Fibroblast growth factor and transforming growth factor beta repress transcription of the myogenic regulatory gene MyoD1.

Abstract

In this report, we demonstrate that myogenic cultures inhibited from differentiating by treatment with fibroblast growth factor or transforming growth factor 11 show reduced levels of MyoDl mRNA. Although this repression may contribute to the inhibition of myogenesis by growth factors, additional regulatory pathways must be affected, since inhibition still occurs in cultures engineered to constitutively express MyoDI mRNA.Skeletal muscle differentiation involves the transcriptional activation of the contractile protein gene set and the formation of multinucleated muscle fibers. The contractile protein genes are controlled by cis and tran.s regulatory systems which appear to respond to exogenous growth factors, since addition of fibroblast growth factor (FGF) or transforming growth factor 3 (TGF-3) to differentiating muscle cells in culture inhibits both fusion and the accumulation of these muscle-specific proteins (7,9,13,14,16,21). It has been hypothesized that FGF and TGF-, may influence one or perhaps several master regulatory pathways. Although the regulatory genes that control the induction of skeletal myogenesis have not been defined completely, at least three genes, MyoDl (8,20), inyd (18), and myogenin (22). play an important role in establishing the myogenic lineage and inducing the expression of muscle-specific genes.To determine whether these regulatory genes are modulated by exogenous growth factors, we investigated the transcriptional activity of the MyoDl gene in cells exposed to FGF or TGF-3. 23A2 myoblasts (12) were induced to differentiate in medium containing insulin, transferrin, and selenium (ITS) (23) to establish the normal expression pattern of MyoDl and the contractile protein gene, troponin I (TnI), during skeletal myogenesis. RNA was isolated from proliferating and differentiation-induced 23A2 cultures, electrophoresed through formaldehyde-agarose gels, and hybridized with nick-translated TnI (cM113) (10) and MyoD1 (pEMC11s) (8) probes as described previously (11). TnI mRNA was detected within 24 h after ITS induction and reached maximal levels by 48 h (Fig. 1) (Fig. 2) showed no TnI mRNA (Fig. 2), no myosin heavy-chain protein, and no fusion (data not shown). Interestingly, MyoD1 mRNA levels also were reduced in growth-factortreated cultures so that by 48 h, MyoD1 mRNA was no longer detected. This growth-factor-induced inhibition of differentiation is reversible, however, since removal of FGF from inhibited cultures restored MyoD1 expression, increased TnI mRNA levels (Fig. 2), and led to a resumption of myoblast fusion. Similar results were obtained when TGF-, was removed, although the recovery time was delayed (data not shown). The growth-factor-induced repression of MyoDi mRNA appears to be specific, since the control pAL15 gene (2, 3) was expressed equally in all experimental groups. In addition. the effects of FGF and TGF-3 on myogenesis and MyoD1 expression are not unique to the 23A2 cell line. C2C12 myoblasts (4) behaved in an identical fashion when treated with these growth fac...

Distribution of FGF‐2 suggests it has a role in chick limb bud growth

“…In vitro, FGF-2 prevents expression of myogenic genes (Vaidya et al, 1989) and represses myogenic differentiation in immortalized muscle cell lines (Olwin and Hauschka, 1986). In contrast, both this report and that of JosephSilverstein et al (1989) show levels of FGF-2 increase in differentiating muscles.…”

The proto-oncogene Bcl6 inhibits apoptotic cell death in differentiation-induced mouse myogenic cells

“…We also investigated the e ects of basic ®broblast growth factor (bFGF), transforming growth factor-b (TGF-b), okadaic acid, and lysophosphatidic acid (LPA) on C2C12 di erentiation: these reagents have been reported to act by interfering with the myogenic di erentiation process through several mechanisms, including the inhibition of transcription, DNA binding, or trans-activation of MyoD (Vaidya et al, 1989;Brennan et al, 1991;Kim et al, 1992;Li et al, 1992). When each of these reagents was added to DM, C2C12 cells failed to di erentiate morphologically, and the expression of Bcl6 mRNA was markedly reduced, along with that of myogenin gene transcripts ( Figure 3).…”

Bone morphogenetic protein-2 converts the differentiation pathway of C2C12 myoblasts into the osteoblast lineage [published erratum appears in J Cell Biol 1995 Feb;128(4):following 713]

“…The cooperative regulation in mRNA expression between the positive (myogenin) and the negative regulators (ld-1) induced by BMP-2 may play, at least in part, an important role in inhibiting myogenic differentiation. Myogenic differentiation is also inhibited by other growth factors such as TGF-/3 and basic FGF (bFGF) (Massagu6 et al, 1986;Spizz et al, 1986Spizz et al, , 1987Florini et al, 1986;Clegg et al, 1987;Vaidya et al, 1989;Brunetti and Goldfine, 1990;Brennan et al, 1991;Martin et al, 1992;Hardy et al, 1993). These growth factors inhibit the expression of MyoD and myogenin mRNAs (Vaidya et al, 1989;Brunetti and Goldfine, 1990).…”

“…Myogenic differentiation is also inhibited by other growth factors such as TGF-/3 and basic FGF (bFGF) (Massagu6 et al, 1986;Spizz et al, 1986Spizz et al, , 1987Florini et al, 1986;Clegg et al, 1987;Vaidya et al, 1989;Brunetti and Goldfine, 1990;Brennan et al, 1991;Martin et al, 1992;Hardy et al, 1993). These growth factors inhibit the expression of MyoD and myogenin mRNAs (Vaidya et al, 1989;Brunetti and Goldfine, 1990). In addition, bFGF induces the phosphorylation by protein kinase C at a conserved site of the DNA-binding domain of myogenin, which causes a loss of DNA-binding activity of myogenin .…”