c-IAP2 is induced by ionizing radiation through NF-kappaB binding sites

A Simple Method for Constructing Artificial Promoters Activated in Response to Ultrasound Stimulation

It has been pointed out that ultrasound could be used as a controller for bioprocesses including gene expression since its energy can noninvasively reach deep in the body. Gene expression may be timely and spatially controlled by ultrasound, thus providing necessary bioactive proteins for the targeted tissue in a timely fashion. Although there are many processes involved in gene expression control, one of the most important processes is transcription, and the promoter plays an essential role in it. There are several promoters known to be activated in response to ultrasound irradiation . However, in our opinion, an artificial promoter is more suitable for clinical use. We herein describe simple methods to construct promoters that are responsive to ultrasound irradiation by randomly combining cis-elements (transcription factor binding motifs) and thereby improve its reactivity to ultrasound irradiation .

NF-κB factors control the induction of NFATc1 in B lymphocytes

In peripheral lymphocytes, the transcription factors (TFs) NF-κB, NFAT, and AP-1 are the prime targets of signals that emerge from immune receptors. Upon activation, these TFs induce gene networks that orchestrate the growth, expansion, and effector function of peripheral lymphocytes. NFAT and NF-κB factors share several properties, such as a similar mode of induction and architecture in their DNA-binding domain, and there is a subgroup of κB-like DNA promoter motifs that are bound by both types of TFs. However, unlike NFAT and AP-1 factors that interact and collaborate in binding to DNA, NFAT, and NF-κB seem neither to interact nor to collaborate. We show here that NF-κB1/p50 and c-Rel, the most prominent NF-κB proteins in BCR-induced splenic B cells, control the induction of NFATc1/αA, a prominent short NFATc1 isoform. In part, this is mediated through two composite κB/NFAT-binding sites in the inducible Nfatc1 P1 promoter that directs the induction of NFATc1/αA by BCR signals. In concert with coreceptor signals that induce NF-κB factors, BCR signaling induces a persistent generation of NFATc1/αA. These data suggest a tight connection between NFATc1 and NF-κB induction in B lymphocytes contributing to the effector function of peripheral B cells.

Bioluminescence imaging: basics and practical limitations

Over the last three decades, imaging has been a thriving field with continuous egression of more reliable and highly sophisticated tools and techniques allowing better understanding of biological processes in living organisms. This field continues to expand and its applications broaden to encompass limitless applications in various biomedical research areas. It is however, of utmost importance to understand the capabilities and limitations of this technique as new challenges and hurdles continue to arise. This chapter describes the general properties of bioluminescence imaging and commonly used reporters while underlining the challenges and limitations with these modalities.

Gamma irradiation and targeted radionuclides enhance the expression of the noradrenaline transporter transgene controlled by the radio-inducible p21(WAF1/CIP1) promoter

The use of radiation-inducible promoters to drive transgene expression offers the possibility of temporal and spatial regulation of gene activation. This study assessed the potential of one such promoter element, p21(WAF1/CIP1) (WAF1), to drive expression of the noradrenaline transporter (NAT) gene, which conveys sensitivity to radioiodinated meta-iodobenzylguanidine (MIBG). An expression vector containing NAT under the control of the radiation-inducible WAF1 promoter (pWAF/NAT) was produced. The non-NAT expressing cell lines UVW (glioma) and HCT116 (colorectal cancer) were transfected with this construct to assess radiation-controlled WAF1 activation of the NAT gene. Transfection of UVW and HCT cells with pWAF/NAT conferred upon them the ability to accumulate [(131)I]MIBG, which led to increased sensitivity to the radiopharmaceutical. Pretreatment of transfected cells with γ radiation or the radiopharmaceuticals [(123)I]MIBG or [(131)I]MIBG induced dose- and time-dependent increases in subsequent [(131)I]MIBG uptake and led to enhanced efficacy of [(131)I]MIBG-mediated cell kill. Gene therapy using WAF1-driven expression of NAT has the potential to expand the use of this therapeutic modality to tumors that lack a radio-targetable feature.

