Inhibition of ornithine decarboxylase activity and cell proliferation by ultraviolet B radiation in EGF-stimulated cultured human epidermal keratinocytes.
Irradiation of EGF-stimulated human keratinocytes in vitro with ultraviolet B (UVB) radiation inhibited both ornithine decarboxylase (ODC) activity and cellular proliferation. A dose-dependent reduction in ODC activity occurred in primary cultures of adult facial keratinocytes and neonatal foreskin keratinocytes, and in an SV40-transformed keratinocyte cell line derived from neonatal foreskin. When SV40-transformed keratinocytes were treated with epidermal growth factor (EGF), ODC activity was induced up to 21 times in the absence of ultraviolet radiation. However, pre-treatment with UVB significantly reduced the EGF induction of ODC. For example, 85% less ODC activity was observed in cultures treated with EGF (10 ng/ml) plus 2.5 mJ/cm2 of UVB than cultures treated with EGF alone. To assess the effect of UVB on cell proliferation, normal human epidermal keratinocytes grown in medium containing EGF were irradiated with 5 and 10 mJ/cm2 UVB. At days 3 and 5 post-irradiation a significant (up to 78%) decrease in proliferation was observed. Nevertheless, the mean proportion of viable to dead cells remained similar in both UVB-treated and non-irradiated cell cultures. Northern blot analysis of total RNA isolated from irradiated and sham-irradiated cultures showed that UVB caused approximately a one third reduction in steady-state ODC mRNA levels in EGF-stimulated keratinocyte cultures. Because ODC is an enzyme required for cell proliferation, we propose that the UVB-induced decrease in cell proliferation may result at least in part from UVB inhibition of ODC mRNA accumulation and reduced enzyme activity.
Prystowsky
J H
JH
Department of Dermatology, Columbia University, New York, New York 10032.
Clevenger
C V
CV
Zheng
Z S
ZS
D002455:Cell Division / Q000187:drug effects / Q000528:radiation effects; D002478:Cells, Cultured; D000078404:Epidermal Cells; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D004817:Epidermis / Q000378:metabolism* / Q000528:radiation effects*; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects*; D009955:Ornithine Decarboxylase / Q000235:genetics; D065108:Ornithine Decarboxylase Inhibitors; D012333:RNA, Messenger / Q000378:metabolism; D014466:Ultraviolet Rays
D065108:Ornithine Decarboxylase Inhibitors; D012333:RNA, Messenger; D004815:Epidermal Growth Factor; D009955:Ornithine Decarboxylase