1. Bcl-2 is the target of a UV-inducible apoptosis switch and a node for UV signaling.
- Author
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Knezevic D, Zhang W, Rochette PJ, and Brash DE
- Subjects
- Animals, Animals, Newborn, Apoptosis genetics, Cells, Cultured, Down-Regulation physiology, Down-Regulation radiation effects, E2F1 Transcription Factor deficiency, E2F1 Transcription Factor genetics, E2F1 Transcription Factor physiology, Mice, Mice, Knockout, Signal Transduction genetics, Tumor Suppressor Protein p53 deficiency, Tumor Suppressor Protein p53 genetics, Tumor Suppressor Protein p53 physiology, Apoptosis physiology, Apoptosis radiation effects, Proto-Oncogene Proteins c-bcl-2 metabolism, Proto-Oncogene Proteins c-bcl-2 radiation effects, Signal Transduction physiology, Signal Transduction radiation effects, Ultraviolet Rays
- Abstract
Sunlight's UVB radiation triggers cell signaling at multiple sites to induce apoptosis. The integration of these signal entry sites is not understood. Here we show that P53 and E2f1 constitute a UV-inducible apoptosis switch. At low-UV doses, wild-type cells resemble the OFF state of an siP53-treated cell, whereas at high-UV doses, the apoptosis frequency transitions to the fully ON behavior of an siE2f1-treated cell. The switch's target is Bcl-2: Rapid Bcl-2 down-regulation in response to UVB-induced DNA photoproducts is lost in P53-deficient cells, but, as for apoptosis, is restored when both P53 and its inhibited target E2f1 are absent. P53's down-regulation of Bcl-2 is mediated entirely through E2f1. Bcl-2 is also down-regulated by a separate pathway triggered by DNA photoproducts in the absence of P53 and E2f1. Four UV pathways terminating on Bcl-2 contribute to apoptosis after UVB irradiation. The apoptosis lost in p53(-/-) is completely restored by siBcl-2, implying that Bcl-2 is a rate-limiting member of this network. These results identify Bcl-2 as an integrator of several UV-induced proapoptotic signals and show that it, in turn, suppresses a direct UV-apoptosis pathway. UV-induced apoptosis requires both UV activation of the direct pathway and a separate UV disinhibition of this pathway through P53-E2f1-Bcl-2.
- Published
- 2007
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