| 1. |
- Appelqvist, Hanna, et al.
(author)
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Lysosomal exocytosis and caspase-8-mediated apoptosis in UVA-irradiated keratinocytes
- 2013
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In: Journal of Cell Science. - : Company of Biologists. - 0021-9533 .- 1477-9137. ; 126:24, s. 5578-5584
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Journal article (peer-reviewed)abstract
- Ultraviolet (UV) irradiation is a major environmental carcinogen involved in the development of skin cancer. To elucidate the initial signaling during UV-induced damage in human keratinocytes, we investigated lysosomal exocytosis and apoptosis induction. UVA, but not UVB, induced plasma membrane damage, which was repaired by Ca2+-dependent lysosomal exocytosis. The lysosomal exocytosis resulted in extracellular release of cathepsin D and acid sphingomyelinase (aSMase). Two hours after UVA irradiation, we detected activation of caspase-8, which was reduced by addition of anti-aSMAse. Furthermore, caspase-8 activation and apoptosis was reduced by prevention of endocytosis and by the use of cathepsin inhibitors. We conclude that lysosomal exocytosis is part of the keratinocyte response to UVA and is followed by cathepsin-dependent activation of caspase-8. The findings have implications for the understanding of UV-induced skin damage and emphasize that UVA and UVB initiate apoptosis through different signaling pathways in keratinocytes.
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| 2. |
- Appelqvist, Hanna, 1981-
(author)
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Lysosomal Membrane Stability and Cathepsins in Cell Death
- 2012
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Doctoral thesis (other academic/artistic)abstract
- Lysosomes are acidic organelles that are critically involved in a number of physiological processes, including macromolecule degradation, endocytosis, autophagy, exocytosis and cholesterol homeostasis. Several pathological conditions, such as cancer, neurodegenerative disorders and lysosomal storage diseases, involve lysosomal disturbances, indicating the importance of the organelle for correct cellular function. The aim of this thesis was to investigate the role of lysosomes in cell death signaling.Previous studies have shown that permeabilization of the lysosomal membrane and release of hydrolytic enzymes such as cathepsin D to the cytosol occurs during apoptosis. We identified Bid and 14-3-3 proteins as cytosolic targets of cathepsin D in human fibroblasts. Truncated Bid, generated by cathepsin D proteolytic cleavage, stimulates Bax-mediated release of pro-apoptotic factors from the mitochondria, thereby engaging the intrinsic pathway to apoptosis.Since the presence of cathepsins in the cytosol is sufficient to induce apoptosis, the permeability of the lysosomal membrane influences the fate of the cell. In this thesis, we demonstrated that the stability of the lysosomal membrane can be manipulated by altering the lysosomal cholesterol content. Cells with high lysosomal cholesterol content were less prone to undergo apoptosis when challenged with stimuli known to induce lysosome-mediated cell death. In addition, cholesterol accumulation was associated with increased expression of lysosome-associated membrane proteins and storage of other lipids; however, these factors did not contribute to lysosomal stabilization.Lysosomal membrane permeabilization and cathepsins contribute to ultraviolet (UV) irradiation-induced apoptosis. We demonstrate plasma membrane damage induced by UVA irradiation to be rapidly repaired by lysosomal exocytosis in human keratinocytes. Despite efficient plasma membrane resealing, the cells underwent apoptosis, which was dependent on early activation of caspase-8. The activation of caspase-8 was lysosome-dependent and occurred in vesicles positive for lysosomal markers.This thesis demonstrates the importance of lysosomal stability for apoptosis regulation and that this stability can be influenced by drug intervention. Modulation of the lysosomal membrane permeability may have potential for use as a therapeutic strategy in conditions associated with accelerated or repressed apoptosis.
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| 3. |
- Appelqvist, Hanna, et al.
