Expression of proteins coincident with inducible radioprotection in human lung epithelial cells

Human lung epithelial cells and many other cell lines are hypersensitive to low doses of ionizing radiation (<0.2 Gy), However, above a threshold dose of 0.4-0.6 Gy, an induced radioprotective response is triggered that prote cts cells at higher radiation doses. At 4 h, when maximal induced radioprot ection is seen in these cells after low-dose priming, the two-dimensional g el protein expression pattern in 0.5-Gy-exposed cells is subtly altered, wi th seven proteins being 2- to 5-fold down-regulated and one being 2-fold up -regulated. They include: (a) the protein kinase C inhibitor 1, or histidin e triad nucleotide-binding motif (HINT) protein; (b) substrates for protein kinase C activity including the chloride intracellular channel protein 1: and (c) a cytoskeletal protein degraded during apoptosis, In addition, a lu ng cancer-specific protein that binds to both telomeres and nascent mRNA mo lecules is down-regulated, as is interleukin 1 alpha. Therefore, at least i n human lung epithelial cells, radioprotection may be the result of signali ng pathway switching, which results in the removal of damaged cells and the preparation for enhanced general transcription in surviving cells during a period in which cell proliferation is repressed. This combination of event s may be cell-type-specific and may have implications for the protection of normal lung tissue during unavoidable radiation exposure such as in radiot herapy.