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A Ballabio

Publications and source records attributed to A Ballabio.

At least 19 recordsLinked to original sources
PubMed2005

Sulfatases and sulfatase modifying factors: an exclusive and promiscuous relationship.

Sulfatases catalyze the hydrolysis of sulfate ester bonds from a wide variety of substrates. Several human inherited diseases are caused by the deficiency of individual sulfatases, while in patients with multiple sulfatase deficiency mutations in the Sulfatase Modifying Factor 1 (SUMF1) gene cause a defect in the post-translational modification of a cysteine residue into C(alpha)-formylglycine (FGly) at the active site of all sulfatases. This unique modification mechanism, which is required for catalytic activity, has been highly conserved during evolution. Here, we used a genomic approach to investigate the relationship between sulfatases and their modifying factors in humans and several model systems. First, we determined the complete catalog of human sulfatases, which comprises 17 members (versus 14 in rodents) including four novel ones (ARSH, ARSI, ARSJ and ARSK). Secondly, we showed that the active site, which is the target of the post-translational modification, is the most evolutionarily constrained region of sulfatases and shows intraspecies sequence convergence. Exhaustive sequence analyses of available proteomes indicate that sulfatases are the only likely targets of their modifying factors. Thirdly, we showed that sulfatases and ectonucleotide pyrophosphatases share significant homology at their active sites, suggesting a common evolutionary origin as well as similar catalytic mechanisms. Most importantly, gene association studies performed on prokaryotes suggested the presence of at least two additional mechanisms of cysteine-to-FGly conversion, which do not require SUMF1. These results may have important implications in the study of diseases caused by sulfatase deficiencies and in the development of therapeutic strategies.

Amino Acid Sequence↗
PubMed2004

Molecular cloning and characterization of NEU4, the fourth member of the human sialidase gene family.

Several mammalian sialidases have been cloned so far and here we describe the identification and expression of a new member of the human sialidase gene family. The NEU4 gene, identified by searching sequence databases for entries showing homologies to the human cytosolic sialidase NEU2, maps in 2q37 and encodes a 484-residue protein. The polypeptide contains all the typical sialidase amino acid motifs and, apart from an amino acid stretch that appears unique among mammalian sialidases, shows a high degree of homology for NEU2 and the plasma membrane-associated (NEU3) sialidases. RNA dot-blot analysis showed a low but wide expression pattern, with the highest level in liver. Transient transfection in COS7 cells allowed the detection of a sialidase activity toward the artificial substrate 4MU-NeuAc in the acidic range of pH. Immunofluorescence staining and Western blot analysis demonstrated the association of NEU4 with the inner cell membranes.

Amino Acid Sequence↗
PubMed2001

Amplification and overexpression of PRUNE in human sarcomas and breast carcinomas-a possible mechanism for altering the nm23-H1 activity.

PRUNE, the human homologue of the Drosophila gene, is located in 1q21.3, a region highly amplified in human sarcomas, malignant tumours of mesenchymal origin. Prune protein interacts with the metastasis suppressor nm23-H1, but shows impaired affinity towards the nm23-H1 S120G mutant associated with advanced neuroblastoma. Based on these observations, we previously suggested that prune may act as a negative regulator of nm23-H1 activity. We found amplification of PRUNE in aggressive sarcoma subtypes, such as leiomyosarcomas and malignant fibrous histiocytomas (MFH) as well as in the less malignant liposarcomas. PRUNE amplification was generally accompanied by high mRNA and moderate to high protein levels. The sarcoma samples expressed nm23-H1 mostly at low or moderate levels, whereas mRNA and protein levels were moderate to high in breast carcinomas. For the more aggressive sarcoma subtypes, 9/13 patients with PRUNE amplification developed metastases. A similar situation was observed in all breast carcinomas with amplification of PRUNE. Infection of NIH3T3 cells with a PRUNE recombinant retrovirus increased cell proliferation. Possibly, amplification and overexpression of PRUNE has the same effect in the tumours. We suggest that amplification and overexpression of PRUNE could be a mechanism for inhibition of nm23-H1 activity that affect the development or progression of these tumours.

3T3 Cells↗
PubMed2001

The tripartite motif family identifies cell compartments.

A functional genomic approach, based on systematic data gathering, was used to characterize a family of proteins containing a tripartite motif (TRIM). A total of 37 TRIM genes/proteins were studied, 21 of which were novel. The results demonstrate that TRIM proteins share a common function: by means of homo-multimerization they identify specific cell compartments.

