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Macrophage‐conditioned medium inhibits the activation of cyclin‐dependent kinase 2 by adipogenic inducers in 3T3‐L1 preadipocytes
Author(s) -
Ide Jennifer,
Gag AnneMarie,
Molgat André S.D.,
Landry Anne,
Foster Charlie,
Sorisky Alexander
Publication year - 2011
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.22566
Subject(s) - adipogenesis , 3t3 l1 , microbiology and biotechnology , cyclin d1 , cyclin e , cyclin dependent kinase , cyclin a , cyclin d , cyclin , cell cycle , cyclin dependent kinase 2 , adipocyte , adipose tissue , chemistry , biology , kinase , protein kinase a , endocrinology , biochemistry , cell
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. J. Cell. Physiol. 226: 2297–2306, 2011. © 2010 Wiley‐Liss, Inc.