A novel but non-pathogenic mutation in exon 4 of the human amyloid precursor protein (APP) gene

Familial Alzheimer disease associated with A713T mutation in APP

Mutations in APP are associated with familial early-onset Alzheimer disease (FAD). Examination of the genomic sequence in one patient with FAD revealed a change located in the axon 17 of the APP gene at position 275329G>A (GenBank accession number: D87675; GI: 2429080); cDNA sequence 2137G>A (GenBank accession number: X06989; GI: 28720). This corresponds to the mutation A713T in APP. AD stage VI of neurofibrillary degeneration and stage C of Abeta-amyloid burden was found at the post-mortem neuropathological examination. Previous studies have suggested that the mutation A713T in APP is a silent mutation or polymorphism. However, we have not found this change in APP in a control population analyzed by the amplification-refractory mutation system (ARMS). It is concluded that A713T in APP is implicated in the pathogenesis of AD. Since the immunohistochemical study indicates that A713T mutation is not likely to relate with Abeta-amyloid processing, the causative role of this rare mutation remains to be warranted.

Amyloid precursor-like protein 2 promotes cell migration toward fibronectin and collagen IV

Previous studies have established that in response to wounding, the expression of amyloid precursor-like protein 2 (APLP2) in the basal cells of migrating corneal epithelium is greatly up-regulated. To further our understanding of the functional significance of APLP2 in wound healing, we have measured the migratory response of transfected Chinese hamster ovary (CHO) cells expressing APLP2 isoforms to a variety of extracellular matrix components including laminin, collagen types I, IV, and VII, fibronectin, and heparan sulfate proteoglycans (HSPGs). CHO cells overexpressing either of two APLP2 variants, differing in chondroitin sulfate (CS) attachment, exhibit a marked increase in chemotaxis toward type IV collagen and fibronectin but not to laminin, collagen types I and VII, and HSPGs. Cells overexpressing APLP2-751 (CS-modified) exhibited a greater migratory response to fibronectin and type IV collagen than their non-CS-attached counterparts (APLP2-763), suggesting that CS modification enhanced APLP2 effects on cell migration. Moreover, in the presence of chondroitin sulfate, transfectants overexpressing APLP2-751 failed to exhibit this enhanced migration toward fibronectin. The APLP2-ECM interactions were also explored by solid phase adhesion assays. While overexpression of APLP2 isoforms moderately enhanced CHO adhesion to laminin, collagen types I and VII, and HSPGs lines, especially those overexpressing APLP2-751, exhibited greatly increased adhesion to type IV collagen and fibronectin. These observations suggest that APLP2 contributes to re-epithelialization during wound healing by supporting epithelial cell adhesion to fibronectin and collagen IV, thus influencing their capacity to migrate over the wound bed. Furthermore, APLP2 interactions with fibronectin and collagen IV appear to be potentiated by the addition of a CS chain to the core proteins.

Analysis of the functional effects of a mutation in SOD1 associated with familial amyotrophic lateral sclerosis

Mutations in the Cu, Zn superoxide dismutase (SOD1) gene have been reported in some pedigrees with Familial Amyotrophic Lateral Sclerosis (FALS). We have investigated the functional and structural effects of a Gly-->Ser mutation at codon 41 of SOD1 in a pedigree with FALS and the topography of SOD1 expression in the mammalian CNS. These analyses show that the 41Gly-->Ser mutation causes a 27% reduction in Cu, Zn SOD activity. SOD1 is transcribed at high levels in rat motoneurons and four other types of neurons homologous to upper motoneurons that degenerate in human ALS. However, SOD1 is transcribed at lower levels in other types of neurons, such as cerebellar Purkinje cells, which are not usually involved significantly in human ALS. On the other hand, immunocytochemical studies indicate that most types of rat neurons contain similar levels of Cu, Zn SOD immunoreactive protein. Nevertheless, these results suggest that the essential feature causing this subtype of ALS is either a reduction in Cu, Zn SOD activity in cell types that presumably critically require Cu, Zn SOD for protection against oxidative damage or the fact that the mutation in SOD1 associated with FALS results in a novel gain of function that is particularly deleterious to those cell types expressing SOD1 at high levels.

