Mechanisms of HIV Receptor and Co-Receptor Down-Regulation by Prostratin: Role of Conventional and Novel PKC Isoforms

Abstract

Prostratin is an unusual non-tumour promoting phorbol ester with potential as an inductive adjuvant therapy for highly active antiretroviral therapy (HAART) due to its ability to up-regulate viral expression from latent provirus. In addition, prostratin is also able to inhibit de novo HIV infection most probably because it induces down-regulation of HIV receptors from the surface of target cells. In this study, we investigate the mechanisms by which prostratin down-regulates HIV receptor and co-receptor surface expression in lymphocytic and monocytic cell lines. Our results indicate that prostratin induces down-regulation of surface expression of CD4 and CXCR4, but not CCR5, in various cell lines. Down-regulation of CD4 and CXCR4 by prostratin is achieved by internalization through receptor-mediated endocytosis and/or macropinocytosis, which is then followed by degradation of these molecules. Because prostratin is a protein kinase C (PKC) activator, we next examined the potential contribution of distinct PKC isoforms to down-regulate CD4 and CXCR4 in response to prostratin stimulation. Although exposure of cells to prostratin or phorbol-myristate-acetate (PMA) induces the translocation of several PKC isoforms to the plasma membrane, the use of specific PKC inhibitors revealed that novel PKCs are the main mediators of the prostratin-induced CD4 down-regulation, whereas both conventional and novel PKCs contribute to CXCR4 down-regulation. Altogether these results showed that prostratin, through the activation of conventional and/or novel PKC isoforms, rapidly reduces cell surface expression of CD4 and CXCR4, but not CCR5, by inducing their internalization and degradation.

Highly potent, synthetically accessible prostratin analogs induce latent HIV expression in vitro and ex vivo

“…It causes down-regulation of CD4, C-X-C chemokine receptor type 4 (CXCR4), and in some cases C-C chemokine receptor type 5 (CCR5), thereby protecting CD4 + T cells from HIV-1 entry (23,24). Other cell surface receptors, such as the early activation marker CD69, are up-regulated, whereas the late activation marker CD25 is little affected by prostratin treatment (25).…”

Potential anticancer effect of prostratin through SIK3 inhibition

“…Prostratin had been shown to elicit anti-HIV effect by inducing down-regulation of CD4, C-X-C chemokine receptor type 4 (CXCR4), and thereby protecting CD4+T cells from HIV-1 entry (12). In acutely infected cells, prostratin is thought to enhance cellular protection possibly due to cytostatic effects (27).…”

“…Molecular studies have demonstrated that prostratin exerts its anti-HIV effect through activation of protein kinase C (11). Importantly, prostratin is shown to induce downregulation of chemokine receptor CXCR4 in CD4+T lymphocytes there by preventing the entry of HIV-1 virus into lymphocytes (12).…”

HIV Toxins: Gp120 as an Independent Modulator of Cell Function

“…Membrane events participating in the regulation of CXCR4 and CCR5 function include dimerization as well as extensive downregulation by endocytosis and/or macropinocytosis. In addition, proteases released by neutrophils cleavage the N-terminus extracellular portion of CXCR4, avoiding ligand interaction (Hezareh et al, 2004;Lévesque et al, 2003). In the last decade, the CXCR4-SF-1 axis has been increasingly involved in the generation, progression and metastasis of a variety of tumors, so that the expression of CXCR4 is currently considered an important biomarker for identification of the metastatic potential of primary tumors and a potential therapeutic target (Nimmagadda et al, 2010;Muller et al, 2001).…”