Journal article
Pleiotropic Effects of Substitutions of a Highly Conserved Leucine in Transmembrane Helix III of the Human Lutropin/Choriogonadotropin Receptor with Respect to Constitutive Activation and Hormone Responsiveness
Molecular endocrinology (Baltimore, Md.), Vol.15(6), pp.972-984
06/01/2001
DOI: 10.1210/mend.15.6.0661
PMID: 11376115
Abstract
It has been shown previously that a naturally occurring mutation of the human LH/CG receptor (hLHR), which replaces L457 in helix III with arginine, results in a receptor that constitutively elevates basal cAMP but does not respond to human CG (hCG) with further cAMP production. In the present study, substitutions of L457 with several amino acids were examined. The constitutive activation of cAMP production was observed only when L457 was replaced with a positively charged residue. Although constitutive activation of the inositol phosphate pathway could not be detected when measuring inositol phosphate production, the use of a more sensitive reporter gene assay for protein kinase C activation revealed the constitutive activation of this pathway by the R- and K-substituted mutants. Therefore, L457 of the hLHR plays a key role in stabilizing the receptor in an inactive conformation. Molecular modeling shows that the insertion of R, K, or H at position 457 triggers the receptor transition toward an active state due to the proximity of an anionic amino acid, D578, in helix VI. These substitutions cause perturbations in helix III-helix VI and helix III-helix VII interactions that culminate in the opening of a solvent-accessible site in the cytosolic domains potentially involved in Gs recognition. Interestingly, L457R was completely unresponsive and the K- and H-substituted L457 hLHR mutants were significantly blunted in their cAMP responses to hCG stimulation. Cells expressing L457R were also unresponsive to hCG with regards to increased inositol phosphate production. Other substitutions of L457 were identified, though, that selectively permit the hormonal stimulation of only one of the two signaling pathways. These results suggest a pivotal role for L457 in hormone-stimulated signal transduction by the hLHR.
Details
- Title: Subtitle
- Pleiotropic Effects of Substitutions of a Highly Conserved Leucine in Transmembrane Helix III of the Human Lutropin/Choriogonadotropin Receptor with Respect to Constitutive Activation and Hormone Responsiveness
- Creators
- Hiromitsu Shinozaki - Department of Physiology and Biophysics (H.S., X.L., J.B., D.L.S.) Iowa 52242Francesca Fanelli - Department of Chemistry (F.F.) University of Modena and Reggio Emilia 41100 Modena, ItalyXuebo Liu - Department of Physiology and Biophysics (H.S., X.L., J.B., D.L.S.) Iowa 52242Julie Jaquette - Department of Physiology and Biophysics (H.S., X.L., J.B., D.L.S.) Iowa 52242Kazuto Nakamura - Department of Pharmacology (K.N.) The University of Iowa Iowa City, Iowa 52242Deborah L Segaloff - Department of Physiology and Biophysics (H.S., X.L., J.B., D.L.S.) Iowa 52242
- Resource Type
- Journal article
- Publication Details
- Molecular endocrinology (Baltimore, Md.), Vol.15(6), pp.972-984
- DOI
- 10.1210/mend.15.6.0661
- PMID
- 11376115
- ISSN
- 0888-8809
- eISSN
- 1944-9917
- Language
- English
- Date published
- 06/01/2001
- Academic Unit
- Molecular Physiology and Biophysics; Obstetrics and Gynecology
- Record Identifier
- 9984083256802771
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