Substance P (NK(1)) 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 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.