title: Midkine is an autocrine activator of signal transducer and activator of transcription 3 in 3T3-L1 cells.
abstract: Mitotic clonal expansion is believed to be necessary for 3T3-L1 adipocyte formation. Signal transducer and activator of transcription 3 (STAT3), a mitogenic signaling protein, is activated through tyrosine phosphorylation during the proliferative phases of adipogenesis. We hypothesize that this signaling protein plays a key role in mitotic clonal expansion and differentiation. Here we determined that the adipocyte differentiation cocktail containing isobutylmethylxanthine, dexamethasone, and insulin (MDI) induced STAT3 tyrosine phosphorylation indirectly through the synthesis of an autocrine/paracrine factor. We further determined that the factor has heparin binding properties and identified the factor as midkine, a pleiotrophic growth factor previously associated with neuronal development and oncogenesis. Recombinant midkine induced STAT3 tyrosine phosphorylation in a time- and dose-dependent manner and stimulated the proliferation of postconfluent 3T3-L1 cells. Midkine neutralizing antibodies inhibited differentiation-induced STAT3 tyrosine phosphorylation as well as adipogenesis. These results show that MDI-induced synthesis and release of midkine explains the delayed activation of STAT3 during adipogenesis and that the midkine-STAT3 signaling pathway plays a necessary role in mitotic clonal expansion and differentiation.
authors.affiliation: Department of Nutrition, CB 7461 McGavran Greenberg Hall, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
authors.forename: Erin R
authors.initials: ER
authors.lastname: Cernkovich
authors.forename: Jianbei
authors.initials: J
authors.lastname: Deng
authors.forename: Kunjie
authors.initials: K
authors.lastname: Hua
authors.forename: Joyce B
authors.initials: JB
authors.lastname: Harp
mesh_terms: D041721:3T3-L1 Cells; D050156:Adipogenesis / Q000187:drug effects; D000818:Animals; D019898:Autocrine Communication; D049109:Cell Proliferation / Q000187:drug effects; D016207:Cytokines / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D051379:Mice; D000078792:Midkine; D019899:Paracrine Communication; D014176:Protein Biosynthesis; D011994:Recombinant Proteins / Q000494:pharmacology; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D016207:Cytokines; D011994:Recombinant Proteins; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse; D000078792:Midkine