Kurdistani S K, Arizti P, Reimer C L, Sugrue M M, Aaronson S A, Lee S W
Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Harvard Institutes of Medicine, Boston, Massachusetts 02115, USA.
Cancer Res. 1998 Oct 1;58(19):4439-44.
Through a differential screening technique, we have identified a cDNA clone with differential expression in normal versus tumor cells. This clone, designated rit42 (reduced in tumor, 42 kDa), was previously isolated as a homocysteine-inducible gene in human endothelial cells (RTP), and the same or a highly related androgen-responsive gene in mouse has also been identified. Both Northern blot analysis and in situ hybridization demonstrated a significantly diminished expression in tumor cells, including those derived from breast and prostate when compared with normal cells. It was shown that RTP/rit42 mRNA cycles with cell division, peaking at G1 and G2-M, with lower expression in S phase. The biphasic expression of RTP/rit42 mRNA was absent in tumor cells. Introduction of rit42 cDNA into human cancer cells reduced cell growth both in vitro and in nude mice. Moreover, analysis of a tetracycline-regulated p53-inducible system in null-p53 cell lines showed that RTP/rit42 mRNA expression increased concomitantly with p53 expression and followed a similar time course. In addition, DNA-damaging agents induced RTP/rit42 expression in a p53-dependent manner but independent of a p53-mediated G1 arrest. Immunofluorescence analysis of a FLAG epitope-tagged RTP/rit42 protein revealed a cytoplasmic localization pattern with redistribution to the nucleus upon DNA damage. We have localized RTP/rit42 to human chromosome 8q24.3. Taken together, these results are consistent with a growth inhibitory role for RTP/rit42, and its down-regulation may contribute to the tumor malignant phenotype.
通过差异筛选技术，我们鉴定出了一个在正常细胞与肿瘤细胞中存在差异表达的cDNA克隆。这个克隆被命名为rit42（在肿瘤中表达降低，42 kDa），它之前作为人内皮细胞中的同型半胱氨酸诱导基因被分离出来（RTP），并且在小鼠中也鉴定出了相同或高度相关的雄激素应答基因。Northern印迹分析和原位杂交均表明，与正常细胞相比，肿瘤细胞中的表达显著降低，包括来自乳腺和前列腺的肿瘤细胞。结果显示，RTP/rit42 mRNA随细胞分裂而循环，在G1期和G2-M期达到峰值，在S期表达较低。肿瘤细胞中不存在RTP/rit42 mRNA的双相表达。将rit42 cDNA导入人癌细胞可在体外和裸鼠体内降低细胞生长。此外，对p53缺失的细胞系中四环素调控的p53诱导系统的分析表明，RTP/rit42 mRNA表达随p53表达而增加，并遵循相似的时间进程。另外，DNA损伤剂以p53依赖的方式诱导RTP/rit42表达，但与p53介导的G1期阻滞无关。对带有FLAG表位标签的RTP/rit42蛋白的免疫荧光分析显示，其在细胞质中的定位模式在DNA损伤时重新分布到细胞核。我们已将RTP/rit42定位到人类染色体8q24.3。综上所述，这些结果与RTP/rit42的生长抑制作用一致，其下调可能有助于肿瘤的恶性表型。
