Objective: A lack of productive HIV-1 infection of Kit225 compared to Jurkat T cells, despite similar levels of CD4 and HIV-1 chemokine co-receptors, was found to correlate with the expression of vasoactive intestinal peptide/pituitary adenylate cyclase activating polypeptide receptor-1 (VPAC1). We therefore examined a role for this seven-transmembrane G protein-coupled neuroendocrine receptor in modulating HIV-1 infection.
Methods: Reverse transcription–PCR was used to show the level of VPAC1 expression in different T-cell lines. A signal-blocking antibody to VPAC1 was used to examine its inhibiting effect on HIV-1 infection. Transfection of VPAC1 cDNA in both sense and anti-sense orientation was used to assess the role of VPAC1 in HIV-1 infection. HIV-1 infection was monitored by gag p24 ELISA using HIV-1IIIB or by luciferase activity using pseudo envelope-typed HXB2-NL4-3-luciferase. Analysis of HIV-1 gag DNA and 2-LTR circles was utilized to examine a possible mechanism for the effect of VPAC1.
Results: Using VPAC1 signal blocking antibody, we showed that up to 80% of productive infection with HIV-1IIIB was inhibited. We also demonstrated that HIV-1 gp120 has sequence similarity to the natural ligand for VPAC1 and postulate that it can activate this receptor directly. Transfection of VPAC1 cDNA in the anti-sense orientation resulted in a significant loss, up to 50% of productive infection. In contrast, transfection of cells with VPAC1 in the sense orientation increased the productive infection by more than 15-fold and caused a profound increase in syncytium formation. Furthermore, stimulation of VPAC1 on primary cells facilitated in vitro infection with HIV-1 HXB2-NL4-3. Analysis of HIV-1 gag DNA indicated that VPAC1 does not affect viral entry; however, cells that show negligible expression of VPAC1 may not be productively infected as indicated by a lack of 2-LTR circle formation.
Conclusion: We have discovered a cellular receptor, VPAC1, that is a novel and potent facilitator of HIV-1 infection and thus, is a potentially important new target for therapeutic intervention.
From the aDepartment of Medicine, and Institute of Medical Science, University of Toronto, the bDivision of Cellular and Molecular Biology, Toronto General Research Institute of the University Health Network, and cCanadian Blood Services, Toronto Centre, Toronto, Ontario, and the dCadham Provincial Laboratory and the Department of Medical Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada.
Requests for reprints to: D. R. Branch, Canadian Blood Services, 67 College Street, Toronto, Ontario M5G 2M1 Canada.
Received: 23 March 2001;
revised: 3 August 2001; accepted: 7 August 2001.
Sponsorship: Supported in part by Medical Research Council of Canada (MRC) grant MT-14980. S. Yousefi is a recipient of a Natural Sciences and Engineering Research Council (NSERC) of Canada Fellowship award. X.-Z. Ma is a recipient of an Ontario HIV Treatment Network Fellowship award.