Myosin IXB protects immune cells from virus infection.

Actin-associated proteins have been implicated in several stages of virus infection. However, the role of myosins, which are actin-dependent molecular motors, during virus infection and pathogenesis is poorly understood. Myosin IXB (Myo9b) is a member of the myosin family abundantly expressed in immune cells. Myo9b displays a RhoGTPase-activating protein domain capable of modulating actin dynamics by inhibiting RhoGTPase activity. To enquire upon Myo9b participation in virus infections, we have silenced Myo9b in U937 and Jurkat cells and infected them with vesicular stomatitis virus glycoprotein (VSV-G)-pseudotyped HIV-1. Myo9b-silenced U937 showed a remarkable increase of above ten times more HIV-VSV-G infection than control cells. We observed a similar pattern in Jurkat cell infection with both WT Env and VSV-G-pseudotyped HIV, albeit to a lesser extent. Myo9b-silenced U937 cells presented elevated levels of phosphorylated cofilin, but lower levels of polymerized actin. The use of a RhoA, B and C inhibitor, as well as a Rac1 inhibitor, reduced virus infection. Finally, we have also observed an increment in virus internalization and fusion in cells knockdown for Myo9b, which may explain the increase in virus infection. Taken together, our data suggests that Myo9b might hinder viral entry and infection by controlling the activity of RhoGTPases in immune cells.