Mechanisms of Nuclear Egress in Gamma-herpesviruses

/ABSTRACT Kaposi’s sarcoma-associated herpesvirus (KSHV) is an enveloped, double-stranded-DNA g-herpesvirus and class I carcinogen. KSHV is the causative agent of Kaposi’s sarcoma, primary effusion lymphomas, and multicentric Castleman’s disease. In sub-Saharan Africa, it has seroprevalence rates as high as 80% and causes endemic disease. The effectiveness of this oncogenic virus is largely attributed to its ability to reactivate at opportune times. During lytic infection, KSHV – like all herpesviruses – translocates newly assembled capsids from the nucleus into the cytoplasm for maturation into infectious virions. To accomplish this, KSHV utilizes an unusual process termed “nuclear egress,” in which viral capsids exit the nucleus by undergoing nuclear membrane budding and fusion events. The nuclear egress complex (NEC) is a conserved, virally encoded heterodimer that is required for nuclear egress and can bud membranes independently. Prior work from distantly related neurotropic a- herpesviruses demonstrated that the NEC promotes budding by oligomerizing into hexagonal, membrane-bound coats. However, recent studies suggested that the oncogenic g-herpesviruses KSHV and EBV may have structurally and functionally distinct NECs. Therefore, I hypothesize the KSHV NEC has a distinct membrane remodeling mechanism to support nuclear egress. The objective of this proposal is to characterize the mechanisms by which KSHV NEC remodels nuclear membranes to mediate nuclear egress. In Aim 1, I will characterize KSHV NEC function in vivo and visualize nuclear egress and nuclear membrane remodeling events in KSHV infected cells using TEM and cryo-electron tomography. In Aim 2, I will use x-ray crystallography, cryo-EM/ET, and structure-guided mutagenesis to determine the geometry of KSHV NEC coats and the role their formation plays in membrane budding and nuclear egress. This proposal is innovative as it will use cutting-edge approaches to yield new mechanistic insights into the process of nuclear egress in g-herpesviruses. It is significant as it will identify key functional regions within the KSHV NEC to inform the development of anti-KSHV therapeutics designed to block nuclear egress. This proposal has the potential to make major contributions for the development of therapeutics against KSHV and its associated cancers. My sponsor, Dr. Ekaterina Heldwein, will ensure that I acquire the technical and conceptual skills necessary for the successful completion of this project and for my development into a premier scientist so that I may achieve my long-term career goal of running my own virology lab. Project Number: 1F31AI191719-01A1 | Fiscal Year: 2026 | NIH Institute/Center: National Institute of Allergy and Infectious Diseases (NIAID) | Principal Investigator: Ariana Calderon-Zavala | Institution: TUFTS UNIVERSITY BOSTON, BOSTON, MA | Award Amount: $46,302 | Activity Code: F31 | Study Section: Special Emphasis Panel[ZRG1 F07C-H (20)] View on NIH RePORTER: https://reporter.nih.gov/project-details/1F31AI19171901A1