Proto-oncogene PML controls genes devoted to MHC class I antigen presentation

PML nuclear bodies and chromatin dynamics: catch me if you can!

Eukaryotic cells compartmentalize their internal milieu in order to achieve specific reactions in time and space. This organization in distinct compartments is essential to allow subcellular processing of regulatory signals and generate specific cellular responses. In the nucleus, genetic information is packaged in the form of chromatin, an organized and repeated nucleoprotein structure that is a source of epigenetic information. In addition, cells organize the distribution of macromolecules via various membrane-less nuclear organelles, which have gathered considerable attention in the last few years. The macromolecular multiprotein complexes known as Promyelocytic Leukemia Nuclear Bodies (PML NBs) are an archetype for nuclear membrane-less organelles. Chromatin interactions with nuclear bodies are important to regulate genome function. In this review, we will focus on the dynamic interplay between PML NBs and chromatin. We report how the structure and formation of PML NBs, which may involve phase separation mechanisms, might impact their functions in the regulation of chromatin dynamics. In particular, we will discuss how PML NBs participate in the chromatinization of viral genomes, as well as in the control of specific cellular chromatin assembly pathways which govern physiological mechanisms such as senescence or telomere maintenance.

Tumor-induced escape mechanisms and their association with resistance to checkpoint inhibitor therapy

Immunotherapy aims to activate the immune system to fight cancer in a very specific and targeted manner. Despite the success of different immunotherapeutic strategies, in particular antibodies directed against checkpoints as well as adoptive T-cell therapy, the response of patients is limited in different types of cancers. This attributes to escape of the tumor from immune surveillance and development of acquired resistances during therapy. In this review, the different evasion and resistance mechanisms that limit the efficacy of immunotherapies targeting tumor-associated antigens presented by major histocompatibility complex molecules on the surface of the malignant cells are summarized. Overcoming these escape mechanisms is a great challenge, but might lead to a better clinical outcome of patients and is therefore currently a major focus of research.

WEE1 kinase inhibition reverses G2/M cell cycle checkpoint activation to sensitize cancer cells to immunotherapy

Intrinsic resistance to cytotoxic T-lymphocyte (CTL) killing limits responses to immune activating anti-cancer therapies. Here, we established that activation of the G2/M cell cycle checkpoint results in tumor cell cycle pause and protection from granzyme B-induced cell death. This was reversed with WEE1 kinase inhibition, leading to enhanced CTL killing of antigen-positive tumor cells. Similarly, but at a later time point, cell cycle pause following TNFα exposure was reversed with WEE1 kinase inhibition, leading to CTL transmembrane TNFα-dependent induction of apoptosis and necroptosis in bystander antigen-negative tumor cells. Results were reproducible in models of oral cavity carcinoma, melanoma and colon adenocarcinoma harboring variable Tp53 genomic alterations. WEE1 kinase inhibition sensitized tumors to PD-1 mAb immune checkpoint blockade in vivo, resulting in CD8⁺-dependent rejection of established tumors harboring antigen-positive or mixed antigen-positive and negative tumor cells. Together, these data describe activation of the G2/M cell cycle checkpoint in response to early and late CTL products as a mechanism of resistance to CTL killing, and provide pre-clinical rationale for the clinical combination of agents that inhibit cell cycle checkpoints and activate anti-tumor immunity.

Bone marrow T-cell percentage: A novel prognostic indicator in acute myeloid leukemia

Acute myeloid leukemia (AML) is an aggressive malignancy for which overall disease-free survival is less than 50%. Manipulation of the immune system is an interesting and promising therapy for AML patients. We aimed to characterize the immune system of AML patients, highlighting the clinical relevance of total bone marrow (BM) lymphocytes and subpopulations. Sixty-six new AML cases diagnosed according to WHO criteria from King Abdullah Medical City, KSA, from October 2012 to February 2015. Analysis of BM lymphocytes and subpopulations was done by flowcytometry. Significantly, high percentages of BM lymphocytes, T cells, and natural killer (NK) cells were detected in the group that achieved complete remission (P values = 0.004, <0.001, and <0.001, respectively). Overall survival (OS) was significantly prolonged in patients with high BM lymphocytes and T cells (P values = 0.047 and P 0.002, respectively). Multivariate analysis indicated that BM T-cell percentage and cytogenetics were independent prognostic factors predictive of OS (HR 4.7, P value = 0.011). BM T-cell percentage constitutes a novel host factor that can be used in combination with cytogenetics to better predict OS. Large-scale multicenter studies are recommended to clarify its role as a predictor of OS and leukemia-free survival.

Progression of EGFR-Mutant Lung Adenocarcinoma is Driven By Alveolar Macrophages

PURPOSE

Lung adenocarcinomas with mutations in the EGFR have unprecedented initial responses to targeted therapy against the EGFR. Over time, however, these tumors invariably develop resistance to these drugs. We set out to investigate alternative treatment approaches for these tumors.

EXPERIMENTAL DESIGN

To investigate the immunologic underpinnings of EGFR-mutant lung adenocarcinoma, we utilized a bitransgenic mouse model in which a mutant human EGFR gene is selectively expressed in the lungs.

RESULTS

EGFR oncogene-dependent progression and remission of lung adenocarcinoma was respectively dependent upon the expansion and contraction of alveolar macrophages, and the mechanism underlying macrophage expansion was local proliferation. In tumor-bearing mice, alveolar macrophages downregulated surface expression of MHC-II and costimulatory molecules; increased production of CXCL1, CXCL2, IL1 receptor antagonist; and increased phagocytosis. Depletion of alveolar macrophages in tumor-bearing mice resulted in reduction of tumor burden, indicating a critical role for these cells in the development of EGFR-mutant adenocarcinoma. Treatment of mice with EGFR-targeting clinical drugs (erlotinib and cetuximab) resulted in a significant decrease in alveolar macrophages in these mice. An activated alveolar macrophage mRNA signature was dominant in human EGFR-mutant lung adenocarcinomas, and the presence of this alveolar macrophage activation signature was associated with unfavorable survival among patients undergoing resection for EGFR-mutant lung adenocarcinoma.

CONCLUSIONS

Because of the inevitability of failure of targeted therapy in EGFR-mutant non-small cell lung cancer (NSCLC), these data suggest that therapeutic strategies targeting alveolar macrophages in EGFR-mutant NSCLC have the potential to mitigate progression and survival in this disease. Clin Cancer Res; 23(3); 778-88. ©2016 AACR.

Emerging Role of PML Nuclear Bodies in Innate Immune Signaling

Research in the last 2 decades has demonstrated that a specific organelle of the cell nucleus, termed PML nuclear body (PML-NB) or nuclear domain 10 (ND10), is frequently modified during viral infection. This correlates with antagonization of a direct repressive function of individual PML-NB components, such as the PML, hDaxx, Sp100, or ATRX protein, that are able to act as cellular restriction factors. Recent studies now reveal an emerging role of PML-NBs as coregulatory structures of both type I and type II interferon responses. This emphasizes that targeting of PML-NBs by viral regulatory proteins has evolved as a strategy to compromise intrinsic antiviral defense and innate immune responses.

Disentangling the relationship between tumor genetic programs and immune responsiveness

Correlative studies in humans have demonstrated that an active immune microenvironment characterized by the presence of a T-helper 1 immune response typifies a tumor phenotype associated with better outcome and increased responsiveness to immune manipulation. This phenotype also signifies the counter activation of immune-regulatory mechanisms. Variables modulating the development of an effective anti-tumor immune response are increasingly scrutinized as potential therapeutic targets. Genetic alterations of cancer cells that functionally influence intratumoral immune response include mutational load, specific mutations of genes involved in oncogenic pathways and copy number aberrations involving chemokine and cytokine genes. Inhibiting oncogenic pathways that prevent the development of the immune-favorable cancer phenotype may complement modern immunotherapeutic approaches.

