title: Elevation of de novo ceramide synthesis in tumor masses and the role of microsomal dihydroceramide synthase.
abstract: Ceramide is formed through sphingomyelin hydrolysis or de novo synthesis and may play a key role in cell growth, differentiation and apoptosis. To clarify which pathway tumor cells use to form ceramide and how its formation is regulated, we determined the levels of dihydroceramide and ceramide in mice inoculated with Sarcoma 180, B16 melanoma or Lewis lung carcinoma cells. The levels in these tumor masses were very high compared to those in other healthy tissues. The high levels were significantly reduced by a single administration of the dihydroceramide synthase inhibitor fumonisin B(1), but not by a sphingomyelinase inhibitor, sphingomyelin analog-1 (SMA-1), suggesting that the tumor cells have a very effective means of synthesizing dihydroceramide and ceramide. To investigate the characteristics of dihydroceramide synthase, we prepared microsomes from Sarcoma 180 tumor masses and healthy mouse liver cells, and compared their catalytic activities on dihydroceramide formation. A kinetic analysis using sphinganine and palmitoyl CoA as substrates revealed that the enzyme present in the tumor formed dihydroceramide 3 times more efficiently than that in healthy liver cells. Partial purification of dihydroceramide synthase from bovine liver microsomes revealed that the enzyme was present in healthy tissues as a 333 kDa form constructed of 47 kDa subunit proteins. However, gel filtration of the enzyme solubilized from the Sarcoma 180 tumor masses demonstrated that its molecular weight was 1300 kDa. These results suggest that malignant transformation causes the cell to produce a form of dihydroceramide synthase with a larger than normal molecular mass; the increased molecular mass may account for the enzyme's increased catalytic efficiency.
authors.affiliation: Faculty of Pharmaceutical Sciences, Fukuoka University, Fukuoka, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Koyanagi
authors.forename: Minoru
authors.initials: M
authors.lastname: Kuga
authors.forename: Shinji
authors.initials: S
authors.lastname: Soeda
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Hosoda
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Yokomatsu
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Takechi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Akiyama
authors.forename: Shiroshi
authors.initials: S
authors.lastname: Shibuya
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Shimeno
mesh_terms: D000577:Amides / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis; D002384:Catalysis; D002417:Cattle; D002518:Ceramides / Q000378:metabolism* / Q000494:pharmacology; D002850:Chromatography, Gel; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D037341:Fumonisins / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008113:Liver Neoplasms / Q000201:enzymology; D008297:Male; D008546:Melanoma, Experimental; D051379:Mice; D008810:Mice, Inbred C57BL; D008813:Mice, Inbred ICR; D008861:Microsomes / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology; D063065:Organophosphonates / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism / Q000502:physiology*; D014407:Tumor Cells, Cultured
chemical_list: C473787:1,1-difluoro-3-hexadecanamido-2-(5-hydroxypentyl)-4-phenylbutanephosphonic acid; D000577:Amides; D002518:Ceramides; D004791:Enzyme Inhibitors; D037341:Fumonisins; D063065:Organophosphonates; C109343:dihydroceramide; C056933:fumonisin B1; C097760:N-palmitoylsphingosine; D010088:Oxidoreductases; C473786:dihydroceramide synthase