AP-2β enhances p53-mediated transcription of the αB-crystallin gene through stabilizing p53.

The αB-crystallin (CRYAB) is a member of the small heat shock protein family that can be induced by various stresses and pathological conditions. Aberrant expression of CRYAB has been shown to be associated with several neurological diseases and malignant neoplasms. To identify transcriptional regulators of CRYAB expression, we examined its promoter for binding sites of transcription factors and identified four potential AP-2 binding sites in addition to a p53 binding site reported previously. Although the CRYAB promoter contains four consensus binding sequences of AP-2 and can be activated by AP-2α either in the presence or absence of p53, the luciferase assay showed that AP-2β alone does not regulate the activity of the CRYAB promoter in the absence of p53. However, in the presence of p53, AP-2β can significantly increase the luciferase activities of both the CRYAB promoter and reporter vector pp53-TA-luc, which contains a p53-responsive element, but no AP-2 binding sites. These data suggest that AP-2β enhances transactivation of p53 and regulates CRYAB transcription via p53. Further study demonstrated that AP-2β interacts with p53 and augments its protein stability. Taken together, our results indicate that AP-2β up-regulates the transcription of the CRYAB gene through stabilizing p53.