Differentiation signals induce APOBEC3A expression via GRHL3 in squamous epithelia and squamous cell carcinoma

Two APOBEC (apolipoprotein-B mRNA editing enzyme catalytic polypeptide-like) DNA cytosine deaminase enzymes (APOBEC3A and APOBEC3B) generate somatic mutations in cancer, driving tumour development and drug resistance. Here we used single cell RNA sequencing to study APOBEC3A and APOBEC3B expression in healthy and malignant mucosal epithelia, validating key observations with immunohistochemistry, spatial transcriptomics and functional experiments. Whereas APOBEC3B is expressed in keratinocytes entering mitosis, we show that APOBEC3A expression is confined largely to terminally differentiating cells and requires Grainyhead-like transcription factor 3 (GRHL3). Thus, in normal tissue, neither deaminase appears to be expressed at high levels during DNA replication, the cell cycle stage associated with APOBEC-mediated mutagenesis. In contrast, we show that in squamous cell carcinoma tissues, there is expansion of GRHL3 expression and activity to a subset of cells undergoing DNA replication and concomitant extension of APOBEC3A expression to proliferating cells. These findings indicate a mechanism for acquisition of APOBEC3A mutagenic activity in tumours.

Dual role of GRHL3 in bladder carcinogenesis depending on histological subtypes

The effect of grainyhead-like transcription factor 3 (GRHL3) on cancer development depends on the cancer subtypes as shown in tumor entities such as colorectal or oral squamous cell carcinomas. Here, we analyzed the subtype-specific role of GRHL3 in bladder carcinogenesis, comparing common urothelial carcinoma (UC) with squamous bladder cancer (sq-BLCA). We examined GRHL3 mRNA and protein expression in cohorts of patient samples, its prognostic role and its functional impact on tumorigeneses in different molecular and histopathological subtypes of bladder cancer. We showed for GRHL3 a reverse expression in squamous and urothelial bladder cancer subtypes. Stably GRHL3-overexpressing EJ28, J82, and SCaBER in vitro models revealed a tumor-suppressive function in squamous and an oncogenic role in the urothelial cancer cells affecting cell and colony growth, and migratory and invasive capacities. Transcriptomic profiling demonstrated highly subtype-specific GRHL3-regulated expression networks coined by the enrichment of genes involved in integrin-mediated pathways. In SCaBER, loss of ras homolog family member A (RHOA) GTPase activity was demonstrated to be associated with co-regulation of eukaryotic translation initiation factor 4E family member 3 (EIF4E3), a potential tumor suppressor gene. Thus, our data provide for the first time a detailed insight into the role of the transcription factor GRHL3 in different histopathological subtypes of bladder cancer.

The GRHL3-regulated long non-coding RNA lnc-DC modulates keratinocytes differentiation by interacting with IGF2BP2 and up-regulating ZNF750

BACKGROUND

Aberrant keratinocytes differentiation has been demonstrated to be associated with a number of skin diseases. The roles of lncRNAs in keratinocytes differentiation remain to be largely unknown.

OBJECTIVE

Here we aim to investigate the role of lnc-DC in regulating epidermal keratinocytes differentiation.

METHODS

Expression of lnc-DC in the skin was queried in AnnoLnc and verified by FISH. The lncRNA expression profiles during keratinocytes differentiation were reanalyzed and verified by qPCR and FISH. Gene knock-down and over-expression were used to explore the role of lnc-DC in keratinocytes differentiation. The downstream target of lnc-DC was screened by whole transcriptome sequencing. CUT&RUN assay and siRNAs transfection was used to reveal the regulatory effect of GRHL3 on lnc-DC. The mechanism of lnc-DC regulating ZNF750 was revealed by RIP assay and RNA stability assay.

RESULTS

Lnc-DC was biasedly expressed in skin and up-regulated during epidermal keratinocytes differentiation. Knockdown lnc-DC repressed epidermal keratinocytes differentiation while over-express lnc-DC showed the opposite effect. GRHL3, a well-known transcription factor regulating keratinocytes differentiation, could bind to the promoter of lnc-DC and regulate its expression. By whole transcriptome sequencing, we identified that ZNF750 was a downstream target of lnc-DC during keratinocytes differentiation. Mechanistically, lnc-DC interacted with RNA binding protein IGF2BP2 to stabilize ZNF750 mRNA and up- regulated its downstream targets TINCR and KLF4.

