2157816

pubmed:Citation

5

The actions of tumor promoters on the coupling of muscarinic receptors to the hydrolysis of inositol lipids and the generation of Ca2+ signals were examined in the human neuroblastoma SH-SY5Y cell line. Pretreatment of SH-SY5Y cells with 50 nM 12-O-tetradecanoylphorbol 13-acetate (TPA) for 5 days resulted in neuronal differentiation, a 28% decrease in both N-[3H]methylscopolamine and [3H]-scopolamine binding, and a significantly larger reduction (48%) in agonist-stimulated 3H-inositol phosphate generation. Whereas mezerein could mimic the effects produced by TPA, the biologically inactive 4 alpha-phorbol 12,13-didecanoate was without effect on both antagonist binding and agonist-stimulated phosphoinositide (PPI) turnover. A decline (approximately 50%) in the agonist-mediated rise in cytoplasmic Ca2+ and a substantial loss of protein kinase C activity also were observed following pretreatment with TPA or mezerein. The ability of fluoride, an agent capable of direct activation of guanine nucleotide binding proteins, to stimulate 3H-inositol phosphate release was significantly reduced in SH-SY5Y cells treated with these agents. Furthermore, pretreatment of SH-SY5Y neuroblastoma cells with TPA or mezerein impaired 3H-inositol phosphate formation induced by the addition of either guanosine 5'-O-(3-thiotriphosphate) or carbamylcholine to digitonin-permeabilized cells, but not that elicited by the addition of 2 mM CaCl2. Although cells cultured in the presence of serum-free media also exhibited neuronal differentiation, no significant alteration in either muscarinic receptor number or agonist-stimulated PPI hydrolysis was observed. The results suggest that TPA and mezerein decrease agonist-stimulated PPI hydrolysis and Ca2+ signaling in SH-SY5Y cells not only by a reduction in muscarinic receptor number but also through an inhibition of guanine nucleotide-stimulated PPI turnover.

eng

IM

MEDLINE

0022-3042

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NLM

1725-34

pubmed-meshheading:2157816-Calcium, pubmed-meshheading:2157816-Culture Media, pubmed-meshheading:2157816-Cytoplasm, pubmed-meshheading:2157816-Diterpenes, pubmed-meshheading:2157816-Guanine Nucleotides, pubmed-meshheading:2157816-Guanosine 5'-O-(3-Thiotriphosphate), pubmed-meshheading:2157816-Guanosine Triphosphate, pubmed-meshheading:2157816-Humans, pubmed-meshheading:2157816-Hydrolysis, pubmed-meshheading:2157816-Inositol Phosphates, pubmed-meshheading:2157816-Neuroblastoma, pubmed-meshheading:2157816-Osmolar Concentration, pubmed-meshheading:2157816-Phosphatidylinositols, pubmed-meshheading:2157816-Protein Kinase C, pubmed-meshheading:2157816-Receptors, Muscarinic, pubmed-meshheading:2157816-Sodium Fluoride, pubmed-meshheading:2157816-Terpenes, pubmed-meshheading:2157816-Tetradecanoylphorbol Acetate, pubmed-meshheading:2157816-Thionucleotides, pubmed-meshheading:2157816-Time Factors, pubmed-meshheading:2157816-Tumor Cells, Cultured

Reduction of muscarinic receptor density and of guanine nucleotide-stimulated phosphoinositide hydrolysis in human SH-SY5Y neuroblastoma cells following long-term treatment with 12-O-tetradecanoylphorbol 13-acetate or mezerein.

Journal Article, Comparative Study, Research Support, U.S. Gov't, P.H.S.