Martin K J, Kwan C P, Nagasaki K, Zhang X, O'Hare M J, Kaelin C M, Burgeson R E, Pardee A B, Sager R
Division of Cancer Genetics, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts, USA.
Mol Med. 1998 Sep;4(9):602-13.
Laminin-5 (ln-5), a large heterotrimeric glycoprotein consisting of an alpha 3, beta 3, and gamma 2 chain, is a component of epithelial cell basement membranes that functions as a ligand of the alpha 3 beta 1 and alpha 6 beta 4 integrins to regulate cell adhesion, migration, and morphogenesis. The ln-5 chains show tissue-specific patterns of regulation in tumors derived from different tissues. For example, ln-5 is often up-regulated in gliomas, gastric carcinomas, and squamous carcinomas and down-regulated in prostate and basal cell carcinomas. Ln-5 expression patterns may represent useful tumor markers and help to elucidate the role of ln-5 in tumor progression in different tissue types.
We have studied ln-5 expression patterns in the breast. mRNA levels were examined in tumor and normal breast epithelial cell lines, tissue samples, and immunomagnetically sorted primary cultures using differential display, Northern blotting, and hybridization arrays. Protein levels were examined by immunoprecipitation. Gene integrity was assessed by Southern blotting of representative cell types.
Ln-5 alpha 3, beta 3, and gamma 2 mRNA expression was found to be markedly down-regulated in a panel of breast tumor cell lines when compared with normal breast epithelial cells. Ln-5 mRNA was expressed at relatively high levels in MCF-10A immortal normal breast epithelial cells, long-term cultures of normal breast cells, and sorted primary cultures of normal breast luminal epithelial and myoepithelial cells. Reduced, but detectable, levels of ln-5 tended to be expressed in cell lines derived from early-stage breast tumors, whereas expression was generally not detected in cell lines derived from later-stage tumors. In breast tumor tissue specimens, expression of ln alpha 3 and beta 3 mRNAs tended to be reduced relative to levels observed in adjacent nontumor tissue, whereas in gamma 2 levels were elevated in specimens with increased amounts of myoepithelial cells. These ln-5 expression changes could not be attributed to large-scale mutations or gene rearrangements. Ln-5 protein levels were found to reflect mRNA levels in representative cell lines. At senescence, a growth state believed to suppress tumorigenesis, expression of all three ln-5 mRNAs was up-regulated.
The down-regulation of ln-5 mRNA expression in breast tumors cells provides a new molecular marker and suggests that ln-5 functions to control tumor progression in the breast.
层粘连蛋白-5（ln-5）是一种由α3、β3和γ2链组成的大型异源三聚体糖蛋白，是上皮细胞基底膜的组成成分，作为α3β1和α6β4整合素的配体发挥作用，调节细胞黏附、迁移和形态发生。ln-5链在源自不同组织的肿瘤中表现出组织特异性的调控模式。例如，ln-5在胶质瘤、胃癌和鳞状细胞癌中常上调，而在前列腺癌和基底细胞癌中下调。ln-5的表达模式可能代表有用的肿瘤标志物，并有助于阐明ln-5在不同组织类型肿瘤进展中的作用。
我们研究了乳腺中ln-5的表达模式。使用差异显示、Northern印迹和杂交阵列检测肿瘤和正常乳腺上皮细胞系、组织样本以及免疫磁珠分选的原代培养物中的mRNA水平。通过免疫沉淀检测蛋白质水平。通过对代表性细胞类型进行Southern印迹评估基因完整性。
与正常乳腺上皮细胞相比，在一组乳腺肿瘤细胞系中发现ln-5的α3、β3和γ2 mRNA表达明显下调。ln-5 mRNA在MCF-10A永生化正常乳腺上皮细胞、正常乳腺细胞的长期培养物以及分选的正常乳腺腔上皮和肌上皮细胞原代培养物中表达水平相对较高。ln-5水平降低但仍可检测到，倾向于在源自早期乳腺肿瘤的细胞系中表达，而在源自晚期肿瘤的细胞系中通常未检测到表达。在乳腺肿瘤组织标本中，相对于相邻非肿瘤组织中观察到的水平，ln α3和β3 mRNA的表达倾向于降低，而在肌上皮细胞数量增加的标本中γ2水平升高。这些ln-5表达变化不能归因于大规模突变或基因重排。发现ln-5蛋白水平反映了代表性细胞系中的mRNA水平。在衰老状态下，一种被认为可抑制肿瘤发生的生长状态，所有三种ln-5 mRNA的表达均上调。
乳腺肿瘤细胞中ln-5 mRNA表达的下调提供了一种新的分子标志物，并表明ln-5在控制乳腺肿瘤进展中发挥作用。