CONCLUSION

Our study revealed the novel role of GRHL3/lnc-DC/ZNF750 axis in regulating epidermal keratinocytes differentiation, which may provide new therapeutic targets of aberrant keratinocytes differentiation related skin diseases.

Transcription factor-target gene regulatory network analysis in human lung adenocarcinoma

Background

Transcription factors (TFs) play a crucial role in the occurrence and progression of lung adenocarcinoma (LUAD), and targeting TFs is an important direction for treating LUAD. However, targeting a single TF often fails to achieve satisfactory therapeutic outcomes. Furthermore, the regulatory TF-target gene networks involved in the development of LUAD is complex and not yet fully understood.

Methods

In this study, we performed RNA sequencing (RNA-seq) to analyze the transcriptome profile of human LUAD tissues and matched adjacent nontumor tissues. We selected the differentially expressed TFs, performed enrichment analysis and survival curve analysis, and predicted the regulatory networks of the top differential TFs with their target genes. Finally, alternative splicing analyses were also performed.

Results

We found that TFs GRHL3, SIX1, SIX2, SPDEF, and ETV4 were upregulated, while TAL1, EPAS1, SOX17, NR4A1, and EGR3 were significantly downregulated in LUAD tissues compared to normal tissues. We propose a potential GRHL3-CDH15-Wnt-β-catenin pro-oncogenic signaling axis and a potential TAL1-ADAMTS1-vascular antioncogenic signaling axis. In addition, we found that alternative splicing of intron retention (IR), approximate IR (XIR), multi-IR (MIR), approximate MIR (XMIR), and approximate alternative exon ends (XAE) showed abnormally increased frequencies in LUAD tissues.

Conclusions

These findings revealed a novel TF-target gene regulatory axis related to tumorigenesis and provided potential therapeutic targets and mechanisms for LUAD.

A Comprehensive Genetic Analysis of Slovenian Families with Multiple Cases of Orofacial Clefts Reveals Novel Variants in the Genes IRF6, GRHL3, and TBX22

Although the aetiology of non-syndromic orofacial clefts (nsOFCs) is usually multifactorial, syndromic OFCs (syOFCs) are often caused by single mutations in known genes. Some syndromes, e.g., Van der Woude syndrome (VWS1; VWS2) and X-linked cleft palate with or without ankyloglossia (CPX), show only minor clinical signs in addition to OFC and are sometimes difficult to differentiate from nsOFCs. We recruited 34 Slovenian multi-case families with apparent nsOFCs (isolated OFCs or OFCs with minor additional facial signs). First, we examined IRF6, GRHL3, and TBX22 by Sanger or whole exome sequencing to identify VWS and CPX families. Next, we examined 72 additional nsOFC genes in the remaining families. Variant validation and co-segregation analysis were performed for each identified variant using Sanger sequencing, real-time quantitative PCR and microarray-based comparative genomic hybridization. We identified six disease-causing variants (three novel) in IRF6, GRHL3, and TBX22 in 21% of families with apparent nsOFCs, suggesting that our sequencing approach is useful for distinguishing syOFCs from nsOFCs. The novel variants, a frameshift variant in exon 7 of IRF6, a splice-altering variant in GRHL3, and a deletion of the coding exons of TBX22, indicate VWS1, VWS2, and CPX, respectively. We also identified five rare variants in nsOFC genes in families without VWS or CPX, but they could not be conclusively linked to nsOFC.

Consistent downregulation of the cleft lip/palate-associated genes IRF6 and GRHL3 in carcinomas

