Ultraviolet radiation sensitivity of proliferating and differentiated human neuroblastoma cells

The effects of ultraviolet (U.V.) radiation were studied on a cloned line of human neuroblastoma cells in proliferative and differentiated growth modes, the latter being induced by serum deprivation. The neuroblastoma cells were found to be unusually sensitive in comparison with HeLa cells when survival was measured by colony formation in soft agar, the differentiated mode being the most sensitive. Ultraviolet radiation sensitivity was associated with very low DNA repair capacity as measured by DNA repair synthesis and by removal of M. luteus endonuclease-sensitive sites from irradiated DNA. The greater sensitivity of the differentiated cells appeared to be related to a greater degree of DNA damage at a given U.V. dose, resulting from altered cell geometry in the growth mode. The neuroblastoma cells showed little or no post-irradiation inhibition of DNA replication at low U.V. doses, suggesting that it is the repair process rather than the DNA damage which is responsible for inhibiting replication.