GAMMA-IRRADIATION-INDUCED CELL-CYCLE ARREST AND CELL-DEATH IN A HUMANSUBMANDIBULAR-GLAND CELL-LINE - EFFECT OF E2F1 EXPRESSION

This study examined the effect of gamma-irradiation (5 and 10 Gy) on t he human submandibular cell line (HSG). Radiation treatment (5 Gy and 10 Gy) induced a dose-dependent decrease in cell proliferation, with a G(2)/M arrest of the cell cycle, and an increase in cell death (cells with <2n DNA increased from 7% in control cells to 34% and 40% in 5 a nd 10 Gy irradiated cells, respectively). [Ca2+](i) measurements demon strated that the status of internal Ca2+ stores, and muscarinic recept or-mediated Ca2+ mobilization, in irradiated cells was comparable to t hat in non-irradiated cells. These data suggest that ii irradiated HSG cells maintain normal physiology and 2) internal Ca2+ store depletion does not account for the decreased cell proliferation. To manipulate the radiation-induced cell cycle arrest, we examined the effect of the transcription factor E2F1, which has been shown to induce cell cycle progression in HSG cells (Lillibridge and O'Connell, 1997, J. Cell. Ph ysiol., 172:343-350). The ability of irradiated HSC cells to express a nd appropriately route proteins was demonstrated by using adenovirus-m ediated expression of beta-galactosidase, alpha 1-antitrypsin, and aqu aporin-1. Infection of HSC cells with an adenoviral vector encoding E2 F1, Either 12 h before or immediately following irradiation, but not p ost-irradiation, induced maintenance of cells in the S phase of the ce ll cycle, reduced the number of cells arrested at G(2)/M, and decrease d the rare of appearance of cells with <2n DNA. While the mechanism of irradiation-induced cell death has not yet been confirmed, these data suggest that expression of the E2F1 gene product in HSC cells can be a useful strategy to manipulate cell cycle events and reduce the initi al loss of cells due to radiation. I. Cell. Physiol. 177:264-273, 1998 . (C) 1998 Wiley-Liss, Inc.dagger.