Activation of caspase-3 noninvolved in the bystander effect of the herpes simplex virus thymidine kinase gene/ganciclovir (HSV-tk/GCV) system

• Published in: Journal of biomedical optics 2008-05, Vol.13 (3), p.031209
• Main Authors: Zhang, Zhihong, Lin, Juqiang, Chu, Jun, Ma, Yan, Zeng, Shaoqun, Luo, Qingming
• Format: Article
• Language: English
• Subjects: Bystander Effect; Carcinoma, Adenoid Cystic - metabolism; Carcinoma, Adenoid Cystic - virology; Caspase 3 - metabolism; Cell Line, Tumor; Fluorescence Resonance Energy Transfer - methods; Ganciclovir - metabolism; Herpes simplex virus; Humans; Thymidine Kinase - metabolism; Viral Proteins - metabolism
• ISSN: 1083-3668
• DOI: 10.1117/1.2937830

Use of the herpes simplex virus thymidine kinase gene/ganciclovir (HSV-tk/GCV) system is one of the promising approaches in the rapidly growing area of gene therapy. The "bystander effect," a phenomenon in which HSV-tk+ cells exposed to GCV are toxic to adjacent HSV-tk- cells, was reported to play an important role in suicide gene therapy. However, the mechanism by which HSV-tk/GCV induces the bystander effect is poorly understood. We monitored the activation of caspase-3 in living cells induced by the HSV-tk/GCV system using a genetically encoded fluorescence resonance energy transfer (FRET) probe CD3, , a caspase-3 recognition site fused with a cyan fluorescent protien (CFP) and a red fluorescent protein (DsRed) which we reported and named in a previous paper. Fluorescence protein (FP)-based multicolor cellular labeling, combined with the multichannel fluorescence imaging and FRET imaging techniques, provides a novel and improved approach to directly determine whether the activation of caspase-3 involved in the HSV-tk/GCV system induces cell apoptosis in tk gene-expressing cells and their neighboring cells. FRET ratio images of CD3, and fluorescence images of the fusion protein of thymidine kinase linked with green fluorescent protein (TK-GFP), indicated that HSV-tk/GCV system-induced apoptosis in human adenoid cystic carcinoma (ACC-M) cells was via a caspase-3 pathway, and the activation of caspase-3 was not involved in the bystander effect of HSV-tk/GCV system.