Elucidation of mechanisms underlying p53-independent growth-suppressive activity for tumor suppressor proteins with p53-activating function.

1）ARF介导的非p53依赖性肿瘤抑制部分通过BCL 6实现。ARF抑癌基因可拮抗多种肿瘤的发生。ARF介导的肿瘤抑制以p53非依赖性方式以及p53依赖性方式发生。在这项研究中，我们证明了BCL 6是ARF肿瘤抑制因子的靶点。小鼠p19^<ARF>或人p14^<ARF>与BCL 6结合并下调BCL 6诱导的转录抑制。p19^N-末端37个氨基酸<ARF>对于ARF介导的BCL 6转录抑制的下调是必需的和足够的。因此，我们得出结论，ARF介导的BCL 6活性下调可能是ARF介导的肿瘤抑制的部分原因。2）IK 3 -1/IK 3 -2诱导的p53非依赖性细胞凋亡部分由CR介导。CR（Cdc 7 expression repressor）/periphilin最初被克隆为与cortex细胞膜前体periplakin相互作用的蛋白，并被认为是一种新型的核基质。我们已经发现CR/periphilin是一种普遍表达的核蛋白，具有斑点状分布。CR/periphilin的过表达诱导S期阻滞。参与DNA复制的调节因子的表达分析表明，CR/periphilin的过表达显著下调了Cdc 7的mRNA和蛋白表达，Cdc 7是DNA复制起始和继续的调节因子。此外，我们还发现CR与组蛋白去乙酰化酶I和mSin 3A相关，它们作为各种转录抑制因子的共抑制因子，这表明CR也是一种共抑制因子。总之，CR介导的p53-非依赖性细胞凋亡诱导的IK 3 -1/IK 3 -2作为一个转录共阻遏物。

1)ARF-mediated p53-independent tumor suppression occurs in part through BCL6.The ARF tumor' suppressor gene antagonizes generation of various tumors. ARF-mediated tumor suppression occurs in a p53-independent manner as well as in a p53-dependent manner. In this study, we demonstrate that BCL6 is a target of the ARF tumor suppressor. Either mouse p19^<ARF> or human p14^<ARF> binds to BCL6 and downregulates BCL6-induced transcriptional repression. The N-terminal 37 amino acids of p19^<ARF> are necessary and sufficient for ARF-mediated downregulation of BCL6 transcriptional repression. Thus, we have concluded that ARF-mediated downregulation of the BCL6 activity may account in part for ARF-mediated tumor suppression. In addition, we have found that Bax is the main mediator of ARF-induced p53-independent apoptosis.2)p53-independent apoptosis induced by ik3-1/ik3-2 is mediated in part by mediated by CR.CR(Cdc7 expression repressor)/periphilin has been originally cloned as an interactor with periplakin, a precursor of the cornified cell envelope, and suggested to constitute a new type of nuclear matrix. We have found that CR/periphilin is a ubiquitously expressed nuclear protein with speckled distribution. Overexpression of CR/periphiilin induces S-phase arrest. Analysis of expression of regulators involved in DNA replication, has revealed that both mRNA and protein expression of Cdc7, a regulator of the initiation and continuation of DNA replication, are markedly downregulated by overexpression of CR/periphilin. In addition, we have found that CR associates with histone deacetylase I and mSin3A that act as co-reppressors for various transcriptional reppressors, suggesting that CR is also a co-repressor. In conclusion, it appears that CR mediates p53-independent apoptosis induced by ik3-1/ik3-2 by acting as a transcriptional co-repressor.