Characterization of two patched receptors for the vertebrate hedgehog protein family

The multitransmembrane protein Patched (PTCH) is the receptor for Sonic Hedgehog (Shh), a secreted molecule implicated in the formation of embryonic structures and in tumorigenesis. Current models suggest that binding of Shh to PTCH prevents the normal inhibition of the seven-transmembrane-protein Smoothened (SMO) by PTCH. According to this model, the inhibition of SMO signaling is relieved after mutational inactivation of PTCH in the basal cell nevus syndrome. Recently, PTCH2, a molecule with sequence homology to PTCH, has been identified. To characterize both PTCH molecules with respect to the various Hedgehog proteins, we have isolated the human PTCH2 gene. Biochemical analysis of PTCH and PTCH2 shows that they both bind to all hedgehog family members with similar affinity and that they can form a complex with SMO. However, the expression patterns of PTCH and PTCH2 do not fully overlap. While PTCH is expressed throughout the mouse embryo, PTCH2 is found at high levels in the skin and in spermatocytes. Because Desert Hedgehog (Dhh) is expressed specifically in the testis and is required for germ cell development, it is likely that PTCH2 mediates its activity in vivo. Chromosomal localization of PTCH2 places it on chromosome 1p33-34, a region deleted in some germ cell tumors, raising the possibility that PTCH2 may be a tumor suppressor in Dhh target cells.     

Mutations of the PATCHED gene in several types of sporadic extracutaneous tumors

Patients with basal cell nevus syndrome have a high incidence of multiple basal cell carcinomas, medulloblastomas, and meningiomas. Because somatic PATCHED (PTCH) mutations have been found in sporadic basal cell carcinomas, we have screened for PTCH mutations in several types of sporadic extracutaneous tumors. We found that 2 of 14 sporadic medulloblastomas bear somatic nonsense mutations in one copy of the gene and also deletion of the other copy. In addition, we identified missense mutations in PTCH in two of seven breast carcinomas, one of nine meningiomas, and one colon cancer cell line. No PTCH gene mutations were detected in 10 primary colon carcinomas and eighteen bladder carcinomas.     

Nevoid basal-cell syndrome: literature review and case report in a family

The Nevoid Basal-Cell Carcinoma Syndrome (NBCC), or as it is also referred to, basal-cell nevus syndrome or Gorlin-Goltz syndrome, is characterized by multiple early-appearing basal cell carcinomas, keratocytosis of the mandible, and anomalies of the ocular, skeletal reproductive system. We describe four patients in the same family, all of them possessing a large number of skin tumors associated with other typical clinical and X-Ray anomalies of NBCC. The definitive treatment of NBCC has yet to be established, however, early diagnosis is very important as well as the periodical follow-up examination of ten patients, mainly due to the transformations in the skin lesions that may occur.     

Medulloblastomas of the desmoplastic variant carry mutations of the human homologue of Drosophila patched

Inactivating mutations in the PTCH gene, a human homologue of the Drosophila segment polarity gene patched, have been identified recently in patients with nevoid basal cell carcinoma syndrome. These patients are predisposed to various neoplasias including basal cell carcinomas and medulloblastomas (MBs). To determine the involvement of PTCH in sporadic MBs, which represent the most frequent malignant brain tumors in children, we screened for PTCH alterations in an unselected panel of 64 biopsy samples from 62 patients and four continuous MB cell lines, all derived from patients with sporadic MBs. Using single-strand conformational polymorphism analysis, we screened exons 2-22 and detected nonconservative PTCH mutations in 3 of 11 samples from sporadic cases of the desmoplastic variant of MB but none in 57 MBs with classical (nondesmoplastic) histology. In two of the tumors with mutations and in two additional desmoplastic cases, loss of heterozygosity was found at 9q22. These findings suggest that PTCH represents a tumor suppressor gene involved in the development of the desmoplastic variant of MB.     

Mutations of the human homolog of Drosophila patched in the nevoid basal cell carcinoma syndrome

The nevoid basal cell carcinoma syndrome (NBCCS) is an autosomal dominant disorder characterized by multiple basal cell carcinomas (BCCs), pits of the palms and soles, jaw keratocysts, a variety of other tumors, and developmental abnormalities. NBCCS maps to chromosome 9q22.3. Familial and sporadic BCCs display loss of heterozygosity in this region, consistent with the gene being a tumor suppressor. A human sequence (PTC) with strong homology to the Drosophila segment polarity gene, patched, was isolated from a YAC and cosmid contig of the NBCCS region. Mutation analysis revealed alterations of PTC in NBCCS patients and in related tumors. We propose that a reduction in expression of the patched gene can lead to the developmental abnormalities observed in the syndrome and that complete loss of patched function contributes to transformation of certain cell types.     

