Abstract
Cellular sumoylation processes are proposed targets for anti-viral and anti-cancer therapies. We reported that Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) dysregulates cellular sumoylation processes, contributing to its oncogenic potential in EBV-associated malignancies. Ginkgolic acid and anacardic acid, known inhibitors of sumoylation, inhibit LMP1-induced protein sumoylation; however, both drugs have adverse effects in hosts. Here we test the effects of glycyrrhizic acid, a medicinal botanical extract with anti-inflammatory, anti-carcinogenic, and anti-viral properties, on cellular sumoylation processes. While glycyrrhizic acid is known to inhibit EBV penetration, its affect on cellular sumoylation processes remains to be documented. We hypothesized that glycyrrhizic acid inhibits cellular sumoylation processes and may be a viable treatment for Epstein-Barr virus-associated malignancies. Results showed that glycyrrhizic acid inhibited sumoylation processes (without affecting ubiquitination processes), limited cell growth, and induced apoptosis in multiple cell lines. Similar to ginkgolic acid; glycyrrhizic acid targeted the first step of the sumoylation process and resulted in low levels of spontaneous EBV reactivation. Glycyrrhizic acid did not affect induced reactivation of the virus, but the presence of the extract did reduce the ability of the produced virus to infect additional cells. Therefore, we propose that glycyrrhizic acid may be a potential therapeutic drug to augment the treatment of EBV-associated lymphoid malignancies.
Highlights
Protein post-translational modifications, such as ubiquitination and phosphorylation, allow cells to respond to both external and internal stimuli and are vital to numerous cellular events
Because we recently identified a role for sumoylation processes in the maintenance of Epstein-Barr virus latency [25], we were interested in determining if one mechanism by which glycyrrhizic acid interrupts herpesvirus latency is by inhibition of cellular sumoylation processes
Glycyrrhizic acid decreased levels of sumoylated proteins in a dosedependent manner To begin our investigation into the effect of glycyrrhizic acid on sumoylation levels, latent membrane protein 1 (LMP1)-expressing Human embryonic kidney (HEK) 293 cells were treated with graduated amounts of glycyrrhizic acid Results showed that as glycyrrhizic acid levels increased, levels of sumoylated proteins, depicted by the laddering of slower migrating bands, decreased (Fig 1A)
Summary
Protein post-translational modifications, such as ubiquitination and phosphorylation, allow cells to respond to both external and internal stimuli and are vital to numerous cellular events. The modification of proteins by the small ubiquitin-like modifier or SUMO was identified in 1997 [1]. There are four characterized human SUMO isoforms (SUMO-1, -2, -3, and -4), and SUMO-1 and SUMO-2/3 are ubiquitously expressed in the body. Protein sumoylation is similar to ubiquitination in that it is a dynamic, multi-step process. The translated SUMOpro-peptide undergoes maturation [2,3,4,5]. Matured SUMO is activated in an ATPdependent manner by the SUMO-activating enzyme [2,3,4,5].
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