Amino Acid Motifs↗
PubMed2001

Linkage mapping of a nonspecific form of X-linked mental retardation (MRX53) in a large Pakistani family.

Nonspecific X-linked mental retardation is a nonprogressive, genetically heterogeneous condition that affects cognitive function in the absence of other distinctive clinical manifestations. We report here linkage data on a large Pakistani family affected by a form of X-linked nonspecific mental retardation. X chromosome genotyping of family members and linkage analysis allowed the identification of a new disease locus, MRX53. The defined critical region spans approximately 15 cM between DXS1210 and DXS1047 in Xq22.2-26. A LOD score value of 3.34 at no recombination was obtained with markers DXS1072 and DXS8081.

Chromosome Mapping↗
PubMed2001

WBSCR14, a gene mapping to the Williams--Beuren syndrome deleted region, is a new member of the Mlx transcription factor network.

Williams-Beuren syndrome (WBS) is a developmental disorder associated with haploinsufficiency of multiple genes at 7q11.23. Here, we report the functional characterization of WBS critical region gene 14 (WBSCR14), a gene contained in the WBS commonly deleted region. It encodes a basic-helix--loop--helix leucine zipper (bHLHZip) transcription factor of the Myc/Max/Mad superfamily. WBSCR14 is expressed in multiple tissues, including regions of the brain and the intestinal tract. WBSCR14 forms heterodimers with the bHLHZip protein Mlx to bind the DNA sequence CACGTG. Like Max, Mlx has no intrinsic transcriptional activity, but its association with Mad1, Mad4, Mnt or WBSCR14 can repress E-box-dependent transcription. Preliminary results suggest a possible role of WBSCR14 in growth control. Our data support the view that the Max-like bHLHZip protein, Mlx, is a key element of a transcription factor network. We thus suggest that WBSCR14 may contribute to some aspects of the WBS pathology.

Amino Acid Sequence↗
PubMed2001

Functional analysis of mutations in SLC7A9, and genotype-phenotype correlation in non-Type I cystinuria.

Cystinuria (OMIM 220100) is a common recessive disorder of renal reabsorption of cystine and dibasic amino acids that results in nephrolithiasis of cystine. Mutations in SLC3A1, which encodes rBAT, cause Type I cystinuria, and mutations in SLC7A9, which encodes a putative subunit of rBAT (b(o,+)AT), cause non-Type I cystinuria. Here we describe the genomic structure of SLC7A9 (13 exons) and 28 new mutations in this gene that, together with the seven previously reported, explain 79% of the alleles in 61 non-Type I cystinuria patients. These data demonstrate that SLC7A9 is the main non-Type I cystinuria gene. Mutations G105R, V170M, A182T and R333W are the most frequent SLC7A9 missense mutations found. Among heterozygotes carrying these mutations, A182T heterozygotes showed the lowest urinary excretion values of cystine and dibasic amino acids. Functional analysis of mutation A182T after co-expression with rBAT in HeLa cells revealed significant residual transport activity. In contrast, mutations G105R, V170M and R333W are associated to a complete or almost complete loss of transport activity, leading to a more severe urinary phenotype in heterozygotes. SLC7A9 mutations located in the putative transmembrane domains of b(o,+)AT and affecting conserved amino acid residues with a small side chain generate a severe phenotype, while mutations in non-conserved residues give rise to a mild phenotype. These data provide the first genotype-phenotype correlation in non-Type I cystinuria, and show that a mild urinary phenotype in heterozygotes may associate with mutations with significant residual transport activity.

Amino Acid Sequence↗
PubMed2001

Identification of the gene for oral-facial-digital type I syndrome.

Oral-facial-digital type 1 syndrome (OFD1 [MIM 311200]) is transmitted as an X-linked dominant condition with lethality in males and is characterized by malformations of the face, oral cavity, and digits, and by a highly variable expressivity even within the same family. Malformation of the brain and polycystic kidneys are commonly associated with this disorder. The locus for OFD1 was mapped by linkage analysis to a 12-Mb interval, flanked by markers DXS85 and DXS7105 in the Xp22 region. To identify the gene responsible for this syndrome, we analyzed several transcripts mapping to the region and found mutations in OFD1 (formerly named "Cxorf5/71-7a"), encoding a protein containing coiled-coil alpha-helical domains. Seven patients with OFD1, including three with familial and four with sporadic cases, were analyzed. Analysis of the familial cases revealed a missense mutation, a 19-bp deletion, and a single base-pair deletion leading to a frameshift. In the sporadic cases, we found a missense (de novo), a nonsense, a splice, and a frameshift mutation. RNA in situ studies on mouse embryo tissue sections show that Ofd1 is developmentally regulated and is expressed in all tissues affected in OFD1 syndrome. The involvement of OFD1 in oral-facial-digital type I syndrome demonstrates an important role of this gene in human development.