(author)
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The lysosome: from waste bag to potential therapeutic target
- 2013
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In: Journal of Molecular Cell Biology. - : Oxford University Press (OUP): Policy B - Oxford Open Option D. - 1674-2788 .- 1759-4685. ; 5:4, s. 214-226
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Research review (peer-reviewed)abstract
- Lysosomes are ubiquitous membrane-bound intracellular organelles with an acidic interior. They are central for degradation and recycling of macromolecules delivered by endocytosis, phagocytosis, and autophagy. In contrast to the rather simplified view of lysosomes as waste bags, nowadays lysosomes are recognized as advanced organelles involved in many cellular processes and are considered crucial regulators of cell homeostasis. The function of lysosomes is critically dependent on soluble lysosomal hydrolases (e.g. cathepsins) as well as lysosomal membrane proteins (e.g. lysosome-associated membrane proteins). This review focuses on lysosomal involvement in digestion of intra- and extracellular material, plasma membrane repair, cholesterol homeostasis, and cell death. Regulation of lysosomal biogenesis and function via the transcription factor EB (TFEB) will also be discussed. In addition, lysosomal contribution to diseases, including lysosomal storage disorders, neurodegenerative disorders, cancer, and cardiovascular diseases, is presented.
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| 4. |
- Thunell, Lena, et al.
(author)
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MDM2 SNP309 promoter polymorphism confers risk for hereditary melanoma
- 2014
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In: Melanoma research. - : Lippincott, Williams andamp; Wilkins. - 0960-8931 .- 1473-5636. ; 24:3, s. 190-197
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Journal article (peer-reviewed)abstract
- The p53 pathway regulates stress response, and variations in p53, MDM2, and MDM4 may predispose an individual to tumor development. The aim of this study was to study the impact of genetic variation on sporadic and hereditary melanoma. We have analyzed a combination of three functionally relevant variants of the p53 pathway in 258 individuals with sporadic malignant melanomas, 50 with hereditary malignant melanomas, and 799 healthy controls. Genotyping was performed by PCR-restriction fragment length polymorphism, pyrosequencing, and allelic discrimination. We found an increased risk for hereditary melanoma in MDM2 GG homozygotes, which was more pronounced among women (P=0.035). In the event of pairwise combinations of the single nucleotide polymorphisms, a risk elevation was shown for MDM2 GG homozygotes/p53 wild-type Arg in hereditary melanoma (P=0.01). Individuals with sporadic melanomas of the superficial spreading type, including melanoma in situ, showed a slightly higher frequency of the MDM2 GG genotype compared with those with nodular melanomas (P=0.04). The dysplastic nevus phenotype, present in the majority of our hereditary melanoma cases and also in some sporadic cases, further enhanced the effect of the MDM2 GG genotype on melanoma risk (P=0.005). In conclusion, the results show an association between MDM2 SNP309 and an increased risk for hereditary melanoma, especially among women. Analysis of sporadic melanoma also shows an association between MDM2 and the superficial spreading melanoma subtype, as well as an association with the presence of dysplastic nevi in sporadic melanoma.
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| 5. |
- Wäster, Petra, et al.
(author)
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Cell fate regulated by nuclear factor-κB- and activator protein-1-dependent signalling in human melanocytes exposed to ultraviolet A and ultraviolet B.
- 2014
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In: British Journal of Dermatology. - : John Wiley & Sons. - 0007-0963 .- 1365-2133. ; 171:6, s. 1336-1346
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Journal article (peer-reviewed)abstract
- BACKGROUND: Ultraviolet (UV) radiation constitutes an important risk factor for malignant melanoma, but the wavelength responsible for the initiation of this disease is not fully elucidated. Solar UV induces multiple signalling pathways that are critical for initiation of apoptotic cell death as a cellular defence against malignant transformation.OBJECTIVES: To evaluate the involvement of the transcription factors nuclear factor (NF)-κB and activator protein (AP)-1 in the signalling pathways induced by UVA or UVB irradiation in human melanocytes.METHODS: Primary cultures of normal human melanocytes were irradiated with UVA or UVB, and the concomitant DNA damage and redox alterations were monitored. The resulting activation of the NF-κB and AP-1 signalling pathways and subsequent apoptosis were studied.RESULTS: UVB irradiation causes DNA damage detected as formation of cyclobutane pyrimidine dimers, while UVA induces increased levels of 8-hydroxydeoxyguanosine and lipid peroxidation. UVA and UVB initiate phosphorylation of c-Jun N-terminal protein kinase and extracellular signal-regulated kinase, and the apoptosis signalling pathways converge into a common mechanism. Downregulation of c-Jun suppresses AP-1-mediated signalling and prevents apoptosis upstream of lysosomal and mitochondrial membrane permeabilization, whereas inhibition of NF-κB by SN50 increases apoptosis.CONCLUSIONS: We conclude that AP-1 induces proapoptotic signalling, whereas NF-κB is a key antiapoptotic/prosurvival factor in both UVA- and UVB-induced cellular damage in human melanocytes, which might in turn impact melanoma development and progression.
