Effects of the microenvironment on Fas/Fas ligand interactions and their implications for UV-induced immune suppression

Skin cancer is the most common malignancy in humans. Although highly treatable, non-melanoma skin cancer is commonly followed by other non-cutaneous malignancies. Ultraviolet radiation (UVR) acts as both tumor initiator and promoter, and also results in the suppression of specific immune responses. The systemic suppression of immune responses is initiated by DNA damage, which promotes IL-10 production, an important cytokine as anti-IL-10 can abrogate the suppression, and upregulates the pro-apoptotic proteins Fas and Fas ligand (FasL). FasL is a critical factor for UV-induced immune suppression, and the suppressor cell induced by UV expresses FasL. ^ We hypothesized that the microenvironment affects Fas/FasL interactions, and that these interactions are important to the phenomenon of UV induced immune suppression. To determine the effects of the interaction of FasL and IL-10, splenocytes isolated from C57Bl/6 mice were cultured in the presence or absence of IL-10 post-mitogenic activation. We determined that IL-10 protects from Fas-mediated apoptosis by lowering Fas sensitivity and lowering the levels of either Fas or FasL. This protection is stronger when IL-10 is given immediately after mitogenic activation, and does not increase any of the inhibitors of apoptosis studied. In vivo, splenocytes from UV-irradiated mice are resistant to Fas-mediated apoptosis and present very high levels of IL-10, lowered Fas sensitivity and lowered caspase cleavage despite higher expression of Fas and FasL than non-irradiated mice. ^ UV-induced immune suppression affects female mice preferentially, which led us to look at prolactin as a possible component of this suppression since this hormone has also been associated with increased skin carcinogenesis. The interaction of FasL and prolactin results in suppression of the delayed type hypersensitivity response to Candida albicans. This lack of response depends on FasL as is not seen in gld mice. Similar to UV-induced immune suppression, the suppression is caused by a Th2 deviation, and correlates with a significant increase in Fas expression. In the presence of UV, the effects of prolactin seemed to be protective, and UV actually restores the DTH response.^ Taken together, these observations suggest that the microenvironment dictates the outcome of the interaction of FasL with Fas going from promoting apoptosis to preventing apoptosis or mediating a Th2 deviation and suppression of a Th1 response. ^

DNA damage-induced Fas ligand expression by epidermal dendritic cells mediates UV-induced immune suppression of contact hypersensitivity

Exposure to UVB radiation induces local and systemic immune suppression, evidenced by inhibition of the contact hypersensitivity response (CHS). Epidermal dendritic cells, the primary antigen presenting cells responsible for the induction of CHS, are profoundly altered in phenotype and function by UVB exposure and possess UV-specific DNA damage upon migrating to skin-draining lymph nodes. Expression of the proapoptotic protein FasL has been demonstrated in both skin and lymph node cells following UVB exposure. Additionally, functional FasL expression has recently been demonstrated to be required in the phenomenon of UV-induced immune suppression. To test the hypothesis that FasL expression by DNA-damaged Langerhans cells migrating to the skin-draining lymph nodes is a crucial event in the generation of this phenomenon, mice were given a single 5KJ/m2 UV-B exposure and sensitized to 0.5% FITC through the exposed area. Dendritic cells (DC) harvested from skin-draining lymph nodes (DLN) 18 hours following sensitization by magnetic CD11c-conjugated microbeads expressed high levels of Iab, CD80 and CD86, DEC-205 and bore the FITC hapten, suggesting epidermal origin. Radioimmunoassay of UV-specific DNA damage showed that DC contained the vast majority of cyclobutane pyrimidine dimers (CPDs) found in the DLN after UVB and exhibited increased FasL mRNA expression, a result which correlated with greatly increased FasL-mediated cytotoxicity. The ability of DCs to transfer sensitization to naïve hosts was lost following UVB exposure, a phenomenon which required DC FasL expression, and was completely reversed by cutaneous DNA repair. Collectively, these results demonstrate the central importance of DNA damage-induced FasL expression on migrating dendritic cells in mediating UV-induced suppression of contact hypersensitivity. ^

