Pin1 Regulates the Dynamics of c-Myc DNA Binding To Facilitate Target Gene Regulation and Oncogenesis

Abstract

The Myc oncoprotein is considered a master regulator of gene transcription by virtue of its ability to modulate the expression of a large percentage of all genes. However, mechanisms that direct Myc's recruitment to DNA and target gene selection to elicit specific cellular functions have not been well elucidated. Here, we report that the Pin1 prolyl isomerase enhances recruitment of serine 62-phosphorylated Myc and its coactivators to select promoters during gene activation, followed by promoting Myc's release associated with its degradation. This facilitates Myc's activation of genes involved in cell growth and metabolism, resulting in enhanced proproliferative activity, even while controlling Myc levels. In cancer cells with impaired Myc degradation, Pin1 still enhances Myc DNA binding, although it no longer facilitates Myc degradation. Thus, we find that Pin1 and Myc are cooverexpressed in cancer, and this drives a gene expression pattern that we show is enriched in poor-outcome breast cancer subtypes. This study provides new insight into mechanisms regulating Myc DNA binding and oncogenic activity, it reveals a novel role for Pin1 in the regulation of transcription factors, and it elucidates a mechanism that can contribute to oncogenic cooperation between Pin1 and Myc.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.01455-12.

ACKNOWLEDGMENTS

We thank Karyn Taylor for her help with the preparation and ordering of reagents and Brittany Allen-Peterson for her helpful comments in preparing the manuscript. We also thank Devorah Goldman, Hilary Clark, and William H. Fleming for providing the NOD/SCID γ-chain-null mice and M. S. Dai for providing the acetylated histone H4 antibody. We thank Megan Troxell and Chris Corless for providing the matched normal and tumor breast cancer patient samples. We thank Paul Spellman for his suggestions regarding bioinformatic analysis of breast tumor samples and Anneleen Daemen for providing us the TCGA data set with associated subtyping. We also thank Jukka Westermarck for thoughtful discussions.

A.S.F. was supported by award number T32CA106195, “Training in the Molecular Basis of Skin/Mucosa Pathobiology,” to OHSU from the National Cancer Institute; a Collins Medical Trust Fund Award; and a Knight Cancer Institute Career Development Award. This work was also supported by R01/grant-num> CA100855 and CA129040, LLS 82325, DOD BC061306, and Komen BCTR0706821 to R.C.S.