title: Low-density lipoprotein-related receptor protein 1 (LRP-1) is not required for insulin-like growth factor binding protein 3 (IGFBP-3) to suppress L6 myogenic cell proliferation.
abstract: Insulin-like growth factor binding protein-3 (IGFBP-3) suppresses proliferation of numerous cell types, including myogenic cells, via both insulin-like growth factor (IGF)-dependent and IGF-independent mechanisms; however, the mechanism of IGF-independent suppression of proliferation is not clearly defined. In nonmuscle cells, binding of IGFBP-3 to the low-density lipoprotein receptor-related protein-1 (LRP-1)/activated α(2)M receptor is reportedly required for IGFBP-3 to inhibit proliferation. These findings suggest that binding to this receptor also may be required for IGFBP-3 to suppress proliferation of cultured myogenic cells. To investigate the role of the LRP-1 receptor in suppression of myogenic cell proliferation by IGFBP-3, we have examined the effect of receptor-associated protein, an LRP-1 receptor antagonist, on recombinant porcine (rp)IGFBP-3 inhibition of L6 myogenic cell proliferation. Treatment with receptor-associated protein results in a 37% decrease (P < 0.05) in the ability of rpIGFBP-3 to inhibit L6-cell proliferation. In L6 cells subjected to LRP-1 small interfering RNA treatment for 48 h (LRP-1 silenced), LRP-1 mRNA levels were reduced by greater than 80% compared with control cultures treated with nonsense small interfering RNA (mock silenced). In addition, the 85-kDa transmembrane subunit of LRP-1 was undetectable in Western immunoblots of total protein lysates from LRP-1-silenced cells. Even though LRP-1 mRNA and protein levels were dramatically reduced in LRP-1-silenced L6 cells compared with mock-silenced controls, rpIGFPB-3 suppressed proliferation rate to the same extent in both LRP-1-silenced and mock-silenced cultures. Our results strongly suggest that, in contrast to data obtained for nonmuscle cell lines, the LRP-1 receptor is not required for IGFBP-3 to suppress proliferation of L6 myogenic cells.
authors.affiliation: Animal Growth and Development Laboratory, Department of Animal Science, University of Minnesota, 1354 Eckles Ave., St. Paul, MN 55108, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Pampusch
authors.forename: E
authors.initials: E
authors.lastname: Kamanga-Sollo
authors.forename: M R
authors.initials: MR
authors.lastname: Hathaway
authors.forename: M E
authors.initials: ME
authors.lastname: White
authors.forename: W R
authors.initials: WR
authors.lastname: Dayton
mesh_terms: D000818:Animals; D015153:Blotting, Western / Q000662:veterinary; D049109:Cell Proliferation; D002478:Cells, Cultured; D007150:Immunohistochemistry / Q000662:veterinary; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism*; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D024510:Muscle Development; D032446:Myoblasts / Q000166:cytology*; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D011994:Recombinant Proteins / Q000494:pharmacology; D013552:Swine / Q000235:genetics / Q000378:metabolism*
chemical_list: D018972:Insulin-Like Growth Factor Binding Protein 3; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011994:Recombinant Proteins