Interferon Regulatory Factor 6 (IRF6) and Grainyhead Like Transcription Factor 3 (GRHL3) are transcription factors that orchestrate gene regulatory networks required for the balance between keratinocyte differentiation and proliferation. Absence of either protein results in the lack of a normal stratified epidermis with keratinocytes failing to stop proliferating and to terminally differentiate. Numerous pathological variants within IRF6 and GRHL3 have been identified in orofacial cleft-affected individuals and expression of the two transcription factors has been found to be often dysregulated in cancers. However, whether orofacial cleft-associated IRF6 and GRHL3 variants in patients might also affect their cancer risk later in life, is not clear yet. The fact that the role of IRF6 and GRHL3 in cancer remains controversial makes this question even more challenging. Some studies identified IRF6 and GRHL3 as oncogenes, while others could attribute tumor suppressive functions to them. Trying to solve this apparent conundrum, we herein aimed to characterize IRF6 and GRHL3 function in various types of carcinomas. We screened multiple cancer and normal cell lines for their expression, and subsequently proceeded with functional assays in cancer cell lines. Our data uncovered consistent downregulation of IRF6 and GRHL3 in all types of carcinomas analyzed. Reduced levels of IRF6 and GRHL3 were found to be associated with several tumorigenic properties, such as enhanced cell proliferation, epithelial mesenchymal transition, migration and reduced differentiation capacity. Based on our findings, IRF6 and GRHL3 can be considered as tumor suppressor genes in various carcinomas, which makes them potential common etiological factors for cancer and CLP in a fraction of CLP-affected patients.

Novel GRHL3 Variants in a South African Cohort With Cleft Lip and Palate

OBJECTIVE

The etiology of cleft palate (CP) is poorly understood compared with that of cleft lip with or without palate (CL ± P). Recently, variants in Grainyhead like transcription factor 3 (GRHL3) were reported to be associated with a risk for CP in European and some African populations including Nigeria, Ghana, and Ethiopia. In order to identify genetic variants that may further explain the etiology of CP, we sequenced GRHL3 in a South African population to determine if rare variants in GRHL3 are associated with the presence of syndromic or nonsyndromic CP.

DESIGN

We sequenced the exons of GRHL3 in 100 cases and where possible, we sequenced the parents of the individuals to determine the segregation pattern and presence of de novo variants.

SETTING

The cleft clinics from 2 public, tertiary hospitals in Durban, South Africa (SA), namely Inkosi Albert Luthuli Central Hospital and KwaZulu-Natal Children's Hospital.

PATIENTS, PARTICIPANTS

One hundred patients with CL ± P and their parents.

INTERVENTIONS

Saliva samples were collected.

MAIN OUTCOME MEASURES

To ascertain the genetic variants in the GRHL3 gene in patients with CL ± P in SA.

RESULTS

Five variants in GRHL3 were observed; 3 were novel and 2 were known variants. The novel variants were intronic variants (c.1062 + 77A>G and c.627 + 1G>A) and missense variant (p.Asp169Gly).

CONCLUSIONS

This study provides further evidence that variants in GRHL3 contribute to the risk of nonsyndromic CP in African populations, specifically, in the South African population.

Lack of IRF6 Disrupts Human Epithelial Homeostasis by Altering Colony Morphology, Migration Pattern, and Differentiation Potential of Keratinocytes

Variants within the gene encoding for the transcription factor Interferon Regulatory Factor 6 (IRF6) are associated with syndromic and non-syndromic Cleft Lip/Palate (CLP) cases. IRF6 plays a vital role in the regulation of the proliferation/differentiation balance in keratinocytes and is involved in wound healing and migration. Since a fraction of CLP patients undergoing corrective cleft surgery experience wound healing complications, IRF6 represents an interesting candidate gene linking the two processes. However, Irf6 function has been mainly studied in mice and knowledge on IRF6 in human cells remains sparse. Here, we aimed to elucidate the role of IRF6 in human postnatal skin- and oral mucosa-derived keratinocytes. To do so, we applied CRISPR/Cas9 to ablate IRF6 in two TERT-immortalized keratinocyte cultures, which we used as model cell lines. We show that IRF6 controls the appearance of single cells and colonies, with the latter being less cohesive in its absence. Consequently, IRF6 knockout keratinocytes often moved as single cells instead of a collective epithelial sheet migration but maintained their epithelial character. Lack of IRF6 triggered severe keratinocyte differentiation defects, which were already apparent in the stratum spinosum and extended to the stratum corneum in 3D organotypic skin cultures, while it did not alter their growth rate. Finally, proteomics revealed that most of the differentially expressed proteins in the absence of IRF6 could be associated with differentiation, cell-cell adhesion as well as immune response. Our data expand the knowledge on IRF6 in human postnatal keratinocytes, which will help to better understand IRF6-related pathologies.

