Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, Massachusetts 02129, USA.
Genes Dev. 2011 Apr 15;25(8):814-30. doi: 10.1101/gad.2000211.
pRB-mediated inhibition of cell proliferation is a complex process that depends on the action of many proteins. However, little is known about the specific pathways that cooperate with the Retinoblastoma protein (pRB) and the variables that influence pRB's ability to arrest tumor cells. Here we describe two shRNA screens that identify kinases that are important for pRB to suppress cell proliferation and pRB-mediated induction of senescence markers. The results reveal an unexpected effect of LATS2, a component of the Hippo pathway, on pRB-induced phenotypes. Partial knockdown of LATS2 strongly suppresses some pRB-induced senescence markers. Further analysis shows that LATS2 cooperates with pRB to promote the silencing of E2F target genes, and that reduced levels of LATS2 lead to defects in the assembly of DREAM (DP, RB [retinoblastoma], E2F, and MuvB) repressor complexes at E2F-regulated promoters. Kinase assays show that LATS2 can phosphorylate DYRK1A, and that it enhances the ability of DYRK1A to phosphorylate the DREAM subunit LIN52. Intriguingly, the LATS2 locus is physically linked with RB1 on 13q, and this region frequently displays loss of heterozygosity in human cancers. Our results reveal a functional connection between the pRB and Hippo tumor suppressor pathways, and suggest that low levels of LATS2 may undermine the ability of pRB to induce a permanent cell cycle arrest in tumor cells.
pRB 介导的细胞增殖抑制是一个复杂的过程，依赖于许多蛋白质的作用。然而，人们对与视网膜母细胞瘤蛋白（pRB）合作的特定途径以及影响 pRB 阻止肿瘤细胞能力的变量知之甚少。在这里，我们描述了两个 shRNA 筛选，这些筛选确定了对 pRB 抑制细胞增殖和 pRB 介导的衰老标志物诱导至关重要的激酶。结果揭示了 Hippo 通路的一个组成部分 LATS2 对 pRB 诱导表型的意外影响。LATS2 的部分敲低强烈抑制了一些 pRB 诱导的衰老标志物。进一步的分析表明，LATS2 与 pRB 合作促进 E2F 靶基因的沉默，并且 LATS2 水平降低导致 DREAM（DP、RB[视网膜母细胞瘤]、E2F 和 MuvB）抑制复合物在 E2F 调节的启动子处组装缺陷。激酶测定表明 LATS2 可以磷酸化 DYRK1A，并且它增强了 DYRK1A 磷酸化 DREAM 亚基 LIN52 的能力。有趣的是，LATS2 基因座在 13q 上与 RB1 物理相连，并且该区域在人类癌症中经常显示杂合性缺失。我们的结果揭示了 pRB 和 Hippo 肿瘤抑制途径之间的功能联系，并表明 LATS2 水平低可能会削弱 pRB 在肿瘤细胞中诱导永久细胞周期停滞的能力。
