A herpesvirus transactivator and cellular POU proteins extensively regulate DNA binding of the host Notch signaling protein RBP-Jκ to the virus genome

A SWI/SNF-dependent transcriptional regulation mediated by POU2AF2/C11orf53 at enhancer

Recent studies have identified a previously uncharacterized protein C11orf53 (now named POU2AF2/OCA-T1), which functions as a robust co-activator of POU2F3, the master transcription factor which is critical for both normal and neoplastic tuft cell identity and viability. Here, we demonstrate that POU2AF2 dictates opposing transcriptional regulation at distal enhance elements. Loss of POU2AF2 leads to an inhibition of active enhancer nearby genes, such as tuft cell identity genes, and a derepression of Polycomb-dependent poised enhancer nearby genes, which are critical for cell viability and differentiation. Mechanistically, depletion of POU2AF2 results in a global redistribution of the chromatin occupancy of the SWI/SNF complex, leading to a significant 3D genome structure change and a subsequent transcriptional reprogramming. Our genome-wide CRISPR screen further demonstrates that POU2AF2 depletion or SWI/SNF inhibition leads to a PTEN-dependent cell growth defect, highlighting a potential role of POU2AF2-SWI/SNF axis in small cell lung cancer (SCLC) pathogenesis. Additionally, pharmacological inhibition of SWI/SNF phenocopies POU2AF2 depletion in terms of gene expression alteration and cell viability decrease in SCLC-P subtype cells. Therefore, impeding POU2AF2-mediated transcriptional regulation represents a potential therapeutic approach for human SCLC therapy.

KSHV RTA utilizes the host E3 ubiquitin ligase complex RNF20/40 to drive lytic reactivation

IMPORTANCE

Kaposi's sarcoma-associated herpesvirus (KSHV) is a cancer-causing human herpesvirus that establishes a persistent infection in humans. The lytic viral cycle plays a crucial part in lifelong infection as it is involved in the viral dissemination. The master regulator of the KSHV lytic replication cycle is the viral replication and transcription activator (RTA) protein, which is necessary and sufficient to push the virus from latency into the lytic phase. Thus, the identification of host factors utilized by RTA for controlling the lytic cycle can help to find novel targets that could be used for the development of antiviral therapies against KSHV. Using a proteomics approach, we have identified a novel interaction between RTA and the cellular E3 ubiquitin ligase complex RNF20/40, which we have shown to be necessary for promoting RTA-induced KSHV lytic cycle.

Protein Degradation by Gammaherpesvirus RTAs: More Than Just Viral Transactivators

Kaposi's sarcoma-associated herpesvirus (KSHV) is a member of the Gammaherpesvirus subfamily that encodes several viral proteins with intrinsic E3 ubiquitin ligase activity or the ability to hijack host E3 ubiquitin ligases to modulate the host's immune response and to support the viral life cycle. This review focuses specifically on how the immediate-early KSHV protein RTA (replication and transcription activator) hijacks the host's ubiquitin-proteasome pathway (UPP) to target cellular and viral factors for protein degradation to allow for robust lytic reactivation. Notably, RTA's targets are either potent transcription repressors or they are activators of the innate and adaptive immune response, which block the lytic cycle of the virus. This review mainly focuses on what is currently known about the role of the E3 ubiquitin ligase activity of KSHV RTA in the regulation of the KSHV life cycle, but we will also discuss the potential role of other gammaherpesviral RTA homologs in UPP-mediated protein degradation.

Clinical Manifestations and Epigenetic Regulation of Oral Herpesvirus Infections

The oral cavity is often the first site where viruses interact with the human body. The oral epithelium is a major site of viral entry, replication and spread to other cell types, where chronic infection can be established. In addition, saliva has been shown as a primary route of person-to-person transmission for many viruses. From a clinical perspective, viral infection can lead to several oral manifestations, ranging from common intraoral lesions to tumors. Despite the clinical and biological relevance of initial oral infection, little is known about the mechanism of regulation of the viral life cycle in the oral cavity. Several viruses utilize host epigenetic machinery to promote their own life cycle. Importantly, viral hijacking of host chromatin-modifying enzymes can also lead to the dysregulation of host factors and in the case of oncogenic viruses may ultimately play a role in promoting tumorigenesis. Given the known roles of epigenetic regulation of viral infection, epigenetic-targeted antiviral therapy has been recently explored as a therapeutic option for chronic viral infection. In this review, we highlight three herpesviruses with known roles in oral infection, including herpes simplex virus type 1, Epstein–Barr virus and Kaposi’s sarcoma-associated herpesvirus. We focus on the respective oral clinical manifestations of these viruses and their epigenetic regulation, with a specific emphasis on the viral life cycle in the oral epithelium.