UC Santa Barbara

ABSTRACT

Inhibition of the eIF4E-kinase MNK as a Strategy for Controlling Kaposi’s Sarcoma-associated Herpesvirus Replication

by

Catya-Luth Faeldonea

During viral infection, viruses hijack the host protein translation machinery to efficiently produce their own proteins for subsequent infection. Cap-dependent translation relies on the formation of the heterotrimeric cap-binding complex, eIF4F. The formation and activity of this complex is regulated by different pathways that modulate the phosphorylation status of the eIF4F components. Two such pathways, p38 and ERK, converge on the phosphorylation of the MAP kinase interacting kinases 1 and 2 (Mnk1 and Mnk2), which are the sole kinases of the cap-binding protein eIF4E, an integral component of eIF4F. These kinases are required for tumor formation and in response to cellular and environmental stress, but are negligible for normal cellular functions and development. The role of these kinases during viral infection have been thoroughly investigated. In the context of infection by herpesviruses, several studies demonstrated that MNK activity is upregulated in cells infected by Herpes Simplex Virus-1 (HSV-1), Human Cytomegalovirus (HCMV) and Kaposi’s Sarcoma Associated Herpesvirus (KSHV). The phosphorylation of eIF4E is critical for herpesvirus replication as genetic and pharmacological inhibition reduces virus production. My goal is to exploit MNK1/2 and eIF4E phosphorylation as a potential therapeutic target for KSHV.KSHV is an oncogenic virus and the etiological agent for Kaposi’s Sarcoma (KS), Multicentric Castleman’s Disease, and primary effusion lymphoma (PEL), which are diseases commonly diagnosed in immunocompromised patients. KSHV is prevalent in 50% of the population in sub-Saharan Africa. Unfortunately, despite its continued occurrence, there are currently no FDA-approved therapeutics against KSHV-related diseases. Because of this, there is strong interest in finding new targets for therapeutic intervention. The eIF4E kinase MNK1/2 has been considered a promising target to reduce KSHV replication. Previous studies demonstrate that inhibition of MNK1 with the small molecule inhibitor CGP57380 (CGP) reduced viral replication; however, this compound does not have an effect on the second eIF4E kinase, MNK2, and has since been reported to have numerous off-target effects. To better evaluate the potential of MNK1/2 as therapeutic targets for KSHV infection, I evaluated pharmacological inhibition of both MNK isoforms with the compound Tomivosertib, and genetic ablation of MNK1/2 in KSHV infected cells. My studies show that treatment with Tomivosertib downregulates the levels of the KSHV structural proteins and inhibits viral replication. Using CRISPRi technology, I established a MNK1/2 double knockdown, KSHV-infected cell line to evaluate the effect of genetic ablation of MNK1/2 on KSHV infection. As seen with the Tomivosertib treated cells, viral reactivation was reduced by over 50% in these cells. These findings suggest that MNK1 and MNK2 are promising therapeutic targets for the treatment of KSHV and its associated malignancies.