Centre for Cancer Therapeutics, Ottawa Hospital Research Institute, 501 Smyth Road, Ottawa K1H 8L6, Canada.
Mol Cancer. 2010 Sep 3;9:233. doi: 10.1186/1476-4598-9-233.
Glioblastoma is one of the deadliest forms of cancer, in part because of its highly invasive nature. The tumor suppressor PTEN is frequently mutated in glioblastoma and is known to contribute to the invasive phenotype. However the downstream events that promote invasion are not fully understood. PTEN loss leads to activation of the atypical protein kinase C, PKCι. We have previously shown that PKCι is required for glioblastoma cell invasion, primarily by enhancing cell motility. Here we have used time-lapse videomicroscopy to more precisely define the role of PKCι in glioblastoma.
Glioblastoma cells in which PKCι was either depleted by shRNA or inhibited pharmacologically were unable to coordinate the formation of a single leading edge lamellipod. Instead, some cells generated multiple small, short-lived protrusions while others generated a diffuse leading edge that formed around the entire circumference of the cell. Confocal microscopy showed that this behavior was associated with altered behavior of the cytoskeletal protein Lgl, which is known to be inactivated by PKCι phosphorylation. Lgl in control cells localized to the lamellipod leading edge and did not associate with its binding partner non-muscle myosin II, consistent with it being in an inactive state. In PKCι-depleted cells, Lgl was concentrated at multiple sites at the periphery of the cell and remained in association with non-muscle myosin II. Videomicroscopy also identified a novel role for PKCι in the cell cycle. Cells in which PKCι was either depleted by shRNA or inhibited pharmacologically entered mitosis normally, but showed marked delays in completing mitosis.
PKCι promotes glioblastoma motility by coordinating the formation of a single leading edge lamellipod and has a role in remodeling the cytoskeleton at the lamellipod leading edge, promoting the dissociation of Lgl from non-muscle myosin II. In addition PKCι is required for the transition of glioblastoma cells through mitosis. PKCι therefore has a role in both glioblastoma invasion and proliferation, two key aspects in the malignant nature of this disease.
胶质母细胞瘤是最致命的癌症之一，部分原因是其高度侵袭性。抑癌基因 PTEN 在胶质母细胞瘤中经常发生突变，已知其有助于侵袭表型。然而，促进侵袭的下游事件尚未完全了解。PTEN 缺失会导致非典型蛋白激酶 C，即 PKCι 的激活。我们之前已经表明，PKCι 是胶质母细胞瘤细胞侵袭所必需的，主要是通过增强细胞迁移。在这里，我们使用延时视频显微镜更精确地定义了 PKCι 在胶质母细胞瘤中的作用。
通过 shRNA 耗竭或药理学抑制 PKCι 的胶质母细胞瘤细胞无法协调单个前缘片状伪足的形成。相反，一些细胞产生多个小的、短暂的突起，而另一些细胞产生弥漫的前缘，围绕细胞的整个圆周形成。共聚焦显微镜显示，这种行为与细胞骨架蛋白 Lgl 的行为改变有关，PKCι 磷酸化会使其失活。在对照细胞中，Lgl 定位于片状伪足前缘，不与非肌肉肌球蛋白 II 结合伴侣结合，这与它处于非活性状态一致。在 PKCι 耗竭的细胞中，Lgl 集中在细胞外周的多个部位，并与非肌肉肌球蛋白 II 保持结合。视频显微镜还确定了 PKCι 在细胞周期中的一个新作用。通过 shRNA 耗竭或药理学抑制 PKCι 的细胞正常进入有丝分裂，但在完成有丝分裂时表现出明显的延迟。
PKCι 通过协调单个前缘片状伪足的形成来促进胶质母细胞瘤的运动，并且在片状伪足前缘重塑细胞骨架方面发挥作用，促进 Lgl 与非肌肉肌球蛋白 II 的解离。此外，PKCι 是胶质母细胞瘤细胞通过有丝分裂所必需的。因此，PKCι 在胶质母细胞瘤的侵袭和增殖中都发挥作用，这是该疾病恶性性质的两个关键方面。
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