Zhang Xiaoying, Guo Cai, Wu Xiwei, Li Arthur X, Liu Limin, Tsark Walter, Dammann Reinhard, Shen Hui, Vonderfecht Steven L, Pfeifer Gerd P
Department of Biology, Beckman Research Institute, City of Hope, Duarte, California.
Department of Molecular and Cellular Biology, Beckman Research Institute, City of Hope, Duarte, California.
Cancer Res. 2016 May 1;76(9):2824-35. doi: 10.1158/0008-5472.CAN-15-3010. Epub 2016 Mar 15.
The tumor suppressor gene RASSF1A is epigenetically silenced in most human cancers. As a binding partner of the kinases MST1 and MST2, the mammalian orthologs of the Drosophila Hippo kinase, RASSF1A is a potential regulator of the Hippo tumor suppressor pathway. RASSF1A shares these properties with the scaffold protein SAV1. The role of this pathway in human cancer has remained enigmatic inasmuch as Hippo pathway components are rarely mutated in tumors. Here we show that Rassf1a homozygous knockout mice develop liver tumors. However, heterozygous deletion of Sav1 or codeletion of Rassf1a and Sav1 produced liver tumors with much higher efficiency than single deletion of Rassf1a. Analysis of RASSF1A-binding partners by mass spectrometry identified the Hippo kinases MST1, MST2, and the oncogenic IκB kinase TBK1 as the most enriched RASSF1A-interacting proteins. The transcriptome of Rassf1a(-/-) livers was more deregulated than that of Sav1(+/-) livers, and the transcriptome of Rassf1a(-/-), Sav1(+/-) livers was similar to that of Rassf1a(-/-) mice. We found that the levels of TBK1 protein were substantially upregulated in livers lacking Rassf1a. Furthermore, transcripts of several β-tubulin isoforms were increased in the Rassf1a-deficient livers presumably reflecting a role of RASSF1A as a microtubule-stabilizing protein. In human liver cancer, RASSF1A frequently undergoes methylation at the promoter but this was not observed for MST1, MST2, or SAV1. Our results suggest a multifactorial role of RASSF1A in suppression of liver carcinogenesis. Cancer Res; 76(9); 2824-35. ©2016 AACR.
肿瘤抑制基因RASSF1A在大多数人类癌症中会发生表观遗传沉默。作为果蝇Hippo激酶的哺乳动物直系同源物激酶MST1和MST2的结合伴侣，RASSF1A是Hippo肿瘤抑制途径的潜在调节因子。RASSF1A与支架蛋白SAV1具有这些共同特性。由于Hippo途径成分在肿瘤中很少发生突变，该途径在人类癌症中的作用一直不明。在此我们表明，Rassf1a纯合敲除小鼠会发生肝肿瘤。然而，Sav1的杂合缺失或Rassf1a与Sav1的共同缺失产生肝肿瘤的效率比单独缺失Rassf1a要高得多。通过质谱分析RASSF1A结合伴侣，确定Hippo激酶MST1、MST2以及致癌性IκB激酶TBK1是最丰富的与RASSF1A相互作用的蛋白。Rassf1a(-/-)肝脏的转录组比Sav1(+/-)肝脏的转录组失调更严重，而Rassf1a(-/-)、Sav1(+/-)肝脏的转录组与Rassf1a(-/-)小鼠的相似。我们发现，在缺乏Rassf1a的肝脏中，TBK1蛋白水平大幅上调。此外，在Rassf1a缺陷的肝脏中，几种β-微管蛋白亚型的转录本增加，这可能反映了RASSF1A作为微管稳定蛋白的作用。在人类肝癌中，RASSF1A在启动子处经常发生甲基化，但MST1、MST2或SAV1未观察到这种情况。我们的结果表明RASSF1A在抑制肝癌发生中具有多因素作用。《癌症研究》；76(9)；2824 - 35。©2016美国癌症研究协会。
