J Biol Chem, Vol. 273, Issue 34, 21634-21641, August 21, 1998

Activation of Receptor Gene Transcription Is Required to Maintain Cell Sensitization after Agonist Exposure
STUDY ON NEUROTENSIN RECEPTOR

Mustapha Najimi, Frédérique Souazé, Milagros Méndez^§, Emmanuel Hermans, Tsouria Berbar, William Rostène, and Patricia Forgez

From INSERM U339, Hôpital Saint-Antoine, 184 rue du Faubourg Saint-Antoine, 75012 Paris, France,  Laboratory of Pharmacology, Université Catholique de Louvain, 54.10, avenue Hippocrate 54, 1200 Brussels, Belgium, and ^§ Instituto Mexicano de Psiquiatría, Calzada México-Xochimilco 101, Col. San Lorenzo Huipulco, 14370 México D. F., Mexico

Neurotensin (NT) acts through specific G protein-coupled receptors to induce effects in the central nervous system and periphery. In this study we have shown that in the human neuroblastoma cell line CHP 212, an NT agonist, JMV 449, induced high affinity neurotensin receptor (NTR) gene activation. ¹²⁵I-NT binding of cells challenged with JMV 449 rapidly decreased then reappeared and subsequently stabilized at 50% of the control values after 48 h of agonist exposure. These receptors, which reappeared at the cell surface, are as active as those found in control cells as demonstrated by Ca²⁺ mobilization. Furthermore, the tyrosine hydroxylase (TH) gene, a known NT target gene, remained activated after prolonged NT agonist exposure in this cell line.

In the murine neuroblastoma cell line, N1E-115, NT did not stimulate NTR gene activation but induced NTR mRNA destabilization after long term agonist exposure. In this cell line, NT binding dropped to 15% of control values and remained at this value after agonist treatment. The TH expression, which was originally activated upon NT agonist exposure, decreased to control values after prolonged agonist exposure.

These observations combined with the data obtained from a complementary study with HT-29 cells (Souazé, F., Rostène, W., and Forgez, P. (1997) J. Biol. Chem. 272, 10087-10094) revealed the crucial role of agonist-induced receptor gene transcription in the maintenance of cell sensitivity. A model for G protein-coupled receptor regulation induced by prolong and intense agonist stimulation is proposed.