title: Molecular imaging of protein-protein interactions: controlled expression of p53 and large T-antigen fusion proteins in vivo.
abstract: Protein-protein interactions control essential steps in signal transduction pathways and other intracellular processes, and assembly of protein complexes modulates and responds to the regulatory events that exist in living animals. We have used microPET and fluorescence imaging to detect interactions between p53 tumor suppressor and large T antigen (TAg) of SV40 virus in a tetracycline-inducible two-hybrid system. To additionally validate this molecular imaging technique, we investigated whether expression of the reporter gene, comprised of a mutant thymidine kinase from herpes simplex virus 1 fused to green fluorescent protein could quantify relative differences in amounts of interacting hybrid proteins. In HeLa cells stably transfected with the reporter gene and interacting (p53-TAg) or noninteracting (p53 and polyoma virus coat protein) pairs of proteins, treatment with doxycycline produced time- and dose-dependent increases in expression of hybrid proteins. Proportional increases in amounts of reporter gene were produced only in cells expressing p53 and TAg. In mice bearing xenografts of these stably transfected HeLa cells, amounts of hybrid proteins were regulated with doxycycline. Both microPET imaging and biodistribution studies showed time- and dose-dependent increases in accumulation of the reporter substrate 9-(4-[(18)F]-fluoro-3-hydroxymethylbutyl)guanine only in p53-TAg tumors. Fluorescence microscopy of excised tumors also showed corresponding changes in expression of the fusion reporter gene in response to binding of p53 and TAg. These data demonstrate that the imaging two-hybrid system responds in a proportional fashion to increasing amounts of interacting proteins in vivo.
authors.affiliation: Molecular Imaging Center, Mallinckrodt Institute of Radiology and Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: Gary D
authors.initials: GD
authors.lastname: Luker
authors.forename: Vijay
authors.initials: V
authors.lastname: Sharma
authors.forename: Christina M
authors.initials: CM
authors.lastname: Pica
authors.forename: Julie L
authors.initials: JL
authors.lastname: Prior
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.forename: David
authors.initials: D
authors.lastname: Piwnica-Worms
mesh_terms: D000212:Acyclovir / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D000818:Animals; D000957:Antigens, Viral, Tumor / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D006147:Guanine; D006367:HeLa Cells; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008164:Luminescent Proteins / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D008819:Mice, Nude; D008856:Microscopy, Fluorescence; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D013937:Thymidine Kinase / Q000096:biosynthesis / Q000235:genetics; D014055:Tomography, Emission-Computed / Q000379:methods; D014162:Transfection; D014316:Tritium; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*
chemical_list: D000957:Antigens, Viral, Tumor; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D016159:Tumor Suppressor Protein p53; D014316:Tritium; D049452:Green Fluorescent Proteins; C053539:penciclovir; D006147:Guanine; D013937:Thymidine Kinase; D000212:Acyclovir