Role of insulin‐like growth factor binding protein (IGFBP)‐3 in TGF‐β‐ and GDF‐8 (myostatin)‐induced suppression of proliferation in porcine embryonic myogenic cell cultures

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Abstract
Both transforming growth factor (TGF‐β) and growth and development factor (GDF)‐8 (myostatin) affect muscle differentiation by suppressing proliferation and differentiation of myogenic cells. In contrast, insulin‐like growth factors (IGFs) stimulate both proliferation and differentiation of myogenic cells. In vivo, IGFs are found in association with a family of high‐affinity insulin‐like growth factor binding proteins (IGFBP 1–6) that affect their biological activity. Treatment of porcine embryonic myogenic cell (PEMC) cultures with either TGF‐β1 or GDF‐8 suppressed proliferation and increased production of IGFBP‐3 protein and mRNA (P < 0.005). An anti‐IGFBP‐3 antibody that neutralizes the biological activity of IGFBP‐3 reduced the ability of either TGF‐β1 or GDF‐8 to suppress PEMC proliferation (P < 0.005). However, this antibody did not affect proliferation rate in the presence of both TGF‐β1 and GDF‐8. These data show that IGFBP‐3 plays a role in mediating the activity of either TGF‐β1 or GDF‐8 alone but not when both TGF‐β1 and GDF‐8 are present. In contrast to findings in T47D breast cancer cells, treatment of PEMC cultures with IGFBP‐3 did not result in increased levels of phosphosmad‐2. Since TGF‐β and GDF‐8 are believed to play a significant role in regulating proliferation and differentiation of myogenic cells, our current data showing that IGFBP‐3 plays a role in mediating the activity of these growth factors in muscle cell cultures strongly suggest that IGFBP‐3 also may be involved in regulating these processes in myogenic cells. J. Cell. Physiol. 197: 225–231, 2003
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