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MDM2 Overexpression Cooperates With Mutant CDK4 in Mammary Cell Transformation and Tumorigenesis

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Annual summary 1 Jul 2003-30 Jun 2004

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In an effort to gain a better understanding of the consequence of deregulated CDK4 activity in vivo, we generated knock-in transgenic mice that expresses a tumor derived mutant form of CDK4 r24c. Interestingly, these mice are very prone to develop tumors of different cellular origins, including breast tumors 1. Since the p53 tumor suppressor pathway is an inhibitor of oncogene induced transformation and is inactivated in a high percentage of mouse and human tumors, we decided to determine if inactivation of the p53 pathway is an important step in CDK4 mutant induced tumorigenesis 2 3. Our investigation revealed that MDM2 is overexpressed in 3 out of 10 breast tumors from these transgenic mice and we have found no evidence that the p53 pathway is inactivated in these tumors that arise in these animals. MDM2 has oncogenic properties when overexpressed and high amounts of the protein are present in human cancers4-8. It is generally accepted that MDM2 promotes tumorigenesis by directly blocking the function of the p53 tumor suppressor. However, recent studies indicate that MDM2 promotes cell proliferation by mechanisms that are independent of inactivating p53, including by inhibiting the anti proliferative activity of Transforming Growth factor-beta 1 TGF beta 1 in breast tumors 9 10. Considering that we have found no evidence for loss of p53 function by p53 gene mutation or loss of p19ARF expression, the scope of this proposal is to address if MDM2 overexpression cooperates with mutant CDK4 in mammary cell transformation and tumorigenesis by affecting p53 independent proliferation control pathways.

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  • Genetic Engineering and Molecular Biology
  • Anatomy and Physiology
  • Medicine and Medical Research

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