Changes in expression of tyrosine hydroxylase immunoreactivity in human SMS-KCNR neuroblastoma following retinoic acid or phorbol ester-induced differentiation

Human SMS-KCNR cells differentiated in response to either retinoic acid or phorbol esters; differentiated cells extended numerous, complex neurites and showed reduced proliferation. Tyrosine hydroxylase (TH) immunoreactivity was measured in this cell line following treatment with retinoic acid (1-10 μM), 12-O-tetradecanoyl-phorbol-13-acetate (TPA; 16-160 nM), or combinations of these agents. After 21 days of treatment with either TPA or retinoic acid (RA), TH immunoreactivity, measured using densitometric scans of Western blots, was doubled relative to untreated or serum-deprived SMS-KCNR cultures. Increases in TH immunoreactivity could be detected after 6 days of treatment. Treatment with RA for 3 days followed by phorbol esters for an additional 3 days resulted in a 3-fold increase in TH immunoreactivity at day 6; reversing the order of drug treatment did not have this effect. Treatment of cultures with the divalent cationophore A23187 caused treated cells to retract neurites; expression of TH immunoreactivity was decreased relative to drug-treated and control cultures. These results suggest that retinoic acid treatment may 'prime' SMS-KCNR cells for the subsequent effects of phorbol esters, and indicate that the patterns of biochemical differentiation induced by TPA or RA are different.