Mammary serine protease inhibitor (Maspin) binds directly to interferon regulatory factor 6: identification of a novel serpin partnership

P176S Mutation Rewires Electrostatic Interactions That Alter Maspin Functionality

Maspin is known to regress tumors by inhibiting angiogenesis; however, its roles have been reported to be context- and sequence-dependent. Various proteins and cofactors bind to maspin, possibly explaining its conflicting roles. Moreover, polymorphic forms of maspin have also been linked to tumor regression and survival; for instance, maspin with Ser at 176 (maspin-S176) promotes tumors, while maspin with Pro at 176 (maspin-P176) has opposing roles in cancer pathogenesis. With the help of long molecular dynamics simulations, a possible link between polymorphic forms and tumor progression has been established. First, maspin is dynamically stable with either amino acid at the 176 position. Second, differential contacts have been observed among various regions; third, these contacts have significantly altered the electrostatic energetics of various residues; finally, these altered electrostatics of maspin-S176 and maspin-P176 rewire the polar contacts that abolished the allosteric control of the protein. By combining these factors, the altered electrostatics substantially affect the localization and preference of maspin-binding partners, thus culminating in a different maspin-protein(cofactor)-interaction landscape that may have been manifested in previous conflicting reports. Here, the underlying reason has been highlighted and discussed, which may be helpful for better therapeutic manipulation.

IRF6 Regulates the Delivery of E-Cadherin to the Plasma Membrane

IRF6 is a transcription factor that is required for craniofacial development and epidermal morphogenesis. Specifically, Irf6-deficient mice lack the terminally differentiated epidermal layers, leading to an absence of barrier function. This phenotype also includes intraoral adhesions due to the absence of the oral periderm, leading to the mislocalization of E-cadherin and other cell‒cell adhesion proteins of the oral epithelium. However, the mechanisms by which IRF6 controls the localization of cell adhesion proteins are not understood. In this study, we show that in human and murine keratinocytes, loss of IRF6 leads to a breakdown of epidermal sheets after mechanical stress. This defect is due to a reduction of adhesion proteins at the plasma membrane. Dynamin inhibitors rescued the IRF6-dependent resistance of epidermal sheets to mechanical stress, but only inhibition of clathrin-mediated endocytosis rescued the localization of junctional proteins at the membrane. Our data show that E-cadherin recycling but not its endocytosis is affected by loss of IRF6. Overall, we demonstrate a role for IRF6 in the delivery of adhesion proteins to the cell membrane.

A Targeted Bioinformatics Assessment of Adrenocortical Carcinoma Reveals Prognostic Implications of GABA System Gene Expression

Adrenocortical carcinoma (ACC) is a rare but deadly cancer for which few treatments exist. Here, we have undertaken a targeted bioinformatics study of The Cancer Genome Atlas (TCGA) ACC dataset focusing on the 30 genes encoding the γ-aminobutyric acid (GABA) system—an under-studied, evolutionarily-conserved system that is an emerging potential player in cancer progression. Our analysis identified a subset of ACC patients whose tumors expressed a distinct GABA system transcriptome. Transcript levels of ABAT (encoding a key GABA shunt enzyme), were upregulated in over 40% of tumors, and this correlated with several favorable clinical outcomes including patient survival; while enrichment and ontology analysis implicated two cancer-related biological pathways involved in metastasis and immune response. The phenotype associated with ABAT upregulation revealed a potential metabolic heterogeneity among ACC tumors associated with enhanced mitochondrial metabolism. Furthermore, many GABA_A receptor subunit-encoding transcripts were expressed, including two (GABRB2 and GABRD) prognostic for patient survival. Transcripts encoding GABA_B receptor subunits and GABA transporters were also ubiquitously expressed. The GABA system transcriptome of ACC tumors is largely mirrored in the ACC NCI-H295R cell line, suggesting that this cell line may be appropriate for future functional studies investigating the role of the GABA system in ACC cell growth phenotypes and metabolism.

Lin28A promotes IRF6-regulated aerobic glycolysis in glioma cells by stabilizing SNHG14

Warburg effect is a hallmark of cancer cells, wherein glycolysis is preferred over oxidative phosphorylation even in aerobic conditions. Reprogramming of glycometabolism is especially crucial for malignancy in glioma. RNA-binding proteins and long noncoding RNAs are important for aerobic glycolysis during malignant transformation. Thus, we determined the expression and function of RNA-binding protein Lin28A, long noncoding RNA SNHG14, and transcription factor IRF6 in human glioma cells to elucidate the mechanism(s) underlying their role in glycolysis. Quantitative real-time polymerase chain reaction and western blotting showed that Lin28A and SNHG14 were overexpressed and IRF6 was downregulated in glioma. Depleting Lin28A from cells decreased the stability and expression of SNHG14. Furthermore, depleting SNHG14 reduced IRF6 mRNA degradation by targeting its 3' untranslated region and inhibiting STAU1-mediated degradation, thereby increasing the expression of IRF6. PKM2 is an important enzyme in aerobic glycolysis, and GLUT1 is the primary transporter that facilitates glucose uptake. IRF6 inhibited the transcription of PKM2 and GLUT1, thereby impairing glycolysis and cell proliferation and inducing apoptosis in glioma. Notably, depleting Lin28A and SNHG14 and overexpressing IRF6 reduced the growth of xenograft tumors in vivo and prolonged the survival of nude mice. Taken together, our data revealed that the Lin28A/SNHG14/IRF6 axis is crucial for reprogramming glucose metabolism and stimulating tumorigenesis in glioma cells. Thus, targeting this axis might help in the development of a novel therapeutic strategy for glioma metabolism.

Functional Characterization of a Novel IRF6 Frameshift Mutation From a Van Der Woude Syndrome Family

Background

Loss-of-function mutations in interferon regulatory factor-6 (IRF6) are responsible for about 70% of cases of Van Der Woude Syndrome (VWS), an autosomal dominant developmental disorder characterized by pits and/or sinuses of the lower lip and cleft lip, cleft palate, or both.

Methods

We collected a Chinese Han VWS pedigree, performed sequencing and screening for the causal gene mutant. Initially, species conservation analysis and homology protein modeling were used to predict the potential pathogenicity of mutations. To test whether a VWS family-derived mutant variant of IRF6 retained function, we carried out rescue assays in irf6 maternal-null mutant zebrafish embryos. To assess protein stability, we overexpressed reference and family-variants of IRF6 in vitro.

Results

We focused on a VWS family that includes a son with bilateral lip pits, uvula fissa and his father with bilateral cleft lip and palate. After sequencing and screening, a frameshift mutation of IRF6 was identified as the potential causal variant (NM.006147.3, c.1088-1091delTCTA; p.Ile363ArgfsTer33). The residues in this position are strongly conserved among species and homology modeling suggests the variant alters the protein structure. In irf6 maternal-null mutant zebrafish embryos the periderm differentiates abnormally and the embryos rupture and die during gastrulation. Injection of mRNA encoding the reference variant of human IRF6, but not of the frame-shift variant, rescued such embryos through gastrulation. Upon overexpression in HEK293FT cells, the IRF6 frame-shift mutant was relatively unstable and was preferentially targeted to the proteasome in comparison to the reference variant.

Conclusion

In this VWS pedigree, a novel frameshift of IRF6 was identified as the likely causative gene variant. It is a lost function mutation which could not rescue abnormal periderm phenotype in irf6 maternal-null zebrafish and which causes the protein be unstable through proteasome-dependent degradation.

