|Tissue-specific regulation of Apaf-1 expression by p53|
Authors: Clement K. Ho, Jason A. Bush, Gang Li
Department of Medicine, Division of Dermatology, Vancouver Hospital and Health Sciences Centre, University of British Columbia, Vancouver, BC, V6H 3Z6, Canada
The p53 tumor suppressor is a transcription factor that regulates cell cycle and apoptosis in response to a variety of environmental stress conditions. Recent studies indicated that the apoptotic protease activating factor-1 (Apaf-1) is a direct transcriptional target of p53 in DNA damage-induced apoptosis. However, the dependence of Apaf-1 expression on p53 has not been shown in normal physiological conditions. To further investigate their relationship, we first examined Apaf-1 protein levels in seven organs including brain, heart, kidney, liver, lung, spleen, and testis of wild-type (p53+/+) and p53-deficent (p53−/−) mice by Western blot analysis. The heart and spleen of the p53−/− mice showed a reduced Apaf-1 protein expression compared with the p53+/+ controls, while other organs did not show significant difference. The results from Western blot analysis were further confirmed by immunohistochemistry. Semi-quantitative RT-PCR was then employed to determine the expression of Apaf-1 transcripts. Similarly, we detected a lower Apaf-1 mRNA level in the heart and spleen of p53−/− mice compared with the p53+/+ controls, supporting a transcriptional upregulation of Apaf-1 by p53. Taken together, these results demonstrate that p53 regulation of Apaf-1 expression is tissue-specific.