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Presenilin 1 negatively regulates beta-catenin/T cell factor/lymphoid enhancer factor-1 signaling independently of beta-amyloid precursor protein and notch processing.

Soriano S, Kang DE, Fu M, Pestell R, Chevallier N, Zheng H, Koo EH - J. Cell Biol. (2001)

Bottom Line: Conversely, PS1 specifically represses LEF-dependent transcription in a dose-dependent manner.The hyperproliferative response can be reversed by reintroducing PS1 expression or overexpressing axin, but not a PS1 mutant that does not bind beta-catenin (PS1Deltacat) or by two different familial Alzheimer's disease mutants.Thus, PS1 adds to the molecules that are known to regulate the rapid turnover of beta-catenin.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurosciences, University of California, San Diego, La Jolla, California 92093, USA.

ABSTRACT
In addition to its documented role in the proteolytic processing of Notch-1 and the beta-amyloid precursor protein, presenilin 1 (PS1) associates with beta-catenin. In this study, we show that this interaction plays a critical role in regulating beta-catenin/T Cell Factor/Lymphoid Enhancer Factor-1 (LEF) signaling. PS1 deficiency results in accumulation of cytosolic beta-catenin, leading to a beta-catenin/LEF-dependent increase in cyclin D1 transcription and accelerated entry into the S phase of the cell cycle. Conversely, PS1 specifically represses LEF-dependent transcription in a dose-dependent manner. The hyperproliferative response can be reversed by reintroducing PS1 expression or overexpressing axin, but not a PS1 mutant that does not bind beta-catenin (PS1Deltacat) or by two different familial Alzheimer's disease mutants. In contrast, PS1Deltacat restores Notch-1 proteolytic cleavage and Abeta generation in PS1-deficient cells, indicating that PS1 function in modulating beta-catenin levels can be separated from its roles in facilitating gamma-secretase cleavage of beta-amyloid precursor protein and in Notch-1 signaling. Finally, we show an altered response to Wnt signaling and impaired ubiquitination of beta-catenin in the absence of PS1, a phenotype that may account for the increased stability in PS1-deficient cells. Thus, PS1 adds to the molecules that are known to regulate the rapid turnover of beta-catenin.

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(a) Abnormal β-catenin turnover after Wnt stimulation in the absence of PS1. Primary PS1−/− and PS1+/− fibroblasts were incubated with Wnt-3a–conditioned medium (Wnt-CM) as described in Materials and Methods. After 2 h of treatment, Wnt-CM was removed, and cells were washed extensively and incubated for the indicated time points with fresh normal medium. Shown are the levels of cytosolic β-catenin. Results are representative of three independent experiments. (b) Cells were treated with Wnt-CM exactly as described for Fig. 5 a, and axin levels were analyzed by Western blot. Note that the axin phosphorylation pattern in response to Wnt is not different between PS1+/− and −/− cells. In marked contrast, restoration of β-catenin levels is delayed in PS1−/− cells with respect to control cells (a).
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Figure 6: (a) Abnormal β-catenin turnover after Wnt stimulation in the absence of PS1. Primary PS1−/− and PS1+/− fibroblasts were incubated with Wnt-3a–conditioned medium (Wnt-CM) as described in Materials and Methods. After 2 h of treatment, Wnt-CM was removed, and cells were washed extensively and incubated for the indicated time points with fresh normal medium. Shown are the levels of cytosolic β-catenin. Results are representative of three independent experiments. (b) Cells were treated with Wnt-CM exactly as described for Fig. 5 a, and axin levels were analyzed by Western blot. Note that the axin phosphorylation pattern in response to Wnt is not different between PS1+/− and −/− cells. In marked contrast, restoration of β-catenin levels is delayed in PS1−/− cells with respect to control cells (a).

