Ilyas Sumera I, Mertens Joachim C, Bronk Steven F, Hirsova Petra, Dai Haiming, Roberts Lewis R, Kaufmann Scott H, Gores Gregory J
Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, Minnesota 55905.
Division of Gastroenterology and Hepatology, University Hospital Zurich, Zurich 8091, Switzerland, and.
J Biol Chem. 2014 Aug 15;289(33):22835-22849. doi: 10.1074/jbc.M114.563064. Epub 2014 Jun 27.
Desmoplastic malignancies such as cholangiocarcinoma (CCA) are characterized by a dense stroma containing an abundance of myofibroblasts termed cancer-associated fibroblasts (CAF). The CAF phenotype represents an "activated state" in which cells are primed for cell death triggered by BH3 mimetics. Accordingly, this primed state may be therapeutically exploited. To elucidate the mechanisms underlying this poorly understood apoptotic priming, we examined the role of platelet-derived growth factor (PDGF) in CAF priming for cell death given its prominent role in CAF activation. PDGF isomers PDGF-B and PDGF-D are abundantly expressed in CCA cells derived from human specimens. Either isomer sensitizes myofibroblasts to cell death triggered by BH3 mimetics. Similar apoptotic sensitization was observed with co-culture of myofibroblasts and CCA cells. Profiling of Bcl-2 proteins expressed by PDGF-primed myofibroblasts demonstrated an increase in cellular levels of Puma. PDGF-mediated increases in cellular Puma levels induced proapoptotic changes in Bak, which resulted in its binding to Bcl-2. Short hairpin RNA-mediated down-regulation of Puma conferred resistance to PDGF-mediated apoptotic priming. Conversely, the BH3 mimetic navitoclax disrupted Bcl-2/Bak heterodimers, allowing Bak to execute the cell death program. Treatment with a Bcl-2-specific BH3 mimetic, ABT-199, reduced tumor formation and tumor burden in a murine model of cholangiocarcinoma. Collectively, these findings indicate that apoptotic priming of CAF by PDGF occurs via Puma-mediated Bak activation, which can be converted to active full-blown apoptosis by navitoclax or ABT-199 for therapeutic benefit.
诸如胆管癌（CCA）之类的促结缔组织增生性恶性肿瘤的特征在于，其致密的基质中含有大量被称为癌症相关成纤维细胞（CAF）的肌成纤维细胞。CAF表型代表一种“激活状态”，在此状态下细胞对BH3模拟物触发的细胞死亡已做好准备。因此，这种准备好的状态可能具有治疗价值。为了阐明这种了解甚少的凋亡致敏的潜在机制，鉴于血小板衍生生长因子（PDGF）在CAF激活中起重要作用，我们研究了其在CAF致敏细胞死亡中的作用。PDGF异构体PDGF-B和PDGF-D在源自人类标本的CCA细胞中大量表达。任何一种异构体均使肌成纤维细胞对BH3模拟物触发的细胞死亡敏感。在肌成纤维细胞与CCA细胞共培养时也观察到了类似的凋亡致敏现象。对PDGF致敏的肌成纤维细胞表达的Bcl-2蛋白进行分析表明，细胞中Puma水平升高。PDGF介导的细胞Puma水平升高诱导了Bak的促凋亡变化，导致其与Bcl-2结合。短发夹RNA介导的Puma下调赋予了对PDGF介导的凋亡致敏的抗性。相反，BH3模拟物navitoclax破坏了Bcl-2/Bak异二聚体，使Bak能够执行细胞死亡程序。用Bcl-2特异性BH3模拟物ABT-199治疗可减少胆管癌小鼠模型中的肿瘤形成和肿瘤负担。总体而言，这些发现表明，PDGF对CAF的凋亡致敏是通过Puma介导的Bak激活发生的，navitoclax或ABT-199可将其转化为活跃的完全凋亡，从而带来治疗益处。
