Characterization of heterogeneous mutations causing constitutive activation of the luteinizing hormone receptor in familial male precocious puberty

Abstract

Familial male precocious puberty (FMPP) is a gonadotropin-independent disorder that is inherited in an autosomal dominant, male-limited pattern. A heterozygous mutation encoding substitution of Asp578 with Gly in transmembrane helix 6 of the G protein-coupled receptor for luteinizing hormone (LHR) has been found in affected males from nine American FMPP families. Cells expressing the mutant LHR exhibit markedly increased cyclic adenosine monophosphate (cAMP) production in the absence of agonist, suggesting that autonomous Leydig cell activity in FMPP is caused by a constitutively activated LHR. We have now analyzed genomic DNA from affected males from six additional FMPP families. PCR was used to amplify a fragment of the LHR gene encoding amino acid residues 441-594. None of the six new samples contained the Asp578-->Gly mutation, as indicated by absence of digestion with MspI. PCR products were then screened for heterozygous mutations using temperature-gradient gel electrophoresis. DNA fragments from two of the patients migrated abnormally. Direct sequencing of PCR product from one affected German male revealed a heterozygous mutation (ATG-->ATA) encoding Met571-->Ile at the cytoplasmic end of helix 6, the same mutation that has been reported in another European FMPP kindred. Affected males in the second family had a novel Thr577-->Ile mutation (ACC-->ATC). Mutations in different portions of the LHR or in a different gene may be responsible for disease in the other FMPP kindreds. Agonist binding and functional coupling of the mutant receptors to the cAMP and inositol phosphate pathways were studied by transiently expressing them in COS-7 cells. Agonist affinity was unaffected by the mutations.(ABSTRACT TRUNCATED AT 250 WORDS)

Two Defective Heterozygous Luteinizing Hormone Receptors Can Rescue Hormone Action

“…This secondary interaction is thought to generate a signal in the endodomain (4 -6, 22). These findings are consistent with the observations that signal generation is generally impacted by endodomain mutants (23), whereas mutations in the exodomain tend to affect hormone binding (24 -26).…”

TSH Receptor and LH Receptor, 1995.

“…In congenital non-autoimmune hyperthyroidism, an activating TSHR mutant with replacement of Phe-631 by Leu was found [85]. In FMPP, other activating mutations in LH/CGR have been reported; Thr-577 to lie, Asp-578 to Tyr, and Cys-581 to Arg in the 6th transmembrane domain, Met-571 to lie on the border of the 6th transmembrane domain and the 3rd cytoplasmic loop, and Ile-542 to Leu in the 5th transmembrane helix [86][87][88]. Replacement of Asp-578 with Gly, the same mutation as found in FMPP, was found in a sporadic case of male-limited precocious puberty in a Japanese patient [89].…”

A missense mutation in the second transmembrane segment of the luteinizing hormone receptor causes familial male-limited precocious puberty.

“…Another approach to characterize domains important for receptor function is to study diseases caused by receptor gene mutations. Patients with the syndrome of familial malelimited precocious puberty (FMPP) have LIT receptor gene mutations (9)(10)(11)(12). FMPP is an autosomal dominant condi tion.…”

“…FMPP is an autosomal dominant condi tion. Affected boys present with early onset of puberty caused by a gonadotropin-independent stimulation of tes ticular androgen production (13 cells revealed constitutively activated receptors in terms of increased basal cAMP production (10), whereas basal inositol phosphate production and hormone binding affinity were comparable to those of the wild-type receptor (11,12). This elevated basal receptor activity that stimulates cAMP pro duction is most likely the cause of autonomous steroid pro duction in these FMPP patients* The location of the amino acid substitutions near the third intracellular loop suggests mutational induction of conformational changes similar to those induced in the mutated a 1B-adrenergic receptor, which partially release the LIT receptor from its inactive conforma tion,…”