The functional GRHL3-filaggrin axis maintains a tumor differentiation potential and influences drug sensitivity

Current therapies for treating heterogeneous cancers such as head and neck squamous cell carcinoma (HNSCC) are non-selective and are administered independent of response biomarkers. Therapy resistance subsequently emerges, resulting in increased cellular proliferation that is associated with loss of differentiation. Whether a cancer cell differentiation potential can dictate therapy responsiveness is still currently unknown. A multi-omic approach integrating whole-genome and whole-transcriptome sequencing with drug sensitivity was employed in a HNSCC mouse model, primary patients’ data, and human cell lines to assess the potential of functional differentiation in predicting therapy response. Interestingly, a subset of HNSCC with effective GRHL3-dependent differentiation was the most sensitive to inhibitors of PI3K/mTOR, c-Myc, and STAT3 signaling. Furthermore, we identified the GRHL3-differentiation target gene Filaggrin (FLG) as a response biomarker and more importantly, stratified HNSCC subsets as treatment resistant based on their FLG mutational profile. The loss of FLG in sensitive HNSCC resulted in a dramatic resistance to targeted therapies while the GRHL3-FLG signature predicted a favorable patient prognosis. This study provides evidence for a functional GRHL3-FLG tumor-specific differentiation axis that regulates targeted therapy response in HNSCC and establishes a rationale for clinical investigation of differentiation-paired targeted therapy in heterogeneous cancers.

Association analysis of SNPs in GRHL3, FAF1, and KCNJ2 with NSCPO sub-phenotypes in Han Chinese

OBJECTIVES

Non-syndromic cleft palate only (NSCPO) is a common congenital deformity with complex etiologies. GRHL3, FAF1, and KCNJ2 have been reported to be involved in the pathogenesis of NSCPO. Up till now, there have been no replication studies based on large Han Chinese. Therefore, this study aimed to investigate associations between GRHL3, FAF1, KCNJ2, and NSCPO sub-phenotypes patients in Han Chinese.

MATERIALS AND METHODS

Firstly, we selected 2 SNPs based on previous literatures: FAF1 (rs3827730) and GRHL3 (rs41268753). Also, we selected 8 tagSNPs in GRHL3 (rs557811, rs609352, rs10903078, rs6659209, rs12401714, rs12568599, rs3887581, rs12024148) and 2 tagSNPs in KCNJ2 (rs75855040 and rs236514). Afterward, we evaluated these SNPs among 1668 NSCPO patients and 1811 normal controls from Han Chinese. Following data were analyzed by PLINK and Haploview program.

RESULTS

Association analysis under additive model showed that allele A at rs12568599 in GRHL3 gene is significantly associated with NSCPO (p = 0.0034, OR = 1.38 and 95%CI: 1.11-1.72) and its sub-phenotype incomplete cleft palate (ICP) (p = 0.0039, OR = 1.4 and 95%CI: 1.11-1.75), and it could increase the risk of both NSCPO and ICP.

CONCLUSIONS

This study firstly found that rs12568599 in GRHL3 is associated with NSCPO and ICP in Han Chinese, indicating that sub-phenotypes of NSCPO have different etiologies.

Association of Nucleotide Variants of GRHL3, IRF6, NAT2, SDC2, BCL3, and PVRL1 Genes with Nonsyndromic Cleft Lip With/Without Cleft Palate in Multigenerational Families: A Retrospective Study

Background:

Several genes are associated with the etiology of cleft lip and palate (CLP) in different populations. Many nucleotide variants on genes such as GRHL3, IRF6, NAT2, SDC2, BCL3, and PVRL1 were reported in different populations, but not studied in multigenerational cases in the Indian population.

Aim and Objective:

The aim of this study is to evaluate whether nucleotide variants rs41268753, rs861020, rs1041983, rs1042381, rs2965169, and rs10790332 are involved in the etiology of nonsyndromic CLP (NSCLP) in multigenerational Indian families.

Study Design:

Retrospective genetic study.

