Deregulated activity of Akt in epithelial basal cells induces spontaneous tumors and heightened sensitivity to skin carcinogenesis.
Aberrant activation of the phosphoinositide-3-kinase (PI3K)/PTEN/Akt pathway, leading to increased proliferation and decreased apoptosis, has been implicated in several human pathologies including cancer. Our previous data have shown that Akt-mediated signaling is an essential mediator in the mouse skin carcinogenesis system during both the tumor promotion and progression stages. In addition, overexpression of Akt is also able to transform keratinocytes through transcriptional and posttranscriptional processes. Here, we report the consequences of the increased expression of Akt1 (wtAkt) or constitutively active Akt1 (myrAkt) in the basal layer of stratified epithelia using the bovine keratin K5 promoter. These mice display alterations in epidermal proliferation and differentiation. In addition, transgenic mice with the highest levels of Akt expression developed spontaneous epithelial tumors in multiple organs with age. Furthermore, both wtAkt and myrAkt transgenic lines displayed heightened sensitivity to the epidermal proliferative effects of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) and heightened sensitivity to two-stage skin carcinogenesis. Finally, enhanced susceptibility to two-stage carcinogenesis correlated with a more sustained proliferative response following treatment with TPA as well as sustained alterations in Akt downstream signaling pathways and elevations in cell cycle regulatory proteins. Collectively, the data provide direct support for an important role for Akt signaling in epithelial carcinogenesis in vivo, especially during the tumor promotion stage.
Segrelles
Carmen
C
Molecular Oncology Unit, Division of Biomedicine, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, Madrid, Spain.
Lu
Jerry
J
Hammann
Brian
B
Santos
Mirentxu
M
Moral
Marta
M
Cascallana
José Luis
JL
Lara
M Fernanda
MF
Rho
Okkyung
O
Carbajal
Steve
S
Traag
Jeanine
J
Beltrán
Linda
L
Martínez-Cruz
Ana Belén
AB
García-Escudero
Ramón
R
Lorz
Corina
C
Ruiz
Sergio
S
Bravo
Ana
A
Paramio
Jesús M
JM
DiGiovanni
John
J
D000818:Animals; D002417:Cattle; D004848:Epithelium / Q000378:metabolism / Q000473:pathology*; D005786:Gene Expression Regulation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D011401:Promoter Regions, Genetic; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction; D012878:Skin Neoplasms / Q000139:chemically induced* / Q000378:metabolism / Q000473:pathology*; D013755:Tetradecanoylphorbol Acetate / Q000633:toxicity
D051057:Proto-Oncogene Proteins c-akt; D013755:Tetradecanoylphorbol Acetate