Pancreatic Cancer Vulnerabilities Downstream of Cooperating Oncogenic Mutations

描述(申请人提供)：在过去的十年中，胰腺导管腺癌(PDA)的预后只有轻微的改善。PDA是一种在几个关键基因座上具有显著同质性的疾病，即KRAS、P53和Ink4a/Arf基因座；与此相关，PDA对许多针对激活的致癌分子的基因引导治疗一直是无效的，这些治疗在其他类型的肿瘤中取得了成功。此前，我们已经发现了一组受RAS和P53突变协同调控的~95个基因，它们对体内各种上皮性癌细胞的恶性表型至关重要。我们将其命名为 这些非突变基因驱动癌症表型的“合作反应基因”(CRGs)。CRG控制一系列细胞过程和途径(信号、新陈代谢、运输等)。并为靶向癌症干预提供新的方法，可能与各种不同的癌症相关。鉴于在PDA(90%的肿瘤)中发现了高频率的协同KRAS和P53途径突变，我们专门评估了胰腺上皮中CRG的表达水平，在那里我们发现这些基因的子集类似地被解除调控，表明它们在胰腺肿瘤发生中的重要性。我们的初步数据表明，其中一个功能未知的协同调控基因PLAC8定位于溶酶体，功能促进自噬小体-溶酶小体(AL)的融合，其基因沉默导致自噬受阻，抑制肿瘤生长。此外，在工程化的小鼠PDA模型中，PLAC8的基因失活阻碍了晚期肿瘤的进展，延长了生存期。相比之下，PLAC8基因敲除小鼠受该基因缺失的影响最小。因此，PLAC8及其调控的溶酶体过程似乎非常适合作为PDA和其他RAS/P53突变的GI癌的治疗靶点，因为抑制PLAC8对肿瘤生物学有很高的影响，对正常细胞功能的影响很小。基于这些数据，我们假设：i)PLAC8促进了癌细胞中AL的融合，ii)这一机制对恶性表型PDA是必不可少的，从而为胰腺癌靶向干预提供了理论基础。这些假说将在一系列实验中得到验证：1)PLAC8在胰腺癌进展和癌症维持中的作用；2)自噬小体-溶酶体融合作为癌症的基本功能的作用；3)PLAC8对癌症中溶酶体完整性的影响。自噬/溶酶体融合和主动保护溶酶体完整性在癌症中的作用和相关性几乎仍未被探索。因此，对相关机制的研究可能会揭示有针对性的癌症特异性干预的新机会，特别是因为PLAC8对正常组织功能不是必需的。

DESCRIPTION (provided by applicant): The prognosis of pancreatic ductal adenocarcinoma (PDA) has improved only marginally in the past decade. PDA is a disease with remarkable homogeneity across several key loci, namely KRAS, p53, and the INK4A/ Arf locus; related to this, PDA has been refractory to the many genetically guided therapies targeting activated oncogenic molecules that have offered success in other tumor types. Previously, we have identified a set of ~95 genes cooperatively regulated by mutation of RAS and p53, that are critical to the malignant phenotype of a variety of epithelial cancer cells in vivo. We have termed these non-mutated genes driving the cancer phenotype 'cooperation response genes' (CRGs). CRGs control a range of cellular processes and pathways (signaling, metabolism, transport etc.) and offer novel approaches to targeted cancer interventions with potential relevance to a variety of diverse cancers. Given the high frequency of cooperating KRAS and P53 pathway mutations found in PDA (>90% of tumors) we have specifically evaluated CRG expression levels in the pancreatic epithelium where we find a subset of these genes similarly deregulated pointing towards their importance in pancreatic oncogenesis. Our preliminary data indicate that one such cooperatively regulated gene with previously unknown function, Plac8, localizes to lysosomes functionally facilitating autophagosome- lysosome (AL) fusion, and that its genetic silencing leads to a block in autophagy and inhibition of tumor growth. Furthermore, genetic inactivation of Plac8 in an engineered murine PDA model impedes the progression of advanced tumors extending survival. In contrast, Plac8 knockout mice are minimally affected by loss of this gene. Thus, Plac8 and the lysosomal processes it regulates appear well suited as therapeutic targets in PDA and other RAS/p53 mutant GI cancers, as Plac8 inhibition has both a high impact on tumor biology and a minimal impact on normal cellular function. Based on these data we hypothesize that i) Plac8 facilitates AL fusion in cancer cells, and ii) that this mechanism is essential to the malignant phenotype PDA, thus providing rationale for targeted pancreatic cancer intervention. These hypotheses will be tested in a series of experiments investigating 1) the role of Plac8 in pancreatic cancer progression and cancer maintenance, 2) the role of autophagosome-lysosome fusion as an essential function in cancer, and 3) the impact of Plac8 on lysosome integrity in cancer. The role and relevance of both autophagosome/ lysosome fusion and active protection of lysosomal integrity in cancer remains virtually unexplored. Investigation of the mechanisms involved is thus likely to reveal novel opportunities for targeted cancer-specific interventions, particularly as Plac8 is non-essential for normal tissue function.