There is significant interest in the development of agents that can ameliorate radiation damage after exposure to radiation has occurred. Here we report that chronic supplementation of the antioxidant Tempol in the diet of mice can reduce body weight without toxicity, decrease cancer, and extend survival when administered after non-lethal total body radiation (TBI). These effects were apparent in two different strains of mice (C3H, CBA) exposed to TBI (3 Gy). Notably, delaying administration of the Tempol diet 1 month after TBI could also enhance survival. Tempol reduced the incidence of hematopoietic neoplasms (lymphomas) in both strains; whereas, both the onset and incidence of non-hematopoietic neoplasms were reduced in CBA mice. These results encourage further study of Tempol as a chemopreventive, to reduce the incidence of radiation-induced second malignancies after a course of definitive radiation therapy. Tempol may also find applications to reduce the risk of cancers in populations exposed to non-lethal radiation due to nuclear accidents or terrorist attacks.
Tempol; radiation; carcinogenesis; antioxidant; chemoprevention
We employed Francisella tularensis live vaccine strain (LVS) to study mechanisms of protective immunity against intracellular pathogens and, specifically, to understand protective correlates. One potential molecular correlate identified previously was interleukin-6 (IL-6), a cytokine with pleotropic roles in immunity, including influences on T and B cell functions. Given its role as an immune modulator and the correlation with successful anti-LVS vaccination, we examined the role IL-6 plays in the host response to LVS. IL-6-deficient (IL-6 knockout [KO]) mice infected with LVS intradermally or intranasally or anti-IL-6-treated mice, showed greatly reduced 50% lethal doses compared to wild-type (WT) mice. Increased susceptibility was not due to altered splenic immune cell populations during infection or decreased serum antibody production, as IL-6 KO mice had similar compositions of each compared to WT mice. Although LVS-infected IL-6 KO mice produced much less serum amyloid A and haptoglobin (two acute-phase proteins) than WT mice, there were no other obvious pathophysiological differences between LVS-infected WT and IL-6 KO mice. IL-6 KO or WT mice that survived primary LVS infection also survived a high-dose LVS secondary challenge. Using an in vitro overlay assay that measured T cell activation, cytokine production, and abilities of primed splenocytes to control intracellular LVS growth, we found that IL-6 KO total splenocytes or purified T cells were slightly defective in controlling intracellular LVS growth but were equivalent in cytokine production. Taken together, IL-6 is an integral part of a successful immune response to primary LVS infection, but its exact role in precipitating adaptive immunity remains elusive.
Changes in dietary selenium and selenoprotein status may influence both anti- and pro-cancer pathways, making the outcome of interventions different from one study to another. To characterize such outcomes in a defined setting, we undertook a controlled hepatocarcinogenesis study involving varying levels of dietary selenium and altered selenoprotein status using mice carrying a mutant (A37G) selenocysteine tRNA transgene (TrsptG37) and/or a cancer driver TGFα transgene. The use of TrsptG37 altered selenoprotein expression in a selenoprotein and tissue specific manner and, at sufficient dietary selenium levels, separate the effect of diet and selenoprotein status. Mice were maintained on diets deficient in selenium (0.02 ppm selenium) or supplemented with 0.1, 0.4 or 2.25 ppm selenium or 30 ppm triphenylselenonium chloride (TPSC), a non-metabolized selenium compound. TrsptG37 transgenic and TGFα/TrsptG37 bi-transgenic mice subjected to selenium-deficient or TPSC diets developed a neurological phenotype associated with early morbidity and mortality prior to hepatocarcinoma development. Pathology analyses revealed widespread disseminated pyogranulomatous inflammation. Pyogranulomas occurred in liver, lungs, heart, spleen, small and large intestine, and mesenteric lymph nodes in these transgenic and bi-transgenic mice. The incidence of liver tumors was significantly increased in mice carrying the TGFα transgene, while dietary selenium and selenoprotein status did not affect tumor number and multiplicity. However, adenoma and carcinoma size and area were smaller in TGFα transgenic mice that were fed 0.4 and 2.25 versus 0.1 ppm of selenium. Thus, selenium and selenoprotein deficiencies led to widespread pyogranuloma formation, while high selenium levels inhibited the size of TGFα–induced liver tumors.
