like containing PHD and ring finger 1 (UHRF1) oncogene in cancer cells in response to natural anticancer drugs, including thymoquinone (TQ), is a key event that induces apoptosis. TQ can induce UHRF1 autoubiquitination via the E3 ligase activity of its RING domain, most likely through the downregulation of herpes virus-associated ubiquitin-specific protease (HAUSP). In this study, we evaluated whether HAUSP downregulation and fast ubiquitination of UHRF1 are prerequisites for UHRF1 degradation in response to TQ in cancer cells and whether doxorubicin can mimic the effects of TQ on UHRF1 ubiquitination. RNA sequencing was performed to investigate differentially expressed genes in TQ-treated Jurkat cells. The protein expression of UHRF1, HAUSP and Bcl-2 was detected by means of Western blot analysis. The proliferation of human colon cancer (HCT-116) and Jurkat cells was analyzed via the WST-1 assay. RNA sequencing data revealed that TQ significantly decreased HAUSP expression. TQ triggered UHRF1 to undergo rapid ubiquitination as the first step in its degradation and the inhibition of its cell proliferation. TQ-induced UHRF1 ubiquitination is associated with HAUSP downregulation. Like TQ, doxorubicin induced a similar dose- and time-dependent downregulation of UHRF1 in cancer cells, but UHRF1 did not undergo ubiquitination as detected in response to TQ. Furthermore, TQ decreased Bcl-2 expression without triggering its ubiquitination. A fast UHRF1 ubiquitination is an indispensable event for its degradation in response to TQ but not for its responses to doxorubicin. TQ appears to trigger ubiquitination of UHRF1 but not of the Bcl-2 oncogene, thereby identifying UHRF1 as a specific target of TQ for cancer therapy.
Highlights
The ubiquitin-like containing PHD and ring finger 1 (UHRF1) oncogene is overexpressed in many human cancers and serves as a master regulator of the epigenome (DNA methylation and histone modifications) through its five functional domains [1,2,3,4,5,6,7], including the RING domain, which is the only domain of UHRF1 that exhibits enzymatic activity [2,8]
These data, taken together, suggest that an intact function of the UHRF1 RING domain is essential for cellular survival and its disruption through the dissociation of herpes virus-associated ubiquitin-specific protease (HAUSP) from the UHRF1 complex significantly enhances the sensitivity of cancer cells to chemotherapeutics, making UHRF1 a promising target in the search for natural compound to target in cancer therapy
We evaluated whether TQ triggers HUASP downregulationmediated fast ubiquitination of UHRF1 in cancer cells and whether the anticancer drug doxorubicin, which is known to decrease the expression of the UHRF1 protein through an unknown mechanism [23], can mimic the effects of TQ on UHRF1
Summary
The ubiquitin-like containing PHD and ring finger 1 (UHRF1) oncogene is overexpressed in many human cancers and serves as a master regulator of the epigenome (DNA methylation and histone modifications) through its five functional domains [1,2,3,4,5,6,7], including the RING domain, which is the only domain of UHRF1 that exhibits enzymatic activity [2,8]. HAUSP physically interacts with UHRF1 and an active HAUSP completely abolished the autoubiquitination of UHRF1 through the removal of ubiquitin adducts [15] These findings indicate that HAUSP positively regulates the expression levels of UHRF1 through targeting the RING domainmediated autoubiquitination activity of UHRF1, preventing proteasomal degradation of UHRF1 [15]. TQ was shown to induce the rapid autoubiquitination of UHRF1 in cancer cells through its RING domain, and this event was correlated with HAUSP downregulation [11], which is known to control the ubiquitination status of UHRF1 and protects it from degradation by the proteasome [15]. We evaluated whether TQ triggers HUASP downregulationmediated fast ubiquitination of UHRF1 in cancer cells and whether the anticancer drug doxorubicin, which is known to decrease the expression of the UHRF1 protein through an unknown mechanism [23], can mimic the effects of TQ on UHRF1
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