Ca(2+)-evoked serotonin secretion by parafollicular cells: roles in signal transduction of phosphatidylinositol 3'-kinase, and the gamma and zeta isoforms of protein kinase C.
Parafollicular (PF) cells secrete 5-HT in response to stimulation of a G-protein-coupled Ca(2+) receptor (CaR) by increased extracellular Ca(2+) (upward arrow[Ca(2+)](e)). We tested the hypothesis that protein kinase C (PKC) participates in stimulus-secretion coupling. Immunoblots from membrane and cytosolic fractions of isolated PF cells revealed conventional (alpha, betaI, and gamma), novel (delta and epsilon), and atypical (iota/lambda and zeta) PKCs. Only PKCgamma was found to have been translocated to the membrane fraction when secretion of 5-HT was evoked by upward arrow[Ca(2+)](e) or phorbol esters. Although phorbol downregulation caused PKCgamma to disappear, secretion was only partially inhibited. A similar reduction of upward arrow[Ca(2+)](e)-evoked secretion was produced by inhibitors of conventional and/or novel PKCs (Gö 6976, calphostin C, and pseudoA), and these compounds did not inhibit secretion at all when applied to phorbol-downregulated cells. In contrast, the phorbol downregulation-resistant component of secretion was abolished by pseudoZ, which inhibits the atypical PKCzeta. Stimulation of PF cells with upward arrow[Ca(2+)](e) increased the activity of immunoprecipitated PKCzeta (but not PKCiota/lambda), and the activity of this PKCzeta was inhibited by pseudoZ. PF cells were found to express regulatory (p85) and catalytic (p110alpha and p110beta) subunits of phosphatidylinositol 3'-kinase (PI3'-kinase). upward arrow[Ca(2+)](e) increased the activity of immunoprecipitated PI3'-kinase; moreover, PI3'-kinase inhibitors (wortmannin and LY294002) antagonized secretion. We suggest that PKC isoforms mediate secretion of 5-HT by PF cells in response to stimulation of the CaR. PKC involvement can be accounted for by PKCgamma and an isoform sensitive to inhibition by pseudoZ, probably PKCzeta, which is activated via PI3'-kinase.
Liu
K
K
Division of Neuroscience, New York State Psychiatric Institute, New York, New York 10032, USA.
Hsiung
S
S
Adlersberg
M
M
Sacktor
T
T
Gershon
M D
MD
Tamir
H
H
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002227:Carbazoles / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D003600:Cytosol / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism*; D009281:Naphthalenes / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism*; D012756:Sheep; D015398:Signal Transduction / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013961:Thyroid Gland / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D000077191:Wortmannin; D000099221:Protein Kinase C zeta
D000730:Androstadienes; D002118:Calcium; D015220:Calcium Channels; D002227:Carbazoles; D004791:Enzyme Inhibitors; D007211:Indoles; D007527:Isoenzymes; D009281:Naphthalenes; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C; D012701:Serotonin; D013755:Tetradecanoylphorbol Acetate; D000077191:Wortmannin; D000099221:Protein Kinase C zeta; C081021:Go 6976; C087857:protein kinase C gamma; C058819:calphostin C