BACH1/FANCJ Checkpoint, Recombination, and Chemoresistance

描述（由申请人提供）：化学抗性是癌症治疗中的主要问题，但很大程度上不清楚癌细胞如何产生抗性。错配修复（MMR）蛋白的缺陷使细胞能够抵抗毒性化疗剂，如DNA甲基化剂。然而，考虑到多种MMR功能，使细胞对DNA甲基化敏感的不同MMR功能并没有明确定义。MMR蛋白的功能是修复DNA复制后的碱基错配，抑制不同DNA序列之间的重组，以及激活DNA损伤后的检查点和凋亡反应。功能分离突变体表明对DNA甲基化的抗性依赖于被破坏的检查点。最近，我们确定MutL 1复合物的MMR蛋白（MLH 1/PMS 2）和BACH 1/FANCJ（BRCA 1相关的C-末端解旋酶/Fanconi贫血互补组J）都是检查点信号传导所必需的。具体而言，我们确定BACH 1直接结合MLH 1，并且针对MLH 1结合而消融的BACH 1的突变形式未能引起链间交联（ICL）诱导的检查点应答。由于ICL激活S期内检查点，并且MLH 1和BACH 1都已被证明独立地在S期内检查点中起作用，因此该检查点可能需要BACH 1/MutL 1复合物的形成。我们将直接测试这种可能性。此外，我们将确定BACH 1是否也参与DNA甲基化诱导的G2/M积累检查点类似于MutL 1。与BACH 1在DNA甲基化诱导的反应中的作用一致，我们的实验室已经表明，与MutL 1缺陷细胞类似，BACH 1缺陷细胞对DNA甲基化具有抗性。相反，BRCA 1缺陷细胞对DNA甲基化敏感，表明BACH 1在DNA甲基化反应中发挥独特的功能。我们建议剖析BACH 1/MutL 1复合物在检查点和修复功能中的作用。我们将确定是否需要形成一个完整的复合物来恢复对耐药无效BACH 1或MutL 1细胞的化学敏感性。理想地，定义BACH 1/MutL 1复合物的功能将为恢复癌细胞的化学敏感性提供见解。沿着这些路线，我们将测试是否操纵BACH 1/BRCA 1复合物的重组功能将独特地使MMR缺陷细胞对化疗敏感。

DESCRIPTION (provided by applicant): Chemoresistance is a major problem in cancer therapy, but it is largely unclear how cancer cells become resistant. Deficiency in the mismatch-repair (MMR) proteins allows cells to resist toxic chemotherapeutic agents such as DNA methylators. However, the distinct MMR function that sensitizes cells to DNA methylation is not clearly defined given the multiple MMR functions. MMR proteins function to repair base mismatches after DNA replication, inhibit recombination between non-identical DNA sequences, as well as activate both checkpoint and apoptotic responses following DNA damage. Separation-of- function mutants, suggest that resistance to DNA methylation is dependent on a disrupted checkpoint. Recently, we established that both MMR proteins of the MutL1 complex (MLH1/PMS2) and BACH1/FANCJ (BRCA1-associated C- terminal helicase/Fanconi Anemia complementation group J) are required for checkpoint signaling. Specifically, we identified that BACH1 binds directly to MLH1 and that a mutant version of BACH1 ablated for MLH1 binding failed to elicit an interstrand crosslink (ICL)-induced checkpoint response. Since ICLs activate the intra S-phase checkpoint, and both MLH1 and BACH1 have been shown independently to function in the intra S-phase checkpoint, this checkpoint likely requires the formation of a BACH1/MutL1 complex. We will test this possibility directly. In addition, we will determine whether BACH1 also participates in the DNA-methylation-induced G2/M accumulation checkpoint similar to MutL1. Consistent with a role for BACH1 in the DNA methylation-induced response, our lab has shown that similar to MutL1 deficient cells, BACH1 deficient cells are resistant to DNA methylation. In contrast, BRCA1 deficient cells are sensitive to DNA methylation, suggesting that BACH1 uniquely functions in the DNA methylati1n response. We propose to dissect the role of a BACH1/MutL1 complex in both checkpoint and repair functions. We will determine whether the formation of an intact complex is required to restore chemosensitivity to resistant null BACH1 or MutL1 cells. Defining the function of the BACH1/MutL1 complex ideally will provide insight towards restoring chemosensitivity to cancer cells. Along these lines, we will test whether manipulation of the recombination function of the BACH1/BRCA1 complex will uniquely sensitizes MMR deficient cells to chemotherapies.