The mouse APLP2 gene. Chromosomal localization and promoter characterization

Amyloid precursor protein and amyloid precursor-like protein 2 in cancer

Amyloid precursor protein (APP) and its family members amyloid precursor-like protein 1 (APLP1) and amyloid precursor-like protein 2 (APLP2) are type 1 transmembrane glycoproteins that are highly conserved across species. The transcriptional regulation of APP and APLP2 is similar but not identical, and the cleavage of both proteins is regulated by phosphorylation. APP has been implicated in Alzheimer's disease causation, and in addition to its importance in neurology, APP is deregulated in cancer cells. APLP2 is likewise overexpressed in cancer cells, and APLP2 and APP are linked to increased tumor cell proliferation, migration, and invasion. In this present review, we discuss the unfolding account of these APP family members’ roles in cancer progression and metastasis.

APLP2 Regulates Refractive Error and Myopia Development in Mice and Humans

Myopia is the most common vision disorder and the leading cause of visual impairment worldwide. However, gene variants identified to date explain less than 10% of the variance in refractive error, leaving the majority of heritability unexplained (“missing heritability”). Previously, we reported that expression of APLP2 was strongly associated with myopia in a primate model. Here, we found that low-frequency variants near the 5’-end of APLP2 were associated with refractive error in a prospective UK birth cohort (n = 3,819 children; top SNP rs188663068, p = 5.0 × 10⁻⁴) and a CREAM consortium panel (n = 45,756 adults; top SNP rs7127037, p = 6.6 × 10⁻³). These variants showed evidence of differential effect on childhood longitudinal refractive error trajectories depending on time spent reading (gene x time spent reading x age interaction, p = 4.0 × 10⁻³). Furthermore, Aplp2 knockout mice developed high degrees of hyperopia (+11.5 ± 2.2 D, p < 1.0 × 10⁻⁴) compared to both heterozygous (-0.8 ± 2.0 D, p < 1.0 × 10⁻⁴) and wild-type (+0.3 ± 2.2 D, p < 1.0 × 10⁻⁴) littermates and exhibited a dose-dependent reduction in susceptibility to environmentally induced myopia (F(2, 33) = 191.0, p < 1.0 × 10⁻⁴). This phenotype was associated with reduced contrast sensitivity (F(12, 120) = 3.6, p = 1.5 × 10⁻⁴) and changes in the electrophysiological properties of retinal amacrine cells, which expressed Aplp2. This work identifies APLP2 as one of the “missing” myopia genes, demonstrating the importance of a low-frequency gene variant in the development of human myopia. It also demonstrates an important role for APLP2 in refractive development in mice and humans, suggesting a high level of evolutionary conservation of the signaling pathways underlying refractive eye development.

Gene variants identified by GWAS studies to date explain only a small fraction of myopia cases because myopia represents a complex disorder thought to be controlled by dozens or even hundreds of genes. The majority of genetic variants underlying myopia seems to be of small effect and/or low frequency, which makes them difficult to identify using classical genetic approaches, such as GWAS, alone. Here, we combined gene expression profiling in a monkey model of myopia, human GWAS, and a gene-targeted mouse model of myopia to identify one of the “missing” myopia genes, APLP2. We found that a low-frequency risk allele of APLP2 confers susceptibility to myopia only in children exposed to large amounts of daily reading, thus, providing an experimental example of the long-hypothesized gene-environment interaction between nearwork and genes underlying myopia. Functional analysis of APLP2 using an APLP2 knockout mouse model confirmed functional significance of APLP2 in refractive development and implicated a potential role of synaptic transmission at the level of glycinergic amacrine cells of the retina for the development of myopia. Furthermore, mouse studies revealed that lack of Aplp2 has a dose-dependent suppressive effect on susceptibility to form-deprivation myopia, providing a potential gene-specific target for therapeutic intervention to treat myopia.

Combined deletions of amyloid precursor protein and amyloid precursor-like protein 2 reveal different effects on mouse brain metal homeostasis

Alterations to the expression of the Amyloid Precursor Protein (APP) and its paralogue Amyloid Precursor-Like Protein 2 (APLP2) affect metal homeostasis in vitro and in vivo. Analysis of the in vivo effects of the APP and APLP2 knockouts on metal homeostasis has been restricted to APP and APLP2 single knockout mice, and up to12 month old animals. To define the redundancy and inter-relationship between the APP and APLP2 genes as regulators of metal homeostasis, and how this is influenced by aging, we investigated copper, iron, zinc and manganese levels in APP and APLP2 single knockout mice as well as homozygous:hemizygous knockout mice at 3, 12 and 18 plus months of age. These studies identified age and genotype dependent changes in metal levels, and established differences in the relative roles played by APP and APLP2 in modulating metal homeostasis.