Diminished regional cerebral blood flow response to vibration in patients with blepharospasm

Mutations of the human Patched gene ( PTCH ) have been identified in individuals with the nevoid basal cell carcinoma syndrome (NBCCS) as well as in sporadic basal cell carcinomas and medulloblastomas. We have isolated a homologue of this tumour suppressor gene and localized it to the short arm of chromosome 1 (1p32.1-32.3). Patched 2 ( PTCH2 ) comprises 22 coding exons and spans approximately 15 kb of genomic DNA. The gene encodes a 1203 amino acid putative transmembrane protein which is highly homologous to the PTCH product. We have characterized the genomic structure of PTCH2 and have used single-stranded conformational polymorphism analysis to search for mutations in PTCH2 in NBCCS patients, basal cell carcinomas and in medulloblastomas. To date, we have identified one truncating mutation in a medulloblastoma and a change in a splice donor site in a basal cell carcinoma, suggesting that the gene plays a role in the development of some tumours.     

Sporadic medulloblastomas contain PTCH mutations

Nevoid basal cell carcinoma syndrome (NBCCS), or Gorlin's syndrome, is an autosomal dominant disorder that predisposes to developmental defects and various forms of cancer. PTCH was recently proposed as a candidate gene for NBCCS due to its frequent mutation in basal cell carcinomas, the cancer most often associated with this syndrome. Another NBCCS-associated cancer is medulloblastoma, a common central nervous system tumor in children. Most medulloblastomas, however, occur without indication of an inherited predisposition. We have examined 24 sporadic medulloblastomas for loss of heterozygosity (LOH) at loci flanking as well as within PTCH. In cases with LOH, single-strand conformational polymorphism and sequencing analysis were performed to determine the status of the remaining PTCH allele. Microsatellite analysis indicated LOH of PTCH in 5 of 24 tumors, and in three of these cases a mutation of the remaining allele was identified. Two of the mutations were duplication insertions, and the third consisted of a single base deletion. It is interesting that all three mutations occur in exon 17 of the PTCH gene. These data suggest that inactivation of PTCH function is involved in the development of at least a subset of sporadic medulloblastomas.     

Congenital homolateral epidermal hyperplasia and hypoplastic hemidysplasia (splitting of the Solomon's syndrome) (author's transl)

The observation of a 16-year-old girl born with an ectromelia and an ipsilateral inflammatory verrucous epidermal nevus led us to a synthetic study of 17 similar cases already published since 1927: all these cases concern female patients and are characterized by a unilateral hypoplastic dysplasia, most often of limbs, and inflammatory epidermal hyperplastic lesions described as ichthyosiform, psoriasiform or verrucous, usually distributed on the same side on the skin overlying the dysplastic body areas. The skin lesions may be partly regressive after birth and their histological features are suggestive of inflammatory linear verrucous epidermal nevus (I. L. V. E. N.). These associations may be representative of a special form of Solomon's syndrome whose heterogeneity has be recently emphasized. We propose to subdivide it in 3 forms: the epidermal nevus syndrome (Solomon's syndrome)--the organoid nevus syndrome (Schimmelpenning's syndrome)--the I. L. V. E. N. syndrome, probably X-linked dominant inherited (lethal for hemizygous males), associated with ipsilateral hypoplastic body lesions and, however less frequently than in the epidermal nevus syndrome, with ocular and nervous abnormalities. The distribution of cutaneous lesions has some similarities with the pattern of skin symptoms of X-linked dominant traits such as chondrodysplasia punctata, focal dermal hypoplasia or incontinentia pigmenti. The most typical feature of this syndrome is the strong inflammatory aspect of the epidermal nevus erroneously described in previous cases as unilateral psoriasis or ichthyosiform erythroderma.     

N-Glycosylation of pig flavin-containing monooxygenase form 1: determination of the site of protein modification by mass spectrometry

Wiskott-Aldrich syndrome (WAS) is an X-linked immunodeficiency disorder associated with lymphocytes and platelet abnormalities. The gene that encodes the Wiskott-Aldrich protein (WASP) was recently isolated, and shown to be defective in WAS patients. WASP contains multiple domains that interact with various signalling proteins, including the guanine triphosphatase (GTPase) Cdc42Hs and SH3 domain-containing proteins. Biochemical and genetic evidence strongly suggests that WASP is an important protein in the regulation of cell morphology. Recent progress in the identification of molecular partners for WASP suggests a molecular mechanism for the cellular abnormalities of WAS.     

