ORF45-induced Filamin A phosphorylation promotes cell motility and cell-contact dependent viral infection of Kaposi's sarcoma-associated herpesvirus.

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi's sarcoma, primary effusion lymphoma and multicentric Castleman disease. Studies have shown that cell-to-cell viral infection plays a key role in KSHV transmission in vivo, and differentiated B cells and endothelial cells might represent two distinct kinds of natural donors or recipients that radically support the lytic cycle of KSHV. Consistent with the observation that endothelial cells exhibit better acceptance and transmissibility than B lymphocytes in cell-cell contact-mediated KSHV transmission, the sequential cell detachment, migration and cell-cell contact is the determinant for this kind of viral transmission. To investigate the processes and regulation of cell-cell contact-mediated viral infection during KSHV lytic replication, we found that Filamin A, a key regulator of cell adhesion and motility, is phosphorylated in KSHV-infected adherent cells by lytic replication and ORF45 expression in an RSK-dependent manner. ORF45-induced Filamin A phosphorylation is important for cell detachment and migration, while both Filamin A knockout and S2152A knockin abolish this function. Interestingly, ORF45 deficiency, Filamin A knockout and S2152A knockin dramatically decreases KSHV de novo infection and cell-contact dependent viral infection in adherent cells. Taken together, our results demonstrated that the ORF45-Filamin A phosphorylation axis promotes cell detachment and migration and facilitates viral de novo infection and cell-to-cell transmission during KSHV lytic cycles.