Non-Canonical Responses to DNA damage in Drosophila Polyploid Cells

 描述（由申请人提供）：多倍体细胞含有两套以上完整的同源染色体。多倍体细胞在自然界和病理学上都存在。一些重要器官，包括心脏、肝脏和胎盘都含有多倍体细胞。此外，许多癌症以多倍体或近多倍体状态存在。尽管多倍体的流行，其生物学意义仍然不清楚。一种模型是多倍体细胞中额外的染色体组缓冲了基因组损伤剂的作用，从而使多倍体细胞对DNA损伤更耐受。当受到DNA损伤时，二倍体细胞激活典型反应，以防止DNA损伤的细胞进入细胞周期。在没有这种反应的情况下，细胞进入有丝分裂，DNA受损，并经常通过被称为有丝分裂灾难（MC）的特征不佳的细胞死亡过程死亡。与二倍体细胞相比，人们对多倍体细胞如何对DNA损伤做出反应知之甚少。我的目标是研究多倍体细胞如何应对DNA损伤。以前，我们的实验室发现，与许多多倍体细胞，果蝇直肠乳头（以下简称：乳头细胞）细胞进行有丝分裂增殖。因此，果蝇乳头状细胞允许我调查自然发生的有丝分裂多倍体细胞的DNA损伤的影响。与二倍体细胞相比，我们的实验室发现乳头状细胞显示出较高的染色体不稳定性，这表明它们缺乏典型的DNA损伤反应。我发现不同类型的DNA损伤会在乳头细胞中引起不同的非典型反应。具体地说，乳头状细胞对X射线照射诱导的DNA损伤具有高度耐受性， 通过异常DNA复制后的非典型（半胱天冬酶非依赖性）MC。因此，我的中心假设是，多倍体有丝分裂细胞采用非典型的机制后，DNA损伤。在目的1中，我将确定多倍体乳头状细胞在辐射诱导的DNA损伤中存活的非经典机制。我期望揭示的基本机制，细胞剥离典型的DNA损伤反应，可以生存高水平的辐射诱导的DNA损伤。在目标2中，我将确定多倍体乳头状细胞在再复制诱导的DNA损伤中发生细胞死亡的非经典机制。这项研究应该阐明MC的机制，MC是一种细胞死亡机制，在缺乏典型DNA损伤反应的细胞中至关重要。总之，我提出的研究将确定多倍体乳头细胞对DNA损伤作出反应的具体机制。多倍性的生物学意义在很大程度上还未被研究。我发现多倍体细胞和二倍体细胞之间的一个主要区别是它们对DNA损伤的反应。由于缺乏典型的DNA损伤反应和多倍体是许多癌症中反复出现的特征，因此了解多倍体细胞对DNA损伤反应的不同方式对于多倍体癌症的治疗至关重要。

 DESCRIPTION (provided by applicant): Polyploid cells contain more than two complete sets of homologous chromosomes. Polyploid cells occur both naturally and pathologically. Several vital organs, including the heart, liver and placenta contain polyploid cells. Further, many cancers exist in a polyploid or near polyploid state. Despite the prevalence of polyploidy, its biological implications remain unclear. One model is that extra sets of chromosomes in polyploid cells buffer the effects of genome damaging agents, thus making polyploid cells more tolerant of DNA damage. When subjected to DNA damage, diploid cells activate a canonical response to prevent cells with DNA damage from entering the cell cycle. In the absence of this response, cells enter mitosis with damaged DNA and frequently die via a poorly characterized cell death process known as mitotic catastrophe (MC). In contrast to diploid cells, little is known about how a polyploid cell responds to DNA damage. My objective is to examine how polyploid cells respond to DNA damage. Previously, our lab found that unlike many polyploid cells, Drosophila rectal papillar (hereafter: papillar cells) cells undergo mitotic proliferation. Thus, Drosophila papillar cells allow me to investigate the effects of DNA damage on naturally occurring mitotic polyploid cells. Compared to diploid cells, our lab has found that papillar cells show elevated rates of chromosomal instability, suggesting that they lack a canonical DNA damage response. I have found that distinct types of DNA damage elicit distinct, non-canonical responses in papillar cells. Specifically, papillar cells are highly tolerant of X-irradiation induced DNA damage but die via non-canonical (caspase-independent) MC following aberrant DNA replication. Therefore, my central hypothesis is that polyploid mitotic cells employ non-canonical mechanisms following DNA damage. In Aim 1 I will determine the non-canonical mechanism by which polyploid papillar cells survive irradiation induced DNA damage. I expect to uncover the basic mechanism by which cells stripped of canonical DNA damage responses can survive high levels of irradiation induced DNA damage. In Aim 2 I will determine the non-canonical mechanism by which polyploid papillar cells undergo cell death in response to re-replication induced DNA damage. This research should shed light on the poorly understood mechanisms of MC, a cell death mechanism that is crucial in cells lacking canonical DNA damage responses. Taken together, my proposed research will identify specific mechanisms by which polyploid papillar cells respond to DNA damage. The biological implications of polyploidy remain largely unstudied. I have found that one main difference between polyploid cells and diploid cells is their response to DNA damage. Since both lack of canonical DNA damage responses and polyploidy are recurring features in numerous cancers, understanding distinct ways by which polyploid cells respond to DNA damage is crucial in treatment of polyploid cancers.