Mutant luteinizing hormone receptors in a compound heterozygous patient with complete Leydig cell hypoplasia: abnormal processing causes signaling deficiency.
Publication year
2002Source
Journal of Clinical Endocrinology and Metabolism, 87, 6, (2002), pp. 2506-13ISSN
Publication type
Article / Letter to editor
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Organization
Human Genetics
Journal title
Journal of Clinical Endocrinology and Metabolism
Volume
vol. 87
Issue
iss. 6
Page start
p. 2506
Page end
p. 13
Subject
Elucidation of hereditary disorders and their molecular diagnosis; Opheldering van erfelijke ziekten en hun moleculaire diagnostiekAbstract
Over the past 5 yr several inactivating mutations in the LH receptor gene have been demonstrated to cause Leydig cell hypoplasia, a rare autosomal recessive form of male pseudohermaphroditism. Here, we report the identification of two new LH receptor mutations in a compound heterozygous case of complete Leydig hypoplasia and determine the cause of the signaling deficiency at a molecular level. On the paternal allele of the patient we identified in codon 343 a T to A transversion that changes a conserved cysteine in the hinge region of the receptor to serine (C343S); on the maternal allele a T to C transition causes another conserved cysteine at codon 543 in trans-membrane segment 5 to be altered to arginine (C543R). Both of these mutant receptors are completely devoid of hormone-induced cAMP reporter gene activation. Using Western blotting of expressed LH receptor protein with a hemagglutinin tag, we further show that despite complete absence of total and cell surface hormone binding, protein levels of both mutant LH receptors are only moderately affected. The expression and study of enhanced green fluorescent protein-tagged receptors confirmed this view and further indicated that initial translocation to the endoplasmic reticulum of these mutant receptors is normal. After that, however, translocation is halted or misrouted, and as a result, neither mutant ever reaches the cell surface, and they cannot bind hormone. This lack of processing is also indicated by reduced presence of an 80-kDa protein, the only N-linked glycosylated protein in the LH receptor protein profile. Thus, complete lack of signaling by the identified mutant LH receptors is caused by insufficient processing from the endoplasmic reticulum to the cell surface and results in complete Leydig cell hypoplasia in this patient.
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- Academic publications [246165]
- Faculty of Medical Sciences [93268]
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