A novel role for IRF-1 as a suppressor of apoptosis

IRF-1 Regulates Mitochondrial Respiration and Intrinsic Apoptosis Under Metabolic Stress through ATP Synthase Ancillary Factor TMEM70

Mitochondrial dysfunction, which can be caused by metabolic stressors such as oxidized low-density lipoprotein (oxLDL), sensitizes the endothelium to pathological changes. The transcription factor interferon regulatory factor 1 (IRF-1) is a master regulator of inflammation, previously shown to promote oxLDL-induced inflammatory pyroptosis in human aortic endothelial cells (HAEC). However, a presumed role for IRF-1 in regulating the intrinsic apoptotic pathway in response to metabolic stress has not been demonstrated. Here targeted deletion of IRF-1 by siRNA in HAEC aggravated oxLDL-induced, mitochondria-mediated intrinsic apoptosis, as evidenced by increased Caspase-3 and Caspase-9 activation, and chromosomal DNA breakage. The increased apoptosis was concomitant with accumulation of mitochondrial ROS, decrease in intracellular ATP production and respiratory oxygen consumption, and abnormal mitochondrial structure. RNA profiling of endothelial cells isolated from wild type and Irf1 knockout mice, followed by quantitative PCR, luciferase activity assay and chromatin immunoprecipitation (ChIP), revealed that IRF-1 directly regulated the expression of transmembrane protein 70 (TMEM70), an ancillary factor required for the assembly of ATP synthase and conversion of an electrochemical gradient to ATP synthesis. Mirroring the effect of IRF1 knockdown, depletion of TMEM70 in HAEC resulted in impaired mitochondrial function and enhanced cell apoptosis. In contrast, overexpression of TMEM70 rescued ATP biosynthesis and suppressed apoptosis in oxLDL-treated, IRF-1-deficient HAEC. These results reveal a novel homeostatic role for IRF-1 in the regulation of mitochondrial function and associated stress-induced apoptosis.

Molecular mechanisms of mammary gland remodeling: A review of the homeostatic versus bisphenol a disrupted microenvironment

Mammary gland (MG) undergoes critical points of structural changes throughout a woman's life. During the perinatal and pubertal stages, MG develops through growth and differentiation to establish a pre-mature feature. If pregnancy and lactation occur, the epithelial compartment branches and differentiates to create a specialized structure for milk secretion and nurturing of the newborn. However, the ultimate MG modification consists of a regression process aiming to reestablish the smaller and less energy demanding structure until another production cycle happens. The unraveling of these fascinating physiologic cycles has helped the scientific community elucidate aspects of molecular regulation of proliferative and apoptotic events and remodeling of the stromal compartment. However, greater understanding of the hormonal pathways involved in MG developmental stages led to concern that endocrine disruptors such as bisphenol A (BPA), may influence these specific development/involution stages, called "windows of susceptibility". Since it is used in the manufacture of polycarbonate plastics and epoxy resins, BPA is a ubiquitous chemical present in human everyday life, exerting an estrogenic effect. Thus, descriptions of its deleterious effects on the MG, especially in terms of serum hormone concentrations, hormonal receptor expression, molecular pathways, and epigenetic alterations, have been widely published. Therefore, allied to a didactic description of the main physiological mechanisms involved in different critical points of MG development, the current review provides a summary of key mechanisms by which the endocrine disruptor BPA impacts MG homeostasis at different windows of susceptibility, causing short- and long-term effects.

Characterization of Organoid Cultures to Study the Effects of Pregnancy Hormones on the Epigenome and Transcriptional Output of Mammary Epithelial Cells

The use of mouse derived mammary organoids can provide a unique strategy to study mammary gland development across a normal life cycle, as well as offering insights into how malignancies form and progress. Substantial cellular and epigenomic changes are triggered in response to pregnancy hormones, a reaction that engages molecular and cellular changes that transform the mammary epithelial cells into "milk producing machines". Such epigenomic alterations remain stable in post-involution mammary epithelial cells and control the reactivation of gene transcription in response to re-exposure to pregnancy hormones. Thus, a system that tightly controls exposure to pregnancy hormones, epigenomic alterations, and activation of transcription will allow for a better understanding of such molecular switches. Here, we describe the characterization of ex vivo cultures to mimic the response of mammary organoid cultures to pregnancy hormones and to understand gene regulation and epigenomic reprogramming on consecutive hormone exposure. Our findings suggest that this system yields similar epigenetic modifications to those reported in vivo, thus representing a suitable model to closely track epigenomic rearrangement and define unknown players of pregnancy-induced development.

UBE3A regulates the transcription of IRF, an antiviral immunity

UBE3A is a gene responsible for the pathogenesis of Angelman syndrome (AS), a neurodevelopmental disorder characterized by symptoms such as intellectual disability, delayed development and severe speech impairment. UBE3A encodes an E3 ubiquitin ligase, for which several targets have been identified, including synaptic molecules. Although proteolysis mainly occurs in the cytoplasm, UBE3A is localized to the cytoplasm and the nucleus. In fact, UBE3A is also known as a transcriptional regulator of the family of nuclear receptors. However, the function of UBE3A in the nucleus remains unclear. Therefore, we examined the involvement of UBE3A in transcription in the nuclei of neurons. Genome-wide transcriptome analysis revealed an enrichment of genes downstream of interferon regulatory factor (IRF) in a UBE3A-deficient AS mouse model. In vitro biochemical analyses further demonstrated that UBE3A interacted with IRF and, more importantly, that UBE3A enhanced IRF-dependent transcription. These results suggest a function for UBE3A as a transcriptional regulator of the immune system in the brain. These findings also provide informative molecular insights into the function of UBE3A in the brain and in AS pathogenesis.

