ULTRAVIOLET RADIATION-INDUCED ALTERATIONS IN CHROMATIN ORGANIZATION OF L5178Y CELL STRAINS WITH DIFFERENT CAPACITY FOR DNA REPAIR

I. Szumiel1, M. Walicka1, I. Buraczewska1, J. Z. Beer2

1 Department of Radiobiology and Health Protection, Institute of Nuclear Chemistry and Technology, Dorodna 16, 03-195 Warsaw, Poland,
2 Center for Devices and Radiological, Health, Food and Drug Administration, HFZ-114, Rockville, MD 20857 USA

Chromatin response to ultraviolet-C (254 nm, UVC) radiation was examined in two strains of mouse lymphoma cells, L5178Y-R (LY-R) and L517SY-S (LY-S), with different UVC sensitivities and post-UVC-exposure repair capacities. UVC sensitive (X-ray resistant) LY-R cells are impaired in DNA excision and post-replication repair as compared to the UVC resistant (X-ray sensitive) LY-S cells. Following UVC exposure, the UVA-assisted photobinding of 8-Methoxypsoralen (8-MOP) to DNA was reduced in LY-S cells (to approximately 60% of the control at 15 min post-exposure), while it was increased in LY-R cells (by approximately 20% at 45 min post-exposure). The nucleoids isolated from irradiated LY-R cells sedimented at a reduced rate, and this effect persisted for 24 h post-exposure. The nucleoids from irradiated LY-S cells sedimented at a control rate or faster, except 30 min after exposure (the time of high incision rate), when they sedimented at a reduced rate. The data indicate qualitative differences in UVC response of LY-R and LY-S cells at the chromatin level that may be related to different processing of DNA damage by the two cell strains and may result in modifying the 8-MOP access to DNA.