Mutations in the valosin-containing protein (VCP, p97) gene on chromosome 9p13-p12 cause a late-onset form of autosomal dominant inclusion body myopathy associated with Paget disease of the bone and frontotemporal dementia (IBMPFD). We report on the pathological consequences of three heterozygous VCP (R93C, R155H, R155C) mutations on human striated muscle. IBMPFD skeletal muscle pathology is characterized by degenerative changes and filamentous VCP- and ubiquitin-positive cytoplasmic and nuclear protein aggregates. Furthermore, this is the first report demonstrating that mutant VCP leads to a novel form of dilatative cardiomyopathy with inclusion bodies. In contrast to post-mitotic striated muscle cells and neurons of IBMPFD patients, evidence of protein aggregate pathology was not detected in primary IBMPFD myoblasts or in transient and stable transfected cells using wild-type-VCP and R93C-, R155H-, R155C-VCP mutants. Glutathione S-transferase pull-down experiments showed that all three VCP mutations do not affect the binding to Ufd1, Npl4 and ataxin-3. Structural analysis demonstrated that R93 and R155 are both surface-accessible residues located in the centre of cavities that may enable ligand-binding. Mutations at R93 and R155 are predicted to induce changes in the tertiary structure of the VCP protein. The search for putative ligands to the R93 and R155 cavities resulted in the identification of cyclic sugar compounds with high binding scores. The latter findings provide a novel link to VCP carbohydrate interactions in the complex pathology of IBMPFD.

Poly-alanine (Ala) tract expansions in transcription factors have been shown to be associated with human birth defects such as malformations of the brain, the digits, and other structures. Expansions of a poly-Ala tract from 15 to 22 (+7)-29 (+14) Ala in Hoxd13, for example, result in the limb malformation synpolydactyly in humans and in mice [synpolydactyly homolog (spdh)]. Here, we show that an increase of the Ala repeat above a certain length (22 Ala) is associated with a shift in the localization of Hoxd13 from nuclear to cytoplasmic, where it forms large amorphous aggregates. We observed similar aggregates for expansion mutations in SOX3, RUNX2 and HOXA13, pointing to a common mechanism. Cytoplasmic aggregation of mutant Hoxd13 protein is influenced by the length of the repeat, the level of expression and the efficacy of degradation by the proteasome. Heat shock proteins Hsp70 and Hsp40 co-localize with the aggregates and activation of the chaperone system by geldanamycin leads to a reduction of aggregate formation. Furthermore, recombinant mutant Hoxd13 protein forms aggregates in vitro demonstrating spontaneous misfolding of the protein. We analyzed the mouse mutant spdh, which harbors a +7 Ala expansion in Hoxd13 similar to the human synpolydactyly mutations, as an in vivo model and were able to show a reduction of mutant Hoxd13 and, in contrast to wt Hoxd13, a primarily cytoplasmic localization of the protein. Our results provide evidence that poly-Ala repeat expansions in transcription factors result in misfolding, degradation and cytoplasmic aggregation of the mutant proteins.

X-linked hypophosphatemic rickets in humans is caused by mutations in the PEX gene which codes for a protein homologous to neutral endopeptidases. Hyp and Gy mice both have X-linked hypophosphatemic rickets, although genetic data and the different phenotypic spectra observed have previously suggested that two different genes are mutated. In addition to the metabolic disorder observed in Hyp mice, male Gy mice are sterile and show circling behavior and reduced viability. We now report the cloning of the mouse homolog of PEX which is highly conserved between man and mouse. The 3' end of this gene is deleted in Hyp mice. In Gy mice, the first three exons and the promotor region are deleted. Thus, Hyp and Gy are allelic mutations and both provide mouse models for X-linked hypophosphatemia.

X-linked dominant hypophosphatemic rickets (HYP) is the most common form of hereditary rickets. Recently we have cloned the PEX gene and shown it to be mutated and deleted in HYP individuals. We have now completely sequenced a 243-kb genomic region containing PEX and have identified all intron-exon boundary sequences. We show that PEX, homologous to members of a neutral endopeptidase family, has an exon organization that is very similar to neprilysin. We have performed an extensive mutation analysis examining all 22 PEX coding exons in 29 familial and 14 sporadic cases of hypophosphatemia. Sequence changes include missense, frameshift, nonsense, and splice site mutations and intragenic deletions. A mutation was found in 25 (86%) of the 29 familial cases and 8 (57%) of the 14 sporadic cases. Our data provide the first evidence that most of the familial and also a large number of the sporadic cases of hypophosphatemia are caused by loss-of-function mutations in PEX.[The sequence data described in this paper have been submitted to GenBank under accession nos. Y08111-Y08132 and Y10196.] X-linked dominant hypophosphatemic rickets [HYP; MIM 307800 (Mendelian inheritance in man number); McKusick 1994] has an incidence of 1 in 20,000 individuals and is the most common form of hypophosphatemia. The main physiological traits of the disease are a leak of phosphate from the kidney causing low phosphate levels in the blood and defective bone mineralization. Patients exhibit rickets and osteomalacia, lower extremity deformities, short stature, bone pain, dental abnormalities, and abnormal vitamin D metabolism. Several other less common disorders of inherited renal phosphate wasting also exist, including an autosomal dominant form (ADHR; McKusick 1994, MIM 193100;Econs and McEnery 1997) and hereditary hypophosphatemic rickets with hypercalciuria (HHRH; McKusick 1994, MIM 241530), which shows a complex inheritance pattern (Tieder et al. 1987). An additional tumor-induced form of hypophosphatemia exists, oncogenic hypophosphatemic osteomalacia, in which removal of the tumor leads to a return in normal phosphate levels (Fukomoto et al. 1979;Lobaugh et al. 1984;Weidner et al. 1985). These additional forms of the disease suggest that phosphate homeostasis is a complex process involving multiple gene products.Recently we cloned a candidate gene, PEX, for the X-linked dominant form of hypophosphatemic rickets, localized to the human Xp22 region (HYP GENOME RESEARCH 573Cold Spring Harbor Laboratory Press on May 10, 2018 -Published by genome.cshlp.org Downloaded from Consortium 1995). PEX has homologies to a family of zinc metalloproteases that includes neprilysin (NEP; D' Adamio et al. 1989), the Kell antigen (KELL; Lee et al. 1991) and endothelin-converting enzymes 1 and 2 (ECE-1 and ECE-2; Schmidt et al. 1994;Xu et al. 1994;Emoto and Yanagisawa 1995). NEP is known to inactivate a wide variety of peptide hormones, whereas ECE-1 and ECE-2 process inactive big endothelin 1 to its active form. A substrate for PEX has not yet been ...

Type II diabetes (T2D) is characterized by diminished insulin production and resistance of cells to insulin. Among others, endoplasmic reticulum (ER) stress is a principal factor contributing to T2D and induces a shift towards a more reducing cellular environment. At the same time, peripheral insulin resistance triggers the over-production of regulatory hormones such as insulin and human islet amyloid polypeptide (hIAPP). We show that the differential aggregation of reduced and oxidized hIAPP assists to maintain the redox equilibrium by restoring redox equivalents. Aggregation thus induces redox balancing which can assist initially to counteract ER stress. Failure of the protein degradation machinery might finally result in β-cell disruption and cell death. We further present a structural characterization of hIAPP in solution, demonstrating that the N-terminus of the oxidized peptide has a high propensity to form an α-helical structure which is lacking in the reduced state of hIAPP. In healthy cells, this residual structure prevents the conversion into amyloidogenic aggregates.