Newcastle Disease Virus V Protein Inhibits Cell Apoptosis and Promotes Viral Replication by Targeting CacyBP/SIP

Newcastle disease virus (NDV) has been classified by the World Organization for Animal Health (OIE) as a notable disease-causing virus, and this virus has the ability to infect a wide range of birds. V protein is a non-structural protein of NDV. V protein has been reported to inhibit cell apoptosis (Park et al., 2003a) and promote viral replication (Huang et al., 2003), however, the mechanisms of action of V protein have not been elucidated. In the present study, a yeast two-hybrid screen was performed, and V protein was found to interact with the CacyBP/SIP protein. The results of co-immunoprecipitation and immuno-colocalization assays confirmed the interaction between V protein and CacyBP/SIP. The results of quantitative-PCR and viral plaque assays showed that overexpression of CacyBP/SIP inhibited viral replication in DF-1 cells. Overexpression of CacyBP/SIP in DF-1 cells induced caspase3-dependent apoptosis. The effect of knocking down CacyBP/SIP by siRNA was the opposite of that observed upon overexpression. Moreover, it is known that NDV induces cell apoptosis via multiple caspase-dependent pathways. Furthermore, V protein inhibited cell apoptosis and downregulated CacyBP/SIP expression in DF-1 cells. Taken together, the findings of the current study indicate that V protein interacts with CacyBP/SIP, thereby regulating cell apoptosis and viral replication.

Progesterone receptors (PR) mediate STAT actions: PR and prolactin receptor signaling crosstalk in breast cancer models

Estrogen is the major mitogenic stimulus of mammary gland development during puberty wherein ER signaling acts to induce abundant PR expression. PR signaling, in contrast, is the primary driver of mammary epithelial cell proliferation in adulthood. The high circulating levels of progesterone during pregnancy signal through PR, inducing expression of the prolactin receptor (PRLR). Cooperation between PR and prolactin (PRL) signaling, via regulation of downstream components in the PRL signaling pathway including JAKs and STATs, facilitates the alveolar morphogenesis observed during pregnancy. Indeed, these pathways are fully integrated via activation of shared signaling pathways (i.e. JAKs, MAPKs) as well as by the convergence of PRs and STATs at target genes relevant to both mammary gland biology and breast cancer progression (i.e. proliferation, stem cell outgrowth, tissue cell type heterogeneity). Thus, rather than a single mediator such as ER, transcription factor cascades (ER>PR>STATs) are responsible for rapid proliferative and developmental programming in the normal mammary gland. It is not surprising that these same mediators typify uncontrolled proliferation in a majority of breast cancers, where ER and PR are most often co-expressed and may cooperate to drive malignant tumor progression. This review will primarily focus on the integration of PR and PRL signaling in breast cancer models and the importance of this cross-talk in cancer progression in the context of mammographic density. Components of these PR/PRL signaling pathways could offer alternative drug targets and logical complements to anti-ER or anti-estrogen-based endocrine therapies.

IRF-1 inhibits NF-κB activity, suppresses TRAF2 and cIAP1 and induces breast cancer cell specific growth inhibition

Interferon Regulatory Factor (IRF)-1, originally identified as a transcription factor of the human interferon (IFN)-β gene, mediates tumor suppression and may inhibit oncogenesis. We have shown that IRF-1 in human breast cancer cells results in the down-regulation of survivin, tumor cell death, and the inhibition of tumor growth in vivo in xenogeneic mouse models. In this current report, we initiate studies comparing the effect of IRF-1 in human nonmalignant breast cell and breast cancer cell lines. While IRF-1 in breast cancer cells results in growth inhibition and cell death, profound growth inhibition and cell death are not observed in nonmalignant human breast cells. We show that TNF-α or IFN-γ induces IRF-1 in breast cancer cells and results in enhanced cell death. Abrogation of IRF-1 diminishes TNF-α and IFN-γ-induced apoptosis. We test the hypothesis that IRF-1 augments TNF-α-induced apoptosis in breast cancer cells. Potential signaling networks elicited by IRF-1 are investigated by evaluating the NF-κB pathway. TNF-α and/or IFN-γ results in decreased presence of NF-κB p65 in the nucleus of breast cancer cells. While TNF-α and/or IFN-γ can induce IRF-1 in nonmalignant breast cells, a marked change in NF-κB p65 is not observed. Moreover, the ectopic expression of IRF-1 in breast cancer cells results in caspase-3, -7, -8 cleavage, inhibits NF-κB activity, and suppresses the expression of molecules involved in the NF-κB pathway. These data show that IRF-1 in human breast cancer cells elicits multiple signaling networks including intrinsic and extrinsic cell death and down-regulates molecules involved in the NF-κB pathway.

