Mechanisms of arsenic-induced carcinogenesis

描述(由申请人提供)： 由于大量妇女在军队服役，越来越多的女退伍军人受到乳腺癌的影响。这项研究的长期目标是开发乳腺癌的化学预防和治疗药物，以减轻女性军人的健康负担。目前这项研究的目标是确定与砷诱发乳腺癌发生有关的机制。为了复制正常的现场暴露条件，我们将乳腺上皮细胞暴露在低剂量的砷中几个月。我们发现，乳腺上皮细胞连续暴露在砷中五个月会导致细胞增殖增加，伤口愈合加快，独立于支抗的生长增加，以及基质侵袭增加。这些研究表明，砷可以诱导乳腺上皮细胞发生致癌转化。我们的初步研究表明，线粒体是砷诱导转化的重要靶点。线粒体控制细胞的生长和死亡。线粒体还具有其他细胞功能，包括通过线粒体氧化磷酸化(MtOXPHOS)产生ATP。我们发现，暴露于砷可诱导5p染色体的亚基因组选择性扩增，该染色体含有许多与线粒体功能相关的基因。与这一发现一致的是，砷转化细胞表现出1)复合体I和IV活性增加；2)复合体I调节亚基NDUFA13或GRIM19(与维甲酸干扰素诱导的死亡相关的基因)和非调节性NDUFB8表达增加，包括mtOXPHOS；3)组成复合体IV的COXII亚单位表达增加。此外，我们的研究表明，砷处理没有1)引起复合体II和III活性的变化，2)改变砷转运体的表达。然而，砷转化的细胞会产生更高水平的活性氧。我们假设，砷破坏了mtOXPHOS功能，而mtOXPHOS功能有助于乳腺上皮细胞的致癌转化。为了解决提出的假设，我们计划：目标1：确定砷诱导的乳腺上皮细胞从1、2、3、4个月到致瘤转化(5个月)过程中mtOXPHOS功能障碍的谱。目的：探讨在乳腺上皮细胞发生发展和癌变过程中，砷对mtOXPHOS超复合体亚单位基因表达、组成和组织的影响。目的3：确定mtOXPHOS复合体I的调节性和非调节性亚基在抵抗砷诱导的细胞死亡和肿瘤发展中的作用。NDUFA13/GRIM19编码mtOXPHOS复合体I的调节成分，对复合体I的组装和酶活性是必不可少的。相比之下，NDUFB8编码一个非调节性辅助亚基，它不参与复合体I的催化作用。本文的研究将有助于深入了解砷诱导乳腺癌的机制(S)，并在未来可能有助于预防或治疗女性退伍军人的乳腺癌。

DESCRIPTION (provided by applicant): Since a significant number of women serve in the military an increasing number of female veterans are impacted by breast cancer. The long-term goal of this research is to develop chemo-preventive and therapeutic agents against breast cancer to reduce the health burden in female military personnel. The current goal of this research is to identify mechanisms involved in the development of arsenic-induced breast cancer. To replicate normal field exposure conditions, we exposed breast epithelial cells to low dose of arsenic for several months. We discovered that a five month continuous exposure of breast epithelial cells to arsenic results in increased cell proliferation, increased wound healing, increased anchorage independent growth, as well as increased matrigel invasion. These studies suggest arsenic induces tumorigenic transformation of breast epithelial cells. Our preliminary studies revealed that mitochondria are important targets of arsenic induced transformation. Mitochondria control cell growth and cell death. Mitochondria perform other cellular functions including ATP production via mitochondrial oxidative phosphorylation (mtOXPHOS). We discovered that exposure to arsenic induces selective subgenomic amplification of chromosome 5p which contains many genes involved in mitochondrial function. Consistent with this finding arsenic-transformed cells show 1) increased Complex I and IV activities; 2) an increased expression of Complex I regulatory subunits NDUFA13 or GRIM19 (gene associated with retinoid interferon induced mortality) and non-regulatory NDUFB8 comprising the mtOXPHOS; and 3) increased expression of COXII subunit comprising complex IV. Furthermore our study suggest that arsenic-treatment did not 1) induce changes in Complex II and III activities and 2) alter the expression of arsenic-transporters. However, arsenic-transformed cells produce an increased level of reactive oxygen species. We hypothesize that arsenic disrupts mtOXPHOS function which contributes to tumorigenic transformation of breast epithelial cells. To address the proposed hypothesis, we plan to: Aim 1: Determine the spectrum of arsenic-induced mtOXPHOS dysfunction during progression (1, 2, 3, 4 months) to tumorigenic transformation (5 months) of mammary epithelial cells. Aim 2: Determine arsenic-induced changes affecting subunit gene expression, composition and organization of mtOXPHOS super-complexes during the progression and tumorigenic transformation of mammary epithelial cells. Aim 3: Determine a role for a regulatory and a non-regulatory subunit of mtOXPHOS Complex I in resistance to arsenic-induced cell death and tumor development. NDUFA13/GRIM19 encodes the regulatory component of mtOXPHOS Complex I and is essential for the assembly and enzymatic activity of Complex I. In contrast, NDUFB8 encodes a non- regulatory accessory subunit that is not involved in the catalysis of Complex I. The proposed studies should provide insight into the mechanism(s) involved in arsenic induced breast cancer and in the future may help prevent or treat breast cancers in female veterans.