title: Nerve growth factor induces a succession of increases in isoprenylated methylated small GTP-binding proteins of PC-12 pheochromocytoma cells.
abstract: Pheochromocytoma (PC-12) cells exposed to nerve growth factor (NGF) acquire a sympathetic neuron-like phenotype. This NGF-response is blocked by methylation inhibitors and can be mimicked by the farnesylated methylated small GTP-binding protein p21ras. The implicated involvement of prenylation, methylation and a small GTP-binding protein in the NGF-response has been studied by directly measuring 3H-mevalonic acid (MVA)-metabolites incorporated into proteins, protein carboxy [methyl-3H]ester formation and levels of [alpha-32P]GTP-binding proteins in NGF-induced PC-12 cells. We demonstrate that NGF induces a 2-3-fold increase in 21-24 kDa methylated membrane proteins that incorporate 3H-MVA-metabolites, and bind GTP. Levels of [alpha-32P]GTP-binding in these proteins were increased by 2-3-fold. Methylation and membrane association of the small GTP-binding proteins were blocked by lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, which also enhanced their labeling by 3H-MVA-metabolites. Cycloheximide reduced the levels of [methyl-3H] labeled 21-24 kDa proteins and of the overlapping [alpha-32P]GTP binding-proteins. About 70% of the [methyl-3H]-groups found in these proteins were recovered from two dimensional gel blots in nine distinct spots of [alpha-32P]GTP-binding proteins. Taken together these results strongly suggest that in PC-12 cells, NGF induces an increase in the synthesis of prenylated methylated small GTP-binding proteins. The efficacy of lovastatin blockage of protein methylation and enhancement of 3H-MVA-metabolites incorporation into GTP-binding proteins was lower in NGF-induced cells than in controls. This suggests that NGF also induces an increase in HMG-CoA reductase activity. At the early phase of the NGF response in PC-12 cells (15 min-1 h), the levels of two small GTP-binding proteins (molecular mass of 21-22 kDa and 23-24 kDa) were increased. Thus, at least two proteins, of which one but not the other may be p21ras, appear to be involved in the early response. After a lag period of 24 h with NGF, a second more robust phase of increase in methylated small GTP-binding proteins was apparent. This relatively late response, which was almost completed within 24 h, may reflect involvement of small GTP-binding proteins in neurite-outgrowth and in the functional activity of the differentiated cells. Many small GTP-binding proteins were increased during the second phase, precluding electrophoretic separation of all of them. 3 proteins, however, were well separated (one 23-24 kDa protein and two 21-22 kDa proteins).(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: Department of Biochemistry, George S. Wise Faculty of Life Sciecnes, Tel Aviv University, Israel.
authors.forename: R
authors.initials: R
authors.lastname: Haklai
authors.forename: S
authors.initials: S
authors.lastname: Lerner
authors.forename: Y
authors.initials: Y
authors.lastname: Kloog
mesh_terms: D000818:Animals; D003513:Cycloheximide / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D019204:GTP-Binding Proteins / Q000096:biosynthesis*; D006160:Guanosine Triphosphate / Q000378:metabolism; D008745:Methylation; D009414:Nerve Growth Factors / Q000494:pharmacology*; D016716:PC12 Cells; D017368:Protein Prenylation; D013268:Stimulation, Chemical
chemical_list: D009414:Nerve Growth Factors; D006160:Guanosine Triphosphate; D003513:Cycloheximide; D019204:GTP-Binding Proteins