p53 staining in the small intestine of codon 72
polymorphic mice (P/P v. R/R)

We have found that a common polymorphism at codon 72 in p53 significantly influences the ability of this protein to induce programmed cell death. Specifically, cells containing the proline 72 variant of p53, which is much more common in African Americans than Caucasian Americans, demonstrate decreased apoptosis by p53. Along with our colleague Monica Hollstein, PhD (University of Leeds, UK), we have created the first mouse model for the codon 72 polymorphism of p53. This knock-in mouse contains a humanized version of p53 (Humanized p53 knock-in, or Hupki), encoding either the P72 or R72 variants. This mouse model shows that mice containing the P72 and R72 variants have significantly altered levels of apoptosis in different tissues. It also shows that these polymorphic variants have distinct transcriptional potential, as assessed by Quantitative RT-PCR. Our mouse model of the codon 72 polymorphism will be important in our efforts to understand inter-individual differences in cancer risk, and tailoring chemotherapy to different individuals based upon their genetics.Top

Increased apoptosis in the thymus of P/P mice

In addition to a common polymorphism at codon 72, p53 also has a rare polymorphism at codon 47. Wild type p53 encodes proline at this residue, but in a small percentage of African Americans it is serine (S47). We found that the S47 variant has reduced phosphorylation on serine 46, and decreased apoptotic function up to three-fold. Therefore, in terms of apoptotic ability, R72 > P72 > S47. In addition, we are in the process of creating an S47 mouse, in an effort to test the hypothesis that the altered apoptotic function of this variant impacts its ability to suppress tumor development.

p53 is a central signaling molecule in tumorigenesis and the response to therapy. We previously reported that three coding region variants in p53 have markedly different apoptotic potential in cell lines, and we now report similar findings in mice. Because the lesser-functioning S47 and P72 variants are significantly more common in African Americans, the proposed research will have direct impact on our understanding of disparities in cancer risk and efficacy of therapy in this population. Top

Silencing ARF suppresses myc-driven lymphoma
development

We have recently found that the p14ARF tumor suppressor induces an alternate form of cell death, known as autophagy. We also found that the pathway of autophagy is important to tumors, which typically exist under conditions of high metabolic stress. Inhibiting this pathway using chemical or genetic inhibitors greatly impedes tumor progression, suggesting that this pathway may be an Achilles Heel for cancer. Recently we have discovered inhibitors of ARF-mediated autophagy, and show that these inhibitors are potent anti-cancer agents and will continue our efforts to understand and exploit the autophagy pathway for cancer therapy. Top