Interferon regulatory factor 6 is required for proper wound healing in vivo

BACKGROUND

Van der Woude syndrome (VWS) is the most common form of syndromic orofacial cleft caused predominantly by mutations in Interferon Regulatory Factor 6 (IRF6). We previously reported that individuals with VWS have increased risk of wound healing complications following cleft repair compared with individuals with nonsyndromic orofacial clefts (nonsyndromic cleft lip and palate-NSCLP). In vitro, absence of IRF6 leads to impaired keratinocyte migration and embryonic wound healing. However, there is currently no data on tissue repair in adult animals and cells with reduced levels of IRF6 like in VWS.

RESULTS

Excisional wounds of Irf6^+/- and wild-type animals were analyzed 4 and 7 days post-wounding. Although all wounds were reepithelialized after 7 days, the epidermal and wound volume of repaired wounds was larger in Irf6^+/- . These data were supported by increased keratinocyte proliferation in the neoformed epidermis and a less mature granulation tissue with increased cytokine levels. This effect was not cell autonomous, as Irf6^+/- neonatal keratinocytes in vitro did not exhibit defects in scratch wound closure or proliferation. Keratinocytes from individuals with VWS also migrated similarly to keratinocytes from NSCLP individuals.

CONCLUSIONS

These data support a role for IRF6 in wound healing by regulating keratinocyte proliferation, granulation tissue maturation, and cytokine levels.

Candidate tumor suppressor gene IRF6 is involved in human breast cancer pathogenesis via modulating PI3K-regulatory subunit PIK3R2 expression

Background/Aims: The tumor-suppressive functions of interferon regulatory factor 6 (IRF6) in some tumors have been preliminarily established, but its pathogenesis and underlying molecular mechanisms in breast cancer, the most common malignancy in women, remains poorly understood. Methods: Pairs of typical breast cancer cell lines (high- and low-aggressive) in addition to 27 breast cancer tissue samples and 31 non-cancerous breast tissues were used to investigate the expression level of IRF6 and Lentivirus-mediated gain-of-function studies, short hairpin RNA-mediated loss-of-function studies in vivo and in vitro were used to validate the role of IRF6 in breast cancer. Next, we performed RNA-Seq analysis to identify the molecular mechanisms of IRF6 involved in breast cancer progression. Results: Our findings showed that IRF6 was downregulated in highly invasive breast cancer cell lines but upregulated in poorly aggressive ones. Functional assays revealed that elevated IRF6 expression could suppress cell proliferation and tumorigenicity, and enhanced cellular chemotherapeutic sensitivity. To identify the molecular mechanisms involved, we performed a genome-wide and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis in breast cancer cells using RNA sequencing of gene expression profiles following the overexpression of IRF6. Genome-wide and KEGG analyses showed that IRF6 might mediate the PI3K-regulatory subunit PIK3R2, which in turn modulated the PI3K/AKT pathway to control breast cancer pathogenesis. Conclusion: We provide the first evidence of the involvement of IRF6 in breast cancer pathogenesis, which was found to modulate the PI3K/AKT pathway via mediating PIK3R2; indicating that IRF6 can be targeted as a potential therapeutic treatment of breast cancer.

IRF6 Is Directly Regulated by ZEB1 and ELF3, and Predicts a Favorable Prognosis in Gastric Cancer

Interferon regulatory factor 6 (IRF6) acts as a tumor suppressor and controls cell differentiation in ectodermal and craniofacial tissues by regulating expression of target genes. However, its function in gastric cancer (GC) remains unknown to date. In this study, we found that the IRF6 expression was significantly downregulated in GC. And the decreased expression of IRF6 was clinically correlated with poor prognosis of GC. Moreover, loss-of-function and gain-of-function studies showed that IRF6 was negatively regulated by ZEB1 but positively regulated by ELF3. Additionally, transcription factor ZEB1 and ELF3 could directly bind on IRF6 promoter, which suggested that transcription factor IRF6 is transcriptionally regulated by ZEB1 and ELF3. Nevertheless, we found that IRF6 expression was negatively related to its promoter methylation in TCGA stomach cancer cohorts. The downregulation of IRF6 in GC might be due to the overexpression of ZEB1 and the DNA methylation of IRF6 promoter.

Silencing of interferon regulatory factor gene 6 in melanoma

BACKGROUND

Methylation of a CpG island (CGI; a dense cluster of CpGs) located in the 5' region of a gene suppresses transcription of that gene. Interferon regulatory factor 6 (IRF6) is associated with the expression of interferon, which is used as an effective adjuvant therapy for melanoma, and is regarded as a tumor suppressor. However, little is known about the methylation status of the IRF6 gene in melanoma.

OBJECTIVE

The purpose was to determine the methylation status of the CGI located in the 5' region of IRF6 (5' IRF6 CGI) in melanoma.

METHODS

Quantitative real-time methylation-specific PCR (RT-MSP) and bisulfite sequencing were performed to examine IRF6 gene methylation status. Quantitative real-time reverse transcription-PCR (RT-PCR) was performed to examine IRF6 expression.

RESULTS

The methylation level of the 5' IRF6 CGI was completely inversely correlated with cell sensitivity to interferon-β in eight examined melanoma cell lines. These methylation levels were high in the melanoma cell lines with suppression of IRF6 expression and were low in the cell lines with IRF6 expression. The methylation levels of the 5' IRF6 CGI ranged widely from 0.0% to 65.4% in 21 clinical melanoma samples but showed a narrow range of low levels between 0.0% to 7.2% in 24 clinical melanocytic nevus samples. These methylation levels were not associated with clinical parameters except for melanoma subtypes.

CONCLUSION

IRF6 is aberrantly silenced by DNA methylation of the 5' IRF6 CGI in melanoma. The methylation status of IRF6 is potentially associated with the sensitivity of melanoma to interferon.

Disrupted IRF6-NME1/2 Complexes as a Cause of Cleft Lip/Palate

Mutations and common polymorphisms in interferon regulatory factor 6 ( IRF6) are associated with both syndromic and nonsyndromic forms of cleft lip/palate (CLP). To date, much of the focus on this transcription factor has been on identifying its direct targets and the gene regulatory network in which it operates. Notably, however, IRF6 is found predominantly in the cytoplasm, with its import into the nucleus tightly regulated like other members of the IRF family. To provide further insight into the role of IRF6 in the pathogenesis of CLP, we sought to identify direct IRF6 protein interactors using a combination of yeast 2-hybrid screens and co-immunoprecipitation assays. Using this approach, we identified NME1 and NME2, well-known regulators of Rho-type GTPases, E-cadherin endocytosis, and epithelial junctional remodeling, as bona fide IRF6 partner proteins. The NME proteins co-localize with IRF6 in the cytoplasm of primary palatal epithelial cells in vivo, and their interaction with IRF6 is significantly enhanced by phosphorylation of key serine residues in the IRF6 C-terminus. Furthermore, CLP associated IRF6 missense mutations disrupt the ability of IRF6 to bind the NME proteins and result in elevated activation of Rac1 and RhoA, compared to wild-type IRF6, when ectopically expressed in 293T epithelial cells. Significantly, we also report the identification of 2 unique missense mutations in the NME proteins in patients with CLP (NME1 R18Q in an IRF6 and GRHL3 mutation-negative patient with van der Woude syndrome and NME2 G71V in a patient with nonsyndromic CLP). Both variants disrupted the ability of the respective proteins to interact with IRF6. The data presented suggest an important role for cytoplasmic IRF6 in regulating the availability or localization of the NME1/2 complex and thus the dynamic behavior of epithelia during lip/palate development.

