Activation of checkpoint pathways in cancer

描述（由申请人提供）：大多数人类癌症在数年内演变，从增生性非侵入性病变开始，进展为高度侵入性和转移性恶性肿瘤。在大多数情况下，该过程与基因组不稳定性的逐渐增加相关，使得增生性病变具有非常少的杂合性缺失（洛）的遗传基因座，而在晚期癌症中，洛涉及大部分遗传基因座。同时，肿瘤进展与关键生长控制基因（如p53）的突变相关。人类癌症中p53突变的高频率提高了人类癌症可能与DNA双链断裂（DSB）检查点通路的失调相关的可能性，因为p53是该通路的组成部分。为了更好地了解人类癌症发展的自然史，我们检查了从增生到浸润性癌的一系列肺部病变中的各种DNA损伤反应标志物。出乎意料的是，在增生性病变中存在DNA损伤反应的证据，如H2AX和Chk2磷酸化、53BP1局灶性染色、p53积累和高频率的凋亡所示。发育不良和癌的进展与p53或53BP1失活和细胞凋亡减少有关。此外，由生长因子诱导变得增生的人皮肤异种移植物的特征在于H2AX和Chk2磷酸化以及p53积累和凋亡。基于这一分析，我们假设，即使在其最早阶段，癌症的发展与DNA DSB的形成有关。由于DNA双链断裂在癌症发展的早期形成，我们还假设它们与端粒磨损无关，而是与异常的DNA复制有关。我们进一步假设DNA双链断裂的存在为癌症中的p53突变提供了选择压力，以及基因组不稳定性的驱动力。在本申请中，我们提出实验来验证我们的假设。我们相信，拟议的研究可以改变我们看待人类癌症发展和进展的方式，并为旨在利用癌症细胞而不是正常细胞中DNA DSB的存在的新型癌症疗法提供潜力。

DESCRIPTION (provided by applicant): Most human cancers evolve over a period of years, starting as hyperplastic non-invasive lesions and progressing to highly invasive and metastatic malignant tumors. This process is in most cases associated with a gradual increase in genomic instability, such that hyperplastic lesions have very few genetic loci with loss-of-heterozygosity (LOH), while in advanced cancers LOH involves a large fraction of genetic loci. In parallel, tumor progression is associated with mutations in key growth controlling genes, such as p53. The high frequency of p53 mutations in human cancer raises the possibility that human cancer might be associated with deregulation of the DNA double-strand break (DSB) checkpoint pathway, because p53 is a component of this pathway. To better understand the natural history of cancer development in humans we examined various DNA damage response markers in a spectrum of lung lesions ranging from hyperplasia to invasive carcinoma. Unexpectedly, in the hyperplastic lesions there was evidence of a DNA damage response, as indicated by H2AX and Chk2 phosphorylation, 53BP1 focal staining, p53 accumulation and a high frequency of apoptosis. Progression to dysplasia and carcinoma was associated with p53 or 53BP1 inactivation and decreased apoptosis. Further, human skin xenografts induced to become hyperplastic by growth factors were characterized by H2AX and Chk2 phosphorylation and p53 accumulation and apoptosis. Based on this analysis we hypothesize that, even in its earliest stages, cancer development is associated with formation of DNA DSBs. Because the DNA DSBs form so early in cancer development, we also hypothesize that they are not linked to telomere attrition, but rather to aberrant DNA replication. We further hypothesize that the presence of DNA DSBs provides the selective pressure for p53 mutations in cancer, as well as the driving force for genomic instability. In this application we propose experiments to test our hypothesis. We believe that the proposed studies can change the way we view human cancer development and progression and provide the potential for novel cancer therapies aiming to exploit the presence of DNA DSBs in cancer, but not normal, cells.