Reducing IRF-1 to Levels Observed in HESN Subjects Limits HIV Replication, But Not the Extent of Host Immune Activation

Cells from women who are epidemiologically deemed resistant to HIV infection exhibit a 40-60% reduction in endogenous IRF-1 (interferon regulatory factor-1), an essential regulator of host antiviral immunity and the early HIV replication. This study examined the functional consequences of reducing endogenous IRF-1 on HIV-1 replication and immune response to HIV in natural HIV target cells. IRF-1 knockdown was achieved in ex vivo CD4(+) T cells and monocytes with siRNA. IRF-1 level was assessed using flow cytometry, prior to infection with HIV-Bal, HIV-IIIB, or HIV-VSV-G. Transactivation of HIV long terminal repeats was assessed by p24 secretion (ELISA) and Gag expression (reverse transcription-polymerase chain reaction (RT-PCR)). The expression of IRF-1-regulated antiviral genes was quantitated with RT-PCR. A modest 20-40% reduction in endogenous IRF-1 was achieved in >87% of ex vivo-derived peripheral CD4(+) T cells and monocytes, resulted in >90% reduction in the transactivation of the HIV-1 genes (Gag, p24) and, hence, HIV replication. Curiously, these HIV-resistant women demonstrated normal immune responses, nor an increased susceptibility to other infection. Similarly, modest IRF-1 knockdown had limited impact on the magnitude of HIV-1-elicited activation of IRF-1-regulated host immunologic genes but resulted in lessened duration of these responses. These data suggest that early expression of HIV-1 genes requires a higher IRF-1 level, compared to the host antiviral genes. Together, these provide one key mechanism underlying the natural resistance against HIV infection and further suggest that modest IRF-1 reduction could effectively limit productive HIV infection yet remain sufficient to activate a robust but transient immune response.

RelA-Induced Interferon Response Negatively Regulates Proliferation

Both oncogenic and tumor-suppressor activities are attributed to the Nuclear Factor kappa B (NF-kB) pathway. Moreover, NF-kB may positively or negatively regulate proliferation. The molecular determinants of these opposing roles of NF-kB are unclear. Using primary human mammary epithelial cells (HMEC) as a model, we show that increased RelA levels and consequent increase in basal transcriptional activity of RelA induces IRF1, a target gene. Induced IRF1 upregulates STAT1 and IRF7, and in consort, these factors induce the expression of interferon response genes. Activation of the interferon pathway down-regulates CDK4 and up-regulates p27 resulting in Rb hypo-phosphorylation and cell cycle arrest. Stimulation of HMEC with IFN-γ elicits similar phenotypic and molecular changes suggesting that basal activity of RelA and IFN-γ converge on IRF1 to regulate proliferation. The anti-proliferative RelA-IRF1-CDK4 signaling axis is retained in ER+/HER2- breast tumors analyzed by The Cancer Genome Atlas (TCGA). Using immuno-histochemical analysis of breast tumors, we confirm the negative correlation between RelA levels and proliferation rate in ER+/HER2- breast tumors. These findings attribute an anti-proliferative tumor-suppressor role to basal RelA activity. Inactivation of Rb, down-regulation of RelA or IRF1, or upregulation of CDK4 or IRF2 rescues the RelA-IRF1-CDK4 induced proliferation arrest in HMEC and are points of disruption in aggressive tumors. Activity of the RelA-IRF1-CDK4 axis may explain favorable response to CDK4/6 inhibition observed in patients with ER+ Rb competent tumors.

The roles of interferon regulatory factors 1 and 2 in the progression of human pancreatic cancer

OBJECTIVE

Pancreatic cancer is one of the most malignant diseases worldwide. Interferon regulatory factor (IRF) 1 and IRF2 function as a tumor suppressor and oncoprotein, respectively, in several types of cancers. We investigated whether IRF1 and IRF2 are involved in the progression of pancreatic cancer.

METHODS

We examined the expressions of IRF1 and IRF2 in pancreatic cancer specimens and analyzed the association with clinicopathologic features. We evaluated the biological effects of IRF1 and IRF2 using a pancreatic cancer cell line.

RESULTS

The expression levels of IRF1 and IRF2 were decreased and increased, respectively, in the pancreatic cancer cells compared with those observed in the paired normal areas. A higher expression of IRF1 was associated with better features of tumor differentiation, infiltration depth, tumor size, and survival, whereas that of IRF2 was associated with a worse feature of tumor infiltration depth. Interferon regulatory factor 2-overexpressing PANC-1 cells exhibited an increase in cell growth, less apoptotic features, and chemoresistance to gemcitabine treatment. In contrast, IRF1-overexpressing cells exhibited the opposite characteristics.

CONCLUSIONS

Interferon regulatory factors 1 and 2 may regulate the progression of pancreatic cancer by functioning as an antioncoprotein and oncoprotein, respectively. These molecules may serve as potential targets of therapy.

The spectrum of STAT functions in mammary gland development

The signal transducer and activator of transcription (STAT) family of transcription factors have a spectrum of functions in mammary gland development. In some cases these roles parallel those of STATs in other organ systems, while in other instances the function of individual STATs in the mammary gland is specific to this tissue. In the immune system, STAT6 is associated with differentiation of T helper cells, while in the mammary gland, it has a fundamental role in the commitment of luminal epithelial cells to the alveolar lineage. STAT5A is required for the production of luminal progenitor cells from mammary stem cells and is essential for the differentiation of milk producing alveolar cells during pregnancy. By contrast, the initiation of regression following weaning heralds a dramatic and specific activation of STAT3, reflecting its pivotal role in the regulation of cell death and tissue remodeling during mammary involution. Although it has been demonstrated that STAT1 is regulated during a mammary developmental cycle, it is not yet determined whether it has a specific, non-redundant function. Thus, the mammary gland constitutes an unusual example of an adult organ in which different STATs are sequentially activated to orchestrate the processes of functional differentiation, cell death and tissue remodeling.

