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Another Key to the p53 Door

July 29, 2004

Researchers at the Uppsala Branch of the Ludwig Institute for Cancer Research (LICR) have discovered that the transcription factor Yin Yang 1 (YY1) is a novel regulator of the tumor suppressor p53, which is inactivated in at least half of all human cancers. The p53 transcription factor plays a vital role in preventing cancer onset, by stimulating cells to commit suicide when their DNA is damaged by chemicals or UV exposure. Because YY1 prevents p53 from removing pre-cancerous cells, YY1 represents a hitherto unsuspected candidate for a source of p53-inactivating mutations, as well as a potential new target for future therapies.

According to the study published today in the Proceedings of the National Academy of Sciences USA, YY1 regulates p53 at multiple levels. First, YY1 uses the novel mechanism of causing Mdm2, a key oncogene that marks proteins for degradation, to have an enhanced interaction with p53. This results in a decrease in the amount of p53 in the cell. YY1 also directly blocks p53's interaction with its cofactors, such that p53 can no longer act as a transcription factor to cause cell suicide in response to DNA damage.

"In terms of possible therapies for the future, YY1's regulation of p53 at different levels means that we have new, different targeting options," says LICR's Dr. Johan Ericsson, the senior author of the study. "We know that we can use small molecules to prevent transcription factors from interacting with other proteins, so we can consider blocking YY1's direct interaction with p53 as a therapy option. We can also think about ways of disrupting the Mdm2 and YY1 interaction, and so prevent the indirect inhibition of p53."

For now, Ericsson and his team are focused on investigating the growing body of evidence that suggests YY1 could be a pivotal transcription factor in cancer. "YY1 interacts with several transcription factors involved in cancer, for example, Myc and Notch, and now we know it also regulates p53," says Ericsson. "No-one has yet looked at mutations in YY1, but the fact that it is associated with so many proteins implicated in tumorigenesis, suggests to me that YY1 could be a lot more important than anyone ever realized."

The present study continues a tradition of p53 research within LICR. The protein was discovered by Dr. Lloyd J. Old, the Director of LICR, in 1979. More recently, the ASPP family of proteins, which act to stimulate p53 activity in counter-balance to YY1, was discovered by Dr. Xin Lu, the Director-Designate of LICR's Branch at University College London, UK.

Ludwig Institute for Cancer Research