Phospho-activated non-muscle myosin IIA heavy chain supports different mechanisms of virus uptake.

Limiting virus entry is crucial to prevent infection, since this step of the virus life cycle is a major determinant of cellular tropism, host range, and pathogenesis. We recently showed that the transmembrane protein signal regulatory protein alpha (SIRPA), a negative regulator of F-actin-dependent phagocytosis, limits endocytosis of enveloped RNA viruses from unrelated families. Mechanistically, surface engagement of SIRPA recruits the SH2 domain-containing protein tyrosine phosphatases (SHP)-1 and -2, initiating a signaling cascade that dephosphorylates different pro-phagocytic proteins, including the heavy chain (MYH9) of the molecular motor non-muscle myosin IIA (NM-IIA), to ultimately suppress phagocytosis. Here, we analyzed whether MYH9 would enhance viral infection, as it does phagocytic engulfment, and how its activity in infection is regulated. We found that MYH9 expression increases the infection of viruses exploiting different endocytic pathways/mechanisms to enter cells, including flavivirus, arenavirus, rhabdovirus, and togavirus, in human and mouse cells. Furthermore, we demonstrated that MYH9 is actively translocated to the plasma membrane upon viral infection to support post-binding steps of entry, and that phosphorylation of two key tyrosine residues in its head and tail domains is essential for its function in viral infection. By using small molecule inhibitors and