Despite high cure rates for pediatric B-lineage acute lymphoblastic leukemia (B-ALL), short-term and long-term toxicities and chemoresistance are shortcomings of standard chemotherapy. Immunotherapy and chemoimmunotherapy based on monoclonal antibodies (mAbs) that target cell surface antigens with restricted expression in pediatric B-ALL may offer the potential to reduce toxicities and prevent or overcome chemoresistance. The receptor tyrosine kinase ROR1 has emerged as a candidate for mAb targeting in select B-cell malignancies.
Methodology and Principal Findings
Using flow cytometry, Western blotting, immunohistochemistry, and confocal immunofluorescence microscopy, we analyzed the cell surface expression of ROR1 across major pediatric ALL subtypes represented by 14 cell lines and 56 primary blasts at diagnosis or relapse as well as in normal adult and pediatric tissues. Cell surface ROR1 expression was found in 45% of pediatric ALL patients, all of which were B-ALL, and was not limited to any particular genotype. All cell lines and primary blasts with E2A-PBX1 translocation and a portion of patients with other high risk genotypes, such as MLL rearrangement, expressed cell surface ROR1. Importantly, cell surface ROR1 expression was found in many of the pediatric B-ALL patients with multiply relapsed and refractory disease and normal karyotype or low risk cytogenetics, such as hyperdiploidy. Notably, cell surface ROR1 was virtually absent in normal adult and pediatric tissues.
Conclusions and Significance
Collectively, this study suggests that ROR1 merits preclinical and clinical investigations as a novel target for mAb-based therapies in pediatric B-ALL. We propose cell surface expression of ROR1 detected by flow cytometry as primary inclusion criterion for pediatric B-ALL patients in future clinical trials of ROR1-targeted therapies.
Cancer cells undergo significant changes in carbohydrate expression, and these alterations can be useful as biomarkers and therapeutic targets. In this study, we investigated the expression of carbohydrate antigens containing a terminal GalNAcα1-3Gal or GalNAcα1-6Gal on human cervix and cervical carcinoma. Monoclonal antibodies to each of these carbohydrates were generated by immunizing rabbits with the corresponding antigen conjugated to KLH followed by hybridoma production. Antibodies were screened and evaluated using a combination of carbohydrate microarray profiling, ELISA, dot blot and immunohistochemical staining to verify specificity. Antibody 132-3 was found to selectively recognize GalNAcα1-3Gal with little cross-reactivity to other structurally similar antigens such as GalNAcα1-6Gal, blood group A, Forssman antigen and the Tn antigen on both solution assays and human tissue. While GalNAcα1-6Gal expression was not detected, GalNAcα1-3Gal expression was found on 55% of squamous cell carcinomas. Expression in normal tissue was observed but was restricted to the suprabasal epithelial layer. Importantly, we found expression of the antigen on cervical cancer had a statistically significant correlation with the 5-year survival rate of the patients (48% vs 85% for antigen neg. vs pos., p = 0.017). Expression of GalNAcα1-3Gal did not correlate with other clinical factors including tumor stage, size, and lymph node metastasis, indicating the antigen is a new, independent biomarker for the prognosis of cervical cancer.
