Regulation of the Multiple Forms of Dopamine , & Hydroxylase by Nerve Growth Factor , Dexamethasone , and Dibutyryl Cyclic AMP in the PC 12 Pheochromocytoma Cell

Treatment with nerve growth factor was found to influence the subunit forms of dopamine @-hydroxylase in PC12 pheochromocytoma cells. In untreated cells, near equal amounts of two subunit forms were observed (apparent M, = 77,000 and 73,000) by labeling with [36S]methionine. Upon treatment of PC12 cells with nerve growth factor for several days, the M, = 73,000 subunit form of dopamine &hydroxylase was almost exclusively observed. The shift in subunit forms became apparent only after a day of treatment and was maximal with 3 days or more of exposure to nerve growth factor. The dose-response curve was similar to most other nerve growth factor-induced responses in PC12 cells. Neurite outgrowth, however, was not essential for the shift in predominance of th M, = 73,000 subunit form. This effect of nerve growth factor also occurred in suspension cultures or in the presence of low concentrations of inhibitors of transcription sufficient to prevent neurite outgrowth. Pulse-chase experiments with nerve growth factor-treated cells indicated that the M, = 77,000 form is initially synthesized (5 min) and is then converted to the M, = 73,000 form by 30-60 min. Insulin (100 ng/ml) and epidermal growth factor (1 ng/ml) had no effect on the subunit forms of dopamine @-hydroxylase. However, treatment of PC12 cells for several days with dexamethasone (lo-‘ M) or dibutyryl cyclic AMP (1 mM) leads to predominance of the M, = 73,000 form of the enzyme. These experiments suggest that the proportions of the subunit forms of dopamine @-hydroxylase can be regulated in cells by external signals and this may reflect alterations in post-translational processing enzymes and may serve as a potential mechanism to regulate catecholamine metabolism.