Conserved U14-Mediated NF-κB Activation in Human Herpesvirus 6A and 6B

Human herpesvirus 6B (HHV-6B) is the most prevalent HHV-6 species in humans and is associated with roseola infantum, febrile seizures, and increased morbidity following reactivation in immunocompromised patients. Herpesviruses frequently modulate NF-κB, a central regulator of inflammatory gene expression, to promote viral gene expression and replication. The HHV-6A tegument protein U14 activates NF-κB, but whether this activity is conserved in HHV-6B and contributes to infection-associated outputs has remained unclear. Here, we evaluated HHV-6A and HHV-6B U14 in a transient NF-κB reporter assay and examined U14 function during HHV-6B infection using two independent U14-targeting shRNAs. Both U14 orthologs activated an NF-κB reporter. During HHV-6B infection in MT-4 cells, U14 knockdown reduced phosphorylation of p65 (Ser536) and was accompanied by decreased mRNA levels of the immediate-early viral gene IE2 and the early viral genes U27 and U38, as well as reduced release of viral genomes into culture supernatants. U14 knockdown also reduced IL-2, IL-6, and IL-8 transcript levels, consistent with attenuation of an NF-κB-linked cytokine transcriptional program. Together, these results extend U14-mediated NF-κB activation to HHV-6B and link U14 depletion to reduced viral gene expression and productive replication.