| 1. |
- Adlerz, Linda, et al.
(author)
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Accumulation of the amyloid precursor-like protein APLP2 and reduction of APLP1 in retinoic acid-differentiated human neuroblastoma cells upon curcumin-induced neurite retraction
- 2003
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In: Brain Research. Molecular Brain Research. - : Elsevier BV. - 0169-328X .- 1872-6941. ; 119:1, s. 62-72
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Journal article (peer-reviewed)abstract
- 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 NFκB, 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.
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| 2. |
- Adlerz, Linda, et al.
(author)
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IGF-1-induced Processing of the Amyloid Precursor Protein Family Is Mediated by Different Signaling Pathways
- 2007
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In: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 282:14, s. 10203-10209
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Journal article (peer-reviewed)abstract
- The mammalian amyloid precursor protein (APP) protein family consists of the APP and the amyloid precursor-like proteins 1 and 2 (APLP1 and APLP2). The neurotoxic amyloid beta-peptide (Abeta) originates from APP, which is the only member of this protein family implicated in Alzheimer disease. However, the three homologous proteins have been proposed to be processed in similar ways and to have essential and overlapping functions. Therefore, it is also important to take into account the effects on the processing and function of the APP-like proteins in the development of therapeutic drugs aimed at decreasing the production of Abeta. Insulin and insulin-like growth factor-1 (IGF-1) have been shown to regulate APP processing and the levels of Abeta in the brain. In the present study, we show that IGF-1 increases alpha-secretase processing of endogenous APP and also increases ectodomain shedding of APLP1 and APLP2 in human SH-SY5Y neuroblastoma cells. We also investigated the role of different IGF-1-induced signaling pathways, using specific inhibitors for phosphatidylinositol 3-kinase and mitogen-activated protein kinase (MAPK). Our results indicate that phosphatidylinositol 3-kinase is involved in ectodomain shedding of APP and APLP1, but not APLP2, and that MAPK is involved only in the ectodomain shedding of APLP1.
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| 3. |
- Axelsson, Viktoria, et al.
(author)
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Gliotoxin induces caspase-dependent neurite degeneration and calpain-mediated general cytotoxicity in differentiated human neuroblastoma SH-SY5Y cells.
- 2006
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In: Biochem Biophys Res Commun. - 0006-291X. ; 345:3, s. 1068-74
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Journal article (peer-reviewed)abstract
- In this study, a significant increase by 50% in intracellular free calcium concentration ([Ca(2+)](i)) was observed in differentiated human neuroblastoma (SH-SY5Y) cells after exposure to 0.25microM of the fungal metabolite gliotoxin for 72h. Further, the involvement of caspases and calpains was demonstrated to underlie the gliotoxin-induced cytotoxic and neurite degenerative effects. The caspase inhibitor Z-VAD-fmk almost completely reduced the neurite degeneration from 40% degeneration of neurites to 5% as compared to control. Inhibition of calpains with calpeptin significantly attenuated gliotoxin-induced cytotoxicity, determined as reduction in total cellular protein content, from 43% to 14% as compared to control cells. Western blot analyses of alphaII-spectrin breakdown fragments confirmed activity of the proteases, and that alphaII-spectrin was cleaved by caspases in gliotoxin-exposed cells. These results show that calpains and caspases have a role in the toxicity of gliotoxin in differentiated SH-SY5Y cells and that the process may be Ca(2+)-mediated.
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| 4. |
- Holback, Sofia, et al.
(author)
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Increased processing of APLP2 and APP with concomitantformation of APP intracellular domains in BDNF and retinoic acid-differentiated human neuroblastoma cells
- 2005
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In: Journal of Neurochemistry. - : Wiley. - 0022-3042 .- 1471-4159. ; 95:4, s. 1059-1068
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Journal article (peer-reviewed)abstract
- The amyloid precursor protein (APP) belongs to a conserved gene family, also including the amyloid precursor-like proteins, APLP1 and APLP2. We have previously shown that all members of the APP protein family are up-regulated upon retinoic acid (RA)-induced neuronal differentiation of SH-SY5Y neuroblastoma cells. Here, we demonstrate that RA also affects the processing of APLP2 and APP, as shown by increased shedding of both sAPLP2 and sAPPalpha as well as elevated levels of the APP intracellular domains (AICDs). Brain-derived neurotrophic factor (BDNF) has been reported to induce APP promoter activity and RA induces expression of the tyrosine kinase receptor B (TrkB) in neuroblastoma cells. We show that the increase in shedding of both APLP2 and APP in response to RA is not mediated through the TrkB receptor. However, BDNF concomitant with RA increased the expression of APP even further. In addition, the secretion of sAPLP2 and sAPPalpha, as well as the levels of AICDs increased in response to BDNF. In contrast, the levels of membrane-bound APP C-terminal fragment C99 significantly decreased. Our results suggest that RA and BDNF shifts APP processing towards the alpha-secretase pathway. In addition, we show that RA and BDNF regulate N-linked glycosylation of APLP1.
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| 5. |
- Holback, Sofia, et al.
