The purpose of the present work was to examine gene expression patterns in a rat keratinocyte line exposed to a ⁵⁶Fe ion beam. The cells were exposed to 1.01 geV/nucleon ⁵⁶Fe ions generated by the NASA Space Radiation Laboratory facility. Data from Affymetrix rat microarrays (RAT 230_2) were processed by BRB ArrayTools 3.3.0 software, and the Gene Ontogeny (GO) database was utilized to categorize significantly responding genes. Cell cycle distribution was analyzed by flow cytometry, and cell survival was based on the colony survival assay. At 24 h after 3.0 Gy of ⁵⁶Fe ion radiation, 69 known genes were significantly (p ≤ 0.001) altered (88% upregulated) and 16 of 97 categories of genes at level 7 in the GO hierarchy were significantly altered (p ≤ 0.01) including "mitosis", "DNA repair" and "positive regulation of cell cycle" in comparison to control. Flow cytometry revealed that 60% of irradiated cells versus 10% of control cells were in G₂/M phase of the cell cycle at 24 h after ⁵⁶Fe ion radiation. Colony survival rate for rat keratinocytes irradiated with 3.0 Gy of ⁵⁶Fe ion was 6.6% versus control at 24 h after irradiation. The results in the present study suggest a link between the increased expression of cell cycle genes and cell death.

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