Materials and Methods:

Based on inclusion and exclusion criteria, 20 multigenerational families with nonsyndromic cleft lip with or without cleft palate (NSCL/P) were selected. Blood samples from both affected and unaffected participants were collected as a source of genomic DNA. Six nucleotide variants on these genes were genotyped to test for the association with NSCL/P. Genotyping was performed with the MassArray method. Genotype distribution was used to calculate the Hardy–Weinberg equilibrium using PLINK, a whole-genome association analysis toolset. The allelic association was compared among cases and controls using Chi-square test as implemented in PLINK. P ≤ 0.05 indicates statistical differences between groups.

Results:

No significant associations were found between individual single-nucleotide polymorphisms and NSCL/P. The odds ratio was 1.531, 1.198, 0.8082, 1.418, 1, and 0.5929 for polymorphisms rs41268753, rs861020, rs1041983, rs1042381, rs2965169, and rs10790332, respectively.

Conclusion:

Our findings suggest that among the multigenerational families in our population, the high-risk nucleotide variants GRHL3 rs41268753, IRF6 rs861020, NAT2 rs1041983, SDC2 rs1042381, BCL3 rs2965169, and PVRL1 rs10790332 are not associated with increased risk of NSCL/P.

Grainyhead-Like 3 Influences Migration and Invasion of Urothelial Carcinoma Cells

Invasive urothelial carcinomas of the bladder (UCB) characteristically show a loss of differentiation markers. The transcription factor Grainyhead-like 3 (GRHL3) plays an important role in the development and differentiation of normal urothelium. The contribution to UCB progression is still elusive. Differential expression of GRHL3 was assessed in normal human urothelium and in non-invasive and invasive bladder cancer cell lines. The contribution of GRHL3 to cell proliferation, viability and invasion in UCB cell lines was determined by gain- and loss-of-function assays in vitro and in an organ culture model using de-epithelialized porcine bladders. GRHL3 expression was detectable in normal human urothelial cells and showed significantly higher mRNA and protein levels in well-differentiated, non-invasive RT4 urothelial carcinoma cells compared to moderately differentiated RT112 cells. GRHL3 expression was absent in anaplastic and invasive T24 cells. Ectopic de novo expression of GRHL3 in T24 cells significantly impaired their migration and invasion properties in vitro and in organ culture. Its downregulation improved the invasive capacity of RT4 cells. The results indicate that GRHL3 may play a role in progression and metastasis in UCB. In addition, this work demonstrates that de-epithelialized porcine bladder organ culture can be a useful, standardized tool to assess the invasive capacity of cancer cells.

Non-syndromic Cleft Palate: An Overview on Human Genetic and Environmental Risk Factors

The epithelial and mesenchymal cells involved in early embryonic facial development are guided by complex regulatory mechanisms. Any factor perturbing the growth, approach and fusion of the frontonasal and maxillary processes could result in orofacial clefts that represent the most common craniofacial malformations in humans. The rarest and, probably for this reason, the least studied form of cleft involves only the secondary palate, which is posterior to the incisive foramen. The etiology of cleft palate only is multifactorial and involves both genetic and environmental risk factors. The intention of this review is to give the reader an overview of the efforts made by researchers to shed light on the underlying causes of this birth defect. Most of the scientific papers suggesting potential environmental and genetic causes of non-syndromic cleft palate are summarized in this review, including genome-wide association and gene–environment interaction studies.

Expression Analysis of GRHL3 and PHLDA3 in Head and Neck Squamous Cell Carcinoma

Background

Head and neck squamous cell carcinoma (HNSCC) includes a group of heterogeneous tumors with generally invasive behavior. The PI3K/AKT pathway plays an important role in the pathogenesis of HNSCC.

Methods

In the current study, we investigated the expression of two negative feedback regulators of the PI3K pathway, namely PHLDA3 and GRHL3, in 45 paired samples of HNSCC and adjacent non-cancerous tissues (ANCTs).

Results

While expression of GRHL3 was down-regulated in tumoral tissues compared with ANCTs by the factor 4.21, PHLDA3 expression levels were up-regulated by 5.99-times. Gender-based analysis revealed a significant down-regulation of GRHL3 gene expression level in male patients compared with the control samples and significant up-regulation of PHLDA3 gene expression level in both sexes compared with the control samples. Differences in the expressions of both genes were significant in patients aged more than 60 years, but not in the younger patients. Expression of GRHL3 was only down-regulated in patients with positive smoking history. Expression of GRHL3 was decreased in grades 2 and 3 samples compared with controls. There was a significant increase in transcript levels of PHLDA3 in stages II and III HNSCC samples compared with the controls group. ROC curve analysis indicated that the expression level of PHLDA3 could be a promising marker for the diagnosis of HNSCC patients with a sensitivity and specificity of 0.666 and 0.688, respectively. In addition, sensitivity and specificity of GRHL3 were 0.755 and 0.577, respectively.