Induction of basal cell carcinoma features in transgenic human skin expressing Sonic Hedgehog

Hedgehog (HH) signaling proteins mediate inductive events during animal development. Mutation of the only known HH receptor gene, Patched (PTC), has recently been implicated in inherited and sporadic forms of the most common human cancer, basal cell carcinoma (BCC). In Drosophila, HH acts by inactivating PTC function, raising the possibility that overexpression of Sonic Hedgehog (SHH) in human epidermis might have a tumorigenic effect equivalent to loss of PTC function. We used retroviral transduction of normal human keratinocytes to constitutively express SHH. SHH-expressing cells demonstrated increased expression of both the known HH target, BMP-2B, as well as bcl-2, a protein prominently expressed by keratinocytes in BCCs. These keratinocytes were then used to regenerate human skin transgenic for long terminal repeat-driven SHH (LTR-SHH) on immune-deficient mice. LTR-SHH human skin consistently displays the abnormal specific histologic features seen in BCCs, including downgrowth of epithelial buds into the dermis, basal cell palisading and separation of epidermis from the underlying dermis. In addition, LTR-SHH skin displays the gene expression abnormalities previously described for human BCCs, including decreased BP180/BPAG2 and laminin 5 adhesion proteins and expression of basal epidermal keratins. These data indicate that expression of SHH in human skin recapitulates features of human BCC in vivo, suggest that activation of this conserved signaling pathway contributes to the development of epithelial neoplasia and describe a new transgenic human tissue model of neoplasia.     

A frequent activated smoothened mutation in sporadic basal cell carcinomas

Basal-cell carcinomas (BCCs) are the most common cancer in Caucasians. It has been reported that the patched gene is inactivated in 30-40% sporadic BCCs and 20% sporadic medulloblastomas via loss of heterozygosity and nonsense mutations. Recently, two activating smoothened mutations have been found in the sporadic basal cell carcinomas. One, at base pair 1604 (G-to-T transversion) of exon 9, changes codon 535 from tryptophan to leucine, and the other, at base pair 1685 (G-to-A transition) of exon 10, changes codon 562 from arginine to glutamine (Xie et al., 1998). In our study, 1604G-->T was found in 20 out of 97 (20.6%) sporadic BCCs. The high prevalence indicates that 1604G is the mutation hot spot in our tumor samples. This mutation was detected in all three histological subtypes of BCCs, suggesting that smoothened mutation is an early event during the development of the tumor. Our finding of a high smoothened mutation rate, together with high frequent patched gene mutations reported recently, indicates that activation of the hedgehog signal transduction pathway is the most common and early event in the development of sporadic BCCs. Additionally, to determine whether smoothened, like patched, is also involved in the carcinogenesis of medulloblastomas, we screened medulloblastoma samples for these two mutations by restriction analysis. We have found the 1604G-->T mutation in 1 out of 21 medulloblastomas. This result confirmed smoothened gene involvement in the carcinogenesis of medulloblastoma.     

Carbohydrate-deficient glycoprotein syndrome type I: determination of the oligosaccharide structure of newly synthesized glycoproteins by analysis of calnexin binding

Familial predisposition to basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) of the skin are apparent in the autosomal dominant syndromes naevoid basal cell carcinoma syndrome (NBCCS) and multiple self-healing squamous epitheliomata (MSSE) respectively. The gene responsible for NBCCS has been proposed to be a tumour-suppressor gene and is mapped to the same 2 Mb interval on 9q22.3 as the MSSE gene ESS1. In an attempt to further map the NBCCS gene, we have examined loss of heterozygosity (LOH) in 16 sporadic BCCs and two familial BCCs using microsatellite markers located within the candidate gene region. The overall frequency of LOH observed was 67% in the BCCs and partial or interstitial deletions were found in eight tumours, with the highest LOH frequency at markers D9S280, D9S287 and D9S180. To determine if the same genomic region also shows frequent LOH in tumours with a squamous phenotype, we have examined 11 SCCs, four actinic keratoses and 13 cases of Bowen's disease for LOH at 9q22.3. An overall LOH frequency of 50% was observed at D9S180, and occurred in all types of squamous tumours. In contrast, a much lower LOH frequency of only 6% was found at the D9S287 locus. Our observation of different patterns of LOH at 9q22.3 in sporadic BCCs and SCCs implies that more than one tumour-suppressor gene might be located in this genomic region.     

