| Summary: | Intercellular induction of apoptosis (IIA) represents a well-defned signaling model by which
precancerous cells are selectively eradicated through reactive oxygen/nitrogen species and cytokine
signaling from neighbour normal cells. Previously, we demonstrated that the IIA process could be
enhanced by exposure of normal cells to very low doses of ionizing radiation as a result of perturbing
the intercellular signaling. In this study, we investigate the kinetic behaviour of both autocrine
destruction (AD) and IIA as a function of cell density of both precancerous and normal cells using an
insert co-culture system and how exposure of normal cells to ionizing radiation infuence the kinetics
of apoptosis induction in precancerous cells. Increasing the seeding density of transformed cells shifts
the kinetics of AD towards earlier times with the response plateauing only at high seeding densities.
Likewise, when co-culturing precancerous cells with normal cells, increasing the seeding density
of either normal or precancerous cells also shifts the kinetics of IIA response towards earlier times
and plateau only at higher seeding densities. Irradiation of normal cells prior to co-culture further
enhances the kinetics of IIA response, with the degree of enhancement dependent on the relative
cell densities. These results demonstrate the pivotal role of the cell seeding density of normal and
precancerous cells in modulating both AD and IIA. These results further support the proposition that
ionizing radiation could result in an enhancement in the rate of removal of precancerous cells through
the IIA process.
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