METALLOTHIONEIN RECEPTOR EXPRESSION IN LEUKOCYTES

Metallothionein (MT) represents a family of low molecular weight, cysteine-rich proteins that play a number of roles in cellular homeostasis. MT is synthesized as a consequence of a variety of cellular stressors, including exposure to toxic metals, increased temperature, tissue wounding, as well as inflammatory and tumorigenic agents. This protein has been found in both intracellular compartments and extracellular spaces, and its function may depend in part on its location. Extracellular MT is able to redistribute heavy metals between tissues, act as a powerful antioxidant, affect cell proliferation, and cause the suppression of T-dependent humoral immunity. The nature of the interaction of MT with the plasma cell membrane has yet to be characterized, despite many observations that there is a significant pool of extracellular MT, and that this extracellular MT will bind to leukocyte plasma membranes. In light of studies that MT can be detected on the surface of leukocytes from animals immunized in the presence of adjuvant, and that an MT specific receptor has been found on the surface of astrocytes, we have investigated the nature of the potential MT-specific surface receptor-binding site(s) on the plasma membrane of leukocytes. The identification of MT-receptors will allow for the characterization of the mechanism MT uses for immunomodulation, for the manipulation of MT in its immunomodulatory role, and for the identification of patients at higher risk for those potentially harmful immunomodulatory effects.

The Dental School Applicant Pool and the Oral Healthcare Workforce

One of the major challenges faced by the dental profession today is the recruitment of the most qualified dental school applicants who are capable of serving the nation’s future oral healthcare needs. The Association of Schools of Public Health (ASPH) also recognizes this challenge, describing one of the three core functions of public health as “assuring that all populations have access to appropriate and cost effective care, including health promotion and disease prevention services.” To achieve this core function, the ASPH cites “a competent public health and personal healthcare workforce” as one of the ten essential public health services. Unfortunately, the goals of both quality and equality in terms of the dental workforce and access to oral healthcare have yet to be realized. When considering access to oral health services on a national or state level, a thoughtful and thorough consideration of the dental school applicant pool is essential. According to a recent study published in the Journal of the American Dental Association, the annual number of retiring dentists will exceed the number of newly licensed dental practitioners in 2009, a trend which is projected to continue throughout the next decade. The approximately 4,400 dentists produced each year from the nation’s 57 accredited dental education programs are charged with the responsibility of meeting the oral healthcare needs of the population at large.

Effects of Food Primes and Thought Suppression on Eating Habits

Food primes and thought suppression have been identified as factors influencing poor eating choices. Primes affect people non-consciously by activating thoughts of food. Suppression of food thoughts leads to a preoccupation with food that is often followed by a hyperaccessibility of food thoughts and increased binging. The current study paired these two processes to examine their interactional effects. We manipulated exposure to food primes and instructions to suppress thoughts of a tasty snack food (M&Ms) for 76 college-aged women. We hypothesized that participants both primed with food images and asked to suppress would consume the most M&Ms at the end of the study. Contrary to predictions, results showed no effects for the manipulations. Perceived weight category, however, did interact with the manipulations, with overweight participants eating more when they got either the food prime or the suppression (but not both together). These findings have important implications for weight-loss strategies.

Le chemin de fer du Congo de Matadi au Stanley-Pool : résultats des études ; rédaction de l'avant-projet ; conclusion avec 24 annexes

Compagnie du Congo pour le Commerce et l'Industrie ...

Elucidation of the role of 53BP1 in DNA double strand break (DSB) repair and tumor suppression

