A cell surface inactive mutant of the human lutropin receptor (hLHR) attenuates signaling of wild-type or constitutively active receptors via heterodimerization.
The D405N and Y546F mutations of the human lutropin receptor (hLHR) have previously been shown to partially attenuate hCG-stimulated cAMP synthesis despite normal cell surface expression and hCG binding affinity (Min, L. and Ascoli, M. Mol. Endocrinol. 14:1797-1810, 2000). We now show that these mutations each stabilize a resting state of the hLHR. A combined mutant D405N,Y546F is similarly expressed at the cell surface and exhibits normal ligand-binding, but is profoundly signaling impaired. Introduction of hLHR(wt) into cells stably expressing the signaling inactive D405N,Y546F resulted in the attenuation of hCG-stimulated cAMP production by hLHR(wt) even if excess Gs is co-expressed. Similarly, co-expression of D405N,Y546F with hLHR constitutively active mutants (CAMs) attenuated their constitutive activity. Quantitative bioluminescence resonance energy transfer (BRET) analyses demonstrated that D405N,Y546F formed heterodimers with both wt and CAM hLHR. In contrast hLHR(D405N,Y546F) did not heterodimerize with the melanocortin 3 receptor (MC3R) and agonist-stimulated cAMP production through the MC3R was not attenuated when these two receptors were co-expressed. Taken altogether, our data demonstrate that a signaling inactive hLHR mutant (that is trafficked normally to the plasma membrane) attenuates the signaling of the cell surface localized wt or the constitutively active hLHR due to receptor heterodimerization. Our studies, therefore, suggest a novel ramification of GPCR signaling resulting from receptor dimerization.
Zhang
Meilin
M
Department of Molecular Biophysics and Physiology, The Roy J. and Lucille A. Carver College of Medicine, 5-470 Bowen Science Building, The University of Iowa, Iowa City, IA 52246, USA.
Feng
Xiuyan
X
Guan
Rongbin
R
Hébert
Terence E
TE
Segaloff
Deborah L
DL
D019943:Amino Acid Substitution; D002460:Cell Line; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D019281:Dimerization; D006801:Humans; D009154:Mutation; D044104:Receptor, Melanocortin, Type 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D011974:Receptors, LH / Q000235:genetics* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction
D006063:Chorionic Gonadotropin; D044104:Receptor, Melanocortin, Type 3; D011974:Receptors, LH; D011994:Recombinant Proteins; D000242:Cyclic AMP