Rapid desensitization of the TRH receptor and persistent desensitization of its constitutively active mutant

Abstract

1 We studied rapid desensitization of the thyrotropin-releasing hormone receptor (TRH-R) or the m1-muscarinic receptor (m1-R) to a short challenge of threshold TRH concentration and persistent desensitization due to constitutive activity of a mutant TRH-R. 2 Xenopus oocytes expressing TRH-Rs and/or m1-Rs were challenged for 15 s with threshold concentrations of TRH ([TRH]) and then immediately with supraoptimal [TRH] or acetylcholine ([ACh]). The threshold challenge caused desensitization of 50 ± 57% of responses to subsequent supraoptimal stimulation with TRH or ACh. 3 The homologous desensitization was reversible within 60 s after removal of the agonist. 4 The protein kinase C (PKC) inhibitor, chelerythrine, inhibited the control responses by 30 ± 40%, without aecting the desensitized responses. Chelerythrine or the phosphatase inhibitor, okadaic acid, had little eect on the kinetics of resensitization, indicating limited involvement of PKC. 5 In oocytes coexpressing wild type TRH-Rs or m1-Rs with a constitutively active TRH-R mutant (C335Stop TRH-R), a persistent desensitization (33 ± 57%) of the responses to TRH or ACh was observed. Additionally, there was a complete loss of the rapid desensitization induced by threshold [TRH]. 6 Chlorodiazepoxide (CDE), a competitive binding antagonist of TRH-Rs and an inverse agonist of C335Stop TRH-Rs, abolished the persistent desensitization induced by C335Stop TRH-Rs and enabled the rapid desensitization, conferring the wild type phenotype on C335Stop TRH-Rs. Chelerythrine had qualitatively the same eect as CDE. 7 In conclusion, unlike the rapid desensitization, the persistent desensitization caused by the constitutively active C335Stop TRH-Rs is largely mediated by PKC. It abrogates, however, the rapid desensitization, suggesting a common mechanistic step(s).

The human 5‐HT7 serotonin receptor splice variants: constitutive activity and inverse agonist effects

“…Possibly, stable expression of h5‐HT 7 receptors may alter G‐protein expression (or available pools) differentially between stable clones, accounting for the apparent receptor‐density independence of basal AC activity. Additionally, desensitization mechanisms evoked by constitutive activity may also contribute to modifications of basal AC activity in stable clones as observed for the thyrotropin‐releasing hormone receptor (Zaltsman et al ., 2000).…”

Excitatory Effects of Thyrotropin-Releasing Hormone in the Thalamus

“…These data, to the extent that they can be extrapolated to the ferret, suggest that although TRH may act on thalamocortical cells via TRHR2, the potent excitatory actions in the PGN are likely mediated by a novel, as yet uncharacterized TRHR. In culture systems, both TRHR1 and TRHR2 display desensitization (O'Dowd et al, 2000;Zaltsman et al, 2000), apparently through receptor internalization (Nussenzveig et al, 1993;Ashworth et al, 1995). Removal of TRHRs from the somatic cell membrane may explain why spindle waves reappeared even in the continued presence of TRH, as well as the attenuated responses to a second TRH application.…”

Random Mutagenesis of the Human Adenosine A2B Receptor Followed by Growth Selection in Yeast. Identification of Constitutively Active and Gain of Function Mutations

“…For example, truncation of the C-terminal tail of the 5HT 4 receptor (Claeysen et al, 1999), the prostaglandin E2 receptor EP4 subtype (Bastepe and Ashby, 1997), the TRHR receptor (Zaltsman et al, 2000), and the rat SSTR2 receptor (Schwartkop et al, 1999) resulted in constitutive activity. The Q214L, I230N, V240M, V250M, N254Y, T257S, K269 stop mutant is very interesting as well.…”