BIRC7 gene in channel catfish (Ictalurus punctatus): identification and expression analysis in response to Edwardsiella tarda, Streptococcus iniae and Channel catfish Hemorrhage Reovirus

A family member of inhibitor of apoptosis protein (IAP) termed baculoviral IAP repeat-containing 7 (BIRC7) from channel catfish (Ictalurus punctatus) was identified, the full length cDNA sequence of channel catfish BIRC7 (CcBIRC7) was 1686 bp, containing a 5'UTR of 93 bp, a 3'UTR of 399 bp with a poly (A) tail and an ORF of 1194 bp encoding a putative protein of 398 amino acids. The putative CcBIRC7 protein contains two BIR super-family conservative domains and a C-terminal RING finger motif. Phylogenetic analysis showed that catfish CcBIRC7 was moderately conserved with other BIRC7. Quantitative real-time PCR was conducted to examine the expression profiles of CcBIRC7 in healthy tissues and responding to different pathogens (Edwardsiella tarda, Streptococcus iniae and Channel catfish Hemorrhage Reovirus (CCRV)). CcBIRC7 was widely expressed in healthy tissues of channel catfish and with the highest 37.28-fold expression in blood. E. tarda and S. iniae could induce CcBIRC7 gene expression drastically in head kidney, liver and spleen, which the peak value reached 31.6-fold, 613.9-fold and 34.4-fold increase by E. tarda infection, and 248.3-fold, 1540.3-fold and 120.4-fold increase post S. iniae challenge, respectively. While, CCRV virus could slightly induce CcBIRC7 expression in head kidney and liver but reduce it in spleen. The result suggested BIRC7 may play a potential role in channel catfish innate immune system against bacterial and virus infections, especially as the anti-bacteria immune gene. This is the first report of BIRC7 gene identification and its expression in fish.

Improvement and induction property of radiation-responsive promoter through DNA shuffling of 5'-flanking regions of the human p21 gene

A promoter that augments gene expression in response to stimulation of ionizing radiation would be a desired tool for radiogenetic therapy, a combination of radiotherapy and gene therapy. Although various promoters occurring naturally or artificially have been used for researches, one showing higher reactivity to ionizing radiation is desirable. In the present study, we attempted to improve a radiation-responsive promoter of the p21 through a technique called DNA shuffling. A library of DNA fragments was constructed by re-ligation of randomly digested promoter fragments and improved promoters were chosen out of the library. We repeated this process twice to obtain a promoter showing 2.6-fold better reactivity to ionizing radiation compared with its parent, p21 promoter after 10 Gy gamma-ray irradiation. Nucleotide sequence analyses revealed that the obtained promoter was densely packed with some of the cis-acting elements including binding sites for p53, NF-kappaB, NRF-2, AP-1 and NF-Y more than p21 promoter. In addition, it was shown that its induction by ionizing radiation was dependent upon p53 status of a cell line, suggesting that the promoter retained properties of the p21 promoter. This technique is simple and efficient to improve a promoter responsive to other stimulus of interest besides IR.

Expression of BIRC7 protein and mRNA in non-Hodgkin's lymphoma

Studies have shown that BIRC7, a new member of inhibitor of the apoptosis protein family, is expressed in fetal tissues and most solid tumors in humans. However, there are no reported data concerning BIRC7 expression in lymphomas. We investigated the expression of BIRC7, survivin, Bcl-2, Bax, p53 and p170 proteins in 167 cases of non-Hodgkin's lymphoma (NHL) and 10 cases of non-specific lymphadenitis by tissue microarray-based immunohistochemistry. BIRC7 mRNA in three cell lines and 16 cases of NHL were detected by reverse transcriptase-polymerase chain reaction. BIRC7 protein was exhibited in the cytoplasm of cells in 25 (31%) of 80 cases of B-NHLs, 32 (37%) of 87 cases of T-NHLs, and none in non-specific lymphadenitis. The positive rate of BIRC7 was lower than that of survivin in almost all types of NHL with no significant differences, and similar to that of Bcl-2, Bax or p53. There was no correlation of protein expression between BIRC7 and any other detected markers, except p170 in T-NHL (P < 0.001). BIRC7 expression did not correlate with clinic pathologic factors such as sex, age, stage and grade, but overexpression of BIRC7 was positively correlated with aggression of NHL cells (P < 0.05). BIRC7 mRNA expressed in six (38%) of 16 cases of NHLs. BIRC7 mRNA expression was approximately consistent with BIRC7 protein in NHL. Our results indicate that the BIRC7 gene might play a role in the development and aggression of NHL and that the inhibition of BIRC7 expression may be important in NHL treatment.

Cytokine-mediated induction of anti-apoptotic genes that are linked to nuclear factor kappa-B (NF-kappaB) signalling in human islets and in a mouse beta cell line

AIMS/HYPOTHESIS

The destruction of pancreatic beta cells leading to type 1 diabetes in humans is thought to occur mainly through apoptosis and necrosis induced by activated macrophages and T cells, and in which secreted cytokines play a significant role. The transcription factor nuclear factor kappa-B (NF-kappaB) plays an important role in mediating the apoptotic action of cytokines in beta cells. We therefore sought to determine the changes in expression of genes modulated by NF-kappaB in human islets exposed to a combination of IL1beta, TNF-alpha and IFN-gamma.

