Assessment of normal and mutant human presenilin function in 
            <i>Caenorhabditis elegans</i>

Levitan, Diane; Doyle, Timothy G.; Brousseau, Denise; Lee, Michael K.; Wang, Shuai; Slunt, Hilda H.; Sisodia, Sangram S.; Greenwald, Iva

doi:10.1073/pnas.93.25.14940

Cited by 356 publications

(271 citation statements)

References 27 publications

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“…Previous studies have demonstrated that the egg-laying defects in C. elegans, lacking the PS1 homologue sel-12, can be rescued by ⌬E9 huPS1 (5). Moreover, we demonstrate here that ⌬E9 huPS1 can be stabilized without cleavage.…”

Section: Discussionsupporting

confidence: 64%

“…In parallel with increased mRNA expression after butyrate, immunoblots with PS1Loop antiserum, which is specific for epitopes in the loop domain of PS1 (9), revealed robust increases in the steady-state levels of wild-type and mutant fulllength huPS1 and in the PS1 17 kDa CTF (Fig. 1, B, lanes 2,3,5,6,8, and 9; C, lanes 2, 3, 5, 6, 8, and 9). Butyrate treatment of untransfected cells did not change the levels of full-length endogenous PS1 polypeptides or the levels of endogenous NTFs and CTFs (data not shown).…”

Section: Inducible Expression Of Wild-type and A246ementioning

confidence: 93%

“…A subset of familial Alzheimer's disease (FAD) 1 cases are caused by mutations in two related genes, termed presenilin 1 (PS1) and presenilin 2 (PS2) (1)(2)(3), which are functionally interchangeable with sel-12, a Caenorhabditis elegans molecule involved in Notch-mediated cell differentiation (4,5). PS1 is a highly hydrophobic protein that spans the membrane eight times (6 -8), projecting the N-and C-terminal hydrophilic domains, as well as a large internal loop domain, into the cytoplasm.…”

mentioning

confidence: 99%

“…However, in cultured cells and in transgenic mice expressing either wild-type or FAD mutant PS1, the predominant PS1 species detected are ϳ27-kDa N-terminal (NTF) and ϳ17-kDa C-terminal fragments (CTF) that appear to be generated by endoproteolysis (9,(11)(12)(13)(14)(15). The role of endoproteolysis in PS1 maturation is not well understood as a noncleavable FAD variant (exon 9 deleted (⌬E9)) rescues the egg-laying defects of sel-12 mutant C. elegans (5,16). Thus, it has been difficult to resolve whether function is provided by full-length PS1 or the endoproteolytic fragments.…”

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confidence: 99%

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Endoproteolytic Processing and Stabilization of Wild-type and Mutant Presenilin

Ratovitski¹,

Slunt²,

Wang³

et al. 1997

Journal of Biological Chemistry

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Presenilin 1 (PS1), mutated in pedigrees of early-onset familial Alzheimer's disease, is a polytopic integral membrane protein that is endoproteolytically cleaved into 27-kDa N-terminal and 17-kDa C-terminal fragments. Although these fragments are the principal PS1 species found in normal mammalian brain, the role of endoproteolysis in the maturation of PS1 has been unclear. The present study, which uses stably transfected mouse neuroblastoma N2a cells, demonstrates that fulllength polypeptides, derived from either wild-type or A246E FAD-mutant human (hu) PS1, are relatively short-lived (t1 ⁄2 1.5 h) proteins that give rise to the N-and C-terminal PS1 fragments, which are more stable (t1 ⁄2 ϳ 24 h). N-terminal fragments, generated artificially by engineering a stop codon at amino acid 306 (PS1-306) of wild-type huPS1, were short-lived, whereas an FADlinked variant that lacked exon 9 (⌬E9) and was not endoproteolytically cleaved exhibited a long half-life. These observations suggest that endoproteolytic cleavage and stability are not linked, leading us to propose a model in which wild-type full-length huPS1 molecules are first stabilized then subsequently endoproteolytically cleaved to generate the N-and C-terminal fragments. These fragments appear to represent the mature and functional forms of wild-type huPS1.A subset of familial Alzheimer's disease (FAD) 1 cases are caused by mutations in two related genes, termed presenilin 1 (PS1) and presenilin 2 (PS2) (1-3), which are functionally interchangeable with sel-12, a Caenorhabditis elegans molecule involved in Notch-mediated cell differentiation (4, 5). PS1 is a highly hydrophobic protein that spans the membrane eight times (6 -8), projecting the N-and C-terminal hydrophilic domains, as well as a large internal loop domain, into the cytoplasm. In transiently transfected cultured cells, PS1 protein, a 467-amino acid polypeptide, exhibits a relative mass of 43 kDa (9 -12). However, in cultured cells and in transgenic mice expressing either wild-type or FAD mutant PS1, the predominant PS1 species detected are ϳ27-kDa N-terminal (NTF) and ϳ17-kDa C-terminal fragments (CTF) that appear to be generated by endoproteolysis (9,(11)(12)(13)(14)(15). The role of endoproteolysis in PS1 maturation is not well understood as a noncleavable FAD variant (exon 9 deleted (⌬E9)) rescues the egg-laying defects of sel-12 mutant C. elegans (5, 16). Thus, it has been difficult to resolve whether function is provided by full-length PS1 or the endoproteolytic fragments.Previous studies of multiple lines of transgenic mice expressing wild-type human (hu) PS1 indicate that the synthesis/ accumulation of PS1 NTFs and CTFs is highly regulated; the levels of full-length PS1 increase in parallel with the levels of transgene-derived huPS1 mRNA, but the levels of huPS1 NTFs and CTFs plateau (9). Moreover, in animals expressing high levels of huPS1, the levels of endogenous mouse NTFs and CTFs fall below the threshold of detection (9, 15). These data suggest that the absolute levels of PS1 NTF an...

