Expression of Inducible 6-Phosphofructo-2-Kinase/Fructose-2,6-Bisphosphatase/PFKFB3 Isoforms in Adipocytes and Their Potential Role in Glycolytic Regulation
- Toshiya Atsumi1,
- Taro Nishio1,
- Hirokatsu Niwa1,
- Jun Takeuchi1,
- Hidenori Bando1,
- Chikara Shimizu1,
- Narihito Yoshioka1,
- Richard Bucala2 and
- Takao Koike1
- 1Department of Medicine II, Graduate School of Medicine, Hokkaido University, Sapporo, Japan
- 2Department of Medicine and Pathology, School of Medicine, Yale University, New Haven, Connecticut
- Address correspondence and reprint requests to Toshiya Atsumi, MD, PhD, Department of Medicine II, Hokkaido University Graduate School of Medicine, kita 15, Nishi 7, kita-ku, Sapporo 060-8638, Japan. E-mail: tatsumi{at}med.hokudai.ac.jp
Abstract
6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase) catalyzes the synthesis and degradation of fructose 2,6-bisphosphate (F2,6BP), which is a powerful activator of 6-phosphofructo-1-kinase, the rate-limiting enzyme of glycolysis. Four genes encode PFK-2/FBPase (PFKFB1–4), and an inducible isoform (iPFK-2/PFKFB3) has been found to mediate F2,6BP production in proliferating cells. We have investigated the role of iPFK-2/PFKFB3 and related isoforms in the regulation of glycolysis in adipocytes. Human visceral fat cells express PFKFB3 mRNA, and three alternatively spliced isoforms of iPFK-2/PFKFB3 are expressed in the epididymal fat pad of the mouse. Forced expression of the iPFK-2/PFKFB3 in COS-7 cells resulted in increased glucose uptake and cellular F2,6BP content. Prolonged insulin treatment of 3T3-L1 adipocytes led to reduced PFKFB3 mRNA expression, and epididymal fat pads from db/db mice also showed decreased expression of PFKFB3 mRNA. Finally, anti–phospho-iPFK-2(Ser461) Western blotting revealed strong reactivity in insulin-treated 3T3-L1 adipocyte, suggesting that insulin induces the phosphorylation of PFKFB3 protein. These data expand the role of these structurally unique iPFK-2/PFKFB3 isoforms in the metabolic regulation of adipocytes.
- DMEM, Dulbecco’s modified Eagle’s medium
- F2,6BP, fructose 2,6-bisphosphate
- FBS, fetal bovine serum
- IBMX, 3-isobutyl-1-methylxanthine
- IRS, insulin receptor substrate
- PFK-1, phosphofructokinase-1
- PFK-2/FBPase, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase
- PPAR, peroxisome proliferator–activated receptor
- UTR, untranslated region
Footnotes
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- Accepted August 29, 2005.
- Received November 29, 2004.
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