(author)
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PI3-K- and PKC-dependent up-regulation of APP processing enzymes by retinoic acid
- 2008
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In: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 365:2, s. 298-303
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Journal article (peer-reviewed)abstract
- Retinoic acid stimulates α-secretase processing of amyloid precursor protein (APP) and decreases β-secretase cleavage that leads to amyloid-β formation. Here, we investigated the effect of retinoic acid on the two putative α-secretases, the disintegrin metalloproteinases ADAM10 and TACE, and the β-site cleaving enzyme BACE1, in human neuroblastoma SH-SY5Y cells. Western blot analysis showed that exposure to retinoic acid resulted in significantly increased levels of ADAM10 and TACE, suggesting that regulation of α-secretases causes the effects on APP processing. The presence of the phosphatidylinositol 3-kinase inhibitor LY 294002 selectively reduced the effect on ADAM10 protein levels but not on ADAM10 mRNA levels as determined by RT-PCR. On the other hand, the effect on TACE was shown to be dependent on protein kinase C, since it was completely blocked in the presence of the inhibitor bisindolylmaleimide XI. Our data indicate that different signalling pathways are involved in retinoic acid-induced up-regulation of the secretases.
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| 6. |
- Holback, Sofia, 1978-
(author)
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Proteolytic processing of the Alzheimer APP protein family during neuronal differentiation
- 2009
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Doctoral thesis (other academic/artistic)abstract
- Increased amyloid-β (Aβ) load in the brain, neurite degeneration, neuronal loss, and decreased levels of several neurotrophins are among the characteristics of Alzheimer’s disease (AD). Generation of Aβ occurs when the amyloid precursor protein (APP) is proteolytically processed by β- and γ-secretases in the amyloidogenic pathway. However, Aβ formation is prevented if APP is cleaved by α- and γ- secretases in the non-amyloidogenic pathway. The normal function of APP is still not fully known. It seems clear that the different fragments that are produced during proteolytic processing have different bioactive properties. APP and its metabolites have been implicated in neurite outgrowth, synaptogenesis, cell adhesion, neuroprotection and apoptosis. The aim of this thesis was to investigate how neurotrophic factors affect the synthesis and processing of APP and its two mammalian paralogues the APP-like protein-1 and-2 (APLP1 and APLP2). We also wanted to determine how the expression levels of α- and β- secretases were affected in response to these factors. In addition, we wanted to analyze if the levels and function of the most well characterized APP adaptor protein, Fe65, was regulated during neuronal differentiation. Our results show that retinoic acid (RA), insulin-like growth factor-1 (IGF-1), and brain derived neurotrophic factor (BDNF) all regulate expression levels and processing of the APP protein family. Interestingly, the increased processing of the APP family involves different signaling pathways. The PI3-K/Akt pathway is involved in IGF-1-induced APP and APLP1, but not APLP2, processing. In addition, RA-induced expression of the α-secretase, a disintegrin and metalloproteinase (ADAM) 10 is dependent on PI3-K, whereas PKC is involved in RA-induced expression of another α-secretase, ADAM17/TACE. Furthermore, we present evidence that maturation of the adaptor protein Fe65, as well as its docking to APP, increases concomitant with neuronal differentiation.
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| 7. |
- Holback, Sofia, 1978-, et al.
(author)
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Retinoic acid stimulates maturation of the adaptor protein Fe65 and its binding to the amyloid precursor protein
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Other publication (other academic/artistic)abstract
- Retinoic acid (RA) stimulates both synthesis and processing of the amyloid precursor protein (APP) and its mammalian paralogues, the APP-like proteins 1 and 2 (APLP1 and APLP2). Previously, we have detected increased levels of the APP and APLP1 intracellular dolmans, AICD and ALID1 respectively, concomitant with RA-induced neuronal differentiation. Here we used Western blot analysis to show increased levels of the mature form of the adaptor protein Fe65 during RA- as well as nerve growth factor-induced differentiation. Co-immunoprecipitation studies also revealed that increased binding of Fe65 to APP and APLP1 occurred during neuronal differentiation. Furthermore, exposure to RA decreased the phosphorylation of Thr668 located in the cytoplasmic domain of APP.
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| 8. |
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| 9. |
- Koistinen, Niina, 1972-, et al.
(author)
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siRNA knock-down of Fe65 in SH-SY5Y cells decreases the levels of C-terminal fragments of APP without any effect on sAPPα secretion
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Other publication (other academic/artistic)abstract
- Fe65 is an adaptor protein that binds to the amyloid precursor protein (APP) within the 82YENPTY687 motif of APP which is important for amyloid β (Aβ) production. Considering that Fe65 binds to this motif, it can be hypothesized that Fe65 may influence the trafficking of APP and hence its processing by α- and/or β-secretase. Therefore in this study we wanted to determine how knock-down of Fe65 effects the processing of endogenous APP in human SH-SY5Y neuroblastoma cells. Our results showed that Fe65 knock-down did not have any effect on sAPPα secretion in SH-SY5Y cells. However, decreased levels of membrane-bound APP stubs C83 and C99 were observed, suggesting that Fe65 has a stabilizing effect on the C-terminal fragments. Furthermore, we wanted to investigate effects of retinoic acid (RA)-induced neronal differentiation on Fe65 expression. It has previously been shown that under these conditions mRNA and protein levels of APP increase concomitant with increased secretion of sAPPα, shifting the processing of APP to the more non-amyloidogenic pathway. We observed that RA-induced neuronal differentiation increases the protein levels of Fe65 in SH-SY5Y cells and gives rise to an electrophoretic mobility shift due to increased phosphorylation. The increased expression levels of Fe65 during neuronal differentiation concomitant with the increase of Fe65 phosphorylation, suggest that Fe65 and its phosphorylation may play a role during neuronal differentiation.
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