Abnormalities, Multiple↗
PubMed2001

Diverse prevalence of large deletions within the OA1 gene in ocular albinism type 1 patients from Europe and North America.

Ocular albinism type 1 (OA1) is an X-linked disorder mainly characterized by congenital nystagmus and photodysphoria, moderate to severe reduction of visual acuity, hypopigmentation of the retina, and the presence of macromelanosomes in the skin and eyes. We have previously isolated the gene for OA1 and characterized its protein product as melanosomal membrane glycoprotein displaying structural and functional features of G protein-coupled receptors. We and others have identified mutations of various types within the OA1 gene in patients with this disorder, including deletions and splice site, frameshift, nonsense, and missense mutations. However, different prevalences of large intragenic deletions have been reported, ranging from 10% to 50% in independent studies. To determine whether these differences might be related to the geographic origin of the OA1 families tested, we performed a further extensive mutation analysis study leading to the identification of pathogenic mutations in 30 unrelated OA1 patients mainly from Europe and North America. These results, together with our earlier mutation reports on OA1, allow us to resolve the apparent discrepancies between previous studies and point to a substantial difference in the frequency of large intragenic deletions in European (<10%) compared with North American (>50%) OA1 families. These observations and our overall refinement of point mutation distribution within the OA1 gene have important implications for the molecular diagnosis of OA1 and for the establishment of any mutation detection program for this disorder.

Albinism, Ocular↗
PubMed2000

Defective intracellular transport and processing of OA1 is a major cause of ocular albinism type 1.

Ocular albinism type 1 (OA1) is an X-linked disorder mainly characterized by a severe reduction of visual acuity, hypopigmentation of the retina and the presence of macromelanosomes in the skin and eyes. Various types of mutation have been identified within the OA1 gene in patients with the disorder, including several missense mutations of unknown functional significance. In order to shed light into the molecular pathogenesis of ocular albinism and possibly define critical functional domains within the OA1 protein, we characterized 19 independent missense mutations with respect to processing and subcellular distribution on expression in COS-7 cells. Our analysis indicates the presence of at least two distinct biochemical defects associated with the different missense mutations. Eleven of the nineteen OA1 mutants (approximately 60%) were retained in the endoplasmic reticulum, showing defecNStive intracellular transport and glycosylation, consistent with protein misfolding. The remaining eight of the nineteen OA1 mutants (approximately 40%) displayed sorting and processing behaviours indistinguishable from those of the wild-type protein. Consistent with our recent findings that OA1 represents a novel type of intracellular G protein-coupled receptor (GPCR), we found that most of these latter mutations cluster within the second and third cytosolic loops, two regions that in canonical GPCRs are known to be critical for their downstream signaling, including G protein-coupling and effector activation. The biochemical analysis of OA1 mutations performed in this study provides important insights into the structure-function relationships of the OA1 protein and implies protein misfolding as a major pathogenic mechanism in OA1.

Albinism, Ocular↗
PubMed2000

A new locus for autosomal dominant nocturnal frontal lobe epilepsy maps to chromosome 1.

BACKGROUND: Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) is caused by mutations in the alpha4 subunit of the neuronal nicotinic acetylcholine receptor (CHRNA4) gene, mapping on chromosome 20q13.2. A second ADNFLE locus was mapped on chromosome 15q24. OBJECTIVE: To report a new third ADNFLE locus on chromosome 1 in a large Italian family. METHODS: The authors performed a clinical and genetic study in a large, three-generation ADNFLE family from southern Italy, including eight affected individuals and three obligate carriers. RESULTS: The age at onset of seizures was around 9 years of age and all affected individuals manifested nocturnal partial seizures of frontal lobe origin. Interictal awake and sleep EEG recordings showed no definite epileptiform abnormalities in most patients. Ictal video-EEG showed that the attacks were partial seizures with a frontal lobe semiology. Intellectual and neurologic examinations, and brain CT or MRI results were always normal. Carbamazepine was effective in all treated patients. Exclusion mapping of the known loci linked to ADNFLE-ENFL1, and ENFL2, on chromosomes 20q13.2 and 15q24-was performed on the pedigree before starting the genome-wide linkage analysis. The whole genome scan mapping allowed the identification of a new ADNFLE locus spanning the pericentromeric region of chromosome 1. CONCLUSIONS: The authors provided evidence for a third locus associated to autosomal dominant nocturnal frontal lobe epilepsy on chromosome 1. Among the known genes mapping within this critical region, the ss2 subunit of the nicotinic receptor (CHRNB2) represents the most obvious candidate.

