BACKGROUND Increased secretion of growth hormone leads to gigantism in children and acromegaly in adults; the genetic causes of gigantism and acromegaly are poorly understood. METHODS We performed clinical and genetic studies of samples obtained from 43 patients with gigantism and then sequenced an implicated gene in samples from 248 patients with acromegaly. RESULTS We observed microduplication on chromosome Xq26.3 in samples from 13 patients with gigantism; of these samples, 4 were obtained from members of two unrelated kindreds, and 9 were from patients with sporadic cases. All the patients had disease onset during early childhood. Of the patients with gigantism who did not carry an Xq26.3 microduplication, none presented before the age of 5 years. Genomic characterization of the Xq26.3 region suggests that the microduplications are generated during chromosome replication and that they contain four protein-coding genes. Only one of these genes, GPR101, which encodes a G-protein–coupled receptor, was overexpressed in patients’ pituitary lesions. We identified a recurrent GPR101 mutation (p.E308D) in 11 of 248 patients with acromegaly, with the mutation found mostly in tumors. When the mutation was transfected into rat GH3 cells, it led to increased release of growth hormone and proliferation of growth hormone–producing cells. CONCLUSIONS We describe a pediatric disorder (which we have termed X-linked acrogigantism [X-LAG]) that is caused by an Xq26.3 genomic duplication and is characterized by early-onset gigantism resulting from an excess of growth hormone. Duplication of GPR101 probably causes X-LAG. We also found a recurrent mutation in GPR101 in some adults with acromegaly. (Funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development and others.)

Sorting nexin (SNX) 1 and SNX2 are mammalian orthologs of Vps5p, a yeast protein that is a subunit of a large multimeric complex, termed the retromer complex, involved in retrograde transport of proteins from endosomes to the trans-Golgi network. We report the cloning and characterization of human orthologs of three additional components of the complex: Vps26p, Vps29p, and Vps35p. The close structural similarity between the yeast and human proteins suggests a similarity in function. We used both yeast two-hybrid assays and expression in mammalian cells to define the binding interactions among these proteins. The data suggest a model in which hVps35 serves as the core of a multimeric complex by binding directly to hVps26, hVps29, and SNX1. Deletional analyses of hVps35 demonstrate that amino acid residues 1-53 and 307-796 of hVps35 bind to the coiled coil-containing domain of SNX1. In contrast, hVps26 binds to amino acid residues 1-172 of hVps35, whereas hVps29 binds to amino acid residues 307-796 of hVps35. Furthermore, hVps35, hVps29, and hVps26 have been found in membrane-associated and cytosolic compartments. Gel filtration chromatography of COS7 cell cytosol showed that both recombinant and endogenous hVps35, hVps29, and hVps26 coelute as a large complex ( approximately 220-440 kDa). In the absence of hVps35, neither hVps26 nor hVps29 is found in the large complex. These data provide the first insights into the binding interactions among subunits of a putative mammalian retromer complex.

Sorting nexin 1 (SNX1) is a protein that binds to the epidermal growth factor (EGF) receptor and is proposed to play a role in directing EGF receptors to lysosomes for degradation (R. C. Kurten, D. L. Cadena, and G. N. Gill, Science 272:1008-1010, 1996). We have obtained full-length cDNAs and deduced the amino acid sequences of three novel homologous proteins, which were denoted human sorting nexins (SNX2, SNX3, and SNX4). In addition, we identified a presumed splice variant isoform of SNX1 (SNX1A). These molecules contain a conserved domain of ϳ100 amino acids, which was termed the phox homology (PX) domain. Human SNX1 (522 amino acids), SNX1A (457 amino acids), SNX2 (519 amino acids), SNX3 (162 amino acids), and SNX4 (450 amino acids) are part of a larger family of hydrophilic molecules including proteins identified in Caenorhabditis elegans and Saccharomyces cerevisiae. Despite their hydrophilic nature, the sorting nexins are found partially associated with cellular membranes. They are widely expressed, although the tissue distribution of each sorting nexin mRNA varies. When expressed in COS7 cells, epitope-tagged sorting nexins SNX1, SNX1A, SNX2, and SNX4 coimmunoprecipitated with receptor tyrosine kinases for EGF, platelet-derived growth factor, and insulin. These sorting nexins also associated with the long isoform of the leptin receptor but not with the short and medium isoforms. Interestingly, endogenous COS7 transferrin receptors associated exclusively with SNX1 and SNX1A, while SNX3 was not found to associate with any of the receptors studied. Our demonstration of a large conserved family of sorting nexins that interact with a variety of receptor types suggests that these proteins may be involved in several stages of intracellular trafficking in mammalian cells.