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参与了细胞的增殖、分化、转化和凋亡。我们认为C-MYC与各种蛋白质合作发挥着千变万化的功能。除了已报道的Max家族蛋白在C-MYC末端通过基本螺旋-环-螺旋亮氨酸拉链结构（bHLHZip）与C-MYC形成二聚体外，我们还筛选了在n端区域通过myc盒子与C-MYC相互作用的蛋白，这些蛋白在myc家族中保存良好。我们应用酵母双杂交系统进行筛选，获得了包括AMY-1和MM-1在内的几个新的伴侣蛋白，以及已报道的CBF/NF-Y、ORC1、CDC6和cdk抑制剂p21。MSSP，我们也已经确定为C-MYC结合蛋白，识别myc盒子。在体外和体内检测了这些蛋白的功能，并将其分类为转录因子（AMY-1， MM-1和CBF/NF-Y）， DNA复制因子（MSS…More P， ORC1和CDC6）和细胞周期运动因子（p21）。对于C-MYC的转录活性，只有AMY-1是正调控因子，MM-1和CBF/NF-Y是负调控因子。AMY-1诱导K562细胞红细胞分化。AMY-1基因的雄性转基因小鼠不育，并克隆了在精子发生中起重要作用的a激酶调控亚基的结合位点AKAP-84的RII结构域为AMY-1结合蛋白。因此，AMY-1可能抑制a激酶的适当定位并诱导生精细胞凋亡。此外，AMY-1被发现与参与肌动蛋白聚合的因子WAVE/AKAP-149结合。MM-1具有抑制肿瘤的特性。在淋巴瘤、白血病和舌癌的细胞和组织中，MM-1的157号氨基酸常由丙氨酸取代为精氨酸。精氨酸突变消除了MM-1对C-MYC的负面影响。ORC1是一种染色质重塑因子，与MSSP家族蛋白SNF5竞争性地结合到C-MYC上，从而从染色质中释放C-MYC。MSSP的零突变在发育阶段具有致死性。这些发现表明，C-MYC结合蛋白除了调节C-MYC的多种功能外，还在细胞成熟、受精的关键步骤中发挥作用。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