Juliani M H, Souza G M, Klein C
Departmento de Bioquímica, Universidade de São Paulo, Brasil.
J Biol Chem. 1990 Jun 5;265(16):9077-82.
Transcription of the 117 gene and changes in its mRNA levels in Dictyostelium discoideum were studied by mRNA hybridization with a cDNA probe. In wild type cells (Ax-2), the expression is developmentally regulated during cell aggregation, while in the aggregateless mutant, Agip 45, 117 mRNA is not detectable during cell starvation. Low concentrations of cAMP, given in the form of extracellular pulses to induce the development of starved Agip 45 cells to aggregation competence, are able to induce the appearance of 117 mRNA. The induction seems to be via the cell surface cAMP receptor and by a mechanism which does not involve changes in intracellular cAMP. Interestingly, high concentrations of cAMP, which down-regulate the cell surface cAMP receptor, elicit a rapid decrease in the level of 117 mRNA in aggregation-competent cells. Nuclear run-off and pulse-chase experiments show that the high concentrations of cAMP selectively destabilize the mRNA for 117 antigen. This destabilization requires both de novo mRNA synthesis and protein synthesis since the addition of inhibitors of these processes eliminates the effects of cAMP on 117 mRNA. The data suggest that a cAMP-induced protein(s) may be involved in the destabilization of selective mRNAs.
通过使用cDNA探针进行mRNA杂交，研究了盘基网柄菌（Dictyostelium discoideum）中117基因的转录及其mRNA水平的变化。在野生型细胞（Ax-2）中，该基因的表达在细胞聚集过程中受到发育调控，而在无聚集能力的突变体Agip 45中，细胞饥饿期间无法检测到117 mRNA。以细胞外脉冲形式给予低浓度的cAMP，以诱导饥饿的Agip 45细胞发育出聚集能力，能够诱导117 mRNA的出现。这种诱导似乎是通过细胞表面的cAMP受体，并且通过一种不涉及细胞内cAMP变化的机制。有趣的是，高浓度的cAMP会下调细胞表面的cAMP受体，导致具有聚集能力的细胞中117 mRNA水平迅速下降。细胞核转录分析和脉冲追踪实验表明，高浓度的cAMP会选择性地使117抗原的mRNA不稳定。这种不稳定需要从头合成mRNA和蛋白质合成，因为添加这些过程的抑制剂会消除cAMP对117 mRNA的影响。数据表明，cAMP诱导的一种或多种蛋白质可能参与了选择性mRNA的不稳定过程。