carbohydrate; prognostic marker; cervical cancer; glycan array
Inhibition of HIF-1 is an attractive therapeutic strategy to target the tumor microenvironment. However, HIF-1 inhibitors may have limited activity as single agents and combination therapies may be required. We tested the hypothesis that HIF-1 inhibition in a hypoxic stressed tumor microenvironment, which could be generated by administration of antiangiogenic agents, may result in a more pronounced therapeutic effect. The activity of bevacizumab, either alone or in combination with the HIF-1α inhibitor topotecan, was evaluated in U251-HRE xenografts. Tumor tissue was collected at the end of treatment and changes in tumor oxygenation, angiogenesis, proliferation, apoptosis, HIF-1α levels, HIF-1 target genes and DNA damage were evaluated. Bevacizumab decreased microvessel-density and increased intratumor-hypoxia, but did not induce apoptosis. Moreover, bevacizumab alone caused a significant increase of HIF-1-dependent gene expression in tumor tissue. Addition of a low dose of daily topotecan to bevacizumab significantly inhibited tumor growth, relative to mice treated with topotecan or bevacizumab alone (p<0.01). The addition of topotecan to bevacizumab was also associated with profound inhibition of HIF-1 transcriptional activity, significant inhibition of proliferation and induction of apoptosis. Importantly, DNA damage induced by topotecan alone was not augmented by addition of bevacizumab, suggesting that increased cytotoxic activity did not account for the increased anti-tumor effects observed.
These results strongly suggest that combination of anti-VEGF antibodies with HIF-1 inhibitors is an attractive therapeutic strategy targeting in the hypoxic tumor microenvironment.
HIF-1; topotecan; bevacizumab; hypoxia; angiogenesis; cancer therapeutics
The tumor-associated Tn antigen has been investigated extensively as a biomarker and therapeutic target. Cancer vaccines containing the Tn antigen as a single tumor antigen or as a component of a polyvalent vaccine have progressed into phase I and phase II clinical trials. One major focus of Tn-based vaccines is the treatment of prostate cancer patients. While expression of the antigen on prostate tumors is a critical prerequisite, previous reports investigating Tn expression in prostate tumors have produced conflicting results. Using a combination of immunohistochemistry and carbohydrate microarray profiling, we show that only 4–26% of prostate tumors express the Tn antigen. Based on our results, the majority of prostate cancer patients do not express the appropriate antigen. Therefore, efforts to pre-select the subset of prostate cancer patients with Tn positive tumors or apply Tn vaccines to other cancers with higher rates of antigen expression could significantly improve clinical response rates. Since conflicting information on carbohydrate expression is a general problem for the field, the approach described in this paper of analyzing antigen expression with multiple antibodies and using carbohydrate microarray profiles to interpret the results will be useful for the development of other carbohydrate-based cancer vaccines and diagnostics.
Controlled protein degradation mediated by ubiquitin/proteasome system (UPS) plays a crucial role in modulating a broad range of cellular responses. Dysregulation of the UPS often accompanies tumorigenesis and progression. Here, we report that Smad ubiquitination regulatory factor 2 (Smurf2), a HECT-domain containing E3 ubiquitin ligase, is up-regulated in certain breast cancer tissues and cells. We show that reduction of Smurf2 expression with specific short interfering RNA in metastatic breast cancer cells induces cell rounding and reorganization of the actin cytoskeleton, which are associated with a less motile and invasive phenotype. Overexpression of Smurf2 promotes metastasis in a nude mouse model and increases migration and invasion of breast cancer cells. Moreover, expression of Smurf2CG, an E3 ligase–defective mutant of Smurf2, suppresses the above metastatic behaviors. These results establish an important role for Smurf2 in breast cancer progression and indicate that Smurf2 is a novel regulator of breast cancer cell migration and invasion.
Interleukin-7 (IL-7) is required for lymphocyte development and homeostasis although the actual sites of IL-7 production have never been clearly identified. We produced a bacterial artificial chromosome (BAC) transgenic mouse expressing ECFP in the Il7 locus. The construct lacked a signal peptide and ECFP (enhanced cyan fluorescent protein ) accumulated inside IL-7-producing stromal cells in thoracic thymus, cervical thymus and bone marrow. In thymus, an extensive reticular network of IL-7-containing processes extended from cortical and medullary epithelial cells, closely contacting thymocytes. Central memory CD8 T cells, which require IL-7 and home to bone marrow, physically associated with IL-7-producing cells as we demonstrate by intravital imaging.