METHODS

Microarray and gene set enrichment analysis were performed to investigate the global response of gene expression and pathways modulated in cultured human islets exposed to cytokines. Validation of a panel of NF-kappaB-regulated genes was performed by quantitative RT-PCR. The mechanism of induction of BIRC3 by cytokines was examined by transient transfection of BIRC3 promoter constructs linked to a luciferase gene in MIN6 cells, a mouse beta cell line.

RESULTS

Enrichment of several metabolic and signalling pathways was observed in cytokine-treated human islets. In addition to the upregulation of known pro-apoptotic genes, a number of anti-apoptotic genes including BIRC3, BCL2A1, TNFAIP3, CFLAR and TRAF1 were induced by cytokines through NF-kappaB. Significant synergy between the cytokines was observed in NF-kappaB-mediated induction of the promoter of BIRC3 in MIN6 cells.

CONCLUSIONS/INTERPRETATION

These findings suggest that, via NF-kappaB activation, cytokines induce a concurrent anti-apoptotic pathway that may be critical for preserving islet integrity and viability during the progression of insulitis in type 1 diabetes.

Tyrosine nitration of IkappaBalpha: a novel mechanism for NF-kappaB activation

The NF-kappaB family of transcription factors is an important component of stress-activated cytoprotective signal transduction pathways. Previous studies demonstrated that some activation mechanisms require phosphorylation, ubiquitination, and degradation of the inhibitor protein, IkappaBalpha. Herein, it is demonstrated that ionizing radiation in the therapeutic dose range stimulates NF-kappaB activity by a mechanism in which IkappaBalpha tyrosine 181 is nitrated as a consequence of constitutive NO* synthase activation, leading to dissociation of intact IkappaBalpha from NF-kappaB. This mechanism does not appear to require IkappaBalpha kinase-dependent phosphorylation or proteolytic degradation of IkappaBalpha. Tyrosine 181 is involved in several noncovalent interactions with the p50 subunit of NF-kappaB stabilizing the IkappaBalpha-NF-kappaB complex. Evaluation of hydropathic interactions of the IkappaBalpha-p50 complex on the basis of the crystal structure of the complex is consistent with nitration disrupting these interactions and dissociating the IkappaBalpha-NF-kappaB complex. Tyrosine nitration is not commonly studied in the context of signal transduction. However, these results indicate that tyrosine nitration is an important post-translational regulatory modification for NF-kappaB activation and possibly for other signaling molecules modulated by mild and transient oxidative and nitrosative stresses.

Knocking out peroxisome proliferator-activated receptor (PPAR) alpha inhibits radiation-induced apoptosis in the mouse kidney through activation of NF-kappaB and increased expression of IAPs

Peroxisome proliferator-activated receptor (PPAR) alpha, a member of the ligand-activated nuclear receptor superfamily, plays an important role in lipid metabolism and glucose homeostasis and is highly expressed in the kidney. The present studies were aimed at testing the hypothesis that PPARalpha knockout mice would exhibit decreased radiation-induced apoptosis due to exacerbated activation of NF-kappaB (NFKB) and expression of pro-survival factors. Thirty wild-type mice (29S1/SvImJ) and 30 PPARalpha knockout mice were irradiated with a single total-body dose 10 Gy of (137)Cs gamma rays; controls were sham-irradiated. Tissue samples were collected at 3, 6, 12, 24 and 48 h postirradiation. Apoptosis was quantified using immunohistochemical staining for apoptotic bodies and cleaved caspase 3. Radiation-induced apoptosis was observed in both mouse strains in a time-dependent manner. However, the level of apoptosis was significantly suppressed in PPARalpha knockout mice compared with wild-type mice at 6 h postirradiation (P < 0.05). This inhibition of radiation-induced apoptosis was associated with time-dependent increases in NF-kappaB DNA-binding activity, IkappaBalpha phosphorylation, and expression of other antiapoptosis factors in the PPARalpha knockout mouse kidneys but not in wild-type animals. These data support the hypothesis that the loss of PPARalpha expression leads to the suppression of radiation-induced apoptosis in the mouse kidney, mediated through activation of NF-kappaB and up-regulation of anti-apoptosis factors.

