Cytotoxic Lymphocytes Target HIV-1 Gag Through Granzyme M-Mediated Cleavage

Abstract

Untreated HIV-1 infection leads to a slow decrease in CD4+ T cell lymphocytes over time resulting in increased susceptibility to opportunistic infections (acquired immunodeficiency syndrome, AIDS) and ultimately death of the infected individual. Initially, the host’s immune response controls the infection, but cannot eliminate the HIV-1 from the host. Cytotoxic lymphocytes are the key effector cells in this response and can mediate crucial antiviral responses through the release of a set of proteases called granzymes towards HIV-1-infected cells. However, little is known about the immunological molecular mechanisms by which granzymes could control HIV-1. Since we noted that HIV-1 subtype C (HIV-1C) Gag with the tetrapeptide insertion PYKE contains a putative granzyme M (GrM) cleavage site (KEPL) that overlaps with the PYKE insertion, we analyzed the proteolytic activity of GrM towards Gag. Immunoblot analysis showed that GrM could cleave Gag proteins from HIV-1B and variants from HIV-1C of which the Gag-PYKE variant was cleaved with extremely high efficiency. The main cleavage site was directly after the insertion after leucine residue 483. GrM-mediated cleavage of Gag was also observed in co-cultures using cytotoxic lymphocytes as effector cells and this cleavage could be inhibited by a GrM inhibitor peptide. Altogether, our data indicate towards a noncytotoxic immunological mechanism by which GrM-positive cytotoxic lymphocytes target the HIV-1 Gag protein within infected cells to potentially control HIV-1 infection. This mechanism could be exploited in new therapeutic strategies to treat HIV-1-infected patients to improve immunological control of the infection.

Contribution of the HIV-1 Envelope Glycoprotein to AIDS Pathogenesis and Clinical Progression

“…Among the HIV- 1 viral proteins, the reverse transcriptase (RT), because of its essential role in replication and because it is the main target of ART, has been extensively studied [ 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 ]. In addition, the proteins of the gag gene are involved in the virion structure and also in the cellular immune response [ 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 ]. Apart from these proteins, the viral envelope gene ( env ) and the derived glycoprotein complex (Env) have attracted numerous studies because of their central role in (i) the initial events (CD4 and co-receptor binding, pore fusion formation) and subsequent step of the biological viral life cycle; (ii) the neutralizing humoral immune response; and (iii) the viral tropism.…”

Natural killer cells induce HIV-1 latency reversal after treatment with pan-caspase inhibitors

“…These cells can eliminate virus-infected cells through the induction of target cell death via multiple mechanisms ( 13 – 15 ). In a previous study, we showed that NK cells target the HIV-1 Gag protein through the release of protease granzyme M (GrM) ( 16 ). Because GrM is known to inhibit replication of other viruses ( 17 – 19 ), we were initially interested in whether NK cells could also inhibit HIV-1 replication in a GrM-dependent manner.…”