Overexpression of transforming growth factor β (TGF-β) is frequently associated with metastasis and poor prognosis, and TGF-β antagonism has been shown to prevent metastasis in preclinical models with surprisingly little toxicity. Here we have used the transplantable 4T1 model of metastatic breast cancer to address underlying mechanisms. We showed that efficacy of the anti-TGF-β antibody 1D11 in suppressing metastasis was dependent on a synergistic combination of effects on both the tumor parenchyma and microenvironment. The main outcome was a highly significant enhancement of the CD8+ T-cell mediated anti-tumor immune response, but effects on the innate immune response and on angiogenesis also contributed to efficacy. Treatment with 1D11 increased infiltration of NK cells and T cells at the metastatic site, and enhanced expression of coactivators (NKG2D) and cytotoxic effectors (perforin and granzyme B) on CD8+ T-cells. On the tumor cells, increased expression of an NKG2D ligand (Rae1γ) and of a death receptor (TNFRSF1A) contributed to enhanced immune cell-mediated recognition and lysis. The data suggest that elevated TGF-β expression in the tumor microenvironment modulates a complex web of intercellular interactions that aggregately promote metastasis and progression. TGF-β antibodies reverse this effect, and the absence of a major effect of TGF-β antagonism on any one cell compartment may be critical for a good therapeutic window and the avoidance of autoimmune complications.
metastasis; anti-TGF-β; immune surveillance; mouse models; breast cancer
The POTE gene family is composed of 13 highly homologous paralogs preferentially expressed in prostate, ovary, testis and placenta. We produced 10 monoclonal antibodies (MAbs) against 3 representative POTE paralogs: POTE-21, POTE-2γC and POTE-22. One reacted with all 3 paralogs, 6 MAbs reacted with POTE-2γC and POTE-22, and 3 MAbs were specific to POTE-21. Epitopes of all 10 MAbs were located in the cysteine-rich repeats (CRRs) motifs located at the N-terminus of each POTE paralog. Testing the reactivity of each MAb with 12 different CRRs revealed slight differences among the antigenic determinants, which accounts for differences in cross-reactivity. Using MAbs HP8 and PG5 we were able to detect a POTE-actin fusion protein in human testis by immunoprecipitation followed by Western blotting. By immunohistochemistry we demonstrated that the POTE protein is expressed in primary spermatocytes, implying a role in spermatogenesis.
POTE paralogs; primary spermatocytes; spermatogenesis
Although severe hepatitis and liver tumors occur in a high percentage of A/J male mice naturally infected with Helicobacter hepaticus, these effects have not been observed after injection of adult mice with the bacteria.
We tested the hypothesis that perinatal exposure to the bacteria is required for liver tumorigenesis.
A/J female mice were infected by intragastric (ig) or intraperitoneal (ip) treatment with 1.5 × 108
H. hepaticus before pregnancy. We examined offspring at progressive time intervals, including some kept until natural death in old age. A/J, BALB/c, and C57BL/6 weanling male mice were similarly treated ig with the bacteria and observed for up to 2 years.
After ip bacterial infection of A/J females, 41% of their male offspring developed hepatitis and 33% had hepatocellular tumors, including 18% with hepatocellular carcinoma. Treatment by the ig route resulted in a similar incidence of hepatitis in offspring (35%) but fewer total liver tumors (8%) and carcinomas (4%). By contrast, ig instillation of H. hepaticus in weanling A/J, C57BL/6, or BALB/c mice resulted in low incidence of hepatitis (0–20%) and few liver tumors, despite presence of bacteria confirmed in feces.
Results indicate that a high incidence of liver tumors in mice infected with H. hepaticus requires perinatal exposure. Contributing perinatal factors could include known high sensitivity of neonatal liver to tumor initiation, and/or modulation of immune response to the bacterium or its toxins. Mechanisms of human perinatal sensitivity to such phenomena can be studied with this model.
