Homologous and heterologous regulation of the helodermin/vasoactive-intestinal-peptide response in the murine radiation leukemia-virus-induced lymphoma cell line BL/VL3

Vasoactive intestinal peptide signaling axis in human leukemia

The vasoactive intestinal peptide (VIP) signaling axis constitutes a master “communication coordinator” between cells of the nervous and immune systems. To date, VIP and its two main receptors expressed in T lymphocytes, vasoactive intestinal peptide receptor (VPAC)1 and VPAC2, mediate critical cellular functions regulating adaptive immunity, including arresting CD4 T cells in G₁ of the cell cycle, protection from apoptosis and a potent chemotactic recruiter of T cells to the mucosa associated lymphoid compartment of the gastrointestinal tissues. Since the discovery of VIP in 1970, followed by the cloning of VPAC1 and VPAC2 in the early 1990s, this signaling axis has been associated with common human cancers, including leukemia. This review highlights the present day knowledge of the VIP ligand and its receptor expression profile in T cell leukemia and cell lines. Also, there will be a discussion describing how the anti-leukemic DNA binding transcription factor, Ikaros, regulates VIP receptor expression in primary human CD4 T lymphocytes and T cell lymphoblastic cell lines (e.g. Hut-78). Lastly, future goals will be mentioned that are expected to uncover the role of how the VIP signaling axis contributes to human leukemogenesis, and to establish whether the VIP receptor signature expressed by leukemic blasts can provide therapeutic and/or diagnostic information.

The significance of vasoactive intestinal peptide in immunomodulation

First identified by Said and Mutt some 30 years ago, the vasoactive intestinal peptide (VIP) was originally isolated as a vasodilator peptide. Subsequently, its biochemistry was elucidated, and within the 1st decade, their signature features as a neuropeptide became consolidated. It did not take long for these insights to permeate the field of immunology, out of which surprising new attributes for VIP were found in the last years. VIP is rapidly transforming into something more than a mere hormone. In evolving scientifically from a hormone to a novel agent for modifying immune function and possibly a cytokine-like molecule, VIP research has engaged many physiologists, molecular biologists, biochemists, endocrinologists, and pharmacologists and it is a paradigm to explore mutual interactions between neural and neuroendocrine links in health and disease. The aim of this review is firstly to update our knowledge of the cellular and molecular events relevant to VIP function on the immune system and secondly to gather together recent data that support its role as a type 2 cytokine. Recognition of the central functions VIP plays in cellular processes is focusing our attention on this "very important peptide" as exciting new candidates for therapeutic intervention and drug development.

Functional and molecular characterization of VIP receptors and signal transduction in human and rodent immune systems

In the last few decades, as a result of the interaction between different areas of research, the new interdisciplinary and exciting field of neuroimmunology has emerged. In this context, it has been demonstrated that small peptides may function in a communication network that links nervous, endocrine, and immune systems. Thus, each peptide may function as a neurotransmitter, peptide hormone, or cytokine, depending on its site of release and the target cell with which it interacts. Among these peptides, vasoactive intestinal peptide (VIP) has been shown to play a very important role in the regulation of immune function. The first stage in the action of VIP with immunocompetent cells is the binding to specific plasma membrane receptors and the generation of an intracellular signal. In this review, we focus and present data about the signal transduction pathway of VIP in both human and rodent immunocompetent cells.

Homologous regulation of vasoactive intestinal peptide (VIP) receptors on rat peritoneal macrophages

In the present study, we examined the effect of pretreatment with VIP and various peptides structurally related to VIP such us PHI, helodermin, and secretin on VIP receptor number and affinity, as well as VIP-stimulated cyclic AMP production in rat peritoneal macrophages. Short-term (5-30 min) exposures of rat peritoneal macrophages to 0.1 microM VIP induced a rapid reduction in specific binding. Pretreatment for 15 and 30 min caused 26% (SEM = 6) and 48% (SEM = 4) reduction in specific binding, respectively. The maximal effect was observed at 120 min, causing a decrease of 67% (SEM = 6) in specific binding. Pretreatment with 0.1 microM VIP for 15, 30, and 120 min caused 23% (SEM = 9), 52% (SEM = 4), and 76% (SEM = 4) reduction in cyclic AMP production, respectively. Only VIP concentrations at the nanomolar level and higher were shown to be effective. The potency of VIP and related peptides to desensitize was similar to their potency to occupy receptors and to activate cyclic AMP production. The internalization of radioiodinated VIP was also studied. It was shown that receptor-bound ligand is internalized during the downregulation process. However, the diminution in VIP binding to macrophages was not completely explained by internalization.

VIP-helodermin receptors in the murine virus-induced T lymphoma cell line BL/VL3 recover less rapidly than beta-adrenoceptors after down regulation

The time course of recovery of beta-adrenergic and VIP/helodermin receptors after homologous and heterologous down regulation was studied in the murine lymphoma cell line BL/VL3, a neoplastic equivalent of immature T cells. The heterologous part of isoproterenol down regulation was rapidly reversed, even in the presence of cycloheximide, suggesting that down regulation was linked to ligand-receptor interaction and/or cyclic AMP increase. Homologous down regulations of beta-adrenoceptors and VIP/helodermin receptors were less rapidly reversible and depended on protein synthesis as they were inhibited by cycloheximide: beta-adrenoceptors recovered faster than VIP/helodermin receptors.

Desensitization and recovery of prostaglandin-stimulated adenylate cyclase activity in a murine virus-induced T lymphoma cell line BL/VL3

Prolonged (16 h) preexposure to prostaglandin E1 (PGE1) of cells from a murine virus-induced T lymphoma cell line BL/VL3 provoked, in their membranes, a dose-dependent reduction of PGE1-mediated adenylate cyclase stimulation. Smaller (but significant) decreases of helodermin- and isoproterenol-mediated stimulations were also observed. After a 16 h incubation of these cells with 1 microM PGE1, that reduced by 85%, the PGE1-mediated adenylate cyclase stimulation in membranes, 50% of the PGE1 response recovered after 2 h of PGE1 withdrawal from the incubation medium. Over the following 2-24 h time interval, further recovery was limited. Protein synthesis was required for this resensitization mechanism of functional PGE1 receptors coupled to adenylate cyclase, as judged by the inhibitory effects of cycloheximide.