Generation and characterization of a conditional allele of Interferon Regulatory Factor 6

Interferon Regulatory Factor 6 (IRF6) is a critical regulator of differentiation, proliferation, and migration of keratinocytes. Mutations in IRF6 cause two autosomal dominant disorders characterized by cleft lip with or without cleft palate. In addition, DNA variation in IRF6 confers significant risk for non-syndromic cleft lip and palate. IRF6 is also implicated in adult onset development and disease processes, including mammary gland development and squamous cell carcinoma. Mice homozygous for a null allele of Irf6 die shortly after birth due to severe skin, limb, and craniofacial defects, thus impeding the study of gene function after birth. To circumvent this, a conditional allele of Irf6 was generated. To validate the functionality of the conditional allele, we used three "deleter" Cre strains: Gdf9-Cre, CAG-Cre, and Ella-Cre. When Cre expression was driven by the Gdf9-Cre or CAG-Cre transgenes, 100% recombination was observed as indicated by DNA genotyping and phenotyping. In contrast, use of the Ella-Cre transgenic line resulted in incomplete recombination, despite expression at the one-cell stage. In sum, we generated a novel tool to delete Irf6 in a tissue specific fashion, allowing for study of gene function past perinatal stages. However, recombination efficiency of this allele was dictated by the Cre-driver used.

The Opportunity of Precision Medicine for Breast Cancer With Context-Sensitive Tumor Suppressor Maspin

To improve the precision of molecular diagnosis and to develop and guide targeted therapies of breast cancer, it is essential to determine the mechanisms that underlie the specific tumor phenotypes. To this end, the application of a snapshot of gene expression profile for breast cancer diagnosis and prognosis is fundamentally challenged since the tissue-based data are derived from heterogonous cell types and are not likely to reflect the dynamics of context-dependent tumor progression and drug sensitivity. The intricate network of epithelial differentiation program can be concertedly controlled by tumor suppressor maspin, a homologue of clade B serine protease inhibitors (serpin), through its multifaceted molecular interactions in multiple subcellular localizations. Unlike most other serpins that are expressed in multiple cell types, maspin is epithelial specific and has distinct roles in luminal and myoepithelial cells. Endogenously expressed maspin has been found in the nucleus and cytoplasm, and detected on the surface of cell membrane. It is also secreted free and as an exosomal cargo protein. Research in the field has led to the identification of the maspin targets and maspin-associated molecules, as well as the structural determinants of its suppressive functions. The current review discusses the possibility for maspin to serve as a cell type-specific and context-sensitive marker to improve the precision of breast cancer diagnosis and prognosis. These advancements further suggest a new window of opportunity for designing novel maspin-based chemotherapeutic agents with improved anti-cancer potency. J. Cell. Biochem. 118: 1639-1647, 2017. © 2017 Wiley Periodicals, Inc.

Disrupted cooperation between transcription factors across diverse cancer types

Background

Transcription Factors (TFs), essential for many cellular processes, generally work coordinately to induce transcriptional change in response to internal and external signals. Disrupted cooperation between TFs, leading to dysregulation of target genes, contributes to the pathogenesis of many diseases, including cancer. Although the aberrant activation of individual TFs and the functional effects have been widely studied, the perturbation of TF cooperativity in cancer has rarely been explored.

Results

We used TF co-expression as proxy as cooperativity and performed a large-scale study on disrupted TF cooperation across seven cancer types. While the connectivity of downstream effectors, like metabolic genes and TF targets, were more or similarly disrupted than/with non-TFs, the cooperativity of TFs (upstream regulators) were consistently less disturbed in all studied cancer types. Highly coordinated TFs in normal, however, generally lost that cooperation in cancer. Although different types of cancer shared very few TF pairs with highly disrupted cooperation, the cooperativity of interferon regulatory factors (IRF) was highly disrupted in six cancer types. Specifically, the cooperativity of IRF8 was highly perturbed in lung cancer, which was further validated by two independent lung squamous cell carcinoma (LUSC) and lung adenocarcinoma (LUAD) datasets. More interestingly, the cooperativity of IRF8 was markedly associated with tumor progression and even contributed to the patient survival independent of tumor stage.

Conclusions

Our findings underscore the far more important role of TF cooperativity in tumorigenesis than previously appreciated. Disrupted cooperation of TFs provides potential clinical utility as prognostic markers for predicting the patient survival.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2842-8) contains supplementary material, which is available to authorized users.

EGFR Signaling Regulates Maspin/SerpinB5 Phosphorylation and Nuclear Localization in Mammary Epithelial Cells

Maspin (SerpinB5) is a non-inhibitory serpin (serine protease inhibitor) with very diverse biological activities including regulation of cell adhesion, migration, death, control of gene expression and oxidative stress response. Initially described as a tumor and metastasis suppressor, clinical data brought controversies to the field, as some studies reported no correlation between SerpinB5 expression and prognosis value. These data underscore the importance of understanding SerpinB5 function in a normal physiological context and the molecular mechanism involved. Several SerpinB5 phosphoforms have been detected in different cell lines, but the signaling pathways involved and the biological significance of this post-translational modification in vivo remains to be explored. In this study we investigated SerpinB5 expression, subcellular localization and phosphorylation in different stages of the mouse mammary gland development and the signaling pathway involved. Here we show that SerpinB5 is first detected in late pregnancy, reaches its highest levels in lactation and remains at constant levels during post-lactational regression (involution). Using high resolution isoelectric focusing followed but immunoblot, we found at least 8 different phosphoforms of SerpinB5 during lactation, which decreases steadily at the onset of involution. In order to investigate the signaling pathway involved in SerpinB5 phosphorylation, we took advantage of the non-transformed MCF-10A model system, as we have previously observed SerpinB5 phosphorylation in these cells. We detected basal levels of SerpinB5 phosphorylation in serum- and growth factor-starved cells, which is due to amphiregulin autocrine activity on MCF-10A cells. EGF and TGF alpha, two other EGFR ligands, promote important SerpinB5 phosphorylation. Interestingly, EGF treatment is followed by SerpinB5 nuclear accumulation. Altogether, these data indicate that SerpinB5 expression and phosphorylation are developmentally regulated. In vitro analyses indicate that SerpinB5 phosphorylation is regulated by EGFR ligands, but EGF appears to be the only able to induce SerpinB5 nuclear localization.

Expression of maspin in testis tumors with germ cells andits relation with angiogenesis factors

BACKGROUND/AIM

We aimed to evaluate the importance of maspin expression in testicular tumors with germ cells, its effect on prognosis, and the relation with angiogenesis factors.

MATERIALS AND METHODS

The paraffin blocks of the orchiectomy materials of 32 patients who had undergone orchiectomy due to testicular tumors were taken within the scope of the study. The specimens of the cases included in the study group were reexamined under light microscope.

RESULTS

While just one maspin-positive sample was found in the seminoma cases, maspin stained positively in 6 of the nonseminoma germ cell tumors (NSGCTs). No statistical difference was found between maspin and tumor stage, size, alpha fetoprotein values, vascular endothelial growth factor, Ki-67, and CD31. A statistically positive correlation was only determined between maspin and p53 (P < 0.001).

CONCLUSION

Maspin protein, whose expression in some tumors is accepted as a poor prognostic factor, is also expressed in testicular tumors with germ cells. However, according to our study, it is difficult to say whether this protein is a favorable or poor prognostic factor in testicular tumors and to understand how the effect mechanism works. The positive correlation between maspin and p53 in the NSGCTs makes us think that maspin might have displayed an effect on the p53 pathway.

