Mechanisms of alpha-Sialosyl cholesterol action to suppress both cyclic AMP production and DNA synthesis of rat glial cells.
alpha-Sialosyl cholesterol (alpha-SC) that elicited morphological differentiation of rat astrocytes not only lowered intracellular cyclic AMP (cAMP) levels but also inhibited cAMP production induced by either alpha-isoproterenol, cholera toxin, or forskolin. The targets of alpha-SC in the cAMP production system of rat astrocytes were investigated to understand the mechanism of the alpha-SC action on cAMP production. cAMP production evoked by alpha-isoproterenol (1 microM) was entirely canceled by beta blockers such as propranolol and timolol (1 microM), but not by alpha-SC. Concentrations of alpha-SC greater than 15 microM were required for 50% inhibition of the activation by a beta agonist. Although alpha-SC inhibited in a dose-dependent manner the activities of membrane-associated adenylate cyclase that had been stimulated by either GTP gamma S of forskolin, alpha-SC inhibited neither GTP-binding activities nor GTPase activities of the membrane-associated G proteins. These findings suggest that alpha-SC suppresses adenylate cyclase directly, but not beta receptors or G proteins, and that it promotes the morphological differentiation of rat astrocytes through a mechanism regulating directly the cytoskeletal organization, regardless of intracellular cAMP level. alpha-SC (30 microM) suppressed 40% of DNA synthesis in the cell-free system, which contained the cytosolic extracts and the nucleus fraction prepared from rat astrocytoma C6 cells. Approximately 25% of alpha-SC incorporated in the astrocyte cytoplasm was transferred to the nuclei by 10 min after the addition.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Biochemistry, Nagoya City University Medical School, Japan.
J
J
Ito
T
T
Kato
R
R
Tanaka
D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D002474:Cell-Free System / Q000378:metabolism; D002788:Cholesterol Esters / Q000494:pharmacology*; D000242:Cyclic AMP / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D004247:DNA / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D007425:Intracellular Membranes / Q000378:metabolism; D051381:Rats; D012794:Sialic Acids / Q000494:pharmacology*; D014018:Tissue Distribution
D002788:Cholesterol Esters; D012794:Sialic Acids; C055195:N-acetylneuraminyl cholesterol; D004247:DNA; D000242:Cyclic AMP