Accumulation of the amyloid precursor-like protein APLP2 and reduction of APLP1 in retinoic acid-differentiated human neuroblastoma cells upon curcumin-induced neurite retraction

Amyloid precursor protein (APP) belongs to a conserved gene family, also including the amyloid precursor-like proteins, APLP1 and APLP2. The function of these three proteins is not yet fully understood. One of the proposed roles of APP is to promote neurite outgrowth. The aim of this study was to investigate the regulation of the expression levels of APP family members during neurite outgrowth. We observed that retinoic acid (RA)-induced neuronal differentiation of human SH-SY5Y cells resulted in increased expression of APP, APLP1 and APLP2. We also examined the effect of the NFkappaB, AP-1 and c-Jun N-terminal kinase inhibitor curcumin (diferuloylmethane) on the RA-induced expression levels of these proteins. We found that treatment with curcumin counteracted the RA-induced mRNA expression of all APP family members. In addition, we observed that curcumin treatment resulted in neurite retraction without any effect on cell viability. Surprisingly, curcumin had differential effects on the APLP protein levels in RA-differentiated cells. RA-induced APLP1 protein expression was blocked by curcumin, while the APLP2 protein levels were further increased. APP protein levels were not affected by curcumin treatment. We propose that the sustained levels of APP and the elevated levels of APLP2, in spite of the reduced mRNA expression, are due to altered proteolytic processing of these proteins. Furthermore, our results suggest that APLP1 does not undergo the same type of regulated processing as APP and APLP2.

The p53-inducible gene EI24/PIG8 localizes to human chromosome 11q23 and the proximal region of mouse chromosome 9

Activation of the p53 tumor suppressor leads to either a cell cycle arrest or to apoptosis and the factors that influence these responses are poorly understood. It is clear, however, that p53 regulates these processes by inducing a series of downstream target genes. One recently identified p53-target gene, EI24 (alias PIG8), induces apoptosis when ectopically expressed. To better understand the biological properties of EI24 and its potential relevance to disease, in particular cancer, we determined the chromosomal location and pattern of gene expression of EI24. EI24 is widely expressed in adult tissues and throughout mouse embryogenesis. The genomic locus of EI24 was mapped to the proximal region of mouse chromosome 9 and human chromosome 11q23-->q24, a region frequently altered in human cancers. These results suggest that EI24 may play an important role in the p53 tumor suppressor pathway.

Genomic structure and chromosome mapping of the genes encoding clathrin-associated adaptor medium chains mu1A (Ap1m1) and mu1B (Ap1m2)

The protein mu1B is a member of the medium chain family of the clathrin-associated adaptor complex and is expressed exclusively in epithelial cells. We determined the genomic structure of previously cloned murine genes for mu1B (Ap1m2) and its closely related homolog, mu1A (Ap1m1). Comparison of their genomic structures revealed that the positions of introns are identical between these two genes, except for the insertion of an additional intron in Ap1m1 (intron 4). By contrast, these structures are different from that of the more distantly related Ap2m1 gene encoding mu2. Taken together with the similarity of amino acid sequences among these genes, the data presented in this study suggest that Ap1m1/2 and Ap2m1 diverged long before the separation of Ap1m1 and Ap1m2, which most likely resulted from a relatively recent gene duplication. We also mapped AP1M2 to human chromosome 19p13.2 and Ap1m2 to the proximal region of mouse chromosome 9. The results are consistent with the fact that these regions are syntenic.