Construction of strong mammalian promoters by random cis-acting element elongation

Synthetic oligonucleotides containing one of four kinds of cis-acting elements, binding sites for activating protein-1 (AP-1), nuclear factor κB (NF-κB), CArG binding factor A (CBF-A), and nuclear factor Y (NF-Y), were randomly ligated to construct DNA fragments. These fragments were inserted into the SalI site of a promoter probe vector, pGL3-TATASal, which is located immediately upstream of the TATA box sequence of the human heme oxygenase 1 gene and linked to the luciferase gene to construct 11 plasmid vectors. When these vectors were introduced into PC-3 cells of human prostate cancer, 6 out of the 11 transfectants showed a significantly higher luciferase activity than pGL3-TATASal. The two strongest promoters (clone 6 and clone 11) were investigated further. Clone 6 turned out to be the strongest, showing a 3.0-and 8.4-fold activity in comparison to the two frequently used promoters—the cytomegalovirus (CMV) immediate early promoter and the simian virus 40 (SV40) early promoter, respectively. Clone 11 was less active than clone 6, but still showed higher activity than the two promoters. When the plasmids were introduced into nine other cell lines, their activities varied but were still comparable to the two promoters. These results indicate that the method used here is simple and efficient for constructing strong promoters that are potentially useful for vectors in either gene therapy or recombinant vaccine.

Overexpression of the prostaglandin E2 receptor EP2 results in enhanced skin tumor development

We previously showed that the EP2 knockout mice were resistant to chemically induced skin carcinogenesis. The purpose of this study was to investigate the role of the overexpression of the EP2 receptor in mouse skin carcinogenesis. To determine the effect of overexpression of EP2, we used EP2 transgenic (TG) mice and wild-type (WT) mice in a DMBA (7,12-dimethylbenz[alpha]anthracene)/TPA (12-O-tetradecanoylphorbol-13-acetate) two-stage carcinogenesis protocol. EP2 TG mice developed significantly more tumors compared with WT mice. Overexpression of the EP2 receptor increased TPA-induced keratinocyte proliferation both in vivo and in vitro. In addition, the epidermis of EP2 TG mice 48 h after topical TPA treatment was significantly thicker compared to that of WT mice. EP2 TG mice showed significantly increased cyclic adenosine monophosphate levels in the epidermis after prostaglandin E2 (PGE2) treatment. The inflammatory response to TPA was increased in EP2 TG mice, as demonstrated by an increased number of macrophages in the dermis. Tumors and 7 x TPA-treated and DMBA-TPA-treated (6 weeks) skins from EP2 TG mice produced more blood vessels than those of WT mice as determined by CD-31 immunostaining. Vascular endothelial growth factor (VEGF) protein expression was significantly increased in squamous cell carcinoma (SCC) samples from EP2 TG mice compared that of WT mice. There was, however, no difference in the number of apoptotic cells in tumors from WT and EP2 TG mice. Together, our results suggest that the overexpression of the EP2 receptor plays a significant role in the protumorigenic action of PGE2 in mouse skin.

Lack of expression of the EP2 but not EP3 receptor for prostaglandin E2 results in suppression of skin tumor development

The EP2 receptor for prostaglandin E2 (PGE2) is a membrane receptor that mediates at least part of the action of PGE2. It has been shown that EP2 plays a critical role in tumorigenesis in mouse mammary gland and colon. However, the possibility that the EP2 receptor is involved in the development of skin tumors was unknown. The purpose of this study was to investigate the role of the EP2 receptor in mouse skin carcinogenesis. Unlike EP3 knockout mice, the EP2 knockout mice produced significantly fewer tumors and reduced tumor incidence compared with wild type (WT) mice in a 7,12-dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) two-stage carcinogenesis protocol. EP2 knockout mice had significantly reduced cellular proliferation of mouse skin keratinocytes in vivo and in vitro compared with that in WT mice. In addition, the epidermis of EP2 knockout mice 48 hours after topical TPA treatment was significantly thinner compared with that of WT mice. The inflammatory response to TPA was reduced in EP2 knockout mice, based on a reduced number of macrophages in the dermis and a reduced level of interleukin-1alpha mRNA expression, compared with WT mice. EP2 knockout mice also had significantly reduced epidermal cyclic AMP levels after PGE2 treatment compared with WT mice. Tumors from WT mice produced more blood vessels and fewer apoptotic cells than those of EP2 knockout mice as determined by immunohistochemical staining. Our data suggest that the EP2 receptor plays a significant role in the protumorigenic action of PGE2 in skin tumor development.