adult exposure; Helicobacter hepaticus; hepatocellular tumors; infection and cancer; perinatal exposure
The TGF-β pathway has tumor suppressor activity in many epithelial tissues. Since TGF-β is a potent inhibitor of epithelial cell proliferation, it has been widely assumed that this property underlies the tumor suppressor effect. Here we have used a xenograft model of breast cancer to show that endogenous TGF-β has the potential to suppress tumorigenesis through a novel mechanism, involving effects at two distinct levels in the hierarchy of cellular progeny that make up the epithelial component of the tumor. Firstly TGF-β reduces the size of the putative cancer stem or early progenitor cell population, and secondly it promotes differentiation of a more committed, but highly proliferative, progenitor cell population to an intrinsically less proliferative state. We further show that reduced expression of the type II TGF-β receptor correlates with loss of luminal differentiation in a clinical breast cancer cohort, suggesting that this mechanism may be clinically relevant. At a molecular level, the induction of differentiation by TGF-β involves down-regulation of Id1, and forced overexpression of Id1 can promote tumorigenesis despite persistence of the anti-proliferative effect of TGF-β. These data suggest new roles for the TGF-β pathway in regulating tumor cell dynamics that are independent of direct effects on proliferation.
Pten is a negative regulator of the Akt pathway, and its inactivation is believed to be an etiological factor in many tumor types. Pten+/- mice are susceptible to a variety of spontaneous tumor types, depending on strain background. Pten+/- mice, in lung tumor-sensitive and -resistant background strains, were treated with a tobacco carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), to determine whether allelic Pten deletion can cooperate with NNK in carcinogenesis in lung or other tissues. In lung tumor-resistant C57BL/6 Pten+/- or +/+ mice, NNK treatment did not lead to any lung tumors and did not increase the incidence or severity of tumors previously reported for this strain. In contrast, in a lung tumor-susceptible pseudo-A/J strain, there was a dose-dependent increase in lung tumor size in Pten+/- compared with +/+ mice, although there was no increase in multiplicity. No other tumor types were observed in pseudo-A/J Pten+/- mice regardless of NNK treatment. Lung tumors from these Pten+/- mice had K-ras mutations, retained Pten expression and had similar Akt pathway activation as lung tumors from +/+ mice. Therefore, deletion of a single copy of Pten does not substantially add to the lung tumor phenotype conferred by mutation of K-ras by NNK, and there is likely no selective advantage for loss of the second Pten allele in lung tumor initiation.
Development of therapies for patients with BRCA1 mutations has been hampered by lack of readily available in vitro and in vivo models. We recently showed that transplantation of transgenic mammary tumors as cell suspensions into naïve recipients generates reproducible tumors with remarkable stability of gene expression profile. We examined the expression profiles of original and serially transplanted mammary tumors from Brca1 deficient mice, and tumor derived cell lines to validate their use for preclinical testing and studies of tumor biology.
Original tumors, serially transplanted and multiple cell lines derived from Brca1 mammary tumors were characterized by morphology, gene and protein expression, and cell surface markers.
Gene expression among Brca1 tumors showed more heterogeneity than among previously characterized tumors from MMTV-PyMT and -Wnt1 models. Gene expression data segregated Brca1 tumors into 3 distinct types: basal, mixed luminal, and tumors with epithelial-to-mesenchymal transition (EMT). Serial transplantation of individual tumors and multiple cell lines derived from the original tumors recapitulated the molecular characteristics of each tumor of origin. One tumor had distinct features of EMT and gave rise to cell lines that contained a distinct CD44+/CD24-/low population that may correlate with human breast cancer stem cells.
Although individual tumors expanded by transplantation maintain the genomic profile of the original tumors, the heterogeneity among Brca1 tumors limits the extent of their use for preclinical testing. However, cell lines offer a robust material for understanding tumor biology and response to therapies driven by BRCA1 deficiency.
