DIFFERENTIATION OF A CATECHOLAMINERGIC CNS CELL-LINE MODIFIES TYROSINE-HYDROXYLASE TRANSCRIPTIONAL REGULATION

Recently, a tyrosine hydroxylase (TH)-expressing CNS-derived cell line , CAD, was obtained that is capable of undergoing reversible morpholog ical differentiation. The isolation of the CAD line allowed us to ask whether different DNA regulatory elements direct TH transcription when cells are growing and undifferentiated versus postmitotic and differe ntiated. To this end, we compared expression of a transiently transfec ted bacterial chloramphenicol acetyltransferase reporter gene under th e transcriptional control of TH 5' flanking DNA in CAD cells grown in the presence and absence of serum. Mutational analysis indicates that CAD cells differently regulate TH transcription depending on their sta te of differentiation. In both states, the cyclic AMP response element and API site each activate transcription. However, in undifferentiate d cells, the dyad/E-box element represses expression by similar to 2.7 -fold, whereas it modestly activates transcription in differentiated c ells. The role of the dyad/E-box as a repressor correlates well with t he two-to threefold lower amount of endogenous TH protein present in t he undifferentiated CAD cells. This study demonstrates the differentia l use of TH DNA regulatory elements in proliferating, undifferentiated and nonproliferating, differentiated immortalized neuronal cells.