Dynamin-2 Stabilizes the HIV-1 Fusion Pore with a Low Oligomeric State

Abstract

SummaryOne of the key research areas surrounding HIV-1 concerns the regulation of the fusion event that occurs between the virus particle and the host cell during entry. Even if it is universally accepted that the large GTPase dynamin-2 is important during HIV-1 entry, its exact role during the first steps of HIV-1 infection is not well characterized. Here, we have utilized a multidisciplinary approach to study the DNM2 role during fusion of HIV-1 in primary resting CD4 T and TZM-bl cells. We have combined advanced light microscopy and functional cell-based assays to experimentally assess the role of dynamin-2 during these processes. Overall, our data suggest that dynamin-2, as a tetramer, might help to establish hemi-fusion and stabilizes the pore during HIV-1 fusion.

Resolving the Sites of HIV Entry: Dynamin Networks Hold the Key

“…For instance, small molecule inhibitor dyngo-4a can block HIV infection at a time consistent with transcriptional silencing but not endocytosis. Similarly, ryngo-1-23 can influence oligomeric states of dynamin to block HIV fusion but not endocytosis [29,49].These observations were further supported by work of Jones and colleagues [28] that indicates that different pools of dynamin oligomers are required for HIV fusion as opposed to the process of endocytosis. We will discuss this at length later in this review with respect to alternate hypotheses of how HIV fusion at the plasma membrane is dynamin dependent.…”

“…Dynamin's role in HIV-fusion reaction is further supported in a recent study by Jones and colleagues wherein using fluorescently tagged dynamin and dual labelled HIV virions. In this latter study, the authors show that dynamin establishes a hemi-fusion state post Env-CD4-chemokine receptor engagement and later aids in stabilising the HIV fusion pore [28] (Figure 2). Based on these independent studies, we can readily conclude that dynamin is recruited to facilitate both early and late events in the HIV fusion reaction.…”

“…Like certain enveloped viruses such as Herpes Simplex virus-1 and Sendai virus, HIV entry was shown to be independent of pH and/or presence of lysosomal enzymes thus suggesting that virus entry into endolysosomal compartments was not required [19][20][21][22][23][24][25][26][27][28][29][30][31]. Studies with CD4 truncation mutations supported this view as mutations that tethered CD4 at the membrane did not impede HIV entry [20,22,23].…”

“…From our own investigations across CD4 T cells, we would readily conclude that the timing of action for fusion peptides is simply consistent with the time they act on the HIV fusion reaction (post chemokine receptor binding) and there is limited evidence both by ourselves and others [26] that the virus can escape the action of these compounds by entering into endosomes. Recently using a spectrum of approaches including small molecule inhibitors that target dynamin, endocytosis, viral fusion and replication pathways, both ourselves and others have demonstrated that HIV fusion in both activated and resting T cell subsets not only proceeds primarily through plasma membrane and but that this fusion reaction is dependent on dynamin [27][28][29].…”

“…While dynamin 2 is ubiquitously expressed, the expression of dynamin 1 is largely restricted to neurons while dynamin 3 is found in brain and testis [55][56][57]. In addition to its role in CME, dynamin can also mediate membrane fission [58], interact with cytoskeletal F actin, promote tethering and hemi-fusion of membranes [28,59], lead to stabilization and expansion of fusion pores [28,60] and regulate cytokinesis by concentrating at sites of abscission [61][62][63]. Each of these roles has the potential to influence HIV infection at various stages of virus life cycle from entry to progression of infection through cell cycle and is independent of the process of endocytosis.…”