Activation of the human LH/CG receptor (LH/CGR) by lutropin (LH) and choriogonadotropin (CG) is essential in the human reproduction. Deletion of the Exon10 (LH/CGR-delExon10) resulting in a lack of 27 amino acids within the extracellular hinge-region of LH/CGR causes Leydig cell hypoplasia type II. To clarify why this deletion impairs LH but not CG action, we investigated the molecular determinants of LH/CGR activation elucidating the different behaviour of both hormones.
It is reported that the LH/CGR exist as oligomers in a unitary signalling unit when activated with CG, since individual binding- and signalling-defective mutants can be rescued by combining both. We performed a similar strategy including also LH/CGR-delExon10 as signalling defective mutant. However, in contrast to CG, the functional rescue was not possible by stimulation with LH, which fails to bypass the lack of Exon10 by trans-activating the neighbouring protomer. Our results indicate different activation mechanisms for LH and CG at LH/CGR-delExon10. Moreover, similar results were also achieved with a complete hinge-region but different signalling disturbing positions. Fluorescence correlation spectroscopy indicates no disturbance in oligomerization of the LH/CGR-delExon10. Homology modelling suggest a helical entity for exon10 region. Substitution of block wise alanine mutations showed no effect on both LH and CG activation.
We conclude that residues comprising Exon10 form a structural interface with helical portion, which might be necessary for cis-interaction of LH and LH/CGR. Thus the LH related dysfunction of LH/CGR-delExon10 is likely caused by disturbed native cis-interaction between LH and receptor in which each protomer bind and signal on its own, rather than by an interrupted LH related trans-activation.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This work was supported, however funding details unavailable.
05 - 09 May 2012
European Society of Endocrinology