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Differential contribution of the three Aph1 genes to gamma-secretase activity in vivo.

ABSTRACT: Gamma-secretase is the protease responsible for amyloid beta peptide release and is needed for Notch, N-Cadherin, and possibly other signaling pathways. The protease complex consists of at least four subunits, i.e., Presenilin, Aph1, Pen2, and Nicastrin. Two different genes encode Aph1A and Aph1B in man. A duplication of Aph1B in rodents has given rise to a third gene, Aph1C. Different mixes of gamma-secretase subunits assemble in at least four human and six rodent complexes but it is not known whether they have different activities in vivo. We report here the inactivation of the three Aph1 genes in mice. Aph1A-/- embryos show a lethal phenotype characterized by angiogenesis defects in the yolk sac, neuronal tube malformations, and mild somitogenesis defects. Aph1B-/- or C-/- or the combined Aph1BC-/- mice (which can be considered as a model for total Aph1B loss in human) survive into adulthood. However, Aph1BC-/- deficiency causes a mild but significant reduction in amyloid beta percursor protein processing in selective regions of the adult brain. We conclude that the biochemical and physiological repercussions of genetically reducing gamma-secretase activity via the different Aph1 components are quite divergent and tissue specific. Our work provides in vivo evidence for the concept that different gamma-secretase complexes may exert different biological functions. In the context of Alzheimer's disease therapy, this implies the theoretical possibility that targeting specific gamma-secretase subunit combinations could yield less toxic drugs than the currently available general inhibitors of gamma-secretase activity.

SUBMITTER: Serneels L

PROVIDER: S-EPMC547495 | biostudies-literature | 2005 Feb

REPOSITORIES: biostudies-literature

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Differential contribution of the three Aph1 genes to gamma-secretase activity in vivo.

Serneels Lutgarde L Dejaegere Tim T Craessaerts Katleen K Horré Katrien K Jorissen Ellen E Tousseyn Thomas T Hébert Sébastien S Coolen Marcel M Martens Gerard G Zwijsen An A Annaert Wim W Hartmann Dieter D De Strooper Bart B

Proceedings of the National Academy of Sciences of the United States of America 20050121 5

Gamma-secretase is the protease responsible for amyloid beta peptide release and is needed for Notch, N-Cadherin, and possibly other signaling pathways. The protease complex consists of at least four subunits, i.e., Presenilin, Aph1, Pen2, and Nicastrin. Two different genes encode Aph1A and Aph1B in man. A duplication of Aph1B in rodents has given rise to a third gene, Aph1C. Different mixes of gamma-secretase subunits assemble in at least four human and six rodent complexes but it is not known ...[more]

PMID: 15665098

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Project description:Î³-secretase is an intra-membrane-cleaving aspartyl protease implicated in the processing of a wide range of type I membrane proteins including the Notch receptor and the amyloid-Î² precursor protein (APP). It thus regulates a diverse array of cellular and biological processes including the differentiation of neuronal embryonic stem cells, or intestinal stem cells, with the latter controlling the self-renewing of the intestinal epithelium. Indeed, proteolysis of these proteins by Î³-secretase triggers signaling cascades by releasing intracellular domains (ICDs) which, following association with adaptor proteins and nuclear translocation, modulate the transcription of different genes by binding directly to their promoters. The pronounced proliferative and regenerative effects of Notch signaling and its implication in the generation of the AÎ²-peptides, makes Î³-secretase a therapeutic target for several types of cancer and for Alzheimerâs disease. To investigate the broad effects of Î³-secretase activity onto the cellular transcriptome, Chinese hamster ovary (CHO) cells with enhanced Î³-secretase were compared to cells with abolished Î³-secretase activity via a microarray designed for a genetically close species, mouse. Our findings will potentially help to decipher the biology of Î³-secretase, including a better understanding of the roles of this enzyme in gene transcription. We compared the transcriptomes of two CHO cell lines displaying extreme differences in Î³-secretase activity. The S-1 cell line overexpressed the four components of Î³-secretase (NCT, APH1aL, PS1, and PEN2) and was characterized by a marked increase in the level of PS1 heterodimers associated with 8-fold increased Î³-secretase activity compared to untransfected controls. The other cell line consisted of wild type CHO cells incubated with DAPT, a well-known Î³-secretase inhibitor. The two cell lines were used in combination with a mouse microarray to analyze gene transcription under enhanced Î³-secretase. Two samples, S1 and DAPT treated CHO- were used in biological triplicates each.

