Phorbol esters selectively downregulate contractile protein gene expression in terminally differentiated myotubes through transcriptional repression and message destabilization

Y. Y. Zhu, R. J. Schwartz, M. T. Crow

Research output: Contribution to journalArticlepeer-review

Abstract

Chronic exposure of differentiated avian skeletal muscle cells in culture to the phorbol ester, 12-O-tetradecanoyl phorbol-13-acetate (PMA), results in the selective disassembly of sarcomeric structures and loss of muscle-specific contractile proteins, leaving cytoskeletal structures and their associated proteins intact. We demonstrate here that these morphological and biochemical changes are accompanied by dramatic and selective decreases in the level of the mRNAs that encode the contractile proteins. We measured the effects of PMA on the transcriptional activity and mRNA stability of four contractile protein genes (α-cardiac and α-skeletal actin, cardiac troponin C [cTnC], and myosin light chain 1f [MLC1f]) and two nonmuscle genes (β-cytoplasmic actin and the glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase [GAPDH]). The transcriptional activity of the α-cardiac actin and cTnC genes dramatically decreased by 8 h after the addition of PMA, while other muscle and nonmuscle genes examined showed no change. Pulse-chase experiments of in vivo labeled RNA showed significant reductions in mRNA half-lifes for all the contractile protein mRNAs examined, while the half-lifes of β-actin and GAPDH mRNA were unchanged. All of the above effects occurred under conditions in which cellular protein kinase C (PKC) levels had been reduced by >90%. The fact that many of the contractile protein genes remained transcriptionally active despite the fact that the cells were unable to accumulate their mRNAs to any significant extent indicated that the treated cells were still committed to skeletal muscle differentiation. The selective changes in the stability of the contractile protein mRNAs suggest that the control of mRNA stability may be part of the normal regulatory program of skeletal muscle differentiation and that this control may be linked to the integrity of the contractile apparatus and mediated by second messenger pathways involving PKC activation.

Original languageEnglish (US)
Pages (from-to)745-754
Number of pages10
JournalJournal of Cell Biology
Volume115
Issue number3 I
DOIs
StatePublished - 1991
Externally publishedYes

ASJC Scopus subject areas

  • Cell Biology

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