Expression of immediate early genes after treatment of human astrocytoma cells with radiation and taxol

c-Fos over-expression promotes radioresistance and predicts poor prognosis in malignant glioma

c-Fos is a major component of activator protein (AP)-1 complex. It has been implicated in cell differentiation, proliferation, angiogenesis, invasion, and metastasis. To investigate the role of c-Fos in glioma radiosensitivity and to understand the underlying molecular mechanisms, we downregulated c-Fos gene expression by lentivirus-mediated shRNA in glioma cell lines and subsequently analyzed the radiosensitivity, DNA damage repair capacity, and cell cycle distribution. Finally, we explored its prognostic value in 41 malignant glioma patients by immunohistochemistry. Our results showed that silencing c-Fos sensitized glioma cells to radiation by increasing radiation-induced DNA double strand breaks (DSBs), disturbing the DNA damage repair process, promoting G2/M cell cycle arrest, and enhancing apoptosis. c-Fos protein overexpression correlated with poor prognosis in malignant glioma patients treated with standard therapy. Our findings provide new insights into the mechanism of radioresistance in malignant glioma and identify c-Fos as a potentially novel therapeutic target for malignant glioma patients.

Dose-dependent biphasic induction and transcriptional activity of nuclear factor kappa B (NF-kappaB) in EA.hy.926 endothelial cells after low-dose X-irradiation

PURPOSE

Low-dose radiotherapy is known to exert an anti-inflammatory effect, but the underlying radiobiological mechanisms are still elusive. It was recently reported that transforming growth factor (TGF) beta1 essentially contributes to the reduced adhesion of peripheral blood mononuclear cells to endothelial cells at low-dose X-irradiation. As the transcription factor nuclear factor kappa B (NF-kappaB) is crucially involved in mediating an inflammatory response by inducing the expression of cytokines and adhesion molecules, NF-kappaB DNA binding and transcriptional activity as well as its impact on the expression of TGF-beta1 in EA.hy.926 endothelial cells were analysed subsequently to low-dose radiotherapy.

MATERIALS AND METHODS

Human EA.hy.926 endothelial cells were grown to subconfluence. Twenty hours after X-irradiation with single doses ranging from 0.3 to 3 Gy, the cells were activated with tumour necrosis factor-alpha. Four hours later, the cells were harvested. NF-kappaB DNA-binding activity of nuclear extracts was analysed by electrophoretic mobility shift assay. The NF-kappaB subunits p50, p65/RelA, c-Rel and RelB of the NF-kappaB complexes were quantified by enzyme-linked immunoabsorbant assay. The transcriptional activity of NF-kappaB was measured using luciferase reporter gene assays in EA.hy.926 endothelial cells transiently transfected with the plasmid pB2xLuc. To correlate transcriptional activity to TGF-beta1 expression, NF-kappaB decoy oligonucleotides were used to inhibit NF-kappaB activity and TGF-beta1 secretion.

RESULTS

After low-dose radiotherapy, an increased NF-kappaB DNA-binding activity was observed in stimulated EA.hy.926 endothelial cells with a relative maximum (threefold induction) at 0.5 Gy. The NF-kappaB activation then decreased after X-irradiation at 0.6-0.8 Gy and subsequently increased again at doses of 1 and 3 Gy. This biphasic induction profile of NF-kappaB was confirmed by the analysis of the NF-kappaB-specific transcriptional activity. The latter showed a relative maximum at 0.5 Gy, a relative minimum between 0.5 and 1.0 Gy, and an increase at 3 Gy. Transfection of EA.hy.926 endothelial cells with NF-kappaB decoy oligonucleotides before irradiation resulted in a 50% reduction of TGF-beta1 secretion at 0.5 Gy compared with control oligonucleotides or untreated cells.

CONCLUSIONS

Low-dose radiotherapy induces a biphasic activation of NF-kappaB with a relative maximum at 0.5 Gy. The induction by NF-kappaB of TGF-beta1 in endothelial cells might contribute to the anti-inflammatory properties of low-dose ionizing irradiation.