Discussion

The current study indicates dysregulation of regulators of PI3K pathway in HNSCC and their potential application as putative biomarkers for this cancer.

Exploring GRHL3 polymorphisms and SNP-SNP interactions in the risk of non-syndromic oral clefts in the Brazilian population

OBJECTIVE

To investigate the association of single-nucleotide polymorphisms (SNP) in grainyhead-like 3 (GRHL3) and to verify its possible interactions with others genes responsible for craniofacial development in the risk of non-syndromic oral cleft (NSOC).

METHODS

Applying TaqMan allelic discrimination assays, we evaluated GRHL3 SNPs (rs10903078, rs41268753, and rs4648975) in an ancestry-structured case-control sample composed of 1,127 Brazilian participants [272 non-syndromic cleft palate only (NSCPO), 242 non-syndromic cleft lip only (NSCLO), 319 non-syndromic cleft lip and palate (NSCLP), and 294 healthy controls]. Additionally, SNP-SNP interactions of GRHL3 and previously reported variants in FAM49A, FOXE1, NTN1, and VAX1 were verified in non-syndromic cleft lip with or without cleft palate (NSCL ± P). To eliminate false-positive associations, Bonferroni correction or 1,000 permutation method was applied.

RESULTS

The multiple logistic regression analysis showed that the CC genotype of rs10903078 (p = .03) and the haplotype C-C formed by the SNPs rs10903078 and rs41268753 (p = .04) were associated with NSCLO, but the p-values did not withstand Bonferroni correction. However, SNP-SNP test revealed significant interactions between GRHL3 SNPs and FAM49A (rs7552), FOXE1 (rs3758249), VAX1 (rs7078160 and rs751231), and NTN1 (rs9891446).

CONCLUSIONS

Our results confirm the importance of GRHL3 and its interactions with previously NSOC-associated genes, including FAM49A, FOXE1, NTN1, and VAX1, in the pathogenesis of NSOC in the Brazilian population.

The Cohesin Complex Is Necessary for Epidermal Progenitor Cell Function through Maintenance of Self-Renewal Genes

Adult stem and progenitor cells are critical for replenishing lost tissue due to injury or normal turnover. How these cells maintain self-renewal and sustain the tissue they populate are areas of active investigation. Here, we show that the cohesin complex, which has previously been implicated in regulating chromosome segregation and gene expression, is necessary to promote epidermal stem and progenitor cell self-renewal through cell-autonomous mechanisms. Cohesin binds to genomic sites associated with open chromatin, including DNase-I-hypersensitive sites, RNA polymerase II, and histone marks such as H3K27ac and H3K4me3. Reduced cohesin expression results in spontaneous epidermal differentiation due to loss of open chromatin structure and expression of key self-renewal genes. Our results demonstrate a prominent role for cohesin in modulating chromatin structure to allow for enforcement of a stem and progenitor cell gene expression program.

CSNK1a1 Regulates PRMT1 to Maintain the Progenitor State in Self-Renewing Somatic Tissue

Somatic progenitors sustain tissue self-renewal while suppressing premature differentiation. Protein arginine methyltransferases (PRMTs) affect many processes; however, their role in progenitor function is incompletely understood. PRMT1 was found to be the most highly expressed PRMT in epidermal progenitors and the most downregulated PRMT during differentiation. In targeted mouse knockouts and in long-term regenerated human mosaic epidermis in vivo, epidermal PRMT1 loss abolished progenitor self-renewal and led to premature differentiation. Mass spectrometry of the PRMT1 protein interactome identified the CSNK1a1 kinase, which also proved essential for progenitor maintenance. CSNK1a1 directly bound and phosphorylated PRMT1 to control its genomic targeting to PRMT1-sustained proliferation genes as well as PRMT1-suppressed differentiation genes. Among the latter were GRHL3, whose derepression was required for the premature differentiation seen with PRMT1 and CSNK1a1 loss. Maintenance of the progenitors thus requires cooperation by PRMT1 and CSNK1a1 to sustain proliferation gene expression and suppress premature differentiation driven by GRHL3.

