Cellular metabolism of substance P produces neurokinin-1 receptor peptide agonists with diminished cyclic AMP signaling

Substance P (SP) is released from sensory nerves in the arteries and heart. It activates neurokinin-1 receptors (NK1Rs) causing vasodilation, immune modulation, and adverse cardiac remodeling. The hypothesis was tested: SP and SP metabolites activate different second messenger signaling pathways. Macrophages, endothelial cells, and fibroblasts metabolized SP to N- and C-terminal metabolites to varying extents. SP 5-11 was the most abundant metabolite followed by SP 1-4, SP 7-11, SP 6-11, SP 3-11, and SP 8-11. In NK1R-expressing human embryonic kidney 293 (HEK293) cells, SP and some C-terminal SP metabolites stimulate the NK1R, promoting the dissociation of several G alpha proteins, including G alpha s and G alpha q from their beta gamma subunits. SP increases intracellular calcium concentrations ([Ca](i)) and cyclic 3 ',5 '-adenosine monophosphate (cAMP) accumulation with similar -log EC50 values of 8.5 +/- 0.3 and 7.8 +/- 0.1 M, respectively. N-terminal metabolism of SP by up to five amino acids and C-terminal deamidation of SP produce peptides that retain activity to increase [Ca](i) but not to increase cAMP. C-terminal metabolism results in the loss of both activities. Thus, [Ca](i) and cAMP signaling are differentially affected by SP metabolism. To assess the role of N-terminal metabolism, SP and SP 6-11 were compared with cAMP-mediated activities in NK1R-expressing 3T3 fibroblasts. SP inhibits nuclear factor kappa B (NF-kappa B) activity, cell proliferation, and wound healing and stimulates collagen production. SP 6-11 had little or no activity. Cyclooxygenase-2 (COX-2) expression is increased by SP but not by SP 6-11. Thus, metabolism may select the cellular response to SP by inhibiting or redirecting the second messenger signaling pathway activated by the NK1R.