Cooking oil fumes improve lung adenocarcinoma cell survival through c-IAP2 induction

Cooking oil fumes (COF) exposure was demonstrated to be associated with lung cancer development in Taiwanese nonsmoking women. Previous studies identified Cox-2 overexpression and oxidative DNA damage in lung adenocarcinoma cells after exposure to COF. Involvement of COF in lung tumorigenesis may be associated with cell survival, as well as proliferation of lung adenocarcinoma. To test this hypothesis, A549, a lung adenocarcinoma cell line, was used, and MTT assay data showed that the cell viability of A549 was significantly increased in a concentration-dependent manner by COF treatment for 48 h. Flow cytometery results indicated that the proportion of A549 cell at S-phase was markedly increased after exposure of COF. To elucidate whether the anti-apoptotic c-IAP2 (IAP2) was involved in COF-improved cell survival, IAP2 protein levels was determined by Western blot, and the results showed it was significantly induced by COF in a concentration-dependent manner. Moreover, the suppression of BAY, a nuclear factor (NF)-kappaB binding inhibitor, or the COF-induced IAP2 protein levels indicated that NF-kappaB activation by COF may partly be involved in IAP2 induction. These results showed that the positive impact of COF on cell survival and proliferation of A549 lung tumor cells may be through an induction of IAP2 overexpression.

Proton radiation and TNF-alpha/Bax gene therapy for orthotopic C6 brain tumor in Wistar rats

High-grade tumors of the brain remain virtually incurable with current therapeutic regimens, new approaches to augment existing therapies need to be explored. The major goal of this pilot study was to evaluate the feasibility of gene therapy using plasmid DNA encoding tumor necrosis factor-alpha and bax together with proton radiation in an immunocompetent animal model with orthotopic brain tumor. C6 glioma cells were stereotactically implanted into the left hemibrain of Wistar rats (day 0). On day 5, the appropriate groups received intratumoral pGL1-TNF-a and pGL1-Bax (10 microg each), parental plasmid pWS4 (20 microg), or PBS. Hemibrain proton irradiation (10 Gy, 90 MeV, single fraction) was delivered 18-20 hr later. Rats were euthanized when signs of illness appeared. In addition, a subset of animals from each group was euthanized on day 9 for immune and other assays. By day 9, 25%, 20%, and 10% of rats treated with PBS, pWS4, or pGL1-TNF-alpha/pGL1-Bax, respectively, had been euthanized due to weight loss or other signs of illness, whereas all rats treated with pGL1-TNF-alpha/pGL1-Bax + radiation or radiation alone were healthy (P<0.05). At this same time, the pGL1-TNF-alpha/pGL1-Bax + radiation group had significantly elevated lymphocyte percentages (P<0.005 or less) and a relatively high level of lymphocytic infiltrate within tumors. Although the rats treated with pGL1-TNF-alpha/pGL1-Bax had the highest levels of activated T helper (CD4+/CD71+) and T cytotoxic (CD8+/CD71+) cells, the values were not significantly different compared to the pWS4-injected control group. Splenocytes in all tumor cell-injected groups had higher mean values for DNA and protein synthesis compared to the non-tumor cell injected control group, whereas oxygen radical production by phagocytes was consistently higher in groups injected with plasmid or treated with radiation. Body, hemibrain, and spleen masses, white blood cell, red blood cell and platelet counts, hemoglobin, hematocrit, and transforming growth factor-beta1 levels in plasma were similar among groups. The results demonstrate that treatment with pGL1-TNF-alpha/pGL1-Bax combined with proton hemibrain irradiation is safe under the conditions used. Overall, these data support further investigation of this unique combination therapy.

Cyclic AMP promotes cAMP-responsive element-binding protein-dependent induction of cellular inhibitor of apoptosis protein-2 and suppresses apoptosis of colon cancer cells through ERK1/2 and p38 MAPK

We recently reported that cAMP suppresses apoptosis in colon cancer cells and induces cellular inhibitor of apoptosis protein-2 (c-IAP2) via a cAMP-responsive element (CRE), suggesting a mechanism for chemoprevention of colon cancer by non-steroidal anti-inflammatory drugs. In this study, we used T84 human colon cancer cells to define the pathway by which increases in cAMP induce c-IAP2 expression. Treatment with several different cAMP agonists stimulated phosphorylation of CRE-binding protein (CREB) and activated expression of c-IAP2 in a CREB-dependent manner. Studies with pharmacological inhibitors revealed that cAMP-dependent phosphorylation of CREB required activation of ERK1/2 and p38 MAPK but was largely independent of protein kinase A. Immunoblots and transcriptional reporter assays using specific inhibitors, as well as expression of constitutively active forms of MEK1 and MKK3, showed that c-IAP2 induction by cAMP is regulated predominantly through ERK1/2 and p38 MAPK and suggested involvement of p90 ribosomal protein S6 kinase and mitogen and stress response kinase-1 as well. Consistent with those results, we found that cAMP-dependent suppression of apoptosis was blocked by treatment with inhibitors of ERK1/2 and p38 MAPK. We conclude that cAMP can induce c-IAP2 expression in colon cancer cells through CREB phosphorylation and CRE-dependent transcription in a manner that involves activation of ERK1/2 and p38 MAPK. These results emphasize that activation of kinases other than protein kinase A can mediate the actions of agents that increase cAMP, particularly in the regulation of CREB-dependent events.

