Sterol-induced upregulation of phosphatidylcholine synthesis in cultured fibroblasts is affected by the double-bond position in the sterol tetracyclic ring structure.
We have examined how a specific enrichment of cultured fibroblasts with various sterols (cholesterol, lathosterol, 7-dehydrocholesterol, allocholesterol and dihydrocholesterol) regulate synthesis de novo of phosphatidylcholine, cholesterol and cholesteryl (or steryl) esters in human skin fibroblasts. When human skin fibroblasts were incubated for 1 h with 130 microM cholesterol/CyD complexes, the mass of cellular free cholesterol increased by 100 nmol.mg-1 protein (from 90 nmol.mg-1 to 190 nmol.mg-1 protein). A similar exposure of cells to different sterol/CyD complexes increased the cell sterol content between 38 and 181 nmol sterol per mg cell protein. In cholesterol-enriched cells, the rate of phosphatidylcholine synthesis was doubled compared to control cells, irrespective of the type of precursor used ([3H]choline, [3H]palmitic acid, or [14C]glycerol). Enrichment of fibroblasts with 7-dehydrocholesterol, allocholesterol, or dihydrocholesterol also upregulated phosphatidylcholine synthesis, whereas cells enriched with lathosterol failed to upregulate their phosphatidylcholine synthesis. The activity of membrane-bound CTP:phosphocholine cytidylyltransferase, the rate-limiting enzyme, was increased by 47 +/- 4% in cholesterol-enriched cells whereas its activity was unchanged in lathosterol-enriched cells. Sterol enrichment with all tested sterols (including lathosterol) down-regulated acetate-incorporation into cholesterol, and upregulated sterol esterification in the sterol-enriched fibroblasts. Using 31P-NMR to measure the lamellar-to-hexagonal (Lalpha-HII) phase transition in multilamellar lipid dispersions, lathosterol-containing membranes underwent their transition at significantly higher temperatures compared to membranes containing any of the other sterols. In a system with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine and either cholesterol or lathosterol (70:30 mol/mol), differential scanning calorimetry also revealed that the Lalpha-HII-transition occurred at a higher temperature with lathosterol compared to either cholesterol, allocholesterol, or dihydrocholesterol. These findings together suggest that there may exist a correlation between the propensity of a sterol to stabilize the Lalpha-HII-transition and its capacity to upregulate the activity of CTP:phosphocholine cytidylyltransferase in cells.
Leppimäki
P
P
Department of Biochemistry, Abo Akademi University, Turku, Finland.
Mattinen
J
J
Slotte
J P
JP
D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002784:Cholesterol / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D019916:Choline-Phosphate Cytidylyltransferase / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D010713:Phosphatidylcholines / Q000096:biosynthesis*; D012867:Skin; D015854:Up-Regulation / Q000187:drug effects
D010713:Phosphatidylcholines; C001521:lathosterol; D002784:Cholesterol; D019916:Choline-Phosphate Cytidylyltransferase