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  • Title: Positive regulation of the skeletal alpha-actin gene by Fos and Jun in cardiac myocytes.
    Author: Bishopric NH, Jayasena V, Webster KA.
    Journal: J Biol Chem; 1992 Dec 15; 267(35):25535-40. PubMed ID: 1460048.
    Abstract:
    Transcription of the skeletal alpha-actin gene is selectively activated in rat myocardiocytes undergoing hypertrophy both in vivo and in vitro. In most of these models, transient expression of certain proto-oncogene transcription factors precedes hypertrophy and sarcomeric gene induction. Using expression vectors encoding Fos and Jun, the main constituents of transcriptional activator protein AP-1, we analyzed the role of these oncoproteins in mediating the transcriptional induction of skeletal alpha-actin by adrenergic stimulation. Both c-fos and c-jun were induced early after beta-adrenergic stimulation, with peak mRNA levels preceding skeletal alpha-actin induction by several hours. A second peak of c-jun mRNA coincided with skeletal alpha-actin induction. Co-transfection assays in cardiac myocytes and P19 teratocarcinoma cells demonstrated that over-expression of c-jun, or c-fos plus c-jun, transactivated the skeletal alpha-actin promoter by about 5-fold. Comparable activation was not seen for alpha-myosin heavy chain or cardiac alpha-actin promoters. Skeletal alpha-actin promoter sequences between -153 and -36 were required for maximal transactivation by c-fos/c-jun, and purified Fos and Jun were bound specifically within this region. A direct physiological role is suggested for the AP-1 transcription factor complex in regulating skeletal alpha-actin gene expression and alpha-actin isoform switching during the onset of signal-mediated cardiac myocyte hypertrophy.
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