Clusterin: A protein with multiple functions as a potential ionizing radiation exposure marker

Secretory clusterin (sCLU), a multifunctional glycoprotein, is induced in response to ionizing radiation (IR) at low and high doses. We are, therefore, developing a cellular biodosimetry system utilizing the CLU promoter-luciferase-neo® genetic construct and a bioluminescent imaging system (BLIS) for the real-time detection of CLU induction as a function of low doses of IR, using both tissue culture and animal systems. In order to develop such a biodosimeter, endogenous sCLU levels in tissues of animals must be characterized using Western blot analyses to ensure that the luciferase reporter gene induction matches induction responses, in terms of dose–responses and time-courses. Whole body 0.1-5 Gy gamma-irradiation of C57BL/6J mice induced CLU levels 2-3 days post-IR in thymus, spleen, and bone marrow. Interestingly, sCLU was not induced in liver, brain, or colon. These data indicate a tissue-specific, and a rather delayed time-course of sCLU induction, matching sCLU IR responses in human MCF-7:WS8 breast cancer cells in culture. To develop a biodosimeter, an MCF-7 1403 cell line expressing the luciferase gene regulated by the 1403 bp CLU promoter was generated, wherein CLU promoter expression mimicked the endogenous CLU gene. In contrast to standard luciferase assays using a luminometer, significant changes in CLU promoter expression in MCF-7 1403 cells were detected after 10 cGy using BLIS, which were comparable with endogenous sCLU protein expression. In summary, sCLU is induced in response to low-dose IR both in vitro using human tissue culture and in vivo in mouse proliferating tissues. Examination of CLU promoter-driven luciferase levels in irradiated MCF-7 1403 cells by BLIS is a promising approach for applications in biodosimetry.