Division of Cell Signalling and Immunology, College of Life Sciences, University of Dundee, Dundee, UK.
Oncogene. 2013 Sep 12;32(37):4417-26. doi: 10.1038/onc.2012.459. Epub 2012 Oct 22.
Genetic changes in HER2, PTEN, PIK3CA and AKT1 are all common in breast cancer and lead to the elevated phosphorylation of downstream targets of the PI3K/AKT signalling pathway. Changes in HER2, PTEN, PIK3CA and AKT have all been reported to lead to both enhanced proliferation and failures in hollow lumen formation in three dimensional epithelial culture models, but it is not clear whether these failures in lumen formation are caused by any failure in the spatial coordination of lumen formation (hollowing) or purely a failure in the apoptosis and clearance of luminal cells (cavitation). Here, we use normal murine mammary gland (NMuMG) epithelial cells, which form a hollow lumen without significant apoptosis, to compare the transformation by these four genetic changes. We find that either mutant PIK3CA expression or PTEN loss, but not mutant AKT1 E17K, cause disrupted epithelial architecture, whereas HER2 overexpression drives strong proliferation without affecting lumen formation in these cells. We also show that PTEN requires both lipid and protein phosphatase activity, its extreme C-terminal PDZ binding sequence and probably Myosin 5A to control lumen formation through a mechanism that does not correlate with its ability to control AKT, but which is selectively lost through mutation in some tumours. These findings correlate AKT-independent signalling activated by mutant PIK3CA or PTEN loss, but not strongly by HER2, with disrupted epithelial architecture and tumour formation.
HER2、PTEN、PIK3CA 和 AKT1 的遗传变化在乳腺癌中都很常见，导致 PI3K/AKT 信号通路下游靶标的磷酸化水平升高。HER2、PTEN、PIK3CA 和 AKT 的变化都被报道导致三维上皮培养模型中细胞增殖增强和中空腔形成失败，但尚不清楚这些腔形成失败是由于腔形成（凹陷）的空间协调失败还是单纯由于管腔细胞的凋亡和清除（空化）失败。在这里，我们使用正常的小鼠乳腺上皮 (NMuMG) 细胞，这些细胞在没有明显凋亡的情况下形成中空腔，来比较这四种遗传变化的转化。我们发现，只有突变 PIK3CA 的表达或 PTEN 的缺失，但不是突变 AKT1 E17K，会导致上皮结构紊乱，而 HER2 的过表达则会驱动强烈的增殖，而不会影响这些细胞中空腔的形成。我们还表明，PTEN 需要脂质和蛋白磷酸酶活性、其极端 C 末端 PDZ 结合序列和可能的肌球蛋白 5A 来控制腔形成，通过一种与 AKT 控制能力无关的机制，但在某些肿瘤中通过突变选择性丧失。这些发现将突变 PIK3CA 或 PTEN 缺失激活的 AKT 非依赖性信号与上皮结构紊乱和肿瘤形成相关联，但与 HER2 相关性不强。