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Site-directed mutagenesis of the ATM promoter: consequences for response to proliferation and ionizing radiation

Although ATM, the protein defective in ataxia-telangiectasia (A-T), is activated primarily by radiation, there is also evidence that expression of the protein can be regulated by both radiation and growth factors. Computer analysis of the ATM promoter proximal 700-bp sequence reveals a number of potentially important cis-regulatory sequences. Using nucleotide substitutions to delete putative functional elements in the promoter of ATM, we examined the importance of some of these sites for both the basal and the radiation-induced activity of the promoter. In lymphoblastoid cells, most of the mutations in transcription factor consensus sequences [Sp1(1), Sp1(2), Cre, Ets, Xre, gammaIre(2), a modified AP1 site (Fse), and GCF] reduced basal activity to various extents, whereas others [gammaIre(1), NF1, Myb] left basal activity unaffected. In human skin fibroblasts, results were generally the same, but the basal activity varied up to 8-fold in these and other cell lines. Radiation activated the promoter approximately 2.5-fold in serum-starved lymphoblastoid cells, reaching a maximum by 3 hr, and all mutated elements equally blocked this activation. Reduction in Sp1 and AP1 DNA binding activity by serum starvation was rapidly reversed by exposure of cells to radiation. This reduction was not evident in A-T cells, and the response to radiation was less marked. Data provided for interaction between ATM and Sp1 by protein binding and co-immunoprecipitation could explain the altered regulation of Sp1 in A-T cells. The data described here provide additional evidence that basal and radiation-induced regulation of the ATM promoter is under multifactorial control.

Transcription factors activated in mammalian cells after clinically relevant doses of ionizing radiation

Over the past 15 years, a wealth of information has been published on transcripts and proteins 'induced' (requiring new protein synthesis) in mammalian cells after ionizing radiation (IR) exposure. Many of these studies have also attempted to elucidate the transcription factors that are 'activated' (i.e., not requiring de novo synthesis) in specific cells by IR. Unfortunately, all too often this information has been obtained using supralethal doses of IR, with investigators assuming that induction of these proteins, or activation of corresponding transcription factors, can be 'extrapolated' to low-dose IR exposures. This review focuses on what is known at the molecular level about transcription factors induced at clinically relevant (< or =2 Gy) doses of IR. A review of the literature demonstrates that extrapolation from high doses of IR to low doses of IR is inaccurate for most transcription factors and most IR-inducible transcripts/proteins, and that induction of transactivating proteins at low doses must be empirically derived. The signal transduction pathways stimulated after high versus low doses of IR, which act to transactivate certain transcription factors in the cell, will be discussed. To date, only three transcription factors appear to be responsive (i.e. activated) after physiological doses (doses wherein cells survive or recover) of IR. These are p53, nuclear factor kappa B(NF-kappaB), and the SP1-related retinoblastoma control proteins (RCPs). Clearly, more information on transcription factors and proteins induced in mammalian cells at clinically or environmentally relevant doses of IR is needed to understand the role of these stress responses in cancer susceptibility/resistance and radio-sensitivity/resistance mechanisms.

The role of the ubiquitin/proteasome system in cellular responses to radiation

In the last few years, the ubiquitin(Ub)/proteasome system has become increasingly recognized as a controller of numerous physiological processes, including signal transduction, DNA repair, chromosome maintenance, transcriptional activation, cell cycle progression, cell survival, and certain immune cell functions. This is in addition to its more established roles in the removal of misfolded, damaged, and effete proteins. This review examines the role of the Ub/proteasome system in processes underlying the classical effects of irradiation on cells, such as radiation-induced gene expression, DNA repair and chromosome instability, oxidative damage, cell cycle arrest, and cell death. Furthermore, recent evidence suggests that the proteasome is a redox-sensitive target for ionizing radiation and other oxidative stress signals. In other words, the Ub/proteasome system may not simply be a passive player in radiation-induced responses, but may modulate them. The extent of the modulation will be influenced by the functional and structural diversity that is expressed by the system. Cell types vary in the Ub/proteasome structures they possess and the level at which they function, and this changes as they go from the normal to the cancerous condition. Cancer-related functional changes within the Ub/proteasome system may therefore present unique targets for cancer therapy, especially when targeting agents are used in combination with radio- or chemotherapy. The peptide boronic acid compound PS-341, which was designed to inhibit proteasome chymotryptic activity, is in clinical trials for the treatment of solid and hematogenous tumors. It has shown some efficacy on its own and in combination with chemotherapy. Preclinical studies have shown that PS-341 will also potentiate the cytotoxic effects of radiation therapy. In addition, other drugs in common clinical use have been shown to affect proteasome function, and their activities may be valuably reconsidered from this perspective.

