XIST RNA and Ovarian Cancer

描述(申请人提供)：Xist是X染色体上已知包含X失活中心的区域内的一个基因，其独特之处在于它只在不活跃的X染色体上表达。基因破坏和cDNA转基因实验表明，XIST是X失活的必要条件和充分条件。XIST的产物是一个大的非编码RNA，它仍然与女性核中不活跃的X染色体有关。然而，XIST介导的基因失活的机制在很大程度上还不清楚。通过对同一卵巢癌患者原发瘤和复发瘤的基因芯片表达分析，我们发现XIST是在复发肿瘤中表达下调的差异最大的基因。随后对一组卵巢癌细胞系和卵巢癌病例的XIST分析表明，XIST的表达与患者对紫杉醇的细胞敏感性和无复发时间显著相关。最近的研究还揭示了乳腺和卵巢肿瘤抑制蛋白BRCA1在支持XIST RNA定位到非活性X染色体上的特殊功能，并可能在基因沉默中发挥作用。抑制BRCA1的合成导致XIST局部染色的丢失和位于非活性X染色体上的沉默标记基因的表达增加。我们推测BRCA1和XIST RNA之间的相互作用可能在影响卵巢癌X连锁基因的表达和化疗敏感性方面发挥重要作用。本研究的具体目的是：1.研究卵巢癌细胞中BRCA1、XIST RNA和X失活状态与药物敏感性的关系；2.研究BRCA1和XIST RNA表达的改变是否能改变癌细胞的X失活状态和化疗反应；3.评价卵巢肿瘤标本中的XIST和其他变量。这些研究有望为XIST和BRCA1在X失活过程中的关系以及可能在影响药物反应方面提供深入的见解。阐明这两个过程的机制及其下游靶点的确定对卵巢癌化疗患者的临床管理和策略的制定具有重要意义。

DESCRIPTION (provided by applicant): XIST is a gene within the region on X chromosome known to contain the X inactivation center and is unique in being expressed exclusively from the inactive X chromosome. Gene disruption and cDNA transgene experiments have shown that XIST is both necessary and sufficient for X inactivation. The product of XIST is a large noncoding RNA that remains associated with the inactive X chromosome in female nuclei. However, the mechanism of XIST-mediated gene inactivation is largely unknown. By cDNA microarray expression analysis of paired primary and recurrent tumors from the same ovarian cancer patient we have identified XIST as the most differentially expressed gene that is down-regulated in the recurrent tumor. Subsequent analysis of XIST in a panel of ovarian cancer cell lines and ovarian cancer cases has shown that XIST expression is significantly correlated with cellular sensitivity to Taxol and relapse-free period of the patients. Recent studies have also revealed a specific function of the breast and ovarian tumor suppressor protein BRCA1 in supporting XIST RNA localization to the inactive X chromosome and probably in gene silencing. Inhibition of BRCA1 synthesis led to loss of focal XIST staining and increased expression of an otherwise silenced marker gene located on inactive X chromosome. We hypothesize that the interaction between BRCA1 and XIST RNA may play a significant role in affecting the expression of X-linked genes and chemosensitivity in ovarian cancer as well. The specific aims of this proposal are: 1. To characterize the relationship between BRCA1, XIST RNA, X inactivation status, and drug sensitivity in ovarian cancer cell lines; 2. To investigate if alterations of BRCA1 and XIST RNA expression can change the X inactivation status and chemoresponse of the cancer cell lines; and 3. To evaluate XIST and other variables in ovarian tumor samples. It is expected that these studies may provide insights into the relationship between XIST and BRCA1 in X inactivation process and probably in affecting drug response. Elucidating the mechanism underlying these two processes and identification of downstream targets may have significant implications in clinical management and development of strategy in treating ovarian cancer patients with chemotherapy.