Hsp70 Interacts with the Retroviral Restriction Factor TRIM5α and Assists the Folding of TRIM5α

Tripartite motif (TRIM) protein TRIM5 alpha has been shown to restrict human immunodeficiency virus, type 1 infection in Old World monkey cells at the early post-entry step by poorly understood mechanisms. Currently, the physiological function of TRIM5 alpha is not known. In this study, we showed that transiently overexpressed TRIM5 alpha causes a morphological change in HEK293T cells. A proteomics analysis of the protein complexes that were pulled down with hemagglutinin-tagged TRIM5 alpha suggested that the heat shock protein 70 (Hsp70) may serve as a TRIM5 alpha-binding partner. The interaction between Hsp70 and TRIM5 alpha was confirmed by co-localization and co-immunoprecipitation assays. Co-expression of Hsp70 reversed the TRIM5 alpha-induced morphological change in HEK293T cells. Another heat shock protein Hsc70 also bound to TRIM5 alpha, but unlike Hsp70, Hsc70 was not able to reverse the TRIM5 alpha-induced morphological change, suggesting that Hsp70 specifically reverses the morphological change caused by TRIM5 alpha. Studies using a series of TRIM5 alpha deletion mutants demonstrate that, although the PRYSPRY domain is critical for binding to Hsp70, the entire TRIM5 alpha structure is necessary to induce the morphological change of cells. When the ATPase domain of Hsp70 was mutated, the mutated Hsp70 could not counteract the morphological change induced by TRIM5 alpha, indicating that the catalytic activity of Hsp70 protein is important for this function. Co-expression of Hsp70 elevated the levels of TRIM5 alpha in the detergent-soluble fraction with a concomitant decrease in the detergent-insoluble fraction. Together these results suggest that Hsp70 plays critical roles in the cellular management against the TRIM5 alpha-induced cellular insults.