α-Galactosidase A is the lysosomal hydrolase that is deficient in patients with Fabry disease. Intravenous infusion of agalsidase alfa, a preparation of α-galactosidase A, is used for enzyme replacement therapy (ERT) in patients with Fabry disease. Although ERT appears to show some beneficial effects, most patients show only a modest response. We investigated using immunohistochemistry the relative tissue and cellular distribution of agalsidase alfa after a single intravenous injection in a mouse knockout model of Fabry disease. Specific immunostaining for agalsidase alfa was found only in liver, kidney, heart, testes, adrenal gland, spleen and bone marrow. There was no difference in distribution of the infused enzyme distribution among tissues sampled 4, 24, and 48 hours post-injection. The intracellular localization of immunopositivity varied considerably between organs with vascular endothelium being the most commonly positive site. α-Galactosidase A specific activity in tissue homogenates matched the relative extent of agalsidase alfa immunostaining distribution in the same organs. We conclude that intravenously injected agalsidase alfa has a very heterogeneous systemic distribution using an immunostaining technique.
The TGF-β signaling network plays a complex role in carcinogenesis because it has the potential to act as either a tumor suppressor or a pro-oncogenic pathway. Currently, it is not known whether TGF-β can switch from tumor suppressor to pro-oncogenic factor during the course of carcinogenic progression in a single cell lineage with a defined initiating oncogenic event or whether the specific nature of the response is determined by cell type and molecular etiology. To address this question, we have introduced a dominant negative type II TGF-β receptor into a series of genetically related human breast–derived cell lines representing different stages in the progression process. We show that decreased TGF-β responsiveness alone cannot initiate tumorigenesis but that it can cooperate with an initiating oncogenic lesion to make a premalignant breast cell tumorigenic and a low-grade tumorigenic cell line histologically and proliferatively more aggressive. In a high-grade tumorigenic cell line, however, reduced TGF-β responsiveness has no effect on primary tumorigenesis but significantly decreases metastasis. Our results demonstrate a causal role for loss of TGF-β responsiveness in promoting breast cancer progression up to the stage of advanced, histologically aggressive, but nonmetastatic disease and suggest that at that point TGF-β switches from tumor suppressor to prometastatic factor.
Retroviruses can be used to accelerate hematopoietic cancers predisposed to neoplastic disease by prior genetic manipulations such as in transgenic or knockout mice. The virus imparts a second neoplastic “hit,” providing evidence that the initial hit is transforming. In the present study, a unique retrovirus was developed that can induce a high incidence of myeloid disease and has a broad host range. This agent is a Moloney murine leukemia virus (Mo-MuLV)-based virus that has most of the U3 region of the long terminal repeat (LTR) replaced with that of retrovirus 4070A. Like Mo-MuLV, this virus, called MOL4070LTR, is NB-tropic and not restricted by Fv1 allelles. MOL4070LTR causes myeloid leukemias in ca. 50% of mice, a finding in contrast to Mo-MuLV, which induces almost exclusively lymphoid disease. The data suggest that the LTR of the 4070A virus expands the tissue tropism of the disease to the myeloid lineage. Interesting, MCF recombinant envelope was expressed in the lymphoid but not the myeloid neoplasms of BALB/c mice. This retrovirus has the potential for accelerating myeloid disease in genetically engineered mice.
TGF-βs play diverse and complex roles in many biological processes. In tumorigenesis, they can function either as tumor suppressors or as pro-oncogenic factors, depending on the stage of the disease. We have developed transgenic mice expressing a TGF-β antagonist of the soluble type II TGF-β receptor:Fc fusion protein class, under the regulation of the mammary-selective MMTV-LTR promoter/enhancer. Biologically significant levels of antagonist were detectable in the serum and most tissues of this mouse line. The mice were resistant to the development of metastases at multiple organ sites when compared with wild-type controls, both in a tail vein metastasis assay using isogenic melanoma cells and in crosses with the MMTV-neu transgenic mouse model of metastatic breast cancer. Importantly, metastasis from endogenous mammary tumors was suppressed without any enhancement of primary tumorigenesis. Furthermore, aged transgenic mice did not exhibit the severe pathology characteristic of TGF-β null mice, despite lifetime exposure to the antagonist. The data suggest that in vivo the antagonist may selectively neutralize the undesirable TGF-β associated with metastasis, while sparing the regulatory roles of TGF-βs in normal tissues. Thus this soluble TGF-β antagonist has potential for long-term clinical use in the prevention of metastasis.
