Effects of modulators of tyrosinase activity on expression of murine interleukin-2 cDNA driven by the tyrosinase promoter

Sequence analysis of the promoter region of the murine tyrosinase gene identified various consensus motifs including AP2 sites, cAMP and TPA response elements (CREs/TREs) and retinoic acid response element (RARE) half-sites. By linking two different promoter lengths (2.5 kb or 769 bp) to murine interleukin-2 (IL-2) cDNA we have used IL-2 production by transduced B16 cells to monitor response to inducing agents capable of acting through these elements. Aminophylline or theophylline (0.1-2 mM) added to the culture medium of transfected B16, but not 3T3, cells, increased IL-2 secretion significantly (P>0.05) in a dose-dependent fashion. This response was comparable in cells transfected with either the full length or the truncated promoter. Therefore, the cAMP responsiveness of the tyrosinase promoter probably is mediated by CREs and not AP2 sites, since the truncated promoter contains the former but not the latter regions. Retinoic acid at various concentrations (0.1-1 μM) evoked a standard increase in IL-2 production. Responses were similar for both promoter constructs, which suggests either that each RARE half-site can confer the full retinoic acid response, or that retinoic acid is mediating its effect through pathways independent of the RARE sites. TPA (2 nM-2 μM) had no effect on IL-2 production. These results demonstrate that the tyrosinase promoter can be induced by certain pharmacological agents and raise the possibility that administration of such substances may enhance expression of therapeutic genes controlled by this promoter.