Predominant expression of type II vasoactive intestinal peptide receptors by human T lymphoblastoma cells: Transduction of both Ca2+ and cyclic AMP signals

An immunoregulatory role for vasoactive intestinal peptide (VIP) is suggested by the high concentrations in subsets of neurons supplying lymphoid organs and by the capacity of VIP to affect T lymphocyte functions. The Tsup-1 line of human T lymphoblastoma cells expresses both type I and type II G protein-coupled VTP receptors (Rs), as shown by detection of the encoding mRNAs with reverse transcription-polymerase chain reaction analyses. Northern blot quantification of the relative amounts of mRNA encoding the two VIPRs in Tsup-1 cells indicated that type II predominates over type I, as it does in human blood CD4(+) T cells. Tsup-1 cells bound I-125-VIP to 8.95 X 10(4) high-affinity sites/cell (K-d = 6.0 nM) and 7.45 x 10(5) low-affinity sites/cell (K-d = 210 nM). VIP increased [cAMP](i) in Tsup-1 cells (EC(50) = 14.4 nM) and stimulated a rapid and transient increase in [Ca2+](i) (EC(50) = 30 nM). Functional coupling of G proteins to type II VIPRs was suggested by the change in binding of I-125-V1P to Tsup-1 cell membranes from two sites with K-d values of 3.8 and 109 nM to one site of K-d 30 nM by GTP-gamma-S and the suppression by pertussis toxin of increases in [Ca2+](i) evoked by VIP. The VIP antagonists, VIP4-28, and (4-Cl-D-Phe(6)-Leu(17)) VIP, inhibited I-125-VIP binding by type II VIPRs, as well as VIP-elicited increases in [Ca2+](i) and [cAMP](i). Type II VIPRs thus are the major transducers of VIP signals to a subset of human T cells.