Effect of differentiation on levels of insulin-like growth factor binding protein mRNAs in cultured porcine embryonic myogenic cells☆

Insulin-like growth factor binding proteins (IGFBPs) have been shown to affect proliferation of several cell types via insulin-like growth factor (IGF)-dependent and IGF-independent mechanisms. The goal of this study was to determine if levels of IGFBP-2, -3, -4 and -5 mRNA changed during differentiation of cultured porcine embryonic myogenic cells. Total RNA was isolated from muscle cultures at various stages of differentiation and Northern blots of this RNA were probed with -labeled cDNA probes specific for individual IGFBPs. Fusion, myogenin mRNA, and creatine phosphokinase activity were used as markers of differentiation. The level of IGFBP-3 mRNA in differentiating cultures (120h in culture) was only one-third of the level in myogenin negative, nonfused cultures (72h in culture) (P<0.05, n=4). In contrast, the level of IGFBP-3 mRNA in extensively fused cultures (144h in culture) was increased by three-fold as compared to the level in myogenin negative, nonfused cultures (P<0.05, n=4) and approximately seven-fold as compared to the 120-h cultures (P<0.05, n=4). No significant change in the level of IGFBP-5 mRNA was observed during differentiation of myogenic cultures. IGFBP-2 mRNA levels were not significantly different at 72, 96 and 120h, but at 144h IGFBP-2 mRNA level was increased three-fold as compared to nonfused cultures (72h) (P<0.05, n=4). IGFBP-4 mRNA was not detectable on Northern blots of total RNA from porcine myogenic cultures at any stage of differentiation. Changes in IGFBP-3 and IGFBP-2 mRNA levels are associated with differentiation of embryonic porcine myogenic cells in culture and this may indicate that these IGFBPs play a role in differentiation of these cells.