Insulin signaling in adipocytes differentiated from mouse stromal MC3T3-G2/PA6 cells.
The stromal MC3T3-G2/PA6 (PA6) cells from mouse clavaria did not require insulin for differentiation into mature adipose cells, although insulin is well known to play a key role in adipocyte differentiation. Large lipid droplets were observed in the cytoplasm of PA6 cells, and mRNA expression of the adipose specific proteins (aP2, PPARgamma, C/EBPalpha, FAS, GLUT4, leptin, and adiponectin) as differentiation markers appeared or increased clearly in the cells at 8 d after stimulation without insulin. In addition, the glycerol released from the cells (lipolysis) was increased in a concentration-dependent manner by isoproterenol. However, the isoproterenol-induced lipolysis in the cells was not influenced by treatment with insulin, although that was observed in extramedullary adipocytes, 3T3-L1 cells. On the other hand, the 2-deoxy-D-[1-3H]glucose uptake in differentiated PA6 cells also increased by insulin, as shown in other adipose cells. In the cells, insulin induced the phosphorylation of extracellular signal-regulated kinases (Erks), Akt at Ser 473 and ribosomal p70 S6 protein kinase (p70 S6K) at Thr 389, and the insulin-induced 2-deoxy-D-[1-3H]glucose uptake was inhibited by pre-treatment with wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3K), or ML-9, an Akt inhibitor. These results suggest that the insulin signal for adipogenesis (lipogenesis) and lipolysis in bone marrow stroma PA6 cells differs from extramedullary adipocytes, such as 3T3-L1 cells.
Morito
Satoshi
S
Department of Clinical Pharmacy, Graduate School of Natural Science and Technology, Kanazawa University, Japan.
Yaguchi
Kuniko
K
Imada
Mikiko
M
Tachikawa
Chihiro
C
Nomura
Masaaki
M
Moritani
Shuzo
S
Igarashi
Manabu
M
Yokogawa
Koichi
K
Miyamoto
Ken-ichi
K
D016475:3T3 Cells; D017667:Adipocytes / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D001391:Azo Compounds; D004396:Coloring Agents; D003847:Deoxyglucose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D015151:Immunoblotting; D007328:Insulin / Q000502:physiology*; D008066:Lipolysis; D051379:Mice; D008810:Mice, Inbred C57BL; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*
D001391:Azo Compounds; D004396:Coloring Agents; D007328:Insulin; D003847:Deoxyglucose; D019869:Phosphatidylinositol 3-Kinases; C011049:oil red O; D005947:Glucose