Insulin translocates PKC-epsilon and phorbol esters induce and persistently translocate PKC-beta 2 in BC3H-1 myocytes.
Initial studies suggested that insulin increases diacylglycerol and activates protein kinase C (PKC) in BC3H-1 myocytes. In these earlier studies, insulin was found to translocate PKC-beta, but the presence of PKC-epsilon was not appreciated. More recently, the presence of PKC-epsilon was documented, but PKC-beta was not detected, and it was questioned whether insulin activates PKC in BC3H-1 myocytes [Stumpo, D.J., Haupt, D.M. and Blackshear, P.J. (1994) J. Biol. Chem. 269:21184-21190]. We questioned whether insulin translocates PKC-epsilon in BC3H-1 myocytes, and re-evaluated the question of whether myocytes truly contain a PKC-beta isoform whose existence can be verified by its response to phorbol ester treatment. We found that PKC-epsilon was acutely translocated by insulin and phorbol esters from the cytosol to the membrane fraction in BC3H-1 myocytes; in addition, PKC-epsilon, like PKC-alpha, was depleted by chronic phorbol ester treatment. We also found that BC3H-1 myocytes containing a 76,000 Mr PKC-beta isoform that is acutely translocated and subsequently depleted by phorbol esters. Moreover, chronic phorbol ester treatment induced an 84,000 Mr PKC-beta 2 isoform that appeared to be persistently translocated and activated, as suggested by studies of myristoylated arginic-rich C kinase substrate (MARCKS) phosphorylation. We conclude that: (1) insulin acutely translocates PKC-epsilon, as well as PKC-beta, in BC3H-1 myocytes; and (2) PKC-beta is not truly downregulated by phorbol esters in BC3H-1 myocytes.
Standaert
M L
ML
J. A. Haley Veterans' Hospital, Tampa, Florida, USA.
Avignon
A
A
Arnold
T
T
Saba-Siddique
S I
SI
Copper
D R
DR
Watson
J
J
Zhou
X
X
Galloway
L
L
Farese
R V
RV
D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology; D003600:Cytosol / Q000201:enzymology; D007328:Insulin / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000378:metabolism*; D008565:Membrane Proteins; D051379:Mice; D008969:Molecular Sequence Data; D009132:Muscles / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D064546:Protein Kinase C beta; D051744:Protein Kinase C-epsilon; D011506:Proteins / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; C000619711:Marcks protein, mouse; D008565:Membrane Proteins; D011506:Proteins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; C497256:Prkce protein, mouse; D011493:Protein Kinase C; D064546:Protein Kinase C beta; D051744:Protein Kinase C-epsilon; D013755:Tetradecanoylphorbol Acetate