Lim F L, Soulez M, Koczan D, Thiesen H J, Knight J C
Department of Cancer Medicine, Imperial College of Science, Technology and Medicine, Hammersmith campus, London, UK.
Oncogene. 1998 Oct 15;17(15):2013-8. doi: 10.1038/sj.onc.1202122.
SSX genes show extensive nucleotide sequence conservation but little is known of their function. Disruption of SSX1 or SSX2, by chromosome translocation and 'in-frame' fusion to SYT, is a consistent feature of synovial sarcomas. The resulting SYT-SSX1/SSX2 proteins are activators of transcription; transactivation function is located in SYT. Unrearranged SSX1 can repress transcription, and this has been attributed to a putative Krüppel associated box (KRAB) repression domain at the N-terminus. Here we isolated SSX-KRAB domains to specifically measure repression activity, using a previously characterized KOX1-KRAB domain as a control. In our repressor assay SSX1- and SSX2-KRAB domains down-modulated the transactivation of a reporter gene by threefold, compared with 83-fold repression achieved by KOX1-KRAB in the assay. Yeast two-hybrid analysis showed that SSX1-KRAB, unlike KOX1-KRAB, fails to interact with the KRAB co-repressor TIF1beta. These results raise questions about the evolutionary and functional relationship of SSX-KRAB and typical KRAB domains of Krüppel zinc finger genes. We found that full-length SSX1 showed potent (74-fold) repression in our repressor assay, indicating the existence of a repression domain distinct from SSX-KRAB. By assaying deletion constructs of SSX1 we localized repression activity to 33 amino acids at the C-terminus. This novel domain is conserved between SSX family members, and, unlike the KRAB-related domain, is retained on fusion with SYT. This has important implications in understanding the mechanism by which the SYT-SSX fusion protein could contribute to neoplasia.
SSX基因显示出广泛的核苷酸序列保守性，但其功能却鲜为人知。滑膜肉瘤的一个一致特征是，通过染色体易位以及与SYT的“读框内”融合，导致SSX1或SSX2发生破坏。由此产生的SYT - SSX1/SSX2蛋白是转录激活因子；反式激活功能位于SYT中。未重排的SSX1可抑制转录，这归因于其N端一个假定的Krüppel相关框（KRAB）抑制结构域。在这里，我们分离出SSX - KRAB结构域，以使用先前表征的KOX1 - KRAB结构域作为对照，专门测量其抑制活性。在我们的抑制因子测定中，与测定中KOX1 - KRAB实现的83倍抑制相比，SSX1 - 和SSX2 - KRAB结构域使报告基因的反式激活下调了三倍。酵母双杂交分析表明，与KOX1 - KRAB不同，SSX1 - KRAB不能与KRAB共抑制因子TIF1β相互作用。这些结果引发了关于SSX - KRAB与Krüppel锌指基因典型KRAB结构域的进化和功能关系的问题。我们发现在我们的抑制因子测定中全长SSX1显示出强效（74倍）抑制作用，表明存在一个不同于SSX - KRAB的抑制结构域。通过检测SSX1的缺失构建体，我们将抑制活性定位到C端的33个氨基酸处。这个新结构域在SSX家族成员之间是保守的，并且与KRAB相关结构域不同，在与SYT融合时仍保留。这对于理解SYT - SSX融合蛋白可能导致肿瘤形成的机制具有重要意义。