The beta-amyloid precursor protein and its derivatives: from biology to learning and memory processes

Intensive investigation towards the understanding of the biology and physiological functions of the beta-amyloid precursor protein (APP) have been supported since it is known that a 39-43 amino acid fragment of APP, called the beta-amyloid protein (Abeta), accumulates in the brain parenchyma to form the typical lesions associated with Alzheimer's disease (AD). It emerges from extensive data that APP and its derivatives show a wide range of contrasting physiological properties and therefore might be involved in distinct physiological functions. Abeta has been shown to disrupt neuronal activity and to demonstrate neurotoxic properties in a wide range of experimental procedures. In contrast, both in vitro and in vivo studies suggest that APP and/or its secreted forms are important factors involved in the viability, growth and morphological and functional plasticity of nerve cells. Furthermore, several recent studies suggest that APP and its derivatives have an important role in learning and memory processes. Memory impairments can be induced in animals by intracerebral treatment with Abeta. Altered expression of the APP gene in aged animals or in genetically-modified animals also leads to memory deficits. By contrast, secreted forms of APP have recently been shown to facilitate learning and memory processes in mice. These interesting findings open novel perspectives to understand the involvement of APP in the development of cognitive deficits associated with AD. In this review, we summarize the current data concerning the biology and the behavioral effects of APP and its derivatives which may be relevant to the roles of these proteins in memory and in AD pathology.

Promoter activity of the beta-amyloid precursor protein gene is negatively modulated by an upstream regulatory element

Alzheimer's disease (AD) is characterized by the aggregation of the amyloid beta-peptide (Abeta) which is generated from a larger beta-amyloid precursor protein (betaAPP). An overexpression of the betaAPP gene in certain areas of the AD brain has been suggested to be an important factor in the neuropathology of AD. Here we have further characterized an upstream regulatory element (URE) located between -2257 and -2234 of the human betaAPP promoter. In addition to its location in the promoter, BLAST search reveals that URE is present in several introns of the betaAPP gene and is also detected in many other genes. For functional studies, two promoter regions were cloned upstream of the reporter gene, chloramphenicol acetyl transferase (CAT): (i) phbetaE-B - the plasmid that contains the human (h) promoter region (-2832 to +101) including URE, and (ii) prhbetaE-B - the plasmid that contains the rhesus (rh) promoter region excluding URE as it lacks a 270 bp region of the hbetaAPP promoter (-2435 to -2165). Transient transfection studies indicate that phbetaE-B displayed significantly less CAT-promoter activity than prhbetaE-B in C6, PC12 and SK-N-SH cells. To determine the role of URE in a heterologous promoter, a pbetaURE construct was made by subcloning URE in an enhancerless promoter vector pCATP. The pbetaURE-CAT construct displayed threefold to fourfold less promoter activity than pCATP when different cell lines were transfected with the plasmids. URE interacts with a novel protein(s) as determined by the electrophoretic mobility shift assay (EMSA). Although the core DNA region of URE resembles with the NF-kB element, URE-binding protein is not related to the NF-kB transcription factor. When EMSA was performed with specific competitors in different cell lines, the labeled URE probe was not competed by the oligonucleotides specific for either the AP3, NF-1 or NF-kB transcription factor. The migration of the URE-protein complex was different from the NF-kB-protein complex in the EMSA gel. A distinct URE-specific nuclear factor was also detected in frontal cortex of a normal human brain. These results suggest that the URE region acts as a repressor element, that the URE-binding protein is not related to the known transcription factors tested, and that the protein is present in astrocytic, neuroblastoma, PC12 cells and in the human brain.

Molecular cloning of the promoter of the gene encoding the Rhesus monkey beta-amyloid precursor protein: structural characterization and a comparative study with other species

Abnormal regulation of transcription of the beta-amyloid precursor protein (betaAPP) gene is implicated in the pathogenesis of Alzheimer's disease (AD). We have examined 17- kb genomic region which contains the 5'-flanking region (promoter), first exon and on of the betaAPP gene of the Rhesus monkey (rhbetaAPP). A predominant scription start site was tified 146 bp upstream of the translation initiation codon. Sequencing 5848 bp of 5'-flanking revealed the presence of multiple near consensus sequences for binding potential transcriptional regulatory factors, such as activator proteins (AP-1, AP-2), an apolipoprotein E-B1 element, estrogen-responsive element, heat shock element and NF-kappaB. The sequence of the rhbetaAPP promoter also contains several sites for the binding of proteins that serve as signal transducers and activators of transcription (STAT1) (GAS). The rhbetaAPP promoter is highly homologous to the human promoter, but less homologous to the rodents. The homology between human and Rhesus monkey of the further upstream region gradually decreased over its length. A region of 270 bp of the human betaAPP promoter is missing from the Rhesus monkey promoter. Structural analysis of the promoter suggests that it contains characteristics of inducible genes and sites for regulated activity by various transcription factors.

