Single UVB Overexposure Stimulates Melanocyte Proliferation in Murine Skin, in Contrast to Fractionated or UVA-1 Exposure

Melanoma, the cancer derived from the melanocytes of the skin, is becoming an ever more common cancer in the ageing population of the developed world and displays an intrinsic resistance to current therapies. This chemo resistance makes metastatic melanoma an extremely difficult cancer to treat leading to a 5 year survival rate of just 20%. As such, it is important to unearth new potential drug targets to increase the prospects for melanoma patients.Bfl-1 is a pro-survival protein of the Bcl-2 family of apoptosis regulating proteins. It has been found to be over-expressed in a small subset of chemo resistant tumours, including melanoma. Accordingly, I characterised the molecule in melanoma cells and determined its role in protecting these cells from chemotherapy-induced apoptosis. I elucidated the expression profile and half-lives of the protein and mRNA across a panel of melanoma cell-lines and healthy melanocytes. I also confirmed, using pathway specific inhibitors, that Bfl-1 was transcriptionally regulated by the NFB pathway and concluded through pulsechase experiments that Bfl-1 protein was degraded, at least in part, by the proteasome. Subcellular fractionation and indirect immunofluorescence techniques elucidated that Bfl-1 was located mostly at the mitochondria in both resting and apoptotic cells, with a diffuse level present throughout the cytoplasm. As well as characterising the protein in both melanoma cells and healthy primary melanocytes, I determined its role in the resistance of these cells to apoptosis. Over-expressed Bfl-1 was found to protect melanoma cells from apoptosis caused by a range of chemotherapeutic agents in A375 melanoma cells, which naturally expressed very low levels of Bfl-1. Further, knock down of Bfl-1 using siRNA technology in melanoma cells revealed the dependence of these cells on Bfl-1 for their resistance to certain chemotherapeutic agents currently used in melanoma treatment, including the MEK inhibitor PD901. All together, this research contributes to our understanding of Bfl-1 and highlights it as a potentially important therapeutic target in metastatic melanoma.

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“…As such, melanocytes in hairless SKH-2 mice were seen to proliferate in response to a single over-exposure of UVB radiation 440 .…”

Section: Introductionmentioning

confidence: 99%

Role of the pro-survival molecule Bfl-1 in melanoma

Hind

Carter

Harris

et al. 2015

The International Journal of Biochemistry & Cell Biology

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“…2 The UV-induced melanocyte proliferaton in the skin in vivo can be studied in laboratory mice. 5 However, mice only rarely develop melanomas after UV-exposure. Recently, genetically engineered mouse models of melanoma provide new opportunities to investigate the impact of UV irradiation on the pathogenesis of melanoma.…”

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confidence: 99%

Neonatal UVB exposure accelerates melanoma growth and enhances distant metastases in Hgf‐Cdk4^R24C C57BL/6 mice

Gaffal

Landsberg

Bald

et al. 2011

Intl Journal of Cancer

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Genetically engineered mouse models offer new opportunities to experimentally investigate the impact of UV on melanoma pathogenesis. Here we irradiated a cohort of newborn 15 Hgf-Cdk4 R24C mice on the pigmented C57BL/6 background with one erythemogenic dose of 6 kJ/m 2 UVB and compared the development of nevi and melanoma with a cohort of 30 untreated HgfCdk4 R24C mice. Neonatal UVB exposure decreased the latency and accelerated the growth of primary melanomas resulting in a significantly decreased time from melanoma onset to melanoma-related death (61 days vs. 96 days). Interestingly, we did not observe differences in the development of melanocytic nevi. Histopathological investigations revealed that UVB irradiation shifted the spectrum of melanomas toward a more aggressive phenotype with increased tumor cell proliferation, invasive growth and enhanced angiogenesis. Accordingly, we observed distal melanoma metastases in the lungs more frequently in the UV-irradiated than in the untreated cohort of Hgf-Cdk4 R24C mice (73% vs. 47%). UVB-induced melanomas only contained very few infiltrating immune cells and expressed very low levels of proinflammatory chemokines. Taken together, our results demonstrate that neonatal UVB exposure promoted the early appearance of rapidly enlarging primary melanomas in HgfCdk4 R24C C57BL/6 mice which showed enhanced invasive and metastatic behaviour without a persistent tumor-associated inflammatory response. The preferential impact of UVB irradiation on the progression of melanoma without an effect on the development of nevi supports the hypothesis that the molecular targets of UVB are involved in bypassing the proliferative arrest of transformed melanocytes without alerting a cellular immune response.Epidemiological studies demonstrate that individuals with fair skin and blond or red hair living in countries at low latitudes with high solar radiation levels have the highest incidence of malignant melanoma. 1 It has been proposed that intermittent intense UV exposure with sunburn during childhood precipitates the development of freckles and nevi because melanocytes with low melanin content and low basal DNA repair capacity are particularly susceptible to UV-induced mutations.2 This hypothesis would explain studies showing a direct correlation between sun exposure and the number of nevi in school children.3 A high nevus count and a family history of melanoma considerably increase the lifetime risk of developing a melanoma. Currently, the mechanisms by which UV radiation as an environmental carcinogen and host factors such as the individual genetic constitution contribute to melanomagenesis are incompletely understood.The biologic effects of UV radiation on cells in the skin have been studied in great detail in vitro and in vivo in mice and man. 4 Particular attention has been paid to the mechanisms responsible for DNA mutations which are of central importance for malignant transformation. UVB can directly induce DNA photoproducts such as cyclobutane pyrimidine dimers. In addition, b...

