Identification of Pdx1-dependent circuits that reprogram cell identity and promote pancreatic carcinogenesis

细胞身份的丧失是胰腺导管腺癌（PDAC）发生和发展的重要前提。恶性细胞转化的特点是遗传改变，但也包括广泛的转录重编程，涉及细胞分化程序的下调和发育信号通路的激活。转录因子Pdx1最初被确定为所有胰腺细胞系的主要调节因子。我们的实验室最近揭示了它作为胰腺腺泡细胞身份的重要守护者的作用。因此，分化的腺泡细胞中Pdx1的缺失与癌基因KrasG12D协同作用，诱导细胞快速而广泛的转化，其特征是腺泡细胞身份的侵蚀和PDAC前体病变和PDAC的形成。然而，这种效应背后的确切机制仍然难以捉摸。我们的初步数据表明，Pdx1靶基因涉及Ras信号级联的重要效应基因，如Egfr。Ras活性水平对PDAC的发展至关重要。因此，通过分析Pdx1和Egfr同时缺失的小鼠模型，结合单细胞分析来定义转录景观，我的目标是确定Pdx1如何抑制Ras通路活性以抵消krasg12d驱动的恶性细胞转化。阐明腺泡细胞身份丧失和致癌Kras信号传导之间的关系，将有助于理解恢复恶性细胞转化的方法。由于DNA甲基化介导的表观遗传沉默，肿瘤细胞重编程向晚期PDAC更具侵袭性的表型和转移是通过下调一系列胰腺转录因子（包括PDX1）来完成的。我们的数据表明，胰腺癌细胞中Pdx1的单一敲低会导致肿瘤细胞恶性性的增强。Pdx1敲低细胞的特征是细胞增殖的暂时减少，通过广泛的转录和代谢重编程绕过，极大地影响谷胱甘肽代谢。谷胱甘肽生物合成中的适应性可以通过影响DNA和组蛋白甲基化所需的甲基的可用性而对表观遗传景观产生深远的影响。通过应用靶向谷胱甘肽生物合成的药物，我将评估DNA甲基化水平的变化，重点关注在进展过程中沉默的基因。我建议确定肿瘤细胞补偿Pdx1缺失的机制，将有助于揭示特定的疾病脆弱性并提供新的治疗策略。

Loss of cell identity is an important prerequisite for the initiation and progression of the pancreatic ductal adenocarcinoma (PDAC). Malignant cell transformation is hallmarked by genetic alterations, but also by a broad transcriptional reprogramming, involving the down-regulation of cell differentiation programs and activation of developmental signaling pathways. The transcription factor Pdx1 was initially identified as the master regulator of all pancreatic cell lineages. Our lab recently unveiled its role as an important guardian of pancreatic acinar cell identity. Consequently, depletion of Pdx1 in differentiated acinar cells cooperated with the oncogene KrasG12D and induced rapid and widespread cell transformation, characterized by an erosion of acinar cell identity and the formation of PDAC precursor lesions and PDAC. However, the exact mechanisms behind the effect remain mostly elusive. Our preliminary data indicate that Pdx1 target genes involve important effectors of the Ras signaling cascade, such as Egfr. Ras activity levels are pivotal for PDAC development. Thus, by analyzing a mouse model with a concomitant loss of Pdx1 and Egfr, combined with single cell analysis to define the transcriptional landscape, I aim to determine how Pdx1 suppresses Ras pathway activity to counteract KrasG12D-driven malignant cell transformation. Elucidating the context between loss of acinar cell identity and oncogenic Kras signaling, will help to comprehend ways to revert malignant cell transformation. Tumor cell reprogramming towards a more aggressive phenotype and metastasis in late stage PDAC is accomplished by the down-regulation of a host of pancreatic transcription factors, including PDX1, due to epigenetic silencing mediated by DNA methylation. As indicated by our data, the sole knockdown of Pdx1 in pancreatic cancer cells leads to the reinforcement of tumor cell malignancy. Pdx1 knockdown cells are characterized by a temporary reduction in cell proliferation that is bypassed through an extensive transcriptional and metabolic reprogramming greatly affecting glutathione metabolism. Adaptations in glutathione biosynthesis can have profound effects on the epigenetic landscape by influencing the availability of methyl groups, needed for DNA and histone methylation. By applying drugs targeting glutathione biosynthesis, I will assess changes in DNA methylation levels, focusing on genes shown to be silenced during progression. I propose that identifying the mechanisms by which tumor cells compensate for Pdx1 loss, will contribute to uncover specific disease vulnerabilities and offer novel therapeutic strategies.