FUNCTIONAL AND HIGH-LEVEL EXPRESSION OF HUMAN DOPAMINE-BETA-HYDROXYLASE IN TRANSGENIC MICE

Dopamine beta-hydroxylase (DBH; EC 1.14.17.1) catalyzes the production of the neurotransmitter and hormone norepinephrine in the third step of the catecholamine biosynthesis pathway. Transgenic mice were genera ted with multiple copies of a human DBH minigene construct containing the full-length cDNA connected downstream of the 4-kilobase upstream p romoter region to achieve overexpression of DBH. Human DBH mRNA and im munoreactivity were detected tissue-specifically in the brain and adre nal gland of these transgenic mice. The transgene products were correc tly processed to a glycosylated mature polypeptide with a molecular ma ss of 72 kDa and existed in the secretory vesicles as both soluble and membrane-bound forms. We detected a marked increase in DBH activity i n various catecholamine-containing tissues of the mice that occurred a s a consequence of expression of the catalytically active human DBH en zyme. However, in these transgenics the steady-state levels of norepin ephrine and epinephrine were normally maintained without the accelerat ion of the catecholamine turnover rate, suggesting that there are some regulatory mechanisms to preserve a constant rate of norepinephrine s ynthesis in spite of the increased amount of DBH protein. These transg enic mice with the minigene construct provide one approach to study th e mechanisms underlying biogenesis of the DBH polypeptide and regulati on of norepinephrine synthesis.