title: Sphingosine kinase 1 expression is downregulated during differentiation of Friend cells due to decreased c-MYB.
abstract: Sphingosine kinase 1 (SPHK1) overexpression in malignant cells has been reported. Mouse Friend cells showed higher SPHK1 but not SPHK2 expression compared with other mouse cell lines. A Sphk1 promoter analysis demonstrated the region between -53bp and the first exon as the minimal promoter. Further promoter truncation revealed the importance of a MYB-binding site. EMSA using this region as the probe demonstrated one band containing c-MYB protein, and its intensity decreased during erythroid differentiation with hexamethylane bisacetamide (HMBA), a potent inducer of erythroid differentiation of Friend cells. ChIP assay also revealed in vivo binding of c-MYB. c-MYB overexpression and siRNA for c-Myb affected SPHK1 expression, confirming the important regulatory role of c-MYB in SPHK1 expression. HMBA reduced c-MYB expression rapidly. Induced differentiation by HMBA caused a marked and rapid reduction of SPHK1 mRNA, protein and enzyme activity leading to the rapid decrease of cellular sphingosine 1-phosphate level. Moreover, terminally differentiated cells did not resume SPHK1 expression. Compared with original Friend cells, stable overexpression of wild-type SPHK1 showed higher cell proliferation, resistance to cell death by serum depletion. Interestingly, HMBA-induced differentiation of these cells was delayed but not completely suppressed. In contrast, SPHK inhibitor and its siRNA inhibited cell growth and enhanced HMBA-induced differentiation significantly, suggesting that SPHK1 delayed HMBA-induced differentiation by its cell proliferation-promoting activity. Effects of pertussis toxin, a G-protein-coupled receptor inhibitor, and S1P receptor antagonist on Friend cell growth and differentiation were negligible, suggesting the importance of the intracellular SPHK1/S1P signaling in Friend cells.
authors: Department of Pathophysiological Laboratory Science, Nagoya University Graduate School of Medicine, Nagoya, Japan.
authors: N
authors: N
authors: Mizutani
authors: M
authors: M
authors: Kobayashi
authors: S
authors: S
authors: Sobue
authors: M
authors: M
authors: Ichihara
authors: H
authors: H
authors: Ito
authors: K
authors: K
authors: Tanaka
authors: S
authors: S
authors: Iwaki
authors: S
authors: S
authors: Fujii
authors: Y
authors: Y
authors: Ito
authors: K
authors: K
authors: Tamiya-Koizumi
authors: A
authors: A
authors: Takagi
authors: T
authors: T
authors: Kojima
authors: T
authors: T
authors: Naoe
authors: M
authors: M
authors: Suzuki
authors: M
authors: M
authors: Nakamura
authors: Y
authors: Y
authors: Banno
authors: Y
authors: Y
authors: Nozawa
authors: T
authors: T
authors: Murate
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000235:genetics*; D002460:Cell Line; D015536:Down-Regulation; D006801:Humans; D051379:Mice; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D020598:Proto-Oncogene Proteins c-myb / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering; D049349:Receptors, Lysosphingolipid / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D000099157:Sphingosine Kinase
chemical_list: D017853:Phosphotransferases (Alcohol Group Acceptor); D020598:Proto-Oncogene Proteins c-myb; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D049349:Receptors, Lysosphingolipid; D000099157:Sphingosine Kinase