An artificially constructed radiation-responsive promoter is activated by doxorubicin

Regulation of gene expression in human prostate cancer cells with artificially constructed promoters that are activated in response to ultrasound stimulation

We chose promoters responsive to sonication in LNCap cells, a prostate cancer cell line, out of a library composed of DNA fragments constructed by linking the TATA box sequence to randomly combined cis-acting elements of transcription factors activated in response to radiation in prostate cancer cells. When a plasmid containing the luciferase gene under control of a promoter was transfected into LNCap cells and sonicated with 1 MHz ultrasound at 0.5 W/cm(2), 10% DF for 60s, 13 promoters showed more than 10-fold enhancement compared with their counterparts without sonication 12h after sonication. As to their responsiveness to sonication, the best two promoters were then compared to clone 880-8, a derivative from clone 880 that was created by random introduction of point mutations and was shown to have an improved response to X-ray irradiation. We then took clone 880-8 for further analyses since it showed the highest enhancement to sonication, though not statistically significant from the others. Next, we employed a retrovirus vector and stably introduced the luciferase gene under control of clone 880-8 into LNCap cells to establish a cell line. When the cell line was sonicated with 1 MHz ultrasound at 0.5 W/cm(2), 10% DF for 60s, luciferase expression was enhanced up to 14.8-fold 12h after sonication. We then established another cell line by replacing the luciferase gene with the fcy::fur gene, a suicide gene, and when the cell line was sonicated with 1 MHz ultrasound at 0.5 W/cm(2), 10% DF for 60s, expression of the gene was enhanced, showing the maximum expression 12-24h after sonication. When the cells were incubated in medium containing 5-fluorocytosine, cell survival ratio decreased dose dependently with 5-fluorocytosine only after sonication treatment, suggesting this promoter could be utilized for gene expression control with ultrasound.

Development of a therapeutically important radiation induced promoter

Radio-genetic therapy is a combination of radiation therapy and gene therapy that may solve some of the problems associated with conventional radiotherapy. A promoter responsive to radiation was obtained from a promoter library composed of DNA fragments created by linking the TATA box signal to randomly combined binding sequences of transcription factors that are reactive to radiation. Each promoter connected to the luciferase gene, was evaluated by luciferase expression enhancement in transfected cells after X-ray irradiation. The reactivity of the best promoter was improved by the random introduction of point mutations and the resultant promoter showed more than a 20-fold enhancement of the luciferase expression after X-ray irradiation at 10 Gy. The expression of downstream genes was also enhanced in stably transfected cells not only by X-rays but also by proton beam irradiation; and either enhancement was attenuated when an anti-oxidant was added, thus suggesting the involvement of oxidative stress in the promoter activation. Constructed promoters were also activated in tumors grown in mice. In addition, cell killing with the fcy::fur gene (a suicide gene converting 5-fluorocytosin to highly toxic 5-fluorouracil) increased dose-dependently with 5-fluorocytosin only after X-ray irradiation in vitro. These results suggest that promoters obtained through this method could be used for possible clinical applications.