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

Deborah L Segaloff,Xiuyan Feng,Francesca Fanelli,Ya-Xiong Tao,Ginny L Ryan,Meilin Zhang

doi:10.1074/jbc.m703500200

Deborah L Segaloff, Xiuyan Feng + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m703500200

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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.

Highlights

In the past several years, numerous mutations of the hLHR gene have been identified in young boys with gonadotropinindependent precocious puberty
Screening of hFSHR Mutants for Constitutive Activity— Previous studies from our laboratory had shown that the hFSHR mutation hFSHR(L460(3.43)R), corresponding to the activating L457(3.43)R mutation of the hLHR, resulted in constitutive activation [26]
To more generally determine if the hFSHR is rendered constitutively active when known hLHR activating mutations are introduced, nine other naturally occurring activating mutations of the hLHR were introduced into the corresponding position of the hFSHR (Table 1)

Summary

Introduction

In the past several years, numerous mutations of the hLHR gene have been identified in young boys with gonadotropinindependent precocious puberty (see Refs. 5 and 6 for reviews). These hLHR CAMs exhibited very receptor, in the solvent-accessible surface area (SAS) of small increases in cAMP in response to high concentrations of selected amino acids at the cytosolic interface between H3, H5, hFSHR and hTSH.

Results

Conclusion