Inhibition of apoptosis in normal and transformed intestinal epithelial cells by cAMP through induction of inhibitor of apoptosis protein (IAP)-2

Cyclooxygenase (COX)-2, a rate-limiting enzyme of prostaglandin (PG) production, is overexpressed in colorectal adenomas and adenocarcinomas, and its inhibition by nonsteroidal antiinflammatory drugs protects against colorectal cancer. Mechanisms of cancer promotion by COX-2 are not fully understood, but signaling through prostaglandin (PG)E2 receptors is a contributing factor. The major PGE2 receptors on epithelial cells, EP2 and EP4, increase cAMP production, which promotes growth and inhibits apoptosis in some cell types. Here, we show that cAMP agonists, including PGE2, cholera toxin, and a membrane-permeant cAMP analog, protect normal and transformed intestinal epithelial cells from apoptosis induced by diverse stimuli. This protection is associated with cAMP-mediated, rapid induction of cellular inhibitor of apoptosis protein (c-IAP)-2 and delayed induction of LIVIN, but not of six other members of the IAP family. Concurrently and characteristic of IAP functions, the activity, but not generation, of the cleaved form of the central executioner caspase 3 is inhibited. Induction of c-IAP2 expression by cAMP agonists is accompanied by phosphorylation of cAMP response element binding protein and cAMP response element-dependent activation of transcriptional reporters. Furthermore, inhibition of COX-2 in cells overexpressing the enzyme decreases c-IAP2 expression and promotes apoptosis, both of which are reversible by PGE2 addition, suggesting that COX-2-promoted antiapoptosis is mediated by release of PGE2 and subsequent cAMP-dependent c-IAP2 induction. These results help to explain the cancer chemoprotective effects of nonsteroidal antiinflammatory drugs by defining a mechanism through which cAMP signaling can promote the development of colorectal and possibly other epithelial cancers by means of disruption of normal apoptotic processes.

Transcriptional Targeting in Cancer Gene Therapy

Cancer gene therapy has been one of the most exciting areas of therapeutic research in the past decade. In this review, we discuss strategies to restrict transcription of transgenes to tumour cells. A range of promoters which are tissue-specific, tumour-specific, or inducible by exogenous agents are presented. Transcriptional targeting should prevent normal tissue toxicities associated with other cancer treatments, such as radiation and chemotherapy. In addition, the specificity of these strategies should provide improved targeting of metastatic tumours following systemic gene delivery. Rapid progress in the ability to specifically control transgenes will allow systemic gene delivery for cancer therapy to become a real possibility in the near future.

Spatial and temporal control of transgene expression in vivo using a heat-sensitive promoter and MRI-guided focused ultrasound

BACKGROUND

Among the techniques used to induce and control gene expression, a non-invasive, physical approach based on local heat in combination with a heat-sensitive promoter represents a promising alternative but requires accurate temperature control in vivo. MRI-guided focused ultrasound (MRI-FUS) with real-time feedback control allows automatic execution of a predefined temperature-time trajectory. The purpose of this study was to demonstrate temporal and spatial control of transgene expression based on a well-defined local hyperthermia generated by MRI-FUS.

METHODS

Expression of the green fluorescent protein (GFP) marker gene was used. Two cell lines were derived from C6 glioma cells. The GFP expression of the first one is under the control of the CMV promoter, whereas it is under the control of the HSP70 promoter in the second one and thus inducible by heat. Subcutaneous tumours were generated by injection in immuno-deficient mice and rats. Tumours were subjected to temperatures varying from 42 to 50 degrees C for 3 to 25 min controlled by MRI-FUS and analyzed 24 h after the heat-shock. Endogenous HSP70 expression and C6 cell distribution were also analyzed.