Methylation-induced silencing of maspin contributes to the proliferation of human glioma cells

Maspin, a member of the serpin superfamily of serine protease inhibitors, has been reported to be involved in cancer initiation and progression. However, the expression of maspin and its expression regulation in glioma remain unknown. In the present study, we aimed to investigate the function of maspin in glioma cells and its regulatory mechanism. We found that the expression of maspin was silenced in glioma cells and tissues. Although maspin had no effect on the migration and invasion of human glioma cells in vitro, overexpression of maspin inhibited cell growth in U87 cells. We showed that the methylase inhibitor 5-Aza-2′-deoxycytidine induced the expression of maspin in glioma cell lines. Furthermore, both U87 and U251 cells showed hypermethylation in the maspin promoter. In addition, bisulphite sequencing analysis indicated that 16 CpG sites in the promoter were completely methylated in glioma cells and cancerous tissues, while CpG dinucleotides in the maspin promoter were unmethylated in normal brain tissues. Our data suggest that methylation-induced silencing of maspin contributes to the proliferation of human glioma cells, and maspin may be a potential therapeutic target in glioma.

Expanding the genetic and phenotypic spectrum of popliteal pterygium disorders

The popliteal pterygia syndromes are a distinct subset of the hundreds of Mendelian orofacial clefting syndromes. Popliteal pterygia syndromes have considerable variability in severity and in the associated phenotypic features but are all characterized by cutaneous webbing across one or more major joints, cleft lip and/or palate, syndactyly, and genital malformations. Heterozygous mutations in IRF6 cause popliteal pterygium syndrome (PPS) while homozygous mutations in RIPK4 or CHUK (IKKA) cause the more severe Bartsocas-Papas syndrome (BPS) and Cocoon syndrome, respectively. In this study, we report mutations in six pedigrees with children affected with PPS or BPS. Using a combination of Sanger and exome sequencing, we report the first case of an autosomal recessive popliteal pterygium syndrome caused by homozygous mutation of IRF6 and the first case of uniparental disomy of chromosome 21 leading to a recessive disorder. We also demonstrate that mutations in RIPK4 can cause features with a range of severity along the PPS-BPS spectrum and that mutations in IKKA can cause a range of features along the BPS-Cocoon spectrum. Our findings have clinical implications for genetic counseling of families with pterygia syndromes and further implicate IRF6, RIPK4, and CHUK (IKKA) in potentially interconnected pathways governing epidermal and craniofacial development.

Interferon Regulatory Factor 6 Controls Proliferation of Keratinocytes From Children With Van der Woude Syndrome

OBJECTIVE

Interferon Regulatory Factor 6 (IRF6) is critical for craniofacial development, epidermal differentiation, and tissue repair. IRF6 mutations cause Van der Woude Syndrome (VWS) and Popliteal Pterygium Syndrome. Individuals with VWS exhibit craniofacial anomalies, including cleft lip and palate and lip pits. Furthermore, they have an increased risk for wound-healing complications following surgical repair when compared with patients with nonsyndromic cleft lip and palate (NSCLP). However, nothing is known about the skin of these patients. The objective was to characterize the skin of patients with VWS. We hypothesize that IRF6 is required for proper skin homeostasis in humans.

DESIGN

Discarded tissue from a hip was collected during surgical alveolar bone graft. Samples from children with VWS harboring IRF6 mutations (n = 2) were compared with samples from children with NSCLP (n = 7). Histology was assessed following hematoxylin and eosin staining. The expressions of Proliferating Cell Nuclear Antigen, IRF6, P63, and Keratin 10 were determined by immunofluorescence. Keratinocytes were isolated and their proliferation potential was assessed by colony-forming efficiency assay.

RESULTS

Hip skin from children with VWS showed a thicker epidermis when compared with that from children with NSCLP. Proliferating Cell Nuclear Antigen staining revealed an increase in proliferation in syndromic tissues when compared with controls. However, P63 and Keratin 10 expression were similar between groups. Finally, keratinocytes from VWS showed increased long-term proliferation when compared with NSCLP.

CONCLUSIONS

These results support, in vivo and in vitro, a previously described role for IRF6 in epidermal proliferation in humans. They further demonstrate a critical function for IRF6 in cutaneous homeostasis.

Interferon Regulatory Factor 6 Has a Protective Role in the Host Response to Endotoxic Shock

Interferon Regulatory Factor (IRF) 6, a member of the IRF family, is essential for epidermal and orofacial embryonic development. Irf6 is strongly expressed in keratinocytes, in which it regulates epidermal proliferation, differentiation, and migration. A recent role for Irf6 in Toll-like receptor 2-dependent chemokine gene expression was also reported in an epithelial cell line. However, a function for Irf6 in innate immune cells was not previously reported. In the present study, we investigated the expression and function of Irf6 in bone marrow-derived neutrophils and macrophages. We show here, using a conditional knockout of Irf6 in lysosymeM expressing cells, that Irf6 is required for resistance to LPS-induced endotoxic shock. In addition, Irf6-deficient bone marrow-derived neutrophils exhibited increased chemotactic index and velocity compared with wild-type cells in vitro. TLR4-specific KC and IL6 secretions were upregulated in Irf6-deficient bone marrow-derived macrophages in vitro. These cells also exhibited an increased level of phosphorylated IkBa. Collectively, our findings suggest a role for Irf6 in the resistance to endotoxic shock due to NFk-B-mediated alteration of cytokine production.

An in silico model to demonstrate the effects of Maspin on cancer cell dynamics

Most cancer treatments efficacy depends on tumor metastasis suppression, where tumor suppressor genes play an important role. Maspin (Mammary Serine Protease Inhibitor), an non-inhibitory serpin has been reported as a potential tumor suppressor to influence cell migration, adhesion, proliferation and apoptosis in in vitro and in vivo experiments in last two decades. Lack of computational investigations hinders its ability to go through clinical trials. Previously, we reported first computational model for maspin effects on tumor growth using artificial neural network and cellular automata paradigm with in vitro data support. This paper extends the previous in silico model by encompassing how maspin influences cell migration and the cell-extracellular matrix interaction in subcellular level. A feedforward neural network was used to define each cell behavior (proliferation, quiescence, apoptosis) which followed a cell-cycle algorithm to show the microenvironment impacts over tumor growth. Furthermore, the model concentrates how the in silico experiments results can further confirm the fact that maspin reduces cell migration using specific in vitro data verification method. The data collected from in vitro and in silico experiments formulates an unsupervised learning problem which can be solved by using different clustering algorithms. A density based clustering technique was developed to measure the similarity between two datasets based on the number of links between instances. Our proposed clustering algorithm first finds the nearest neighbors of each instance, and then redefines the similarity between pairs of instances in terms of how many nearest neighbors share the two instances. The number of links between two instances is defined as the number of common neighbors they have. The results showed significant resemblances with in vitro experimental data. The results also offer a new insight into the dynamics of maspin and establish as a metastasis suppressor gene for further molecular research.