In search of a function for the TIS21/PC3/BTG1/TOB family

The Btg family of anti-proliferative gene products includes Pc 3/Tis 21/Btg 2, Btg 1, Tob, Tob2, Ana/Btg3, Pc3k and others. These proteins are characterized by similarities in their amino-terminal region: the Btg1 homology domain. However, the pleiotropic nature of these family proteins has been observed and no common physiological function among family members was suggested from the history of their identification. Recent progress in the search for Btg family functions has come from the analysis of cell regulation and of cell differentiation. It is now emerging that every member of this family has a potential to regulate cell growth. We would like to propose here to use a nomenclature APRO as a new term for the family.

Ionizing radiation affects 26s proteasome function and associated molecular responses, even at low doses

BACKGROUND AND PURPOSE

Ionizing radiation is known to activate certain signal transduction pathways, the regulation of which could involve post-transcriptional as well as transcriptional mechanisms. One of the most important post-transcriptional pathways in eukaryotic cells is the ATP- and ubiquitin-dependent degradation of proteins by the 26s proteasome. This process controls initiation of many cellular stress responses, as well as inflammatory responses under control of the transcription factor NF-kappaB. The literature on the relationship between radiation and inflammation seems somewhat paradoxical. At high doses, radiation is generally pro-inflammatory. On the other hand, low dose radiation has a long history of use in the treatment of inflammatory disease. This suggests the involvement of multiple mechanisms that may operate differentially at different dose levels.

MATERIALS AND METHODS

In this paper, the ability of different doses of ionizing radiation to directly affect 26s proteasome activity was tested in ECV 304 cells. Proteasome activity, IkappaBalpha protein levels, and NF-kappaB activation were monitored.

RESULTS

Inhibition of chymotrypsin-like 20s and 26s proteasome activity was observed immediately after low- and high-dose irradiation either of cells or purified proteasomes. The inhibitory effect was independent of the availability of the known endogenous proteasome inhibitor heat shock protein 90 (hsp90). Levels of IkappaBalpha, a physiological 26s proteasome substrate, were increased only at low doses (0.25 Gy) and unaltered at higher doses whereas only the highest doses (8 and 20 Gy) activated NF-kappaB.

CONCLUSIONS

We conclude that the proteasome is a direct target of ionizing radiation and suggest that inhibition of proteasome function provides a molecular framework within which low dose anti-inflammatory effects of radiation, and radiation-induced molecular responses in general, should be considered.

Green tea protects against psoralen plus ultraviolet A-induced photochemical damage to skin