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Section: Discussionsupporting

confidence: 64%

Section: Inducible Expression Of Wild-type and A246ementioning

confidence: 93%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Endoproteolytic Processing and Stabilization of Wild-type and Mutant Presenilin

Ratovitski¹,

Slunt²,

Wang³

et al. 1997

Journal of Biological Chemistry

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191

161

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“…Furthermore, the membrane topology of SEL-12 and PS1 appears to be similar (8)(9)(10). In addition to the functional and structural similarities, expression studies indicate that SEL-12 and human presenilins are expressed throughout development in many different cell types (3,4,7).…”

mentioning

confidence: 94%

HOP-1, a Caenorhabditis elegans presenilin, appears to be functionally redundant with SEL-12 presenilin and to facilitate LIN-12 and GLP-1 signaling

Greenwald

1997

Proc. Natl. Acad. Sci. U.S.A.

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Mutant presenilins have been found to cause Alzheimer disease. Here, we describe the identification and characterization of HOP-1, a Caenorhabditis elegans presenilin that displays much more lower sequence identity with human presenilins than does the other C. elegans presenilin, SEL-12. Despite considerable divergence, HOP-1 appears to be a bona fide presenilin, because HOP-1 can rescue the egg-laying defect caused by mutations in sel-12 when hop-1 is expressed under the control of sel-12 regulatory sequences. HOP-1 also has the essential topological characteristics of the other presenilins. Reducing hop-1 activity in a sel-12 mutant background causes synthetic lethality and terminal phenotypes associated with reducing the function of the C. elegans lin-12 and glp-1 genes. These observations suggest that hop-1 is functionally redundant with sel-12 and underscore the intimate connection between presenilin activity and LIN-12͞ Notch activity inferred from genetic studies in C. elegans and mammals.Genetic linkage studies have identified a number of loci associated with familial Alzheimer disease (1). Two of these loci encode related multipass transmembrane proteins, presenilins 1 and 2 (PS1 and PS2). Mutations in the genes encoding PS1 and PS2 loci are dominant and fully penetrant for early onset Alzheimer disease (2-4). The presenilins are ubiquitously expressed (3, 4) and found in conjunction with intracellular membranes (5). However, the normal role of presenilins, and the mechanism by which mutant presenilins cause Alzheimer disease, are not known.Genetic studies in simple organisms offer a powerful approach to understanding the normal role of presenilins. The Caenorhabditis elegans sel-12 gene encodes a protein that displays about 50% amino acid sequence identity to PS1 and PS2 (6). Genetic analysis established that reducing or eliminating sel-12 activity causes an egg-laying defective (Egl) phenotype, and that sel-12 activity facilitates the activity of LIN-12 and GLP-1, two receptors of the LIN-12͞Notch family (6). SEL-12 appears to be a bona fide presenilin, because human PS1 and PS2 can rescue the Egl phenotype of a sel-12 mutant (7). Furthermore, the membrane topology of SEL-12 and PS1 appears to be similar (8-10). In addition to the functional and structural similarities, expression studies indicate that SEL-12 and human presenilins are expressed throughout development in many different cell types (3, 4, 7).We have identified another candidate C. elegans presenilin based on predicted amino acid sequence by searching the genomic sequence database (11,12). Here, we show that this gene, which we have named hop-1 (hop ϭ homolog of presenilin), encodes a functional presenilin, by demonstrating that HOP-1 can rescue the egg-laying defect of a sel-12 mutant. We also show that HOP-1 has characteristic features of presenilin membrane topology. Finally, we show that reducing hop-1 activity in a sel-12 mutant background results in novel phenotypes, suggesting that hop-1 and sel-12 are functionally redundant.

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