The homeoprotein DLX3 and tumor suppressor p53 co-regulate cell cycle progression and squamous tumor growth

The role of p21 in cellular senescence and aging-related diseases

During the aging process or disease progression, normal cells and tissues in the body undergo various stresses, leading to cell damage and the need for repair, adaptation, apoptosis, or defense responses. Cellular senescence is a key player in this process, influencing the rate of aging and disease progression. It can be triggered by different stress factors, resulting in irreversible cell cycle arrest and functional decline. Senescent cells often show high expression of cell cycle factors such as p21 and p16, which are involved in cell cycle arrest. p16 has long been recognized as a significant marker of aging. Recent evidence suggests that p21high cells and p16high cells represent distinct cell populations in terms of cell type, tissue location, accumulation kinetics, and physiological functions. This article focuses on recent advancements in understanding p21-dependent cellular senescence. It starts by providing an overview of the role of p21 in 3 primary cellular senescence phenotypes where it plays a crucial role. It then delves into the pathogenesis of diseases closely linked to p21-dependent cellular senescence, particularly metabolic disorders and cardiovascular diseases. The article also discusses progress in p21-related animal models and outlines strategies for utilizing p21 to intervene in cellular senescence by delaying aging, eliminating senescent cells, and rejuvenating senescent cells. This review systematically examines the pathogenesis of p21-dependent cellular senescence, emphasizing its importance in studying aging heterogeneity and developing new senolytic therapies. It aims to stimulate future research on leveraging p21 to enhance the characteristics of senescent cells, allowing more precise methods for eliminating harmful senescent cells at the right time, thereby delaying aging and potentially achieving rejuvenation.

A heterozygous missense variant in DLX3 leads to uterine leiomyomas and pregnancy losses in a consanguineous Iranian family

Uterine leiomyomas (ULs) are benign solid tumors arising from the uterine myometrium. They are the most common pelvic tumors among females of reproductive age. Despite the universal prevalence of ULs and its huge impact on women's lives, the exact etiology and pathophysiologic mechanisms have not been fully understood. Numerous studies indicate that genetic factors play a crucial role in ULs development. This study aims to identify the probable genetic causes of ULs in a consanguineous Iranian family. Whole-exome sequencing (WES) on five family members with ULs revealed a likely pathogenic missense variant encoding for Y88C in the transactivation (TA) domain of DLX3 gene (c.263A > G; p.Y88C). Sanger sequencing of a total of 9 affected and non-affected family members indicated a segregation with disease with autosomal dominant inheritance. Moreover, targeted Sanger sequencing on 32 additional non-related patients with ULs showed none was heterozygous for this variant. MutPred2 predicted the pathogenicity of candidate variant by both phosphorylation and sulfation loss as actionable hypotheses. Project HOPE revealed that the identified variant residue is smaller and more hydrophobic comparing to the wild-type residue. I-TASSER and UCSF Chimera were also used for modeling and visualizing the predicted variant, respectively. This WES analysis is the first to report a variant in DLX3 variation associated with ULs pathogenicity in Iranian population highlighting the effectiveness of WES as a strong diagnostic method. However, further functional studies on this variant are needed to confirm the potential pathogenicity of this mutation.

Identification and validation of DLX4 as a prognostic and diagnostic biomarker for clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is a lethal cancer, and biomarkers for exact diagnosis and predicting prognosis are urgently needed. The present study aimed to determine the roles of distal-less homeobox (DLX) family genes in ccRCC. The clinicopathological and mRNA expression data of patients with ccRCC were derived from The Cancer Genome Atlas database. Kaplan-Meier curves, univariate and multivariate Cox hazard analyses, in addition to receiver operator characteristic curves were used to evaluate the prognostic and diagnostic values. A single-sample gene set enrichment analysis was used to quantify the infiltration levels of immune cells. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry were conducted to examine the expression levels of DLX4 in tumor and adjacent tissue; the results demonstrated that DLX4 was highly expressed in ccRCC tissues compared with normal renal tissues. Furthermore, DLX4 expression was associated with tumor stage and grade. High proportions of males, advanced pathological stage, higher tumor grade and T, N and M stage were also observed in the high DLX4 expression group. Patients with the high DLX4 expression levels tended to have lower overall survival and disease-free survival rates compared with those with low DLX4 expression. DLX4 expression also showed favorable diagnostic efficiency in ccRCC patients. Based on functional enrichment analysis, cell cycle related pathways, epithelial-mesenchymal transition, glycolysis and inflammatory response were associated with the expression levels of DLX4. Furthermore, DLX4 expression was revealed to be associated with tumor immunosuppressive microenvironment. Overall, the expression level of DLX4 may be considered a novel prognostic indicator in ccRCC and a specific diagnostic biomarker for patients with ccRCC.

Long non-coding RNA DICER1-AS1-low expression in arsenic-treated A549 cells inhibits cell proliferation by regulating the cell cycle pathway

Arsenic, an environmental pollution with diverse toxicities, incurs public health problems. Arsenic trioxide could inhibit cell proliferation in vitro experiments, but the underlying mechanisms are not fully known. LncRNAs are also involved in the arsenic-induced toxicological responses. In our study, we found that the expression of lncRNA DICER1-AS1 was significantly inhibited by sodium arsenite in a dose-dependent manner. DICER1-AS1 silencing decreased the A549 cell proliferation and inhibited cell cycle progression. Importantly, DICER1-AS1 silencing induced upregulation of p21 and downregulation of Cyclin A2, Cyclin E2, CDK1 and PCNA. In conclusion, our study provided a new lncRNA-dictated regulatory mechanism participating in arsenic-induced inhibition of cell proliferation.

