Insulin-like growth factor binding protein (IGFBP)-3 and IGFBP-5 mediate TGF-beta- and myostatin-induced suppression of proliferation in porcine embryonic myogenic cell cultures.
We have previously shown that cultured porcine embryonic myogenic cells (PEMC) produce both insulin-like growth factor binding protein (IGFBP)-3 and IGFBP-5 and secrete these proteins into their media. Exogenously added recombinant porcine (rp) IGFBP-3 and rpIGFBP-5 act via IGF-dependent and IGF-independent mechanisms to suppress proliferation of PEMC cultures. Furthermore, immunoneutralization of endogenous IGFBP-3 and IGFBP-5 in the PEMC culture medium results in increased DNA synthesis rate suggesting that endogenous IGFBP-3 and IGFBP-5 suppress PEMC proliferation. TGF-beta superfamily members myostatin and TGF-beta1 have also been shown to suppress proliferation of myogenic cells, and treatment of cultured PEMC with either TGF-beta1 or myostatin significantly (P < 0.01) increases levels of IGFBP-3 and -5 mRNA. We have previously shown that immunoneutralization of IGFBP-3 decreases the proliferation-suppressing activity of TGF-beta1 and myostatin. Here, we show that immunoneutralization of IGFBP-5 also significantly (P < 0.05) decreases the DNA synthesis-suppressing activity of these molecules. Simultaneous immunoneutralization of both IGFBP-3 and IGFBP-5 in TGF-beta1 or myostatin-treated PEMC cultures restores Long-R3-IGF-I-stimulated DNA synthesis rates to 90% of the levels observed in control cultures receiving no TGF-beta1 or myostatin treatment (P < 0.05). Even though immunoneutralization of IGFBP-3 and -5 increased DNA synthesis rates in TGF-beta1 or myostatin-treated PEMC cultures, phosphosmad2 levels in these cultures were not affected. These findings strongly suggest that IGFBP-3 and IGFBP-5 affect processes downstream from receptor-mediated Smad phosphorylation that facilitate the ability of TGF-beta and myostatin to suppress proliferation of PEMC.
Kamanga-Sollo
E
E
Department of Animal Science, University of Minnesota, 348 Andrew Boss Laboratory, 1354 Eckles Avenue, St. Paul, MN 55108, USA.
Pampusch
M S
MS
White
M E
ME
Hathaway
M R
MR
Dayton
W R
WR
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D004247:DNA / Q000378:metabolism; D005333:Fetus; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000502:physiology*; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000502:physiology*; D032446:Myoblasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D055435:Myostatin; D010766:Phosphorylation; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051899:Smad2 Protein / Q000378:metabolism; D013552:Swine; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1
D000911:Antibodies, Monoclonal; D018972:Insulin-Like Growth Factor Binding Protein 3; D018975:Insulin-Like Growth Factor Binding Protein 5; C525911:MSTN protein, human; D055435:Myostatin; D012333:RNA, Messenger; D051899:Smad2 Protein; C508960:TGFB1 protein, human; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D004247:DNA