Toward an orofacial gene regulatory network

Orofacial clefting is a common birth defect with significant morbidity. A panoply of candidate genes have been discovered through synergy of animal models and human genetics. Among these, variants in interferon regulatory factor 6 (IRF6) cause syndromic orofacial clefting and contribute risk toward isolated cleft lip and palate (1/700 live births). Rare variants in IRF6 can lead to Van der Woude syndrome (1/35,000 live births) and popliteal pterygium syndrome (1/300,000 live births). Furthermore, IRF6 regulates GRHL3 and rare variants in this downstream target can also lead to Van der Woude syndrome. In addition, a common variant (rs642961) in the IRF6 locus is found in 30% of the world's population and contributes risk for isolated orofacial clefting. Biochemical studies revealed that rs642961 abrogates one of four AP-2alpha binding sites. Like IRF6 and GRHL3, rare variants in TFAP2A can also lead to syndromic orofacial clefting with lip pits (branchio-oculo-facial syndrome). The literature suggests that AP-2alpha, IRF6 and GRHL3 are part of a pathway that is essential for lip and palate development. In addition to updating the pathways, players and pursuits, this review will highlight some of the current questions in the study of orofacial clefting.

IRF6 is the mediator of TGFβ3 during regulation of the epithelial mesenchymal transition and palatal fusion

Mutation in interferon regulatory factor 6 (IRF6) is known to cause syndromic and non-syndromic cleft lip/palate in human. In this study, we investigated the molecular mechanisms related to IRF6 during palatal fusion using palatal shelves organ culture. The results showed that ablation of Irf6 resulted in a delay in TGFβ3-regulated palatal fusion. Ectopic expression of IRF6 was able to promote palatal fusion and rescue shTgfβ3-induced fusion defect. These findings indicate that IRF6 is involved in TGFβ3-mediated palatal fusion. Molecular analysis revealed that ectopic expression of IRF6 increased the expression of SNAI2, an epithelial mesenchymal transition (EMT) regulator, and diminished the expression of various epithelial markers, such as E-cadherin, Plakophilin and ZO-1. In addition, knockdown of Irf6 expression decreased SNAI2 expression, and restored the expression of ZO-1 and Plakophilin that were diminished by TGFβ3. Blocking of Snai2 expression delayed palatal fusion and abolished the IRF6 rescuing effect associated with shTgfβ3-induced fusion defect. These findings indicate that TGFβ3 increases IRF6 expression and subsequently regulates SNAI2 expression, and IRF6 appears to regulate EMT during palatal fusion via SNAI2. Taken together, this study demonstrates that IRF6 is a mediator of TGFβ3, which regulates EMT and fusion process during the embryonic palate development.

IRF6 Is Involved in the Regulation of Cell Proliferation and Transformation in MCF10A Cells Downstream of Notch Signaling

IRF6, a member of Interferon Regulatory Factors (IRF) family, is involved in orofacial and epidermal development. In breast cancer cell lines ectopic expression of IRF6 reduces cell numbers suggesting a role as negative regulator of cell cycle. IRF6 is a direct target of canonical Notch signaling in keratinocyte differentiation. Notch is involved in luminal cell fate determination and stem cell regulation in the normal breast and is implicated as an oncogene in breast cancer. Notch activation is sufficient to induce proliferation and transformation in non-tumorigenic breast epithelial cell line, MCF10A. ΔNp63, which is downregulated by Notch activation in the breast, regulates IRF6 expression in keratinocytes. In this report, we investigate Notch-IRF6 and ΔNp63-IRF6 interactions in MCF10A and MDA MB 231 cells. We observed that in these cells, IRF6 expression is partially regulated by canonical Notch signaling and ΔNp63 downregulation. Furthermore, we demonstrate that IRF6 abrogation impairs Notch-induced proliferation and transformation in MCF10A cells. Thus, we confirm the previous findings by showing a tissue independent regulation of IRF6 by Notch signaling, and extend them by proposing a context dependent role for IRF6, which acts as a positive regulator of proliferation and transformation in MCF10A cells downstream of Notch signaling.

Triple negative breast cancer: a multi-omics network discovery strategy for candidate targets and driving pathways

Triple negative breast cancer (TNBC) represents approximately 15% of breast cancers and is characterized by lack of expression of both estrogen receptor (ER) and progesterone receptor (PR), together with absence of human epidermal growth factor 2 (HER2). TNBC has attracted considerable attention due to its aggressiveness such as large tumor size, high proliferation rate, and metastasis. The absence of clinically efficient molecular targets is of great concern in treatment of patients with TNBC. In light of the complexity of TNBC, we applied a systematic and integrative transcriptomics and interactomics approach utilizing transcriptional regulatory and protein-protein interaction networks to discover putative transcriptional control mechanisms of TNBC. To this end, we identified TNBC-driven molecular pathways such as the Janus kinase-signal transducers, and activators of transcription (JAK-STAT) and tumor necrosis factor (TNF) signaling pathways. The multi-omics molecular target and biomarker discovery approach presented here can offer ways forward on novel diagnostics and potentially help to design personalized therapeutics for TNBC in the future.

Interferon regulatory factor 6 differentially regulates Toll-like receptor 2-dependent chemokine gene expression in epithelial cells

Epidermal and mucosal epithelial cells are integral to host defense. They not only act as a physical barrier but also utilize pattern recognition receptors, such as the Toll-like receptors (TLRs), to detect and respond to pathogens. Members of the interferon regulatory factor (IRF) family of transcription factors are key components of TLR signaling as they impart specificity to downstream responses. Although IRF6 is a critical regulator of epithelial cell proliferation and differentiation, its role in TLR signaling has not previously been addressed. We show here that IRF6 is activated by IRAK1 as well as by MyD88 but not by TRIF or TBK1. Co-immunoprecipitation experiments further demonstrated that IRF6 can interact with IRAK1. Gene silencing in epithelial cells along with gene promoter reporter assays showed that IRAK1 mediates TLR2-inducible CCL5 gene expression at least in part by promoting IRF6 activation. Conversely, IRAK1 regulated CXCL8 gene expression independently of IRF6, thus identifying a molecular mechanism by which TLR2 signaling differentially regulates the expression of specific chemokines in epithelial cells. Bioinformatics analysis and mutagenesis-based experiments identified Ser-413 and Ser-424 as key regulatory sites in IRF6. Phosphomimetic mutation of these residues resulted in greatly enhanced IRF6 dimerization and trans-activator function. Collectively, our findings suggest that, in addition to its importance for epithelial barrier function, IRF6 also contributes to host defense by providing specificity to the regulation of inflammatory chemokine expression by TLR2 in epithelial cells.

Nuclear location of tumor suppressor protein maspin inhibits proliferation of breast cancer cells without affecting proliferation of normal epithelial cells

Background

Maspin, which is classified as a tumor suppressor protein, is downregulated in many types of cancer. Several studies have suggested potential anti-proliferative activity of maspin as well as sensitizing activity of maspin for therapeutic cytotoxic agents in breast cancer tissue culture and animal models. All of the experimental data gathered so far have been based on studies with maspin localized cytoplasmically, while maspin in breast cancer tumor cells may be located in the cytoplasm, nucleus or both. In this study, the effect of maspin cytoplasmic and nuclear location and expression level on breast cancer proliferation and patient survival was studied.

Methods

Tissue sections from 166 patients with invasive ductal breast cancer were stained by immunohistochemistry for maspin and Ki-67 protein. The localization and expression level of maspin were correlated with estimated patient overall survival and percent of Ki-67-positive cells. In further studies, we created constructs for transient transfection of maspin into breast cancer cells with targeted cytoplasmic and nuclear location. We analyzed the effect of maspin location in normal epithelial cell line MCF10A and three breast cancer cell lines - MCF-7, MDA-MB-231 and SKBR-3 - by immunofluorescence and proliferation assay.

