INCREASED SUSCEPTIBILITY TO APOPTOSIS INDUCED BY ANTI-FAS ANTIBODY INA ROTHMUND-THOMSON SYNDROME LYMPHOBLASTOID CELL-LINE

Dysregulation of apoptosis leading to reduced DNA repair capacity, inc reased DNA mutation, and chromosomal instability is one of the patholo gical mechanisms associated with aging. Rothmund-Thomson syndrome (RTS ) is a human genetic disease characterized by several features of prem ature aging. Although the genetic defect has not been identified, defe cts in DNA repair capacity have been implicated in the pathogenesis of this disease. To determine whether dysregulation of apoptosis is asso ciated with the pathogenesis of RTS symptoms, we investigated the sens itivity of a lymphoblastoid cell line-derived from a young (10-year-ol d) individual with RTS-to cell death induced by anti-Fas antibody (clo ne: CH-11). Cell lines derived from a normal young (14-year-old) indiv idual and a normal aged (79-year-old) individual were used as controls . Treatment with CH-11 (500 ng/ml) resulted in significantly decreased cell viability in the RTS cell line (42.4% +/- 4.2%) and that derived from the aged individual (47.3% +/- 9.2%) as compared to the normal y oung cell line (66,9% +/- 7.0%). The concentrations of CH-11 required to induce 50% cell death in the RTS (IC50 890 ng/ml) and that derived from the aged individual (IC50, 3640 ng/ml) were lower than that of th e control young cell line (IC50 > 10(5) ng/ml). The lower viability wa s due to increased susceptibility to apoptosis to CH-11 in the RTS (59 .0% +/- 2.0%) compared to that in the normal young cell line (40.9% +/ - 0.9%) as shown by 7-amino-actino-mycin D (7-AAD) staining (p <.005). Treatment of the RTS cell line with acetyl-Asp-Glu-Val-Asp-aldehyde ( Ac-DEVD-CHO), a specific inhibitor of caspase-3, significantly increas ed the cell viability after CH-11 treat ment (75.9% +/- 2.2%). Taken t ogether, these results provide the first evidence to show that RTS lym phoblastoid has an increased sensitivity to cell death mediated by Fas and that inhibition of caspase-3 activity may be a potential target i n reversing the sensitivity of RTS cells to Fas-mediated apoptosis in vitro.