Modulation of serotonin transporter activity by a protein kinase C activator and an inhibitor of type 1 and 2A serine/threonine phosphatases

J Neurochem. 1997 Jun;68(6):2618-24. doi: 10.1046/j.1471-4159.1997.68062618.x.


We studied the effects of 12-O-tetradecanoylphorbol 13-acetate (TPA), a protein kinase C (PKC) activator, and calyculin A (CLA), an inhibitor of type 1 and 2A serine/threonine phosphatases, on serotonin uptake by a human placenta choriocarcinoma cell line (BeWo) and COS-7 cells expressing recombinant serotonin transporter (SET). In BeWo cells, treatment with TPA decreased imipramine-sensitive serotonin uptake with a reduction in Vmax without affecting Km. CLA also decreased imipramine-sensitive serotonin uptake in a manner similar to that of TPA. TPA and CLA also decreased the uptake activity of recombinant SET expressed in COS-7 cells as seen in BeWo cells. These effects of TPA and CLA were reversed by staurosporine, a protein kinase inhibitor. To elucidate whether the inhibitory effects of TPA and CLA were due to direct phosphorylation of SET by PKC, site-directed mutagenesis of five putative PKC phosphorylation sites in SET was performed. Serotonin uptake was also down-regulated by TPA and CLA in all nine mutants, suggesting that these inhibitory modulation of SET activity did not act via direct phosphorylation of SET by PKC.

MeSH terms

  • Adrenergic Uptake Inhibitors / pharmacology
  • Animals
  • COS Cells / chemistry
  • COS Cells / enzymology
  • Carcinogens / pharmacology
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Choriocarcinoma
  • Humans
  • Imipramine / pharmacology
  • Membrane Glycoproteins / genetics
  • Membrane Glycoproteins / metabolism*
  • Membrane Transport Proteins*
  • Mutagenesis, Site-Directed / physiology
  • Nerve Tissue Proteins*
  • Oxazoles / pharmacology
  • Phosphoprotein Phosphatases / antagonists & inhibitors*
  • Protein Kinase C / metabolism*
  • Protein Phosphatase 1
  • Rats
  • Serotonin / metabolism
  • Serotonin / pharmacokinetics
  • Serotonin Plasma Membrane Transport Proteins
  • Tetradecanoylphorbol Acetate / pharmacology
  • Time Factors
  • Transfection
  • Tritium
  • Tumor Cells, Cultured / chemistry
  • Tumor Cells, Cultured / enzymology


  • Adrenergic Uptake Inhibitors
  • Carcinogens
  • Carrier Proteins
  • Membrane Glycoproteins
  • Membrane Transport Proteins
  • Nerve Tissue Proteins
  • Oxazoles
  • SLC6A4 protein, human
  • Serotonin Plasma Membrane Transport Proteins
  • Slc6a4 protein, rat
  • Tritium
  • Serotonin
  • calyculin A
  • Protein Kinase C
  • Phosphoprotein Phosphatases
  • Protein Phosphatase 1
  • Tetradecanoylphorbol Acetate
  • Imipramine