Role of SUMO-1 and SUMO interacting motifs in rhesus TRIM5α-mediated restriction

Background: TRIM5 alpha is a member of the tripartite motif family of proteins that restricts retroviral infection in a species-specific manner. The restriction requires an interaction between the viral capsid lattice and the B30.2/SPRY domain of TRIM5 alpha. Previously, we determined that two SUMO interacting motifs (SIMs) present in the B30.2/SPRY domain of human TRIM5 alpha (huTRIM5 alpha) were important for the restriction of N-tropic Murine Leukemia Virus. Here, we examined whether SUMO expression and the SIM1 and SIM2 motifs in rhesus monkey TRIM5 alpha (rhTRIM5 alpha) are similarly important for Human Immunodeficiency Type 1 (HIV-) restriction. Results: We found that mutation of SIM1 and SIM2 of rhTRIM5 alpha abolished the restriction of HIV-1 virus. Further, knockdown of SUMO-1 in rhTRIM5 alpha expressing cells abolished restriction of HIV-1. These results may be due, in part, to the ability of SUMO-1 to stabilize rhTRIM5 alpha protein expression, as SUMO-1 knockdown increased rhTRIM5 alpha turnover and the mutations in SIM1 and SIM2 led to more rapid degradation than the wild type protein. The NF-kappa B signaling ability of rhTRIM5 alpha was also attenuated by SUMO-1 knockdown. Finally, upon inhibition of CRM1-dependent nuclear export with Leptomycin B (LMB), wild type rhTRIM5 alpha localized to SUMO-1 bodies in the nucleus, while the SIM1 and SIM2 mutants did not localize to SUMO-1. Conclusions: Our results suggest that the rhTRIM5a B30.2/SPRY domain is not only important for the recognition of the HIV-1 CA, but it is also important for its association with SUMO-1 or SUMO-1 modified proteins. These interactions help to maintain TRIM5 alpha protein levels and its nuclear localization into specific nuclear bodies.