Xie Yuntao, Skytting Björn, Nilsson Gunnar, Gasbarri Alessandra, Haslam Karl, Bartolazzi Armando, Brodin Bertha, Mandahl Nils, Larsson Olle
Department of Oncology and Pathology, Karolinska Hospital, SE-171 76 Stockholm, Sweden.
Cancer Res. 2002 Jul 1;62(13):3861-7.
The SYT-SSX fusion gene has been implicated in the malignant tumor cell growth of synovial sarcoma, but the underlying molecular mechanisms are still poorly understood. Here we demonstrate that SYT-SSX is critical for the protein level of cyclin D1 in synovial sarcoma cells. Antisense oligonucleotides to SYT-SSX mRNA rapidly and drastically decreased cyclin D1 and subsequently inhibited cell growth. This effect is specific for SYT-SSX, without involving the wild-type genes SYT or SSX. The decrease in cyclin D1 expression, which occurred shortly after inhibition of SYT-SSX expression, was found to be primarily dependent on an increased degradation of the cyclin D1 protein, as assessed by pulse-chase experiments using [(35)S]methionine. Furthermore, transfection of mouse fibroblasts with SYT-SSX cDNA increased the stability of cyclin D1. Because treatment with a proteasome inhibitor restored cyclin D1 expression, it seems like SYT-SSX interferes with ubiquitin-dependent degradation of cyclin D1. However, SYT-SSX-regulated cyclin D1 expression was proven to be independent of the glycogen synthetase kinase-3beta pathway. Taken together, our study provides evidence that SYT-SSX stabilizes cyclin D1 and is critical for cyclin D1 expression in synovial sarcoma cells. SYT-SSX-dependent expression of cyclin D1 may be an important mechanism in the development and progression of synovial sarcoma and also raises the possibility for targeted therapy.
SYT-SSX融合基因与滑膜肉瘤的恶性肿瘤细胞生长有关，但其潜在的分子机制仍知之甚少。在此我们证明，SYT-SSX对滑膜肉瘤细胞中细胞周期蛋白D1的蛋白水平至关重要。针对SYT-SSX mRNA的反义寡核苷酸迅速且显著地降低了细胞周期蛋白D1的水平，随后抑制了细胞生长。这种效应是SYT-SSX特有的，不涉及野生型基因SYT或SSX。通过使用[（35）S]甲硫氨酸的脉冲追踪实验评估发现，在抑制SYT-SSX表达后不久发生的细胞周期蛋白D1表达降低主要依赖于细胞周期蛋白D1蛋白降解的增加。此外，用SYT-SSX cDNA转染小鼠成纤维细胞可提高细胞周期蛋白D1的稳定性。因为用蛋白酶体抑制剂处理可恢复细胞周期蛋白D1的表达，所以似乎SYT-SSX干扰了细胞周期蛋白D1的泛素依赖性降解。然而，已证明SYT-SSX调节的细胞周期蛋白D1表达独立于糖原合成酶激酶-3β途径。综上所述，我们的研究提供了证据表明SYT-SSX可稳定细胞周期蛋白D1，并且对滑膜肉瘤细胞中细胞周期蛋白D1的表达至关重要。细胞周期蛋白D1的SYT-SSX依赖性表达可能是滑膜肉瘤发生和发展的重要机制，也为靶向治疗提供了可能性。
