RESUMEN
Amyloid beta-peptide (A beta), the major component of senile plaques, is generated by proteolytic processing from the beta-amyloid precursor protein (beta APP). Mutations within the beta APP gene cause early onset familial AD (FAD) by affecting A beta generation. Interestingly, the much more abundant mutations within the presenilin (PS) genes also result in the abnormal generation of a 42 residue A beta (A beta 42), thus clearly supporting a pivotal role of A beta for the pathology of AD. PS proteins are proteolytically processed into stable 30 kDa N-terminal fragments (NTF) and 20 kDa C-terminal fragments (CTF). Beside the conventional proteolytic pathway. PS proteins can also be cleaved further C-terminal by proteases of the caspase superfamily. PS proteins were localized within the endoplasmic reticulum (ER) and early Golgi, compartments which we have demonstrated to be involved in A beta 42 generation and intracellular accumulation. Using Caenorhabditis elegans as a simple animal model, we demonstrate that PS proteins are involved in NOTCH signaling FAD causing mutations interfere with the biological function of PS proteins in NOTCH signaling.
Asunto(s)
Enfermedad de Alzheimer/metabolismo , Endopeptidasas/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Enfermedad de Alzheimer/enzimología , Secuencia de Aminoácidos , Péptidos beta-Amiloides/genética , Péptidos beta-Amiloides/metabolismo , Humanos , Proteínas de la Membrana/metabolismo , Datos de Secuencia Molecular , Presenilina-1 , Presenilina-2RESUMEN
The majority of cases with familial Alzheimer's disease (FAD) are linked to mutations of the presenilin (PS) genes. These genes show considerable sequence similarity to the sel-12 gene of Caenorhabditis elegans, which has been postulated to function in the facilitated signalling by lin-12 and glp-1. In order to analyse the functional conservation of the presenilins, we introduced the human PS-1 cDNA, as well as clinical and deletion mutant proteins, into sel-12 mutant animals and tested their potential to rescue the egg-laying defect. Human PS-1 expressed from the sel-12 promoter fully rescued the sel-12 phenotype, whereas two missense mutations, C410Y and A246E, identified in pedigrees with FAD, exhibited a strongly decreased rescuing activity. The large hydrophilic loop and transmembrane domain 7 are required for the biological activity of PS-1. PS-1 protein was proteolytically cleaved in C. elegans as it is in human cells. A PS-1 splice variant (FAD mutation deltaexon9) that does not undergo proteolytic cleavage also substituted for sel-12. The conservation of function of human PS-1 and C. elegans sel-12 suggests that presenilin proteins are required, directly or indirectly, for the proper operation of the Notch signalling pathway. FAD-associated mutant proteins tested showed different rescuing activities, indicating that they might affect different functional or regulatory aspects of PS-1. Proteolytic processing is not a prerequisite for PS-1 function in C. elegans.
Asunto(s)
Enfermedad de Alzheimer/genética , Caenorhabditis elegans/metabolismo , Proteínas de la Membrana/genética , Proteínas de la Membrana/metabolismo , Mutación , Procesamiento Proteico-Postraduccional , Animales , Animales Modificados Genéticamente , Caenorhabditis elegans/genética , Humanos , Hidrólisis , Fenotipo , Plásmidos , Presenilina-1 , Receptores Notch , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismoRESUMEN
The chromosomal breakpoint and fusion transcripts of the pre-B-leukaemia-derived SEM cell line carrying a reciprocal t(4;11)(q21;q23) translocation were analysed. The breakpoint from derivative chromosome der4 was cloned and sequenced. The crossover site was localized in intron 7 of the ALL-1 gene on chromosome 11q23 and in a large intron of the AF-4 (FEL) gene. RNA transcripts from both wild-type genes and both hybrid genes were detected by reverse transcriptase polymerase chain reaction (RT-PCR) assays. In addition, alternatively spliced mRNA species derived from the der4 chromosome were found. They were generated by using the exon 5' of the breakpoint on der4 as a common splice donor site and the 5' boundaries of exons 8 or 9 of the ALL-1 gene as alternative splice acceptor sites. The hypothesis is proposed that selective pressure operators to maintain the presence of both derivative chromosomes as important elements in the leukaemogenic process.