Cyclophilin A enables specific HIV-1 Tat palmitoylation and accumulation in uninfected cells

Abstract

Most HIV-1 Tat is unconventionally secreted by infected cells following Tat interaction with phosphatidylinositol (4,5) bisphosphate (PI(4,5)P2) at the plasma membrane. Extracellular Tat is endocytosed by uninfected cells before escaping from endosomes to reach the cytosol and bind PI(4,5)P2. It is not clear whether and how incoming Tat concentrates in uninfected cells. Here we show that, in uninfected cells, the S-acyl transferase DHHC-20 together with the prolylisomerases cyclophilin A (CypA) and FKBP12 palmitoylate Tat on Cys31 thereby increasing Tat affinity for PI(4,5)P2. In infected cells, CypA is bound by HIV-1 Gag, resulting in its encapsidation and CypA depletion from cells. Because of the lack of this essential cofactor, Tat is not palmitoylated in infected cells but strongly secreted. Hence, Tat palmitoylation specifically takes place in uninfected cells. Moreover, palmitoylation is required for Tat to accumulate at the plasma membrane and affect PI(4,5)P2-dependent membrane traffic such as phagocytosis and neurosecretion.

Fatty acids – from energy substrates to key regulators of cell survival, proliferation and effector function

“…Palmitoylation is catalysed by aspartate-histidine-histidine-cysteine (DHHC) acyl transferases and can deeply affect the trafficking, localisation and activity of proteins [74]. Recently, Chopard et al have highlighted how palmitoylation is important for HIV-1 infection [75]. The viral protein Tat can be secreted by infected cells and subsequently be endocytosed by many different cell types altering the expression of genes related to HIV-associated cancers [76].…”

“…T cells, macrophages and neurosecretory cells) is attributed to its palmitoylation by S-acyl transferase DHHC-20 on Cys31, which stabilises the interaction with PI(4,5)P2 thus preventing Tat secretion. The persistence of Tat on plasma membranes and its stable interaction with PI(4,5)P2 interferes with PI(4,5)P2-dependent membrane trafficking, with important consequences for Tat-mediated toxicity in HIV-1 infected individuals [75].…”

“…S-acylation is a modification important for the regulation of protein trafficking and function, providing new pharmacological targets that can be exploited in the context of a wide range of pathological conditions, spanning from infection to cancer [75,114]. Inhibition of this process by limiting the availability of fatty acids or direct pharmacological inhibition of acyltransferases, could prove a viable approach applicable to different clinical scenarios.…”

Effects of HIV‐1 Tat on oligodendrocyte viability are mediated by CaMKIIβ–GSK3β interactions

“…The expression of Tat starts early during HIV infection and continues through the viral lifespan, even during cARTmediated suppression of viral replication (Heaton et al 2010;Bagashev and Sawaya 2013;Johnson and Nath 2016). Significant quantities of Tat are released from infected cells, and extracellular or exogenous Tat can be actively internalized by (Frankel and Pabo 1988;Ensoli et al 1993), or palmitoylated within the cell membrane (Chopard et al 2018) of different bystander cell types, and can modulate host gene expression and cellular functions, including cell survival and development. Previously, we reported that Tat activates OL surface ionotropic glutamate receptors (iGluRs), resulting in elevated intracellular calcium ([Ca 2+ ] i ) and Ca 2+ / calmodulin-dependent kinase IIb (CaMKIIb) activity.…”

“…), or palmitoylated within the cell membrane (Chopard et al . ) of different bystander cell types, and can modulate host gene expression and cellular functions, including cell survival and development. Previously, we reported that Tat activates OL surface ionotropic glutamate receptors (iGluRs), resulting in elevated intracellular calcium ([Ca 2+ ] i ) and Ca 2+ /calmodulin‐dependent kinase IIβ (CaMKIIβ) activity.…”