Oculocerebral dysgenesis in the linear nevus sebaceous syndrome

PURPOSE: The authors document the association of peripapillary staphyloma and an atypical variant of hemimegalencephaly with the linear nevus sebaceous syndrome. BACKGROUND: Linear nevus sebaceous syndrome is an uncommon neurocutaneous disorder that has a propensity to involve the eyes. METHODS: Clinical, histopathologic, and neuroimaging findings are examined in a child with linear nevus sebaceous syndrome. RESULTS: In addition to bilateral peripapillary staphylomas, ophthalmologic abnormalities included a corneal dermoid, a complex conjunctival choristoma, macular hypoplasia, and optic nerve hypoplasia with contralateral optic atrophy. Magnetic resonance imaging disclosed a rare form of hemimegalencephaly characterized by hypoplasia of an optic radiation within the enlarged, dysgenetic cerebral hemisphere. CONCLUSION: The spectrum of oculocerebral dysgenesis in the linear nevus sebaceous syndrome can be expanded to include peripapillary staphyloma and atypical hemimegalencephaly with hypoplasia of an optic radiation.     

Mutations in exon 7 of the GTP-binding protein Gs alpha were not a common cause of pseudohypoparathyroidism with Albright's hereditary osteodystrophy in Japanese

The identification of unique point mutations in patients with pseudohypoparathyroidism (PHP) with Albright's hereditary osteodystrophy (AHO) in different ethnic backgrounds has proved that defects within the Gs alpha gene account for Gs alpha deficiency in those patients. To search a mutation hot spot of the Gs alpha gene in Japanese patients, we have screened exons 2-13 of the Gs alpha gene for mutations in three unrelated Japanese PHP patients with AHO. We could find no abnormalities by denaturing gradient gel electrophoresis and no mutations of sequencing of exon 7 in these subjects. This suggests that mutations in exon 7 of the Gs alpha gene may not be a common cause of PHP with AHO in Japanese.     

Expression of transporter associated with antigen processing-1 in the endocrine cells of human pancreatic islets: effect of cytokines and evidence of hyperexpression in IDDM

Increased knowledge of the biochemical composition of the glomerular basement membrane (GBM) and the introduction of molecular genetics has shed new light on the hereditary disorders of the GBM. In this review three disorders are highlighted. About 85% of the cases reported as Alport syndrome are transmitted as the X-linked form and are due to mutations of the COl4A5 chain localized at Xq22. The autosomal recessive form can be explained by mutations in the COl4A3 and COl4A4 gene. Anti-GBM nephritis leading to loss of the renal allograft in about 1%-5% of transplanted Alport patients can be the tragic consequence of this disorder. Some patients with familial benign hematuria have an abnormality of COl4A4. The nail-patella syndrome is a rare autosomal dominant disorder defined by the association of nail dysplasia, bone abnormalities, and frequently renal disease. The gene is localized in region 9q34.1, COl5A1 is not involved. The Finnish type is the best known of the different forms of congenital nephrotic syndrome. The gene has been mapped to the long arm of chromosome 19. Diffuse mesangial sclerosis occurs in the isolated form and as part of the Denys Drash syndrome. Disturbances of the WT1 function in the epithelial cells can have a role in the renal abnormalities of the Denys Drash syndrome.     

Further delineation of renal-coloboma syndrome in patients with extreme variability of phenotype and identical PAX2 mutations

Renal-coloboma syndrome is a recently described autosomal dominant syndrome of abnormal optic nerve and renal development. Two families have been reported with renal-coloboma syndrome and mutations of the PAX2 gene. The PAX2 gene, which encodes a DNA-binding protein, is expressed in the developing ear, CNS, eye, and urogenital tract. Ocular and/or renal abnormalities have been consistently noted in the five reports of patients with renal-coloboma syndrome, to date, but PAX2 expression patterns suggest that auditory and CNS abnormalities may be additional features of renal-coloboma syndrome. To determine whether additional clinical features are associated with PAX2 mutations, we have used PCR-SSCP to identify PAX2 gene mutations in patients. We report here four patients with mutations in exon 2, one of whom has severe ocular and renal disease, microcephaly, and retardation, and another who has ocular and renal disease with high-frequency hearing loss. Unexpectedly, extreme variability in clinical presentation was observed between a mother, her son, and an unrelated patient, all of whom had the same PAX2 mutation as previously described in two siblings with renal-coloboma syndrome. These results suggest that a sequence of seven Gs in PAX2 exon 2 may be particularly prone to mutation.