Mentions: Because aberrant Wnt stimulation is believed to result in tumorigenesis in several tissues (reviewed in Barker et al. 2000), we asked whether loss of PS1 alters the response to Wnt signaling. In primary mouse embryonic fibroblasts with or without PS1, the levels of cytosolic β-catenin and axin phosphorylation, parameters that have been shown to be modulated by Wnt signaling (Willert et al. 1999, and references therein) were determined after Wnt-3a stimulation. Specifically, we examined axin phosphorylation and β-catenin levels under the following conditions: (a) basal, unstimulated state, (b) Wnt stimulation, and (c) after removal of the Wnt signal. We chose these conditions because an adequate response to Wnt signaling in vivo involves not only the adequate upregulation of β-catenin levels and nuclear signaling after stimulation, but presumably the timely restoration of basal levels once Wnt activation is switched off. As shown before, under basal conditions, β-catenin levels were higher in the absence of PS1 (Fig. 6 a, lane 1, compare top and bottom). After treatment with conditioned medium from Wnt-3a–transfected cells (Wnt3a-CM) for 2 h, β-catenin increased substantially in both PS1+/− and −/− cells, likely due to inactivation of GSK-3β (Fig. 6 a, lane 2). Concomitantly, there was the appearance of a faint, faster migrating, dephosphorylated axin species (Fig. 6 b, lanes 2 and 3, arrowheads), consistent with dephosphorylated forms of axin, as previously described (Willert et al. 1999). This species was indistinguishable between PS1+/− and −/− cells, and was no longer detectable 5 h after Wnt3a withdrawal (Fig. 6 b, lane 4). In contrast, while cytosolic levels of β-catenin were consistently restored in PS1+/− cells within 7.5 h after Wnt3a withdrawal (Fig. 6 a, bottom, lane 5), β-catenin levels remained consistently elevated at this same time point in PS1−/− (Fig. 6 a, top, lane 5). Thus, our results showed that, although Wnt stimulation properly elevates β-catenin levels in PS1 cells, the signal is abnormally prolonged.


Presenilin 1 negatively regulates beta-catenin/T cell factor/lymphoid enhancer factor-1 signaling independently of beta-amyloid precursor protein and notch processing.

Soriano S, Kang DE, Fu M, Pestell R, Chevallier N, Zheng H, Koo EH - J. Cell Biol. (2001)

(a) Abnormal β-catenin turnover after Wnt stimulation in the absence of PS1. Primary PS1−/− and PS1+/− fibroblasts were incubated with Wnt-3a–conditioned medium (Wnt-CM) as described in Materials and Methods. After 2 h of treatment, Wnt-CM was removed, and cells were washed extensively and incubated for the indicated time points with fresh normal medium. Shown are the levels of cytosolic β-catenin. Results are representative of three independent experiments. (b) Cells were treated with Wnt-CM exactly as described for Fig. 5 a, and axin levels were analyzed by Western blot. Note that the axin phosphorylation pattern in response to Wnt is not different between PS1+/− and −/− cells. In marked contrast, restoration of β-catenin levels is delayed in PS1−/− cells with respect to control cells (a).
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Related In: Results  -  Collection