Adolescent↗
PubMed2000

Oa1 knock-out: new insights on the pathogenesis of ocular albinism type 1.

Ocular albinism type I (OA1) is an X-linked disorder characterized by severe reduction of visual acuity, strabismus, photophobia and nystagmus. Ophthalmologic examination reveals hypopigmentation of the retina, foveal hypoplasia and iris translucency. Microscopic examination of both retinal pigment epithelium (RPE) and skin melanocytes shows the presence of large pigment granules called giant melanosomes or macromelanosomes. In this study, we have generated and characterized Oa1-deficient mice by gene targeting (KO). The KO males are viable, fertile and phenotypically indistinguishable from the wild-type littermates. Ophthalmologic examination shows hypopigmentation of the ocular fundus in mutant animals compared with wild-type. Analysis of the retinofugal pathway reveals a reduction in the size of the uncrossed pathway, demonstrating a misrouting of the optic fibres at the chiasm, as observed in OA1 patients. Microscopic examination of the RPE shows the presence of giant melanosomes comparable with those described in OA1 patients. Ultrastructural analysis of the RPE cells, suggests that the giant melanosomes may form by abnormal growth of single melanosomes, rather than the fusion of several, shedding light on the pathogenesis of ocular albinism.

Albinism, Ocular↗
PubMed2000

Cloning of the gene encoding a novel integral membrane protein, mucolipidin-and identification of the two major founder mutations causing mucolipidosis type IV.

Mucolipidosis type IV (MLIV) is an autosomal recessive lysosomal storage disorder characterized by severe psychomotor retardation and ophthalmologic abnormalities, including corneal opacity, retinal degeneration, and strabismus. Unlike the situation in other lysosomal disorders, the accumulation of heterogeneous storage material observed in MLIV does not result from a block in the catabolic pathways but is due to an ill-defined transport defect in the late steps of endocytosis. With the aim of cloning the MLIV gene, we searched in the 19p13.2-13.3 region, where the locus previously had been assigned by linkage mapping. In this region, we have identified a novel gene that is mutated in all patients with MLIV who were enrolled in our study. One patient was homozygous for the splice-acceptor mutation, and another was homozygous for a deletion removing the first six exons of the gene. In addition, four compound heterozygotes for these two mutations were identified. Haplotype analysis indicates that we have identified the two major founder mutations, which account for >95% of MLIV chromosomes in Ashkenazi Jewish patients. The gene, ML4, encodes a protein named "mucolipidin, " which localizes on the plasma membrane and, in the carboxy-terminal region, shows homologies to polycystin-2, the product of the polycystic kidney disease 2 gene (PKD2) and to the family of transient receptor potential Ca(2+) channels. Mucolipidin is likely to play an important role in endocytosis.

Alternative Splicing↗
PubMed2000

A member of a gene family on Xp22.3, VCX-A, is deleted in patients with X-linked nonspecific mental retardation.

X-linked nonspecific mental retardation (MRX) has a frequency of 0.15% in the male population and is caused by defects in several different genes on the human X chromosome. Genotype-phenotype correlations in male patients with a partial nullisomy of the X chromosome have suggested that at least one locus involved in MRX is on Xp22.3. Previous deletion mapping has shown that this gene resides between markers DXS1060 and DXS1139, a region encompassing approximately 1.5 Mb of DNA. Analyzing the DNA of 15 males with Xp deletions, we were able to narrow this MRX critical interval to approximately 15 kb of DNA. Only one gene, VCX-A (variably charged, X chromosome mRNA on CRI-S232A), was shown to reside in this interval. Because of a variable number of tandem 30-bp repeats in the VCX-A gene, the size of the predicted protein is 186-226 amino acids. VCX-A belongs to a gene family containing at least four nearly identical paralogues on Xp22.3 (VCX-A, -B, -B1, and -C) and two on Yq11.2 (VCY-D, VCY-E), suggesting that the X and Y copies were created by duplication events. We have found that VCX-A is retained in all patients with normal intelligence and is deleted in all patients with mental retardation. There is no correlation between the presence or absence of VCX-B1, -B, and VCX-C and mental status in our patients. These results suggest that VCX-A is sufficient to maintain normal mental development.

