Activation of Receptor Gene Transcription Is Required to Maintain Cell Sensitization after Agonist Exposure

Abstract

The G protein-coupled receptor constitutes a large family of plasma membrane receptors, representing 1% of the total genome, and are implicated in a diverse variety of cellular functions (1-3). The understanding of how the expression of these receptors are regulated should provide a better comprehension regarding agonist function.Until now, most studies have reported on the effects of desensitization, receptor coupling, and second messenger stimulation of G protein-coupled receptors (4, 5). To elucidate these mechanisms, experiments were carried out on agonist-deprived cultured cells and then triggered with a rapid burst of high agonist concentrations. Under these conditions, cells would remain desensitized for long periods of time (6, 7). However, in vivo, cells are constantly surrounded by agonists, each possessing a characteristic basal level. In the stimulated state, receptors are triggered by "waves" of agonist such as the hormones released into the blood circulation, and the neurotransmitters released into the synaptic cleft, which are more or less intense or frequent.The complete desensitization of a cell would have grave consequences in vivo, because the cell's triggering mechanisms would be essentially inoperable for long periods of time. Rather it would seem required that the cell's machinery would provide a means to remain sensitized to agonist during standard stimulated conditions. By examining the long term effect of agonist exposure on high affinity neurotensin receptor (NTR) 1 expression, we were able to clarify a potential mechanism responsible for maintain of cell sensitization to neurotensin (NT) agonist.

Receptor Trafficking via the Perinuclear Recycling Compartment Accompanied by Cell Division Is Necessary for Permanent Neurotensin Cell Sensitization and Leads to Chronic Mitogen-activated Protein Kinase Activation

“…Previous studies demonstrated that human colon adenocarcinoma cells, HT-29, or human neuroblastoma cells, CHP 212, challenged for 48 h with high concentrations of a NT agonist recovered and maintained NT sensitization (23,24). In these studies, a correlation was made between an intensive NT1 receptor internalization, occurring in the early phases of cell stimulation, and the activation of NT1 receptor gene by NT agonist and cell resensitization.…”

“…As shown in To verify that the accumulation of the NT1 receptor in the juxtanuclear compartment was not fibroblast-specific, the experiments were repeated in CHP 212 cells, a human neuroblastoma cell line that endogenously expresses NT1 receptor (24), and in N1E-115 cells, a murine neuroblastoma cell line (28). Both cell lines were stably transfected with the pNT1-EGFP plasmid (29).…”

Europium-Labeled Epidermal Growth Factor and Neurotensin: Novel Probes for Receptor-Binding Studies

“…Moreover, the disappearance, overexpression, or malfunctions of these receptors serve as clinical diagnostic tools (1). For instance, overexpression of the epidermal growth factor (EGF) 2 receptor is associated with the prognosis of certain types of breast cancer (2), and the overexpression of neurotensin (NT) receptors has been linked to ductal pancreatic adenocarcinoma and colorectal carcinoma (3,4).…”

“…Receptor binding assays using EGF or NT are commonly performed with labeled 125 I or 3 H peptides (4,5) and are considered highly sensitive, permitting the detection of the respective receptors in the femtomolar to picomolar range. However, radioactively labeled ligands have drawbacks including their short shelf life, their high costs, the logistics involved in their handling, and often the need to prepare them shortly before use, as well as the safety hazards involved (6).…”

Neurotensin Receptor 1 Determines the Outcome of Non–Small Cell Lung Cancer

“…The disruption of the neurotensinergic pathway through a specific antagonist, in experimental tumors from colon, breast, and small cell lung cancer cells, caused a strong reduction in tumor growth (14)(15)(16). We had previously shown the presence of a chronic self-activation loop between neurotensin and NTSR1, as one mechanism responsible for the constitutive activation of the mitogen-activated protein kinase mitogenic signaling pathways along with sustained target gene activation (17)(18)(19)(20). More recently, NTSR1 expression level was associated with poor prognosis in patients with ductal breast cancer, and similar results have been found in head and neck squamous cell carcinomas (21,22).…”