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Figure 6: (a) Abnormal β-catenin turnover after Wnt stimulation in the absence of PS1. Primary PS1−/− and PS1+/− fibroblasts were incubated with Wnt-3a–conditioned medium (Wnt-CM) as described in Materials and Methods. After 2 h of treatment, Wnt-CM was removed, and cells were washed extensively and incubated for the indicated time points with fresh normal medium. Shown are the levels of cytosolic β-catenin. Results are representative of three independent experiments. (b) Cells were treated with Wnt-CM exactly as described for Fig. 5 a, and axin levels were analyzed by Western blot. Note that the axin phosphorylation pattern in response to Wnt is not different between PS1+/− and −/− cells. In marked contrast, restoration of β-catenin levels is delayed in PS1−/− cells with respect to control cells (a).
Mentions: Because aberrant Wnt stimulation is believed to result in tumorigenesis in several tissues (reviewed in Barker et al. 2000), we asked whether loss of PS1 alters the response to Wnt signaling. In primary mouse embryonic fibroblasts with or without PS1, the levels of cytosolic β-catenin and axin phosphorylation, parameters that have been shown to be modulated by Wnt signaling (Willert et al. 1999, and references therein) were determined after Wnt-3a stimulation. Specifically, we examined axin phosphorylation and β-catenin levels under the following conditions: (a) basal, unstimulated state, (b) Wnt stimulation, and (c) after removal of the Wnt signal. We chose these conditions because an adequate response to Wnt signaling in vivo involves not only the adequate upregulation of β-catenin levels and nuclear signaling after stimulation, but presumably the timely restoration of basal levels once Wnt activation is switched off. As shown before, under basal conditions, β-catenin levels were higher in the absence of PS1 (Fig. 6 a, lane 1, compare top and bottom). After treatment with conditioned medium from Wnt-3a–transfected cells (Wnt3a-CM) for 2 h, β-catenin increased substantially in both PS1+/− and −/− cells, likely due to inactivation of GSK-3β (Fig. 6 a, lane 2). Concomitantly, there was the appearance of a faint, faster migrating, dephosphorylated axin species (Fig. 6 b, lanes 2 and 3, arrowheads), consistent with dephosphorylated forms of axin, as previously described (Willert et al. 1999). This species was indistinguishable between PS1+/− and −/− cells, and was no longer detectable 5 h after Wnt3a withdrawal (Fig. 6 b, lane 4). In contrast, while cytosolic levels of β-catenin were consistently restored in PS1+/− cells within 7.5 h after Wnt3a withdrawal (Fig. 6 a, bottom, lane 5), β-catenin levels remained consistently elevated at this same time point in PS1−/− (Fig. 6 a, top, lane 5). Thus, our results showed that, although Wnt stimulation properly elevates β-catenin levels in PS1 cells, the signal is abnormally prolonged.

Bottom Line: Conversely, PS1 specifically represses LEF-dependent transcription in a dose-dependent manner.The hyperproliferative response can be reversed by reintroducing PS1 expression or overexpressing axin, but not a PS1 mutant that does not bind beta-catenin (PS1Deltacat) or by two different familial Alzheimer's disease mutants.Thus, PS1 adds to the molecules that are known to regulate the rapid turnover of beta-catenin.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurosciences, University of California, San Diego, La Jolla, California 92093, USA.

ABSTRACT
In addition to its documented role in the proteolytic processing of Notch-1 and the beta-amyloid precursor protein, presenilin 1 (PS1) associates with beta-catenin. In this study, we show that this interaction plays a critical role in regulating beta-catenin/T Cell Factor/Lymphoid Enhancer Factor-1 (LEF) signaling. PS1 deficiency results in accumulation of cytosolic beta-catenin, leading to a beta-catenin/LEF-dependent increase in cyclin D1 transcription and accelerated entry into the S phase of the cell cycle. Conversely, PS1 specifically represses LEF-dependent transcription in a dose-dependent manner. The hyperproliferative response can be reversed by reintroducing PS1 expression or overexpressing axin, but not a PS1 mutant that does not bind beta-catenin (PS1Deltacat) or by two different familial Alzheimer's disease mutants. In contrast, PS1Deltacat restores Notch-1 proteolytic cleavage and Abeta generation in PS1-deficient cells, indicating that PS1 function in modulating beta-catenin levels can be separated from its roles in facilitating gamma-secretase cleavage of beta-amyloid precursor protein and in Notch-1 signaling. Finally, we show an altered response to Wnt signaling and impaired ubiquitination of beta-catenin in the absence of PS1, a phenotype that may account for the increased stability in PS1-deficient cells. Thus, PS1 adds to the molecules that are known to regulate the rapid turnover of beta-catenin.

Show MeSH
Related in: MedlinePlus