p55PIK transcriptionally activated by MZF1 promotes colorectal cancer cell proliferation

p55PIK, regulatory subunit of class IA phosphatidylinositol 3-kinase (PI3K), plays a crucial role in cell cycle progression by interaction with tumor repressor retinoblastoma (Rb) protein. A recent study showed that Rb protein can localize to the mitochondria in proliferative cells. Aberrant p55PIK expression may contribute to mitochondrial dysfunction in cancer progression. To reveal the mechanisms of p55PIK transcriptional regulation, the p55PIK promoter characteristics were analyzed. The data show that myeloid zinc finger 1, MZF1, is necessary for p55PIK gene transcription activation. ChIP (Chromatin immuno-precipitation) assay shows that MZF1 binds to the cis-element "TGGGGA" in p55PIK promoter. In MZF1 overexpressed cells, the promoter activity, expression of p55PIK, and cell proliferation rate were observed to be significantly enhanced. Whereas in MZF1-silenced cells, the promoter activity and expression of p55PIK and cell proliferation level was statistically decreased. In CRC tissues, MZF1 and p55PIK mRNA expression were increased (P = 0.046, P = 0.047, resp.). A strong positive correlation (Rs = 0.94) between MZF1 and p55PIK mRNA expression was observed. Taken together, we concluded that p55PIK is transcriptionally activated by MZF1, resulting in increased proliferation of colorectal cancer cells.

Roles of stress-activated protein kinases in the replication of Singapore grouper iridovirus and regulation of the inflammatory responses in grouper cells

Stress-activated protein kinases (SAPKs), including p38 mitogen-activated protein kinase (p38 MAPK) and c-Jun N-terminal kinase (JNK), are usually activated in response to different environmental stimuli, including virus infection. In the present study, the roles of SAPKs during Singapore grouper iridovirus (SGIV) infection were investigated in fish cells. The results showed that increased phosphorylation of JNK1/2 and p38 MAPK occurred during active replication of SGIV in grouper cell cultures. Moreover, downstream effectors (c-Jun, MAPK-activated protein kinase 2, p53, activator protein 1, Myc and nuclear factor of activated T cells) were activated after SGIV infection, suggesting that SGIV replication activated the JNK and p38 MAPK signalling pathways. Notably, using specific inhibitors, it was found that viral gene transcripts, protein expression and viral titres were not affected by inhibition of p38 MAPK but were suppressed significantly by inhibiting JNK1/2 activation. In addition, transcription of grouper immune genes including interferon regulatory factor 1, interleukin-8 and tumour necrosis factor alpha (TNF-α) were regulated by JNK, whilst only TNF-α was regulated by p38 MAPK. It is proposed that the JNK pathway is important for SGIV replication and modulates the inflammatory responses during virus infection.

Downregulation of microRNA-383 is associated with male infertility and promotes testicular embryonal carcinoma cell proliferation by targeting IRF1

Our previous studies have shown that microRNA-383 (miR-383) expression is downregulated in the testes of infertile men with maturation arrest (MA). However, the underlying mechanisms of miR-383 involved in the pathogenesis of MA remain unknown. In this study, we showed that downregulation of miR-383 was associated with hyperactive proliferation of germ cells in patients with mixed patterns of MA. Overexpression of miR-383 in NT2 (testicular embryonal carcinoma) cells resulted in suppression of proliferation, G1-phase arrest and induction of apoptosis, whereas silencing of miR-383 reversed these effects. The effects of miR-383 were mediated through targeting a tumor suppressor, interferon regulatory factor-1 (IRF1), and miR-383 was negatively correlated with IRF1 protein expression in vivo. miR-383 inhibited IRF1 by affecting its mRNA stability, which subsequently reduced the levels of the targets of IRF1, namely cyclin D1, CDK2 and p21. Downregulation of IRF1 or cyclin D1, but not that of CDK2, enhanced miR-383-mediated effects, whereas silencing of p21 partially inhibited the effects of miR-383. Moreover, miR-383 downregulated CDK4 by increasing proteasome-dependent degradation of CDK4, which in turn resulted in an inhibition of phosphorylated retinoblastoma protein (pRb) phosphorylation. These results suggest that miR-383 functions as a negative regulator of proliferation by targeting IRF1, in part, through inactivation of the pRb pathway. Abnormal testicular miR-383 expression may potentiate the connections between male infertility and testicular germ cell tumor.

Epigenetic silencing of a proapoptotic cell adhesion molecule, the immunoglobulin superfamily member IGSF4, by promoter CpG methylation protects Hodgkin lymphoma cells from apoptosis

The malignant Hodgkin/Reed-Sternberg (HRS) cells of Hodgkin lymphoma (HL) are believed to derive from germinal center (GC) B cells, but lack expression of a functional B cell receptor. As apoptosis is the normal fate of B-cell receptor-negative GC B cells, mechanisms that abrogate apoptosis are thus critical in HL development, such as epigenetic disruption of certain pro-apoptotic cancer genes including tumor suppressor genes. Identifying methylated genes elucidates oncogenic mechanisms and provides valuable biomarkers; therefore, we performed a chemical epigenetic screening for methylated genes in HL through pharmacological demethylation and expression profiling. IGSF4/CADM1/TSLC1, a pro-apoptotic cell adhesion molecule of the immunoglobulin superfamily, was identified together with other methylated targets. In contrast to its expression in normal GC B cells, IGSF4 was down-regulated and methylated in HL cell lines, most primary HL, and microdissected HRS cells of 3/5 cases, but not in normal peripheral blood mononuclear cells and seldom in normal lymph nodes. We also detected IGSF4 methylation in sera of 14/18 (78%) HL patients but seldom in normal sera. Ectopic IGSF4 expression decreased HL cells survival and increased their sensitivity to apoptosis. IGSF4 induction that normally follows heat shock stress treatment was also abrogated in methylated lymphoma cells. Thus, our data demonstrate that IGSF4 silencing by CpG methylation provides an anti-apoptotic signal to HRS cells important in HL pathogenesis.

Mammary involution and breast cancer risk: transgenic models and clinical studies

Postlactational involution is the process following weaning during which the mammary gland undergoes massive cell death and tissue remodeling as it returns to the pre-pregnant state. Lobular involution is the process by which the breast epithelial tissue is gradually lost with aging of the mammary gland. While postlactational involution and lobular involution are distinct processes, recent studies have indicated that both are related to breast cancer development. Experiments using a variety of rodent models, as well as observations in human populations, suggest that deregulation of postlactational involution may act to facilitate tumor formation. By contrast, new human studies show that completion of lobular involution protects against subsequent breast cancer incidence.

The molecular culprits underlying precocious mammary gland involution

Mammary gland involution, characterized by extensive apoptosis and structural remodelling of the gland, is the process by which the gland is returned to the pre-pregnant state. A key advantage of the mammary gland is the ability to synchronize involution through forced weaning, thus allowing the dissection of biochemical pathways involved in the involution process. Over the past few years, significant advances have been made in understanding the signaling pathways and downstream effectors that regulate epithelial cell apoptosis in the first phase of involution, and the importance of matrix metalloproteinases and their inhibitors in both phases of involution. The precise nature of the triggers for apoptosis, however, and the ultimate perpetrators of cell death are not yet clear. This review focuses on genes whose perturbation, either by targeted deletion or overexpression in transgenic mouse models, leads to precocious involution. The accumulating data point to a complex network of signal transduction pathways that synergize to regulate apoptosis in the involuting mammary gland.

Acute myeloid leukemia-associated Mkl1 (Mrtf-a) is a key regulator of mammary gland function

Transcription of immediate-early genes--as well as multiple genes affecting muscle function, cytoskeletal integrity, apoptosis control, and wound healing/angiogenesis--is regulated by serum response factor (Srf). Extracellular signals regulate Srf in part via a pathway involving megakaryoblastic leukemia 1 (Mkl1, also known as myocardin-related transcription factor A [Mrtf-a]), which coactivates Srf-responsive genes downstream of Rho GTPases. Here we investigate Mkl1 function using gene targeting and show the protein to be essential for the physiologic preparation of the mammary gland during pregnancy and the maintenance of lactation. Lack of Mkl1 causes premature involution and impairs expression of Srf-dependent genes in the mammary myoepithelial cells, which control milk ejection following oxytocin-induced contraction. Despite the importance of Srf in multiple transcriptional pathways and widespread Mkl1 expression, the spectrum of abnormalities associated with Mkl1 absence appears surprisingly restricted.

The polymeric immunoglobulin receptor: bridging innate and adaptive immune responses at mucosal surfaces

Secretory antibodies of the immunoglobulin A (IgA) class form the first line of antigen-specific immune protection against inhaled, ingested, and sexually transmitted pathogens and antigens at mucosal surfaces. Epithelial transcytosis of polymeric IgA (pIgA) is mediated by the polymeric immunoglobulin receptor (pIgR). At the apical surface, the extracellular ligand-binding region of pIgR, known as secretory component (SC), is cleaved and released in free form or as a component of secretory IgA (SIgA). SC has innate anti-microbial properties, and it protects SIgA from proteolytic degradation. Expression of pIgR is regulated by microbial products through Toll-like receptor signaling and by host factors such as cytokines and hormones. Recent studies of the structure of the extracellular ligand-binding domain of pIgR have revealed mechanisms by which it binds pIgA and other ligands. During transcytosis, pIgA has been shown to neutralize pathogens and antigens within intracellular vesicular compartments. The recent identification of disease-associated polymorphisms in human pIgR near the cleavage site may help to unravel the mystery of how pIgR is cleaved to SC. The identification of novel functions for SC and SIgA has expanded our view of the immunobiology of pIgR, a key component of the mucosal immune system that bridges innate and adaptive immune defense.

The role of IGFBP-5 in mammary gland development and involution

Insulin-like growth factor-I (IGF-I) plays an important role as a survival factor during mammary gland development and remodelling during involution of the mature/lactating mammary gland, and elevated concentrations have been associated with increased risk of breast cancer. The actions of IGF-I are modulated by a family of binding proteins (IGFBPs) and we have shown that IGFBP-5 is associated with cell death in the mammary gland and more recently provided the first evidence that it is causally related to apoptosis of the mammary gland. A transgenic mouse expressing IGFBP-5 on a mammary-specific promoter led to impaired mammary development involving inhibition of IGF-signalling and involving members of the Bcl-2 family. Subsequent studies in vitro and in vivo using exogenous IGFBP-5 treatment have added support to this concept. Although the effects of IGFBP-5 did appear to involve inhibition of IGF action, a role for IGF-independent effects cannot be ruled out. Such IGF-independent effects involve potential interactions with components of the extracellular matrix involved in tissue remodelling including plasminogen activator inhibitor-1 (PAI-1). In addition, intracellular events involving nuclear localisation of IGFBP-5 have been shown to have the ability to inhibit cell proliferation. Thus, IGFBP-5 seems important for regulating both apoptosis and cell proliferation in the mammary gland during development and post-lactation involution.

Apoptosis regulation in the mammary gland

Epithelial apoptosis has a key role in the development and function of the mammary gland. It is involved with the formation of ducts during puberty and is required to remove excess epithelial cells after lactation so that the gland can be prepared for future pregnancies. Deregulated apoptosis contributes to malignant progression in the genesis of breast cancer. Since epithelial cell apoptosis in the lactating mammary gland can be synchronised by forced weaning, it has been possible to undertake biochemical analysis of the pathways involved. Together with the targeted overexpression or deletion of candidate genes, these approaches have provided a unique insight into the complex mechanisms of apoptosis regulation in vivo. This review explores what is currently known about the triggers for apoptosis in the normal mammary gland, and how they link with the intrinsic apoptotic machinery.

IRF-1 expression induces apoptosis and inhibits tumor growth in mouse mammary cancer cells in vitro and in vivo

Interferon regulatory factor-1 (IRF-1) is a nuclear transcription factor that mediates interferon and other cytokine effects and appears to have antitumor activity in vitro and in vivo in cancer cells. We have constructed a recombinant adenoviral vector (Ad-IRF-1) that infects mammary cells with high efficiency and results in high levels of functional IRF-1 protein in transfected cells. Overexpression of IRF-1 in two mouse breast cancer cell lines, C3-L5 and TS/A, resulted in apoptosis in these cell lines as assessed by Annexin V staining. The involvement of caspases was confirmed by significant inhibition of apoptosis by a caspase inhibitor, and by demonstration of caspase-3 activity, cleavage of caspase-3, and PARP cleavage. Interestingly, the growth of nonmalignant breast cell lines C127I and NMuMG did not appear to be inhibited by IRF-1 overexpression. Suppression of growth for breast cancer cell lines in vivo was demonstrated by both preinfection of breast cancer cells ex vivo and by intratumoral injection of Ad-IRF-1 into established tumors in their natural hosts. The mechanism of apoptosis may involve the transcriptional upregulation of bak, caspase-8, and caspase-7 expression. These data support the antitumor potential of IRF-1 and the use of agents that increase IRF-1 in breast cancer.

Taking it to the max: The genetic and developmental mechanisms coordinating midfacial morphogenesis and dysmorphology

The rapid proliferative expansion and complex morphogenetic events that coordinate the development of the face underpin the sensitivity of this structure to genetic and environmental insult and provide an explanation for the high incidence of midfacial malformation. Most notable of these malformations is cleft lip with or without cleft palate (CLP) that, with an incidence of between one in 600 and one in 1000 live births, is the fourth most common congenital disorder in humans. Despite the obvious global impact of the disorder and some recent progress in identifying causative genes for some prominent syndromal forms, our knowledge of the key genetic factors contributing to the more common isolated cases of CLP is still remarkably patchy. The current understanding of the molecular and cellular processes that orchestrate morphogenesis of the midface, with emphasis on events leading to fusion of the lip and primary palate, is detailed in this review. The roles of crucial factors identified from relevant animal model systems, including BMP4 and SHH, and the likely events perturbed by key genes pinpointed in human studies [such as PVRL1, IRF6p63, MID1, MSX1, and PTCH1] are discussed in this light. New candidates for human CLP genes are also proposed.

Mullerian inhibiting substance promotes interferon gamma-induced gene expression and apoptosis in breast cancer cells

This report demonstrates that in addition to interferons and cytokines, members of the TGF beta superfamily such as Mullerian inhibiting substance (MIS) and activin A also regulate IRF-1 expression. MIS induced IRF-1 expression in the mammary glands of mice in vivo and in breast cancer cells in vitro and stimulation of IRF-1 by MIS was dependent on activation of the NF kappa B pathway. In the rat mammary gland, IRF-1 expression gradually decreased during pregnancy and lactation but increased at involution. In breast cancer, the IRF-1 protein was absent in 13% of tumors tested compared with matched normal glands. Consistent with its growth suppressive activity, expression of IRF-1 in breast cancer cells induced apoptosis. Treatment of breast cancer cells with MIS and interferon gamma (IFN-gamma) co-stimulated IRF-1 and CEACAM1 expression and synergistic induction of CEACAM1 by a combination of MIS and IFN-gamma was impaired by antisense IRF-1 expression. Furthermore, a combination of IFN-gamma and MIS inhibited the growth of breast cancer cells to a greater extent than either one alone. Both reagents alone significantly decreased the fraction of cells in the S-phase of the cell cycle, an effect not enhanced when they were used in combination. However, MIS promoted IFN-gamma-induced apoptosis demonstrating a functional interaction between these two classes of signaling molecules in regulation of breast cancer cell growth.

Microarray analysis of the involution switch

Mammary epithelial cells (MEC) undergo a series of developmental decisions during a pregnancy cycle. The switches from proliferation to differentiation to secretion and then to cell death are precisely controlled. In order to identify critical changes associated with the transition from a secretory phenotype during lactation to dedifferentiation and cell death, we have undertaken a microarray analysis of mouse mammary gland development. We have focused on the involution switch and on the transcription profiles of genes that are targets of transcription factors known to influence involution and apoptosis. Our results show that both Stat3 and NF-kB target genes are induced by the involution switch while Stat5 target genes are distinct from Stat3 induced genes. Furthermore, a substantial number of genes that were specifically upregulated at the start of involution are regulators of inflammation and the acute phase response. These results provide a novel insight into the involution process and demonstrate the value of microarray analysis in defining molecular events associated with critical developmental transitions in mammary gland.

Activating transcription factor 4 overexpression inhibits proliferation and differentiation of mammary epithelium resulting in impaired lactation and accelerated involution

The basic leucine zipper containing activating transcription factors (ATFs) modulates the expression of growth-regulating genes. In this study, we sought to determine specifically the consequences of ATF4 expression on mammary gland development in transgenic mice. Overexpression of ATF4 severely impaired normal development of the mammary gland, which was associated with reduced proliferation and differentiation of mammary alveolar epithelium and up-regulation of p21(WAF1) and p27(Kip1). In addition, there was also impaired lactation accompanied by decreased expression of alpha-lactoalbumin, whey acidic protein, and beta-casein, possibly because of the down-regulation of STAT5a tyrosine phosphorylation. Mammary gland involution in ATF4-transgenic mice was accelerated, compared with wild type littermates by whole mount analysis. In addition, day 18 of lactation in transgenic mice was phenotypically equivalent to day 3 of involution in wild type mice, as determined by the TUNEL assay and expression of Bax. The concentration of the proapoptotic molecule caspase-3 was increased during lactation in ATF4-transgenic animal. Mammary glands from ATF4-transgenic mice also showed significant nuclear translocation of activated STAT3 and up-regulation of one of its target genes, insulin-like growth factor-binding protein-5, which is thought to facilitate apoptosis by sequestering insulin-like growth factor. Together, these findings suggest that ATF4 may play a role during mammary gland development and that down-regulation of ATF4 may be important for the onset of involution in the mammary gland.

Interferon regulatory factor-1 (IRF-1) is a mediator for interferon-gamma induced attenuation of telomerase activity and human telomerase reverse transcriptase (hTERT) expression

Constitutive activation of the telomerase is a key step in the development of human cancers. Interferon-gamma (IFN-gamma) signaling induces growth arrest in many tumors through multiple regulatory mechanisms. In this study, we show that IFN-gamma signaling represses telomerase activity and human telomerase reverse transcriptase (hTERT) transcription, and suggest that this signaling is mediated by IRF-1. Ectopic expression of IRF-1 attenuated hTERT promoter activity. Murine embryonic fibroblasts (MEFs) genetically deficient in IRF-1 (IRF-1(-/-)) showed an elevated level (>15 times) of hTERT promoter activity as compared to the hTERT promoter activity of wild-type MEFs. The telomerase activity and hTERT expression in IRF-1(-/-) MEFs were downregulated by IRF-1 transfection. Interestingly, less extent of telomerase repression was observed in HPV E6 and E7 negative, p53 mutant HT-3 cells than in HPV 18 E6 and E7 positive HeLa cells (intact p53). These findings provide evidence that IRF-1 is a potential mediator of IFN-gamma-induced attenuation of telomerase activity and hTERT expression.

Growth hormone, acting in part through the insulin-like growth factor axis, rescues developmental, but not metabolic, activity in the mammary gland of mice expressing a single allele of the prolactin receptor

The heterozygous prolactin (PRL) receptor (PRLR(+/-)) mouse fails to develop a fully functional mammary gland at the end of the first pregnancy and shows markedly impaired lobuloalveolar development and milk secretion in young females. PRL and GH, acting through the IGF system, have interactive effects to enhance epithelial cell survival. Thus, we propose that a reduction in the expression of the PRLR may lead to increased IGFBP-5 expression (proapoptotic) and that GH may rescue mammary development by increasing IGF-I, an important mitogen and survival factor for the mammary epithelium. Mammary IGF-binding protein-5 (IGFBP-5) concentrations and plasmin activity in PRLR(+/-) mice were increased on d 2 postpartum, indicative of increased cell death and extracellular matrix remodeling. After GH treatment, a restoration of mammary alveolar development and a reduction in the activities of IGFBP-5 and plasmin were observed. Despite the severely impaired mammary development in PRLR(+/-) mice, both mRNA and protein expression for caseins and acetyl-coenzyme A (acetyl-CoA) carboxylase and acetyl-CoA caboxylase-alpha mRNA increased at parturition, although not to the extent in wild-type animals. Surprisingly, GH treatment actually led to a further decrease in milk protein and acetyl-CoA carboxylase-alphaexpression when expressed per cell. This was confirmed by the smaller alveolar size, the relative paucity of milk in the mammary glands of GH-treated animals, and the inability of their pups to gain weight. In a subsequent study IGFBP-5 was administered to wild-type mice and produced a 45% decrease in mammary DNA content, a 30% decrease in parenchymal tissue, and impaired lactation. These results suggest that GH can improve mammary development in PRLR(+/-) mice, but that it fails to enhance metabolic activity. This may be due to the maintenance by GH/IGF-I of a proliferative, rather than a differentiative, phenotype.

Insulin-like growth factor binding protein-5 (IGFBP-5) induces premature cell death in the mammary glands of transgenic mice

We have previously demonstrated that IGFBP-5 production by mammary epithelial cells increases dramatically during involution of the mammary gland. To demonstrate a causal relationship between IGFBP-5 and cell death we created transgenic mice expressing IGFBP-5 in the mammary gland using a mammary-specific promoter, β-lactoglobulin. DNA content in the mammary glands of transgenic mice was decreased as early as day 10 of pregnancy. Histological analysis indicated reduced numbers of alveolar end buds, with decreased ductal branching. Transgenic dams produced IGFBP-5 in their milk at concentrations similar to those achieved at the end of normal lactation. Mammary cell number and milk synthesis were both decreased by approximately 50% during the first 10 days of lactation. BrdU labelling was decreased, whereas DNA ladders were increased in transgenic animals on day 1 of lactation. On day 2 postpartum, the epithelial invasion of the mammary fat pad was clearly impaired in transgenic animals. The concentrations of the pro-apoptotic molecule caspase-3 and of plasmin were both increased in transgenic animals whilst the concentrations of 2 prosurvival molecules Bcl-2 and Bcl-xLwere both decreased. In order to examine whether IGFBP-5 acts by inhibiting the survival effect of IGF-I we examined IGF receptor phosphorylation and Akt phosphorylation and showed that both were inhibited. We attempted to “rescue” the transgenic phenotype by using growth hormone to increase endogenous IGF-I concentrations or by implanting minipumps delivering an IGF-1 analogue, R3-IGF-1, which binds weakly to IGFBP-5. Growth hormone treatment failed to affect mammary development suggesting that increased concentrations of endogenous IGF-1 are insufficient to overcome the high concentrations of IGFBP-5 produced by these transgenic animals. In contrast mammary development (gland weight and DNA content) was normalised by R3-IGF-I although milk production was only partially restored. This is the first demonstration that over-expression of IGFBP-5 can lead to; impaired mammary development, increased expression of the pro-apoptotic molecule caspase-3, increased plasmin generation and decreased expression of pro-survival molecules of the Bcl-2 family. It clearly demonstrates that IGF-I is an important developmental/survival factor for the mammary gland and, furthermore, this cell death programme may be utilised in a wide variety of tissues.

Deletion of Stat3 blocks mammary gland involution and extends functional competence of the secretory epithelium in the absence of lactogenic stimuli

The transcription factor Stat3 is activated through tyrosine phosphorylation by many cytokines and is a fundamental mediator of their signals. In the mammary gland, Stat3 activity increases sharply shortly after weaning, and involution is delayed in mice, that contain a mutant Stat3 lacking 33 amino acids including the key tyrosine residue. We have now generated a more extensive mutation of Stat3 through the deletion of exons 15-21 in mammary epithelium. This resulted in the loss of 245 amino acids including the DNA binding and SH2 domains, and Stat3 protein was undetectable. Pregnancy-mediated mammary development and lactation were normal in these mice. Involution was delayed and, remarkably, Stat3-null mammary epithelium maintained its functional integrity and competence even 6 d after weaning, whereas control mammary tissue was rendered nonfunctional within 2 d. The lack of remodeling and functional stasis of the epithelium correlated with the disruption of proteinase activity. Our data demonstrate that mammary tissue can retain its functional competence in the absence of external lactogenic stimuli and demonstrate a delay in the initiation of the irreversible stage of involution.

Insulin-like growth factors and insulin-like growth factor binding proteins in mammary gland function

Insulin-like growth factor (IGF)-mediated proliferation and survival are essential for normal development in the mammary gland during puberty and pregnancy. IGFs interact with IGF-binding proteins and regulate their function. The present review focuses on the role of IGFs and IGF-binding proteins in the mammary gland and describes how modulation of their actions occurs by association with hormones, other growth factors and the extracellular matrix. The review will also highlight the involvement of the IGF axis in breast cancer.

Stromal effects on mammary gland development and breast cancer

Breast cancer manifests itself in the mammary epithelium, yet there is a growing recognition that mammary stromal cells also play an important role in tumorigenesis. During its developmental cycle, the mammary gland displays many of the properties associated with breast cancer, and many of the stromal factors necessary for mammary development also promote or protect against breast cancer. Here we review our present knowledge of the specific factors and cell types that contribute to epithelial-stromal crosstalk during mammary development. To find cures for diseases like breast cancer that rely on epithelial-stromal crosstalk, we must understand how these different cell types communicate with each other.

Regulation of apoptosis during mammary involution by the p53 tumor suppressor gene

Regulation and functions of the p53 tumor suppressor gene have been studied extensively with respect to its critical role in maintaining the stability of genomic DNA following genotoxic insults. However, p53 is also induced by physiologic stimuli resulting in cell cycle arrest and apoptosis. In other situations, the activity of p53 must be repressed to prevent inappropriate removal of cells. The mammary gland provides a valuable system in which to study the mechanisms by which the expression and biological responses to p53 can be regulated under a variety of physiological circumstances. The pro-apoptotic role of p53 in the secretory mammary epithelium may be especially relevant to lactation in livestock. We have utilized p53-deficient mice to establish the molecular targets of p53 in the mammary gland and biological consequences when it is absent. The p21/WAF1 gene (Cdkn1a) is a transcriptional target gene of the p53 protein that responds to elevated levels of p53 during milk stasis providing an endogenous reporter of p53 activity. Abrogation of p53 resulted in delayed involution of the mammary epithelium, demonstrating the physiological role of p53 in regulating involution. Though delayed, stromal proteases were induced in the mammary gland by 5 d postweaning, providing a p53-independent mechanism that resulted in removal of the residual secretory epithelium. These processes can be interrupted by treatment with hydrocortisone. These data establish p53 as a physiological regulator of involution that acts to rapidly initiate apoptosis in the secretory epithelium in response to stress signals, but also indicate the presence of compensatory pathways to effect involution. Additional mechanisms involving intracellular stress signaling pathways (e.g., Stat3) and stromal-mediated pathways have been identified and, together with p53 pathways, may be used to identify animals with greater persistency of lactation.

Insulin-like growth factors and insulin-like growth factor binding proteins in mammary gland function

Insulin-like growth factor (IGF)-mediated proliferation and survival are essential for normal development in the mammary gland during puberty and pregnancy. IGFs interact with IGF-binding proteins and regulate their function. The present review focuses on the role of IGFs and IGF-binding proteins in the mammary gland and describes how modulation of their actions occurs by association with hormones, other growth factors and the extracellular matrix. The review will also highlight the involvement of the IGF axis in breast cancer.

Activities of IRF-1

Interferon (IFN) regulatory factor-1 (IRF-1) was isolated by virtue of its affinity to specific DNA sequences in the IFN-beta promoter that mediate virus responsiveness. IRF-1 was the first factor identified of the IRF family and was most extensively characterized at the molecular level. Also, its physiologic role in host defense against pathogens, tumor prevention, and development of the immune system was investigated in detail. Even though some of the functions first associated with IRF-1 were later found to be mediated in part or predominantly by other activators of the IRF family of transcription factors, IRF-1 has remained a central paradigm in the transcriptional regulation of the IFN response.