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

Abstract 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 NK 1 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 NK 1 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 NK 1 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 NK 1 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 NK 1 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 NK 1 receptor agonist in contrast to the nonpeptide antagonist CP-96,345.