Coordinated expression of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 4 and heme oxygenase 2: evidence for a regulatory link between glycolysis and heme catabolism.
Heme is an essential requirement for cell survival.  Heme oxygenase (HO) is the rate-limiting enzyme in heme catabolism and consists of two isozymes, HO-1 and HO-2.  To identify the protein that regulates the expression or function of HO-1 or HO-2, we searched for proteins that interact with both isozymes, using protein microarrays.  We thus identified 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 4 (PFKFB4) that synthesizes or degrades fructose-2,6-bisphosphate, a key activator of glycolysis, depending on cellular microenvironments.  Importantly, HO-2 and PFKFB4 are predominantly expressed in haploid spermatids.  Here, we show a drastic reduction in expression levels of PFKFB4 mRNA and protein and HO-2 mRNA in HepG2 human hepatoma cells in responses to glucose deprivation (≤ 2.5 mM), which occurred concurrently with remarkable induction of HO-1 mRNA and protein.  Knockdown of HO-2 expression in HepG2 cells, using small interfering RNA, caused PFKFB4 mRNA levels to decrease with a concurrent increase in HO-1 expression.  Thus, in HepG2 cells, HO-1 expression was increased, when expression levels of HO-2 and PFKFB4 mRNAs were decreased.  Conversely, overexpression of HO-2 in HepG2 cells caused the level of co-expressed PFKFB4 protein to increase.  These results suggest a potential regulatory role for HO-2 in ensuring PFKFB4 expression.  Moreover, in D407 human retinal pigment epithelial cells, glucose deprivation decreased the expression levels of PFKFB4, HO-1, and HO-2 mRNAs.  Thus, glucose deprivation consistently down-regulated the expression of PFKFB4 and HO-2 mRNAs in both HepG2 cells and RPE cells.  We therefore postulate that PFKFB4 and HO-2 are expressed in a coordinated manner to maintain glucose homeostasis.
Department of Molecular Biology and Applied Physiology, Tohoku University School of Medicine, Sendai, Japan.
Bin
B
Li
Kazuhisa
K
Takeda
Kazunobu
K
Ishikawa
Miki
M
Yoshizawa
Michihiko
M
Sato
Shigeki
S
Shibahara
Kazumichi
K
Furuyama
D000818:Animals; D015536:Down-Regulation / Q000235:genetics; D004847:Epithelial Cells / Q000201:enzymology; D015971:Gene Expression Regulation, Enzymologic; D055785:Gene Knockdown Techniques; D005947:Glucose / Q000172:deficiency; D006019:Glycolysis / Q000235:genetics*; D006367:HeLa Cells; D006418:Heme / Q000378:metabolism*; D006419:Heme Oxygenase (Decyclizing) / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D051547:Heme Oxygenase-1 / Q000235:genetics / Q000378:metabolism; D056945:Hep G2 Cells; D006801:Humans; D008099:Liver / Q000201:enzymology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D009928:Organ Specificity; D025481:Phosphofructokinase-2 / Q000235:genetics* / Q000378:metabolism; D040081:Protein Array Analysis; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013737:Testis / Q000201:enzymology
C506672:PFKFB4 protein, human; D012333:RNA, Messenger; D006418:Heme; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; C105245:heme oxygenase-2; D025481:Phosphofructokinase-2; D005947:Glucose