Epstein-barr Virus Viral Protein Lmp1 Increases Rap1 Sumoylation, Enhancing Telomere Maintenance During Tumorigenesis

Abstract

Cancer remains the second leading cause of death in the USA, and there are multiple avenues of study to decipher how to combat the disease [1]. One approach in cancer treatments is to attack the tumor’s ability to replicate indefinitely. Normally healthy cells can only replicate a finite number of times before reaching their senescence limit due to loss of telomere DNA. During tumorigenesis, cells must gain the ability of maintaining chromosomal telomeres through continuous cycles of replication. Two mechanisms by which telomeres can be maintained are through activation of the telomerase complex and alternate lengthening of telomeres (ALT), a telomerase-independent mechanism that uses homologous recombination to maintain telomere length. Epstein-Barr Virus (EBV), a ubiquitous ϒ-herpesvirus, establishes a life-long latent infection within the host, and latent EBV infections are linked to the development of several epithelial and lymphoid malignancies. The principal viral oncoprotein is latent membrane protein-1 (LMP1). Early during the establishment of latency, EBV relies on ALT for maintaining telomeres [2]. However, telomerase-dependent telomere maintenance is observed in EBV-associated lymphomas. Understanding how and when the switch from ALT/telomerase-independent to telomerase-dependent telomere maintenance occurs could open new paths to the prevention or treatment of EBV-associated lymphomas. We focused on the Human Repressor Activator Protein 1 (RAP1) because it is involved in both telomerase-independent and telomerase-dependent telomere maintenance. We hypothesize that LMP1 CTAR3 induces the SUMOylation of RAP1, which contributes to LMP1-mediated oncogenesis through the maintenance of telomeres initially by ALT processes before switching to telomerase-dependent telomere elongation. Here we show conditions for telomerase-independent telomere maintenance improve when LMP1 induces the SUMOylation of PML and increases formation of PML nuclear bodies. We also show LMP1 blocks the interaction of PML with RAP1 while also increasing RAP1 association with SUMO proteins and telomerase activity. RAP1 point mutants that prevent the increased association of RAP1 with SUMO proteins also demonstrated a decrease in telomerase activity in conjuncture with increased association with PML. This data confirms that LMP1 contributes to maintaining telomeres, which not only aids EBV latency but also tumorigenesis. By better understanding how LMP1 affects telomere maintenance via its interaction with RAP1 we may discover novel therapies to prevent LMP1-mediated tumorigenesis.