Mechanism of Functional Switching of C-MYC: Formation of Different Protein Complexes and Expression of Activities in DNA Replication, Transcription and Apoptosis Induction during the Cell Cycle.

C-myc被认为参与细胞的增殖、分化、转化和凋亡。我们推测C-MYC与多种蛋白质共同发挥着万花筒般的功能。除了已报道的通过C-MYC C-末端的基本螺旋-环-螺旋亮氨酸拉链结构(BHLHZip)与C-MYC形成二聚体的Max家族蛋白质外，我们还筛选出在N-末端区域通过在Myc家族中保守的myc盒与C-MYC相互作用的蛋白质。我们应用酵母双杂交系统进行筛选，获得了几个新的配对蛋白，包括AMY-1和MM-1，以及已报道的CBF/NF-Y、ORC1、CDC6和CDK抑制蛋白p21。MSSP也是一种C-myc结合蛋白，它识别myc盒。对这些蛋白质在体外和体内的功能进行了检测，并将其分类为转录因子(AMY-1、MM-1和CbF/NF-Y)、DNA复制因子(MS…更多的P，ORC1和CDC6)和细胞周期运动(P21)。对于C-MYC的转录活性，只有AMY-1是正向调节因子，其余MM-1和CBF/NF-Y是负向调节因子。AMY-1诱导K562细胞向红细胞分化。将转AMY-1基因的雄性小鼠不育，并克隆了AKAP-84的RII结构域。AKAP-84是精子发生过程中重要的A-激酶调节亚基的结合部位。因此，AMY-1被认为可以抑制A-激酶的适当定位，并诱导生精细胞的凋亡。此外，还发现AMY-1与WAVE/AKAP-149结合，而WAVE/AKAP-149是肌动蛋白多聚化的相关因子。MM-1具有肿瘤抑制因子的性质。在淋巴瘤、白血病和舌癌的细胞和组织中，MM-1的#157氨基酸由丙氨酸替换为精氨酸是常见的现象。精氨酸突变消除了MM-1对C-MYC的负性作用。染色质重塑因子ORC1与MSSP家族蛋白SNF5竞争结合C-MYC，从染色质中释放C-MYC。MSSP零突变在发育阶段趋于致死。这些发现表明，C-MYC结合蛋白除了对C-MYC的多种功能进行调节外，还在细胞成熟、受精的关键步骤中发挥作用。较少

C-MYC has been suggested to be involved in cell proliferation, differentiation, transformation and apoptosis. We supposed that C-MYC plays such kaleidoscopic functions in partnership with various proteins. Besides the reported Max family proteins forming dimers with C-MYC via the basic helix-loop-helix leucine-zipper structure (bHLHZip) in the C-terminal region of C-MYC, we have screened proteins which interacts with C-MYC via the myc boxes, well-conserved among the myc family, in the N-terminal region. We applied the yeast two-hybrid system in the screening and have obtained several novel partner proteins including AMY-1 and MM-1 as well as reported proteins, CBF/NF-Y, ORC1, CDC6 and cdk inhibitor p21. MSSP, which we have also identified as a C-MYC binding protein, recognized the myc boxes. These proteins were examined for their functions both in vitro and in vivo and were classified to the categories including factors for transcription (AMY-1, MM-1 and CBF/NF-Y), DNA replication (MSS … More P, ORC1 and CDC6) and cell-cycle movement (p21). As for the transcriptional activity of C-MYC, only AMY-1 acted as a positive regulatory factor while the others, MM-1 and CBF/NF-Y, were negative factors. AMY-1 induced the erythrocyte differentiation of K562 cells. Male transgenic mice of the AMY-1 gene were sterile and the RII domain of AKAP-84, the binding site of the regulatory subunit of A-kinase which is important in spermatogenesis, was cloned as a AMY-1 binding protein. AMY-1 was thus suggested to inhibit the appropriate localization of the A-kinase and to induce apoptosis of spermatogenic cells. In addition, AMY-1 was found to bind to WAVE/AKAP-149, a factor involved in actin polimerization. MM-1 has a character for putatice tumor suppressor. The substitution of the amino acid #157 of MM-1 from alanine to arginine was frequently observed in the cells and tissues of lymphoma, leukemia and tongue cancer. The arginine mutation abrogated the negative effects of MM-1 on C-MYC. ORC1, a remodeling factor of chromatin, bound to C-MYC competitively with SNF5, an MSSP family protein, to release C-MYC from chromatin. Null-mutation of MSSP tended to be lethal during developmental stage. These findings altogether suggest that C-MYC binding proteins play roles at crucial steps of cell maturation, fertilazation in addition to the modulation of versatile functions of C-MYC. Less