Cardiac glycoside/aglycones inhibit HIV-1 gene expression by a mechanism requiring MEK1/2-ERK1/2 signaling

The capacity of HIV-1 to develop resistance to current drugs calls for innovative strategies to control this infection. We aimed at developing novel inhibitors of HIV-1 replication by targeting viral RNA processing—a stage dependent on conserved host processes. We previously reported that digoxin is a potent inhibitor of this stage. Herein, we identify 12 other cardiac glycoside/aglycones or cardiotonic steroids (CSs) that impede HIV growth in HIV-infected T cells from clinical patients at IC(50)s (1.1–1.3 nM) that are 2–26 times below concentrations used in patients with heart conditions. We subsequently demonstrate that CSs inhibit HIV-1 gene expression in part through modulation of MEK1/2-ERK1/2 signaling via interaction with the Na(+)/K(+)-ATPase, independent of alterations in intracellular Ca(2+). Supporting this hypothesis, depletion of the Na(+)/K(+)-ATPase or addition of a MEK1/2-ERK1/2 activator also impairs HIV-1 gene expression. Similar to digoxin, all CSs tested induce oversplicing of HIV-1 RNAs, reducing unspliced (Gag) and singly spliced RNAs (Env/p14-Tat) encoding essential HIV-1 structural/regulatory proteins. Furthermore, all CSs cause nuclear retention of genomic/unspliced RNAs, supporting viral RNA processing as the underlying mechanism for their disruption of HIV-1 replication. These findings call for further in vivo validation and supports the targeting of cellular processes to control HIV-1 infection.