Abdollahi A, Bao R, Hamilton T C
Department of Medical Oncology, Fox Chase Cancer Center, Philadelphia, Pennsylvannia, PA 19111, USA.
Oncogene. 1999 Nov 11;18(47):6477-87. doi: 10.1038/sj.onc.1203067.
We previously reported cloning the rLot1 gene, and its human homolog (hLOT1), through analysis of differential gene expression in normal and malignant rat ovarian surface epithelial cells. Both human and rat ovarian carcinoma cell lines exhibited lost or decreased expression of this gene. Interestingly, the LOT1 gene localized at band q25 of human chromosome 6 which is a frequent site for LOH in many solid tumors including ovarian cancer. In this report we have further characterized the potential role of LOT1 in malignant transformation and developed evidence that the gene is a novel target of growth factor signaling pathway. Assays using transient transfections showed that LOT1 is a nuclear protein and may act as a transcription factor. In vitro and in vivo studies involving ovarian cancer cell lines revealed that expression of LOT1 is directly associated with inhibition of cellular proliferation and induction of morphological transformations. Additionally, we show that in normal rat ovarian surface epithelial cells Lot1 gene expression is responsive to growth factor stimulation. Its mRNA is strongly down-regulated by epidermal growth factor receptor (EGFR) ligands, namely EGF and TGF-alpha. Blocking the ligand-activated EGFR signal transduction pathway by the specific EGF receptor inhibitor, tyrphostin AG1478, and the MEK inhibitor, PD098059, restores the normal level of Lot1 gene expression. It appears that the regulation of Lot1 gene is unique to these ligands, as well as the growth promoting agent TPA, since other factors either did not affect Lot1 expression, or the effect was modest and transient. Altogether, the results suggest that Lot1 expression is primarily mediated via EGF receptor or a related pathway and it may regulate the growth promoting signals as a zinc-finger motif containing nuclear transcription factor.
我们之前报道过，通过分析正常和恶性大鼠卵巢表面上皮细胞中的差异基因表达，克隆了rLot1基因及其人类同源基因（hLOT1）。人类和大鼠卵巢癌细胞系均表现出该基因表达缺失或降低。有趣的是，LOT1基因定位于人类6号染色体的q25带，在包括卵巢癌在内的许多实体瘤中，该区域是杂合性缺失的常见位点。在本报告中，我们进一步阐述了LOT1在恶性转化中的潜在作用，并提供证据表明该基因是生长因子信号通路的一个新靶点。瞬时转染实验表明，LOT1是一种核蛋白，可能作为转录因子发挥作用。涉及卵巢癌细胞系的体外和体内研究表明，LOT1的表达与细胞增殖抑制和形态转化诱导直接相关。此外，我们发现，在正常大鼠卵巢表面上皮细胞中，Lot1基因表达对生长因子刺激有反应。其mRNA受到表皮生长因子受体（EGFR）配体，即EGF和TGF-α的强烈下调。通过特异性EGF受体抑制剂 tyrphostin AG1478和MEK抑制剂PD098059阻断配体激活的EGFR信号转导通路，可恢复Lot1基因表达的正常水平。似乎Lot1基因的调控对这些配体以及促生长剂TPA具有特异性，因为其他因子要么不影响Lot1表达，要么影响较小且短暂。总之，结果表明Lot1表达主要通过EGF受体或相关途径介导，它可能作为一种含锌指基序的核转录因子调节促生长信号。