We examined the effects of human immunodeficiency virus infection on the turnover of CD4 and CD8 T lymphocytes in 17 HIV-infected patients by 30 min in vivo pulse labeling with bromodeoxyuridine (BrdU). The percentage of labeled CD4 and CD8 T lymphocytes was initially higher in lymph nodes than in blood. Labeled cells equilibrated between the two compartments within 24 h. Based on mathematical modeling of the dynamics of BrdU-labeled cells in the blood, we identified rapidly and slowly proliferating subpopulations of CD4 and CD8 T lymphocytes. The percentage, but not the decay rate, of labeled CD4 or CD8 cells in the rapidly proliferating pool correlated significantly with plasma HIV RNA levels for both CD4 (r = 0.77, P < 0.001) and CD8 (r = 0.81, P < 0.001) T cells. In six patients there was a geometric mean decrease of greater than 2 logs in HIV levels within 2 to 6 mo after the initiation of highly active antiretroviral therapy; this was associated with a significant decrease in the percentage (but not the decay rate) of labeled cells in the rapidly proliferating pool for both CD4 (P = 0.03) and CD8 (P < 0.001) T lymphocytes. Neither plasma viral levels nor therapy had an effect on the decay rate constants or the percentage of labeled cells in the slowly proliferating pool. Monocyte production was inversely related to viral load (r = −0.56, P = 0.003) and increased with therapy (P = 0.01). These findings demonstrate that HIV does not impair CD4 T cell production but does increase CD4 and CD8 lymphocyte proliferation and death by inducing entry into a rapidly proliferating subpopulation of cells.
AIDS; bromodeoxyuridine; CD4 T lymphocyte proliferation; CD8 T lymphocyte proliferation; highly active antiretroviral therapy
Ionizing radiation (IR) exposure causes mammalian cells to undergo p53-dependent cell cycle arrest and/or apoptosis. The in vivo role of DNA-dependent protein kinase (DNA-PK) in the transduction of the DNA damage signal to p53 remains unresolved. To determine the relationship between DNA-PK and p53, we studied the cell cycle and apoptotic responses to IR in mice deficient in DNA-PK. Using the slip mouse, which harbors an inactivating mutation of the DNA-PK catalytic subunit (DNA-PKcs), we demonstrated not only that these DNA-PKcs null mutants were highly radiosensitive but also that upon IR treatment, p53 accumulated in their cultured cells and tissue. Induced p53 was transcriptionally active and mediated the induction of p21 and Bax in slip cells. Examination of the thymic cell cycle response to IR treatment indicated that the slip G1/S-phase cell cycle checkpoint function was intact. We further show that slip mice exhibited a higher level of spontaneous thymic apoptosis as well as a more robust apoptotic response to IR than wild-type mice. Together, these data demonstrate that the p53-mediated response to DNA damage is intact in cells devoid of DNA-PK activity and suggest that other kinases, such as the product of the gene (ATM) mutated in ataxia telangiectasia, are better candidates for regulating IR-induced phosphorylation and accumulation of p53.
Malignant melanoma of the skin (CMM) is associated with ultraviolet radiation exposure, but the mechanisms and even the wavelengths responsible are unclear. Here we use a mammalian model to investigate melanoma formed in response to precise spectrally defined ultraviolet wavelengths and biologically relevant doses. We show that melanoma induction by ultraviolet A (320–400 nm) requires the presence of melanin pigment and is associated with oxidative DNA damage within melanocytes. In contrast, ultraviolet B radiation (280–320 nm) initiates melanoma in a pigment-independent manner associated with direct ultraviolet B DNA damage. Thus, we identified two ultraviolet wavelength-dependent pathways for the induction of CMM and describe an unexpected and significant role for melanin within the melanocyte in melanomagenesis.
Exposure to ultraviolet light is responsible for a large proportion of melanomas but the molecular mechanisms are unknown. In this study, melanoma is found to be induced in mice by UVA and UVB light in a pigment-dependent and -independent manner, respectively, resulting in different types of DNA damage.