Characterization of Recombinant Human Cytomegaloviruses Encoding IE1 Mutants L174P and 1-382 Reveals that Viral Targeting of PML Bodies Perturbs both Intrinsic and Innate Immune Responses

PML is the organizer of cellular structures termed nuclear domain 10 (ND10) or PML-nuclear bodies (PML-NBs) that act as key mediators of intrinsic immunity against human cytomegalovirus (HCMV) and other viruses. The antiviral function of ND10 is antagonized by viral regulatory proteins such as the immediate early protein IE1 of HCMV. IE1 interacts with PML through its globular core domain (IE1CORE) and induces ND10 disruption in order to initiate lytic HCMV infection. Here, we investigate the consequences of a point mutation (L174P) in IE1CORE, which was shown to abrogate the interaction with PML, for lytic HCMV infection. We found that a recombinant HCMV encoding IE1-L174P displays a severe growth defect similar to that of an IE1 deletion virus. Bioinformatic modeling based on the crystal structure of IE1CORE suggested that insertion of proline into the highly alpha-helical domain severely affects its structural integrity. Consistently, L174P mutation abrogates the functionality of IE1CORE and results in degradation of the IE1 protein during infection. In addition, our data provide evidence that IE1CORE as expressed by a recombinant HCMV encoding IE1 1-382 not only is required to antagonize PML-mediated intrinsic immunity but also affects a recently described function of PML in innate immune signaling. We demonstrate a coregulatory role of PML in type I and type II interferon-induced gene expression and provide evidence that upregulation of interferon-induced genes is inhibited by IE1CORE. In conclusion, our data suggest that targeting PML by viral regulatory proteins represents a strategy to antagonize both intrinsic and innate immune mechanisms.

IMPORTANCE

PML nuclear bodies (PML-NBs), which represent nuclear multiprotein complexes consisting of PML and additional proteins, represent important cellular structures that mediate intrinsic resistance against many viruses, including human cytomegalovirus (HCMV). During HCMV infection, the major immediate early protein IE1 binds to PML via a central globular domain (IE1CORE), and we have shown previously that this is sufficient to antagonize intrinsic immunity. Here, we demonstrate that modification of PML by IE1CORE not only abrogates intrinsic defense mechanisms but also attenuates the interferon response during infection. Our data show that PML plays a novel coregulatory role in type I as well as type II interferon-induced gene expression, which is antagonized by IE1CORE. Importantly, our finding supports the view that targeting of PML-NBs by viral regulatory proteins has evolved as a strategy to inhibit both intrinsic and innate immune defense mechanisms.

The function, regulation and therapeutic implications of the tumor suppressor protein, PML

The tumor suppressor protein, promyelocytic leukemia protein (PML), was originally identified in acute promyelocytic leukemia due to a chromosomal translocation between chromosomes 15 and 17. PML is the core component of subnuclear structures called PML nuclear bodies (PML-NBs), which are disrupted in acute promyelocytic leukemia cells. PML plays important roles in cell cycle regulation, survival and apoptosis, and inactivation or down-regulation of PML is frequently found in cancer cells. More than 120 proteins have been experimentally identified to physically associate with PML, and most of them either transiently or constitutively co-localize with PML-NBs. These interactions are associated with many cellular processes, including cell cycle arrest, apoptosis, senescence, transcriptional regulation, DNA repair and intermediary metabolism. Importantly, PML inactivation in cancer cells can occur at the transcriptional-, translational- or post-translational- levels. However, only a few somatic mutations have been found in cancer cells. A better understanding of its regulation and its role in tumor suppression will provide potential therapeutic opportunities. In this review, we discuss the role of PML in multiple tumor suppression pathways and summarize the players and stimuli that control PML protein expression or subcellular distribution.

Positive role of promyelocytic leukemia protein in type I interferon response and its regulation by human cytomegalovirus

Promyelocytic leukemia protein (PML), a major component of PML nuclear bodies (also known as nuclear domain 10), is involved in diverse cellular processes such as cell proliferation, apoptosis, gene regulation, and DNA damage response. PML also acts as a restriction factor that suppresses incoming viral genomes, therefore playing an important role in intrinsic defense. Here, we show that PML positively regulates type I interferon response by promoting transcription of interferon-stimulated genes (ISGs) and that this regulation by PML is counteracted by human cytomegalovirus (HCMV) IE1 protein. Small hairpin RNA-mediated PML knockdown in human fibroblasts reduced ISG induction by treatment of interferon-β or infection with UV-inactivated HCMV. PML was required for accumulation of activated STAT1 and STAT2, interacted with them and HDAC1 and HDAC2, and was associated with ISG promoters after HCMV infection. During HCMV infection, viral IE1 protein interacted with PML, STAT1, STAT2, and HDACs. Analysis of IE1 mutant viruses revealed that, in addition to the STAT2-binding domain, the PML-binding domain of IE1 was necessary for suppression of interferon-β-mediated ISG transcription, and that IE1 inhibited ISG transcription by sequestering interferon-stimulated gene factor 3 (ISGF3) in a manner requiring its binding of PML and STAT2, but not of HDACs. In conclusion, our results demonstrate that PML participates in type I interferon-induced ISG expression by regulating ISGF3, and that this regulation by PML is counteracted by HCMV IE1, highlighting a widely shared viral strategy targeting PML to evade intrinsic and innate defense mechanisms.

For productive viral infection, virus needs to overcome successive host defenses including intrinsic defense and innate and acquired immunity. Promyelocytic leukemia protein (PML) has been shown to play an important role in intrinsic defense by acting as a nuclear restriction factor that suppresses incoming viral genomes. In this study, we demonstrate that PML also positively regulates type I interferon response by promoting transcription of interferon-stimulated genes (ISGs). Therefore, PML is a key player in both intrinsic and innate host defenses. We further show that this regulation by PML in type I interferon response is inhibited by human cytomegalovirus (HCMV) IE1 protein, which forms a complex with PML, STAT1, STAT2, and HDACs in virus-infected cells. By analyzing mutant viruses, we demonstrate that IE1 inhibits ISG transcription by sequestering interferon-stimulated gene factor 3 (ISGF3) in a manner requiring its binding of PML and STAT2, but not of HDACs. Our findings reveal that PML is a regulator of ISGF3 in type I interferon response and that this PML activity is counteracted by HCMV IE1. Our study explains why PML targeting activity is widely conserved among many viruses.

Cytoplasmic PML: from molecular regulation to biological functions

The tumor suppressor promyelocytic leukemia protein (PML) is predominantly localized in the nucleus, where it is essential for the formation and stabilization of the PML nuclear bodies (PML-NBs). PML-NBs are involved in the regulation of numerous cellular functions, such as tumorigenesis, DNA damage and antiviral responses. Despite its nuclear localization, a small portion of PML has been found in the cytoplasm. A number of studies recently demonstrated that the cytoplasmic PML (cPML) has diverse functions in many cellular processes including tumorigenesis, metabolism, antiviral responses, cell cycle regulation, and laminopothies. In this prospective, we will summarize the current viewpoints on the regulation and biological significance of cPML and discuss the important questions that still need to be further answered.

The acute promyelocytic leukaemia success story: curing leukaemia through targeted therapies

The recent finding that almost all patients with acute promyelocytic leukaemia (APL) may be cured using a combination of retinoic acid (RA) and arsenic trioxide (As(2)O(3)) (N Engl J Med, 369, 2013 and 111) highlights the progress made in our understanding of APL pathogenesis and therapeutic approaches over the past 25 years. The study of APL has revealed many important lessons related to transcriptional control, nuclear organization, epigenetics and the role of proteolysis in biological control. Even more important has been the clinical demonstration that molecularly targeted therapy can eradicate disease.

The genotype of the transporter associated with antigen processing gene affects susceptibility to colorectal cancer in Japanese

OBJECTIVE

Although colorectal cancer (CRC) is one of the most frequent malignancies in Japan, the associated genetic factors remain to be elucidated. Functional loss of the transporter associated with antigen processing (TAP) 1 gene induces carcinogenesis. We investigated whether single nucleotide polymorphisms (SNPs) in the TAP1 gene (rs735883) are associated with susceptibility to CRC in a Japanese population.

METHODS

The study participants were 143 cases and 243 clinical controls. After extracting DNA from their peripheral blood cells, genotyping was conducted by the polymerase chain reaction-restriction fragment length polymorphism method.

RESULTS

Participants with a mutated allele had an increased risk for CRC. The adjusted odds ratios for the C/T, T/T, and the mutation type (C/T + T/T) compared to that of wild type (C/C) were 2.27 [95 % confidence interval (CI), 1.43-3.67], 1.95 (95 % CI, 0.88-4.30), and 2.22 (95 % CI, 1.42-3.55), respectively. Furthermore, a significant trend in the rate of cases was observed with an increasing number of mutated alleles (P for trend = 0.0068).

CONCLUSIONS

The genotype of the TAP1 gene is associated with susceptibility to CRC.

Adoptive cell therapies for glioblastoma

Glioblastoma (GBM) is the most common and most aggressive primary brain malignancy and, as it stands, is virtually incurable. With the current standard of care, maximum feasible surgical resection followed by radical radiotherapy and adjuvant temozolomide, survival rates are at a median of 14.6 months from diagnosis in molecularly unselected patients (1). Collectively, the current knowledge suggests that the continued tumor growth and survival is in part due to failure to mount an effective immune response. While this tolerance is subtended by the tumor being utterly “self,” it is to a great extent due to local and systemic immune compromise mediated by the tumor. Different cell modalities including lymphokine-activated killer cells, natural killer cells, cytotoxic T lymphocytes, and transgenic chimeric antigen receptor or αβ T cell receptor grafted T cells are being explored to recover and or redirect the specificity of the cellular arm of the immune system toward the tumor complex. Promising phase I/II trials of such modalities have shown early indications of potential efficacy while maintaining a favorable toxicity profile. Efficacy will need to be formally tested in phase II/III clinical trials. Given the high morbidity and mortality of GBM, it is imperative to further investigate and possibly integrate such novel cell-based therapies into the current standards-of-care and herein we collectively assess and critique the state-of-the-knowledge pertaining to these efforts.

Effects of the deletion of early region 4 (E4) open reading frame 1 (orf1), orf1-2, orf1-3 and orf1-4 on virus-host cell interaction, transgene expression, and immunogenicity of replicating adenovirus HIV vaccine vectors

The global health burden engendered by human immunodeficiency virus (HIV)-induced acquired immunodeficiency syndrome (AIDS) is a sobering reminder of the pressing need for a preventative vaccine. In non-human primate models replicating adenovirus (Ad)-HIV/SIV recombinant vaccine vectors have been shown to stimulate potent immune responses culminating in protection against challenge exposures. Nonetheless, an increase in the transgene carrying capacity of these Ad vectors, currently limited to approximately 3000 base pairs, would greatly enhance their utility. Using a replicating, E3-deleted Ad type 5 host range mutant (Ad5 hr) encoding full-length single-chain HIVBaLgp120 linked to the D1 and D2 domains of rhesus macaque CD4 (rhFLSC) we systematically deleted the genes encoding early region 4 open reading frame 1 (E4orf1) through E4orf4. All the Ad-rhFLSC vectors produced similar levels of viral progeny. Cell cycle analysis of infected human and monkey cells revealed no differences in virus-host interaction. The parental and E4-deleted viruses expressed comparable levels of the transgene with kinetics similar to Ad late proteins. Similar levels of cellular immune responses and transgene-specific antibodies were elicited in vaccinated mice. However, differences in recognition of Ad proteins and induced antibody subtypes were observed, suggesting that the E4 gene products might modulate antibody responses by as yet unknown mechanisms. In short, we have improved the transgene carrying capacity by one thousand base pairs while preserving the replicability, levels of transgene expression, and immunogenicity critical to these vaccine vectors. This additional space allows for flexibility in vaccine design that could not be obtained with the current vector and as such should facilitate the goal of improving vaccine efficacy. To the best of our knowledge, this is the first report describing the effects of these E4 deletions on transgene expression and immunogenicity in a replicating Ad vector.

Promyelocytic leukaemia protein links DNA damage response and repair to hepatitis B virus-related hepatocarcinogenesis

DNA damage response and repair pathways are important barriers to carcinogenesis. Here, we show that promyelocytic leukaemia (PML, also known as TRIM19), involved in sensing DNA damage and executing homologous recombination repair, is down-regulated in non-tumour liver cells surrounding hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC). No PML mutation or deletion was found in HBV-infected liver or HCC cells. Immunohistochemical analysis of liver biopsies from patients with breast or liver cancer and HBV reactivation after chemotherapy revealed PML up-regulation and HBV exacerbation in normal liver tissue in response to DNA damage (functional PML), PML down-regulation in HCC peritumour cells associated with high HBsAg accumulation and low HBV replication activity (suppressive PML), and heterogeneous nuclear PML expression in HCC cells that lost HBV DNA and HBsAg and were non-reactive to DNA damage (dysregulated PML). Loss of PML in HBsAg-transgenic mice promoted chromosome breaks in liver cells and accelerated the accumulation of body and liver fat and the development of a liver steatosis-dysplasia-adenoma-carcinoma sequence in an inflammation-independent and male-predominant manner, compared to PML knock-out or HBsAg-transgenic mice during the same time period. These results indicate that PML deficiency facilitates genomic instability and promotes HBsAg-related hepatocarcinogenesis, which also involves androgen and lipid metabolism. These findings uncover a novel PML link between HBV-related tumourigenesis, DNA repair, and metabolism.

Local secretion of IL-12 augments the therapeutic impact of dendritic cell-tumor cell fusion vaccination

BACKGROUND

The development of dendritic cell (DC)-tumor fusion vaccines is a promising approach in cancer immunotherapy. Using fusion vaccines allows a broad spectrum of known and unidentified tumor-associated antigens to be presented in the context of MHC class I and class II molecules, with potent co-stimulation provided by the DCs. Although DC-tumor fusion cells are immunogenic, murine studies have shown that effective immunotherapy requires a third signal, which can be provided by exogenous interleukin 12 (IL-12). Unfortunately, systemic administration of IL-12 induces severe toxicity in cancer patients, potentially precluding clinical use of this cytokine to augment fusion vaccine efficacy. To overcome this limitation, we developed a novel approach in which DC-tumor fusion cells locally secrete IL-12, then evaluated the effectiveness of this approach in a murine B16 melanoma model.

MATERIALS AND METHODS

Tumor cells were stably transduced to secrete murine IL-12p70. These tumor cells were then electrofused to DC to form DC-tumor heterokaryons. These cells were used to treat established B16 pulmonary metastases. Enumeration of these metastases was performed and compared between experimental groups using Wilcoxon rank sum test. Interferon γ enzyme-linked immunosorbent spot assay was performed on splenocytes from treated mice.

RESULTS

We show that vaccination with DCs fused to syngeneic melanoma cells that stably express murine IL-12p70 significantly reduces counts of established lung metastases in treated animals when compared with DC-tumor alone (P = 0.029). Interferon γ enzyme-linked immunosorbent spot assays suggest that this antitumor response is mediated by CD4(+) T cells, in the absence of a tumor-specific CD8(+) T cell response, and that the concomitant induction of antitumor CD4(+) and CD8(+) T cell responses required exogenous IL-12.

CONCLUSIONS

This study is, to the best of our knowledge, the first report that investigates the impact of local secretion of IL-12 on antitumor immunity induced by a DC-tumor fusion cell vaccine in a melanoma model and may aid the rational design of future clinical trials.

Coordinated regulation of the immunoproteasome subunits by PML/RARα and PU.1 in acute promyelocytic leukemia

Recognition and elimination of malignant cells by cytotoxic T lymphocytes depends on antigenic peptides generated by proteasomes. It has been established that impairment of the immunoproteasome subunits, that is, PSMB8, PSMB9 and PSMB10 (PSMBs), is critical for malignant cells to escape immune recognition. We report here the regulatory mechanism of the repression of PU.1-dependent activation of PSMBs by PML/RARα in the pathogenesis of acute promyelocytic leukemia (APL) and the unidentified function of all-trans retinoic acid (ATRA) as an immunomodulator in the treatment of APL. Chromatin immunoprecipitation and luciferase reporter assays showed that PU.1 directly bound to and coordinately transactivated the promoters of PSMBs, indicating that PSMBs were transcriptional targets of PU.1 and PU.1 regulated their basal expression. Analysis of expression profiling data from a large population of acute myeloid leukemia (AML) patients revealed that the expression levels of PSMBs were significantly lower in APL patients than in non-APL AML patients. Further evidence demonstrated that the decrease in their expression was achieved through PML/RARα-mediated repression of both PU.1-dependent transactivation and PU.1 expression. Moreover, ATRA but not arsenic trioxide induced the expression of PSMBs in APL cells, indicating that ATRA treatment might activate the antigen-processing/presentation machinery. Finally, the above observations were confirmed in primary APL samples. Collectively, our data demonstrate that PML/RARα suppresses PU.1-dependent activation of the immunosubunits, which may facilitate the escape of APL cells from immune surveillance in leukemia development, and ATRA treatment is able to reactivate their expression, which would promote more efficient T-cell-mediated recognition in the treatment.

Emerging Cellular Functions of Cytoplasmic PML

The tumor suppressor promyelocytic leukemia protein (PML) is located primarily in the nucleus, where it is the scaffold component of the PML nuclear bodies (PML-NBs). PML-NBs regulate multiple cellular functions, such as apoptosis, senescence, DNA damage response, and resistance to viral infection. Despite its nuclear localization, a small portion of PML has been identified in the cytoplasm. The cytoplasmic PML (cPML) could be originally derived from the retention of exported nuclear PML (nPML). In addition, bona fide cPML isoforms devoid of nuclear localization signal (NLS) have also been identified. Recently, emerging evidence showed that cPML performs its specific cellular functions in tumorigenesis, glycolysis, antiviral responses, laminopothies, and cell cycle regulation. In this review, we will summarize the emerging roles of cPML in cellular functions.

Low dose decitabine treatment induces CD80 expression in cancer cells and stimulates tumor specific cytotoxic T lymphocyte responses

Lack of immunogenicity of cancer cells has been considered a major reason for their failure in induction of a tumor specific T cell response. In this paper, we present evidence that decitabine (DAC), a DNA methylation inhibitor that is currently used for the treatment of myelodysplastic syndrome (MDS), acute myeloid leukemia (AML) and other malignant neoplasms, is capable of eliciting an anti-tumor cytotoxic T lymphocyte (CTL) response in mouse EL4 tumor model. C57BL/6 mice with established EL4 tumors were treated with DAC (1.0 mg/kg body weight) once daily for 5 days. We found that DAC treatment resulted in infiltration of IFN-γ producing T lymphocytes into tumors and caused tumor rejection. Depletion of CD8⁺, but not CD4⁺ T cells resumed tumor growth. DAC-induced CTL response appeared to be elicited by the induction of CD80 expression on tumor cells. Epigenetic evidence suggests that DAC induces CD80 expression in EL4 cells via demethylation of CpG dinucleotide sites in the promoter of CD80 gene. In addition, we also showed that a transient, low-dose DAC treatment can induce CD80 gene expression in a variety of human cancer cells. This study provides the first evidence that epigenetic modulation can induce the expression of a major T cell co-stimulatory molecule on cancer cells, which can overcome immune tolerance, and induce an efficient anti-tumor CTL response. The results have important implications in designing DAC-based cancer immunotherapy.

Noncanonical roles of the immune system in eliciting oncogene addiction

Cancer is highly complex. The magnitude of this complexity makes it highly surprising that even the brief suppression of an oncogene can sometimes result in rapid and sustained tumor regression, illustrating that cancers can be 'oncogene addicted' [1-10]. The essential implication is that oncogenes may not only fuel the initiation of tumorigenesis, but in some cases must be excessively activated to maintain a neoplastic state [11]. Oncogene suppression acutely restores normal physiological programs that effectively overrides secondary genetic events and a cancer collapses [12,13]. Oncogene addiction is the description of the dramatic and sustained regression of some cancers upon the specific inactivation of a single oncogene [1-13,14(••),15,16(••)], that can occur through tumor intrinsic [1,2,4,12], but also host immune mechanisms [17-23]. Notably, oncogene inactivation elicits a host immune response that involves specific immune effectors and cytokines that facilitate a remodeling of the tumor microenvironment including the shut down of angiogenesis and the induction of cellular senescence of tumor cells [16(••)]. Hence, immune effectors are not only critically involved in tumor prevention, initiation [17-19], and progression [20], but also appear to be essential to tumor regression upon oncogene inactivation [21,22(••),23(••)]. Understanding how the inactivation of an oncogene elicits a systemic signal in the host that prompts a deconstruction of a tumor could have important implications. The combination of oncogene-targeted therapy together with immunomodulatory therapy may be ideal for the development of both robust tumor intrinsic and immunological responses, effectively leading to sustained tumor regression.

Tumor dormancy, oncogene addiction, cellular senescence, and self-renewal programs

Cancers are frequently addicted to initiating oncogenes that elicit aberrant cellular proliferation, self-renewal, and apoptosis. Restoration of oncogenes to normal physiologic regulation can elicit dramatic reversal of the neoplastic phenotype, including reduced proliferation and increased apoptosis of tumor cells (Science 297(5578):63-64, 2002). In some cases, oncogene inactivation is associated with compete elimination of a tumor. However, in other cases, oncogene inactivation induces a conversion of tumor cells to a dormant state that is associated with cellular differentiation and/or loss of the ability to self-replicate. Importantly, this dormant state is reversible, with tumor cells regaining the ability to self-renew upon oncogene reactivation. Thus, understanding the mechanism of oncogene inactivation-induced dormancy may be crucial for predicting therapeutic outcome of targeted therapy. One important mechanistic insight into tumor dormancy is that oncogene addiction might involve regulation of a decision between self-renewal and cellular senescence. Recent evidence suggests that this decision is regulated by multiple mechanisms that include tumor cell-intrinsic, cell-autonomous mechanisms and host-dependent, tumor cell-non-autonomous programs (Mol Cell 4(2):199-207, 1999; Science 297(5578):102-104, 2002; Nature 431(7012):1112-1117, 2004; Proc Natl Acad Sci U S A 104(32):13028-13033, 2007). In particular, the tumor microenvironment, which is known to be critical during tumor initiation (Cancer Cell 7(5):411-423, 2005; J Clin Invest 121(6):2436-2446, 2011), prevention (Nature 410(6832):1107-1111, 2001), and progression (Cytokine Growth Factor Rev 21(1):3-10, 2010), also appears to dictate when oncogene inactivation elicits the permanent loss of self-renewal through induction of cellular senescence (Nat Rev Clin Oncol 8(3):151-160, 2011; Science 313(5795):1960-1964, 2006; N Engl J Med 351(21):2159-21569, 2004). Thus, oncogene addiction may be best modeled as a consequence of the interplay amongst cell-autonomous and host-dependent programs that define when a therapy will result in tumor dormancy.

Defective DNA damage response and repair in liver cells expressing hepatitis B virus surface antigen

Hepatitis B virus (HBV) is implicated in liver cancer. The aim of this study was to find out whether HBV or its components [HBV surface antigen (HBsAg), HBV core protein (HBc), and HBV X protein (HBx)] could interfere with the host DNA damage response and repair pathway. The full HBV genome or individual HBV open-reading frame (ORF) was introduced into HepG2 cells to examine the effect on host genomic stability, DNA repair efficacy in response to double-strand DNA damage, and DNA damage-induced cell death. Responses to apoptosis induction in the HBV ORF-transfected HepG2 cells were also compared with those in HBV-positive and HBV-negative human hepatocellular carcinoma (HCC) cells. In the absence of HBV replication, accumulation of HBsAg in liver cells without other HBV proteins enhanced DNA repair protein and tumor suppressor promyelocytic leukemia (PML) degradation, which resulted in resistance to apoptosis induction and deficient double-strand DNA repair. However, HBsAg-positive cells exhibited increased cell death with exposure to the poly(ADP-ribose) polymerase inhibitor that blocks single-strand DNA repair. These results indicate that suppression of PML by HBsAg disrupts cellular mechanisms that respond to double-strand DNA damage for DNA repair or apoptosis induction, which may facilitate hepatocarcinogenesis and open up a synthetic lethality strategy for HBsAg-positive HCC treatment.

NK cells are strongly activated by Lassa and Mopeia virus-infected human macrophages in vitro but do not mediate virus suppression

Lassa virus (LASV) and Mopeia virus (MOPV) are closely related Arenaviruses. LASV causes hemorrhagic fever, whereas MOPV is not pathogenic. Both viruses display tropism for APCs such as DCs and macrophages. During viral infections, NK cells are involved in the clearance of infected cells and promote optimal immune responses by interacting with APCs. We used an in vitro model of human NK and APC coculture to study the role of NK cells and to characterize their interactions with APCs during LASV and MOPV infections. As expected, NK cells alone were neither infected nor activated by LASV and MOPV, and infected DCs did not activate NK cells. By contrast, LASV- and MOPV-infected macrophages activated NK cells, as shown by the upregulation of CD69, NKp30, and NKp44, the downregulation of CXCR3, and an increase in NK-cell proliferation. NK cells acquired enhanced cytotoxicity, as illustrated by the increase in granzyme B (GrzB) expression and killing of K562 targets, but did not produce IFN-γ. Contact between NK cells and infected macrophages and type I IFNs were essential for activation; however, NK cells could not kill infected cells and control infection. Overall, these findings show that MOPV- as well as pathogenic LASV-infected macrophages mediate NK-cell activation.

Novel insights into the molecular mechanisms of HLA class I abnormalities

Alterations in the MHC class I surface antigens represent one mechanism of tumor cells to escape from natural or immunotherapy-induced antitumor immune responses. In order to restore MHC class I expression, knowledge about the underlying molecular mechanisms of MHC class I defects in different tumor types is required. In most cases, abnormalities of MHC class I expression are reversible by cytokines suggesting a deregulation rather than structural abnormalities of members of the antigen-processing and presentation machinery (APM). The impaired expression of APM components could be controlled at the epigenetic, transcriptional and/or posttranscriptional level. Furthermore, a direct link between altered transcription factor binding, interferon signal transduction and MHC class I APM component expression has been shown, which might be further associated with cell cycle progression. This information will not only give novel insights into the (patho) physiology of the antigen-processing and presenting pathway, but will help in the future to design effective T cell-based immunotherapies.

Immunology in the clinic review series; focus on cancer: multiple roles for the immune system in oncogene addiction

Despite complex genomic and epigenetic abnormalities, many cancers are irrevocably dependent on an initiating oncogenic lesion whose restoration to a normal physiological activation can elicit a dramatic and sudden reversal of their neoplastic properties. This phenomenon of the reversal of tumorigenesis has been described as oncogene addiction. Oncogene addiction had been thought to occur largely through tumour cell-autonomous mechanisms such as proliferative arrest, apoptosis, differentiation and cellular senescence. However, the immune system plays an integral role in almost every aspect of tumorigenesis, including tumour initiation, prevention and progression as well as the response to therapeutics. Here we highlight more recent evidence suggesting that oncogene addiction may be integrally dependent upon host immune-mediated mechanisms, including specific immune effectors and cytokines that regulate tumour cell senescence and tumour-associated angiogenesis. Hence, the host immune system is essential to oncogene addiction.

The nuclear bodies inside out: PML conquers the cytoplasm

The promyelocytic leukemia (PML) protein is the core component of nuclear substructures that host more than 70 proteins, termed nuclear domains 10 or PML-nuclear bodies. PML was first identified as the gene participating in the translocation responsible for the pathogenesis of acute promyelocytic leukemia (APL). The notion that PML is a tumor suppressor gene was soon extrapolated from leukemia to solid tumors. The last decade has radically changed the view of how this tumor suppressor is regulated, how it can be therapeutically targeted, and how it functions. Notably, one of the most recent and striking features uncovered is how PML regulates cellular homeostasis outside its original niche in the nucleus. These new findings open an exciting new area of research in extra-nuclear PML functions.

Identification of E2F1 as an important transcription factor for the regulation of tapasin expression

HER-2/neu overexpression in tumor cells caused abnormalities of MHC class I surface expression due to impaired expression of components of the antigen-processing machinery (APM) including the low molecular weight proteins, the transporter associated with antigen processing (TAP), and the chaperone tapasin, whereas the expression of MHC class I heavy chain as well as β(2)-microglobulin was only marginally affected. This oncogene-mediated deficient APM component expression could be reverted by interferon-γ treatment, suggesting a deregulation rather than structural alterations as underlying molecular mechanisms. To determine the level of regulation, the transcriptional activity of APM components was analyzed in HER-2/neu(-) and HER-2/neu(+) cells. All major APM components were transcriptionally down-regulated in HER-2/neu(+) when compared with HER-2/neu(-) cells, which was accompanied by a reduced binding of RNA polymerase II to the APM promoters. Site-directed mutagenesis of the p300- and E2F-binding sites in the APM promoters did not reconstitute the oncogene-mediated decreased transcription rate with the exception of tapasin, which was restored in HER-2/neu(+) cells to levels of wild type tapasin promoter activity in HER-2/neu(-) fibroblasts. The E2F-directed control of tapasin expression was further confirmed by chromatin immunoprecipitation analyses showing that E2F1 and p300 bind to the tapasin and APM promoters in both cell lines. Moreover, siRNA-mediated silencing of E2F1 was associated with an increased tapasin expression, whereas transient overexpression of E2F1 launch a reduced tapasin transcription, suggesting that E2F1 is an essential transcription factor for tapasin.

Targeting activation-induced cytidine deaminase overcomes tumor evasion of immunotherapy by CTLs

Activation-induced cytidine deaminase (AID) is an enzyme essential for the generation of Ab diversity in B cells and is considered to be a general gene mutator. In addition, AID expression was also implicated in the pathogenesis of human B cell malignancies and associated with poor prognosis. In this study, we report that small interfering RNA silencing of AID in plasmacytoma dramatically increased its susceptibility to immunotherapy by CTLs. AID silencing did not decrease the mutation frequencies of tumor Ag gene P1A. Gene-array analysis showed dramatically altered expression of a number of genes in AID-silenced plasmacytoma cells, and upregulation of CD200 was shown to be in favor of tumor eradication by CTLs. Taken together, we demonstrate a novel function of AID in tumor evasion of CTL therapy and that targeting AID should be beneficial in the immunotherapy of AID-positive tumors.

Innate and adaptive immune responses to herpes simplex virus

Immune responses against HSV-1 and HSV-2 are complex and involve a delicate interplay between innate signaling pathways and adaptive immune responses. The innate response to HSV involves the induction of type I IFN, whose role in protection against disease is well characterized in vitro and in vivo. Cell types such as NK cells and pDCs contribute to innate anti-HSV responses in vivo. Finally, the adaptive response includes both humoral and cellular components that play important roles in antiviral control and latency. This review summarizes the innate and adaptive effectors that contribute to susceptibility, immune control and pathogenesis of HSV, and highlights the delicate interplay between these two important arms of immunity.

Promyelocytic leukemia nuclear bodies link the DNA damage repair pathway with hepatitis B virus replication: implications for hepatitis B virus exacerbation during chemotherapy and radiotherapy

The mechanism responsible for hepatitis B virus (HBV) exacerbation during chemotherapy and radiotherapy remains unknown. We investigated whether the activation of DNA repair pathways influences HBV replication. The upregulation of the promyelocytic leukemia (PML) protein and its associated PML nuclear body (PML-NB) by chemotherapy and irradiation-induced DNA repair signaling correlated with the upregulation of HBV pregenomic transcription, HBV-core expression, and HBV DNA replication. The HBV-core protein and HBV DNA localized to PML-NBs, where they associated with PML and histone deacetylase 1 (HDAC1). Chemotherapy and radiotherapy affected the interactions between PML, HBV-core, and HDAC1. The enhanced protein-protein interaction between PML and HBV-core inhibited PML-mediated apoptosis and decreased PML-associated HDAC activity. The reversal of HDAC-mediated repression on the HBV covalently closed circular DNA basal core promoter resulted in the amplification of HBV-core and pregenomic expression. These results suggest that PML in PML-NBs links the DNA damage response with HBV replication and may cooperate with HBV-core and HDAC1 on the HBV covalently closed circular DNA basal core promoter to form a positive feedback loop for HBV exacerbation during chemotherapy and radiotherapy.

PML-IV functions as a negative regulator of telomerase by interacting with TERT

Maintaining proper telomere length requires the presence of the telomerase enzyme. Here we show that telomerase reverse transcriptase (TERT), a catalytic component of telomerase, is recruited to promyelocytic leukemia (PML) nuclear bodies through its interaction with PML-IV. Treatment of interferon-alpha (IFNalpha) in H1299 cells resulted in the increase of PML proteins with a concurrent decrease of telomerase activity, as previously reported. PML depletion, however, stimulated telomerase activity that had been inhibited by IFNalpha with no changes in TERT mRNA levels. Upon treatment with IFNalpha, exogenous TERT localized to PML nuclear bodies and binding between TERT and PML increased. Immunoprecipitation and immunofluorescence analyses showed that TERT specifically bound to PML-IV. Residues 553-633 of the C-terminal region of PML-IV were required for its interaction with the TERT region spanning residues 1-350 and 595-946. The expression of PML-IV and its deletion mutant, 553-633, suppressed intrinsic telomerase activity in H1299. TERT-mediated immunoprecipitation of PML or the 553-633 fragment demonstrated that these interactions inhibited telomerase activity. H1299 cell lines stably expressing PML-IV displayed decreased telomerase activity with no change of TERT mRNA levels. Accordingly, telomere length of PML-IV stable cell lines was shortened. These results indicate that PML-IV is a negative regulator of telomerase in the post-translational state.

Telomere-associated proteins: cross-talk between telomere maintenance and telomere-lengthening mechanisms

Telomeres, the ends of eukaryotic chromosomes, have been the subject of intense investigation over the last decade. As telomere dysfunction has been associated with ageing and developing cancer, understanding the exact mechanisms regulating telomere structure and function is essential for the prevention and treatment of human cancers and age-related diseases. The mechanisms by which cells maintain telomere lengthening involve either telomerase or the alternative lengthening of the telomere pathway, although specific mechanisms of the latter and the relationship between the two are as yet unknown. Many cellular factors directly (TRF1/TRF2) and indirectly (shelterin-complex, PinX, Apollo and tankyrase) interact with telomeres, and their interplay influences telomere structure and function. One challenge comes from the observation that many DNA damage response proteins are stably associated with telomeres and contribute to several other aspects of telomere function. This review focuses on the different components involved in telomere maintenance and their role in telomere length homeostasis. Special attention is paid to understanding how these telomere-associated factors, and mainly those involved in double-strand break repair, perform their activities at the telomere ends.

New insights into the role of PML in tumour suppression

The PML gene is involved in the t(15;17) translocation of acute promyelocytic leukaemia (APL), which generates the oncogenic fusion protein PML (promyelocytic leukaemia protein)-retinoic acid receptor alpha. The PML protein localises to a subnuclear structure called the PML nuclear domain (PML-ND), of which PML is the essential structural component. In APL, PML-NDs are disrupted, thus implicating these structures in the pathogenesis of this leukaemia. Unexpectedly, recent studies indicate that PML and the PML-ND play a tumour suppressive role in several different types of human neoplasms in addition to APL. Because of PML's extreme versatility and involvement in multiple cellular pathways, understanding the mechanisms underlying its function, and therefore role in tumour suppression, has been a challenging task. In this review, we attempt to critically appraise the more recent advances in this field and propose new avenues of investigation.

Pondering the puzzle of PML (promyelocytic leukemia) nuclear bodies: can we fit the pieces together using an RNA regulon?

The promyelocytic leukemia protein PML and its associated nuclear bodies are hot topics of investigation. This interest arises for multiple reasons including the tight link between the integrity of PML nuclear bodies and several disease states and the impact of the PML protein and PML nuclear bodies on proliferation, apoptosis and viral infection. Unfortunately, an understanding of the molecular underpinnings of PML nuclear body function remains elusive. Here, a general overview of the PML field is provided and is extended to discuss whether some of the basic tenets of "PML-ology" are still valid. For instance, recent findings suggest that some components of PML nuclear bodies form bodies in the absence of the PML protein. Also, a new model for PML nuclear body function is proposed which provides a unifying framework for its effects on diverse biochemical pathways such as Akt signaling and the p53-Mdm2 axis. In this model, the PML protein acts as an inhibitor of gene expression post-transcriptionally via inhibiting a network node in the eIF4E RNA regulon. An example is given for how the PML RNA regulon model provided the basis for the development of a new anti-cancer strategy being tested in the clinic.

A role for cytoplasmic PML in cellular resistance to viral infection

PML gene was discovered as a fusion partner with retinoic acid receptor (RAR) α in the t(15:17) chromosomal translocation associated with acute promyelocytic leukemia (APL). Nuclear PML protein has been implicated in cell growth, tumor suppression, apoptosis, transcriptional regulation, chromatin remodeling, DNA repair, and anti-viral defense. The localization pattern of promyelocytic leukemia (PML) protein is drastically altered during viral infection. This alteration is traditionally viewed as a viral strategy to promote viral replication. Although multiple PML splice variants exist, we demonstrate that the ratio of a subset of cytoplasmic PML isoforms lacking exons 5 & 6 is enriched in cells exposed to herpes simplex virus-1 (HSV-1). In particular, we demonstrate that a PML isoform lacking exons 5 & 6, called PML Ib, mediates the intrinsic cellular defense against HSV-1 via the cytoplasmic sequestration of the infected cell protein (ICP) 0 of HSV-1. The results herein highlight the importance of cytoplasmic PML and call for an alternative, although not necessarily exclusive, interpretation regarding the redistribution of PML that is seen in virally infected cells.

Functionally important interactions between the nucleotide-binding domains of an antigenic peptide transporter

The transporter associated with antigen processing (TAP), an ABC transporter, pumps cytosolic peptides into the endoplasmic reticulum, where the peptides are loaded onto class I MHC molecules for presentation to the immune system. Transport is fueled by the binding of ATP to two cytosolic nucleotide-binding domains (NBDs) and ATP hydrolysis. We demonstrate biochemically that there are two electrostatic interactions across the interface between the two TAP NBDs and that these interactions are important for peptide transport. Notably, disrupting these interactions by mutagenesis does not greatly alter the ATP hydrolysis rate in an isolated NBD model system, suggesting that the interactions function at alternative stages in the transport cycle. The data support the general model for ABC transporters in which the NBDs form a tight, closed conformation during transport. Our results are discussed in relation to other ABC transporters that do or do not conserve potential interacting residues of opposite charges at the homologous positions.

Enhanced expression of interferon-gamma-induced antigen-processing machinery components in a spontaneously occurring cancer

In human tumors, changes in the surface expression and/or function of major histocompatibility complex (MHC) class I antigens are frequently found and may provide malignant cells with a mechanism to escape control of the immune system. This altered human lymphocyte antigen (HLA) class I phenotype can be caused by either structural alterations or dysregulation of genes encoding subunits of HLA class I antigens and/or components of the MHC class I antigen-processing machinery (APM). Herein we analyze the expression of several proteins involved in the generation of MHC class I epitopes in feline injection site sarcoma, a spontaneously occurring tumor in cats that is an informative model for the study of tumor biology in other species, including humans. Eighteen surgically removed primary fibrosarcoma lesions were analyzed, and an enhanced expression of two catalytic subunits of immunoproteasomes, PA28 and leucine aminopeptidase, was found in tumors compared to matched normal tissues. As a functional counterpart of these changes in protein levels, proteasomal activities were increased in tissue extracts from fibrosarcomas. Taken together, these results suggest that alterations in the APM system may account for reduced processing of selected tumor antigens and may potentially provide neoplastic fibroblasts with a mechanism for escape from T-cell recognition and destruction.

Different lineages of P1A-expressing cancer cells use divergent modes of immune evasion for T-cell adoptive therapy

Tumor evasion of T-cell immunity remains a significant obstacle to adoptive T-cell therapy. It is unknown whether the mode of immune evasion is dictated by the cancer cells or by the tumor antigens. Taking advantage of the fact that multiple lineages of tumor cells share the tumor antigen P1A, we adoptively transferred transgenic T cells specific for P1A (P1CTL) into mice with established P1A-expressing tumors, including mastocytoma P815, plasmocytoma J558, and fibrosarcoma Meth A. Although P1CTL conferred partial protection, tumors recurred in almost all mice. Analysis of the status of the tumor antigen revealed that all J558 tumors underwent antigenic drift whereas all P815 tumors experienced antigenic loss. Interestingly, although Meth A cells are capable of both antigenic loss and antigenic drift, the majority of recurrent Meth A tumors retained P1A antigen. The ability of Meth A to induce apoptosis of P1CTL in vivo alleviated the need for antigenic drift and antigenic loss. Our data showed that, in spite of their shared tumor antigen, different lineages of cancer cells use different mechanisms to evade T-cell therapy.

Concordant expression of proto-oncogene promyelocytic leukemia and major histocompatibility antigen HLA class I in human hepatocellular carcinoma

Many malignant cancer cells downregulate human leukocyte antigen (HLA) class I antigen expression to evade T cell recognition. However, hepatocellular carcinoma (HCC) is exceptional to the general findings in cancer cells, and the mechanisms for its upregulation remain unclear. It has been reported that promyelocytic leukemia (PML) proto-oncogene controls the transcription of multiple class I antigen presentation genes in murine cancer cells. To find out the functional role of PML gene on the increased HLA class I antigen expression in HCC cells, we analyzed the expression of proto-oncogene PML and multiple class I antigen presentation genes in HCC specimens obtained in China. The results showed concordant changes of proto-oncogene PML and cell surface HLA-A expression in 44 paraffin-embedded HCC tissues. Furthermore, co-upregulated expression of PML genes and class I antigen presentation genes could be detected in 9 of 15 fresh HCC tissues by reverse transcription polymerase chain reaction (RT-PCR). In addition, studies using HCC cell lines showed that increased expression of HLA class I molecules paralleled with PML upregulation were detected in QGY-7701 HCC cell line with RT-PCR, western blot, and flow cytometry, and that the overexpression of exogenous PML in a low-expression class I cell line BEL-7405 could induce the expression of multiple class I antigen-presenting molecule genes and slightly but significantly increase the expression of cell surface HLA class I molecules. In conclusion, the expression of proto-oncogene PML and HLA class I molecules were concordantly upregulated and the expression of PML gene might be one of the mechanisms that leads to the increased expression of class I antigen in HCC.

Physiological deterioration associated with breeding in female mice: a model for the study of senescence and aging

Longevity is a complex and dynamic process influenced by a diversity of factors. Amongst other, gestation and lactation contribute to organismal decline because they represent a great energetic investment in mammals. Here we compared the rate of senescence onset observed in primary fibroblast obtained from the lungs of retired female breeder mice (12 months old), with the senescence arrival observed in fibroblasts derived from age-matched nulliparous mice. Two-month-old animals were also used as controls of young, fully-developed adults. Cell proliferation, DNA synthesis, and expression of senescence-associated beta-galactosidase activity were evaluated as senescent parameters. In order to test differences in energetic competence at a systemic level, mitochondrial respiration was also evaluated in mitochondria isolated from the livers of the same animals used for the primary cultures. Our data indicated that the cells derived from female mice subjected to the physiological stress of breeding onset into replicative senescence prior than the cells from female mice age-matched without that particular stress. Thus validating the use of retired breeders as a model to study aging and senescence at the cellular level.

Induction of promyelocytic leukemia (PML) oncogenic domains (PODs) by papillomavirus

Promyelocytic leukemia oncogenic domains (PODs), also called nuclear domain 10 (ND10), are subnuclear structures that have been implicated in a variety of cellular processes as well as the life cycle of DNA viruses including papillomaviruses. In order to investigate the interplay between papillomaviruses and PODs, we analyzed the status of PODs in organotypic raft cultures of human keratinocytes harboring HPV genome that support the differentiation-dependent HPV life cycle. The number of PODs per nucleus was increased in the presence of HPV genomes selectively within the poorly differentiated layers but was absent in the terminally differentiated layers of the stratified epithelium. This increase in PODs was correlated with an increase in abundance of post-translationally modified PML protein. Neither the E2-dependent transcription nor viral DNA replication was reliant upon the presence of PML. Implications of these findings in terms of HPV's interaction with its host are discussed.

Functional interaction between PML and SATB1 regulates chromatin-loop architecture and transcription of the MHC class I locus

The function of the subnuclear structure the promyelocytic leukaemia (PML) body is unclear largely because of the functional heterogeneity of its constituents. Here, we provide the evidence for a direct link between PML, higher-order chromatin organization and gene regulation. We show that PML physically and functionally interacts with the matrix attachment region (MAR)-binding protein, special AT-rich sequence binding protein 1 (SATB1) to organize the major histocompatibility complex (MHC) class I locus into distinct higher-order chromatin-loop structures. Interferon gamma (IFNgamma) treatment and silencing of either SATB1 or PML dynamically alter chromatin architecture, thus affecting the expression profile of a subset of MHC class I genes. Our studies identify PML and SATB1 as a regulatory complex that governs transcription by orchestrating dynamic chromatin-loop architecture.

Transcriptional regulation is affected by subnuclear targeting of reporter plasmids to PML nuclear bodies

Whereas the PML protein has been reported to have both transcriptional coactivator and corepressor potential, the contribution of the PML nuclear body (PML NB) itself to transcriptional regulation is not well understood. Here we demonstrate that plasmid DNA artificially tethered to PML or the PML NB-targeting domain of Sp100 is preferentially localized to PML NBs. Using the tethering technique, we targeted a simian virus 40 promoter-driven luciferase reporter plasmid to PML NBs, resulting in the repression of the transgene transcriptional activity. Conversely, the tethering of a cytomegalovirus promoter-containing reporter plasmid resulted in activation. Targeting a minimal eukaryotic promoter did not affect its activity. The expression of targeted promoters could be modulated by altering the cellular concentration of PML NB components, including Sp100 and isoforms of the PML protein. Finally, we demonstrate that ICP0, the promiscuous herpes simplex virus transactivator, increases the level of transcriptional activation of plasmid DNA tethered to the PML NB. We conclude that when PML NB components are artificially tethered to reporter plasmids, the PML NB contributes to the regulation of the tethered DNA in a promoter-dependent manner. Our findings demonstrate that transient transcription assays are sensitive to the subnuclear localization of the transgene plasmid.

Cytoplasmic function of mutant promyelocytic leukemia (PML) and PML-retinoic acid receptor-alpha

The promyelocytic leukemia (PML) tumor suppressor of acute promyelocytic leukemia (APL) regulates major apoptotic and growth-suppressive pathways. In APL, PML is involved in a chromosomal translocation generating the PML-retinoic acid receptor-alpha (RARalpha) fusion protein. Two missense mutations in the remaining PML alleles have been identified, which give rise to a truncated cytoplasmic PML protein (Mut PML). APL patients carrying these mutations display resistance to retinoic acid (RA) and very poor prognosis. Here we show that Mut PML associates with the cytoplasmic regions we refer to as PML-cytoplasmic bodies (PML-CBs). Mut PML interacts with PML-RARalpha in PML-CB and potentiates PML-RARalpha-mediated inhibition of RA-dependent transcription. Remarkably, Mut PML stabilizes PML-RARalpha and inhibits differentiation induced by pharmacological doses of RA. A mutant form of PML-RARalpha that accumulates in the cytoplasm inhibits RA-dependent transcription and differentiation, thus suggesting that cytoplasmic localization of PML-RARalpha may contribute to transformation. Finally, we show that the bcr3 PML-RARalpha form is predominantly cytoplasmic and accumulates in PML-CBs. Taken together, these findings reveal novel insights into the molecular mechanisms contributing to APL.

Innate NKT lymphocytes confer superior adaptive immunity via tumor-capturing dendritic cells

If irradiated tumor cells could be rendered immunogenic, they would provide a safe, broad, and patient-specific array of antigens for immunotherapies. Prior approaches have emphasized genetic transduction of live tumor cells to express cytokines, costimulators, and surrogate foreign antigens. We asked if immunity could be achieved by delivering irradiated, major histocompatibility complex–negative plasmacytoma cells to maturing mouse dendritic cells (DCs) within lymphoid organs. Tumor cells injected intravenously (i.v.) were captured by splenic DCs, whereas subcutaneous (s.c.) injection led only to weak uptake in lymph node or spleen. The natural killer T (NKT) cells mobilizing glycolipid α-galactosyl ceramide, used to mature splenic DCs, served as an effective adjuvant to induce protective immunity. This adjuvant function was mimicked by a combination of poly IC and agonistic αCD40 antibody. The adjuvant glycolipid had to be coadministered with tumor cells i.v. rather than s.c. Specific resistance was generated both to a plasmacytoma and lymphoma. The resistance afforded by a single vaccination lasted >2 mo and required both CD4⁺ and CD8⁺ T cells. Mature tumor capturing DCs stimulated the differentiation of P1A tumor antigen-specific, CD8⁺ T cells and uniquely transferred tumor resistance to naive mice. Therefore, the access of dying tumor cells to DCs that are maturing to activated NKT cells efficiently induces long-lived adaptive resistance.

Functional interactions between the Epstein-Barr virus BZLF1 protein and the promyelocytic leukemia protein

The Epstein-Barr virus immediate-early protein BZLF1 (Z) has been shown to alter the cellular localization of the promyelocytic leukemia (PML) protein. PML has important implications for growth control, apoptosis, anti-viral effects and many more processes. Here we further examined the relationship between PML and the Epstein-Barr virus Z protein. We examined the effect of Z expression on PML protein levels, and the effect of increased PML protein levels on Z-mediated dispersion of PML bodies. We found that increased levels of PML protein, such as through interferon treatment, were able to suppress Z-mediated PML body dispersion. We also studied the consequences of PML dispersion by Z, by examining p21 transactivation, A20 transactivation, and MHC Class I presentation levels in Z-expressing cells. We found that, while Z-mediated dispersion of PML did not affect MHC Class I presentation, it did alter p21 and A20 expression. In addition, we found that increased levels of PML were able to prevent Z protein binding to mitotic chromosomes. Our work implies that the balance of PML and Z levels in cells may affect how each protein functions.

A Rare Transporter Associated with Antigen Processing Polymorphism Overpresented in HLAlow Colon Cancer Reveals the Functional Significance of the Signature Domain in Antigen Processing

Transporter associated with antigen processing (TAP), a member of the ATP-binding cassette transporter superfamily, is composed of two integral membrane proteins, TAP-1 and TAP-2. Each subunit has a C-terminal nucleotide-binding domain that binds and hydrolyzes ATP to energize peptide translocation across the endoplasmic reticulum membrane. A motif comprising the sequence LSGGQ (called the signature motif) and the amino acid that is immediately C-terminal to this motif are highly conserved in the nucleotide-binding domains of ATP-binding cassette transporters. To search for natural variants of TAP-1 with alterations in or near the signature motif, we sequenced the TAP-1 exon 10 amplified from 103 human colon cancer samples. We found a rare TAP-1 allele with an R>Q alteration at a residue immediately C-terminal to the signature motif (R648) that occurred 17.5 times more frequently in colon cancers with down-regulated surface class I MHC than those with normal MHC levels (P = 0.01). Functional analysis revealed that the Q648 variant had significantly reduced peptide translocation activity compared with TAP-1 (R648). In addition, we found that mutations S644R, G645R, G646S, and G646D interfered with TAP-1 activity. TAP-1 G646D, which showed the most severe defect, resided normally in the endoplasmic reticulum and associated with the peptide loading complex, but failed to transport peptide across the endoplasmic reticulum membrane. Thus, a TAP-1 polymorphism adjacent to the signature motif may be a contributing factor for MHC class I down-regulation in colon cancer. Given the widespread defects in DNA mismatch repair in colon cancer, mutations at or near the signature domain can potentially modulate antigen processing.