APLP2, a member of the Alzheimer precursor protein family, is required for correct genomic segregation in dividing mouse cells

The mouse amyloid precursor-like protein 2 (APLP2) belongs to the Alzheimer peptide precursor family. A possible role in pre-implantation development had been suggested previously, and was investigated further by creating a large deletion in the genomic locus. While heterozygous mice developed normally, homozygous embryos were arrested before reaching the blastocyst stage. One-cell embryos which contained protein of maternal origin underwent a limited number of cleavages. The progressive disappearance of the protein at stages 4 and beyond correlated with the appearance of extensive cytopathological effects. Nuclear DNA contents of the arrested embryos departed widely from the normal 2-4C value, thus suggesting a role for the protein in replication and/or segregation of the embryonic genome. Embryonic mortality was not due to the untimely initiation of programmed cell death, and it occurred before the stage at which apoptotic cells normally appear. The same abnormal distribution of DNA contents was seen in primary cultures of Aplp2 +/- embryonic fibroblasts following transfection of an expression vector for Aplp2 antisense RNA with green fluorescent protein (GFP) expressed from a co-transfected construct. Daughter cells derived from a GFP-positive cell showed abnormal DNA contents both >4C and <2C, thus indicating a role for the protein in the mitotic segregation of the genome and establishment of the proper nuclear structure.

An region upstream of the gene promoter for the beta-amyloid precursor protein interacts with proteins from nuclear extracts of the human brain and PC12 cells

The amyloid beta-protein (Abeta) is the major proteinaceous component of the amyloid deposits that accumulate extracellularly in the brain of Alzheimer's disease (AD). Abeta is generated proteolytically from a larger beta-amyloid precursor protein (betaAPP). The apparent overexpression of the betaAPP gene in certain areas of AD brains indicate that abnormalities in gene regulation might be an important factor in AD. Here, I report that an upstream regulatory element (URE) located between -2257 to -2234 base pair (bp) of the human betaAPP promoter may interact with a novel protein(s) as determined by a gel shift assay. To determine whether this novel protein is related to an already characterized transcription factor, a gel shift assay was performed using various specific competitors in human neuroblastoma and rat pheochromocytoma (PC12) cells. The labeled URE probe could interact with a distinct nuclear factor which was not competed by the oligonucleotides specific for the different transcription factors, AP1, AP2, AP3, GRE, Oct1, NF1 and NF-kappaB. Alternatively the specific protein band(s) detected with either the labeled NF-kappaB or NF1 probe could not be competed out with an excess of unlabeled URE. To determine if such a band could be detected in human brain tissue samples, a gel shift assay from the nuclear extracts of the human brain was performed. A distinct URE-specific nuclear factor was detected in different regions of the brain as well. To determine the size of the protein(s) that were specifically bound in the DNA-protein complexes, Southwestern blotting was performed. Using the URE probe, two major protein bands of approximately 53 and 116 kDa were detected in PC12 nuclear extracts. These results suggest that the protein factor(s) interacting with URE is not related to the known transcription factors tested, and that the protein is expressed in certain cell types and different regions of the human brain.

Generation of APLP2 KO mice and early postnatal lethality in APLP2/APP double KO mice

Amyloid precursor protein (APP) is a member of a larger gene family including amyloid precursor-like proteins (APLP), APLP2 and APLP1. To examine the function of APLP2 in vivo, we generated APLP2 knockout (KO) mice. They are of normal size, fertile, and appear healthy up to 22 months of age. We observed no impaired axonal outgrowth of olfactory sensory neurons following bulbectomy, suggesting against an important role for APLP2 alone in this process. Because APLP2 and APP are highly homologous and may serve similar functions in vivo, we generated mice with targeted APLP2 and APP alleles. Approximately 80% of double KO mice die within the first week after birth, suggesting that APLP2 and APP are required for early postnatal development. The surviving approximately 20% of double KO mice are 20-30% reduced in weight and show difficulty in righting, ataxia, spinning behavior, and a head tilt, suggesting a deficit in balance and/or strength. Adult double KO mice mate poorly, despite apparent normal ovarian and testicular development. Otherwise, double KO mice appear healthy up to 13 months of age. We conclude, that APLP2 and APP can substitute for each other functionally.

