Substance P (NK1) receptor expression by human colonic epithelial cell line Caco-2

The peptide substance P (SP) is known to take part in the regulation of the Cl--dependent secretion in the animal and human colonic mucosa. However, no conclusive evidence for the expression of the functional tachykinin NK1 receptor has been found in the human colonic epithelial cells. Using the reverse transcription-polymerase chain reaction (RT-PCR) method we could detect the transcripts of the NK1 receptor in the human colonic epithelial cell line Caco-2. Furthermore, we characterized the mechanism of substance P-induced intracellular signaling in Caco-2 cells. While substance P had no effect on intracellular calcium concentration as measured by fura-2 AM, it induced the activation of the mitogen-activated protein kinases (MAPKs) in a time- and dose-dependent manner. Surprisingly, the peptide NK1 receptor antagonist [D-Pro 2, D-Trp(7,9)]SP stimulated the activity of MAPKs in the same manner as substance P. In contrast, the specific nonpeptide NK1 receptor antagonist CP-96,345 clearly abolished the effect of substance P and [D-Pro 2, D-Trp(7,9)]SP on MAPK activity. CP-96,345 itself did not increase the activity of MAPKs. Thus, we provide the first evidence that a functional NK1 receptor is expressed in the human colonic epithelial cell line Caco-2. The results show that in Caco-2 cells the peptide antagonist [D-Pro 2, D-Trp(7,9)]SP acts as a NK1 receptor agonist in contrast to the nonpeptide antagonist CP-96,345. (C) 2002 Elsevier Science Inc. All rights reserved.