title: Protein kinase inhibitor γ reciprocally regulates osteoblast and adipocyte differentiation by downregulating leukemia inhibitory factor.
abstract: The protein kinase inhibitor (Pki) gene family inactivates nuclear protein kinase A (PKA) and terminates PKA-induced gene expression. We previously showed that Pkig is the primary family member expressed in osteoblasts and that Pkig knockdown increases the effects of parathyroid hormone and isoproterenol on PKA activation, gene expression, and inhibition of apoptosis. Here, we determined whether endogenous levels of Pkig regulate osteoblast differentiation. Pkig is the primary family member in murine embryonic fibroblasts (MEFs), murine marrow-derived mesenchymal stem cells, and human mesenchymal stem cells. Pkig deletion increased forskolin-dependent nuclear PKA activation and gene expression and Pkig deletion or knockdown increased osteoblast differentiation. PKA signaling is known to stimulate adipogenesis; however, adipogenesis and osteogenesis are often reciprocally regulated. We found that the reciprocal regulation predominates over the direct effects of PKA since adipogenesis was decreased by Pkig deletion or knockdown. Pkig deletion or knockdown also simultaneously increased osteogenesis and decreased adipogenesis in mixed osteogenic/adipogenic medium. Pkig deletion increased PKA-induced expression of leukemia inhibitory factor (Lif) mRNA and LIF protein. LIF neutralizing antibodies inhibited the effects on osteogenesis and adipogenesis of either Pkig deletion in MEFs or PKIγ knockdown in both murine and human mesenchymal stem cells. Collectively, our results show that endogenous levels of Pkig reciprocally regulate osteoblast and adipocyte differentiation and that this reciprocal regulation is mediated in part by LIF. Stem Cells 2013;31:2789-2799.
authors: Department of Orthopaedics, University of North Carolina, Chapel Hill, North Carolina, USA.
authors: Xin
authors: X
authors: Chen
authors: Bryan S
authors: BS
authors: Hausman
authors: Guangbin
authors: G
authors: Luo
authors: Guang
authors: G
authors: Zhou
authors: Shunichi
authors: S
authors: Murakami
authors: Janet
authors: J
authors: Rubin
authors: Edward M
authors: EM
authors: Greenfield
mesh_terms: D017667:Adipocytes / Q000166:cytology* / Q000378:metabolism; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D015536:Down-Regulation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D053605:Leukemia Inhibitory Factor / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; C507837:LIF protein, human; D053605:Leukemia Inhibitory Factor; C107592:PKIG protein, human; C515309:Pkig protein, mouse; D012333:RNA, Messenger
keywords: Adipogenesis; Leukemia inhibitory factor; Mesenchymal stem cell; Osteogenesis; Protein kinase inhibitor
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