Functional Definition of MYC Acetylation

MYC是一种靶向大部分基因组（约15%）的转录因子，在正常细胞中受到严格调控，对大多数动物的正常发育和体内平衡至关重要。MYC表达失控（如过表达）在小鼠中具有致瘤性，并与人类大多数类型的癌症相关。MYC解除管制可能通过c-myc基因本身的改变（例如，易位和扩增）或上游信号通路的异常激活而发生，上游信号通路激活c-myc基因表达和/或通过翻译后修饰（PTMs）增加MYC蛋白的稳定性。然而，MYC的PTMs特征尚不明确，其在MYC的多种细胞和分子活动中的作用仍不明确且存在争议。直到最近，一些残基的磷酸化和o -糖基化是唯一被报道的PTMs，它们影响MYC的泛素化和蛋白酶体的降解。我们的实验室最近发现了MYC的新型PTMs，并发现MYC在几个赖氨酸(K)残基上被具有组蛋白乙酰转移酶（HAT）活性的转录共激活因子（即GCN5和p300）乙酰化。我研究的总体目标是提供明确的证据，证明哺乳动物细胞中的天然MYC是通过乙酰化调节的，并确定MYC乙酰化在特定残基上的细胞和分子功能。

MYC is a transcription factor that targets a large fraction (~15%) of the genome and is tightly regulated in normal cells and essential for normal development and homeostasis in most animals. Deregulated MYC expression (e.g., overexpression) is tumorigenic in mice and associated with most types of cancer in humans. MYC deregulation may occur via alterations of the c-myc gene itself (e.g., translocation and amplification) or via aberrant activation of upstream signaling pathways that activate c-myc gene expression and/or increase MYC protein stability via post-translational modifications (PTMs). The PTMs of MYC are, however, poorly characterized and their roles in the multiple cellular and molecular activities of MYC are still poorly defined and controversial. Until recently phosphorylation and O-glycosylation of a few residues were the only PTMs reported, which affect MYC ubiqitination and degradation by the proteasome. Our lab recently uncovered novel PTMs of MYC and found that MYC is acetylated at several lysine (K) residues by transcription coactivators with histone acetyltransferase (HAT) activity (i.e., GCN5 and p300). The general objective of my research is to provide definitive evidence that native MYC in mammalian cells is regulated via acetylation and to define the cellular and molecular functions of MYC acetylation at specific residues. AIM 1: To establish and characterize acetylation of native MYC in mammalian cells using acetylated site-specific antibodies (MYC-K148Ac, MYC-K157Ac, MYC-K323Ac) Acetylation of endogenous MYC has yet to be demonstrated in any cell type. I will use new antibodies that recognize specifically human MYC acetylated residues K148, K157, and K323 to profile acetylation of MYC at these different sites in several non-transformed and transformed/cancer cell lines. AIM 2: To identify functions of MYC acetylated residues K148(149) and K157(158) I will test the role of MYC acetylated residues K148 and K157 (human coordinates homologous to mouse MYC K149 and K158) in MYC-induced cell proliferation, transformation and apoptosis. AIM 3: To establish and define the role(s) of MYC acetylation in target gene regulation Selected MYC target genes affected by the R158 (or R149) substitution identified in preliminary experiments (e.g. Nrf1) and in Aim 2 will be analyzed to tes the possible role of acetylation at K158 (or K149) in regulating MYC transcription functions. Various methods, including chromatin immunoprecipitation (ChIP) assays, RNA interference (RNAi), and reporter gene assays will be used.