Results

We observed a strong positive correlation between moderate and high nuclear maspin level and survival of patients. Moreover, a statistically significant negative relationship was observed between nuclear maspin and Ki-67 expression in patients with invasive ductal breast cancer. Spearman’s correlation analysis showed a negative correlation between level of maspin localized in nucleus and percentage of Ki-67 positive cells. No such differences were observed in cells with cytoplasmic maspin. We found a strong correlation between nuclear maspin and loss of Ki-67 protein in breast cancer cell lines, while there was no effect in normal epithelial cells from breast. The anti-proliferative effect of nuclear maspin on breast cancer cells was statistically significant in comparison to cytoplasmic maspin.

Conclusions

Our results suggest that nuclear maspin localization may be a prognostic factor in breast cancer and may have a strong therapeutic potential in gene therapy. Moreover, these data provide a new insight into the role of cytoplasmic and nuclear fractions of maspin in breast cancer.

Serpin B5 is a CEA-interacting biomarker for colorectal cancer

Serpin B5 is a candidate tumour suppressor, but its oncogenic activity has also been reported. Its function may be affected by protein interactions. The aim of this study was to assess the relationship between serpin B5 and carcinoembryonic antigen (CEA) expression in colorectal cancer (CRC). We also analysed the clinicopathological significance of serpin B5 expression in patients with CRC. Downregulation of serpin B5 was identified in a CEA-suppressed LoVo cell line using two-dimensional gel electrophoresis (2-DE) and matrix-associated laser desorption ionisation-mass spectrometry (MALDI-MS). The specific interaction and co-localisation of serpin B5 with CEA were confirmed by co-immunoprecipitation and confocal microscopy. Western blot analysis and ELISAs revealed significant positive correlations between levels of serpin B5 and CEA in human colon cancer cell lines and in the blood of patients with CRC. Tissue expression of serpin B5 in 377 patients with CRC was significantly associated with serum CEA, histological grade, stage, lymph node metastasis, lymphatic and perineural invasion, and infiltrative border. Strong expression of serpin B5 was also associated with a reduced DFS (p = 0.001) and OS (p = 0.017). Together, these findings describe a relationship between serpin B5 and CEA expression in CRC. Strong expression of serpin B5 was associated with a worse prognosis in patients with CRC and its expression may correlate with CEA levels in CRC.

Reactive center loop moiety is essential for the maspin activity on cellular invasion and ubiquitin-proteasome level

Maspin, a tumor suppressor (SERPINB5), inhibits cancer migration, invasion, and metastasis in vitro and in vivo. The tumor-suppressing effects of maspin depend in part on its ability to enhance cell adhesion to extracellular matrix. Although the molecular mechanism of maspin's action is still unclear, its functional domain is believed to be located at the reactive center loop (RCL). We have elucidated the role of maspin RCL on adhesion, migration, and invasion by transfecting the highly invasive human breast carcinoma MDA-MB-231 cell line with pcDNA3.1-His/FLAG containing wild-type maspin, ovalbumin, or maspin/ovalbumin RCL chimeric mutants in which maspin RCL is replaced by ovalbumin (MOM) and vice versa (OMO). MDA-MB-231 cells transfected with maspin- or OMO-containing recombinant expression plasmid manifested significant increase in adhesion to fibronectin and reduction in in vitro migration and invasion through Matrigel compared with mock transfection or cells transfected with ovalbumin or MOM. Proteomics analysis of maspin- or OMO-transfected MDA-MB-231 cells revealed reduction in contents of proteins known to promote cancer metastasis and those of ubiquitin-proteasome pathway, while those with tumor-suppressing properties were increased. Furthermore, MDA-MB-231 cells containing maspin or OMO transgene have significantly higher levels of ubiquitin and ubiquitinated conjugates, but reduced 20S proteasome chymotrypsin-like activity. These results clearly demonstrate that the tumor-suppressive properties of maspin reside in its RCL domain.

Maspin: molecular mechanisms and therapeutic implications

Maspin, a non-inhibitory member of the serine protease inhibitor superfamily, has been characterized as a tumor suppressor gene in multiple cancer types. Among the established anti-tumor effects of Maspin are the inhibition of cancer cell invasion, attachment to extracellular matrices, increased sensitivity to apoptosis, and inhibition of angiogenesis. However, while significant experimental data support the role of Maspin as a tumor suppressor, clinical data regarding the prognostic implications of Maspin expression have led to conflicting results. This highlights the need for a better understanding of the context dependencies of Maspin in normal biology and how these are perturbed in the context of cancer. In this review, we outline the regulation and roles of Maspin in normal and developmental biology while discussing novel evidence and emerging theories related to its functions in cancer. We provide insight into the immense therapeutic potential of Maspin and the challenges related to its successful clinical translation.

A versatile monoclonal antibody specific to human SERPINB5

Maspin (SERPINB5) is a member of the Clade B subgroup of the large superfamily of serine protease inhibitors. It is proposed that maspin is a tumor suppressor; however, its molecular role remains to be elucidated. Here we report the characterization of a mouse monoclonal antibody directed against human maspin. This antibody, 16F7, recognizes maspin in both its native and denatured form, unlike several other commercial antibodies tested in this study. It will be a useful and versatile tool for future analyses of the biological function of maspin.

Tumor-suppressive maspin functions as a reactive oxygen species scavenger: importance of cysteine residues

Maspin is a member of the serine protease inhibitor (serpin) superfamily and displays tumor-suppressing activity by controlling cell migration, proliferation, apoptosis, and adhesion. Here, we provide evidence that maspin acts as a reactive oxygen species (ROS) scavenger through oxidation of three structurally exposed cysteine thiols to sulfenic acid. Ablation of these cysteine residues in maspin resulted in a significant increase in total ROS production in mouse mammary TM40D cells. Also, cells containing a triple-cysteine mutant of maspin showed elevated ERK1/2 activity, a downstream target of ROS, and enhanced proliferation and colony formation. These findings establish a novel mechanism by which maspin utilizes its cysteine thiols to inhibit oxidative stress and cell growth.

Function and mechanism by which interferon regulatory factor-1 inhibits oncogenesis

The present review focuses on recent advances in the understanding of the molecular mechnisms by which interferon regulatory factor (IRF)-1 inhibits oncogenesis. IRF-1 is associated with regulation of interferon α and β transcription. In addition, numerous clinical studies have indicated that IRF-1 gene deletion or rearrangement correlates with development of specific forms of human cancer. IRF-1 has been revealed to exhibit marked functional diversity in the regulation of oncogenesis. IRF-1 activates a set of target genes associated with regulation of the cell cycle, apoptosis and the immune response. The role of IRF-1 in the regulation of various types of human tumor has important implications for understanding the susceptibility and progression of cancer. In addition, an improved understanding of the role of IRF-1 in the pathological processes that lead to human malignant diseases may aid development of novel therapeutic strategies.

Transforming growth factor Beta 3 is required for excisional wound repair in vivo

Wound healing is a complex process that relies on proper levels of cytokines and growth factors to successfully repair the tissue. Of particular interest are the members of the transforming growth factor family. There are three TGF-ß isoforms-TGF- ß 1, 2, and 3, each isoform showing a unique expression pattern, suggesting that they each play a distinct function during development and repair. Previous studies reported an exclusive role for TGF-ß 3 in orofacial development and a potent anti-scarring effect. However, the role of TGF- ß 3 in excisional wound healing and keratinocyte migration remains poorly understood. We tested the effect of TGF-ß 3 levels on excisional cutaneous wounds in the adult mouse by directly injecting recombinant TGF-ß 3 or neutralizing antibody against TGF-ß 3 (NAB) in the wounds. Our results demonstrate that TGF-ß 3 does not promote epithelialization. However, TGF-ß 3 is necessary for wound closure as wounds injected with neutralizing antibody against TGF-ß 3 showed increased epidermal volume and proliferation in conjunction with a delay in keratinocyte migration. Wild type keratinocytes treated with NAB and Tgfb3-deficient keratinocytes closed an in vitro scratch wound with no delay, suggesting that our in vivo observations likely result from a paracrine effect.

