Kuroda M, Ishida T, Takanashi M, Satoh M, Machinami R, Watanabe T
Department of Pathology, University of Tokyo, Japan.
Am J Pathol. 1997 Sep;151(3):735-44.
Myxoid liposarcomas are characterized by t(12; 16)(q13;p11) translocation and expression of TLS/ FUS-CHOP chimeric transcripts (types I to III). Among these, the type II transcript is expressed in the majority of cases of myxoid and round cell liposarcoma. To investigate the function of the type II chimeric protein, we obtained stable transformants of ST-13, a murine preadipocytic cell line, which express TLS/FUS-CHOP type II protein (ST-TC) or CHOP protein (ST-C) as well as vector-transfected controls (ST-V). ST-TC and ST-C cells showed almost complete or partial resistance to adipogenic conversion by insulin and thiazolidinedione, respectively. Induction by adipogenic stimulation of the adipocytic genes such as C/EBP alpha, aP2, and adipsin was almost totally suppressed in the ST-TC cells, whereas in ST-C cells C/EBP alpha alone was induced without induction of aP2 and adipsin. Transcriptional suppression of the C/EBP alpha gene in ST-TC cells was suggested by the results of chloramphenicol acetyltransferase (CAT) assay showing a significantly lower C/EBP alpha promoter activity compared with findings in ST-C and ST-V cells. Failure to rescue adipogenic conversion by ectopic expression of C/EBP alpha in ST-TC cells suggested a functional impairment of C/EBP alpha to induce expression of downstream genes. TLS/FUS-CHOP type II protein showed transforming activity, as evidenced by loss of contact inhibition of growth, anchorage-independent growth in soft agar, and tumor formation in nude mice, showing typical histological features of myxoid liposarcoma seen in humans. These findings suggest important roles for TLS/FUS-CHOP type II protein in the oncogenesis of myxoid liposarcoma.
黏液样脂肪肉瘤的特征是存在t(12; 16)(q13;p11)易位以及TLS/FUS-CHOP嵌合转录本（I至III型）的表达。其中，II型转录本在大多数黏液样和圆形细胞脂肪肉瘤病例中表达。为了研究II型嵌合蛋白的功能，我们获得了ST-13（一种小鼠前脂肪细胞系）的稳定转化体，其表达TLS/FUS-CHOP II型蛋白（ST-TC）或CHOP蛋白（ST-C）以及载体转染对照（ST-V）。ST-TC和ST-C细胞分别对胰岛素和噻唑烷二酮诱导的脂肪生成转化表现出几乎完全或部分抗性。脂肪生成刺激对脂肪细胞基因如C/EBPα、aP2和脂肪酶的诱导在ST-TC细胞中几乎完全受到抑制，而在ST-C细胞中仅诱导了C/EBPα，未诱导aP2和脂肪酶。氯霉素乙酰转移酶（CAT）分析结果表明，与ST-C和ST-V细胞相比，ST-TC细胞中C/EBPα启动子活性显著降低，提示ST-TC细胞中C/EBPα基因的转录受到抑制。在ST-TC细胞中通过异位表达C/EBPα未能挽救脂肪生成转化，这表明C/EBPα诱导下游基因表达的功能受损。TLS/FUS-CHOP II型蛋白表现出转化活性，生长接触抑制丧失、在软琼脂中不依赖贴壁生长以及在裸鼠中形成肿瘤均证明了这一点，肿瘤呈现出人类黏液样脂肪肉瘤的典型组织学特征。这些发现表明TLS/FUS-CHOP II型蛋白在黏液样脂肪肉瘤的肿瘤发生中起重要作用。
