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Cyclic AMP-dependent protein kinase inhibits the activity of myogenic helix-loop-helix proteins
L Li1, R Heller-Harrison, M Czech
1Department of Biochemistry and Molecular Biology, University of Texas M. D. Anderson Cancer Center, Houston 77030.
Abstract:
Differentiation of skeletal muscle cells is inhibited by the cyclic AMP (cAMP) signal transduction pathway. Here we report that the catalytic subunit of cAMP-dependent protein kinase (PKA) can substitute for cAMP and suppress muscle-specific transcription by silencing the activity of the MyoD family of regulatory factors, which includes MyoD, myogenin, myf5, and MRF4. Repression by the PKA catalytic (C) subunit is directed at the consensus sequence CANNTG, the target for DNA binding and transcriptional activation by these myogenic regulators. Phosphopeptide mapping of myogenin in vitro and in vivo revealed two PKA phosphorylation sites, both within the basic region. However, repression of myogenin function by PKA does not require direct phosphorylation of these sites but instead involves an indirect mechanism with one or more intermediate steps. Regulation of the transcriptional activity of the MyoD family by modulation of the cAMP signaling pathway may account for the inhibitory effects of certain peptide growth factors on muscle-specific gene expression and may also determine the responsiveness of different cell types to myogenic conversion by these myogenic regulators.
Insights
The cyclic AMP (cAMP) pathway inhibits muscle cell differentiation. Protein kinase A (PKA) catalytic subunit suppresses muscle-specific transcription by targeting MyoD family factors, impacting gene expression.
Area of Science:
- Molecular Biology
- Cell Signaling
- Developmental Biology
Background:
- Skeletal muscle cell differentiation is a complex process regulated by various signaling pathways.
- The cyclic AMP (cAMP) signal transduction pathway is known to inhibit this differentiation process.
Purpose of the Study:
- To investigate the role of the catalytic subunit of cAMP-dependent protein kinase (PKA) in suppressing muscle-specific transcription.
- To elucidate the mechanism by which PKA affects the MyoD family of regulatory factors.
Main Methods:
- Utilized phosphopeptide mapping to identify PKA phosphorylation sites on myogenin in vitro and in vivo.
- Investigated the effects of PKA catalytic subunit on the activity of MyoD family proteins.
Main Results:
- The PKA catalytic subunit can substitute for cAMP in suppressing muscle-specific transcription.
- PKA represses the activity of the MyoD family (MyoD, myogenin, myf5, MRF4) by targeting the CANNTG consensus sequence.
- PKA-mediated repression of myogenin function occurs via an indirect mechanism, not requiring direct phosphorylation of identified sites.
Conclusions:
- Modulation of the cAMP signaling pathway, specifically via PKA, is a key regulator of MyoD family transcriptional activity.
- This regulation may explain inhibitory effects of peptide growth factors on muscle gene expression and cell-type specific myogenic conversion.