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Targeted expression of c-Myc in the epidermis alters normal proliferation, differentiation and UV-B induced apoptosis
R L Waikel1, X J Wang, D R Roop
1Department of Cell Biology, Baylor College of Medicine, One Baylor Plaza, Houston, Texas, TX 77030, USA.
Abstract:
c-Myc overexpression has been associated with several types of human cancers. To study the role of c-myc in epidermal differentiation and carcinogenesis, a transgenic mouse model was created to overexpress c-Myc in the epidermis. Human c-myc 2 cDNA was subcloned into a 6.5 kb mouse loricrin expression vector, ML.myc2. This loricrin promoter primarily directs expression in the epidermis in both proliferating and differentiated keratinocytes. On day 4, ML.myc2 transgenic pups develop a hyperkeratotic phenotype, which progressively worsens until day 7. Upon histological analysis, both hyperplasia and hyperkeratosis were evident. Bromodeoxyuridine (BrdU) incorporation revealed that transgenic mice had a threefold increase in the number of proliferating cells as compared with a normal littermate. Proliferative cells in the ML.myc2 epidermis were also found to be suprabasal, suggesting an inhibition of terminal differentiation in keratinocytes. Inhibition of terminal differentiation by c-Myc overexpression was further suggested by aberrant expression of differentiation markers, keratin 1, keratin 6, loricrin, and filaggrin in ML.myc2 transgenic mice. Interestingly, ML.myc2 keratinocytes exhibit a reduced sensitivity to UV-B induced apoptosis, in vivo. In vitro studies reveal the reduced sensitivity of ML.myc2 keratinocytes to UV-B irradiation is growth factor dependent. These findings provide evidence that overexpression of c-Myc in the epidermis induces proliferation, inhibits terminal differentiation and decreases the sensitivity of keratinocytes to UV-B induced apoptosis.
Insights
Overexpression of c-Myc in mouse epidermis causes skin thickening and inhibits normal cell differentiation. This also reduces keratinocyte sensitivity to UV-B induced apoptosis, suggesting a role in skin cancer development.
Area of Science:
- Molecular Biology
- Dermatology
- Oncology
Background:
- c-Myc overexpression is linked to human cancers.
- Understanding c-Myc's role in epidermal differentiation and carcinogenesis is crucial.
Purpose of the Study:
- To investigate the function of c-Myc in epidermal differentiation and carcinogenesis.
- To create and analyze a transgenic mouse model overexpressing c-Myc in the epidermis.
Main Methods:
- Generated transgenic mice (ML.myc2) using a loricrin promoter to drive human c-myc 2 cDNA expression in epidermal keratinocytes.
- Performed histological analysis, Bromodeoxyuridine (BrdU) incorporation assays, and assessed differentiation marker expression (keratin 1, keratin 6, loricrin, filaggrin).
- Evaluated UV-B induced apoptosis sensitivity in ML.myc2 keratinocytes both in vivo and in vitro.
Main Results:
- ML.myc2 transgenic mice exhibited a progressive hyperkeratotic phenotype starting from day 4.
- Histological analysis revealed significant hyperplasia and hyperkeratosis.
- Transgenic mice showed a threefold increase in proliferating cells, with proliferation occurring in suprabasal layers, indicating inhibited terminal differentiation.
- Aberrant expression of key differentiation markers was observed.
- ML.myc2 keratinocytes demonstrated reduced sensitivity to UV-B induced apoptosis, which was growth factor dependent in vitro.
Conclusions:
- Epidermal c-Myc overexpression induces keratinocyte proliferation and inhibits terminal differentiation.
- c-Myc overexpression in the epidermis reduces keratinocyte sensitivity to UV-B induced apoptosis.
- These findings highlight c-Myc's role in epidermal carcinogenesis and UV-B response.