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.