The Human EKC/KEOPS Complex Is Recruited to Cullin2 Ubiquitin Ligases by the Human Tumour Antigen PRAME

The human tumour antigen PRAME (preferentially expressed antigen in melanoma) is frequently overexpressed during oncogenesis, and high PRAME levels are associated with poor clinical outcome in a variety of cancers. However, the molecular pathways in which PRAME is implicated are not well understood. We recently characterized PRAME as a BC-box subunit of a Cullin2-based E3 ubiquitin ligase. In this study, we mined the PRAME interactome to a deeper level and identified specific interactions with OSGEP and LAGE3, which are human orthologues of the ancient EKC/KEOPS complex. By characterizing biochemically the human EKC complex and its interactions with PRAME, we show that PRAME recruits a Cul2 ubiquitin ligase to EKC. Moreover, EKC subunits associate with PRAME target sites on chromatin. Our data reveal a novel link between the oncoprotein PRAME and the conserved EKC complex and support a role for both complexes in the same pathways.人类肿瘤抗原PRAME（preferentially expressed antigen in melanoma，黑色素瘤优先表达抗原）在肿瘤发生过程中常出现过表达，且在多种癌症中，PRAME高表达与不良临床预后密切相关。然而，PRAME所参与的分子通路目前尚未被充分阐明。我们近期将PRAME鉴定为基于Cullin2的E3泛素连接酶的BC盒亚基。本研究中，我们对PRAME相互作用组进行了更深入的挖掘，鉴定出其与OSGEP和LAGE3存在特异性相互作用——这二者均为古老的EKC/KEOPS复合物的人类同源物。通过对人类EKC复合物及其与PRAME的相互作用进行生化表征，我们证实PRAME可将Cul2泛素连接酶招募至EKC复合物。此外，EKC亚基可与染色质上的PRAME靶位点相结合。本研究数据揭示了癌蛋白PRAME与保守型EKC复合物之间的新型关联，并证实两种复合物可在同一通路中发挥功能。