Intrinsic Differences in the Response of the Human Lutropin Receptor Versus the Human Follitropin Receptor to Activating Mutations

doi:10.1074/jbc.M703500200

Intrinsic Differences in the Response of the Human Lutropin Receptor Versus the Human Follitropin Receptor to Activating Mutations^*

^‡Department of Molecular Physiology and Biophysics, the University of Iowa Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242 and the ^§Dulbecco Telethon Institute and Department of Chemistry, University of Modena e Reggio Emilia, Via Campi 183, 41100 Modena, Italy

3 To whom correspondence should be addressed: Dept. of Molecular Physiology and Biophysics, 5-470 Bowen Science Bldg., University of Iowa, Iowa City, IA 52246. Tel.: 319-335-7850; Fax: 319-335-7330; E-mail: deborah-segaloff{at}uiowa.edu.

Abstract

In contrast to the human lutropin receptor (hLHR), very few naturally occurring activating mutations of the structurally related human follitropin receptor (hFSHR) have been identified. The present study was undertaken to determine if one aspect underlying this discrepancy might be a general resistance of the hFSHR to mutation-induced constitutive activity. Five different mutations were introduced into both the hLHR and hFSHR (four based on activating mutations of the hLHR gene, one based on an activating mutation of the hFSHR gene). Our results demonstrate that hFSHR constitutively activating mutants (CAMs) were not as active as hLHR CAMs containing the comparable mutation. Furthermore, although all hFSHR CAMs exhibited strong promiscuous activation by high concentrations of the other glycoprotein hormone receptors, hLHR CAMs showed little or no promiscuous activation. Our in vitro findings are consistent with in vivo observations of known pathophysiological conditions associated with hLHR CAMs, but not hFSHR CAMs, and with promiscuous activation of hFSHR CAMs, but not hLHR CAMs. Computational experiments suggest that the mechanisms through which homologous mutations increase the basal activity of the hLHR and the hFSHR are similar. This is particularly true for the strongest CAMs like L460^(3.43)R. Disparate properties of the hLHR versus hFSHR CAMs may, therefore, be due to differences in shape and electrostatics features of the solvent-exposed cytosolic receptor domains involved in the receptor-G protein interface rather than to differences in the nature of local perturbation at the mutation site or in the way local perturbation is transferred to the putative G protein binding domains.

Footnotes

↵4 The abbreviations used are: LHR, LH receptor; FSHR, FSH receptor; hFSH and hFSHR, human FSH and FSHR, respectively; CAM, constitutively activating mutant; OHSS, ovarian hyperstimulation syndrome; WT, wild type; SAS, solvent-accessible surface area.
↵5 The amino acid numbering in superscript is that proposed by Ballesteros and Weinstein (7). In this nomenclature, the first number indicates the helix and the numbers thereafter indicate the position of the helical residue relative to the most highly conserved residue within that helix, which is denoted as 50.
↵* These studies were supported by National Institutes of Health Grant HD22196 (to D. L. S.) and Telethon Italy Grant S00068TELU (to F. F.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵1 Present address: Dept. of Anatomy, Physiology, and Pharmacology, College of Veterinary Medicine, Auburn University, Auburn, AL 36849.
↵2 Present address: Dept. of Obstetrics and Gynecology, University of Iowa Carver College of Medicine, University of Iowa, Iowa City, IA 52242.
- Received April 26, 2007.
- Revision received June 21, 2007.