Yap/Taz promote the scavenging of extracellular nutrients through macropinocytosis [RNA-Seq]

The uptake of macromolecules and cellular debris through macropinocytosis has emerged as an important nutrient acquisition strategy of cancer cells. Genetic alterations commonly found in human cancers (e.g. mutations in KRAS or loss of PTEN) have been shown to increase macropinocytosis. To identify additional effectors that enable cell growth dependent on the uptake of extracellular proteins, pancreatic ductal adenocarcinoma (PDA) cells were selected for growth in medium where extracellular albumin was the obligate source of the essential amino acid leucine. Analysis of global changes in chromatin availability and gene expression revealed that PDA cells selected under these conditions exhibited elevated activity of the transcriptional activators Yap/Taz. Knockout of Yap/Taz prevented growth of PDA cells in leucine-deficient medium, but not in complete medium. Furthermore, constitutively active forms of Yap or Taz were sufficient to stimulate macropinocytosis of extracellular protein. Together, these studies suggest that the Hippo pathway effectors Yap and Taz are important transcriptional regulators of endocytic nutrient uptake. Murine pancreatic adenocarcinoma cells (KRPC) were cultured short-term (16h) or long-term (21d) in leucine-deficient media +/- 3% bovine serum albumin and subjected to RNA-seq analysis.

通过巨胞饮作用（macropinocytosis）摄取大分子与细胞碎片，现已成为癌细胞关键的营养获取策略。人类癌症中常见的遗传改变（如KRAS突变或PTEN缺失）已被证实可增强巨胞饮作用。为鉴定能够依赖摄取胞外蛋白维持细胞生长的其他效应因子，研究人员将胰腺导管腺癌（Pancreatic Ductal Adenocarcinoma, PDA）细胞置于以胞外白蛋白作为必需氨基酸亮氨酸唯一来源的培养基中进行筛选培养。对染色质开放性与基因表达的全局变化分析显示，经上述条件筛选的PDA细胞表现出转录激活因子Yap/Taz的活性升高。敲除Yap/Taz可阻止PDA细胞在亮氨酸缺陷培养基中的生长，但不会影响其在完全培养基中的增殖。此外，组成型激活形式的Yap或Taz足以刺激胞外蛋白的巨胞饮作用。综上，本研究表明Hippo通路（Hippo pathway）效应因子Yap与Taz是内吞营养摄取的重要转录调控因子。将小鼠胰腺腺癌细胞（KRPC）在添加或不添加3%牛血清白蛋白（bovine serum albumin）的亮氨酸缺陷培养基中短期（16小时）或长期（21天）培养后，进行RNA测序（RNA-seq）分析。