Knockdown of the host cellular protein transportin 3 attenuates prototype foamy virus infection

Abstract

Transportin 3 (TNPO3) is a member of the importin-ß superfamily proteins. Despite numerous studies, the exact molecular mechanism of TNPO3 in retroviral infection is still controversial. Here, we provide evidence for the role and mechanism of TNPO3 in the replication of prototype foamy virus (PFV). Our findings revealed that PFV infection was reduced 2-fold by knockdown (KD) of TNPO3. However, late stage of viral replication including transcription, translation, viral assembly, and release was not influenced. The differential cellular localization of PFV integrase (IN) in KD cells pinpointed a remarkable reduction of viral replication at the nuclear import step. We also found that TNPO3 interacted with PFV IN but not with Gag, suggesting that IN-TNPO3 interaction is important for nuclear import of PFV pre-integration complex. Our report enlightens the mechanism of PFV interaction with TNPO3 and support ongoing research on PFV as a promising safe vector for gene therapy.

Cellular and viral determinants of retroviral nuclear entry

“…Afterward, the Ran-GTP concentration gradient generated between the nucleus and cytoplasm causes discharge of both subtypes of importin to the cytoplasm using several exportins, such as Crm1. However, this nuclear import mechanism is subverted by some viruses for import of their PIC, allowing cDNA to be successfully incorporated into the host genome (Stewart 2007;Hossain et al 2014;Ali et al 2015).…”

“…Different research groups have succeeded in detecting the cellular import systems by genome-wide or yeast 2-hybrid (Y2H) screening. However, the roles of their components have not been determined by single or double mutations because viral infection is not inhibited (Cribier et al 2011;De Iaco et al 2013;De Houwer et al 2014;Ali et al 2015).…”

“…Since the identification of TNPO3 as a binding partner of HIV-1 IN through Y2H screening and pulldown assays, the role of TNPO3 in the retrovirus life cycle has been investigated (Christ et al 2008). Interactions of TNPO3 with the HIV-1 PIC components IN (Christ et al 2008;De Iaco and Luban, 2011;Larue et al 2012;Ali et al 2015) and CA (Valle-Casuso et al 2012) were also identified by co-immunoprecipitation and pull-down assays.…”

“…For example, simian immunodeficiency virus (SIV), HIV-1, and HIV-2 production declines approximately 15-fold in TNPO3 knockdown (KD) HeLa cells, but feline immunodeficiency virus (FIV) and MLV do not show any sensitivity (Valle-Casuso et al 2012). The infection of PFV is reduced by only 2-fold in TNPO3 KD baby hamster kidney (BHK-21) cells with no effect on late stages, including viral assembly and release (Ali et al 2015), indicating that replication of PFV is less dependent on TNPO3. Consistently, beta-retroviruses, such as mouse mammary tumor virus, can import genetic material via a TNPO3-independent pathway in nondividing cells and can integrate randomly when using a split genome due to low viral titer (Konstantoulas and Indik 2014).…”

Apoptotic events induced by prototype foamy virus infection

“…Briefly, the FAB cell line has a single integrated copy of a long terminal repeat (LTR)-driven by the β-Gal gene. Viral infection causes the PFV-LTR promoter to be transactivated by the viral Tas protein, resulting in a blue color in the infected cells after X-gal staining (Hossain et al 2014;Ali et al 2015).…”