Amino Acid Sequence↗
PubMed2000

Mlx, a new Max-like bHLHZip family member: the center stage of a novel transcription factors regulatory pathway?

The Myc proto-oncogene family members have been identified as the cellular homologs of the transforming oncogene of avian retroviruses. They encode central regulators of mammalian cell proliferation and apoptosis, and they associate with the bHLHZip protein Max to bind specific DNA sequences and regulate the expression of genes important for cell cycle progression. The other family members, Mad1, Mxi1, Mad3, Mad4 and Rox (Mnt) antagonize their activities. The Mads and Rox compete with Myc in heterodimerizing with Max and in binding to the same specific target sequences. These Mads:Max and Rox:Max dimers repress transcription through binding to the mSIN3 corepressor protein and by tethering histone deacetylase-containing complexes to the DNA. In a screen for Rox interactors we isolated Mlx, a bHLHZip protein previously identified in a screen for Mad1 interactors. In the present work we extend the known dimerization partners of Mlx by demonstrating its ability to interact with Rox. Moreover, we show that contrary to previous reports Mlx is able to homodimerize and to bind E-box sequences at low concentration levels. The possible role of Mlx in an emerging regulatory pathway and acting parallel to the Max driven network is discussed.

Amino Acid Sequence↗
PubMed2000

Identification and expression of NEU3, a novel human sialidase associated to the plasma membrane.

Several mammalian sialidases have been described so far, suggesting the existence of numerous polypeptides with different tissue distributions, subcellular localizations and substrate specificities. Among these enzymes, plasma-membrane-associated sialidase(s) have a pivotal role in modulating the ganglioside content of the lipid bilayer, suggesting their involvement in the complex mechanisms governing cell-surface biological functions. Here we describe the identification and expression of a human plasma-membrane-associated sialidase, NEU3, isolated starting from an expressed sequence tag (EST) clone. The cDNA for this sialidase encodes a 428-residue protein containing a putative transmembrane helix, a YRIP (single-letter amino acid codes) motif and three Asp boxes characteristic of sialidases. The polypeptide shows high sequence identity (78%) with the membrane-associated sialidase recently purified and cloned from Bos taurus. Northern blot analysis showed a wide pattern of expression of the gene, in both adult and fetal human tissues. Transient expression in COS7 cells permitted the detection of a sialidase activity with high activity towards ganglioside substrates at a pH optimum of 3.8. Immunofluorescence staining of the transfected COS7 cells demonstrated the protein's localization in the plasma membrane.

Alternative Splicing↗
PubMed2000

Barhl1, a gene belonging to a new subfamily of mammalian homeobox genes, is expressed in migrating neurons of the CNS.

The BarH1 and BarH2 ( Bar ) Drosophila genes are homeobox-containing genes, which are required for the fate determination of external sensory organs in the fly. By means of a bioinformatic approach, we have identified in mouse and human two homeobox genes highly related to the Bar Drosophila genes, Barhl1 and Barhl2. While Barhl1 represents a novel gene, Barhl2 turned out to correspond to the mBH1 cDNA recently described in rat. We isolated and sequenced the full-length mouse Barhl1 and mapped both the human BARHL1 and BARHL2 genes to chromosomes 9q34 and 1p22, respectively. Detailed analysis of the murine Barhl1 expression pattern by in situ hybridization revealed that this transcript is exclusively expressed in restricted domains of the developing CNS, which suggests that this gene, similar to its Drosophila counterparts BarH1 and BarH2, may play a crucial role in cell fate determination of neural structures. In particular, Barhl1 showed specific domains of expression in the diencephalon and in the rhombencephalon where it was found to be expressed in migrating cells giving rise to the cerebellar external granular layer and to specific populations of dorsal sensory interneurons of the spinal cord. Thus, Barhl1 function may be required for the generation of these specific subtypes of neuronal progenitors. Furthermore, the mapping assignment and the expression pattern make BARHL1 an attractive positional candidate gene for a form of Joubert syndrome, a rare developmental anomaly of the cerebellum in humans.

Amino Acid Sequence↗