Human Herpesvirus 6A Induces Dendritic Cell Death and HMGB1 Release without Virus Replication

High mobility group box 1 knockdown inhibits EV71 replication and attenuates cell pyroptosis through TLR4/NF-κB/NLRP3 axis

Enterovirus 71 (EV71) is a major causative agent of hand, foot, and mouth disease (HFMD) in children. Nowadays, there are still no effective antiviral drugs for EV71 infection. High mobility group box 1 (HMGB1) is reported to be highly expressed in HFMD patients. However, the role and underlying mechanism of HMGB1 in EV71-associated HFMD are still unclear. HMGB1 expression was detected using RT-qPCR and western blot assays. Loss- and gain-function experiments were performed to evaluate the effects of HMGB1 on EV71-infected cells. The virus titer was examined by TCID50. CCK-8 and flow cytometry assays were applied to detect the cell viability and cell cycle. Oxidative stress was determined by relative commercial kits. HMGB1 level was elevated in the serum of EV71-infected patients with HFMD and EV71-induced RD cells. EV71 infection induced the transfer of HMGB1 from the nucleus into the cytoplasm. HMGB1 knockdown inhibited virus replication, viral protein (VP1) expression and promoted antiviral factor expression. In addition, the inhibition of HMGB1 improved cell viability, protected against S phase arrest, and inhibited EV71-induced cell injury and oxidative stress, whereas HMGB1 overexpression showed the opposite effects. In terms of mechanism, HMGB1 overexpression activated the TLR4/NF-κB/NLRP3 signaling pathway and promoted cell pyroptosis. The inhibition of TLR4 and NF-κB reversed the effects of HMGB1 overexpression on virus replication, oxidative stress, and pyroptosis. In conclusion, HMGB1 knockdown inhibits EV71 replication and attenuates pyroptosis through TLR4/NF-κB/NLRP3 axis.

Human Herpesvirus 6A Is a Risk Factor for Multiple Sclerosis

The role for human herpesvirus (HHV)-6A or HHV-6B in multiple sclerosis (MS) pathogenesis has been controversial. Possibly because the damage of the virus infection may occur before onset of clinical symptoms and because it has been difficult to detect active infection and separate serological responses to HHV-6A or 6B. Recent studies report that in MS patients the serological response against HHV-6A is increased whereas it is decreased against HHV-6B. This effect seems to be even more pronounced in MS patients prior to diagnosis and supports previous studies postulating a predomination for HHV-6A in MS disease and suggests that the infection is important at early stages of the disease. Furthermore, HHV-6A infection interacts with other factors suspected of modulating MS susceptibility and progression such as infection with Epstein-Barr virus (EBV) and Cytomegalovirus (CMV), tobacco smoking, HLA alleles, UV irradiation and vitamin D levels. The multifactorial nature of MS and pathophysiological role for HHV-6A in inflammation and autoimmunity are discussed.

HMGB1 Knockout Decreases Kaposi's Sarcoma-Associated Herpesvirus Virion Production in iSLK BAC16 Cells by Attenuating Viral Gene Expression

Multiple host proteins affect the gene expression of Kaposi's sarcoma-associated herpesvirus (KSHV) during latent and lytic replication. High-mobility group box 1 (HMGB1) serves as a highly conserved chromosomal protein inside the cell and a prototypical damage-associated molecular pattern molecule outside the cell. HMGB1 has been shown to play a pathogenic role in viral infectious diseases and to regulate the lytic replication of KSHV. However, its functional effects on the KSHV life cycle in KSHV-infected cells have not been fully elucidated. Here, we explored the role of intracellular and extracellular HMGB1 in KSHV virion production by employing CRISPR/Cas9-mediated HMGB1 knockout in the KSHV-producing iSLK BAC16 cell line. Intracellular HMGB1 formed complexes with various proteins, and the abundance of HMGB1-interacting proteins changed during latent and lytic replication. Moreover, extracellular HMGB1 was found to enhance lytic replication by phosphorylating JNK. Of note, the expression of viral genes was attenuated during lytic replication in HMGB1 knockout iSLK BAC16 cells, with significantly decreased production of infectious virions compared to that of wild-type cells. Collectively, our results demonstrate that HMGB1 is an important cellular cofactor that affects the generation of infectious KSHV progeny during lytic replication. IMPORTANCE The high-mobility group box 1 (HMGB1) protein has many intra- and extracellular biological functions with an intricate role in various diseases. In certain viral infections, HMGB1 affects the viral life cycle and pathogenesis. In this study, we explored the effects of HMGB1 knockout on the production of Kaposi's sarcoma-associated herpesvirus (KSHV). HMGB1 knockout decreased virion production in KSHV-producing cells by decreasing the expression of viral genes. The processes by which HMGB1 affects KSHV production may occur inside or outside infected cells. For instance, several cellular and viral proteins interacted with intracellular HMGB1 in a nucleosomal complex, whereas extracellular HMGB1 induced JNK phosphorylation, thereby enhancing lytic replication. Our results suggest that both intracellular and extracellular HMGB1 are necessary for efficient KSHV replication. Thus, HMGB1 may represent an effective therapeutic target for the regulation of KSHV production.

Evasion of the Host Immune Response by Betaherpesviruses

The human immune system boasts a diverse array of strategies for recognizing and eradicating invading pathogens. Human betaherpesviruses, a highly prevalent subfamily of viruses, include human cytomegalovirus (HCMV), human herpesvirus (HHV) 6A, HHV-6B, and HHV-7. These viruses have evolved numerous mechanisms for evading the host response. In this review, we will highlight the complex interplay between betaherpesviruses and the human immune response, focusing on protein function. We will explore methods by which the immune system first responds to betaherpesvirus infection as well as mechanisms by which viruses subvert normal cellular functions to evade the immune system and facilitate viral latency, persistence, and reactivation. Lastly, we will briefly discuss recent advances in vaccine technology targeting betaherpesviruses. This review aims to further elucidate the dynamic interactions between betaherpesviruses and the human immune system.