Graham K A, Richardson C L, Minden M D, Trent J M, Buick R N
Cancer Res. 1985 May;45(5):2201-5.
The oncogene N-ras has been found to be amplified (congruent to 20 copies) in the human breast carcinoma cell line MCF-7. The amplified sequences have been localized to a marker chromosome by in situ hybridization. Sublines of MCF-7, serially passaged in different laboratories, have marked variation in the degree of N-ras amplification. The differing degrees of amplification of N-ras are further evidence of heterogeneity within MCF-7 subclones. The phenomenon may not have general relevance for breast cancer, since other breast cancer cell lines and DNA from patient biopsies failed to show evidence of N-ras amplification.
已发现癌基因N-ras在人乳腺癌细胞系MCF-7中发生扩增（相当于20个拷贝）。通过原位杂交已将扩增序列定位到一条标记染色体上。在不同实验室连续传代的MCF-7亚系中，N-ras扩增程度有显著差异。N-ras不同程度的扩增进一步证明了MCF-7亚克隆内的异质性。由于其他乳腺癌细胞系和患者活检组织的DNA未显示N-ras扩增的证据，该现象可能与乳腺癌不具有普遍相关性。
