HIV-1 Matrix Protein p17 Prevents Loss of CD28 Expression During IL-2–Induced Maturation of Naïve CD8+T Cells

Simian immunodeficiency virus and human immunodeficiency virus type 1 matrix proteins specify different capabilities to modulate B cell growth

Exogenous HIV-1 matrix protein p17 (p17) deregulates the function of different cells after its N-terminal loop (AT20) binding to the chemokine receptors CXCR1 and CXCR2. One site within AT20 has been recently found to be the major determinant of viral fitness following transmission of simian immunodeficiency virus (SIV) to the human host. Therefore, we sought to determine whether SIV matrix protein (MA) was already capable of interacting with CXCR1 and CXCR2 and mimic p17 biological activities rather than this being a newly acquired function during host adaptation. We show here that SIV MA binds with the same affinity of p17 to CXCR1 and CXCR2 and displays both p17 proangiogenic on human primary endothelial cells and chemotactic activity on human primary monocytes and B cells. However, SIV MA exhibited a higher degree of plasticity than p17 in the C terminus, a region known to play a role in modulating B cell growth. Indeed, in contrast to p17, SIV MA was found to activate the phosphatidylinositol 3-kinase/Akt signaling pathway and strongly promote B cell proliferation and clonogenic activity. Interestingly, we have recently highlighted the existence of a Ugandan HIV-1 strain-derived p17 variant (S75X) with the same B cell growth-promoting activity of SIV MA. Computational modeling allowed us to hypothesize an altered C terminus/core region interaction behind SIV MA and S75X activity. Our findings suggest the appearance of a structural constraint in the p17 C terminus that controls B cell growth, which may help to elucidate the evolutionary trajectory of HIV-1.

IMPORTANCE

The HIV-1 matrix protein p17 (p17) deregulates the biological activities of different cells after binding to the chemokine receptors CXCR1 and CXCR2. The p17 functional domain responsible for receptors interaction includes an amino acid which is considered the major determinant of SIV replication in humans. Therefore, we sought to determine whether SIV matrix protein (SIV MA) already had the ability to bind to both chemokine receptors rather than being a function newly acquired during host adaptation. We show here that SIV MA binds to CXCR1 and CXCR2 and fully mimics the p17 proangiogenic and chemokine activity. However, it differs from p17 in its ability to signal into B cells and promote B cell growth and clonogenicity. Computational analysis suggests that the accumulation of mutations in the C-terminal region may have led to a further SIV MA adaptation to the human host. This finding in turn sheds light on the evolutionary trajectory of HIV-1.

HIV-1 matrix protein p17: a candidate antigen for therapeutic vaccines against AIDS

The success in the development of anti-retroviral therapies (HAART) that contain human immunodeficiency virus type 1 (HIV-1) infection is challenged by the cost of this lifelong therapy and by its toxicity. Immune-based therapeutic strategies that boost the immune response against HIV-1 proteins or protein subunits have been recently proposed to control virus replication in order to provide protection from disease development, reduce virus transmission, and help limit the use of anti-retroviral treatments. HIV-1 matrix protein p17 is a structural protein that is critically involved in most stages of the life cycle of the retrovirus. Besides its well established role in the virus life cycle, increasing evidence suggests that p17 may also be active extracellularly in deregulating biological activities of many different immune cells that are directly or indirectly involved in AIDS pathogenesis. Thus, p17 might represent a promising target for developing a therapeutic vaccine as a contribution to combating AIDS. In this article we review the biological characteristics of HIV-1 matrix protein p17 and we describe why a synthetic peptide representative of the p17 functional epitope may work as a vaccine molecule capable of inducing anti-p17 neutralizing response against p17 derived from divergent HIV-1 strains.