Proteinase inhibitor 9, an inhibitor of granzyme B-mediated apoptosis, is a primary estrogen-inducible gene in human liver cells

The biological function of Serpinb9 and Serpinb9-based therapy

Recent breakthroughs in discovering novel immune signaling pathways have revolutionized different disease treatments. SERPINB9 (Sb9), also known as Proteinase Inhibitor 9 (PI-9), is a well-known endogenous inhibitor of Granzyme B (GzmB). GzmB is a potent cytotoxic molecule secreted by cytotoxic T lymphocytes and natural killer cells, which plays a crucial role in inducing apoptosis in target cells during immune responses. Sb9 acts as a protective mechanism against the potentially harmful effects of GzmB within the cells of the immune system itself. On the other hand, overexpression of Sb9 is an important mechanism of immune evasion in diseases like cancers and viral infections. The intricate functions of Sb9 in different cell types represent a fine-tuned regulatory mechanism for preventing immunopathology, protection against autoimmune diseases, and the regulation of cell death, all of which are essential for maintaining health and responding effectively to disease challenges. Dysregulation of the Sb9 will disrupt human normal physiological condition, potentially leading to a range of diseases, including cancers, inflammatory conditions, viral infections or other pathological disorders. Deepening our understanding of the role of Sb9 will aid in the discovery of innovative and effective treatments for various medical conditions. Therefore, the objective of this review is to consolidate current knowledge regarding the biological role of Sb9. It aims to offer insights into its discovery, structure, functions, distribution, its association with various diseases, and the potential of nanoparticle-based therapies targeting Sb9.

Signaling by Type I Interferons in Immune Cells: Disease Consequences

This review addresses interferon (IFN) signaling in immune cells and the tumor microenvironment (TME) and examines how this affects cancer progression. The data reveal that IFNs exert dual roles in cancers, dependent on the TME, exhibiting both anti-tumor activity and promoting cancer progression. We discuss the abnormal IFN signaling induced by cancerous cells that alters immune responses to permit their survival and proliferation.

Hormone Receptor Signaling and Breast Cancer Resistance to Anti-Tumor Immunity

Breast cancers regroup many heterogeneous diseases unevenly responding to currently available therapies. Approximately 70-80% of breast cancers express hormone (estrogen or progesterone) receptors. Patients with these hormone-dependent breast malignancies benefit from therapies targeting endocrine pathways. Nevertheless, metastatic disease remains a major challenge despite available treatments, and relapses frequently ensue. By improving patient survival and quality of life, cancer immunotherapies have sparked considerable enthusiasm and hope in the last decade but have led to only limited success in breast cancers. In addition, only patients with hormone-independent breast cancers seem to benefit from these immune-based approaches. The present review examines and discusses the current literature related to the role of hormone receptor signaling (specifically, an estrogen receptor) and the impact of its modulation on the sensitivity of breast cancer cells to the effector mechanisms of anti-tumor immune responses and on the capability of breast cancers to escape from protective anti-cancer immunity. Future research prospects related to the possibility of promoting the efficacy of immune-based interventions using hormone therapy agents are considered.

Sexual dimorphism and the role of estrogen in the immune microenvironment of liver metastases

Liver metastases (LM) remain a major cause of cancer-associated death and a clinical challenge. Here we explore a sexual dimorphism observed in the regulation of the tumor immune microenvironment (TIME) of LM, wherein the accumulation of myeloid-derived suppressor cells (MDSC) and regulatory T cells in colon and lung carcinoma LM is TNFR2-dependent in female, but not in male mice. In ovariectomized mice, a marked reduction is observed in colorectal, lung and pancreatic carcinoma LM that is reversible by estradiol reconstitution. This is associated with reduced liver MDSC accumulation, increased interferon-gamma (IFN-γ) and granzyme B production in CD8+ T cells and reduced TNFR2, IDO2, TDO and Serpin B9 expression levels. Treatment with tamoxifen increases liver cytotoxic T cell accumulation and reduces colon cancer LM. The results identify estrogen as a regulator of a pro-metastatic immune microenvironment in the liver and a potential target in the management of liver metastatic disease.

Type I IFN protects cancer cells from CD8+ T cell-mediated cytotoxicity after radiation

Treatment of tumors with ionizing radiation stimulates an antitumor immune response partly dependent on induction of IFNs. These IFNs directly enhance dendritic cell and CD8+ T cell activity. Here we show that resistance to an effective antitumor immune response is also a result of IFN signaling in a different cellular compartment of the tumor, the cancer cells themselves. We abolished type I IFN signaling in cancer cells by genetic elimination of its receptor, IFNAR1. Pronounced immune responses were provoked after ionizing radiation of tumors from 4 mouse cancer cell lines with Ifnar1 knockout. This enhanced response depended on CD8+ T cells and was mediated by enhanced susceptibility to T cell-mediated killing. Induction of Serpinb9 proved to be the mechanism underlying control of susceptibility to T cell killing after radiation. Ifnar1-deficient tumors had an augmented response to anti-PD-L1 immunotherapy with or without radiation. We conclude that type I IFN can protect cancer cells from T cell-mediated cytotoxicity through regulation of Serpinb9. This result helps explain why radiation of tumors can stimulate antitumor immunity yet also result in resistance. It further suggests potential targets for intervention to improve therapy and to predict responses.

Interaction of host immunity with HER2-targeted treatment and tumor heterogeneity in HER2-positive breast cancer

Growing evidence suggests a clear role of the host immune system in HER2+ breast cancer. In addition, HER2+ breast cancer is generally considered more immunogenic than hormone receptor-positive (HR+)/HER2-, and specific molecular HER2+ subgroups (e.g. HER2-enriched disease) are more immunogenic than others (e.g. Luminal A or B). From a clinical perspective, the immune system plays a relevant prognostic role in HER2+ breast cancer and contributes to the therapeutic effects of trastuzumab. However, as more HER2-targeted agents become available, a better understanding of the role played by the immune system in modulating therapy response to different agents will be needed. Furthermore, the recent introduction in oncology of immune checkpoint inhibitors capable of unleashing anti-tumor immune response opens new possibilities for therapeutic combinations in HER2+ breast cancer. Here, we review the current pre-clinical and clinical data on the interplay between the immune system and HER2+ breast cancer, focusing on different HER2-targeted treatments and the biological heterogeneity that exists within HER2+ disease. Finally, we discuss new therapeutic approaches exploiting the immune system to increase activity or revert resistance to HER2-targeted agents.

Estrogen matters in metastasis

Metastatic cancer cells meet several physical, biochemical and immunological barriers before colonizing a new territory. Cancerous cells turn invasive, mobile and eventually disengage from their native niche. This is followed by their intravasation, extravasation, survival, proliferation, and colonization into distant organs. Unlike well-confined tumors, which respond favorably to anti-cancer therapeutics, metastatic tumors are life-threatening and incurable. More than 90% of cancer-related mortality is caused by metastases, hence the emphasis is now on developing the strategies to block or reverse the process of metastasis. This has ensued intensive research with a focus on the mechanisms underlying metastasis. Substantial work carried out in this direction has led to the identification of specific enzymes, proteins, cytokines, chemokines, growth factors, exosomes, miRNA and lipids, etc. as the facilitators of metastasis. Metastatic cells are exposed to a diverse array of local and systemic signals. Among these, estrogens are of great relevance. Estrogens have been strongly linked to cancers, especially of breast and uterine origin. Recent data hint that estrogens, well recognized for their role in proliferation, may have a role in metastasis also. It is proposed that influence of estrogen on metastasis may be independent of its proliferation-inducing ability. Data are emerging to suggest that estrogens have potential to modulate various events of the metastatic cascade such as local invasion, intravasation, anoikis, immune evasion, extravasation, angiogenesis and metastatic colonization. This review summarizes some of the recent advances in our knowledge on the role of estrogens in the metastatic cascade of cancerous cells.

The F domain of estrogen receptor α is involved in species-specific, tamoxifen-mediated transactivation

Estrogen receptor α (ERα) is a major transducer of estrogen-mediated physiological signals. ERα is a member of the nuclear receptor superfamily, which encompasses ligand-dependent transcription factors. The C terminus of nuclear receptors, termed the F domain, is the least homologous region among the members of this family. The ERα F domain possesses 45 amino acids; however, its function remains unclear. We noticed that the homology of the F domains between mouse and human ERαs is remarkably lower (75.6% similarity) than that between the entire proteins (94.7% similarity). To assess the functionality of the ERα F domains, here we generated chimeric ERα expression constructs with mouse-human-exchanged F domains. Using cell-based in vitro assays, we analyzed the transcriptional coactivator interaction and ligand-binding domain dimerization activities of these mouse-human F domain-swapped ERαs. We found that the transcriptional activity of the mouse WT ERα is more potent than that of the human WT ERα in the human hepatoma cell line HepG2. 4-Hydroxytamoxifen (4OHT)-mediated transcriptional activity of mouse-human F domain-swapped ERαs was the inverse of the WT ERα activities but not estradiol-mediated transcriptional activities. Further experiments with constructs containing deletion or point mutations of a predicted β-strand region within the F domain suggested that this region governs the species-specific 4OHT-mediated transcriptional activity of ERα. We conclude that the ERα F domain has a species-specific function in 4OHT-mediated receptor transactivation and that mouse-human F domain-swapped ERα mutants enable key insights into ERα F domain structure and function.

Interplay between Natural Killer Cells and Anti-HER2 Antibodies: Perspectives for Breast Cancer Immunotherapy

Overexpression of the human epidermal growth factor receptor 2 (HER2) defines a subgroup of breast tumors with aggressive behavior. The addition of HER2-targeted antibodies (i.e., trastuzumab, pertuzumab) to chemotherapy significantly improves relapse-free and overall survival in patients with early-stage and advanced disease. Nonetheless, considerable proportions of patients develop resistance to treatment, highlighting the need for additional and co-adjuvant therapeutic strategies. HER2-specific antibodies can trigger natural killer (NK) cell-mediated antibody-dependent cellular cytotoxicity and indirectly enhance the development of tumor-specific T cell immunity; both mechanisms contributing to their antitumor efficacy in preclinical models. Antibody-dependent NK cell activation results in the release of cytotoxic granules as well as the secretion of pro-inflammatory cytokines (i.e., IFNγ and TNFα) and chemokines. Hence, NK cell tumor suppressive functions include direct cytolytic killing of tumor cells as well as the regulation of subsequent antitumor adaptive immunity. Albeit tumors with gene expression signatures associated to the presence of cytotoxic lymphocyte infiltrates benefit from trastuzumab-based treatment, NK cell-related biomarkers of response/resistance to HER2-specific therapeutic antibodies in breast cancer patients remain elusive. Several variables, including (i) the configuration of the patient NK cell repertoire; (ii) tumor molecular features (i.e., estrogen receptor expression); (iii) concomitant therapeutic regimens (i.e., chemotherapeutic agents, tyrosine kinase inhibitors); and (iv) evasion mechanisms developed by progressive breast tumors, have been shown to quantitatively and qualitatively influence antibody-triggered NK cell responses. In this review, we discuss possible interventions for restoring/enhancing the therapeutic activity of HER2 therapeutic antibodies by harnessing NK cell antitumor potential through combinatorial approaches, including immune checkpoint blocking/stimulatory antibodies, cytokines and toll-like receptor agonists.

Administration of 17β-Estradiol Improves Motoneuron Survival and Down-regulates Inflammasome Activation in Male SOD1(G93A) ALS Mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease manifested by the progressive loss of upper and lower motoneurons. The pathomechanism of ALS is complex and not yet fully understood. Neuroinflammation is believed to significantly contribute to disease progression. Inflammasome activation was recently shown in the spinal cord of human sporadic ALS patients and in the SOD1(G93A) mouse model for ALS. In the present study, we investigated the neuroprotective and anti-inflammatory effects of 17β-estradiol (E2) treatment in pre-symptomatic and symptomatic male SOD1(G93A) mice. Symptomatic mice with E2 substitution exhibited improved motor performance correlating with an increased survival of motoneurons in the lumbar spinal cord. Expression of NLRP3 inflammasome proteins and levels of activated caspase 1 and mature interleukin 1 beta were significantly reduced in SOD1(G93A) mice supplemented with E2.

Estrogen receptor-α and aryl hydrocarbon receptor involvement in the actions of botanical estrogens in target cells

Botanical estrogen (BE) dietary supplements are consumed by women as substitutes for loss of endogenous estrogens at menopause. To examine the roles of estrogen receptor α (ERα) and aryl hydrocarbon receptor (AhR) and their crosstalk in the actions of BEs, we studied gene regulation and proliferation responses to four widely used BEs, genistein, daidzein, and S-equol from soy, and liquiritigen from licorice root in breast cancer and liver cells. BEs and estradiol (E2), acting through ERα, stimulated proliferation, ERα chromatin binding and target-gene expression. BEs but not E2, acting through AhR, bound to xenobiotic response element-containing chromatin sites and enhanced AhR target-gene expression (CYP1A1, CYP1B1). While E2 and TCDD acted quite selectively through their respective receptors, BEs acted via both receptors, with their AhR activity moderated by negative crosstalk through ERα. Both ERα and AhR should be considered as mediators of the biology and pharmacology of BEs.

Licorice root components in dietary supplements are selective estrogen receptor modulators with a spectrum of estrogenic and anti-estrogenic activities

Licorice root extracts are often consumed as botanical dietary supplements by menopausal women as a natural alternative to pharmaceutical hormone replacement therapy. In addition to their components liquiritigenin (Liq) and isoliquiritigenin (Iso-Liq), known to have estrogenic activity, licorice root extracts also contain a number of other flavonoids, isoflavonoids, and chalcones. We have investigated the estrogenic activity of 7 of these components, obtained from an extract of Glycyrrhiza glabra powder, namely Glabridin (L1), Calycosin (L2), Methoxychalcone (L3), Vestitol (L4), Glyasperin C (L5), Glycycoumarin (L6), and Glicoricone (L7), and compared them with Liq, Iso-Liq, and estradiol (E2). All components, including Liq and Iso-Liq, have low binding affinity for estrogen receptors (ERs). Their potency and efficacy in stimulating the expression of estrogen-regulated genes reveal that Liq and Iso-Liq and L2, L3, L4, and L6 are estrogen agonists. Interestingly, L3 and L4 have an efficacy nearly equivalent to E2 but with a potency ca. 10,000-fold less. The other components, L1, L5 and L7, acted as partial estrogen antagonists. All agonist activities were reversed by the antiestrogen, ICI 182,780, or by knockdown of ERα with siRNA, indicating that they are ER dependent. In HepG2 hepatoma cells stably expressing ERα, only Liq, Iso-Liq, and L3 stimulated estrogen-regulated gene expression, and in all cases gene stimulation did not occur in HepG2 cells lacking ERα. Collectively, these findings classify the components of licorice root extracts as low potency, mixed ER agonists and antagonists, having a character akin to that of selective estrogen receptor modulators or SERMs.

Dioxin and estrogen signaling in lung adenocarcinoma cells with different aryl hydrocarbon receptor/estrogen receptor α phenotypes

Evidence suggests that estrogen affects the pulmonary response to carcinogenic pollutants, such as dioxins. In this study, we examined dioxin and estrogen signaling cross-talk in lung adenocarcinoma cell lines that were engineered to exhibit different aryl hydrocarbon receptor (AhR)/estrogen receptor (ER) α phenotypes. Data showed that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) weakly antagonized estrogen-activated ERα activity in cells expressing abundant ERα, but little AhR. Increase of AhR expression or presence of a dioxin-responsive element in proximity silenced the antiestrogenic effect of TCDD. AhR was bound to dioxin-responsive element and transcriptionally active in both TCDD-untreated and -treated lung adenocarcinoma cells. 17β-estradiol (E2) reduced basal and TCDD-induced AhR activity only in ERα-positive cells. AhR and ERα exhibited a protein-protein interaction in the presence of E2. Cotreatment with TCDD moderated this protein interaction. Colocalization of ERα and AhR at the estrogen-responsive site under E2 and TCDD/E2 treatments implied that E2 ∣ ERα might hijack AhR away from the dioxin-responsive site. Increasing the relative expression of AhR to ERα counteracted inhibition of AhR activity by E2 ∣ ERα. When AhR and ERα were both highly expressed, TCDD and E2 up-regulated expression of dual-responsive genes cytochrome P450 (CYP) 1A1 and CYP1B1 in a cumulative manner, increasing the danger of metabolic activation of carcinogens. Whereas TCDD ∣ AhR and E2 ∣ ERα appeared to regulate CYP1B1 separately through their binding sites, E2 ∣ ERα increased the TCDD responsiveness and mRNA expression of CYP1A1 in a noncanonical way. In conclusion, AhR/ERα expression pattern, estrogen level, and promoter context determine the genomic action of dioxin in lung adenocarcinoma cells.

The immune system and inflammation in breast cancer

During different stages of tumor development the immune system can either identify and destroy tumors, or promote their growth. Therapies targeting the immune system have emerged as a promising treatment modality for breast cancer, and immunotherapeutic strategies are being examined in preclinical and clinical models. However, our understanding of the complex interplay between cells of the immune system and breast cancer cells is incomplete. In this article, we review recent findings showing how the immune system plays dual host-protective and tumor-promoting roles in breast cancer initiation and progression. We then discuss estrogen receptor α (ERα)-dependent and ERα-independent mechanisms that shield breast cancers from immunosurveillance and enable breast cancer cells to evade immune cell induced apoptosis and produce an immunosuppressive tumor microenvironment. Finally, we discuss protumorigenic inflammation that is induced during tumor progression and therapy, and how inflammation promotes more aggressive phenotypes in ERα positive breast cancers.

Decreased Expression of Protease Inhibitor 9, a Granzyme B Inhibitor, in Celiac Disease: A Potential Mechanism in Enterocyte Destruction and Villous Atrophy

The objective of this study was to assess the expression of protease inhibitor 9, a granzyme B inhibitor, in human small intestine, and to evaluate its cytoprotective role in the celiac disease of children. Twelve subjects with untreated celiac disease and thirteen healthy controls were examined by endoscopy. The expression of protease inhibitor 9 was analyzed immunohistochemically from duodenal biopsies and compared to granzyme B expression, apoptosis rate, number of intraepithelial lymphocytes and villus and crypt height data from the biopsies. We discovered that protease inhibitor 9 is expressed in the cytoplasm of the duodenal epithelial cells in the majority of cases. The enterocyte expression of protease inhibitor 9 was lower in celiac disease patients than in controls. Protease inhibitor 9 expression also showed a negative correlation with the number of apoptotic cells, overall density of granzyme B expressing intraepithelial lymphocytes, the height of the crypts and the severity of villous atrophy in duodenum. Therefore, we conclude that the protease inhibitor 9 is constantly expressed in the enterocytes of normal duodenum and the expression is decreased in celiac disease. These findings suggest that protease inhibitor 9 has a role in duodenal homeostasis and in the protection of enterocytes from misdirected granzyme B. Indeed, observed associations of lowered protease inhibitor 9 expression together with increased granzyme B expression, apoptosis rate and severity of villous atrophy suggest that impaired balance between granzyme B mediated cytotoxicity and its inhibition by protease inhibitor 9 forms an important factor in the pathogenesis of villous atrophy in celiac disease.

Estrogen fueled, nuclear kiss: did it move for you?

A paper appearing in late 2008,1 attracted considerable attention with its description of a dramatic juxtaposition of two estrogen responsive genes on different chromosomes within 15-60 minutes of adding estradiol. These results challenged a growing consensus of limited chromosome mobility within interphase nuclei, while raising questions of whether a hitherto unknown molecular mechanism might exist to move chromosomes long distances within the nucleus. These results also raised the fascinating question of how two genes on widely separated chromosomes might find each other over such a short time span. Now, a more recent paper reports no such long-range interaction or chromosome movements in the same cell types under what appear to be well replicated conditions, forcing a reexamination of the prior results.

Intracellular versus extracellular granzyme B in immunity and disease: challenging the dogma

The cytotoxic granzyme B (GrB)/perforin pathway has been traditionally viewed as a primary mechanism that is used by cytotoxic lymphocytes to eliminate allogeneic, virally infected and/or transformed cells. Although originally proposed to have intracellular and extracellular functions, upon the discovery that perforin, in combination with GrB, could induce apoptosis, other potential functions for this protease were, for the most part, disregarded. As there are 5 granzymes in humans and 11 granzymes in mice, many studies used perforin knockout mice as an initial screen to evaluate the role of granzymes in disease. However, in recent years, emerging clinical and biochemical evidence has shown that the latter approach may have overlooked a critical perforin-independent, pathogenic role for these proteases in disease. This review focuses on GrB, the most characterized of the granzyme family, in disease. Long known to be a pro-apoptotic protease expressed by cytotoxic lymphocytes and natural killer cells, it is now accepted that GrB can be expressed in other cell types of immune and nonimmune origin. To the latter, an emerging immune-independent role for GrB has been forwarded due to recent discoveries that GrB may be expressed in nonimmune cells such as smooth muscle cells, keratinocytes, and chondrocytes in certain disease states. Given that GrB retains its activity in the blood, can cleave extracellular matrix, and its levels are often elevated in chronic inflammatory diseases, this protease may be an important contributor to certain pathologies. The implications of sustained elevations of intracellular and extracellular GrB in chronic vascular, dermatological, and neurological diseases, among others, are developing. This review examines, for the first time, the multiple roles of GrB in disease pathogenesis.

Death by a thousand cuts: granzyme pathways of programmed cell death

The granzymes are cell death-inducing enzymes, stored in the cytotoxic granules of cytotoxic T lymphocytes and natural killer cells, that are released during granule exocytosis when a specific virus-infected or transformed target cell is marked for elimination. Recent work suggests that this homologous family of serine esterases can activate at least three distinct pathways of cell death. This redundancy likely evolved to provide protection against pathogens and tumors with diverse strategies for evading cell death. This review discusses what is known about granzyme-mediated pathways of cell death as well as recent studies that implicate granzymes in immune regulation and extracellular proteolytic functions in inflammation.

Phosphatidylethanolamine N-methyltransferase (PEMT) gene expression is induced by estrogen in human and mouse primary hepatocytes

Choline is an essential nutrient for humans, though some of the requirement can be met by endogenous synthesis catalyzed by phosphatidylethanolamine N-methyltransferase (PEMT). Premenopausal women are relatively resistant to choline deficiency compared with postmenopausal women and men. Studies in animals suggest that estrogen treatment can increase PEMT activity. In this study we investigated whether the PEMT gene is regulated by estrogen. PEMT transcription was increased in a dose-dependent manner when primary mouse and human hepatocytes were treated with 17-beta-estradiol for 24 h. This increased message was associated with an increase in protein expression and enzyme activity. In addition, we report a region that contains a perfect estrogen response element (ERE) approximately 7.5 kb from the transcription start site corresponding to transcript variants NM_007169 and NM-008819 of the human and murine PEMT genes, respectively, three imperfect EREs in evolutionarily conserved regions and multiple imperfect EREs in nonconserved regions in the putative promoter regions. We predict that both the mouse and human PEMT genes have three unique transcription start sites, which are indicative of either multiple promoters and/or alternative splicing. This study is the first to explore the underlying mechanism of why dietary requirements for choline vary with estrogen status in humans.

Expression of high levels of human proteinase inhibitor 9 blocks both perforin/granzyme and Fas/Fas ligand-mediated cytotoxicity

Proteinase inhibitor 9 (PI-9, SerpinB9) is the only known human intracellular granzyme B inhibitor. Whether expression of PI-9 is sufficient to block cytolysis induced by cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells remains controversial. To evaluate the roles of PI-9, we isolated and tested three lines of stably transfected HeLa cells expressing wild-type PI-9 and one line expressing an inactive mutant PI-9. Expressions of wild-type PI-9, but not the inactive mutant PI-9, inhibited cytolysis induced by human NK92 and NKL natural killer cells. Expression of high levels of PI-9 is therefore sufficient to protect human cells against NK cell-mediated cell death. Using two assays, we show that expressing wild-type PI-9, but not the inactive mutant PI-9, blocks Fas/Fas ligand (Fas/FasL)-mediated apoptosis. PI-9 expression has no effect on etoposide-induced apoptosis. HeLa cells exhibiting substantial resistance to Fas/FasL-mediated apoptosis contain 2- to 3-fold higher PI-9 levels than HCT116 human colon cancer cells and 2- to 3-fold lower PI-9 levels than MCF7/ERHA breast cancer cells, in which PI-9 is strongly induced by estrogens, and by tamoxifen. Expression of increasing levels of PI-9 in target cells may progressively inhibit immune surveillance by blocking NK and CTL-induced cytotoxicity through the perforin/granzyme pathway and then through the Fas/FasL pathway.

Interplay between the levels of estrogen and estrogen receptor controls the level of the granzyme inhibitor, proteinase inhibitor 9 and susceptibility to immune surveillance by natural killer cells

Estrogens promote cell proliferation and metastases in several human cancers. Here, we describe a different action of estrogens likely to contribute to tumor development-blocking immunosurveillance. In breast cancer cells, increasing concentrations of estrogen induce increasing levels of the granzyme B inhibitor, SerpinB9/proteinase inhibitor 9 (PI-9) and progressively block cell death induced by NK92 natural killer (NK) cells, but do not block killing by a second NK cell line, NKL cells. RNA interference knockdown of PI-9 abolishes estrogen's ability to block NK92 cell-induced cytotoxicity. Expressing elevated levels of estrogen receptor alpha (ERalpha) increases the induced level of PI-9, and makes tamoxifen (TAM), but not raloxifene or ICI 182,780, a potent inducer of PI-9. At elevated levels of ERalpha, induction of PI-9 by estradiol or TAM blocks killing by both NK92 and NKL cells. When the Erk pathway is activated with epidermal growth factor, the concentration of estrogen required to induce a protective level of PI-9 is reduced to 10 pM. Elevated concentrations of estrogen and ER may provide a dual selective advantage to breast cancer cells by controlling PI-9 levels and thereby blocking immunosurveillance. Expressing elevated levels of ERalpha reveals a potentially important difference in the effects of TAM, raloxifene and ICI 182,780 on immunosurveillance in breast cancer.

Modulation of the granzyme B inhibitor proteinase inhibitor 9 (PI-9) by activation of lymphocytes and monocytes in vitro and by Epstein-Barr virus and bacterial infection

Proteinase inhibitor 9 (PI-9) is an intracellular serpin expressed in lymphocytes and monocyte-derived cells. It is the only known endogenous natural antagonist of granzyme B (GrB), and its proposed function is protection of cells from misdirected GrB. We have studied the regulation of PI-9 in primary peripheral blood mononuclear cells (PBMCs) following ex-vivo stimulation, and in PBMCs from patients suffering from viral or bacterial infections. By intracellular flow cytometry, we found identical PI-9 expression in all lymphocyte subsets, lower levels in monocytes and none in granulocytes. PI-9 was stable for 48 h in the presence of cycloheximide, indicating slow protein turnover. Incubation of PBMCs with several stimuli including lipopolysaccharide (LPS) led to up-regulation in the monocyte, but not the lymphocyte fraction, within 48 h, inhibitable by the NF-kappaB inhibitor pyrrolidin dithiocarbamate (PTDC). Up-regulation of PI-9 was observed in lymphocytes and monocytes of patients with acute Epstein-Barr virus (EBV), but not bacterial infection. Preterm infants had similar PI-9 expression as adults in monocytes, but lower in lymphocytes, decreasing during bacterial infection. Taken together, our data indicate that PI-9 is rapidly up-regulated upon stimulation of monocytes, but not lymphocytes. By protecting monocytes and macrophages from misdirected GrB in the inflammatory process, PI-9 might be involved in the regulation of antigen presentation.

Estrogen induction of the granzyme B inhibitor, proteinase inhibitor 9, protects cells against apoptosis mediated by cytotoxic T lymphocytes and natural killer cells

Exposure to estrogens is associated with an increased risk of developing breast, cervical, and liver cancer. Estrogens strongly induce the human granzyme B inhibitor, proteinase inhibitor 9 (PI-9). Because cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells use the granzyme pathway to induce apoptosis of target cells, we tested the ability of activated CTLs and the human NK cell line, YT cells, to lyse human liver cells. Estrogen induction of PI-9 protected the liver cells against CTL and NK cell-mediated, granzyme-dependent, apoptosis. Knockdown of PI-9 by RNA interference blocked the protective effect of estrogen. This work demonstrates that estrogens can act on target cells to control their destruction by immune system cells and shows that induction of PI-9 expression can inhibit both CTL and NK cell-mediated apoptosis. Estrogen induction of PI-9 may reduce the ability of cytolytic lymphocytes-mediated immune surveillance to destroy newly transformed cells, possibly providing a novel mechanism for an estrogen-mediated increase in tumor incidence.

Fluorescence anisotropy microplate assay for analysis of steroid receptor-DNA interactions

To analyze the interactions of steroid/nuclear hormone receptors with their DNA response elements, we used ultra low-volume microplates to develop a simple and rapid fluorescence anisotropy assay. The novel fluorescence anisotropy microplate assay (FAMA) was applied to the binding of estrogen and progesterone receptors (ER and PR, respectively) to their respective DNA response elements. The FAMA offers exceptional flexibility in its ability to test a variety of binding conditions and DNA response elements in real time. This assay can differentiate between, and quantitate, sequence-specific and nonspecific binding of receptors to DNA and offers the possibility of true solution analysis of the interaction of coregulators with the estrogen response element (ERE)-ER complex. To test suitability for screening large compound libraries, we demonstrated that the FAMA generates stable signals for more than 4 hours, is insensitive to inhibition by dimethyl sulfoxide (DMSO), and works well in 384-well plates. We analyzed inhibition of receptor-DNA interaction by several zinc chelators and demonstrated zinc dependence and a generally higher sensitivity to inhibition for PR-progesterone response element (PRE) interactions than for ER-ERE interactions. The FAMA is the first system suitable for screening large compound libraries to identify novel compounds that antagonize (or stimulate) binding of steroid receptors to their DNA response elements.

A Central Role for Bid in Granzyme B-induced Apoptosis

Granzyme B, a protease released from cytotoxic lymphocytes, has been proposed to induce target cell death by cleaving and activating the pro-apoptotic Bcl-2 family member Bid. It has also been proposed that granzyme B can induce target cell death by activating caspases directly, by cleaving caspase substrates, and/or by cleaving several non-caspase substrates. The relative importance of Bid in granzyme B-induced cell death has therefore remained unclear. Here we report that cells isolated from various tissues of Bid-deficient mice were resistant to granzyme B-induced cell death. Consistent with the proposed role of Bid in regulating mitochondrial outer membrane permeabilization, cytochrome c remained in the mitochondria of Bid-deficient cells treated with granzyme B. Unlike wild type cells, Bid-deficient cells survived and were then able to proliferate normally, demonstrating the critical role for Bid in mediating granzyme B-induced apoptosis.

The granzyme B inhibitor, PI-9, is differentially expressed during placental development and up-regulated in hydatidiform moles

The intracellular serpin Proteinase Inhibitor-9 (PI-9) is a potent inhibitor of the cytotoxic lymphocyte (CL) proteinase granzyme B, a major effector molecule used by CLs to induce target cell apoptosis. PI-9 is produced by CLs to protect against mis-directed granzyme B. However, PI-9 expression has also been reported in immune privileged tissues. In the present study, cell-specific expression of PI-9 in placental tissue of various gestational ages was examined by immunohistochemistry. PI-9 is highly expressed by the extravillous trophoblasts that have invaded the decidua, and this high expression is maintained throughout pregnancy. Similar levels were also observed in proliferative villous cytotrophoblasts. Syncytial trophoblasts generally do not produce PI-9 to a significant level until the last few weeks of pregnancy. The villous stroma contains mixed populations of PI-9 positive and negative cells throughout pregnancy, with highest expression during the second trimester. Compared to first trimester placentas, syncytial trophoblasts of partial and complete hydatidiform moles showed marked up-regulation of PI-9. Examination of choriocarcinoma cell lines also demonstrated a very high level of PI-9 is produced by these cells, which may provide protection from granzyme B-mediated apoptosis. The cell-specific expression of PI-9 in the placenta is consistent with a function in the maintenance of immune privilege, and it is proposed that up-regulated expression of PI-9 in gestational trophoblastic diseases contributes to disease pathogenesis via immune evasion.

Differential Expression of Proteinase Inhibitor-9 and Granzyme B mRNAs in Activated Immunocompetent Cells

The role of proteinase inhibitor (PI)-9 in hematopoietic cells remains unclear. To clarify the role of PI-9 in these cells, we compared the expressions of PI-9 mRNA and antigen with those of granzyme B (GrB). While the strongest expression of PI-9 mRNA was observed in a NK cell line YT-N10, it was also expressed in a B-acute lymphoblastic leukemia cell line U-Tree02, an Epstein-Barr Virus (EBV)-transformed B cell clone, a CD8+ T lymphocyte clone and a megakaryocytic cell line CMK, but not in a T cell line Jurkat. Phorbol 12-myristate 13 acetate (PMA) enhanced PI-9 mRNA expression in the CD8+ T lymphocyte clone and YT-N10 cells prior to GrB mRNA expression. IL-2 and IL-12 also had similar effects. PMA increased PI-9 mRNA expression in the EBV-transformed B cell clone and CMK cells, but IL-6 showed no effect. No changes were noted in PI-9 and GrB antigens after the addition of these agonists. Patients with graft-versus-host disease (GVHD) may have activated CTLs and NK cells. We therefore examined the expression of PI-9 and GrB mRNAs in eight patients after allogeneic hematopoietic stem cell transplantation with GVHD (n = 4) or without chronic GVHD (n = 4). Expression of GrB mRNA was significantly increased in three patients with GVHD and one patient without GVHD. Surprisingly, PI-9 mRNA expression was decreased in the eight patients. These results indicate that earlier synthesis of PI-9 may be essential for the prevention of autolysis of immunocompetent cells, and that the expression of PI-9 and GrB mRNAs may be controlled through different pathways.

Antiviral Cytokines Induce Hepatic Expression of the Granzyme B Inhibitors, Proteinase Inhibitor 9 and Serine Proteinase Inhibitor 6

Expression of the granzyme B inhibitors, human proteinase inhibitor 9 (PI-9), or the murine orthologue, serine proteinase inhibitor 6 (SPI-6), confers resistance to CTL or NK killing by perforin- and granzyme-dependent effector mechanisms. In light of prior studies indicating that virally infected hepatocytes are selectively resistant to this CTL effector mechanism, the present studies investigated PI-9 and SPI-6 expression in hepatocytes and hepatoma cells in response to adenoviral infection and to cytokines produced during antiviral immune responses. Neither PI-9 nor SPI-6 expression was detected by immunoblotting in uninfected murine or human hepatocytes. Similarly, human Huh-7 hepatoma cells were found to express only very low levels of PI-9 relative to levels detected in perforin- and granzyme-resistant CTL or lymphokine-activated killer cells. Following in vivo adenoviral infection or in vitro culture with IFN-alphabeta or IFN-gamma, SPI-6 expression was induced in murine hepatocytes. Similarly, after culture with IFN-alpha, induction of PI-9 mRNA and protein expression was observed in human hepatocytes and Huh-7 cells. IFN-gamma and TNF-alpha also induced 4- to 10-fold higher levels of PI-9 mRNA expression in Huh-7 cells, whereas levels of mRNA encoding a related serine proteinase inhibitor, proteinase inhibitor 8, were unaffected by culture of Huh-7 cells with IFN-alpha, IFN-gamma, or TNF-alpha. These findings indicate that cytokines that promote antiviral cytopathic responses also regulate expression of the cytoprotective molecules, PI-9 and SPI-6, in hepatocytes that are potential targets of CTL and NK effector mechanisms.

Interplay between estrogen response element sequence and ligands controls in vivo binding of estrogen receptor to regulated genes

To examine the role of the estrogen response element (ERE) sequence in binding of liganded estrogen receptor (ER) to promoters, we analyzed in vivo interaction of liganded ER with the imperfect ERE in the pS2 gene and the composite estrogen-responsive unit (ERU) in the proteinase inhibitor 9 (PI-9) gene. In transient transfections of ER-positive HepG2-ER7 cells, PI-9 was strongly induced by estrogen, moxestrol (MOX), and 4-hydroxytamoxifen (OHT). PI-9 was not induced by raloxifene or ICI 182,780. Quantitative reverse transcriptase-PCR showed that moxestrol strongly induced cellular PI-9 and pS2 mRNAs, whereas OHT moderately induced PI-9 mRNA and weakly induced pS2 mRNA. Chromatin immunoprecipitation experiments demonstrated strong and similar association of 17beta-estradiol-hERalpha and MOX-hERalpha with the PI-9 ERU and with the pS2 ERE. Binding of MOX-hERalpha to the PI-9 ERU and the pS2 ERE was rapid and continuous. Although MOX-hERalpha bound strongly to the PI-9 ERU and less well to the pS2 ERE in chromatin immunoprecipitation, gel shift assays showed that estrogen-hERalpha binds with higher affinity to the deproteinized pS2 ERE than to the PI-9 ERU. Across a broad range of OHT concentrations, OHT-hERalpha associated strongly with the pS2 ERE and weakly with the PI-9 ERU. ICI-hERalpha bound poorly to the PI-9 ERU and effectively to the pS2 ERE. Raloxifene-hERalpha and MOX-hERalpha exhibited similar binding to the PI-9 ERU and the pS2 ERE. These studies demonstrate that ER ligand and ERE sequence work together to regulate in vivo binding of ER to estrogen-responsive promoters.

Estrogen receptor alpha regulates expression of the orphan receptor small heterodimer partner

Hormonal status can influence diverse metabolic pathways. Small heterodimer partner (SHP) is an orphan nuclear receptor that can modulate the activity of several transcription factors. Estrogens are here shown to directly induce expression of the SHP in the mouse and rat liver and in human HepG2 cells. SHP is rapidly induced within 2 h following treatment of mice with ethynylestradiol (EE) or the estrogen receptor alpha (ERalpha)-selective compound propyl pyrazole triol (PPT). SHP induction by these estrogens is completely absent in ERalphaKO mice. Mutation of the human SHP promoter defined HNF-3, HNF-4, GATA, and AP-1 sites as important for basal activity, whereas EE induction required two distinct elements located between -309 and -267. One of these elements contains an estrogen response element half-site that bound purified ERalpha, and ERalpha with a mutated DNA binding domain was unable to stimulate SHP promoter activity. This ERalpha binding site overlaps the known farnesoid X receptor (FXR) binding site in the SHP promoter, and the combination of EE plus FXR agonists did not produce an additive induction of SHP expression in mice. Surprisingly, induction of SHP by EE did not inhibit expression of the known SHP target genes cholesterol 7alpha-hydroxylase (CYP7A1) or sterol 12alpha-hydroxylase (CYP8B1). However, the direct regulation of SHP expression may provide a basis for some of the numerous biological effects of estrogens.

Natural cellular inhibitors of caspases

The crucial role of cell death in many diseases is obvious and has spurred intense research to understand the regulation of apoptotic pathways. Caspase activation is central to many of the apoptotic pathways. In recent years, the study of the regulation of caspase activation and activity in various cell lines and in diseases has revealed highly complex mechanisms regulating cell survival or cell death. In this review, the major natural cellular anticaspase factors are described with particular attention to the inhibitors that prevent active caspases from committing the cell to irreversible destruction. The major group of caspase inhibitors known is the inhibitor of apoptosis proteins (IAP) and this review describes the characteristics of IAP, regulation of IAP expression, and mechanisms of action of IAP. However, other proteins including Bcl-2 family members, heat shock proteins, caspase-like decoy, calpains and proteases, and lipid moieties in the form of phosphoinositides also can function as caspase inhibitors. The current knowledge of the inhibition of these non-IAP factors is described herein.

Modulators of inflammation use nuclear factor-kappa B and activator protein-1 sites to induce the caspase-1 and granzyme B inhibitor, proteinase inhibitor 9

Proteinase inhibitor 9 (PI-9) inhibits caspase-1 (interleukin (IL)-1beta-converting enzyme) and granzyme B, thereby regulating production of the pro-inflammatory cytokine IL-1beta and susceptibility to granzyme B-induced apoptosis. We show that cellular PI-9 mRNA and protein are induced by IL-1beta, lipopolysaccharide, and 12-O-tetradecanoylphorbol-13-acetate. We identified functional imperfect nuclear factor-kappaB (NF-kappaB) sites at -135 and -88 and a consensus activator protein-1 (AP-1) site at -308 in the PI-9 promoter region. Using transient transfections in HepG2 cells to assay PI-9 promoter mutations, we find that mutational ablation of the AP-1 site or of either NF-kappaB site reduces IL-1beta-induced expression of PI-9 by approximately 60%. Mutational ablation of the two NF-kappaB sites and of the AP-1 site nearly abolishes both basal and IL-1beta-induced expression of PI-9. Nuclear extracts from IL-1beta-treated HepG2 cells exhibited strong, IL-1beta-inducible binding to the NF-kappaB sites and to the AP-1 site. Electrophoretic mobility shift assays show that after IL-1beta treatment c-Jun/c-Fos and JunD bind to the AP-1 site, whereas the p50/p65 heterodimer binds to the two NF-kappaB sites. Estrogens induce PI-9, but induction of PI-9 by estrogens and IL-1beta is not synergistic. In transiently transfected, estrogen receptor-positive HepG2ER7 cells, estrogens do not interfere with IL-1beta induction, whereas IL-1beta exhibits dose-dependent repression of estrogen-inducible PI-9 expression. Our surprising finding that the pro-inflammatory cytokine IL-1beta strongly induces PI-9 suggests a novel mechanism for regulating inflammation and apoptosis through a negative feedback loop controlling expression of the anti-inflammatory and anti-apoptotic protein, PI-9.

Maspin sensitizes breast carcinoma cells to induced apoptosis

Maspin, a novel serine protease inhibitor (serpin), suppresses the growth and metastasis of breast tumor in vivo. However, the underlying molecular mechanism is unclear. In the current study, we report the first evidence that endogenous maspin expression in mammary carcinoma cells MDA-MB-435 enhanced staurosporine (STS)-induced apoptosis as judged by the increased fragmentation of DNA, increased proteolytic inactivation of poly-[ADP-ribose]-polymerase (PARP), as well as the increased activation of caspase-8 and caspase-3. In parallel, recombinant maspin did not directly regulate the proteolytic activities of either caspase-3 or caspase-8 in vitro. Consistent with this result, maspin expressing normal mammary epithelial cells underwent more rapid STS-induced apoptosis as compared to breast carcinoma cells. Interestingly, maspin transfectant cells did not undergo spontaneous apoptosis in the absence of STS. Moreover, neither purified maspin protein added from outside nor endogenous maspin secreted to the cell culture media sensitized cells to STS-induced apoptosis. To investigate the structural determinants of maspin in its apoptosis-sensitizing effect, MDA-MB-435 cells were also transfected with maspin/PAI-1 and PAI-1/maspin chimeric constructs resulting from swapping the N-terminal and the C-terminal domains between maspin and PAI-1 (plasminogen activator inhibitor type 1). The resulting stable transfectant clones expressing maspin/PAI-1 and PAI-1/maspin, respectively, did not undergo spontaneous apoptosis, and were similarly inhibited as maspin transfectant cells in motility assay. Interestingly, however, expression of both maspin/PAI-1 and PAI-1/maspin in MDA-MB-435 cells failed to sensitize these cells to STS-induced apoptosis. Taken together, our evidence provides new insights into the complex molecular mechanisms of maspin that may suppress breast tumor progression not only at the step of invasion and motility, but also by regulating tumor cell apoptosis. The sensitizing effect of maspin on apoptosis is to be contrasted by the pro-survival effect of several other serpins.

Serine proteinase inhibitor 9 can be recognized by cytotoxic T lymphocytes of epithelial cancer patients

Serine proteinase inhibitor 9 (PI-9) inhibits granzyme B-mediated apoptosis and interleukin-1beta-converting enzyme activity. In this study, we report that the PI-9 gene encodes antigenic epitopes recognized by the HLA-A24-restricted and tumor-reactive cytotoxic T lymphocytes (CTLs) of epithelial cancer patients. Screening of an autologous cDNA library using a CTL line recognizing HLA-A24+ tumor cells resulted in the isolation of a cDNA, which had an identical coding region to the previously described PI-9 genes. PI-9 gene was expressed in approximately three-fourths of epithelial cancer cell lines and all leukemic cell lines tested. It was also expressed in normal peripheral blood mononuclear cells (PBMCs), but not in a normal fibroblast cell line. CTL sublines contained T cells capable of recognizing the PI-9(292-300) and PI-9(348-356) peptides among 13 different peptides having the HLA-A24 binding motifs. These two peptides were recognized by the CTL line in a dose-dependent and HLA class-I-restricted manner, and also possessed the ability to induce HLA class I-restricted and tumor-reactive CTLs in PBMCs from HLA-A24+ cancer patients. These results demonstrate that PI-9 is recognized by HLA class I-restricted and tumor-reactive CTLs of epithelial cancer patients.

A histone deacetylase inhibitor potentiates estrogen receptor activation of a stably integrated vitellogenin promoter in HepG2 cells

To compare the role of histone deactylation in estrogen activation of a transiently transfected vitellogenin (VIT) promoter and an integrated VIT promoter in the same cells, we produced three HepG2, human hepatoma, cell lines (HepG2ERV cells) stably expressing human estrogen receptor alpha (hERalpha) and containing an integrated VIT promoter-chloramphenicol acetyltransferase (VIT-CAT) reporter gene. The three ER-positive HepG2ERV cell lines and wild-type, ER-negative, HepG2 cells cotransfected with cytomegalovirus-hERalpha exhibited similar MOX-dependent inductions of 20- to 50-fold with a transiently transfected VIT-luciferase reporter and 15- to 50-fold with a transfected 4-estrogen response element-TATA-luciferase reporter gene. The histone deacetylase inhibitor, trichostatin A, did not enhance MOX induction of the transiently transfected VIT promoter in the HepG2ERV cells. In contrast, trichostatin A dramatically potentiated MOX induction of the stably integrated VIT-CAT reporter gene, resulting in MOX-ER-dependent increases in CAT activity of up to 600-fold. These data demonstrate that although liganded ER exhibits the capacity to fully activate a transiently transfected VIT promoter, under some circumstances the ability to reorganize a repressive chromatin structure may be limiting for steroid receptor action.