Molecular characterization of helodermin-preferring VIP receptors in SUP T1 lymphoma cells: evidence for receptor glycosylation

Human H9 cells proliferation is differently controlled by vasoactive intestinal peptide or peptide histidine methionine: implication of a GTP-insensitive form of VPAC1 receptor

The proliferation of human lymphoblastoma cell line (H9) was differently stimulated by Peptide Histidine Methionine (PHM) and Vasoactive Intestinal Peptide (VIP). PHM induced a cyclic AMP (cAMP) accumulation, abolished by Adenylate Cyclase (AC) inhibitors leading to a loss of proliferative effect. VIP mitogenic activity was Pertussis toxin (PTX) sensitive and AC inhibitors insensitive. Pharmacological experiments performed on H9 membranes with or without a GTP analogue indicated expression of both GTP-insensitive and -sensitive PHM/VIP high-affinity binding sites (HA). H9 cells expressed only the VPAC1 receptor. VIP(10-28), known as a VPAC1 antagonist, bond to all GTP-insensitive PHM sites and inhibited evenly the PHM and VIP mitogenic actions. These data strongly suggested different mechanisms initiated by VIP and PHM and highlighted the key role of GTP-insensitive binding sites in the control of cell proliferation.

Functional characterization of a receptor for vasoactive-intestinal-peptide-related peptides in cultured dermal melanophores from Xenopus laevis

A receptor for vasoactive-intestinal-peptide (VIP)-related peptides was functionally characterized in a cell line derived from Xenopus melanophores using a recently described microtiter-plate-based bioassay. Activation of the melanophore VIP receptor by VIP or the peptides pituitary-adenylate-cyclase-activating polypeptide (PACAP 38), PACAP 27, and helodermin stimulated intracellular 3'-5' cyclic adenosine monophosphate (cAMP) accumulation and pigment dispersion in the cells. Helodermin, with an EC50 (concentration of peptide inducing half-maximal melanosome dispersion) of 46.5 pM, was the most potent activator of pigment dispersion, followed by PACAP 38 > VIP > PACAP 27. A similar order of potencies was observed for the peptides to induce cAMP accumulation. The responses to VIP agonists were selectively inhibited by the VIP antagonists PACAP-(6-27) and (N-Ac-Tyr(1)-D-Phe2)-growth-hormone-releasing factor[GRF](1-29)-NH2. Taken together, the results suggest that the melanophores express a VIP receptor that shares certain characteristics of, but also differs significantly from, other previously identified VIP receptors.

Analogues of VIP, helodermin, and PACAP discriminate between rat and human VIP1 and VIP2 receptors

Vasoactive intestinal polypeptide (VIP) acts through interaction with two subclasses of seven transmembrane G protein-coupled receptors named VIP1 and VIP2 receptors. These receptors have been cloned in different species, such as rat and human. Considering the different distribution of both receptor subclasses, there is considerable interest in the development of selective agonists and antagonists. The present study compares the binding properties of VIP, PACAP, GRF, secretin, and helodermin analogues on recombinant rat and human VIP1 and VIP2 receptors. On both rat and human receptors, secretin and GRF had a higher affinity for the VIP1 receptor subtypes. The amino-shortened VIP, and the carboxy terminal-shortened VIP and PACAP analogues also presented a higher affinity for the VIP1 receptor. PHI, PHV, helodermin, and helospectin were selective for the human VIP2 receptor subtypes. These results suggest that the helical structure of the carboxy terminal end is necessary for VIP2 recognition. The differences between species were the following: PHI, PHV, helodermin, and helospectin had a higher affinity for the rat VIP1 receptor than for the human VIP1 receptor. On both rat and human receptors, D-Ala4 VIP and D-Phe4 VIP had a high affinity for the VIP1 receptor and a low affinity for the VIP2 receptor. Thus, three domains of the ligand involved in VIP1/VIP2 receptor discrimination were identified: the amino acid residue in position 4 ([D-Ala4], [D-Phe4]VIP), in positions 8 and 9 (the effects of helodermin and helospectin), and the carboxy terminal end (the effects of the shortened VIP and pituitary adenylate cyclase activating polypeptide analogues).

VIP and pituitary adenylate cyclase activating polypeptide (PACAP) have an antiproliferative effect on the T98G human glioblastoma cell line through interaction with VIP2 receptor

Functional VIP/PACAP receptors were identified in the human glioblastoma cell line T98G, based on the relative potency of VIP, PACAP and PACAP-38 to stimulate adenylate cyclase activity. Analysis of the T98G cells mRNA by reverse transcription followed by a polymerase chain reaction (RT-PCR) demonstrated the expression of the mRNA coding for the VIP2 receptor subclass only. VIP, PACAP-27 and PACAP-38 were potent and efficIent inhibitors of cell proliferation, assessed by the colorimetric MTT assay. VIP, PACAP-27 and PACAP-38 also reduced the incorporation of 3H-thymidine in T98G cells, but did not significantly alter the percentage of cells present at each stage of the cell cycle. Thus, VIP and PACAP, probably acting through a VIP2 receptor subtype, decreased cell proliferation.

Characterization of the VIP receptor from SUP T1 lymphoblasts

The SUP T1 lymphoblasts express an original subtype of VIP receptors characterized by a high affinity for the VIP analogue from lizard venom named helodermin, a preference for the neuropeptide PACAP-38 over PACAP-27 and VIP, and an extremely low affinity for secretin. The molecular cloning of that receptor revealed its identity with the VIP2 receptor subtype first cloned in rat and mouse tissues. The access to selective probes permits the detection of the mRNA coding for the VIP2 receptor by Northern blot, reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization. These highly selective and sensitive techniques identify the cell types that are equipped to synthesize the receptor but do not prove that the receptor is indeed efficiently expressed at the cell surface. VIP2 mRNA was detected in selected areas of the brain different from that expressing the classical VIP1 receptor, in pituitary, in pineal, in pancreatic islets, in testes and ovary. It was also detected in the stomach, in the thymus and in spleen and in T lymphoblastic cell lines. A systematic screening of the immunocompetent cells must still be performed.