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Mutant Luteinizing Hormone Receptors in a Compound Heterozygous Patient with Complete Leydig Cell Hypoplasia: Abnormal Processing Causes Signaling Deficiency

Departments of Endocrinology and Reproduction and Internal Medicine, Erasmus University (J.W.M.M., M.V.-P., A.P.N.T.), 3000 DR Rotterdam, The Netherlands; Hormonologie du Développement et de la Reproduction, Hôpital Lapeyronie and INSERM, U-439 (S.L., V.G., C.S.), 34090 Montpellier, France; Endocrinologie et Gynécologie Pédiatriques, Hôpital A. de Villeneuve (C.S.), 34295 Montpellier, France; Department of Pediatric Endocrinology, University Children’s Hospital, University of Essen (A.R.-U.), 45122 Essen, Germany; Department of Pediatric Endocrinology, Children’s Memorial Health Institute (M.S.-C., T.E.R.), 04-730 Warsaw, Poland; and Department of Human Genetics, University Hospital (H.G.B.), 6500 HB Nijmegen, The Netherlands

Address all correspondence and requests for reprints to: Dr. Axel P. N. Themmen, Department of Internal Medicine, Erasmus University Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands. E-mail: . themmen{at}endov.fgg.eur.nl

Abstract

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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