Gene expression profiling identifies ESRP1 as a potential regulator of epithelial mesenchymal transition in somatotroph adenomas from a large cohort of patients with acromegaly

CONTEXT

The epithelial marker E-cadherin plays a crucial role in epithelial-mesenchymal transition (EMT). Decreased protein content in somatotroph adenomas has been associated with increased tumor size, invasion, and poor response to somatostatin analog (SA) treatment, but the potential mechanisms of EMT progression in these adenomas are lacking.

OBJECTIVE

We hypothesized that characterization of EMT-related transcripts in somatotroph adenomas could identify novel therapeutic targets in individuals with poor response to SA treatment and provide more knowledge of the mechanism of EMT progression.

PATIENTS

Fifty-three patients with acromegaly participated in the study.

RESEARCH DESIGN AND METHODS

We performed microarray analysis of 16 adenomas, eight with high expression and eight with low expression of E-cadherin, in order to identify EMT-related transcripts. Candidate transcripts were further explored in vivo in 53 adenomas and in vitro in a rat pituitary GH-producing cell (GH3) after exploring three models for reducing E-cadherin and inducing a mesenchymal phenotype.

RESULTS

In vivo E-cadherin mRNA expression in tumor tissue is associated negatively with tumor size and invasiveness and positively with GH and IGF-I levels in serum and response to SA treatment. Microarray and subsequent PCR analysis identify several EMT-related genes associated with E-cadherin expression. In vitro, few of these EMT-related genes were regulated by silencing E-cadherin or by TGF-β1 treatment in GH3 cells. In contrast, silencing Esrp1 in GH3 cells regulated many of the EMT-related transcripts.

CONCLUSION

These results indicate that ESRP1 could be a master regulator of the EMT process in pituitary adenomas causing acromegaly.

Tyrosine phosphorylation plays a role in increasing maspin protein levels and its cytoplasmic accumulation

Maspin is a tumor suppressor with many biological activities, multiple ligands and different subcellular localizations. Its underlying molecular mechanism remains elusive. We hypothesized that phosphorylation might regulate maspin localization and function. Using two-dimensional gel electrophoresis with different focusing power followed by Western blot we identified four different maspin forms with the same molecular weight (42 kDa), but different isoelectric points. Three of these forms were sensitive to acidic phosphatase treatment, suggesting that they are phosphorylated. Sodium peroxidovanadate treatment, a protein-tyrosine phosphatase inhibitor, resulted in a rapid increase in maspin protein levels and cytoplasmic accumulation. These data show that there are three different maspin tyrosine phosphoforms. Inhibition of tyrosine phosphatases increased maspin protein levels and leads to its cytoplasmic accumulation.

MCS9.7 enhancer activity is highly, but not completely, associated with expression of Irf6 and p63

BACKGROUND

DNA variation in Interferon Regulatory Factor 6 (IRF6) contributes risk for orofacial clefting, including a common DNA variant rs642961. This DNA variant is located in a multi-species conserved sequence that is 9.7 kb upstream from the IRF6 transcriptional start site (MCS9.7). The MCS9.7 element was shown to possess enhancer activity that mimicked the expression of endogenous Irf6 at embryonic day 11.5 in transient transgenic embryos, and also contains a p63 binding site that transactivates IRF6 expression. To analyze whether the MCS9.7 enhancer is sufficient to drive IRF6 expression, we generated stable transgenic murine lines that carry a MCS9.7-lacZ transgene. We hypothesized that MCS9.7 was sufficient to recapitulate the endogenous expression of Irf6 at other time-points during embryonic development.

RESULTS

We observed that MCS9.7 activity recapitulated endogenous Irf6 expression in most tissues, but not in the medial edge epithelium (MEE) at E14.5, when Irf6 expression was high during secondary palatal fusion. Also, while MCS9.7 activity and Irf6 expression were associated with p63 expression, we observed MCS9.7 activity and Irf6 expression in periderm, although p63 was absent.

CONCLUSION

These data suggest that MCS9.7 enhancer activity is not sufficient to recapitulate IRF6 expression, and that p63 expression is not always necessary nor sufficient for transactivation of IRF6.

IRF6 is a mediator of Notch pro-differentiation and tumour suppressive function in keratinocytes

While the pro-differentiation and tumour suppressive functions of Notch signalling in keratinocytes are well established, the underlying mechanisms remain poorly understood. We report here that interferon regulatory factor 6 (IRF6), an IRF family member with an essential role in epidermal development, is induced in differentiation through a Notch-dependent mechanism and is a primary Notch target in keratinocytes and keratinocyte-derived SCC cells. Increased IRF6 expression contributes to the impact of Notch activation on growth/differentiation-related genes, while it is not required for induction of 'canonical' Notch targets like p21(WAF1/Cip1), Hes1 and Hey1. Down-modulation of IRF6 counteracts differentiation of primary human keratinocytes in vitro and in vivo, promoting ras-induced tumour formation. The clinical relevance of these findings is illustrated by the strikingly opposite pattern of expression of Notch1 and IRF6 versus epidermal growth factor receptor in a cohort of clinical SCCs, as a function of their grade of differentiation. Thus, IRF6 is a primary Notch target in keratinocytes, which contributes to the role of this pathway in differentiation and tumour suppression.

An emerging role for the nuclear localization of maspin in the suppression of tumor progression and metastasis

Maspin, a member of the serpin family of serine protease inhibitors, was originally identified as a tumor suppressor that is expressed in normal mammary epithelial cells but is reduced or absent in breast carcinomas. Early enthusiasm for maspin as a biomarker for disease progression has been tempered by clinical data that associates maspin with favourable outcomes in some studies and poor prognosis in others. Here, we review all of the published clinical studies for maspin in breast and ovarian cancers and propose that the apparent discordance between clinical reports is a consequence of differential cellular distribution of maspin. Indeed, it was thought that an extracellular pool of maspin possessed tumor suppressor activity, acting by inhibiting migration and increasing cell adhesion. Recent evidence from our group and others indicates, however, that the nuclear localization of maspin in cancer cells is necessary for its tumor suppressor activity. We provide additional data here to demonstrate that nuclear-localized maspin binds to chromatin and is required to effectively prevent cells from metastasizing. Our knowledge of other serpins that localize to the nucleus should help to inform future studies of nuclear maspin. Elucidation of the molecular mechanisms regulating the localization and activities of maspin should pave the way for the development of improved diagnostics and therapies for cancer.

