Murine leukemia virus infection of non-dividing dendritic cells is dependent on nucleoporins

Retroviral reverse transcription starts within the capsid and uncoating and reverse transcription are mutually dependent. There is still debate regarding the timing and cellular location of HIV's uncoating and reverse transcription and whether it occurs solely in the cytoplasm, nucleus or both. HIV can infect non-dividing cells because there is active transport of the preintegration complex (PIC) across the nuclear membrane, but Murine Leukemia Virus (MLV) is thought to depend on cell division for replication and whether MLV uncoating and reverse transcription is solely cytoplasmic has not been studied. Here, we used NIH3T3 and primary mouse dendritic cells to determine where the different stages of reverse transcription occur and whether cell division is needed for nuclear entry. Our data strongly suggest that in both NIH3T3 cells and dendritic cells (DCs), the initial step of reverse transcription occurs in the cytoplasm. However, we detected MLV RNA/DNA hybrid intermediates in the nucleus of dividing NIH3T3 cells and non-dividing DCs, suggesting that reverse transcription can continue after nuclear entry. We also confirmed that the MLV PIC requires cell division to enter the nucleus of NIH3T3 cells. In contrast, we show that MLV can infect non-dividing primary DCs, although integration of MLV DNA in DCs still required the viral p12 protein. Knockdown of several nuclear pore proteins dramatically reduced the appearance of integrated MLV DNA in DCs but not NIH3T3 cells. Additionally, MLV capsid associated with the nuclear pore proteins NUP358 and NUP62 during infection. These findings suggest that simple retroviruses, like the complex retrovirus HIV, gain nuclear entry by traversing the nuclear pore complex in non-mitotic cells. Retrovirus replication requires nuclear entry of reverse-transcribed double-stranded viral DNA and integration into the host cell chromosomes. It is widely believed that unlike lentiviruses, simple retroviruses like MLV require nuclear membrane breakdown during cell division to achieve nuclear entry of viral reverse transcription products to complete their replication. We show here that while this is true for rapidly dividing tissue culture cells, in quiescent primary cells like dendritic cells, the likely initial targets of in vivo MLV infection, the virus establishes infection without cell division. MLV accomplishes this because the viral capsid protein interacts with proteins in the nuclear membrane in DCs. In contrast, while this interaction occurs in dividing tissue culture cells, it is not sufficient for nuclear entry of viral DNA. These studies show that the requirements for retrovirus infection depend on the cell type and moreover, partially overturn the dogma that simple retroviruses need cell division to complete replication.