title: Macrophage-conditioned medium inhibits the activation of cyclin-dependent kinase 2 by adipogenic inducers in 3T3-L1 preadipocytes.
abstract: Macrophage infiltration into adipose tissue, associated with obesity, is thought to contribute to abnormal adipose tissue remodeling, low-grade inflammation, and insulin resistance. Medium conditioned by macrophages (MacCM) inhibits 3T3-L1 and human adipocyte differentiation, as well as early adipogenic cell cycle events including MCE and retinoblastoma protein (Rb) phosphorylation. Our objective was to determine if the inhibition of Rb phosphorylation was linked to changes in cell cycle-related proteins. We treated 3T3-L1 preadipocytes with adipogenic inducers for 24 h in control medium versus J774A.1-MacCM. The differentiation-induced mRNA and protein expression of cyclin A, an activator of cyclin-dependent kinase (cdk) 2 which phosphorylates Rb, was inhibited by 82% and 73%, respectively, by J774A.1-MacCM; adipogenic expression of Myc, a transcriptional regulator of cyclin A, was also suppressed significantly. Consistent with the reduction in cyclin A levels, the activation of cdk2 by adipogenic inducers was inhibited by 75% by J774A.1-MacCM. J774A.1-MacCM also lowered levels of cyclins D1 and D2. Inhibition studies demonstrated that platelet-derived growth factor, an anti-adipogenic factor found in J774A.1-MacCM, was not responsible for the inhibitory effect on differentiation. The anti-adipogenic effect of J774A.1-MacCM was resistant to proteinase K and heat treatment, and was present in a <3 kDa fraction. Our data indicate that J774A.1-MacCM interferes with the upregulation of cyclin A levels and cdk2 activity that are required for Rb phosphorylation and MCE in 3T3-L1 adipogenesis.
authors.affiliation: Ottawa Hospital Research Institute and Department of Medicine and Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Ide
authors.forename: Annemarie
authors.initials: A
authors.lastname: Gagnon
authors.forename: André S D
authors.initials: AS
authors.lastname: Molgat
authors.forename: Anne
authors.initials: A
authors.lastname: Landry
authors.forename: Charlie
authors.initials: C
authors.lastname: Foster
authors.forename: Alexander
authors.initials: A
authors.lastname: Sorisky
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology*; D050156:Adipogenesis / Q000187:drug effects*; D000818:Animals; D017077:Culture Media, Conditioned / Q000494:pharmacology*; D019925:Cyclin A / Q000378:metabolism; D056741:Cyclin D / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism*; D019286:Endopeptidase K / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D006358:Hot Temperature; D006801:Humans; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D016160:Retinoblastoma Protein / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D017077:Culture Media, Conditioned; D019925:Cyclin A; D056741:Cyclin D; D010982:Platelet-Derived Growth Factor; D016160:Retinoblastoma Protein; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D019286:Endopeptidase K