Coordinated expression of five tropomyosin isoforms and beta-actin in astrocytes treated with dibutyryl cAMP and cytochalasin D.
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.
Laboratoire de Neurobiologie Endocrinologique, URA 1197 CNRS, Université Montpellier II, France.
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R
Ferrier
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L
Had
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A
Rabié
C
C
Faivre-Sarrailh
D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000096:biosynthesis* / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001483:Base Sequence; D001769:Blood; D003994:Bucladesine / Q000494:pharmacology*; D002478:Cells, Cultured; D003470:Culture Media; D003513:Cycloheximide / Q000494:pharmacology; D015638:Cytochalasin D / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D014335:Tropomyosin / Q000096:biosynthesis* / Q000235:genetics
D000199:Actins; D003470:Culture Media; D012333:RNA, Messenger; D014335:Tropomyosin; D015638:Cytochalasin D; D003994:Bucladesine; D003513:Cycloheximide