HTLV-1 bZIP FACTOR ACTIVATES MYOFERLIN EXPRESSION TO FACILITATE HTLV-1 INFECTION AND MIGRATION OF INFECTED T-CELLS

Abstract

Human T-cell Leukemia Virus type 1 (HTLV-1) is a complex retrovirus responsible for diseases such as Adult T-cell Leukemia (ATL) and HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP). The viral protein HBZ is consistently expressed in infected individuals and plays a crucial role in viral persistence and disease progression. This dissertation investigates the role of the cellular protein Myoferlin (MyoF) as a downstream effector of HBZ, focusing on its impact on HTLV-1 infection and the motile properties of infected T-cells. The research first establishes that HBZ directly upregulates the transcription of the MYOF gene. Mechanistically, HBZ forms a complex with AP-1 family members (c-Jun and JunB) and recruits the coactivator p300/CBP to enhancer sites within the MYOF gene, thereby activating its expression. Consequently, MyoF expression is elevated in HTLV-1-infected T-cell lines and in CD4+ T-cells from HTLV-1 infected individuals, including those with ATL and HAM/TSP. The study further demonstrates that this HBZ-induced MyoF expression enhances HTLV-1 infection efficiency. This pro-viral effect is linked to MyoF's role in modulating the post-translational fate of the HTLV-1 envelope (Env) protein. MyoF increases the intracellular abundance of mature Env (SU and TM subunits) by restricting its trafficking to lysosomes for degradation, thus augmenting the pool of functional Env for virion assembly. Additionally, MyoF was found to enhance general T-cell adhesion, which is important for the cell-to-cell contact required for efficient HTLV-1 transmission. Beyond its role in viral infection, the dissertation reveals that MyoF is crucial for the pathogenic dissemination of HTLV-1-infected T-cells. Depletion of MyoF in infected T-cells significantly reduced their adhesion to endothelial cell monolayers, a key step in extravasation. Furthermore, MyoF knockdown impaired the migratory capacity and invasive potential of these cells through endothelial and basement membrane-like barriers. Mechanistically, MyoF influences the expression of genes involved in cell adhesion, migration, and cytoskeletal organization. Notably, MyoF depletion led to reduced expression of ITGA4 (encoding integrin α4), correlating with decreased adhesion to VCAM-1, and COTL1 (encoding an F-actin binding protein). Knockdown of COTL1 itself reduced migration and invasion, and both MyoF and COTL1 depletion resulted in decreased cellular F-actin intensity, highlighting the importance of MyoF in modulating cytoskeletal dynamics essential for cell motility. In conclusion, this dissertation identifies a novel HBZ-MyoF molecular axis that is critical for both enhancing HTLV-1 infection efficiency and promoting the adhesion, migration, and invasion of infected T-cells. These findings significantly advance the understanding of how HTLV-1 manipulates host cell functions to drive its pathogenic lifecycle and associated diseases, highlighting this pathway as a potential therapeutic target.