The use of psoralens combined with exposure to ultraviolet A radiation is a major form of treatment for psoriasis and a number of other common skin diseases. Although psoralen plus ultraviolet A treatment is highly effective, careful follow-up cohort studies have shown that it greatly increases risk for the development of cutaneous squamous cell carcinoma and melanoma. Strategies to reduce the risk of cancer development in psoralen plus ultraviolet A-treated populations are highly desirable. In prior studies, we demonstrated that green tea and constituent polyphenols protect against ultraviolet B-induced carcinogenesis and reduce the growth rate of established tumors in skin. In this study, we show that pre- and post-treatment with standardized green tea extract in psoralen plus ultraviolet A treatment populations abrogates the psoralen plus ultraviolet A-induced photochemical damage to skin. Intact mouse and human skin and reconstituted human skin were employed to assess the effect of both topical and oral administration of standardized green tea extract against psoralen plus ultraviolet A-induced photodamage. Oral administration of standardized green tea extract prior to and during multiple psoralen plus ultraviolet A treatments reduced hyperplasia and hyperkeratosis in murine skin. Standardized green tea extract treatment also inhibited accumulation of c-fos and p53 protein induction following a single exposure to psoralen plus ultraviolet A. c-fos and p53 positive cells in psoralen plus ultraviolet A-treated skin were found to be increased by 55.4 +/- 13. 6% and 62.3 +/- 10.5%, respectively, compared with saline-treated unexposed control skin. Oral administration of 0.4 or 0.8% standardized green tea extract inhibited c-fos protein accumulation by 18.5% and 46.2% (p < 0.05), respectively, and p53 protein accumulation by 26.1% and 54.3% (p < 0.05), respectively. Similarly proliferating cell nuclear antigen staining, a marker of cell proliferation was induced (73.7%) in psoralen plus ultraviolet A-treated skin. Oral administration of 0.4% or 0.8% standardized green tea extract 1 d after psoralen plus ultraviolet A treatment was effective in reducing psoralen plus ultraviolet A-induced inflammatory responses including erythema and edema formation. When standardized green tea extract was applied to EpiDerm, a reconstituted human skin equivalent, psoralen plus ultraviolet A-induced 8-methoxypsoralen-DNA adduct formation and p53 protein accumulation were inhibited. Topical application of 0.2 mg 8-methoxypsoralen per cm2 followed by exposure to ultraviolet A (2.5 J per cm2) resulted in delayed erythema formation in human subjects. Pretreatment of human skin with topical application of 0.2 mg standardized green tea extract per cm2 30 min prior to psoralen plus ultraviolet A treatment resulted in an almost complete abrogation of psoralen plus ultraviolet A-induced erythema. In summary, these data demonstrate that standardized green tea extract protects against psoralen plus ultraviolet A-induced phototoxicity by inhibiting DNA damage and diminishing the inflammatory effects of this modality.

Reconstituted 3-dimensional human skin as a novel in vitro model for studies of carcinogenesis

EpiDerm (MatTek Co., MA) is a reconstituted human skin equivalent which exhibits morphological and growth characteristics similar to human skin. This model has previously been utilized to evaluate the cytotoxicity and irritant potential of various cosmetic and household products. In this study, we show for the first time that EpiDerm can be used successfully to evaluate the genotoxicity of different types of known carcinogenic agents such as benzo[a]pyrene (BaP), ultraviolet B radiation (UVB), ultraviolet A radiation (UVA), and psoralen-ultraviolet A radiation (PUVA) at the molecular level. The topical application of 50 microg/cm2 BaP to EpiDerm resulted in the accumulation of BaP-DNA adducts and c-fos and p53 proteins as evidenced by immunohistochemical localization. Similarly, exposure to UVB (50 mJ/cm2) and UVA (2.5 J/cm2) enhanced the epidermal expression of c-fos and p53 proteins in the human skin equivalent. PUVA treatment of EpiDerm, however, resulted in the formation of both DNA-8-MOP adducts and augmented expression of c-fos and p53 proteins. Most of these changes reached a peak 8 h after the treatments except in the case of UVA where maximum changes in the expression of c-fos and p53 proteins were observed 24 h after treatment. These results are similar to those previously reported in human and murine skin following exposure to BaP, UVB, UVA, or PUVA indicating that human skin equivalents can be used as a convenient and cost-effective alternative to animal testing for assessing the genotoxicity and mechanism of action of mutagens/carcinogens in human skin.

Induction of c-fos and junB mRNA following in vivo brain irradiation

Although radiotherapy is a front line treatment for brain tumors, little is known about the in vivo molecular responses of brain to irradiation. In this study, expression of c-fos, c-jun and junB immediate-early genes were followed in mouse brain after irradiation. C-fos and junB, but not c-jun, mRNA was induced within 15 min in unanesthetized irradiated mice. Induction was transient and lasted < 4 h. The response was dose-dependent with increases in c-fos and junB mRNA levels after dose of > or = 2 and 7 Gy, respectively. Anesthesia of mice with pentobarbitol delayed the increases in mRNA expression and the response was attenuated. Pre-treatment of mice with dexamethasone, in a schedule which suppressed acute-phase gene expression after brain irradiation, did not significantly change c-fos and junB induction. Our results show that c-fos and junB responses occur in the brain in response to irradiation and that they can be modified by pentobarbital treatment but suggest that there is no direct correlation between the level of mRNA expression and later expression of cytokines or other acute-phase response genes.