The protein p53 binding protein one (53BP1) was discovered in a yeast two-hybrid screen that used the DNA binding domain of p53 as bait. Cloning of full-length 53BP1 showed that this protein contains several protein domains which help make up the protein, which include two tandem BRCT domains and a amino-terminal serine/glutamine cluster domain (SCD). These are two protein domains are often seen in factors that are involved in the cellular response to DNA damage and control of cell cycle checkpoints and we hypothesize that 53BP1 is involved in the cellular response to DNA damage. In support of this hypothesis we observe that 53BP1 is phosphorylated and undergoes a dramatic nuclear re-localization in response to DNA damaging agents. 53BP1 also interacts with several factors that are important in the cellular response to DNA damage, such as the BRCA1 tumor suppressor, ATM and Rad3 related (ATR), and the phosphorylated version of the histone variant H2AX. Mice deficient in 53BP1 display increased sensitivity ionizing radiation (IR), a DNA damaging agent that introduces DNA double strand breaks (DSBs). In addition, 53BP1-deficient mice do not properly undergo the process of class switch recombination (CSR). We also observe that when a defect in 53BP1 is combined with a defect in p53; the resulting mice have an increased rate of formation of spontaneous tumors, notably the formation of B and T lineage lymphomas. The T lineage tumors arise by two distinct mechanisms: one driven by defects in cell cycle regulation and a second driven by defects in the ability to repair DNA DSBs. The B lineage tumors arise by the inability to repair DNA damage and over-expression of the oncogene c-myc. ^ With these observations, we conclude that not only does 53BP1 function in the cellular response to DNA damage, but it also works in concert with p53 to suppress tumor formation. ^

Mechanisms involved in suppression of the elicitation of immune responses by ultraviolet light

The ultraviolet radiation (UVR) present in sunlight is the primary cause of nonmelanoma skin cancer and has been implicated in the development of cutaneous malignant melanoma. Ultraviolet radiation also suppresses the immune response. In the majority of studies investigating the mechanisms regulating UV-induced immune suppression, UV is used to suppress the induction of immune responses. Equally important, is the ability of UVR to suppress established immune responses, such as the recall reaction in humans, which protects against microbial infections. We established a murine model to help elucidate the immunological mechanisms governing UV-induced suppression of the elicitation of immune responses. 80 kJ/m2 of UVR nine days after sensitization consistently suppressed the elicitation of delayed type hypersensitivity reaction to C. albicans . We found ultraviolet A (320±400 nm) radiation was as effective as solar-simulated ultraviolet A + B (290±400 nm) in suppressing the elicitation of an established immune response. The mechanisms involved in UV-induced suppression of the induction & elicitation of the immune response are similar. For example, mice irradiated with UV after immunization generated antigen-specific T suppressor cells. Injection of monoclonal antibodies to IL-10 or recombinant IL-12 immediately after exposure to UVR blocked immune suppression. Liposomes containing bacteriophage T4N5 to the skin of mice also prevented immune suppression, demonstrating an essential role for ultraviolet-induced DNA damage in the suppression of established immune reactions. ^ In addition to damaging DNA, UV initiates immune suppression through the isomerization of urocanic acid in the epidermis. Here we provide evidence that cis-UCA induces systemic immunosuppression via the serotonin (5-hydroxyyryptamine; 5-HT) receptor. Biochemical and immunological analysis indicate that cis-UCA binds to, and activates, the serotonin receptor. Moreover, serotonin specific antibodies block UV- and/or cis-UCA-induced immune suppression. Our findings identify cis-UCA as novel serotonin receptor ligand and indicate that serotonin receptor engagement can activate immune suppression. Cumulatively, our data suggest that similar immune regulatory mechanisms are activated regardless of whether we expose mice to solar-simulated UV (UVA + UVB) radiation or UVA only, and that ultraviolet radiation activates similar immunologic pathways to suppress the induction or the elicitation of the immune response. ^

