[Specific activity of the promoter containing Myc-Max response elements in c-myc-overexpressing cells]

To investigate the specific activity of a hybrid promoter which is constructed by replacing the third domain of herpes simplex virus (HSV) thymidine kinase (TK) promoter with the Myc-Max response elements.

Myc-Max response elements were ligated with a third domain-deleted HSV-TK promoter by cloning and subcloning PCR products. Then a luciferase-expressing plasmid, in which the luciferase gene was put under the control of hybrid promoter, was constructed and transfected transiently into the cell lines which had been demonstrated to be c-myc over- or low-expressing by Northern blot hybridization. The luciferase activities in these cells were detected.

In c-myc over-expressing cells, the hybrid promoter (Mpr) led to high levels of (81,966 +/- 43,238) relative light units (RLUs) in PC-2 cells and (70,563 +/- 22,435) RLUs in PC-7 cells, which were 78- and 150-fold higher than those coming from the third domain-deleted TK promoter (Epr), and also 6.9- and 1.7-fold higher than the activities controlled by TK promoter. However, Mpr showed a very low activity in c-myc low-expressing cells, in which the luciferase activity was (431 +/- 73) RLUs, similar to (601 +/- 141) RLUs produced by Epr.

The activity of hybrid promoter, which is composed of Myc-Max response elements and the third domain-deleted TK promoter, possesses cell-type specificity for c-myc-overexpressing cells.