Effects of cardiotrophin on adipocytes.
Cardiotrophin (CT-1) is a naturally occurring protein member of the interleukin (IL)-6 cytokine family and signals through the gp130/leukemia inhibitory factor receptor (LIFR) heterodimer. The formation of gp130/LIFR complex triggers the auto/trans-phosphorylation of associated Janus kinases, leading to the activation of Janus kinase/STAT and MAPK (ERK1 and -2) signaling pathways. Since adipocytes express both gp130 and LIFR proteins and are responsive to other IL-6 family cytokines, we examined the effects of CT-1 on 3T3-L1 adipocytes. Our studies have shown that CT-1 administration results in a dose- and time-dependent activation and nuclear translocation of STAT1, -3, -5A, and -5B as well as ERK1 and -2. We also confirmed the ability of CT-1 to induce signaling in fat cells in vivo. Our studies revealed that neither CT-1 nor ciliary neurotrophic factor treatment affected adipocyte differentiation. However, acute CT-1 treatment caused an increase in SOCS-3 mRNA in adipocytes and a transient decrease in peroxisome proliferator-activated receptor gamma (PPARgamma) mRNA that was regulated by the binding of STAT1 to the PPARgamma2 promoter. The effects of CT-1 on SOCS-3 and PPARgamma mRNA were independent of MAPK activation. Chronic administration of CT-1 to 3T3-L1 adipocytes resulted in a decrease of both fatty acid synthase and insulin receptor substrate-1 protein expression yet did not effect the expression of a variety of other adipocyte proteins. Moreover, chronic CT-1 treatment resulted in the development of insulin resistance as judged by a decrease in insulin-stimulated glucose uptake. In summary, CT-1 is a potent regulator of signaling in adipocytes in vitro and in vivo, and our current efforts are focused on determining the role of this cardioprotective cytokine on adipocyte physiology.
Zvonic
Sanjin
S
Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
Hogan
Jessica C
JC
Arbour-Reily
Patricia
P
Mynatt
Randall L
RL
Stephens
Jacqueline M
JM
D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D016207:Cytokines / Q000378:metabolism / Q000494:pharmacology*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D047495:PPAR gamma / Q000235:genetics / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D050794:STAT1 Transcription Factor; D015398:Signal Transduction / Q000502:physiology*; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D016207:Cytokines; D004268:DNA-Binding Proteins; D007328:Insulin; D047495:PPAR gamma; D012097:Repressor Proteins; C106644:SOCS3 protein, human; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; C494080:Stat1 protein, mouse; C494081:Stat1 protein, rat; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C092073:cardiotrophin 1; D011505:Protein-Tyrosine Kinases; D020928:Mitogen-Activated Protein Kinases; D005947:Glucose