Correction Of Radioresistant Dna Synthesis In Ataxia Telangiectasia Fibroblasts By Prostaglandin E-2 Treatment

Cultured cells from patients inheriting the rare cancer-prone and radiotherapy-sensitive disorder ataxia telangiectasia (AT) exhibit defects in the activation of cell-cycle checkpoints after exposure to ionizing radiation. In particular, the failure of AT cells to arrest transiently the DNA de novo replication machinery immediately after irradiation-so-called radioresistant DNA synthesis (RDS) -is often taken as a molecular hallmark of the disease. Recently we reported that: (i) the radiation-responsive S-phase checkpoint operating in normal human cells is mediated by a signal transduction pathway involving Ca (2+)/calmodulin-dependent protein kinase II (CaMKII); and (ii) the RIDS phenotype of AT cells is associated with failure to mobilize Ca2+ from intracellular stores, which is required for activation of the CaMKII-dependent S-phase arrest. In the present study, we demonstrate that the RIDS phenotype of AT dermal fibroblasts can be rectified in the absence of ectopic expression of functional ATM, the 350-kDa protein kinase encoded by the gene mutated in AT. Correction of RIDS was observed when AT fibroblasts were coincubated with normal fibroblasts under conditions in which the 2 different cell cultures shared the same medium but were completely separated physically. The RDS trait was also rectified when AT fibroblasts were briefly incubated with prostaglandin E-2 in the absence of normal feeder cells, signifying that this ubiquitous eicosanoid can serve as the diffusible "RDS-correction factor" for AT cells in the aforementioned cocultivation studies. It would therefore appear that prostaglandin E2 can assume the role of an extracellular signaling modulator of the S-phase checkpoint in AT cells exposed to ionizing radiation, inducing DNA synthesis shutdown via an alternative, ATM-independent signal transduction pathway. (C) 2001 Wiley-Liss, Inc.