Freije J M, MacDonald N J, Steeg P S
Women's Cancers Section, National Cancer Institute, Bethesda, MD 20892, USA.
Biochem Soc Symp. 1998;63:261-71.
The nm23 genes were discovered on the basis of their reduced expression by highly metastatic cell lines. This trend was confirmed in cohorts of several types of human carcinomas and melanomas. Several transfection studies have demonstrated the suppressive effect of nm23 overexpression on the metastatic aggressiveness of melanoma and breast carcinoma cells in vivo. These transfection experiments have also demonstrated an effect of nm23 overexpression on cellular functions involved in the metastatic phenotype, such as cell motility, and point to a regulatory role for Nm23 proteins in cellular signalling pathways. Nm23 homologues from various species are also involved in normal tissue development and differentiation. Transfection of nm23-H1 into breast cancer cells provided a functional demonstration of the involvement of this gene in the differentiation of mammary epithelial cells. However, the molecular mechanism of these biological effects remains unknown. Several biochemical activities have been reported for Nm23, including NDP kinase activity, serine autophosphorylation and protein-histidine kinase activity. To define the possible significance of these biochemical activities, we carried out site-directed mutagenesis of the relevant codons of nm23-H1 cDNA and studied the effects upon transfection into MDA-MB-435 human breast carcinoma cells. We have also used Nm23 expression as a molecular marker to identify novel compounds that are active against the most aggressive tumour cells. This approach revealed that none of the standard agents currently in clinical use is preferentially active against the most aggressive tumour cells, and allowed us to identify new compounds that are preferentially inhibitory towards low-Nm23-expressing breast carcinoma and melanoma cell lines. This analysis also revealed a significant correlation between Nm23 levels and sensitivity of the tumour cells to alkylating agents. A functional implication of Nm23 proteins in this phenomenon was demonstrated after transfection of nm23 cDNAs into melanoma and breast and ovarian carcinoma cells.
nm23基因是基于其在高转移细胞系中表达降低而被发现的。这种趋势在几种类型的人类癌症和黑色素瘤队列中得到了证实。多项转染研究表明，nm23过表达对黑色素瘤和乳腺癌细胞在体内的转移侵袭性具有抑制作用。这些转染实验还证明了nm23过表达对参与转移表型的细胞功能（如细胞运动）的影响，并指出Nm23蛋白在细胞信号通路中具有调节作用。来自不同物种的Nm23同源物也参与正常组织的发育和分化。将nm23-H1转染到乳腺癌细胞中，为该基因参与乳腺上皮细胞分化提供了功能证明。然而，这些生物学效应的分子机制仍然未知。已报道Nm23具有多种生化活性，包括NDP激酶活性、丝氨酸自磷酸化和蛋白-组氨酸激酶活性。为了确定这些生化活性的可能意义，我们对nm23-H1 cDNA的相关密码子进行了定点诱变，并研究了其对转染到MDA-MB-435人乳腺癌细胞中的影响。我们还将Nm23表达用作分子标记，以鉴定对最具侵袭性的肿瘤细胞有活性的新型化合物。这种方法表明，目前临床使用的标准药物中没有一种对最具侵袭性的肿瘤细胞具有优先活性，并使我们能够鉴定出对低Nm23表达的乳腺癌和黑色素瘤细胞系具有优先抑制作用的新化合物。该分析还揭示了Nm23水平与肿瘤细胞对烷化剂敏感性之间的显著相关性。将nm23 cDNA转染到黑色素瘤、乳腺癌和卵巢癌细胞中后，证明了Nm23蛋白在这一现象中的功能意义。