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| 6. |
- Wäster, Petra, et al.
(author)
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Sunbathing : What’ve lysosomes got to do with it?
- 2014
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In: Communicative & Integrative Biology. - Austin, Texas, USA : Landes Biosciences. - 1942-0889. ; 7:1, s. e28723-1-e28723-5
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Journal article (peer-reviewed)abstract
- Solar radiation is an important risk factor for skin cancer, the incidence of which is increasing, especially in the fair-skinned populations of the world. While the ultraviolet (UV)B component has direct DNA damaging ability, UVA-induced effects are currently mainly attributed to the production of reactive oxygen species. In our recent study, we compared the effects of UVA and UVB radiation on human keratinocytes and found that UVA-induced plasma membrane damage was rapidly repaired by lysosomal exocytosis, which was detected based on the expression of lysosomal membrane associated protein-1 (LAMP-1) on the plasma membrane of non-permeabilized cells. Later, the keratinocytes died through caspase-8 mediated apoptosis. In contrast, the plasma membranes of keratinocytes exposed to UVB showed no LAMP-1 expression, and, although the cells died by apoptosis, no initial caspase-8 activity was detected. We have also demonstrated the occurrence of UVA-induced lysosomal exocytosis in reconstructed skin and shown the relocation of lysosomes from the center of cells to the vicinity of the plasma membrane. Thus, we suggest that lysosomal exocytosis also occurs in keratinocytes covered by the stratum corneum following exposure to UVA. Our findings provide new insight into the mechanism of UVA-induced skin damage.
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| 7. |
- Wäster, Petra, et al.
(author)
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Ultraviolet exposure of melanoma cells induces fibroblast activation protein-alpha in fibroblasts: Implications for melanoma invasion
- 2011
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In: International Journal of Oncology. - : Spandidos Publications. - 1019-6439 .- 1791-2423. ; 39:1, s. 193-202
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Journal article (peer-reviewed)abstract
- Fibroblast activation protein-alpha (FAP-alpha) promotes tumor growth and cell invasiveness through extracellular matrix degradation. How ultraviolet radiation (UVR), the major risk factor for malignant melanoma, influences the expression of FAP-alpha is unknown. We examined the effect of UVR on FAP-alpha expression in melanocytes, keratinocytes and fibroblasts from the skin and in melanoma cells. UVR induces upregulation of FAP-alpha in fibroblasts, melanocytes and primary melanoma cells (PM) whereas keratinocytes and metastatic melanoma cells remained FAP-alpha negative. UVA and UVB stimulated FAP-alpha-driven migration and invasion in fibroblasts, melanocytes and PM. In co-culture systems UVR of melanocytes, PM and cells from regional metastases upregulated FAP-alpha in fibroblasts but only supernatants from non-irradiated PM were able to induce FAP-alpha in fibroblasts. Further, UV-radiated melanocytes and PM significantly increased FAP-alpha expression in fibroblasts through secretory crosstalk via Wnt5a, PDGF-BB and TGF-beta 1. Moreover, UV radiated melanocytes and PM increased collagen I invasion and migration of fibroblasts. The FAP-alpha/DPPIV inhibitor Gly-ProP(OPh)(2) significantly decreased this response implicating FAP-alpha/DPPIV as an important protein complex in cell migration and invasion. These experiments suggest a functional association between UVR and FAP-alpha expression in fibroblasts, melanocytes and melanoma cells implicating that UVR of malignant melanoma converts fibroblasts into FAP-alpha expressing and ECM degrading fibroblasts thus facilitating invasion and migration. The secretory crosstalk between melanoma and tumor surrounding fibroblasts is mediated via PDGF-BB, TGF-beta 1 and Wnt5a and these factors should be evaluated as targets to reduce FAP-alpha activity and prevent early melanoma dissemination.
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