Abstract

HIV-1 integrase (IN) is a key viral enzymatic protein acting in several viral replication steps, including integration. IN has been shown to be an unstable protein degraded by the N-end rule pathway through the host ubiquitin-proteasome machinery. However, it is still not fully understood how this viral protein is protected from the host ubiquitin-proteasome system within cells during HIV replication. In the present study, we provide evidence that the host protein Ku70 interacts with HIV-1 IN and protects it from the Lys(48)-linked polyubiquitination proteasomal pathway. Moreover, Ku70 is able to down-regulate the overall protein polyubiquitination level within the host cells and to specifically deubiquitinate IN through their interaction. Mutagenic studies revealed that the C terminus of IN (residues 230-288) is required for IN binding to the N-terminal part of Ku70 (Ku70(1-430)), and their interaction is independent of Ku70/80 heterodimerization. Finally, knockdown of Ku70 expression in both virus-producing and target CD4(+) T cells significantly disrupted HIV-1 replication and rendered two-long terminal repeat circles and integration undetectable, indicating that Ku70 is required for both the early and the late stages of the HIV-1 life cycle. Interestingly, Ku70 was incorporated into the progeny virus in an IN-dependent way. We proposed that Ku70 may interact with IN during viral assembly and accompany HIV-1 IN upon entry into the new target cells, acting to 1) protect IN from the host defense system and 2) assist IN integration activity. Overall, this report provides another example of how HIV-1 hijacks host cellular machinery to protect the virus itself and to facilitate its replication.

Highlights

  • (IN).5 During HIV-1 integration, IN catalyzes the insertion of newly reverse-transcribed ϳ10-kb viral DNA into the host genome

  • nonhomologous end-joining (NHEJ) activity is required for two-long terminal repeat (2-LTR) circle formation, and Ku70 has been detected in Moloney murine leukemia virus (MMLV) preintegration complexes (PICs) (24, 26 –28)

  • Cellular Protein Ku70 Protects HIV-1 IN from Proteasomal Degradation—As a part of the NHEJ machinery, the host protein Ku70 has been shown to participate in HIV integration and in the circularization of unintegrated viral DNAs (25, 27)

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Summary

Introduction

(IN).5 During HIV-1 integration, IN catalyzes the insertion of newly reverse-transcribed ϳ10-kb viral DNA into the host genome. All of these results suggest that Ku70 may interact with IN during viral assembly and accompany HIV-1 IN into newly infected cells to assist IN integration activity and protect IN from host-mediated degradation.

Results
Conclusion
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