Mechanism and Regulation of Baxdelta2 in Colorectal Cancer

 描述(申请人提供)：促凋亡肿瘤抑制基因Bax的表达可通过其微卫星编码区的移码突变而沉默，导致Bax阴性表型。在遗传性非息肉病性结直肠癌(HNPCC)中，由于错配修复系统相关的微卫星不稳定性(MSI)的缺失，这种Bax突变发生在约50%的HNPCC中。Bax基因的缺失已被证明会增加化疗耐药性，并与不良预后有关。最近，我们发现一些“BAX阴性”的肿瘤细胞实际上含有一个功能性的BAX亚型，BAXΔ2，它是在选择性剪接纠正突变诱导的移码时产生的。因此，baxΔ2只存在于微卫星突变的细胞中。我们已经证明了这种“挽救的”bax∆2是亲死亡的，类似于原型bax，但通过非线粒体死亡途径诱导细胞死亡。重要的是，表达bax∆2的结肠癌细胞对所选化疗药物更敏感。因此，我们假设BAXΔ2通过一个非典型的BAX-死亡途径决定了肿瘤恶性潜能和对“BAX阴性”微结直肠癌细胞的化疗选择性。我们有两个具体的目标：1)研究bax∆2介导的细胞死亡的机制；2)确定负责控制bax∆2表达水平的关键调控因子 在MSI结直肠癌细胞中。由于在这项研究之前并不知道在“Bax阴性”的结肠癌中存在Bax异构体，我们认为这项拨款申请中提出的研究在概念上是创新的和有意义的，因为它们将改变目前理解“Bax阴性”微卫星定位结肠癌的发展和预后的范式，并有助于为这类“Bax阴性”结肠癌患者选择特定的化疗药物。伊利诺伊理工学院(IIT)是一所私立大学，拥有广泛的学术学科。该大学鼓励生物研究，并促进具有潜在翻译影响的综合生物医学研究。IIT目前缺乏几个生物医学设施，如高水平的基因组和成像设施， 功能齐全的动物设施和临床资源。然而，IIT确实有一大批渴望参与生物医学研究的本科生和研究生。PI在教育和研究方面都拥有很高的学术资历。建议的项目是精心设计的，以利用IIT的研究环境的优势，并最大限度地增加学生实践研究经验的机会。拟议研究的成功完成将对IIT的生物医学研究能力产生重大的积极影响。

 DESCRIPTION (provided by applicant): Expression of the pro-apoptotic tumor suppressor Bax can be silenced by frameshift mutations in its microsatellite coding region, leading to a Bax-negative phenotype. Such Bax mutations occur in ~50% of hereditary nonpolyposis colorectal cancer (HNPCC) due to deficiency of mismatch repair system associated microsatellite instability (MSI). Loss of Bax has been demonstrated to increase chemoresistance and is associated with poor prognosis. Recently, we found that some "Bax-negative" tumor cells actually contain a functional Bax isoform, BaxΔ2, which is generated when alternative splicing corrects the mutation-induced frameshift. Therefore, BaxΔ2 only exists in microsatellite-mutated cells. We have demonstrated that this "salvaged" Bax∆2 is pro-death, similar to prototype Bax, but induce cell death potential through a non- mitochondrial death pathway. Importantly, colon cancer cells expressing Bax∆2 are more sensitive to selected chemotherapeutics. Therefore, we hypothesize that BaxΔ2 determines tumor malignant potential and chemotherapeutic selectivity in "Bax-negative" MSI colorectal cancer cells through a non-canonical Bax- death pathway. We have two specific aims: 1) to study the mechanism underlying Bax∆2-mediated cell death; and 2) to identify key regulators responsible for controlling Bax∆2 expression levels in MSI colorectal tumor cells. Since there was no awareness of the existence of a Bax isoform in the "Bax-negative" cancer prior to this study, we think the studies proposed in this grant application are conceptually innovative and significant because they will change the current paradigm for understanding the development and prognosis of the "Bax-negative" MSI colorectal cancer and facilitating selection of specific chemotherapeutics for this subgroup of "Bax-negative" colon cancer patients. The Illinois Institute of Technology (IIT) is a private university with a wide range of academic disciplines. The University encourages biological research and promotes integrative biomedical research with potential translational impact. IIT currently lacks several biomedical facilities, such as high-level genomic and imaging facilities, a full-featured animal facility, and clinical resources. However, IIT does have a large body of undergraduate and graduate students eager to participate in biomedical research. The PI has a strong academic credential for both education and research. The proposed project is carefully designed to exploit the strengths of IIT's research environment and maximize opportunities for student hands-on research experiences. Successful completion of the proposed studies will have a substantial positive impact on IIT's biomedical research capacity.