Project description:BackgroundProcessing by gamma-secretase of many type-I membrane protein substrates triggers signaling cascades by releasing intracellular domains (ICDs) that, following nuclear translocation, modulate the transcription of different genes regulating a diverse array of cellular and biological processes. Because the list of gamma-secretase substrates is growing quickly and this enzyme is a cancer and Alzheimer's disease therapeutic target, the mapping of gamma-secretase activity susceptible gene transcription is important for sharpening our view of specific affected genes, molecular functions and biological pathways.Methodology/principal findingsTo identify genes and molecular functions transcriptionally affected by gamma-secretase activity, the cellular transcriptomes of Chinese hamster ovary (CHO) cells with enhanced and inhibited gamma-secretase activity were analyzed and compared by cDNA microarray. The functional clustering by FatiGO of the 1,981 identified genes revealed over- and under-represented groups with multiple activities and functions. Single genes with the most pronounced transcriptional susceptibility to gamma-secretase activity were evaluated by real-time PCR. Among the 21 validated genes, the strikingly decreased transcription of PTPRG and AMN1 and increased transcription of UPP1 potentially support data on cell cycle disturbances relevant to cancer, stem cell and neurodegenerative diseases' research. The mapping of interactions of proteins encoded by the validated genes exclusively relied on evidence-based data and revealed broad effects on Wnt pathway members, including WNT3A and DVL3. Intriguingly, the transcription of TERA, a gene of unknown function, is affected by gamma-secretase activity and was significantly altered in the analyzed human Alzheimer's disease brain cortices.Conclusions/significanceInvestigating the effects of gamma-secretase activity on gene transcription has revealed several affected clusters of molecular functions and, more specifically, 21 genes that hold significant potential for a better understanding of the biology of gamma-secretase and its roles in cancer and Alzheimer's disease pathology.

Project description:The majority of TP53 missense mutations identified in cancer patients are in the DNA-binding domain and are characterized as either structural or contact mutations. These missense mutations exhibit inhibitory effects on wild-type p53 activity. More importantly, these mutations also demonstrate gain-of-function (GOF) activities characterized by increased metastasis, poor prognosis, and drug resistance. To better understand the activities by which TP53 mutations, identified in Li-Fraumeni syndrome, contribute to tumorigenesis, we generated mice harboring a novel germline Trp53R245W allele (contact mutation) and compared them with existing models with Trp53R172H (structural mutation) and Trp53R270H (contact mutation) alleles. Thymocytes from heterozygous mice showed that all three hotspot mutations exhibited similar inhibitory effects on wild-type p53 transcription in vivo, and tumors from these mice had similar levels of loss of heterozygosity. However, the overall survival of Trp53R245W/+ and Trp53R270H/+ mice, but not Trp53R172H/+ mice, was significantly shorter than that of Trp53+/- mice, providing strong evidence for p53-mutant-specific GOF contributions to tumor development. Furthermore, Trp53R245W/+ and Trp53R270H/+ mice had more osteosarcoma metastases than Trp53R172H/+ mice, suggesting that these two contact mutants have stronger GOF in driving osteosarcoma metastasis. Transcriptomic analyses using RNA sequencing data from Trp53R172H/+, Trp53R245W/+, and Trp53R270H/+ primary osteosarcomas in comparison with Trp53+/- indicated that GOF of the three mutants was mediated by distinct pathways. Thus, both the inhibitory effect of mutant over wild-type p53 and GOF activities of mutant p53 contributed to tumorigenesis in vivo. Targeting p53 mutant-specific pathways may be important for therapeutic outcomes in osteosarcoma.Significancep53 hotspot mutants inhibit wild-type p53 similarly but differ in their GOF activities, with stronger tumor-promoting activity in contact mutants and distinct protein partners of each mutant driving tumorigenesis and metastasis.

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Differential contribution of the three Aph1 genes to gamma-secretase activity in vivo.

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Differential contribution of the three Aph1 genes to gamma-secretase activity in vivo.

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