Oster Sara K, Mao Daniel Y L, Kennedy James, Penn Linda Z
Ontario Cancer Institute, University of Toronto, Canada.
Oncogene. 2003 Apr 3;22(13):1998-2010. doi: 10.1038/sj.onc.1206228.
Myc is a multifunctional nuclear phosphoprotein that can drive cell cycle progression, apoptosis and cellular transformation. Myc orchestrates these activities at the molecular level by functioning as a regulator of gene transcription to activate or repress specific target genes. Previous studies have shown that both the Myc N-terminal domain (NTD) and the C-terminal domain (CTD) are essential for Myc functions. The role of the CTD is relatively well understood as it encodes a basic helix-loop-helix leucine zipper motif important for DNA binding and protein-protein interactions. By contrast, the role of the NTD and the specific domains responsible for different Myc activities are not as well defined. To investigate the regions of the NTD necessary for Myc function and to determine whether these activities are overlapping or independent of one another, we have conducted a detailed structure-function analysis of the Myc NTD. We assessed the ability of a number of deletion and point mutants within the highly conserved regions of the Myc NTD to induce cell cycle progression, apoptosis and transformation as well as repress and activate expression of endogenous target genes. Our analyses highlight the complexity of the Myc NTD and extend previous studies. For example, we show most Myc mutants that were compromised as repressors of gene transcription retained the ability to activate gene transcription, reinforcing the concept that these activities can be uncoupled. Repression of two different target genes could be distinguished by specific mutants, further supporting the notion of at least two different Myc repression mechanisms. Mutants disabled at both inducing and repressing gene transcription could not maximally drive the biological activities of Myc, indicating these functions are tightly linked. Indeed, a close association of Myc repression and apoptosis was also observed.
Myc是一种多功能核磷蛋白,可驱动细胞周期进程、凋亡和细胞转化。Myc通过作为基因转录调节因子来激活或抑制特定靶基因,在分子水平上协调这些活动。先前的研究表明,Myc的N端结构域(NTD)和C端结构域(CTD)对Myc的功能均至关重要。CTD的作用相对较为清楚,因为它编码一个对DNA结合和蛋白质-蛋白质相互作用很重要的碱性螺旋-环-螺旋亮氨酸拉链基序。相比之下,NTD的作用以及负责Myc不同活性的特定结构域尚未明确界定。为了研究Myc功能所需的NTD区域,并确定这些活性是重叠的还是相互独立的,我们对Myc NTD进行了详细的结构-功能分析。我们评估了Myc NTD高度保守区域内多个缺失和点突变体诱导细胞周期进程、凋亡和转化以及抑制和激活内源性靶基因表达的能力。我们的分析突出了Myc NTD的复杂性,并扩展了先前的研究。例如,我们发现大多数作为基因转录抑制因子受损的Myc突变体仍保留激活基因转录的能力,强化了这些活性可以解偶联的概念。特定突变体可以区分对两种不同靶基因的抑制作用,进一步支持了至少存在两种不同Myc抑制机制的观点。在诱导和抑制基因转录方面均失活的突变体无法最大程度地驱动Myc的生物学活性,表明这些功能紧密相连。事实上,还观察到Myc抑制与凋亡之间存在密切关联。