IRF6 expression in basal epithelium partially rescues Irf6 knockout mice

BACKGROUND

Mutations in IRF6, CHUK (IKKA), and RIPK4 can lead to a disease spectrum that includes cutaneous, limb, and craniofacial malformations. Loss of these alleles in the mouse leads to perinatal lethality and severe cutaneous, limb, and craniofacial defects also. Genetic rescue in the mouse has been shown for Ikka and Ripk4.

RESULTS

Here, we show partial genetic rescue of Irf6 knockout embryos using the KRT14 promoter to drive Irf6 expression in the basal epithelium. In contrast to Irf6 knockout embryos, rescue embryos survive the immediate perinatal period. Macroscopic examination reveals rescue of skin adhesions between the axial and appendicular skeleton. Unexpectedly, KRT14-driven Irf6 expression does not completely rescue orofacial clefting and adhesions between the palate and tongue, suggesting the importance of cell-autonomous IRF6 expression in periderm. Like knockout embryos, Irf6 rescue embryos also have persistent esophageal adhesions, which likely contribute to postnatal demise.

CONCLUSIONS

Together, these data suggest that targeted expression of IRF6 can significantly reduce disease severity, but that a minimum level of Irf6 in both periderm and basal epithelial cells is necessary for orofacial development. Therefore, homologous human and mouse phenotypes are observed for IRF6, IKKA, and RIPK4. In this work, we show that altering the expression level of IRF6 dramatically modified this phenotype in utero. Developmental Dynamics 246:670-681, 2017. © 2017 Wiley Periodicals, Inc.

Interferon Regulatory Factor 6 Promotes Keratinocyte Differentiation in Response to Porphyromonas gingivalis

We recently demonstrated that the expression of the interferon regulatory factor 6 (IRF6) transcription factor in oral keratinocytes was stimulated by the periodontal pathogen Porphyromonas gingivalis Here, we have established that IRF6 promotes the differentiation of oral keratinocytes in response to P. gingivalis This was evidenced by the IRF6-dependent upregulation of specific markers of keratinocyte terminal differentiation (e.g., involucrin [IVL] and keratin 13 [KRT13]), together with additional transcriptional regulators of keratinocyte differentiation, including Grainyhead-like 3 (GRHL3) and Ovo-like zinc finger 1 (OVOL1). We have previously established that the transactivator function of IRF6 is activated by receptor-interacting protein kinase 4 (RIPK4). Consistently, the silencing of RIPK4 inhibited the stimulation of IVL, KRT13, GRHL3, and OVOL1 gene expression. IRF6 was shown to also regulate the stimulation of transglutaminase-1 (TGM1) gene expression by P. gingivalis, as well as that of small proline-rich proteins (e.g., SPRR1), which are covalently cross-linked by TGM1 to other proteins, including IVL, during cornification. The expression of the tight junction protein occludin (OCLN) was found to also be upregulated in an IRF6-dependent manner. IRF6 was demonstrated to be important for the barrier function of oral keratinocytes; specifically, silencing of IRF6 increased P. gingivalis-induced intercellular permeability and cell invasion. Taken together, our findings potentially position IRF6 as an important mediator of barrier defense against P. gingivalis.

Rare deleterious variants in GRHL3 are associated with human spina bifida

Neural tube defects, including spina bifida, are among the most common birth defects caused by failure of neural tube closure during development. They have a complex etiology involving largely undetermined environmental and genetic factors. Previous studies in mouse models have implicated the transcription factor Grhl3 as an important factor in the pathogenesis of spina bifida. In the present study, we conducted a resequencing analysis of GRHL3 in a cohort of 233 familial and sporadic cases of spina bifida. We identified two novel truncating variants: one homozygous frameshift variant, p.Asp16Aspfs*10, in two affected siblings and one heterozygous intronic splicing variant, p.Ala318Glyfs*26. We also identified five missense variants, one of which was demonstrated to reduce the activation of gene targets in a luciferase reporter assay. With the previously identified p.Arg391Cys variant, eight variants were found in GRHL3. Comparison of the variant rate between our cohort and the ExAC database identified a significant enrichment of deleterious variants in GRHL3 in the whole gene and the transactivation region in spina bifida patients. These data provide strong evidence for a role of GRHL3 as a predisposing factor to spina bifida and will help dissect the complex etiology and pathogenic mechanisms of these malformations.

