Medina D, Schwartz M, Taha M, Oborn C J, Smith G H
Cancer Res. 1987 Sep 1;47(17):4686-93.
The levels of milk-specific mRNAs (alpha-casein, whey acidic protein) and proteins (casein, alpha-lactalbumin) were examined in the DIM series of mammary preneoplastic outgrowth lines and tumors. The constitutive production of casein protein was variable among the preneoplastic DIM outgrowth lines maintained in virgin mice. Outgrowth line DIM-2 consistently expressed a very low level of casein mRNA and protein but no detectable alpha-lactalbumin protein. Outgrowth line DIM-4 expressed a high level of casein protein and no alpha-lactalbumin; however, by transplant generation 9, the levels of casein mRNA and protein were significantly decreased but remained greater than those found in DIM-2. Outgrowth line DIM-3 expressed high levels of casein protein during all transplant generations examined and sporadically exhibited detectable amounts of alpha-lactalbumin. The level of beta-casein mRNA in DIM-3 was 7 times greater than seen in DIM-4 outgrowths, but still only 2% of that measured in the normal mammary gland from lactating mice. The majority of tumors derived from the DIM outgrowth lines expressed very low levels of beta-casein mRNA and total casein protein, although occasionally tumors were observed with very high levels of casein expression. Immunoblot analysis of cellular extracts indicated that alpha, beta-, and gamma-caseins were expressed in the three outgrowth lines to varying degrees. Whey acidic protein mRNA attained barely detectable levels in the best of cases. Only outgrowth line DIM-3 responded to a normal lactogenic stimulus (lactating mouse) with significantly increased levels of milk-specific products. As determined by avidin-biotin peroxidase staining, the percentage of alveoli expressing beta-casein and alpha-lactalbumin proteins in lactating mice increased from 20 and 0%, respectively, in virgin mice to 85 and 40%, respectively, in lactating mice. Similarly, the levels of mRNA for beta-casein and whey acidic protein increased 8- and 5.5-fold, respectively. These results indicate that the cell populations selected by serial transplantation of preneoplastic mammary tissues fall into at least three categories with respect to expression of mammary-specific differentiation products: uninducible, inducible, constitutive. The DIM-3 outgrowth line appears to represent a highly inducible cell population. As concluded in earlier investigations, there was no correlation between secretory activity, morphology of the outgrowths, and tumor-producing capabilities in virgin mice. The effect of a normal lactogenic stimulus on the tumor potential of the DIM-3 line is currently under investigation.
在乳腺肿瘤前生长系和肿瘤的泌乳天数（DIM）系列中，检测了乳特异性mRNA（α-酪蛋白、乳清酸性蛋白）和蛋白质（酪蛋白、α-乳白蛋白）的水平。在处女小鼠中维持的肿瘤前DIM生长系中，酪蛋白的组成型产生存在差异。生长系DIM-2始终表达极低水平的酪蛋白mRNA和蛋白质，但未检测到α-乳白蛋白。生长系DIM-4表达高水平的酪蛋白且无α-乳白蛋白；然而，到移植第9代时，酪蛋白mRNA和蛋白质水平显著下降，但仍高于DIM-2中的水平。生长系DIM-3在所有检测的移植代中均表达高水平的酪蛋白，且偶尔可检测到α-乳白蛋白。DIM-3中β-酪蛋白mRNA水平比DIM-4生长系中的高7倍，但仍仅为泌乳小鼠正常乳腺中测得水平的2%。源自DIM生长系的大多数肿瘤表达极低水平的β-酪蛋白mRNA和总酪蛋白，尽管偶尔会观察到酪蛋白表达水平非常高的肿瘤。细胞提取物的免疫印迹分析表明，α、β-和γ-酪蛋白在三个生长系中均有不同程度的表达。在最佳情况下，乳清酸性蛋白mRNA水平仅勉强可检测到。只有生长系DIM-3对正常泌乳刺激（泌乳小鼠）有反应，其乳特异性产物水平显著增加。通过抗生物素蛋白-生物素过氧化物酶染色确定，泌乳小鼠中表达β-酪蛋白和α-乳白蛋白的肺泡百分比分别从处女小鼠中的20%和0%增加到泌乳小鼠中的85%和40%。同样，β-酪蛋白和乳清酸性蛋白的mRNA水平分别增加了8倍和5.5倍。这些结果表明，肿瘤前乳腺组织连续移植所选择的细胞群体在乳腺特异性分化产物的表达方面至少可分为三类：不可诱导型、可诱导型、组成型。DIM-3生长系似乎代表了一个高度可诱导的细胞群体。如早期研究所总结的，在处女小鼠中，分泌活性、生长系形态与肿瘤产生能力之间没有相关性。目前正在研究正常泌乳刺激对DIM-3系肿瘤潜能的影响。
