Localization of insulin-like growth factor (IGFBP)-3 in cultured porcine embryonic myogenic cells before and after TGF-beta1 treatment.
Insulin-like growth factor binding protein (IGFBP)-3 binds IGFs with high affinity and affects their biological activity. IGFBP-3 that is not bound to IGF also affects cells via mechanisms involving binding to specific cell surface receptors and/or transport into the cell. IGFBP-3 is produced by porcine embryonic myogenic cell (PEMC) cultures. Additionally, IGFBP-3 facilitates the proliferation-suppressing actions of TGF-beta(1) and myostatin in PEMC cultures via mechanisms that do not involve IGF binding. Moreover, these mechanisms do not involve preventing myostatin or TGF-beta(1)-induced increases in phosphosmad2 or phosphosmad3 level. Consequently, the mechanism(s) by which IGFBP-3 facilitates the proliferation-suppressing actions of TGF-beta(1) and myostatin in PEMC is unclear. Since IGFBP-3 reportedly interacts with nuclear proteins that regulate transcription, TGF-beta(1) or myostatin-induced translocation of IGFBP-3 into the nucleus may facilitate the proliferation-suppressing actions of these cytokines. Here, we show that IGFBP-3 is localized in cells containing the muscle specific protein desmin, thus establishing the presence of this IGFBP in myogenic cells. IGFBP-3 is present in the cytoplasm of all myogenic cells and approximately 50% of the nuclei of proliferating PEMC. IGFBP-3 is also detectable in fused myotubes. IGFBP-3 suppresses IGF-I-stimulated differentiation of PEMC but has no affect on Long-R3-IGF-I-stimulated differentiation of PEMC. Treatment of PEMC for 24h with TGF-beta(1) (20 ng/ml) results in a 78% (p<0.01) increase in the number of nuclei that contain detectable IGFBP-3. These results suggest that translocation of IGFBP-3 into the nucleus of PEMC could play a role in mediating the proliferation-suppressing action of TGF-beta(1).
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Animal Growth and Development Laboratory, Department of Animal Science, University of Minnesota, 348 Andrew Boss Laboratory, 1354 Eckles Avenue, St. Paul, MN 55108, USA.
Hathaway
M R
MR
White
M E
ME
Dayton
W R
WR
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002467:Cell Nucleus / Q000737:chemistry; D002478:Cells, Cultured; D003593:Cytoplasm / Q000737:chemistry; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000032:analysis* / Q000494:pharmacology; D009132:Muscles / Q000737:chemistry* / Q000196:embryology* / Q000648:ultrastructure; D011994:Recombinant Proteins / Q000494:pharmacology; D013552:Swine / Q000196:embryology*; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology*
D018972:Insulin-Like Growth Factor Binding Protein 3; D011994:Recombinant Proteins; D053773:Transforming Growth Factor beta1