Association study between Van der Woude Syndrome causative gene GRHL3 and nonsyndromic cleft lip with or without cleft palate in a Chinese cohort

Cleft lip with or without cleft palate (CL/P) is one of the most common birth defects worldwide and is characterized by abnormalities of the orofacial structure. Syndromic CL/P is mainly caused by Mendelian disorders such as Van der Woude Syndrome (VWS). However, >70% of CL/P cases are nonsyndromic, characterized by isolated orofacial cleft without any known syndrome. The etiology of nonsyndromic CL/P (NSCL/P) remains elusive, but it has been suggested that causative genes of syndromic CL/P might also contribute to NSCL/P. As such, the VWS causative gene IRF6 has been extensively studied in NSCL/P. Recently, GRHL3 was identified as another VWS causative gene. Thus, it may be a novel candidate gene for NSCL/P. In the present study, we genotyped 10 tag SNPs covering GRHL3 and performed association analysis with NSCL/P in 504 cases and 455 healthy controls. Our preliminary results identified rs10903078, rs4638975, and a haplotype rs10903078-rs6659209 of GRHL3 that exceeded the significance threshold (p<0.05), though none survived Bonferroni correction for multiple comparisons. As the first study between GRHL3 and NSCL/P, the contribution of this gene to NSCL/P etiology should be interpreted with caution based on existing evidence. Further, the robustness of association between GRHL3 and NSCL/P should be further validated in expanded cohorts.

Clinical significance of GRHL3 expression in diffuse large B cell lymphoma

In the present study, we assessed the GRHL3 expression in 967 patients with diffuse large B cell lymphomas to identify the potential prognostic value and the development of specific therapeutic strategies. All patients enrolled were from a previous study by Hao Zhang et al. (BMC Cancer 14:333, 2014). GRHL3 expression status was evaluated by immunohistochemical analysis. Survival analysis using the Kaplan-Meier method and multivariate analysis were conducted to adjust the effect of GRHL3 expression as a potential independent prognostic factor. In the enrolled 967 patients, GRHL3 expression was detected in 398 (41.16 %) patients under immunohistochemical analysis. The 5-year survival rate in patients with GRHL3 expression was significantly lower than that in those without GRHL3 expression (37.8 vs 52.8 %, P < 0.001). Multivariate analysis identified GRHL3 expression as an independent predictor of poor survival. The sensitivity and specificity of GRHL3 for the diagnosis of germinal center B cell (GCB)/non-GCB was 89.2 % (182/204) and 82.1 % (174/212), respectively. GRHL3 expression may be useful as a prognostic factor and for the diagnosis GCB/non-GCB of diffuse large B cell lymphoma.

SNAI2 controls the undifferentiated state of human epidermal progenitor cells

The transcription factor, SNAI2, is an inducer of the epithelial to mesenchymal transition (EMT) which mediates cell migration during development and tumor invasion. SNAI2 can also promote the generation of mammary epithelial stem cells from differentiated luminal cells when overexpressed. How SNAI2 regulates these critical and diverse functions is unclear. Here, we show that the levels of SNAI2 expression are important for epidermal cell fate decisions. The expression of SNAI2 was found to be enriched in the basal layer of the interfollicular epidermis where progenitor cells reside and extinguished upon differentiation. Loss of SNAI2 resulted in premature differentiation whereas gain of SNAI2 expression inhibited differentiation. SNAI2 controls the differentiation status of epidermal progenitor cells by binding to and repressing the expression of differentiation genes with increased binding leading to further transcriptional silencing. Thus, the levels of SNAI2 binding to genomic targets determine the differentiation status of epithelial cells with increased levels triggering EMT and dedifferentiation, moderate (physiological) levels promoting epidermal progenitor function, and low levels leading to epidermal differentiation.

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.