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“…The MED of Xpa and Csb mutants was between 135 and 270 J m À2 and the MED of Xpc knockouts and control mice was between 1080 and 2160 J m À2 (Berg et al, 2000). A lower MED for Xpa mice (62.5 Jm À2 ) was reported by van Schanke et al (2005), but the MED for control mice was also lower (500 Jm À2 ). Another acute effect of UVB is to elicit epidermal hyperplasia.…”

Section: Discussionmentioning

confidence: 63%

Mice with skin-specific DNA repair gene (Ercc1) inactivation are hypersensitive to ultraviolet irradiation-induced skin cancer and show more rapid actinic progression

et al. 2006

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Ercc1 has an essential role in the nucleotide excision repair (NER) pathway that protects against ultraviolet (UV)-induced DNA damage and is also involved in additional repair pathways. The premature death of simple Ercc1 mouse knockouts meant that we were unable to study the role of Ercc1 in the skin. To do this, we have used the Cre-lox system to generate a skin-specific Ercc1 knockout. With a Cre transgene under control of the bovine keratin 5 promoter we achieved 100% recombination of the Ercc1 gene in the epidermis. Hairless mice with Ercc1-deficient skin were hypersensitive to the short-term effects of UV irradiation, showing a very low minimal erythemal dose and a dramatic hyperproliferative response. Ultraviolet-irradiated mice with Ercc1-deficient skin developed epidermal skin tumours much more rapidly than controls. These tumours appeared to arise earlier in actinic progression and grew more rapidly than tumours on control mice. These responses are more pronounced than have been reported for other NER-deficient mice, demonstrating that Ercc1 has a key role in protecting against UV-induced skin cancer.

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Single UVB Overexposure Stimulates Melanocyte Proliferation in Murine Skin, in Contrast to Fractionated or UVA-1 Exposure

Cited by 51 publications

References 28 publications

Role of the pro-survival molecule Bfl-1 in melanoma

Role of the pro-survival molecule Bfl-1 in melanoma

Neonatal UVB exposure accelerates melanoma growth and enhances distant metastases in Hgf‐Cdk4^R24C C57BL/6 mice

Mice with skin-specific DNA repair gene (Ercc1) inactivation are hypersensitive to ultraviolet irradiation-induced skin cancer and show more rapid actinic progression

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Single UVB Overexposure Stimulates Melanocyte Proliferation in Murine Skin, in Contrast to Fractionated or UVA-1 Exposure

Cited by 51 publications

References 28 publications

Role of the pro-survival molecule Bfl-1 in melanoma

Role of the pro-survival molecule Bfl-1 in melanoma

Neonatal UVB exposure accelerates melanoma growth and enhances distant metastases in Hgf‐Cdk4R24C C57BL/6 mice

Mice with skin-specific DNA repair gene (Ercc1) inactivation are hypersensitive to ultraviolet irradiation-induced skin cancer and show more rapid actinic progression

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Neonatal UVB exposure accelerates melanoma growth and enhances distant metastases in Hgf‐Cdk4^R24C C57BL/6 mice