Molecular mechanism of jet fuel induced immune suppression

Dermal exposure to jet fuel suppresses the immune response. Immune regulatory cytokines, and biological modifiers, including platelet activating factor, prostaglandin E2, and interleukin-10 have all been implicated in the pathway leading to immunosuppression. It is estimated that approximately 260 different hydrocarbons are found in JP-8 (jet propulsion-8) jet fuel, and the identity of the immunotoxic compound is not known. The recent availability of synthetic jet fuel (S-8), which is devoid of aromatic hydrocarbons, made it feasible to design experiments to test the hypothesis that the aromatic hydrocarbons are responsible for jet fuel induced immune suppression. Applying S-8 to the skin of mice does not up-regulate the expression of epidermal cyclooxygenase-2 nor does it induce immune suppression. Adding back a cocktail of 7 of the most prevalent aromatic hydrocarbons found in jet fuel to S-8 up-regulated cyclooxygenase-2 expression and induced immune suppression. Cyclooxygenase-2 induction can be initiated by reactive oxygen species (ROS). JP-8 treated keratinocytes increased ROS production, S-8 did not. Antioxidant pre-treatment blocked jet fuel induced immune suppression and cyclooxygenase-2 up-regulation. Accumulation of reactive oxygen species induces oxidant stress and affects activity of ROS sensitive transcription factors. JP-8 induced activation of NFκB while S-8 did not. Pre-treatment with antioxidants blocked activation of NFκB and parthenolide, an NFκB inhibitor, blocked jet fuel induced immune suppression and cyclooxygenase-2 expression in skin of treated mice. p65 siRNA transfected keratinocytes demonstrated NFκB is critically involved in jet fuel induced COX-2 expression. These findings clearly implicate the aromatic hydrocarbons found in jet fuel as the agents responsible for inducing immune suppression, in part by the production of reaction oxygen species, NFκB dependent up-regulation of cyclooxygenase-2, and the production of immune regulatory factors and cytokines. ^

The role of AKT-mediated phosphorylation in suppression of MAD1 and the development of new approach in protein complex detection

MAX dimerization protein 1 (MAD1) is a basic-helix-loop-helix transcription factors that recruits transcription repressor such as HDAC to suppress target genes transcription. It antagonizes to MYC because the promoter binding sites for MYC are usually also serve as the binding sites for MAD1 so they compete for it. However, the mechanism of the switch between MYC and MAD1 in turning on and off of genes' transcription is obscure. In this study, we demonstrated that AKT-mediated MAD1 phosphorylation inhibits MAD1 transcription repression function. The association between MAD1 and its target genes' promoter is reduced after been phosphorylated by AKT; therefore, consequently, allows MYC to occupy the binding site and activates transcription. Mutation of such phosphorylation site abrogates the inhibition from AKT. In addition, functional assays demonstrated that AKT suppressed MAD1-mediated transcription repression of its target genes hTERT and ODC. Cell cycle and cell growth were also been released from inhibition by MAD1 in the presents of AKT. Taken together, our study suggests that MAD1 is a novel substrate of AKT and AKT-mediated MAD1 phosphorylation inhibits MAD1function; therefore, activates MAD1 target genes expression. ^ Furthermore, analysis of protein-protein interaction is indispensable for current molecular biology research, but multiplex protein dynamics in cells is too complicated to be analyzed by using existing biochemical methods. To overcome the disadvantage, we have developed a single molecule level detection system with nanofluidic chip. Single molecule was analyzed based on their fluorescent profile and their profiles were plotted into 2 dimensional time co-incident photon burst diagram (2DTP). From this 2DTP, protein complexes were characterized. These results demonstrate that the nanochannel protein detection system is a promising tool for future molecular biology. ^

Effects of thymus size and involution on the contribution of recent thymic emigrants to the peripheral T cell pool

The contribution of recent thymic emigrants (RTEs) to the peripheral naïve T cell population is necessary to maintain diversity of the T cell receptor (TCR) repertoire and produce immune responses against newly encountered antigens. The thymus involutes with age, after irradiation or chemotherapy, and due to severe viral infections. Thymus involution results in decreased thymopoiesis and RTE output leading to a reduced diversity of peripheral T cells. This increases susceptibility to disease and impairs immune responsiveness to vaccines. Therefore, studies aimed at maintaining or regenerating thymic function are integral for maintaining and restoring peripheral TCR diversity. Mice that express a K5.CyclinD1 transgene expression have a severely hyperplastic thymus that fails to undergo involution. Both thymocyte and TEC development appear normal in these mice. We have used the K5.CyclinD1 transgenic model to test the hypothesis that preventing thymus involution will sustain RTE output and incorporation into the peripheral T cell pool to prevent naïve T cell depletion with age. The K5.CyclinD1 transgene was crossed to the RAG2p-GFP transgenic model so that RTEs could be tracked by the intensity of the GFP signal. The frequency and number of RTEs in naïve CD4 splenic T cells was analyzed at monthly intervals to 5 months of age. Using this double transgenic approach, we determined that preventing thymus involution does maintain or enhance the number of RTEs in the peripheral T cell pool before and after thymus involution.

