Induction of HIV expression through lymphocyte activation has been proposed as a strategy to purge latent reservoirs.
Prostratin is a non-tumourogenic
phorbol ester that delays HIV replication in vitro, but paradoxically activates HIV expression in latently infected cells. To get a better insight into the mechanisms of action of
prostratin, we have analysed the effect of
prostratin on HIV activation and HIV receptor and coreceptors' surface expression in human lymphocytes. Peripheral blood mononuclear cells (PBMCs) were transfected with
luciferase expression constructs under the control of wild type HIV-long terminal repeat (LTR) and consensus sequences for
transcription factors involved in HIV-LTR transactivation (
NF-kappaB, SP1, NFAT).
Prostratin stimulates transactivation of LTR vectors, kappaB- and SP-1-driven
luciferase constructs. In another set of experiments, PBMCs were transfected with a full-length infectious viral clone.
Prostratin induced HIV transcription and viral expression as detected by
luciferase activity in cellular extracts and p24 levels in culture supernatants, respectively. Expression of the HIV coreceptors CCR5 and CXCR4 was decreased by
prostratin and, concomitantly,
prostratin inhibited the
infection of PBMCs with R5 and X4 strains. However,
prostratin did not inhibit
infection with a pseudotyped viral clone that enters into the cells independently of
HIV receptors. These results help to explain the paradoxical effects of
prostratin. On one hand,
prostratin induces HIV activation in latently infected cells through the induction of
NF-kappaB and Sp1. On the other hand, strong and persistent downregulation of
HIV receptors decreases
infection of new targets and delays HIV propagation. These data support the potential use of
prostratin to activate HIV from latency and purge viral reservoirs.