Amy Kronenberg, D. Sc.
Lawrence Berkeley National Laboratory

Mutagenesis in Human Cells
with Accelerated H and Fe Ions

The overall goal of the proposed studies is to determine the impact of genes that regulate apoptosis in modulating the risk of mutation induction in human cells exposed to the radiations of greatest importance for spaceflight.

Apoptosis is a genetically controlled program leading to the death and disposal of cells. A wide variety of human mutations in one of a series of genes that suppress apoptosis. We recently showed tumors have mutations in one of a series of genes that suppress of Bcl-2 or Bcl-xL lead to increased cell survival and frequency of x-ray induced mutations. Here, we focus on the role of these anti-apoptotic proteins in modulating susceptibility to mutation in cells exposed to 1 GeV/amu Fe ions or 55 MeV protons. We will employ syngenic human B-lymphoblastoid cell lines expressing normal p⁵³ protein that we engineered to constituitively overexpress either Bcl-2 or Bcl-xL. We will use these cells and appropriate controls to determine the fluence response for apoptosis induction and to ascertain whether the spatial pattern of energy deposition influences the magnitude or the timing of the apoptotic response. We will test the hypothesis that cellular apoptotic capacity is lesser importance in determining susceptibility to cell killing and mutation induction following exposure to densely ionizing Fe ions than after exposure to sparsely ionizing protons. We will determine if suppression of apoptosis alters mutation spectra. We will test the hypothesis that Bcl-xL can augment the enhanced mutagenic risk conferred on cells by a pre-existing mutation in the p⁵³ gene.

The results of our investigations will provide information on the genetic basis of radiation risk within an individual and among individuals exposed to the charged particles of greatest importance to manned space flight. These mechanistic studies may provide insight into novel strategies for intervention.