Differential action of nerve growth factor and phorbol ester TPA on rat synaptosomal PKC isoenzymes.
The subcellular redistribution of protein kinase C family members (alpha, beta, gamma, delta, epsilon and zeta isoforms) was examined in response to treatment with 12-O-tetradecanoyl-phorbol-13 acetate (TPA) or nerve growth factor (NGF) in a synaptosomal-enriched P2 fraction from rat brain. Treatment with TPA affected members of the classical-PKC family (alpha, beta and gamma), resulting in a final loss of total protein of each isoenzyme. The kinetics of changes of members of the novel-PKC family are different, the delta isoform being translocated, but not down-regulated, while the epsilon isoform showing only a slight diminishing of immunoreactivity in the soluble and particulate fractions. The atypical-PKC zeta isoform was not translocated in response to TPA. Incubation with NGF induced a loss of immunoreactivity of the cytosolic alpha, beta and epsilon isoforms, but the membrane fractions of these isoforms were not appreciably affected. In contrast, a marked translocation from cytosol to membrane was observed in the case of the gamma and delta isoforms. The zeta isoform presented a slight translocation from the particulate fraction to the soluble fraction. Thus, the results show that the effects of TPA and NGF on PKC isoforms are not coincident in synaptosomes, the 6 isoform being activated and not down-regulated by both treatments, whereas the gamma isoform is only down-regulated in the case of TPA, but presents sustained translocation with NGF, indicating that PKC isoform-specific degradation pathways exist in synaptic terminals. The effects of NGF on PKC isoforms coexist with an increase in NGF-induced polyphosphoinositide hydrolysis, suggesting the participation of phospholipases.
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Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, Universitat Autònoma de Barcelona, Spain.
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Aguilera
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D000818:Animals; D001921:Brain / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism*; D009414:Nerve Growth Factors / Q000494:pharmacology*; D010716:Phosphatidylinositols / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013574:Synaptosomes / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D007527:Isoenzymes; D009414:Nerve Growth Factors; D010716:Phosphatidylinositols; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate