Oxidative stress, signal transduction, and intercellular communication in radiation carcinogenesis

During the evolution of multicellular organisms, survival in an aerobic environment came about by adaptive responses, both to the endogenous oxidative metabolism within the cells of the organism as well as the chemicals and low-level radiation to which they are exposed. In addition to defense mechanisms shared with single-cell organisms, multicellular organisms are equipped with gap junctions which allow electrotonic and/or metabolic synchronization of processes between coupled cells. The connexin genes, which code for the proteins comprising the gap junctions, provide homeostatic regulation of cell proliferation, differentiation, and adaptive responses of individual cells through a mechanism of "gap junctional intercellular communication." The biological consequences of the response of a multicellular organism to low-level radiation exceeding the background level of oxidative damage to a cell in a tissue could be apoptosis, cell proliferation, or cell differentiation.