Speth C, Oberbäumer I
Department of Connective Tissue Research, Max-Planck-Institut für Biochemie, Martinsried, Germany.
Exp Cell Res. 1993 Feb;204(2):302-10. doi: 10.1006/excr.1993.1037.
Differentiated murine teratocarcinoma cell lines have been widely used as sources for the basement membrane proteins laminin and collagen IV. In order to understand the control of their expression, we have measured the transcription rates of the corresponding genes in nuclear run-on assays. The ratios of transcripts obtained from the five different genes of interest (for laminins A, B1, and B2 and alpha 1(IV), alpha 2(IV)) are rather different from the ratios of the corresponding mRNAs, which are again different from the protein levels needed. The gene for alpha 2(IV) is transcribed at a higher rate than the one for alpha 1(IV) and, similarly, the gene for laminin A is transcribed at a higher rate than the other two laminin genes, respectively. However, the alpha 2(IV) and laminin A mRNA levels are lower than those for the other chains of the same molecule. The alpha 1(IV) mRNA is 3- to 15-fold more abundant than the alpha 2(IV) mRNA, depending on the cell line. At the protein level, the A chain seems to be limiting for the assembly of laminin, in accordance with its low mRNA level. The two collagen chains have variable pool sizes, but the triple helical molecules always seem to be composed of two alpha 1(IV) and one alpha 2(IV) chains. These results point to extensive control mechanisms at various stages of posttranscriptional events, some of which we could identify.
分化的小鼠畸胎瘤细胞系已被广泛用作基底膜蛋白层粘连蛋白和IV型胶原的来源。为了了解它们表达的调控机制，我们在核转录分析中测量了相应基因的转录速率。从五个不同的感兴趣基因（层粘连蛋白A、B1和B2以及α1(IV)、α2(IV)）获得的转录本比率与相应mRNA的比率有很大不同，而mRNA的比率又与所需的蛋白质水平不同。α2(IV)基因的转录速率高于α1(IV)基因，同样，层粘连蛋白A基因的转录速率分别高于其他两个层粘连蛋白基因。然而，α2(IV)和层粘连蛋白A的mRNA水平低于同一分子其他链的水平。根据细胞系的不同，α1(IV)mRNA的丰度比α2(IV)mRNA高3至15倍。在蛋白质水平上，A链似乎是层粘连蛋白组装的限制因素，这与其低mRNA水平一致。两条胶原链的库大小不同，但三螺旋分子似乎总是由两条α1(IV)链和一条α2(IV)链组成。这些结果表明在转录后事件的各个阶段存在广泛的调控机制，其中一些我们已经能够识别。
