A two-gene cassette to protect against prostate cancer . Gene 1 codes for ecdysone receptor, which is expressed from a prostate specific transcription factor. Ecdysone receptor functions as an ecdysone-dependent transcription factor to control the expression of Gene 2, which codes for Diphtheria toxin. When ecdysone is present, the toxin gene is expressed in prostate cells and the cells die. The toxin gene is not expressed in any other cells, because none synthesizes the ecdysone-dependent transcription factor.
Cancer is a second important target for germline engineering.
It presents a complex challenge. The key to one strategy for treating cancer is that certain transcription factors activate their promoters only in the presence of a hormone, such as testosterone. Such transcription factors are called hormone receptors because they function only when they bind a hormone molecule. The bound hormone bends the shape of the receptor so that it can attach to its promoter and activate the gene. The testosterone receptor is, in essence, a switch that testosterone flips on or off.