We are interested in determining the function of the c-myc proto-oncogene in normal cells and how misregulation or overexpression of the c-Myc protein can induce cell transformation. Functional studies have demonstrated the requirement for a small 20 amino acid segment from the N-terminus (called Myc homology box II or MBII) that is conserved in all members of the Myc family of proteins. We purified, cloned and characterized a nuclear cofactor, called TRRAP, for TRansformation/tRansactivation Associated Protein, that is dependent on MBII for binding to Myc. The discovery of TRRAP proved to be a seminal discovery in the Myc field because it provided a link between Myc and chromatin modifying complexes that acetylate histones. While the recruitment of HAT activity by Myc is clearly important for its function, we have recently discovered a second mechanism through which Myc can activate gene expression (Cowling and Cole, Mol. Cell. Biol. 27, 2059-2073). We found that Myc can induce elevated phosphorylation of the RNA polymerase II carboxy- terminal domain (CTD) and increased methylation of mRNA caps to enhance the translation of both Myc target gene and other mRNAs. Modulation of cap methylation has not previously been considered as a regulated step in mammalian gene expression, but our published and preliminary data argue that cap methylation has a substantial role in regulating gene expression that has been completely overlooked by the molecular biology field. Cap methylation provides a mechanism to directly link transcription and translation of specific genes. The characterization of the precise mechanism governing this novel mode of gene regulation is in its infancy and will be a major focus of the project.
The specific aims are as follows:
Specific Aim 1 : Myc-dependent mRNA cap methylation. We will determine the mechanism of a novel Myc- dependent differential mRNA cap methylation. Studies will range from defining the fundamental mechanism of differential cap methylation to mapping of the cis-acting determinants governing which mRNAs are affected.
Specific Aim 2 : Nuclear factors involved in Myc target gene activation. We will determine the role of individual HATs and cofactors in the activation of specific Myc target genes. A particular focus will be the EPC1 protein, which appears to be excluded from TRRAP complexes by Myc binding. We will also examine potential HAT-independent functions of TRRAP complexes which may involve a recently described histone deubiquitinating protease.
Specific Aim 3 : In vivo acetylation of Myc protein. We will determine the functional significance of lysine acetylation found on native Myc protein. We will determine which HAT is responsible for acetylation and if acetylation is regulated by growth or oncogenic transformation.
Cancer is one of the leading causes of death worldwide, and mutations in the gene called c-myc are found in 15-20% of all cancer. Myc functions by binding to DNA and regulating other genes, but how it achieves this remains poorly understood. The goal of this project is to determine which cellular proteins associate tightly with Myc and how these Myc-associated proteins mediate Myc regulatory activity. A better understanding of Myc function will open new avenues for the diagnosis and treatment of cancer. ? ? ? ? ?
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