Maspin reprograms the gene expression profile of prostate carcinoma cells for differentiation

Maspin is an epithelial-specific tumor suppressor gene. Previous data suggest that maspin expression may redirect poorly differentiated tumor cells to better differentiated phenotypes. Further, maspin is the first and only endogenous polypeptide inhibitor of histone deacetylase 1 (HDAC1) identified thus far. In the current study, to address what central program of tumor cell redifferentiation is regulated by maspin and how tumor microenvironments further define the effects of maspin, we conducted a systematic and extensive comparison of prostate tumor cells grown in 2-dimensional culture, in 3-dimensional collagen I culture, and as in vivo bone tumors. We showed that maspin was sufficient to drive prostate tumor cells through a spectrum of temporally and spatially polarized cellular processes of redifferentiation, a reversal of epithelial-to-mesenchymal transition (EMT). Genes commonly regulated by maspin were a small subset of HDAC target genes that are closely associated with epithelial differentiation and TGFβ signaling. These results suggest that a specific endogenous HDAC inhibitor may regulate one functionally related subset of HDAC target genes, although additional maspin-induced changes of gene expression may result from tumor interaction with its specific microenvironments. Currently, EMT is recognized as a critical step in tumor progression. To this end, our current study uncovered a link between maspin and a specific mechanism of prostate epithelial differentiation that can reverse EMT.

Interferon regulatory factor 6 is necessary, but not sufficient, for keratinocyte differentiation

Regulation of epidermal proliferation and differentiation is critical for maintenance of cutaneous homeostasis. Interferon Regulatory Factor 6 (Irf6)-deficient mice die perinatally and exhibit ectopic proliferation and defective epidermal differentiation. We sought to determine whether these disruptions of epidermal function were cell autonomous, and used embryonic Irf6(-/-) keratinocytes to understand the specific role of Irf6 in keratinocyte proliferation and differentiation. In the absence of Irf6, keratinocytes exhibited a heterogeneous phenotype with the presence of large cells. Irf6(-/-) keratinocytes displayed increased colony-forming efficiency compared with wild-type cells, suggesting that Irf6 represses long-term proliferation. Irf6 was present at low levels in wild-type keratinocytes in culture, and upregulated after induction of differentiation in vitro, along with upregulation of markers of early differentiation. However, Irf6(-/-) keratinocytes did not express markers of terminal differentiation. Overexpression of Irf6 in wild-type keratinocytes was insufficient to induce expression of markers of differentiation under growing conditions. Together, these results indicated that Irf6 is necessary, but not sufficient, for keratinocyte differentiation. Finally, using a transgenic mouse expressing Lac-Z under the regulation of an enhancer element 9.7  kb upstream of the Irf6 start site, we demonstrated that this element contributes to the regulation of Irf6 in the epidermis and keratinocytes in culture.

An in vitro model that recapitulates the epithelial to mesenchymal transition (EMT) in human breast cancer

The epithelial to mesenchymal transition (EMT) is a developmental program in which epithelial cells down-regulate their cell-cell junctions, acquire spindle cell morphology and exhibit cellular motility. In human breast cancer, invasion into surrounding tissue is the first step in metastatic progression. Here, we devised an in vitro model using selected cell lines, which recapitulates many features of EMT as observed in human breast cancer. By comparing the gene expression profiles of claudin-low breast cancers with the experimental model, we identified a 9-gene signature characteristic of EMT. This signature was found to distinguish a series of breast cancer cell lines that have demonstrable, classical EMT hallmarks, including loss of E-cadherin protein and acquisition of N-cadherin and vimentin expression. We subsequently developed a three-dimensional model to recapitulate the process of EMT with these cell lines. The cells maintain epithelial morphology when encapsulated in a reconstituted basement membrane, but undergo spontaneous EMT and invade into surrounding collagen in the absence of exogenous cues. Collectively, this model of EMT in vitro reveals the behaviour of breast cancer cells beyond the basement membrane breach and recapitulates the in vivo context for further investigation into EMT and drugs that may interfere with it.

ΔNp63α/IRF6 interplay activates NOS2 transcription and induces autophagy upon tobacco exposure

Tobacco-induced oxidative stress leads to chronic inflammation and is implicated in the development of many human epithelial cancers, including head and neck cancer. Cigarette smoke exposure was shown to induce the expression of the ΔNp63α and nitric oxide synthase (NOS)-2 in head and neck squamous cell carcinoma cells and immortalized oral keratinocytes. The NOS2 promoter was found to contain various cognate sequences for several transcription factors including interferon regulatory factor (IRF)-6 and p63, which were shown in vivo binding to the NOS2 promoter in response to smoke exposure. Small interfering (si)-RNAs against both ΔNp63α and IRF6 decreased the induction of NOS2 promoter-driven reporter luciferase activity and were shown to inhibit NOS2 activity. Furthermore, both mainstream (MSE) and sidestream (SSE) smoking extracts induced changes in expression of autophagic marker, LC3B, while siRNA against ΔNp63α, IRF6 and NOS2 modulated these autophagic changes. Overall, these data support the notion that ΔNp63α/IRF6 interplay regulates NOS2 transcription, thereby underlying the autophagic-related cancer cell response to tobacco exposure.

Two missense mutations of the IRF6 gene in two Japanese families with popliteal pterygium syndrome

Mutations in the interferon regulatory factor 6 gene (IRF6) cause either popliteal pterygium syndrome (PPS) or Van der Woude syndrome (VWS), allelic autosomal dominant orofacial clefting conditions. To further investigate the IRF6 mutation profile in PPS, we performed mutation analysis of patients from two unrelated Japanese families with PPS and identified mutations in IRF6: c.251G>T (R84L) and c.1271C>T (S424L). We also found R84L, which together with previous reports on R84 mutations, provided another line of evidence that both syndromes could result from the same mutation probably under an influence of a modifier gene(s). This supports the idea that the R84 residue in the DNA binding domain of IRF6 is a mutational hot spot for PPS. A luciferase assay of the S424L protein in the other family demonstrated that the mutation decreased the IRF6 transcriptional activity significantly to 6% of that of the wild-type. This finding suggests that the C-terminus region of IRF6 could have an important function in phosphorylation or protein interaction. To our knowledge, this is the first report of mutations observed in Japanese PPS patients.

G-helix of maspin mediates effects on cell migration and adhesion

Maspin is a member of the serine protease inhibitor (serpin) superfamily that lacks protease inhibitory ability, although displaying tumor metastasis-suppressing activity resulting from its influence on cell migration, invasion, proliferation, apoptosis, and adhesion. The molecular mechanisms of these actions of maspin are as yet undefined. Here, we sought to identify critical functional motifs by the expression of maspin with point mutations at sites potentially involved in protein-protein interactions: the G α-helix (G-helix), an internal salt bridge or the P1 position of the reactive center loop. Our findings indicate that only mutations in the G-helix attenuated inhibition of cell migration by maspin and that this structural element is also involved in the effect of maspin on cell adhesion. The action of maspin on cell migration could be mimicked by a 15-mer G-helix peptide, indicating that the G-helix is both essential and sufficient for this effect. In addition, we provide evidence that the effects of the G-helix of maspin are dependent on β1 integrins. These data reveal that the major extracellular functions associated with the tumor suppressive action of maspin likely involve interactions in which the G-helix plays a key role.

Serpins flex their muscle: II. Structural insights into target peptidase recognition, polymerization, and transport functions

Inhibitory serpins are metastable proteins that undergo a substantial conformational rearrangement to covalently trap target peptidases. The serpin reactive center loop contributes a majority of the interactions that serpins make during the initial binding to target peptidases. However, structural studies on serpin-peptidase complexes reveal a broader set of contacts on the scaffold of inhibitory serpins that have substantial influence on guiding peptidase recognition. Structural and biophysical studies also reveal how aberrant serpin folding can lead to the formation of domain-swapped serpin multimers rather than the monomeric metastable state. Serpin domain swapping may therefore underlie the polymerization events characteristic of the serpinopathies. Finally, recent structural studies reveal how the serpin fold has been adapted for non-inhibitory functions such as hormone binding.