The mechanisms by which the p53 response is triggered following exposure to DNA-damaging agents have not yet been clearly elucidated. We and others have previously suggested that blockage of RNA polymerase II may be the trigger for induction of the p53 response following exposure to ultraviolet light. Here we report on the correlation between inhibition of mRNA synthesis and the induction of p53, p21 WAF1 and apoptosis in diploid human ®broblasts treated with either UV light, cisplatin or the RNA synthesis inhibitors actinomycin D, DRB, H7 and a-amanitin. Exposure to ionizing radiation or the proteasome inhibitor LLnL, however, induced p53 and p21 WAF1 without aecting mRNA synthesis. Importantly, induction of p53 by the RNA synthesis or proteasome inhibitors did not correlate with the induction of DNA strand breaks. Furthermore, cisplatin-induced accumulation of active p53 in repair-de®cient XP-A cells occurred despite the lack of DNA strand break induction. Our results suggest that the induction of the p53 response by certain toxic agents is not triggered by DNA strand breaks but rather, may be linked to inhibition of mRNA synthesis either directly by the poisoning of RNA polymerase II or indirectly by the induction of elongation-blocking DNA lesions.

Herpes simplex virus (HSV) glycoproteins E and I (gE and gI) can act as a receptor for the Fc domain of immunoglobulin G (IgG). To examine the role of HSV IgG Fc receptor in viral pathogenesis, rabbits and mice were infected by the corneal route with HSV gEor gImutants. Wild-type HSV-1 produced large dendritic lesions in the corneal epithelium and subsequent stromal disease leading to viral encephalitis, whereas gEand gImutant viruses produced microscopic punctate or small dendritic lesions in the epithelium and no corneal disease or encephalitis. These differences were not related to the ability of the gE-gI oligomer to bind IgG because the differences were observed before the appearance of anti-HSV IgG and in mice, in which IgG binds to the Fc receptor poorly or not at all. Mutant viruses produced small plaques on monolayers of normal human fibroblasts and epithelial cells. Replication of gE-and gImutant viruses in human fibroblasts were normal, and the rates of entry of mutant and wild-type viruses into fibroblasts were similar; however, spread of gEand gImutant viruses from cell to cell was significantly slower than that of wild-type HSV-1. In experiments in which fibroblast monolayers were infected with low multiplicities of virus and multiple rounds of infection occurred, the presence of neutralizing antibodies in the culture medium caused the yields of mutant viruses to drop dramatically, whereas there was a lesser effect on the production of wild-type HSV. It appears that cell-to-cell transmission of wild-type HSV-1 occurs by at least two mechanisms: (i) release of virus from cells and entry of extracellular virus into a neighboring cell and (ii) transfer of virus across cell junctions in a manner resistant to neutralizing antibodies. Our results suggest that gEand gImutants are defective in the latter mechanism of spread, suggesting the possibility that the gE-gI complex facilitates virus transfer across cell junctions, a mode of spread which may predominate in some tissues. It is ironic that the gE-gI complex, usually considered an IgG Fc receptor, may, through its ability to mediate cell-to-cell spread, actually protect HSV from IgG in a manner different than previously thought.

SummaryThe diagnosis of suspected venous thromboembolic disease during pregnancy is problematic because of the fear of fetal irradiation with routine diagnostic procedures. In order to develop rational guidelines, we have calculated levels of radiation exposure to the fetus for the common diagnostic procedures and conducted a literature review to examine the fetal risks associated with these levels of radiation. A small increase in the relative risk of childhood cancer is suggested by a literature review of outcomes following low dose (less than 5 rads), in utero radiation exposure. With careful use of the available procedures, a diagnosis of venous thrombosis is possible with fetal radiation exposure of less than 0.50 rads and a diagnosis of pulmonary embolism is possible with fetal radiation exposure of less than 0.05 rads. The risk of such exposure is small, both in relative and absolute terms.

Our low-dose CT protocol is superior to IVU and clinically adequate for diagnosis of renal colic.

Ultraviolet light (UV) induced DNA lesions eciently block transcript elongation and induce the p53 response. Although p53 contributes to transcriptional activation of the p21 waf1 and bax genes, accumulation of these proteins requires that these genes are free of UV induced pyrimidine dimers. We assessed the level of expression of p53 and the p53 regulated p21 waf1 and bax gene products in normal diploid ®broblasts (NDF) and several nucleotide excision repair de®cient ®broblasts following UV-irradiation. At low UV¯uences, increased expression of p53, p21 waf1 and bax was only observed in ®broblasts de®cient in transcription coupled repair (TCR). Whereas p53 protein levels increased in all cell types at high UV¯uences, p21 waf1 levels initially decreased and then recovered in a manner dependent on TCR. At later times, expression of p21 waf1 and bax was only elevated in TCR-pro®cient cells. The lack of TCR strongly correlated with an enhanced induction of apoptosis. Furthermore, we assessed the eect of modulation of the p53/p21 waf1 /pRb pathway on clonogenic survival following UV irradiation. Expression of E2F-1, E2F-4, and the large tumour antigens of SV40 and Polyomavirus conferred UV sensitivity to NDF whereas p21 waf1 protected cells against UV treatment. We propose that the¯uence dependent attenuation of protective functions of p53 by blockage of transcription favours apoptosis following UV exposure.