Mouse chromosomal locations of nine genes encoding homologs of human paraneoplastic neurologic disorder antigens

The paraneoplastic neurologic disorders (PND) are a rare group of neurologic syndromes that arise when an immune response to systemic tumors expressing neuronal proteins ("onconeural antigens") develops into an autoimmune neuronal degeneration. The use of patient antisera to clone the genes encoding PND antigens has led to new insight into the mechanism of these autoimmune disorders. The tumor antigens can now be grouped into three classes: (1) neuron-specific RNA-binding proteins, (2) nerve terminal vesicle-associated proteins, and (3) cytoplasmic signaling proteins. To understand better the evolutionary relatedness of these genes and to evaluate them as candidates for inherited neurological disorders, we have determined the mouse chromosomal locations of nine of these genes-Hua, Hub, Huc, Hud, Nova1, Nova2, Natpb, Cdr2, and Cdr3. These data suggest that the Hua-Hud genes arose from gene duplication and dispersion, while the other genes are dispersed in the genome. We also predict the chromosomal locations of these genes in human and discuss the potential of these genes as candidates for uncloned mouse and human mutations.

Presenilin-1, amyloid precursor protein and amyloid precursor-like protein 2 mRNA levels in human superior frontal cortex during aging

The presenilin-1 (PS-1) and amyloid precursor protein (APP) genes carry mutations which co-segregate with early-onset familial Alzheimer's disease. The APP and PS-1 gene products may be involved in the aetiology of the more common late onset form of Alzheimer's disease, where increasing age is a major risk factor. To investigate whether age affected mRNA expression of these genes, we quantified PS-1, total APP, APP containing the kunitz-type protease inhibitor (KPI) domain and amyloid precursor-like protein 2 (APLP2) mRNAs in post-mortem superior frontal cortices from 23 control subjects aged 38 to 89 years using solution hybridisation-RNase protection assays. PS-1, total APP, APP KPI and APLP2 mRNA levels were unchanged over this age range. PS-1 was the least abundant mRNA, at approximately 7% of total APP, the most highly expressed mRNA studied (10.8 copies/pg total RNA). The proportion of total APP encoding the KPI domain (approximately 52%) was unaffected by age. APLP2 mRNA was present at approximately 29% of the total APP mRNA level. Significant positive correlations were present between total APP, APP KPI and APLP2 mRNA levels. These results indicate that the increased prevalence of Alzheimer's disease cannot be attributed to alterations in cortical PS-1, APP and APLP2 mRNA levels or APP KPI splicing during aging.

Genomic organization and chromosomal localization of the mouse telencephalin gene, a neuronal member of the ICAM family

Telencephalin is a cell adhesion molecule belonging to the immunoglobulin (Ig) superfamily, whose expression is restricted to subsets of neurons in the telencephalon, the most rostral segment of brain. Of all the Ig superfamily molecules so far identified, the structure of telencephalin is most closely related to those of intercellular adhesion molecules (ICAMs)-1 and -3. Here we report the cloning, characterization, and chromosomal localization of the mouse telencephalin gene (Tlcn). The Tlcn gene spanned about 6.3 kb and consisted of 11 exons. A signal peptide and individual nine Ig-like domains of telencephalin were encoded by a single exon, while the transmembrane and cytoplasmic regions were fused in a same exon. The primer extension technique was used to establish that the transcription initiation sites were located 92-95 bp upstream from the ATG start codon. DNA sequencing of the 5'-flanking region revealed the presence of a strong initiator element for TATA-less genes, two CAAT boxes, and numerous potential transcription factor binding sites including four E-box and two N-box sequences. Interspecific backcross analysis demonstrated that the Tlcn gene was mapped in the proximal region of mouse chromosome 9 in close vicinity to the Icam-1 gene, suggesting that Tlcn and Icam-1 are derived from a common ancestral gene by gene duplication.

Increased gene expression of beta-amyloid precursor protein and its homologues APLP1 and APLP2 in human neuroblastoma cells in response to retinoic acid

beta-Amyloid precursor protein (APP) belongs to a family of homologous beta-amyloid precursor-like proteins (APLPs) including APLP1 and APLP2. Previously it has been shown that APP is subject to regulation by retinoic acid (RA). In this paper we show that APLP1 and APLP2 mRNA expression is upregulated during RA-induced differentiation of human SH-SY5Y neuroblastoma cells. The cells were treated with RA (10 microM) for 3 and 6 days and mRNA levels were analysed by a non-radioactive Northern blot assay. RA induced a 2- to 3-fold increase in the gene expression of both APLP2 and APP, whereas the increase in APLP1 mRNA expression was significantly higher. Our results support a role for APLPs during neuronal differentiation.