RESULTS

The results demonstrate strong expression at 50 degrees C applied during a short time period (3 min) without affecting cell viability. Induced expression was also clearly shown for temperature in the range 44-48 degrees C but not at 42 degrees C.

CONCLUSIONS

Heating with MRI-FUS allows a tight and non-invasive control of transgene expression in a tumour.

Evaluation of TNF-alpha/Bax gene therapy and radiation against C6 glioma xenografts

Successful therapy of high-grade tumors of the brain is likely to require a combination of new therapeutic approaches. The major goal of the present study was to construct a plasmid-based bax gene vector (pGL1-Bax) and evaluate its expression in vitro and in vivo using athymic mice with subcutaneously growing C6 glioma. Preliminary experiments of efficacy and safety were also performed using pGL1-Bax alone and in combination with previously constructed pGL1-TNF-alpha, as well as with radiation. pGL1-Bax was expressed by C6 cells and was correlated with apoptosis, indicating that the construct and the bax protein were functional. Although intratumoral injections of pGL1-Bax alone, up to total doses of 450 micro g, did not significantly affect tumor growth, consistently smaller tumors were obtained when pGL1-TNF-alpha plus pGL1-Bax were injected 16-18 hr prior to tumor irradiation. Furthermore, in mice with two tumors, one treated and one untreated, progression of the untreated tumor was delayed in the animals receiving all three modalities. No prohibitive toxicities were noted, based on mouse body weights and in vitro assays of blood and spleen. Significant increases in spleen mass, total leukocyte counts, percentage of granulocytes, spontaneous blastogenesis, and CD71-expressing B cells were primarily associated with tumor presence and not treatment type. Overall, the results are promising and suggest that TNF-alpha/Bax gene therapy may be beneficial against highly malignant tumors of the brain. To our knowledge, this is the first report of bax gene therapy used together with radiation in an in vivo glioma model.

Image-guided Control of Transgene Expression Based on Local Hyperthermia

Spatial and temporal control of transgene expression is one of the major prerequisites of efficient gene therapy. Recently, a noninvasive, physical approach has been presented based on local heat in combination with a heat-sensitive promoter. This strategy requires tight temperature control in vivo. Here, we use MRI-guided focused ultrasound (MRI-FUS) with real-time feedback control on a whole-body clinical MRI system for a completely automatic execution of a predefined temperature-time trajectory in the focal point. Feasibility studies on expression control were carried out on subcutaneously implanted rat tumors. A stable modified C6 glioma cell line was used carrying a fused gene coding for thymidine kinase (TK) and green fluorescent protein (GFP) under control of the human heat-shock protein 70 (HSP70) promoter. In vitro studies showed strong induction of the TK-GFP gene expression upon heat shock under various conditions and localization of the protein product in the nucleus. In vivo tumors were subjected to a 3-min temperature elevation using MRI-FUS with a constant temperature, and were analysed 24 hr after the heat shock with respect to GFP fluorescence. Preliminary results showed strong local induction in regions heated above 40°C, and a good correspondence between temperature maps at the end of the heating period and elevated expression of TK-GFP.

Cyclic AMP increases rat inhibitor of apoptosis protein (RIAP1) mRNA in renal mesangial cells

BACKGROUND

The cyclic adenosine 3',5'-monophosphate (cAMP) pathway plays a central role in the regulation of cell proliferation, differentiation and apoptosis. Cyclic AMP has been identified as a bifunctional regulator of apoptosis. The inhibitor of apoptosis proteins (IAP) regulates apoptosis by directly inhibiting distinct caspases.

METHODS

Expression levels of rat IAP (RIAP)-1 were investigated by RNase protection assay in rat mesangial cells after stimulation with diverse agents that modulate cellular levels of cAMP.

RESULTS

Rat mesangial cells up-regulated RIAP1 mRNA levels after cAMP stimulation. Membrane-permeable cAMP analogs, as well as cAMP production in response to the beta-adrenergic receptor agonist salbutamol caused a large increase in RIAP1 mRNA level, which could be inhibited by the protein kinase A inhibitors H89 and Rp-cAMPS, or by the nuclear factor-kappaB (NF-kappaB) inhibitor BAY117085. Inhibition of phosphodiesterase type IV by denbufyllin or rolipram potentiated the cAMP-mediated increase in RIAP1 mRNA. In contrast, the cyclic guanosine 3',5'-monophosphate (cGMP) analog Bt2cGMP did not affect the RIAP1 mRNA level.

CONCLUSIONS

These data establish, to our knowledge for the first time, that RIAP1 mRNA levels are regulated by the cAMP-signaling pathway and suggest potential new avenues of therapy to modulate apoptosis.