Molecular genetics of Alzheimer's disease in Italian families

We screened 11 families from different regions of Italy by direct sequencing of exon 17 of the APP gene. Two unrelated families carried the APP717 mutation segregating with the disease. These two families originate from two Italian regions which are considered genetically separate. Published studies have demonstrated the presence of the APP717 Val-->Ile mutation in kindreds of British or Japanese origin with early onset familial Alzheimer's disease. These data suggest that the APP717 mutation is not confined to islander families which may share common founders. From the molecular genetic point of view we also did linkage analysis. Several families, in fact, have not shown a linkage with chromosome 21 and the resolution of this dilemma required investigation of those pedigrees both with additional markers from chromosome 21 and with markers from other chromosomes.

Protein-DNA interactions in the promoter region of the amyloid precursor protein (APP) gene in human neocortex

We have investigated protein-DNA interactions in the proximal promoter of the human amyloid precursor protein (APP) gene in temporal lobe neocortical nuclei isolated from control and Alzheimer disease (AD) affected brains. We report that the human APP 5' promoter sequence from -203 to +55 bp, which has been previously reported to contain essential regulatory elements for APP gene transcription, lies in a deoxyribonuclease I, micrococcal nuclease- and restriction endonuclease-sensitive, G+C-rich nucleosome-free gap flanked both 5' and 3' by typical nucleosome structures. As analyzed by electrophoretic mobility shift assay, this extended internucleosomal linker DNA is heavily occupied by nuclear protein factors, and interacts differentially with nuclear protein extracts obtained from HeLa and human brain neocortical nuclei. This suggests that the chromatin conformation of the APP gene promoter may vary in different cell types, and may correlate with differences in APP gene expression. Human recombinant transcription factors AP1, SP1 and TFIID (but not AP2 or brain histones H1, H2B and H4) interact with the -203 to +55 bp of the human APP promoter sequence. Only minor differences were observed in the chromatin structure of the immediate APP promoter between non-AD and AD affected neocortical nuclei, suggesting either that post-transcriptional processes, or that regulatory elements lying elsewhere in the APP gene may be important in the aberrant accumulation of the APP gene product.

Absence of APP713 mutation in Italian and Russian families with schizophrenia

A recent study has shown a mutation at codon 713 of the amyloid precursor protein (APP) gene in a schizophrenic patient. We have analyzed the MaeIII restriction site caused by that mutation in Italian and Russian families with schizophrenia. No mutations were observed suggesting that the APP713 mutation is unlikely to be linked to the pathogenesis of such a psychiatric disorder.

Identification of the genetic locus for keratosis palmaris et plantaris on chromosome 17 near the RARA and keratin type I genes

Familial keratosis palmaris et plantaris (KPPF) is characterized by extreme keratinization and desquamation of the skin of the palmar and plantar surfaces of the hands and feet. We have mapped the causative genetic defect to an 8 cM interval on 17q12-24 in or close to the acidic keratin (type I) gene cluster. We show that KPPF co-segregates with a rare, high molecular weight allele of an insertion-deletion polymorphism in the C-terminal coding region of the keratin 10 gene (Z = 8.36 at theta = 0.00) and segrates as a true autosomal dominant trait. Some pedigrees with familial hyperkeratosis of the palms and soles have co-inherited diseases such as congenital malformations and familial cancers. Our analysis provide a region which should be investigated for contiguous gene syndromes in such pedigrees.

Mutation of the gene for the human lysosomal serine protease cathepsin G is not the cause of aberrant APP processing in familial Alzheimer disease

Recent genetic linkage studies have implicated a gene on chromosome 14 in the pathogenesis of FAD. The identity of this gene remains unknown but it has been speculated that it may be involved in the cellular processing of the amyloid precursor protein (APP). We have analyzed the nucleotide sequence of the entire open reading frame of the cathepsin G gene located on chromosome 14q. No mutations were observed, suggesting that defects in this lysosomal protease are not responsible for aberrant accumulation of proteolytic products of APP in FAD brain tissue.