Ferrier R, Had L, Rabié A, Faivre-Sarrailh C
Laboratoire de Neurobiologie Endocrinologique, URA 1197 CNRS, Université Montpellier II, France.
Cell Motil Cytoskeleton. 1994;28(4):303-16. doi: 10.1002/cm.970280404.
Cytochalasin D and dBcAMP cause cultured astrocytes to change from flat cells to retracted process-bearing cells. F-actin was present throughout cells stimulated with dBcAMP for 16 h, whereas cytochalasin D caused F-actin to form massive aggregates at the tips of the cell processes. The two drugs differently regulated the expression of both beta-actin and tropomyosin genes in astrocytes cultured in the presence or absence of serum: dBcAMP caused down-regulation and cytochalasin D caused up-regulation. Northern blot analyses indicated that: (1) serum deprivation halved the concentration of all tropomyosin transcripts (TM-1, TM-2, TM-4, TMBr-1, TMBr-2). Serum induced TM-4 via transcriptional activation, independent of protein synthesis, (2) dBcAMP induced down-regulation of beta-actin (-50%) and tropomyosin transcripts (-35 to 52%) even in the presence of serum. The concentration of profilin mRNA decreased in dBcAMP-reactive astrocytes (-46%). The decrease in beta-actin mRNA concentration was not blocked by cycloheximide, whereas down-regulation of tropomyosin transcripts was completely reversed when protein synthesis was inhibited, and (3) cytochalasin D induced an increase in the concentration of tropomyosin transcripts (+69 to 185%) which was cumulative with serum stimulation. Cytochalasin D induction of both beta-actin and TM-4 operated through transcriptional activation, independent of protein synthesis. The production of all tropomyosin transcripts examined here were strictly coordinated with beta-actin expression in serum-, dBcAMP- and cytochalasin D-treated astrocytes. This indicates that the differential expression of tropomyosin isoforms occurring during astrocyte maturation is due to more complex regulation than that involved in serum- or cAMP-stimulated astrocytes.
细胞松弛素D和二丁酰环磷腺苷（dBcAMP）可使培养的星形胶质细胞从扁平细胞转变为具有收缩突起的细胞。在用dBcAMP刺激16小时的整个细胞中均存在丝状肌动蛋白（F-肌动蛋白），而细胞松弛素D则导致F-肌动蛋白在细胞突起的尖端形成大量聚集物。这两种药物对在有血清或无血清条件下培养的星形胶质细胞中β-肌动蛋白和原肌球蛋白基因的表达有不同的调节作用：dBcAMP导致基因表达下调，而细胞松弛素D导致基因表达上调。Northern印迹分析表明：（1）血清剥夺使所有原肌球蛋白转录本（TM-1、TM-2、TM-4、TMBr-1、TMBr-2）的浓度减半。血清通过转录激活诱导TM-4，与蛋白质合成无关；（2）即使在有血清的情况下，dBcAMP也会诱导β-肌动蛋白（-50%）和原肌球蛋白转录本（-35%至52%）的表达下调。在对dBcAMP有反应的星形胶质细胞中，丝切蛋白mRNA的浓度降低（-46%）。β-肌动蛋白mRNA浓度的降低未被环己酰亚胺阻断，而当蛋白质合成受到抑制时，原肌球蛋白转录本的下调则完全逆转；（3）细胞松弛素D诱导原肌球蛋白转录本的浓度增加（+69%至185%），这与血清刺激具有累积效应。细胞松弛素D对β-肌动蛋白和TM-4的诱导作用均通过转录激活实现，与蛋白质合成无关。在这里检测的所有原肌球蛋白转录本的产生与血清、dBcAMP和细胞松弛素D处理的星形胶质细胞中β-肌动蛋白的表达严格协调。这表明星形胶质细胞成熟过程中原肌球蛋白异构体的差异表达是由于比血清或cAMP刺激的星形胶质细胞更复杂的调节所致。
