Overall Program Narrative
The present Columbia University Center for Radiological Research program project grant entitled “Radiation Bystander Effects: Mechanism” is an ever evolving program currently in the 17th year funding. The program project was first funded in 1988 and was entitled “Radiation Biology of Simulated Radon-daughter Alphas”. The program direction was stimulated by, on the one hand, the pervading national interest in radon at that time and on the other hand, the beginning of the development of the Columbia single-particle microbeam which we thought was uniquely capable of addressing some basic issues of the radon problem. Over the years, the research focus has shifted from radon based risk assessment to the characterization and mechanism of radiation induced bystander effects. Research performed under the umbrella of this grant figured prominently in the BEIR VI Report entitled, “Health Effects of Exposure to Radon” and other national and international policy document.

What is a bystander effect?
Radiation-induced bystander effect represents a paradigm shift in our understanding of the radiobiological effects of ionizing radiation in that extranuclear and extracellular effects may also contribute to the final biological consequences of exposure to low doses of radiation. There is evidence that targeted cytoplasmic irradiation results in mutation in the nucleus of the hit cells and that cells that are not directly hit by an alpha particle, whether nuclear or cytoplasm, but in the vicinity of one that does, contribute to the genotoxic response of the cell population. Although radiation induced bystander effects have been well documented in a variety of biological systems, including three dimensional human tissues, the mechanism is not known.

This program project brings together and links 3 projects that all address the common goal of understanding the how and why of the bystander phenomenon. The central hypothesis of the overall program is that the bystander effect involves multiple pathways and that an initiating event in the hit cells and a subsequent downstream signaling step involving the arachidonic acid cascade in the bystander cells play an important role in mediating the process.

Project 1 will harness the power of microarray profiling and functional genomics in order to gain insight into the cascade of signaling events between cellular targets and between cells. This study will be extended to a 3D tissue model as well as to single cells.
Project 2 will follow up on the preliminary observations that reactive nitrogen species may be involved in the signaling process and that the COX-2 enzyme is consistently elevated in bystander cells.
Project 3 will examine the contribution of genomic instability as a precipitating event in the induction of the bystander effect.

In between the projects, we will examine the gene profiling of nuclear versus cytoplasmic irradiation and whether the latter can induce bystander response in a manner similar to nuclear traversals. These studies are entirely dependent on the technology of the Columbia microbeam, which makes it possible to aim a defined number of α-particles (including one) at either the nucleus or cytoplasm of a cell with a precision of a few microns. The unequivocal demonstration of the bystander effect represents a paradigm shift in radiation biology since generations of students had been taught that heritable effects required the direct deposition of radiant energy in DNA. It is now apparent that the target for heritable damage is not only larger than the DNA, but larger than the cell itself.

Hypotheses to be addressed in this program

• The bystander effect involves multiple pathways, and an initiating event in the hit cells and a subsequent downstream signaling step involving the arachidonic acid cascade in the bystander cells play an important role in mediating the process.


• Both reactive radical species and signaling pathways involving the COX-2 gene are mediators of the bystander signaling process.


• Gene expression signatures will reflect the signal transduction pathways responding to extranuclear, extracellular signaling and that interruption of these gene pathways using functional analyses can mitigate the bystander effects.


• The basic signaling network mediating bystander response in cell culture system is similar in 3D tissue microenvironment.


• Cytoplasmic irradiation can result not only in bystander effect, but in delayed chromosomal effects as well, and finally,


• The signaling molecule(s) and mechanism(s) that mediate the bystander effect can also induce genomic instability in mammalian cells.