Understanding TGFβ driven mitotic errors and chromosomal instability in SMAD4-deficient PDAC subtypes

全染色体不稳定性（W-CIN）是癌症的一个标志，被定义为有丝分裂过程中染色体错误分离率的增加，导致进化的非整倍体。通过永久改变癌细胞的遗传组成，W-CIN可以促进肿瘤的克隆进化、肿瘤进展和治疗耐药性的发展。尽管CIN在癌症中的重要性，但引起CIN的分子机制仍不完全清楚。在PDAC中，CIN的作用总体上定义不清。此外，有丝分裂错误和非整倍体的类型以及导致W-CIN的分子机制在PDAC中尚未得到解决。我们的初步结果令人惊讶地表明，TGFβ信号是诱导各种癌细胞和PDAC细胞中W-CIN所必需的。在机制上，我们发现基础TGFβ信号介导有丝分裂纺锤体内微管动力学的增加，这导致微管-着丝点附着异常，导致整个染色体错误分离。此外，我们发现SMAD4的缺失（代表PDAC的主要遗传畸变之一）促进了W-CIN的诱导，可能是通过将TGFβ信号重定向到非smad信号通路。基于这些结果，我们假设以高tgf - β信号传导为特征的PDAC亚组，以及SMAD4的缺失，容易诱导染色体稳定性，从而支持肿瘤进展、肿瘤侵袭性和治疗抵抗。科学项目6将系统地研究W-CIN在PDAC中的存在及其机制，这将导致以有丝分裂错误和W-CIN为特征的PDAC亚型的第一个定义。此外，计划中的实验旨在阐明细胞系和pdx衍生细胞中染色体不稳定的PDACs中存在的有丝分裂错误的性质。我们将研究tgf - β信号的cin介导作用，特别是在SMAD4缺失的PDAC亚组中非smad通路的作用。通过干扰tgf - β信号和微管动力学，我们将开发抑制PDAC细胞模型中CIN的实验途径，以直接解决CIN在获得侵袭性肿瘤表型和介导对临床相关治疗方案的抗性中的作用问题。

Whole chromosome instability (W-CIN) is a hallmark of cancer and is defined as an increased rate of chromosome missegregation during mitosis leading to evolving aneuploidy. By perpetually altering the genetic composition of cancer cells W-CIN can fuel clonal evolution of tumors, tumor progression and the development of therapy resistance. Despite the importance of CIN in cancer the molecular mechanisms causing CIN are still incompletely understood. In PDAC, the role CIN is overall poorly defined. Moreover, the type of mitotic errors and aneuploidy as well as the molecular mechanisms leading to W-CIN have not been addressed in PDAC so far. Our preliminary results surprisingly indicated that TGFβ signaling is required for the induction of W-CIN in various cancer cells and also in PDAC cells. Mechanistically, we found that basal TGFβ signaling mediates increased microtubule dynamics within mitotic spindles, which causes abnormal microtubule-kinetochore attachments leading to whole chromosome missegregation. Moreover, we found that loss of SMAD4, which represents one of the major genetic aberrations in PDAC, fosters the induction of W-CIN, possibly by re-directing TGFβ signaling into non-SMAD signaling pathways. Based on these results we hypothesize that PDAC subgroups characterized by high TGFβ signaling, but also by loss of SMAD4 are prone for the induction of chromosomal stability, which supports tumor progression, tumor aggressiveness and therapy resistance. The scientific project 6 will systematically investigate the presence and the mechanisms of W-CIN in PDAC, which will lead to a first definition of PDAC sub-types characterized by mitotic errors and W-CIN. Furthermore, the planned experiments aim to elucidate the nature of mitotic errors present in chromosomally unstable PDACs, both in cell lines and in PDX-derived cells. We will investigate the CIN-mediating role of TGFβ signaling and in particular of non-SMAD pathways in PDAC subgroups with loss of SMAD4. By interfering with TGFβ signaling and with microtubule dynamics we will develop experimental routes to suppress CIN in PDAC cell models to directly address the question for the role of CIN in acquiring aggressive tumor phenotypes and in mediating resistance towards clinically relevant therapy regimens.