Protein kinase C regulates nutrient uptake and growth in hepatoma cells.
BACKGROUND
Human hepatoma cells extract glutamine at rates severalfold greater than normal hepatocytes through a high-affinity transporter encoded by the ATB0 gene, which contains two putative phosphorylation sites for protein kinase C (PKC). The studies presented here were undertaken to determine whether System B0-mediated glutamine uptake regulates hepatoma growth and whether PKC regulates the activity of this transporter.


METHODS
SK-Hep cells were treated with the PKC activator phorbol 12-myristate 13-acetate (PMA) and the initial-rate transport of glutamine and other nutrients measured at specific times thereafter. Growth rates were monitored during culture +/- PMA or an excess of system B0 substrates relative to glutamine.


RESULTS
PMA treatment exerted a rapid (half-life approximately 15 minutes) concentration-dependent inhibition of glutamine uptake rates to 50% of control values via a posttranslational mechanism that decreased transporter maximum velocity. This effect persisted after 24 hours and was abrogated by the PKC inhibitor staurosporine. PMA also significantly decreased amino acid transport System y+ and System L activities but no System A. Chronic treatment with PMA (PKC depletion) inhibited SK-Hep growth, as did attenuation of System B0-mediated glutamine uptake with other B0 substrates.


CONCLUSIONS
System B0-mediated glutamine uptake regulates hepatoma cell growth, whereas PKC influences both processes.
Division of Surgical Oncology, Massachusetts General Hospital, Boston, USA.
B P
BP
Bode
N
N
Reuter
J L
JL
Conroy
W W
WW
Souba
D026905:Amino Acid Transport Systems; D001692:Biological Transport / Q000187:drug effects; D002273:Carcinogens / Q000494:pharmacology; D006528:Carcinoma, Hepatocellular; D002352:Carrier Proteins / Q000378:metabolism; D002455:Cell Division / Q000502:physiology; D004789:Enzyme Activation / Q000502:physiology; D005973:Glutamine / Q000493:pharmacokinetics* / Q000502:physiology; D006801:Humans; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D013379:Substrate Specificity; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000737:chemistry / Q000187:drug effects / Q000201:enzymology
D026905:Amino Acid Transport Systems; D002273:Carcinogens; D002352:Carrier Proteins; D005973:Glutamine; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate