c-myc as a mediator of accelerated apoptosis and involution in mammary glands lacking Socs3

Intracellular calcium links milk stasis to lysosome-dependent cell death during early mammary gland involution

Involution of the mammary gland after lactation is a dramatic example of coordinated cell death. Weaning causes distension of the alveolar structures due to the accumulation of milk, which, in turn, activates STAT3 and initiates a caspase-independent but lysosome-dependent cell death (LDCD) pathway. Although the importance of STAT3 and LDCD in early mammary involution is well established, it has not been entirely clear how milk stasis activates STAT3. In this report, we demonstrate that protein levels of the PMCA2 calcium pump are significantly downregulated within 2-4 h of experimental milk stasis. Reductions in PMCA2 expression correlate with an increase in cytoplasmic calcium in vivo as measured by multiphoton intravital imaging of GCaMP6f fluorescence. These events occur concomitant with the appearance of nuclear pSTAT3 expression but prior to significant activation of LDCD or its previously implicated mediators such as LIF, IL6, and TGFβ3, all of which appear to be upregulated by increased intracellular calcium. We further demonstrate that increased intracellular calcium activates STAT3 by inducing degradation of its negative regulator, SOCS3. We also observed that milk stasis, loss of PMCA2 expression and increased intracellular calcium levels activate TFEB, an important regulator of lysosome biogenesis through a process involving inhibition of CDK4/6 and cell cycle progression. In summary, these data suggest that intracellular calcium serves as an important proximal biochemical signal linking milk stasis to STAT3 activation, increased lysosomal biogenesis, and lysosome-mediated cell death.

Intracellular Calcium links Milk Stasis to Lysosome Dependent Cell Death by Activating a TGFβ3/TFEB/STAT3 Pathway Early during Mammary Gland Involution

Involution of the mammary gland after lactation is a dramatic example of coordinated cell death. Weaning causes distension of the alveolar structures due to the accumulation of milk, which, in turn, activates STAT3 and initiates a caspase-independent but lysosome-dependent cell death (LDCD) pathway. Although the importance of STAT3 and LDCD in early mammary involution is well established, it has not been entirely clear how milk stasis activates STAT3. In this report, we demonstrate that protein levels of the PMCA2 calcium pump are significantly downregulated within 2-4 hours of experimental milk stasis. Reductions in PMCA2 expression correlate with an increase in cytoplasmic calcium in vivo as measured by multiphoton intravital imaging of GCaMP6f fluorescence. These events occur concomitant with the appearance of nuclear pSTAT3 expression but prior to significant activation of LDCD or its previously implicated mediators such as LIF, IL6 and TGFβ3, all of which appear to be upregulated by increased intracellular calcium. We also observed that milk stasis, loss of PMCA2 expression and increased intracellular calcium levels activate TFEB, an important regulator of lysosome biogenesis. This is the result of increased TGFβ signaling and inhibition of cell cycle progression. Finally, we demonstrate that increased intracellular calcium activates STAT3 by inducing degradation of its negative regulator, SOCS3, a process which also appears to be mediated by TGFβ signaling. In summary, these data suggest that intracellular calcium serves as an important proximal biochemical signal linking milk stasis to STAT3 activation, increased lysosomal biogenesis, and lysosome-mediated cell death.

Development of a Novel Immune-Related Gene Prognostic Index for Breast Cancer

Objective

To construct an immune-related gene prognostic index (IRGPI) for breast cancer (BC) and investigate its prognostic specificity and the molecular and immune characteristics.

Methods

BC hub genes were identified from The Cancer Genome Atlas and immune-related databases using weighted gene co-expression network analysis (WGCNA). IRGPI was constructed using univariate, LASSO, and multivariate regression analyses, and was validated with GSE58812 and GSE97342 in the Gene Expression Omnibus database (GEO). At the same time, we evaluated the predictive ability of IRGPI for different BC subtypes. Subsequently, the molecular and immune characteristics, clinical relevance, and benefits of immune checkpoint inhibitor treatment were analyzed for different IRGPI subgroups.

Results

IRGPI consisted of six genes: SOCS3, TCF7L2, TSLP NPR3, ANO6, and HMGB3. The IRGPI 1-, 5-, and 10-years area under curve (AUC) values were 0.635, 0.752, and 0.753, respectively, indicating that IRGPI has good potential in predicting the long-term survival of BC patients, consistent with the results in the GEO cohort. IRGPI showed good predictive power in four different breast cancer subtypes: ER positive, PR positive, HER2 positive and triple-negative (P<0.01). Compared with the low-IRGPI group, the high-IRGPI group had a worse prognosis and a lower degree of immune infiltrating cells (p < 0.05). IRGPI showed specificity in distinguishing age, TNM stage, ER, and HER2 statuses, and our study found that the high-IRGPI group had low tumor immune dysfunction and exclusion (TIDE), microsatellite instability (MSI), and T cell dysfunction scores (p < 0.05). In addition, compared with the TIDE and TIS models, showed that the AUCs of IRGPI were better during the 5-year follow-up.

Conclusion

IRGPI can be used as an independent prognostic indicator of breast cancer, providing a method for monitoring the long-term treatment of BC.

Knockdown of miR-92a suppresses the stemness of colorectal cancer cells via mediating SOCS3

MiRNAs (microRNAs) participate in colorectal cancer (CRC) progression and act as potential biomarkers for CRC prognosis. In this study, we investigated the mechanisms of microRNA-92a (miR-92a) in CRC. Expressions of miR-92a and SOCS3 (Suppressor Of Cytokine Signaling 3) were investigated by qRT-PCR in CRC cell lines and 30 cases of CRC. The self-renewal capacity and proliferation of CRC stem cells were estimated by the sphere formation assay, EdU staining, and Flow cytometry analysis. Moreover, the interplay between miR-92a and SOCS3 in CRC cells was validated by luciferase reporter experiments. MiR-92a was found to be remarkably increased while SOCS3 was significantly downregulated in CRC tissues. Inhibition of miR-92a or SOCS3 attenuated the sphere formation capacity, decreased expressions of stemness-related proteins, and inhibited the proliferation of cancer stem-like cells. Knockdown of SOCS3 reversed the repressive impacts of miR-92a inhibitors on self-renewal and growth of CRC cancer stem cells. This study suggested that miR-92a functions as an oncogene of CRC through mediating the stemness of colorectal cancer cells by directly binding and repressing SOCS3.

Emerging roles of suppressor of cytokine signaling 3 in human cancers

As a member of the suppressor of cytokine signaling (SOCS) family, SOCS3 is a cytokine-inducible protein that inhibits cytokine signaling in a variety of signaling pathways. Increasing evidence shows that SOCS3 regulates tumor development through multiple pathological and physiological processes. It is worth mentioning that SOCS3 negatively regulates JAK/STAT signaling by binding to JAK/cytokine receptors or phosphorylation docking sites on STAT receptors, thus preventing tumor cell proliferation and inhibiting tumor cell invasion and metastasis. The kinase inhibitory region KIR of SOCS3 is the key to JAK inhibition. In addition, SOCS3 may also regulate tumor progression through other molecules or signaling pathways, such as microRNAs (miRNAs), IL-6 and NF-κB signaling pathway. MicroRNAs inhibit SOCS3 expression by binding to the 3' untranslated region of SOCS3 mRNA, thus regulating tumor development processes, including tumor cell proliferation, invasion, metastasis, differentiation, cell cycle and apoptosis, as well as tumor metastasis and chemotherapy resistance. On the whole, SOCS3 acts as an inhibitor of the majority of tumors through various pathways. In the present review, the role of SOCS3 in multitudinous tumors was comprehensively summarized, the molecular mechanisms and modes of action of SOCS3 in tumors were discussed, and the association between SOCS3 expression and the clinical characteristics of patients with cancer were emphasized.

Lactation Associated Genes Revealed in Holstein Dairy Cows by Weighted Gene Co-Expression Network Analysis (WGCNA)

Simple Summary

Weighted gene coexpression network analysis (WGCNA) is a novel approach that can quickly analyze the relationships between genes and traits. In the past few years, studies on the gene expression changes of dairy cow mammary glands were only based on transcriptome comparisons between two lactation stages. Few studies focused on the relationships between gene expression of the dairy mammary gland and lactation stage or milk composition in a lactation cycle. In this study, we detected milk yield and composition in a lactation cycle. For the first time, we constructed a gene coexpression network using WGCNA on the basis of 18 gene expression profiles during six stages of a lactation cycle by transcriptome sequencing, generating 10 specific modules. Genes in each module were performed with gene ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. Module–trait relationship analysis showed a series of potential candidates related to milk yield and composition. The current study provides an important theoretical basis for the further molecular breeding of dairy cows.

Abstract

Weighted gene coexpression network analysis (WGCNA) is a novel approach that can quickly analyze the relationships between genes and traits. In this study, the milk yield, lactose, fat, and protein of Holstein dairy cows were detected in a lactation cycle. Meanwhile, a total of 18 gene expression profiles were detected using mammary glands from six lactation stages (day 7 to calving, −7 d; day 30 post-calving, 30 d; day 90 post-calving, 90 d; day 180 post-calving, 180 d; day 270 post-calving, 270 d; day 315 post-calving, 315 d). On the basis of the 18 profiles, WGCNA identified for the first time 10 significant modules that may be related to lactation stage, milk yield, and the main milk composition content. Genes in the 10 significant modules were examined with gene ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. The results revealed that the galactose metabolism pathway was a potential candidate for milk yield and milk lactose synthesis. In −7 d, ion transportation was more frequent and cell proliferation related terms became active. In late lactation, the suppressor of cytokine signaling 3 (SOCS3) might play a role in apoptosis. The sphingolipid signaling pathway was a potential candidate for milk fat synthesis. Dairy cows at 315 d were in a period of cell proliferation. Another notable phenomenon was that nonlactating dairy cows had a more regular circadian rhythm after a cycle of lactation. The results provide an important theoretical basis for the further molecular breeding of dairy cows.

SNIP1 Recruits TET2 to Regulate c-MYC Target Genes and Cellular DNA Damage Response

The TET2 DNA dioxygenase regulates gene expression by catalyzing demethylation of 5-methylcytosine, thus epigenetically modulating the genome. TET2 does not contain a sequence-specific DNA-binding domain, and how it is recruited to specific genomic sites is not fully understood. Here we carried out a mammalian two-hybrid screen and identified multiple transcriptional regulators potentially interacting with TET2. The SMAD nuclear interacting protein 1 (SNIP1) physically interacts with TET2 and bridges TET2 to bind several transcription factors, including c-MYC. SNIP1 recruits TET2 to the promoters of c-MYC target genes, including those involved in DNA damage response and cell viability. TET2 protects cells from DNA damage-induced apoptosis dependending on SNIP1. Our observations uncover a mechanism for targeting TET2 to specific promoters through a ternary interaction with a co-activator and many sequence-specific DNA-binding factors. This study also reveals a TET2-SNIP1-c-MYC pathway in mediating DNA damage response, thereby connecting epigenetic control to maintenance of genome stability.

Stat3 accelerates Myc induced tumor formation while reducing growth rate in a mouse model of breast cancer

Elevated Myc expression has been noted in basal breast cancer but therapies targeting Myc directly are lacking. It is therefore critical to characterize the interaction of Myc with other genes and pathways to uncover future potential therapeutic strategies. In this study, we bioinformatically predicted a role for Stat3 in Myc induced mammary tumors and tested it using mouse models. During normal mammary function, loss of Stat3 in Myc transgenic dams resulted in lethality of pups due to lactation deficiencies. We also observed that deletion of Stat3 in the mammary glands of MMTV-Myc mice unexpectedly resulted in increased and earlier hyperplasia and expedited tumorigenesis. However, despite arising earlier, Myc tumors lacking Stat3 grew more slowly with alterations in the resulting histological subtypes, including a dramatic increase in EMT-like tumors. We also observed that these tumors had impaired angiogenesis and a slight decrease in lung metastases. This metastatic finding is distinct from previously published findings in both MMTV-Neu and MMTV-PyMT mouse models. Together, the literature and our current research demonstrate that Stat3 can function as an oncogene or as a tumor repressor depending on the oncogenic driver and developmental context.

The relationship between total and phosphorylated STAT1 and STAT3 tumour cell expression, components of tumour microenvironment and survival in patients with invasive ductal breast cancer

The aim of the present study was to examine the relationship between tumour cell expression of total and phosphorylated STAT1 (ph-STAT1) and STAT3 (ph-STAT-3), components of tumour microenvironment and survival in patients with invasive ductal breast cancer.

Immunohistochemical analysis of total and ph-STAT1, and STAT3 were performed on tissue microarray of 384 breast cancer specimens. Tumour cell expression of STAT1 and STAT3 at both cytoplasmic and nuclear locations were combined and identified as STAT1/STAT3 tumour cell expression. These results were related to cancer specific survival (CSS) and phenotypic features of the tumour and the host.

High ph-STAT1 and ph-STAT3 tumour cell expression were associated with increased ER (both P≤0.001) and PR (both P <0.05), reduced tumour grade (P=0.015 and P<0.001 respectively) and necrosis (both P=0.001). Ph-STAT1 was associated with increased general inflammatory infiltrate (P=0.007) and ph-STAT3 was associated with lower CD4+ infiltration (P=0.024). In multivariate survival analysis, only high ph-STAT3 tumour cell expression was a predictor of improved CSS (P=0.010) independent of other tumour and host-based factors.

STAT1 and STAT3 tumour cell expression appeared to be an important determinant of favourable outcome in patients with invasive ductal breast cancer. The present results suggest that STAT1 and STAT3 may affect disease outcome through direct impact on tumour cells, counteracting aggressive tumour features, as well as interaction with the surrounding microenvironment.

Th-POK regulates mammary gland lactation through mTOR-SREBP pathway

The Th-inducing POK (Th-POK, also known as ZBTB7B or cKrox) transcription factor is a key regulator of lineage commitment of immature T cell precursors. It is yet unclear the physiological functions of Th-POK besides helper T cell differentiation. Here we show that Th-POK is restrictedly expressed in the luminal epithelial cells in the mammary glands that is upregulated at late pregnancy and lactation. Lineage restrictedly expressed Th-POK exerts distinct biological functions in the mammary epithelial cells and T cells in a tissue-specific manner. Th-POK is not required for mammary epithelial cell fate determination. Mammary gland morphogenesis in puberty and alveologenesis in pregnancy are phenotypically normal in the Th-POK-deficient mice. However, Th-POK-deficient mice are defective in triggering the onset of lactation upon parturition with large cellular lipid droplets retained within alveolar epithelial cells. As a result, Th-POK knockout mice are unable to efficiently secret milk lipid and to nurse the offspring. Such defect is mainly attributed to the malfunctioned mammary epithelial cells, but not the tissue microenvironment in the Th-POK deficient mice. Th-POK directly regulates expression of insulin receptor substrate-1 (IRS-1) and insulin-induced Akt-mTOR-SREBP signaling. Th-POK deficiency compromises IRS-1 expression and Akt-mTOR-SREBP signaling in the lactating mammary glands. Conversely, insulin induces Th-POK expression. Thus, Th-POK functions as an important feed-forward regulator of insulin signaling in mammary gland lactation.

Hypothyroidism advances mammary involution in lactating rats through inhibition of PRL signaling and induction of LIF/STAT3 mRNAs

Thyroid diseases have deleterious effects on lactation, litter growth and survival, and hinder the suckling-induced hormone release, leading in the case of hyperthyroidism, to premature mammary involution. To determine the effects of hypothyroidism (HypoT) on late lactation, we analyzed the effect of chronic 6-propyl-2-thiouracil (PTU)-induced HypoT on mammary histology and the expression of members of the JAK/STAT/SOCS signaling pathway, milk proteins, prolactin (PRLR), estrogen (ER), progesterone (PR) and thyroid hormone (TR) receptors, markers of involution (such as stat3, lif, bcl2, BAX and PARP) on lactation (L) day 21. HypoT mothers showed increased histological markers of involution compared with control rats, such as adipose/epithelial ratio, inactive alveoli, picnotic nuclei and numerous detached apoptotic cells within the alveolar lumina. We also found decreased PRLR, β-casein and α-lactoalbumin mRNAs, but increased SOCS1, SOCS3, STAT3 and LIF mRNAs, suggesting a decrease in PRL signaling and induction of involution markers. Furthermore, Caspase-3 and 8 and PARP labeled cells and the expression of structural proteins such as β-Actin, α-Tubulin and Lamin B were increased, indicating the activation of apoptotic pathways and tissue remodelation. HypoT also increased PRA (mRNA and protein) and erβ and decreased erα mRNAs, and increased strongly TRα1, TRβ1, PRA and ERα protein levels. These results show that lactating HypoT rats have premature mammary involution, most probably induced by the inhibition of prolactin signaling along with the activation of the LIF-STAT3 pathway.

Direct and immune-mediated cytotoxicity of interleukin-21 contributes to antitumor effects in mantle cell lymphoma

Mantle cell lymphoma (MCL) is a distinct subtype of non-Hodgkin lymphoma characterized by overexpression of cyclin D1 in 95% of patients. MCL patients experience frequent relapses resulting in median survival of 3 to 5 years, requiring more efficient therapeutic regimens. Interleukin (IL)-21, a member of the IL-2 cytokine family, possesses potent antitumor activity against a variety of cancers not expressing the IL-21 receptor (IL-21R) through immune activation. Previously, we established that IL-21 exerts direct cytotoxicity on IL-21R-expressing diffuse large B-cell lymphoma cells. Herein, we demonstrate that IL-21 possesses potent cytotoxicity against MCL cell lines and primary tumors. We identify that IL-21-induced direct cytotoxicity is mediated through signal transducer and activator of transcription 3-dependent cMyc upregulation, resulting in activation of Bax and inhibition of Bcl-2 and Bcl-XL. IL-21-mediated cMyc upregulation is only observed in IL-21-sensitive cells. Further, we demonstrate that IL-21 leads to natural killer (NK)-cell-dependent lysis of MCL cell lines that were resistant to direct cytotoxicity. In vivo treatment with IL-21 results in complete FC-muMCL1 tumor regression in syngeneic mice via NK- and T-cell-dependent mechanisms. Together, these data indicate that IL-21 has potent antitumor activity against MCL cells via direct cytotoxic and indirect, immune-mediated effects.

The BH3-only protein BIM contributes to late-stage involution in the mouse mammary gland

After cessation of lactation, involution of the mouse mammary gland proceeds in two distinct phases, a reversible and an irreversible one, which leads to the death and removal of alveolar cells. Cell death is preceded by the loss of STAT5 activity, which abrogates cell differentiation and gain of STAT3 activity. Despite early observations implicating BCL2 (B cell lymphoma 2) family proteins in this process, recent evidence suggests that STAT3-controlled cathepsin activity is most critical for cell death at the early stage of involution. Somewhat surprisingly, this cell death associates with but does not depend on the activation of pro-apoptotic effector caspases. However, transgenic overexpression of BCL2, that blocks caspase activation, delays involution while conditional deletion of BclX accelerates this process, suggesting that BCL2 family proteins are needed for the effective execution of involution. Here, we report on the transcriptional induction of multiple pro-apoptotic BCL2 family proteins of the 'BH3-only' subgroup during involution and the rate-limiting role of BIM in this process. Loss of Bim delayed epithelial cell clearance during involution after forced weaning in mice, whereas the absence of related Bmf had minor and loss of Bad or Noxa no impact on this process. Consistent with a contribution of BCL2 family proteins to the second wave of cell death during involution, loss of Bim reduced the number of apoptotic cells in this irreversible phase. Notably, the expression changes observed within the BCL2 family did not depend on STAT3 signalling, in line with its initiating role early in the process, but rather appear to result from relief of repression by STAT5. Our findings support the existence of a signalling circuitry regulating the irreversible phase of involution in mice by engaging BH3-only protein-driven mitochondrial apoptosis.

SOCS3 expression is inversely correlated with Pyk2 in non-small cell lung cancer and exogenous SOCS3 inhibits proliferation and invasion of A549 cells

AIMS

We have confirmed that suppressor of cytokine signalling 3 (SOCS3) is silenced and proline-rich tyrosine kinase 2 (Pyk2) is over-expressed in non-small cell lung cancer (NSCLC). The aim of this study was to investigate the correlation of SOCS3 and Pyk2 expression in NSCLC, and the effects of SOCS3 up-regulation on A549 cells.

METHODS

One hundred cases of NSCLC were detected for the expression of SOCS3 and Pyk2 by immunohistochemistry. The expression of SOCS3 and Pyk2 were also examined in human bronchial epithelial cells (HBE) and six lung cancer cell lines using Western blot and immunofluorescence staining. Then plasmid containing full-length SOCS3 was transfected into A549 cells to further investigate the effects of SOCS3 over-expression on proliferation, apoptosis and invasion of transfected cells, which were examined using MTT, flow cytometry and Transwell assays.

RESULTS

Our results showed a significant negative correlation between SOCS3 and Pyk2 in both NSCLC tissues and cell lines. Up-regulation of SOCS3 increased the apoptotic rates of transfected cells, while the numbers of proliferative and invasive cells were decreased.

CONCLUSIONS

Our data indicate that SOCS3 definitely plays roles in regulating Pyk2 expression, and up-regulation of SOCS3 could be an effective way to prevent the progression of NSCLC.

SOCS3: An essential physiological inhibitor of signaling by interleukin-6 and G-CSF family cytokines

SOCS3 is an inducible negative feedback inhibitor of cytokine signaling. Conditional deletion of SOCS3 in mice using the Cre-lox system has now been applied to a range of cell types in the steady-state and under inflammatory, pathogenic, or tumorigenic stress, with the resulting phenotypes demonstrating the effects of SOCS3 in physiological and disease contexts. Together with recent structural and biochemical studies on the mechanisms of SOCS3 binding to cytokine receptors and associated kinases, we now have a better understanding of the non-redundant roles of SOCS3 in the inhibition of cytokine signaling via the receptors gp130, G-CSFR, leptinR, and IL-12Rβ. This review discusses the known functional activities of SOCS3 in fertility and development, inflammation, innate and adaptive immunity, and malignancy as determined by genetic studies in mice.

Hunk negatively regulates c-myc to promote Akt-mediated cell survival and mammary tumorigenesis induced by loss of Pten

The protooncogenes Akt and c-myc each positively regulate cell growth and proliferation, but have opposing effects on cell survival. These oncogenes cooperate to promote tumorigenesis, in part because the prosurvival effects of Akt offset the proapoptotic effects of c-myc. Akt's ability to counterbalance c-myc's proapoptotic effects has primarily been attributed to Akt-induced stimulation of prosurvival pathways that indirectly antagonize the effects of c-myc. We report a more direct mechanism by which Akt modulates the proapoptotic effects of c-myc. Specifically, we demonstrate that Akt up-regulates the adenosine monophosphate-associated kinase (AMPK)-related protein kinase, Hormonally up-regulated neu-associated kinase (Hunk), which serves as an effector of Akt prosurvival signaling by suppressing c-myc expression in a kinase-dependent manner to levels that are compatible with cell survival. Consequently, Akt pathway activation in the mammary glands of Hunk(-/-) mice results in induction of c-myc expression to levels that induce apoptosis. c-myc knockdown rescues the increase in apoptosis induced by Hunk deletion in cells in which Akt has been activated, indicating that repression of c-myc is a principal mechanism by which Hunk mediates the prosurvival effects of Akt. Consistent with this mechanism of action, we find that Hunk is required for c-myc suppression and mammary tumorigenesis induced by phosphatase and tensin homolog (Pten) deletion in mice. Together, our findings establish a prosurvival function for Hunk in tumorigenesis, define an essential mechanism by which Akt suppresses c-myc-induced apoptosis, and identify Hunk as a previously unrecognized link between the Akt and c-myc oncogenic pathways.

Tissue microarray-based study of patients with lymph node-positive breast cancer shows tyrosine phosphorylation of signal transducer and activator of transcription 3 (tyrosine705-STAT3) is a marker of good prognosis

BACKGROUND

Although lymph node-positive breast cancers are associated with poorer prognosis, individual patients may have different clinical outcomes. Signal transducer and activator of transcription 3 (STAT3) is a point of convergence for numerous oncogenic signalling pathways. The goal of this study was to determine the prognostic value of phosphorylated (tyrosine705)-STAT3 in node-positive breast cancer patients.

METHODS

Immunohistochemical analysis of Phospho- STAT3 was performed on a tissue microarray of breast cancer specimens. The expression pattern of Phospho-STAT3 was correlated with survival outcome, and clinical and pathological parameters.

RESULTS

Out of 125 interpretable tumours, positive Phospho- STAT3 nuclear expression was seen in 35 (28%) of tumours. There was no significant relationship between Phospho-STAT3 expression and clinical-pathological parameters including age, hormonal receptor status, grade and tumour size. Interestingly positive tumours had a significantly improved disease-free survival at 5 years (p=0.035). Additionally, positive Phospho-STAT3 nuclear expression was correlated with significantly improved survival at both 5 years (p=0.023) and 10 years (p=0.026). Finally, in multivariate analyses Phospho-STAT3 was found to be an independent prognostic marker of overall survival in node-positive breast cancer patients.

CONCLUSION

These findings support the role of Phospho- STAT3 as an important independent prognostic marker in node-positive breast cancer patients.

Replacement of E-cadherin by N-cadherin in the mammary gland leads to fibrocystic changes and tumor formation

Introduction

E-cadherin (E-cad; cadherin 1) and N-cadherin (N-cad; cadherin 2) are the most prominent members of the cadherin family of cell adhesion molecules. Although they share many structural and functional features, they are expressed in an almost mutually exclusive manner in vivo.

Methods

To explore functional differences between the two cadherins in vivo, we recently generated a knock-in line in which N-cad is expressed from the E-cad locus. In combination with a conditional gene inactivation approach, we expressed N-cad in the absence of E-cad (referred to as Ncadk.i.) in alveolar epithelial cells of the mammary gland starting in late pregnancy.

Results

We found that the sole presence of N-cad induces constitutively active fibroblast growth factor (Fgf) signaling and a precocious involution resulting in massive apoptosis of alveolar cells. To block apoptosis, we conditionally deleted one allele of p53 in Ncadk.i. mice and observed a temporal rescue of alveolar morphology and function. However, an accumulation of fibrotic tissue and cysts with increasing age and lactation cycles was observed. This phenotype closely resembled fibrocystic mastopathy (FM), a common disorder in humans, which is thought to precede breast cancer. Concordantly, 55% of Ncadk.i. mice harboring a heterozygous p53 deletion developed malignant and invasive tumors.

Conclusions

Our results demonstrate a possible role for N-cad in the formation of fibrosis and cysts in the mammary gland. Moreover, we show that these lesions precede the development of malignant tumors. Thus, we provide a new mouse model to investigate the molecular mechanisms of fibrocystic mastopathy and the transition from benign to malignant tumors.

c-Myc induction of programmed cell death may contribute to carcinogenesis: a perspective inspired by several concepts of chemical carcinogenesis

The c-Myc protein, encoded by c-myc gene, in its wild-type form can induce tumors with a high frequency and can induce massive programmed cell death (PCD) in most transgenic mouse models, with greater efficiency than other oncogenes. Evidence also indicates that c-Myc can cause proliferative inhibition, i.e. mitoinhibition. The c-Myc-induced PCD and mitoinhibition, which may be attributable to its inhibition of cyclin D1 and induction of p53, may impose a pressure of compensatory proliferation, i.e. regeneration, onto the initiated cells (cancer progenitor cells) that occur sporadically and are resistant to the mitoinhibition. The initiated cells can thus proliferate robustly and progress to a malignancy. This hypothetical thinking, i.e. the concurrent PCD and mitoinhibition induced by c-Myc can promote carcinogenesis, predicts that an optimal balance is achieved between cell death and ensuing regeneration during oncogenic transformation by c-Myc, which can better promote carcinogenesis. In this perspective, we summarize accumulating evidence and challenge the current model that oncoprotein induces carcinogenesis by promoting cellular proliferation and/or inhibiting PCD. Inspired by c-myc oncogene, we surmise that many tumor-suppressive or growth-inhibitory genes may also be able to promote carcinogenesis in a similar way, i.e. by inducing PCD and/or mitoinhibition of normal cells to create a need for compensatory proliferation that drives a robust replication of initiating cells.

Acute involution in the tammar wallaby: identification of genes and putative novel milk proteins implicated in mammary gland function

Marsupials provide a suitable alternative model to studying mammary gland involution. They have evolved a different reproductive strategy from eutherians, giving birth to an altricial young and secreting milk that changes in composition during lactation. In this study, we used a marsupial-specific EST microarray to identify 47 up-regulated genes during mammary gland involution in the tammar wallaby (Macropus eugenii). These include the pro-apoptotic tumour necrosis factor receptor superfamily 21 (TNFRSF21) gene, whose expression in the mammary gland has not previously been reported. Genes encoding putative novel milk proteins which may protect the mammary gland from infection were also found to be up-regulated, such as amiloride binding protein 1 (ABP1), complement component 1QB (C1QB), complement component 4A (C4A) and colony stimulating factor 2 receptor β (CSF2Rβ). Our results show that the marsupial reproductive strategy was successfully exploited to identify genes and putative novel milk proteins implicated in mammary gland involution.

Protective properties of inhaled IL-22 in a model of ventilator-induced lung injury

High-pressure ventilation induces barotrauma and pulmonary inflammation, thus leading to ventilator-induced lung injury (VILI). IL-22 has both immunoregulatory and tissue-protective properties. Functional IL-22 receptor expression is restricted to nonleukocytic cells, such as alveolar epithelial cells. When applied via inhalation, IL-22 reaches the pulmonary system directly and in high concentrations, and may protect alveolar epithelial cells against cellular stress and biotrauma associated with VILI. In A549 lung epithelial cells, IL-22 was able to induce rapid signal transducer and activator of transcription (STAT)-3 phosphorylation/activation, and hereon mediated stable suppressor of cytokine signaling (SOCS) 3 expression detectable even 24 hours after onset of stimulation. In a rat model of VILI, the prophylactic inhalation of IL-22 before induction of VILI (peak airway pressure = 45 cm H(2)O) protected the lung against pulmonary disintegration and edema. IL-22 reduced VILI-associated biotrauma (i.e., pulmonary concentrations of macrophage inflammatory protein-2, IL-6, and matrix metalloproteinase 9) and mediated pulmonary STAT3/SOCS3 activation. In addition, despite a short observation period of 4 hours, inhaled IL-22 resulted in an improved survival of the rats. These data support the hypothesis that IL-22, likely via activation of STAT3 and downstream genes (e.g., SOCS3), is able to protect against cell stretch and pulmonary baro-/biotrauma by enhancing epithelial cell resistibility.

Forced involution of the functionally differentiated mammary gland by overexpression of the pro-apoptotic protein bax

The mammary gland is a developmentally dynamic, hormone-responsive organ that undergoes proliferation and differentiation within the secretory epithelial compartment during pregnancy. The epithelia are maintained by pro-survival signals (e.g., Stat5, Akt1) during lactation, but undergo apoptosis during involution through inactivation of cell survival pathways and upregulation of pro-apoptotic proteins. To assess if the survival signals in the functionally differentiated mammary epithelial cells can override a pro-apoptotic signal, we generated transgenic mice that express Bax under the whey acidic protein (WAP) promoter. WAP-Bax females exhibited a lactation defect and were unable to nourish their offspring. Mammary glands demonstrated: (1) a reduction in epithelial content, (2) hallmark signs of mitochondria-mediated cell death, (3) an increase in apoptotic cells by TUNEL assay, and (4) precocious Stat3 activation. This suggests that upregulation of a single pro-apoptotic factor of the Bcl-2 family is sufficient to initiate apoptosis of functionally differentiated mammary epithelial cells in vivo.

Arsenic trioxide-mediated growth inhibition of myeloma cells is associated with an extrinsic or intrinsic signaling pathway through activation of TRAIL or TRAIL receptor 2

Arsenic trioxide (ATO) is a well-known inhibitor of cell proliferation. Preclinical and clinical studies showed that ATO has anti-myeloma effects. However, the underlying mechanism remains elusive. In this study, the molecular mechanisms of ATO-induced myeloma apoptosis were explored on four myeloma cell lines of wild type or mutant p53 status and also on six primary myeloma cells. ATO induced potent inhibition of myeloma cell growth and myeloma cell apoptosis compared with controls. Further investigation showed that ATO down-regulated c-Myc and phosphorylated (p)-Rb while up-regulating p53, p21Cip1, and p27Kip1 proteins, resulting in G0/G1 or G2/M cell cycle arrest. ATO treatment increased mRNA levels of interferon regulatory factor-1 and TRAIL, as well as protein levels of caspase 8 and cleaved caspase 3, indicating the involvement of the extrinsic apoptotic pathway in the mutated p53 myeloma cells. ATO also activated caspases 3 and 9, indicating involvement of the intrinsic apoptotic pathway in the wild type p53 myeloma cells. More importantly, these molecular changes induced by ATO-treated myeloma cells are very similar to the baseline expression pattern of hyperdiploid myeloma, which has a relative good prognosis with high expression of TRAIL and interferon related genes. Together, our data suggest that ATO induces apoptosis in MM through either extrinsic or intrinsic signaling pathway, depending on the p53 genetic background. These observations may be employed as prognostic tools and lead to novel therapies in primary myelomas.

Expression of metabolic, tissue remodeling, oxidative stress, and inflammatory pathways in mammary tissue during involution in lactating dairy cows

Histological and functional changes associated with involution in the mammary gland are partly regulated by changes in gene expression. At 42 d postpartum, Holstein cows underwent a period of 5 d during which they were milked 1X daily until complete cessation of milking. Percutaneous mammary biopsies (n = 5/time point) were obtained on d 1, 5, 14, and 21 relative to the start of 1X milking for transcript profiling via qPCR of 57 genes associated with metabolism, apoptosis/proliferation, immune response/inflammation, oxidative stress, and tissue remodeling. Not surprisingly, there was clear downregulation of genes associated with milk fat synthesis (FASN, ACACA, CD36, FABP3, SCD) and lipid-related transcription regulation (SREBF1, SREBF2). Similar to milk fat synthesis-related genes, those encoding proteins required for glucose uptake (SLC2A1), casein synthesis (CSN2, CSN3), and lactose synthesis (LALBA) decreased during involution. Unlike metabolic genes, those associated with immune response and inflammation (C3, LTF, SAA3), oxidative stress (GPX1, SOD2), and pro-inflammatory cytokine signaling (SPP1, TNF) increased to peak levels by d 14 from the start of 1X milking. These adaptations appeared to be related with tissue remodeling as indicated by upregulation of proteins encoding matrix proteinases (MMP2), IGFBP3, and transcriptional regulation of apoptosis/cell proliferation (MYC). In contrast, the concerted upregulation of STAT3, TGFB1, and TGFB1R during the first 14 d was suggestive of an activation of these signaling pathways probably as an acute response to regulate differentiation and/or mammary cell survival upon the onset of a marked pro-inflammatory and oxidative stress response induced by the gradual reduction in milk removal. Results suggest a central role of STAT3, MYC, PPARG, SREBF1, and SREBF2 in regulating concerted alterations in metabolic and cell survival mechanisms, which were induced partly via oxidative stressed-triggered inflammation and the decline in metabolic activity.

Key signalling nodes in mammary gland development and cancer: Myc

Myc has been intensely studied since its discovery more than 25 years ago. Insight has been gained into Myc's function in normal physiology, where its role appears to be organ specific, and in cancer where many mechanisms contribute to aberrant Myc expression. Numerous signals and pathways converge on Myc, which in turn acts on a continuously growing number of identified targets, via transcriptional and nontranscriptional mechanisms. This review will concentrate on Myc as a signaling mediator in the mammary gland, discussing its regulation and function during normal development, as well as its activation and roles in breast cancer.

Novel IL-21 signaling pathway up-regulates c-Myc and induces apoptosis of diffuse large B-cell lymphomas

Interleukin-21 (IL-21), a member of the IL-2 cytokine family, has diverse regulatory effects on natural killer (NK), T, and B cells. In contrast to other cytokines that are usually immunostimulatory, IL-21 can induce apoptosis of murine B cells at specific activation-differentiation stages. This effect may be used for treatment of B-cell malignancies. Herein we report that diffuse large B-cell lymphoma (DLBCL) cell lines exhibit widespread expression of the IL-21 receptor (IL-21R) and that IL-21 stimulation leads to cell-cycle arrest and caspase-dependent apoptosis. IL-21 also induces apoptosis in de novo DLBCL primary tumors but does not affect viability of human healthy B cells. Furthermore, IL-21 promotes tumor regression and prolongs survival of mice harboring xenograft DLBCL tumors. The antilymphoma effects of this cytokine are dependent on a mechanism involving IL-21-activated signal transducer and activator of transcription 3 (STAT3) up-regulating expression of c-Myc. This up-regulation promotes a decrease in expression of antiapoptotic Bcl-2 and Bcl-X(L) proteins triggering cell death. Our results represent one of the first examples in which the STAT3-c-Myc signaling pathway, which can promote survival and oncogenesis, can induce apoptosis in neoplastic cells. Moreover, based on IL-21's potency in vitro and in animal models, our findings indicate that this cytokine should be examined in clinical studies of DLBCL.

c-Myc affects mRNA translation, cell proliferation and progenitor cell function in the mammary gland

Background

The oncoprotein c-Myc has been intensely studied in breast cancer and mouse mammary tumor models, but relatively little is known about the normal physiological role of c-Myc in the mammary gland. Here we investigated functions of c-Myc during mouse mammary gland development using a conditional knockout approach.

Results

Generation of c-myc^fl/fl mice carrying the mammary gland-specific WAPiCre transgene resulted in c-Myc loss in alveolar epithelial cells starting in mid-pregnancy. Three major phenotypes were observed in glands of mutant mice. First, c-Myc-deficient alveolar cells had a slower proliferative response at the start of pregnancy, causing a delay but not a block of alveolar development. Second, while milk composition was comparable between wild type and mutant animals, milk production was reduced in mutant glands, leading to slower pup weight-gain. Electron microscopy and polysome fractionation revealed a general decrease in translational efficiency. Furthermore, analysis of mRNA distribution along the polysome gradient demonstrated that this effect was specific for mRNAs whose protein products are involved in milk synthesis. Moreover, quantitative reverse transcription-polymerase chain reaction analysis revealed decreased levels of ribosomal RNAs and ribosomal protein-encoding mRNAs in mutant glands. Third, using the mammary transplantation technique to functionally identify alveolar progenitor cells, we observed that the mutant epithelium has a reduced ability to repopulate the gland when transplanted into NOD/SCID recipients.

Conclusion

We have demonstrated that c-Myc plays multiple roles in the mouse mammary gland during pregnancy and lactation. c-Myc loss delayed, but did not block proliferation and differentiation in pregnancy. During lactation, lower levels of ribosomal RNAs and proteins were present and translation was generally decreased in mutant glands. Finally, the transplantation studies suggest a role for c-Myc in progenitor cell proliferation and/or survival.

See related minireview by Evan et al:

Differentiation of the mammary epithelial cell during involution: implications for breast cancer

That milk secretion is not the final differentiated state of the mammary alveolar cells is a relatively new concept. Recent work has suggested that secreting, mammary epithelial cells (MECs) have another function to perform before they undergo cell death in the involuting mammary gland. That is, they help in the final clearance and breakdown of their neighboring cells (and likely residual milk as well.) They become, for a short time, amateur phagocytes, or efferocytes, and then are believed to die and be cleared themselves. Although relatively little study has been made of this change in the functional state of the MEC, nevertheless we may speculate from the involution literature, and extend findings from other systems of apoptotic cell clearance, on some of the mechanisms involved. And with the finding that involution may represent a unique susceptibility window for the progression of metastatic breast cancer, we may suggest areas for future research along these lines as well.

Stat3 and the inflammation/acute phase response in involution and breast cancer

The transcription factor Stat3 is essential for timely initiation of post-lactational regression and orchestrates the processes of cell death and tissue remodelling that occur during the first 6 days of involution in the mouse. Paradoxically, STAT3 is also frequently found to be constitutively active in breast cancer and tumors can become addicted to STAT3. This raises two interesting questions: 1) do the high levels of active Stat3 present in the mammary epithelium during involution promote tumor spread and 2) how do tumor cells escape the pro-apoptotic effects of Stat3? In order to address these questions, it is essential to understand the role of Stat3 in involution and the mechanisms by which Stat3 regulates both cell death and tissue remodelling. A number of studies have been undertaken using genetically modified mice and microarray analyses and two significant findings arose from these investigations. Firstly, post-lactational regression is associated with an acute phase and inflammatory response in addition to cell death and secondly, Stat3 alone is insufficient to induce involution in the absence of the NF-kappaB regulatory kinase IKKbeta. Both Stat3 and NF-kappaB have been shown to regulate the expression of genes involved in inflammatory signalling and the acute phase response. These findings suggest a role for the innate immune response in mammary epithelial cell fate during involution and highlight potential roles for this response in tissue remodelling-associated breast cancer metastasis.

Murine models of colorectal cancer

Colorectal cancer is one of the most prevalent cancers of humans. To experimentally investigate this common disease, numerous murine models have been established. These models accurately recapitulate the molecular and pathologic characteristics of human colorectal cancers, including activation of the myelocytomatosis oncogene (MYC), which has recently been suggested to be a key mediator of colorectal cancer development. This review focuses on the variety of murine models of human colorectal cancer that are available to the research community and on their use to identify common and distinct characteristics of colorectal cancer.

Deletion of the SOCS box of suppressor of cytokine signaling 3 (SOCS3) in embryonic stem cells reveals SOCS box-dependent regulation of JAK but not STAT phosphorylation

The mechanism by which Suppressor of Cytokine Signaling-3 (SOCS3) negatively regulates cytokine signaling has been widely investigated using over-expression studies in cell lines and is thought to involve interactions with both the gp130 receptor and JAK1. Here, we compare the endogenous JAK/STAT signaling pathway downstream of Leukemia Inhibitory Factor (LIF) signaling in wild type (WT) Embryonic Stem (ES) cells and in ES cells lacking either the entire Socs3 gene or bearing a truncated form of SOCS3 (SOCS3DeltaSB) lacking the C-terminal SOCS box motif (SOCS3(DeltaSB/DeltaSB)). In SOCS3(DeltaSB/DeltaSB) cells phosphorylated JAK1 accumulated at much higher levels than in WT cells or even cells lacking SOCS3 (SOCS3(-/-)). In contrast enhanced activation of STAT3 and SHP2 was seen in SOCS3(-/-) cells. Size exclusion chromatography of cell extracts showed that in unstimulated cells, JAK1 was exclusively associated with receptors but following cytokine stimulation hyperphosphorylated JAK1 (pJAK1) appeared to dissociate from the receptor complex in a manner independent of SOCS3. In WT and SOCS3(DeltaSB/DeltaSB) cells SOCS3 was associated with pJAK1. The data suggest that dissociation of activated JAK1 from the receptor results in separate targeting of JAK1 for proteasomal degradation through a mechanism dependent on the SOCS3 SOCS box thus preventing further activation of STAT3.

Immune cell regulators in mouse mammary development and involution

Dramatic changes in cell composition and function occur in the mammary gland during a pregnancy-lactation-involution cycle. We investigated the transcriptional changes associated with these biological events by using microarray analysis and identified the critical genes involved by using genetically modified mice. Two surprising findings arose from these studies. First, the microarray data showed that postlactational regression was associated with an acute phase inflammatory response, in addition to cell death. Conditional deletion of signal transducer and activator of transcription (Stat)3 or the nuclear factor-kappaB regulatory kinase inhibitor of kappa B kinase beta resulted in a failure of cell death induction during involution, an indication that these signaling pathways are essential mediators of the involution process. Both Stat3 and nuclear factor-kappaB have been shown to regulate acute phase gene expression in addition to apoptosis regulators. Four distinct transcriptional profiles are present in the first 4 d of involution, whereas there are 3 in lactation. At the peak of lactation (i.e., d 10 in mouse), more than 400 genes reach their maximum expression before declining dramatically in the first 12 h of involution. A reciprocal pattern was observed for more than 500 genes that were specifically upregulated within the first 12 h of forced involution. We are now investigating the role of a subset of these genes in involution. We also uncovered a role for genes normally associated with immune cell signaling in the differentiation of luminal mammary epithelial cells during pregnancy. Genetic deletion of the transcription factor Stat6 resulted in delayed development during pregnancy, and this phenotype was recapitulated in mammary tissue from IL-4 and IL-13 doubly deficient mice. Furthermore, we showed that mammary epithelial cells secrete T-cell regulatory cytokines. T-helper type 1 cytokines, such as interferon-gamma and IL-12a, are secreted by undifferentiated mammary epithelial cells, whereas T-helper type 2 cytokines, including IL-4 and IL-13, are secreted by differentiated cells. This unexpected finding demonstrates a role for immune cell signaling in mammary epithelial cell fate and function.

Deaf-1 regulates epithelial cell proliferation and side-branching in the mammary gland

Background

The transcription factor DEAF-1 has been identified as a high affinity binding partner of the LIM-only protein LMO4 that plays important roles in mammary gland development and breast cancer. Here we investigated the influence of DEAF-1 on human and mouse mammary epithelial cells both in vitro and in vivo and identified a potential target gene.

Results

Overexpression of DEAF-1 in human breast epithelial MCF10A cells enhanced cell proliferation in the mammary acini that develop in 3D cultures. To investigate the effects of Deaf-1 on mammary gland development and oncogenesis, we generated MMTV-Deaf-1 transgenic mice. Increased ductal side-branching was observed in young virgin mammary glands, accompanied by augmented cell proliferation. In addition, the ratio of the progesterone receptor isoforms PRA and PRB, previously implicated in regulating ductal side-branching, was altered. Affymetrix gene profiling studies revealed Rac3 as a potential target gene and quantitative RT-PCR analysis confirmed that Rac3 was upregulated by Deaf-1 in immortalized mouse mammary epithelial cells. Furthermore, MMTV-Deaf-1 transgenic mammary glands were found to have elevated levels of Rac3 mRNA, suggesting that it is a bona fide target.

Conclusion

We have demonstrated that overexpression of Deaf-1 enhances the proliferation of human breast epithelial cells in vitro and mouse epithelial cells in vivo. Transgenic mammary glands overexpressing Deaf-1 exhibited a modest side-branching phenotype, accompanied by an increase in the number of BrdU-positive cells and a decrease in the proportion of PRA-expressing cells. Although proliferation was enhanced in Deaf-1 transgenic mice, overexpression of this gene was not sufficient to induce the formation of mammary tumors. In addition, our studies identified Rac3, encoding a small Rho-like GTPase, as a potential target of Deaf-1 in mouse mammary epithelial cells.

The Stat family of transcription factors have diverse roles in mammary gland development

The Stat family of transcription factors have diverse roles in mammary gland development. Genetic studies in mice have revealed an essential requirement for Stat5a in development of secretory alveolar cells during pregnancy while Stat6, which is normally associated with differentiation of T helper cells, is important in the commitment of luminal cells to this alveolar lineage. In contrast, Stat3 is specifically activated at the initiation of post-lactational regression when it has an essential function in the regulation of cell death and tissue remodelling. Stat1 and Stat4 have been shown to be regulated during a mammary developmental cycle although whether they have specific, non-redundant roles is not clear. Thus, the adult mammary gland is somewhat unusual in that it is a tissue where different Stats are sequentially activated to orchestrate the processes of functional differentiation, cell death and tissue remodelling.

Prolactin regulation of mammary gland development

Mammary morphogenesis is orchestrated with other reproductive events by pituitary-driven changes to the systemic hormone environment, initiating the formation of a mammary ductal network during puberty and the addition of secretory alveoli during pregnancy. Prolactin is the major driver of development during pregnancy via regulation of ovarian progesterone production (in many species) and direct effects on mammary epithelial cells (in all species). Together these hormones regulate two aspects of development that are the subject of intense interest: (1) a genomic regulatory network that integrates many additional spatial and temporal cues to control gene expression and (2), the activity of a stem and progenitor cell hierarchy. Amalgamation of these two aspects will increase our understanding of cell proliferation and differentiation within the mammary gland, with clear application to our attempts to control breast cancer. Here we focus on providing an over-view of prolactin action during development of the model murine mammary gland.

Socs 3 modulates the activity of the transcription factor Stat3 in mammary tissue and controls alveolar homeostasis

Signal transducer and activator of transcription 5 and 3 (Stat5 and Stat3) control pregnancy-mediated mammary development and involution-dependent remodeling, respectively. Suppressor of cytokine signaling 3 (Socs3) has been implicated in the modulation of both Stat3 and Stat5 activity. To explore the biology of Socs3 in mammary tissue, the gene was deleted using Cre-mediated recombination. Deletion of the Socs3 gene from mammary stem or early progenitor cells did not grossly alter pregnancy-mediated mammary development but resulted in impaired lactation due to attenuated proliferation. Loss of Socs3 from differentiated luminal cells did not interfere with glandular function during lactation, but resulted in accelerated tissue remodeling upon weaning. Loss of Socs3 led to enhanced and precocious Stat3 activation. Thus, Socs3 serves as a modulator of Stat3 activity to ensure controlled proliferation and apoptosis in pregnancy and involution, respectively.

Characterization of the SOCS3 promoter response to prostaglandin E2 in T47D cells

Suppressor of cytokine signaling 3 (SOCS3), a negative regulator of cytokine signaling, is expressed in breast cancer cells where it can modify sensitivity and responsiveness to cytokine signaling through the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathways. Although it is widely accepted that SOCS3 expression is in itself regulated by STATs, we and others have shown that prostaglandins can also up-regulate SOCS3 expression. Here we used T47D breast cancer cells treated with prostaglandin E2 (PGE2) to examine this pathway. T47D cells responded to PGE2 stimulation with a significant increase in SOCS3 mRNA that was independent of de novo protein synthesis. PGE2 stimulation resulted in STAT3 serine and tyrosine phosphorylation, although mutation of either of the two previously characterized STAT response elements on the SOCS3 promoter did not affect SOCS3 promoter activation by PGE2. In addition, overexpression of STAT3 wild-type, constitutively active or dominant-negative constructs did not affect PGE2-induced SOCS3 promoter activation, indicating that STATs are unlikely mediators of this pathway in these cells. PGE2 is a known activator of the cAMP/protein kinase A (PKA) pathway, and in T47D cells, up-regulation of SOCS3 mRNA by PGE2 was abolished by pretreatment with H89, a PKA inhibitor and increased by cAMP and forskolin treatment. Consistent with this, PGE2 treatment increased cAMP response element (CRE)-binding protein serine phosphorylation. However, mutation of the activator protein 1/CRE on the promoter did not affect basal or PGE2-stimulated activation, suggesting a role for cAMP/PKA that is independent of CRE-binding protein binding. Mutation of the GC-rich region of the SOCS3 promoter, a putative Sp1/Sp3 binding site, abolished both basal and PGE2-stimulated activation. Gel-shift assays showed increased complex formation after treatment, and this was inhibited by the addition of an Sp1 antibody or pretreatment with PKA inhibitor. Chromatin immunoprecipitation assay verified Sp1 binding to the promoter in response to PGE2. Sp1 overexpression increased SOCS3 promoter activation, and both basal and PGE2-induced SOCS3 mRNA expression was prevented by mithramycin, an inhibitor of Sp1 DNA binding. Finally, a physiological role for PGE2 was demonstrated with PGE2 pretreatment reducing lipopolysaccharide-induced STAT3 activation. Collectively, this study details a novel mechanism of SOCS3 up-regulation by PGE2 in breast cancer cells that appears to be STAT independent and involve Sp1 binding to the promoter. This process has possible implications for cytokine responsiveness and tumor progression.

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.