IKKalpha mediated NOTCH1 Activation Promotes Tumorigenesis via FOXA2 Suppression

Proinflammatory cytokine TNFa plays critical roles in promoting malignant cell proliferation, angiogenesis, and tumor metastasis in many cancers. However, the mechanism of TNFa-mediated tumor development remains unclear. Here, we show that IKKa, an important downstream kinase of TNFa, interacts with and phosphorylates FOXA2 at S107/S111, thereby suppressing FOXA2 transactivation activity and leading to decreased NUMB expression, and further activates the downstream NOTCH pathway and promotes cell proliferation and tumorigenesis. Moreover, we found that levels of IKKa, pFOXA2 (S107/ 111), and activated NOTCH1 were significantly higher in hepatocellular carcinoma tumors than in normal liver tissues and that pFOXA2 (S107/111) expression was positively correlated with IKKa and activated NOTCH1 expression in tumor tissues. Therefore, dysregulation of NUMB-mediated suppression of NOTCH1 by TNFa/IKKa-associated FOXA2 inhibition likely contributes to inflammationmediated cancer pathogenesis. Here, we report a TNFa/IKKa/FOXA2/NUMB/NOTCH1 pathway that is critical for inflammation-mediated tumorigenesis and may provide a target for clinical intervention in human cancer.

Regulation of myogenesis and suppression of {\it mck\/} 5$\sp\prime$ enhancer elements by TGF$\beta$ and RAS

The regulation of muscle differentiation, like cell differentiation in general, is only now beginning to be understood. Here are described several key features to myogenesis: a beginning, some intermediary events, and an endpoint. Muscle differentiation proceeds spontaneously when myoblasts are cultured in serum-poor medium. Transforming growth factor type $\beta$ (TGF$\beta$), a component of fetal serum, was found to potently suppress muscle differentiation. Prolonged blockade of differentiation required replenishing TGF$\beta$. When TGF$\beta$ was removed, cells rapidly differentiated. Both TGF$\beta$ and RAS, which also blocks myogenesis, suppress the genes for a series of muscle-specific proteins. Regions that regulate transcription of one such gene, muscle creatine kinase (mck), were located by linking progressively smaller parts of the mck 5$\sp\prime$ region to the marker gene cat and testing the constructs for regulated expression of cat in myoblasts and muscle cells. The mck promoter is not muscle-specific but requires activation. Two enhancers were found: a weak, developmentally regulated enhancer within the first intron, and a strong, compact, and tightly developmentally regulated enhancer about 1.2 Kb upstream of the transcription start site. Activity of this enhancer is eliminated by activated ras. Suppression of activated N-RAS restores potency to the upstream enhancer. Further deletion shows the mck 5$\sp\prime$ enhancer to contain an enhancer core with low but significant muscle-specific activity, and at least one peripheral element that augments core activity. The core and this peripheral element were comprised almost entirely of factor-binding motifs. The peripheral element was inactive as a single copy, but was constitutively active in multiple copies. Regions flanking the peripheral element augmented its activity and conferred partial muscle-specificity. The enhancer core is also modulated by its 5$\sp\prime$ flanking region in a complex manner. Site-specific mutants covering most of the enhancer core and interesting flanking sequences have been made; all mutants tested diminish the activity of the 5$\sp\prime$ enhancer. Alteration of the site to which MyoD1 is reported to bind completely inactivates the enhancer. A theoretical analysis of cooperativity is presented, through which the binding of a constitutively expressed nuclear factor is shown to have weak positive cooperativity. In summary, TGF$\beta$, RAS, and enhancer-binding factors are found to be initial, intermediary, and final regulators, respectively, of muscle differentiation. ^