The different activities of the tumor suppressor p53 are tightly regulated by various negative and positive feedback loops, which allow accurate control of its function. Here we show that the p53-inducible ubiquitin E3 ligase Siah-1L can bind to the p53 phosphorylating kinase HIPK2 and thus allows its ubiquitination and proteasomal elimination. Siah-1L also eliminates the HIPK family member HIPK3, indicating that its activity is not restricted to one member of the HIPK family. The stimulating effect of HIPK2 on p53-triggered transcription is counteracted by Siah-1L, thus showing the occurrence of another negative feedback loop controlling the p53 response.
©2009 by Walter de Gruyter Berlin New York