VIP Signaling Fails to Alter Gene Expression but Induces Different [cAMP]i Responses in Human Malignant Hut-78 and Molt-4 T Cell Lines; Implications for Different G-protein Coupling for VIP Receptors

Background: Vasoactive intestinal peptide (VIP) is a 3.3 kDa pleiotropic protein with a broad expression profile that displays immune modulating activities. VIP binds two G protein-coupled receptors called Vasoactive Intestinal Pepide/Pituitary Adenylate Cyclase activating polypeptide receptor (VPAC) 1 and 2 that elicit multiple downstream signaling molecules, including adenylate cyclase. VIP differentially regulates over 300 genes in resting and activated murine CD4 T cells, and is chemotactic to resting and Th2 effector T cells. Objective: This study is focused on delineating which human VIP receptor, called VPAC1 and VPAC2, controls T cell biology pertaining to gene expression, signaling and chemotaxis. Method: To this end, we utilized human T cell lines known to exclusively express VPAC1, (HuT-78) or VPAC2 (Molt-4) in an attempt to identify VIP-receptor mediated changes in gene expression, signaling and chemotaxis. Results: This research successfully demonstrated three major findings. First, malignant or primary human T cells failed to differentially regulate any gene targets when treated with VIP ligand as assessed by an Agilent whole human microarray. Second, despite drastically different [cAMP]i profiles, both T cell lines responded similarly to VIP in Boyden Chamber assays showing both chemorepulsion and chemoattraction at low versus high VIP concentrations. Lastly, both T cell lines were equally sensitive to AC and PKA inhibitors that blocked VIP-induced chemotaxis, but were differentially sensitive to PKC inhibitors. Conclusion: Collectively, these results indicate that VIP signaling in resting human T cells is ineffective at altering mRNA expression changes, unlike their rodent counterparts, but can influence similar chemotactic effects, possibly through different signaling pathways elicited through VPAC1 versus VPAC2.