MONOCYTES EXPRESS A NON-NEUROKININ SUBSTANCE-P RECEPTOR THAT IS FUNCTIONALLY COUPLED TO MAP KINASE

The data presented in this paper demonstrate a new substance P (SP) bi nding site that is expressed on human monocytes. The apparent dissocia tion constant (K-d) for binding of I-125-labeled Bolton Hunter-SP (I-1 25-BH-SP) to the receptor on monocyte membranes is 2.24 +/- 0.9 X 10(- 7) M and the maximum binding capacity (B-max) is 4.7 +/- 0.5 pmol/mg m embrane protein. It could be excluded that this receptor is one of the known neurokinin (NK) type of receptors on the basis of binding chara cteristics for NK1, NK2, and NK3 agonists. Moreover, we demonstrate th at the binding site is neither the bombesin receptor nor the serpin en zyme complex receptor nor the FMLP receptor. The order of potency for inhibition of I-125-BH-SP binding to the receptor on monocyte membrane s is NK1 antagonist [D-Pro(2),D-Trp(7,9)]SP > SP > NK3 agonist [MePhe( 7)]SP > bombesin. Cross-linking studies with disuccinimidylsuberate, f ollowed by SDS-PAGE analysis, revealed that I-125-BH-SP is specificall y bound to a membrane protein with an apparent molecular mass of 47 kD a. At a functional level, SP induces the activation of MAP kinase in h uman monocytes. The ED(50) for activation of MAP kinase positively cor related (r = 0.999, p < 0.0005) with the apparent affinity of the liga nds applied in the I-125-BH-SP displacement studies. From these result s, we conclude that this SP binding site on monocytes is a non-NK rece ptor protein that is functionally linked to the activation of MAP kina se.