ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract: In cultured bovine adrenal chromaffin cells, our[3H]saxitoxin ([3H]STX) binding, immunoblot, andnorthern blot analyses specified protein kinase C (PKC) isoform-specificposttranscriptional and posttranslational mechanisms that directdown-regulation of cell surface Na channels. Immunoblot analysis showed thatamong 11 PKC isoforms, adrenal chromaffin cells contained only conventional(c)PKC-α, novel (n)PKC-ε, and atypical (a)PKC-ζ. Treatment ofadrenal chromaffin cells with 100 nM12-O-tetradecanoylphorbol 13-acetate (TPA) or 100 nM phorbol12,13-dibutyrate (PDBu) caused a rapid (〈 15 min) and sustained (〉 15 h)translocation of PKC-α and -ε (but not -ζ) from cytosol tomembranes, whereas a biologically inactive 4α-TPA had no effect.Thymeleatoxin (TMX), an activator of cPKC, produced similar membraneassociation of only PKC-α at 100 nM, with the potency of TMXbeing comparable with those of TPA and PDBu. Treatment with either 100nM TPA or 100 nM TMX reduced cell surface [3H]STXbinding to a comparable extent at 3, 6, and 12 h, whereas TPA lowered thebinding to a greater extent than TMX at 15, 18, and 24 h; at 15 h,Gö6976, a specific inhibitor of cPKC, completelyblocked TMX-induced decrease of [3H]STX binding while preventing bymerely 57% TPA-induced decrease of [3H]STX binding. Treatment with100 nM TPA lowered the Na channel α-subunit mRNA level between3 and 12 h, with its maximum 52% fall at 6 h, and it was accompanied by asubsequent 61% rise of the β1-subunit mRNA level at 24 h.Gö6976 failed to prevent TPA-induced reductionof the α-subunit mRNA level; TMX did not change the α-andβ1-subunit mRNA levels throughout the 24-h treatment.Brefeldin A, an inhibitor of vesicular exit from the trans-Golginetwork, augmented TPA- and TMX-induced decrease of [3H]STX binding at 1 and 3 h. Our previous and present studies suggest that PKC down-regulates cell surface Na channels without altering the allosteric gating of Na channels via PKC isoform-specific mechanisms; cPKC-α promotes Na channel internalization, whereas nPKC-ε decreases the α-subunit mRNA level by shortening the half-life of α-subunit mRNA without changing its gene transcription.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1046/j.1471-4159.2000.0741674.x
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