Identification of genes regulated by UV/salicylic acid.

PURPOSE: Previous work from the authors' group and others has demonstrated that some of the effects of UV irradiation on gene expression are modulated in response to the addition of salicylic acid to irradiated cells. The presumed effector molecule responsible for this modulation is NF-kappaB. In the experiments described here, differential-display RT-PCR was used to identify those cDNAs that are differentially modulated by UV radiation with and without the addition of salicylic acid. MATERIALS AND METHODS: Differential-display RT-PCR was used to identify differentially expressed genes. RESULTS: Eight such cDNAs are presented: lactate dehydrogenase (LDH-beta), nuclear encoded mitochondrial NADH ubiquinone reductase 24 kDa (NDUFV2), elongation initiation factor 4B (eIF4B), nuclear dots protein SP100, nuclear encoded mitochondrial ATPase inhibitor (IF1), a cDNA similar to a subunit of yeast CCAAT transcription factor HAP5, and two expressed sequence tags (AA187906 and AA513156). CONCLUSIONS: Sequences of four of these genes contained NF-kappaB DNA binding sites of the type that may attract transrepressor p55/p55 NF-kappaB homodimers. Down-regulation of these genes upon UV irradiation may contribute to increased cell survival via suppression of p53 independent apoptosis.

Regulation of protein kinase C by ionizing radiation.

Members of the protein kinase C (PKC) gene family have been shown to play an important role in tumor promotion and regulation of cell growth. Experiments were designed to examine the effects of different qualities of ionizing radiation administered at a variety of doses and dose rates on the expression of PKC-specific mRNA in confluent Syrian hamster embryo cells. The results of these experiments showed that low-linear energy of transfer (LET) radiations (such as X-rays and gamma-rays) can induce increased expression of PKC mRNA within 1 h after radiation exposure. Levels of expression of PKC mRNA were increased 4- to 6-fold over unirradiated controls. Dose effects were evident, with increased accumulation of PKC mRNA at higher doses (ranging from 6 to 200 cGy). Induction of PKC mRNA occurred at a time when total cellular transcription was reduced following irradiation. Similar exposure of the cells to fission spectrum JANUS neutrons, however, had little effect on PKC mRNA expression. Modest induction (2-fold compared to untreated cells) occurred when irradiations were at very low dose rates (0.5 cGy/min). These results suggest that induction of PKC mRNA may be a step in the transformation process caused by ionizing radiation. In addition, they demonstrate that different qualities of radiation may regulate PKC differently.

Effects of ionizing radiation on expression of genes encoding cytoskeletal elements: kinetics and dose effects.

We examined the modulation in expression of genes encoding three cytoskeletal elements (beta-actin, gamma-actin, and alpha-tubulin) in Syrian hamster embryo (SHE) cells following exposure to ionizing radiations. Early-passage SHE cells were irradiated in plateau phase with various low doses (12-200 cGy) of neutrons, gamma-rays, or x-rays. RNA samples were prepared from cells at different times postexposure and were analyzed for levels of specific transcripts by northern blots. The results revealed that alpha-tubulin was induced by both high-linear energy of transfer (LET) (neutrons) and low-LET (gamma-rays and x-rays) radiations with similar kinetics. The peak in alpha-tubulin mRNA accumulation occurred between 1 and 3 h postexposure; for gamma-actin mRNA, accumulation was similarly induced. For both gamma-actin and alpha-tubulin, the higher the dose during the first hour postexposure (up to 200 cGy gamma-rays), the greater the level of mRNA induction. In contrast, mRNA specific for beta-actin showed decreased accumulation during the first hour following radiation exposure, and remained low up to 3 h postexposure. These results document the differential modulation of genes specific for cytoskeletal elements following radiation exposure. In addition, they demonstrate a decrease in the ratio of beta-actin:gamma-actin mRNA within the first 3 h following gamma-ray exposure. These changes in mRNA accumulation are similar to those reported in some transformed cell lines and in cells treated with tumor promoters, which suggests a role for changes in actin- and tubulin-mRNA expression in radiation-mediated transformation.