Enhancement of glucagon secretion in mouse and human pancreatic alpha cells by protein kinase C (PKC) involves intracellular trafficking of PKCalpha and PKCdelta.
OBJECTIVE
Protein kinase C (PKC) regulates exocytosis in various secretory cells. Here we studied intracellular translocation of the PKC isoenzymes PKCalpha and PKCdelta, and investigated how activation of PKC influences glucagon secretion in mouse and human pancreatic alpha cells.


METHODS
Glucagon release from intact islets was measured in static incubations, and the amounts released were determined by RIA. Exocytosis was monitored as increases in membrane capacitance using the patch-clamp technique. The expression of genes encoding PKC isoforms was analysed by real-time PCR. Intracellular PKC distribution was assessed by confocal microscopy.


RESULTS
The PKC activator phorbol 12-myristate 13-acetate (PMA) stimulated glucagon secretion from mouse and human islets about fivefold (p < 0.01). This stimulation was abolished by the PKC inhibitor bisindolylmaleimide (BIM). Whereas PMA potentiated exocytosis more than threefold (p < 0.001), BIM inhibited alpha cell exocytosis by 60% (p < 0.05). In mouse islets, the PKC isoenzymes, PKCalpha and PKCbeta1, were highly abundant, while in human islets PKCeta, PKCepsilon and PKCzeta were the dominant variants. PMA stimulation of human alpha cells correlated with the translocation of PKCalpha and PKCdelta from the cytosol to the cell periphery. In the mouse alpha cells, PKCdelta was similarly affected by PMA, whereas PKCalpha was already present at the cell membrane in the absence of PMA. This association of PKCalpha in alpha cells was principally dependent on Ca(2+) influx through the L-type Ca(2+) channel.


CONCLUSIONS
PKC activation augments glucagon secretion in mouse and human alpha cells. This effect involves translocation of PKCalpha and PKCdelta to the plasma membrane, culminating in increased Ca(2+)-dependent exocytosis. In addition, we demonstrated that PKCalpha translocation and exocytosis exhibit differential Ca(2+) channel dependence.
De Marinis
Y Z
YZ
Lund University Diabetes Centre, Department of Clinical Sciences, Clinical Research Centre, Lund University, CRC 91-11, UMAS entrance 72, SE-20502 Malmö, Sweden. Yang.De_Marinis@med.lu.se
Zhang
E
E
Amisten
S
S
Taneera
J
J
Renström
E
E
Rorsman
P
P
Eliasson
L
L
D000328:Adult; D000368:Aged; D000818:Animals; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D005934:Glucagon / Q000378:metabolism*; D050416:Glucagon-Secreting Cells / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008875:Middle Aged; D011493:Protein Kinase C / Q000378:metabolism*; D051571:Protein Kinase C-alpha / Q000187:drug effects / Q000502:physiology*; D051745:Protein Kinase C-delta / Q000187:drug effects / Q000502:physiology*; D021381:Protein Transport; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D005934:Glucagon; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D051745:Protein Kinase C-delta; D013755:Tetradecanoylphorbol Acetate