Expression of calmodulin-dependent phosphodiesterase, calmodulin-dependent protein phosphatase, and other calmodulin-binding proteins in human SMS-KCNR neuroblastoma cells.
Calmodulin (CaM)-dependent enzymes, such as CaM-dependent phosphodiesterase (CaM-PDE), CaM-dependent protein phosphatase (CN), and CaM-dependent protein kinase II (CaM kinase II), are found in high concentrations in differentiated mammalian neurons. In order to determine whether neuroblastoma cells express these CaM-dependent enzymes as a consequence of cellular differentiation, a series of experiments was performed on human SMS-KCNR neuroblastoma cells; these cells morphologically differentiate in response to retinoic acid and phorbol esters [12-O-tetradecanoylphorbol 13-acetate (TPA)]. Using biotinylated CaM overlay procedures, immunoblotting, and protein phosphorylation assays, we found that SMS-KCNR cells expressed CN and CaM-PDE, but did not appear to have other neuronal CaM-binding proteins. Exposure to retinoic acid, TPA, or conditioned media from human HTB-14 glioma cells did not markedly alter the expression of CaM-binding proteins; 21-day treatment with retinoic acid, however, did induce expression of novel CaM-binding proteins of 74 and 76 kilodaltons. Using affinity-purified polyclonal antibodies, CaM-PDE immunoreactivity was detected as a 75-kilodalton peptide in undifferentiated cells, but as a 61-kilodalton peptide in differentiated cells. CaM kinase II activity and subunit autophosphorylation was not evident in either undifferentiated or neurite-bearing cells; however, CaM-dependent phosphatase activity was seen. Immunoblot analysis with affinity-purified antibodies against CN indicated that this enzyme was present in SMS-KCNR cells regardless of their state of differentiation. Although SMS-KCNR cells did not show a complete pattern of neuronal CaM-binding proteins, particularly because CaM kinase II activity was lacking, they may be useful models for examination of CaM-PDE and CN expression. It is possible that CaM-dependent enzymes can be used as sensitive markers for terminal neuronal differentiation.
Pennypacker
K R
KR
Department of Pharmacology, Milton S. Hershey Medical Center, The Pennsylvania State University College of Medicine, Hershey 17033.
Kincaid
R L
RL
Polli
J W
JW
Billingsley
M L
ML
D001360:Avidin / Q000378:metabolism; D019703:Calcineurin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002147:Calmodulin / Q000494:pharmacology*; D002148:Calmodulin-Binding Proteins / Q000032:analysis / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D015151:Immunoblotting; D009447:Neuroblastoma / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D013574:Synaptosomes / Q000032:analysis; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014212:Tretinoin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D001360:Avidin; D014212:Tretinoin; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D010727:Phosphoric Diester Hydrolases; D013755:Tetradecanoylphorbol Acetate