Role of CD44 in adaptive plasticity of pancreatic cancer

 描述（由申请人提供）： 适应性可塑性是一个短语，用于解释癌细胞如何通过表型变化来响应其环境而获得选择性生长和存活能力。适应性可塑性的例子是上皮间质转化（EMT），这是一个过程，使癌细胞能够迁移和侵入，以及增加生存特性。这一过程可以逆转为间充质向上皮转化（MET），这被认为有利于肿瘤移植和癌细胞在转移部位的生长。癌细胞中的EMT与跨膜蛋白CD 44从表达CD 44变体同种型（CD 44 v）到表达CD 44标准形式（CD 44 s）的同种型转换有关。在这种情况下，我们发现用吉西他滨处理BxPC 3胰腺导管腺癌（PDAC）细胞系诱导EMT和高水平的CD 44 ε表达，同时降低CD 44 v同种型的表达。这表明化疗的副作用可能会驱动EMT，增强侵袭性并使肿瘤细胞对化疗更具抵抗力。此外，我们能够使用流式细胞术从PDAC细胞系（CFPAC-1和AsPC 1）中选择出表达高水平CD 44的细胞亚群。在这些细胞中，CD 44的敲低使它们经历MET，侵入性更小，对化疗更敏感。这些研究表明，化疗或其他环境应激可能会诱导CD 44 s表型，促进生存，更具侵袭性;然而，化疗后的最佳肿瘤再生长或微转移植入后的生长可能需要重新转换为CD 44 v表型和下调CD 44 s表达。我们假设CD 44及其变体亚型是胰腺癌细胞适应性可塑性的关键调节因子。我们进一步假设，了解适应性可塑性的分子基础将为改善治疗提供新的策略。这些研究代表了我们实验室的新数据，并建立在20年的研究基础上，这些研究仅专注于胰腺癌的生物学和治疗。 为了解决这些假设，我们提出了以下三个目标。目的1.确定CD 44 s和CD 44 v在PDAC中的功能相关性。这一目标将解决使用等基因匹配的细胞系模型，其中表达的CD 44和CD 44 v亚型的调节。将针对表型、侵袭性、对化疗的反应、肿瘤植入和生长评估对调节CD 44 v和CD 44 s表达的影响。目标2.确定调节CD 44亚型转换和CD 44表达的机制。这一目标将确定EMT相关的转录抑制因子Snail和Zeb 1在抑制CD 44 v亚型表达所需的ESRP 1中的潜在作用，并进一步确定导致CD 44 s转录增加的机制。目标3.确定抗CD 44抗体是否阻止CD 44同种型转换或表达水平，以及这是否改善了对化疗的反应并减少了转移。这些研究将提供与适应性可塑性相关的重要新见解，并确定这些知识是否可用于对抗化疗诱导的表型转换的不良反应。抑制或逆转向EMT表型的转变可能被证明是增加对化疗的反应和患者生存的重要策略。

 DESCRIPTION (provided by applicant): Adaptive plasticity is a phrase used to explain how cancer cells gain selective growth and survival capabilities through phenotypic changes in response to their environment. Adaptive plasticity is exemplified by epithelial to mesenchymal transition (EMT) a process, which enables cancer cells to become migratory and invasive as well as having an increase in survival properties. This process can be reversed to a mesenchymal to epithelial transition (MET), which is believed to favor tumor engraftment and growth of cancer cells at metastatic sites. EMT in cancer cells is linked with isoform switching of the transmembrane protein CD44 from expressing the CD44 variant isoform (CD44v) to expressing CD44 standard form (CD44s). In this context we found that treatment of BxPC3 pancreatic ductal adenocarcinoma (PDAC) cell line with gemcitabine induces EMT and a high level of expression of CD44s with a decrease in expression of CD44v isoforms. This suggests that an adverse effect of chemotherapy may drive EMT, enhancing invasiveness and rendering tumor cells more resistant to chemotherapy. Moreover, we were able to use flow cytometry to select out from a PDAC cell lines (CFPAC-1 and AsPC1) a subpopulation of cells expressing high levels of CD44s. Knockdown of CD44s, in these cells, caused them to undergo MET, to be less invasive and to become more responsive to chemotherapy. These studies suggest that chemotherapy or other environmental stresses may induce a CD44s phenotype that promotes survival and is more invasive; however optimal tumor regrowth following chemotherapy or growth after engraftment of micrometastases may require re-switching to a CD44v phenotype and down regulation of CD44s expression. We hypothesize that CD44s and its variant isoforms are key regulators of adaptive plasticity in pancreatic cancer cells. We further hypothesize that understanding the molecular basis for adaptive plasticity will provide new strategies for improving therapy. These studies represent new data from our laboratory and build on 20 years of research solely focused on the biology and treatment of pancreatic cancer. To address these hypotheses we propose the following three objectives. Objective 1. Determine the functional relevance of CD44s and CD44v in PDAC. This objective will be addressed using isogenic matched cell line models in which expression of CD44s and CD44v isoforms are regulated. The effects on modulating expression of CD44v and CD44s will be assessed for phenotype, invasiveness, response to chemotherapy, tumor engraftment and growth. Objective 2. Determine the mechanism(s) that regulates CD44 isoform switching and CD44 expression. This objective will determine the potential role of EMT related transcriptional repressors Snail and Zeb1 in suppressing ESRP1 that is required for expression of CD44v isoforms and further identify the mechanisms that lead to the increased transcription of CD44s. Objective 3. Determine whether anti-CD44 antibody prevents CD44 isotype switching or expression level and whether this improves response to chemotherapy and reduces metastasis. These studies will provide important new insights related to adaptive plasticity and determine whether this knowledge can be used to counter act adverse effects of chemotherapy induced phenotypic switching. Inhibiting or reversing the switch towards an EMT phenotype may prove to be an important strategy for increasing the response to chemotherapy and patient survival.