Abstract
Following entry into the target cell, human immunodeficiency virus type 1 (HIV-1) must reverse transcribe its RNA genome to DNA and traffic to the nuclear envelope, where the viral genome is translocated into the nucleus for subsequent integration into the host cell chromosome. During this time, the viral core, which houses the genome, undergoes a poorly understood process of disassembly, known as uncoating. Collectively, many studies suggest that uncoating is tightly regulated to allow nuclear import of the genome while minimizing the exposure of the newly synthesized DNA to cytosolic DNA sensors. However, whether host cellular proteins facilitate this process remains poorly understood. Here we report that intact microtubules facilitate HIV-1 uncoating in target cells. Disruption of microtubules with nocodazole substantially delays HIV-1 uncoating, as revealed with three different assay systems. This defect in uncoating did not correlate with defective reverse transcription at early times postinfection, demonstrating that microtubule-facilitated uncoating is distinct from the previously reported role of viral reverse transcription in the uncoating process. We also find that pharmacological or small interfering RNA (siRNA)-mediated inhibition of cytoplasmic dynein or the kinesin 1 heavy chain KIF5B delays uncoating, providing detailed insight into how microtubules facilitate the uncoating process. These studies reveal a previously unappreciated role for microtubules and microtubule motor function in HIV-1 uncoating, establishing a functional link between viral trafficking and uncoating. Targeted disruption of the capsid motor interaction may reveal novel mechanisms of inhibition of viral infection or provide opportunities to activate cytoplasmic antiviral responses directed against capsid or viral DNA. IMPORTANCE: During HIV-1 infection, fusion of viral and target cell membranes dispenses the viral ribonucleoprotein complex into the cytoplasm of target cells. During this time, the virus must reverse transcribe its RNA genome, traffic from the location of fusion to the nuclear membrane, and undergo the process of uncoating, whereby the viral capsid core disassembles to allow the subsequent nuclear import of the viral genome. Numerous cellular restriction factors target the viral capsid, suggesting that perturbation of the uncoating process represents an excellent antiviral target. However, this uncoating process, and the cellular factors that facilitate uncoating, remains poorly understood. The main observation of this study is that normal uncoating requires intact microtubules and is facilitated by dynein and kinesin motors. Targeting these factors may either directly inhibit infection or delay it enough to trigger mediators of intrinsic immunity that recognize cytoplasmic capsid or DNA and subsequently induce an antiviral state in these cells.