INDUCTION OF SERUM AMYLOID-A INFLAMMATORY RESPONSE GENES IN IRRADIATED BONE-MARROW CELLS

The molecular mechanisms underlying radiation-induced defects in the b one marrow which may contribute to the development of radiation-induce d hematopoietic disorders such as aplastic anemia and leukemia are not known. Persistent changes in gene expression were examined after expo sure of cells of a murine bone marrow stromal cell line to ionizing ra diation, Analysis of mRNA transcript levels by differential display le d to the identification of a band, C122, which increased in abundance 1 week after exposure. Northern blot hybridization verified these resu lts and revealed a 12-fold increase in abundance of this message for u p to 3 weeks after irradiation in vitro. DNA sequence analysis identif ied clone C122 as murine serum amyloid A 3 (Saa3), a member of the Saa family of acute-phase or inflammatory response genes. Saa message lev els were then examined in vivo in the bone marrow of mice exposed to t otal-body irradiation. Semi-quantitative reverse transcription-polymer ase chain reaction revealed a 15-20-fold increase in Saa3 message leve ls in the bone marrow of irradiated mice from 3 days to 2 weeks after exposure. Saa3 message levels continued to be 2-3-fold above control f or up to 28 weeks in vivo. Two additional members of the murine Saa ge ne family, Saa1 and Saa2, were also detected in irradiated bone marrow . The expression of SAA1 and SAA2 was also detected in irradiated cell s of human bone marrow stromal cell lines in vitro. These results sugg est that SAA genes are involved in the radiation response in the bone marrow, but their role in the recovery of the marrow after irradiation or in the development of radiation-induced hematopoietic disorders re mains to be established. Additionally, the persistent radiation-induce d increase in expression suggests the potential utility of using SAA3 transcript levels as a molecular marker of past radiation exposure. (C ) 1998 by Radiation Research Society.