Taxol pretreatment of tumor targets amplifies natural killer cell mediated lysis

Taxol is known to polymerize and stabilize microtubules and thereby alter many cellular functions. Our studies examined the effects of taxol pretreatment of tumor targets and cytotoxic effector cells in an effort to determine whether such treatment would result in increased tumor cell lysis without affecting cytotoxic cell function. Our studies demonstrated that taxol concentrations of 6-30 ng/ml which induced approximately 50% growth inhibition and > or = 50% block in the G2/M phase of the K562 cell targets did not have any significant effect on the functional ability of NK cells to lyse K562 cells. Pretreatment of K562 cells with taxol (6 and 30 ng/ml) resulted in an increase in K562 cell lysis by NK cells (or NK cells stimulated with 100 units/ml of rIL-2) in 7 out of 9 donors. The amplification of NK cell-mediated lysis of tumor targets due to taxol pretreatment may provide a combination therapeutic approach which includes taxol treatment followed by rIL-2 stimulation of the immune killer cell function.

Induction of the suicide HSV-TK gene by activation of the Egr-1 promoter with radioisotopes

In investigating new methods for the treatment of pancreatic cancer, we have explored the possibility of using a combination of radiation and gene therapies. We demonstrate herein that the early growth response gene 1 promoter (Egr-1) is sufficient to confer selective expression of the luciferase gene (Luc) in a human pancreatic tumor cell line (AsPc-1) when exposed to ionizing radiation. The Egr-1 promoter directed the radioinducible expression of luciferase, and yielded higher levels of Luc activity than that in nonirradiated lines. The radioisotopes Tc-99m, I-131, and Ga-67-citrate were selected as Egr-1 activators for their potential to accumulate in tumors. We studied Ga-67-citrate, a radioisotope employed in tumor scintigraphy, for its suitability for selective gene induction. The plasmid vector pEgr-1-Luc was transfected into AsPc-1 cells and then exposed to radioisotopes. Luciferase activity increased by 100-300 times over control. We also inserted the herpes thymidine kinase gene (TK) downstream of Egr-1 and transfected this construct into AsPc-1 cells. Ga-67-citrate and ganciclovir were added to the cells and cell survival was assessed by MTT assay. The growth of AsPc-1 cells transfected with the pEgr-TK construct was suppressed 2 days after exposure of the cells to Ga-67-citrate. The results indicate that Ga-67-citrate may be useful in combining radiation and gene therapies.

Induction of tetradecanoyl phorbol acetate-inducible sequence (TIS) genes by electroconvulsive shock in rat brain

We studied the induction of tetradecanoyl phorbol acetate-inducible sequences (TIS)1, 7, 8, 11, and 21 in rat cerebral cortex, hippocampus, and cerebellum after electroconvulsive shock (ECS). These genes were reported to be induced by depolarization in PC-12 cells. Single ECS induced TIS1, 8, 11, and 21, but not TIS7 genes in the rat brain regions examined. In cerebral cortex and hippocampus, induction of TIS1, TIS8, and TIS21 reached peak at 30 or 45 min after ECS. The induced mRNA of TIS1 and 21 decreased rapidly and returned almost to the basal level by 90 min after ECS, whereas those of TIS8 and 11 lasted longer. In cerebellum, TIS genes were induced and disappeared more rapidly than in the other two regions. The 10 and 20 daily ECSs did not affect the inducibility of TIS1, 11, and 21 in cerebellum, but the induction of TIS8 was attenuated by 35% after 20 daily ECSs. Our study indicated that ECS could induce some of the TIS genes in various rat brain regions, but the induction patterns were different depending on the TIS genes and brain regions. Our study also suggested that chronic ECS could not attenuate the induction of some immediate early genes.