Loss of DLX3 tumor suppressive function promotes progression of SCC through EGFR-ERBB2 pathway

Cutaneous squamous cell carcinoma (cSCC) ranks second in the frequency of all skin cancers. The balance between keratinocyte proliferation and differentiation is disrupted in the pathological development of cSCC. DLX3 is a homeobox transcription factor which plays pivotal roles in embryonic development and epidermal homeostasis. To investigate the impact of DLX3 expression on cSCC prognosis, we carried out clinicopathologic analysis of DLX3 expression which showed statistical correlation between tumors of higher pathologic grade and levels of DLX3 protein expression. Further, Kaplan-Meier survival curve analysis demonstrated that low DLX3 expression correlated with poor patient survival. To model the function of Dlx3 in skin tumorigenesis, a two-stage dimethylbenzanthracene (DMBA)/12-O-tetradecanoylphorbol 13-acetate (TPA) study was performed on mice genetically depleted of Dlx3 in skin epithelium (Dlx3cKO). Dlx3cKO mice developed significantly more tumors, with more rapid tumorigenesis compared to control mice. In Dlx3cKO mice treated only with DMBA, tumors developed after ~16 weeks suggesting that loss of Dlx3 has a tumor promoting effect. Whole transcriptome analysis of tumor and skin tissue from our mouse model revealed spontaneous activation of the EGFR-ERBB2 pathway in the absence of Dlx3. Together, our findings from human and mouse model system support a tumor suppressive function for DLX3 in skin and underscore the efficacy of therapeutic approaches that target EGFR-ERBB2 pathway.

Genome-Wide DNA Methylation and Gene Expression Profiles in Cows Subjected to Different Stress Level as Assessed by Cortisol in Milk

Dairy cattle health, wellbeing and productivity are deeply affected by stress. Its influence on metabolism and immune response is well known, but the underlying epigenetic mechanisms require further investigation. In this study, we compared DNA methylation and gene expression signatures between two dairy cattle populations falling in the high- and low-variant tails of the distribution of milk cortisol concentration (MC), a neuroendocrine marker of stress in dairy cows. Reduced Representation Bisulfite Sequencing was used to obtain a methylation map from blood samples of these animals. The high and low groups exhibited similar amounts of methylated CpGs, while we found differences among non-CpG sites. Significant methylation changes were detected in 248 genes. We also identified significant fold differences in the expression of 324 genes. KEGG and Gene Ontology (GO) analysis showed that genes of both groups act together in several pathways, such as nervous system activity, immune regulatory functions and glucocorticoid metabolism. These preliminary results suggest that, in livestock, cortisol secretion could act as a trigger for epigenetic regulation and that peripheral changes in methylation can provide an insight into central nervous system functions.

Identification of prognostic gene biomarkers for metastatic skin cancer using data mining

Skin cancer is a common malignant tumor in China and throughout the world, and the rate of recurrence is considerably high, thus endangering the quality of life and health of patients, and increasing the economic burden and pressure to the families of those afflicted. Due to the limitations of traditional drug treatments, it is difficult to achieve the desired therapeutic effect of complete removal. However, targeted gene therapy may be a novel means of treating skin cancer, as the targeted nature of treatment may improve therapeutic outcomes. However, targeted gene therapy requires physicians to select the appropriate gene, which means suitable genetic biomarkers must be identified from complex genetic data. In the present study, the least absolute shrinkage and selection operator regression analysis method was used with 10-fold cross verification to reduce the dimensions of gene data in patients with skin cancer, and subsequently, 20 gene biomarkers were screened. A prognostic model was constructed using these 20 gene biomarkers, and the validity of the model was assessed using a training set and a verification set, which showed that the model performed well. Finally, gene function analysis of these 20 gene biomarkers was determined. Relevant studies were found to show that the genetic biomarkers identified in this paper may possess value for the follow-up clinical treatment of skin cancer.

Do DLX3 and CD271 Protect Human Keratinocytes from Squamous Tumor Development?

Well-regulated epidermal homeostasis depends on the function of different classes of factors, such as transcription regulators and receptors. Alterations in this homeostatic balance may lead to the development of cutaneous squamous tumorigenesis. The homeobox transcription factor DLX3 is determinant for a p53-dependent regulation of epidermal differentiation and modulates skin carcinogenesis. The maintenance of skin homeostasis also involves the action of neurotrophins (NTs) and their receptors, Trk and CD271. While Trk receptor overexpression is a hallmark of cancer, there are conflicting data on CD271 expression and function in cutaneous SCC (cSCC). Previous studies have reported NT receptors expression in head and neck SSC (HNSCC). We show that CD271 is expressed at low levels in primary cSCC cells and the number of CD271+ cells correlates with cell cohesion in SCC spheroids. In normal epidermis, CD271 is expressed in proliferative progenitor cells and DLX3 in terminally differentiated keratinocytes. Brain-derived neurotrophic factor (BDNF) and neurotrophin 3 (NT3) increase DLX3 expression. In the absence of a functional BDNF receptor TrkB in keratinocytes, we hypothesize that the BDNF-dependent DLX3 response could be mediated via CD271. Altogether, our results support a putative CD271-DLX3 connection in keratinocytes, which might be crucial to preventing squamous skin cancer.

p53-Family Proteins in Odontogenic Cysts: An Immunohistochemical Study

The present study investigated the immunohistochemical expression of p53, p63, and p73 in different types of odontogenic cysts (OC), a group of common intraosseous jaw lesions, to provide a better understanding of p53-family functions in odontogenic lesions. We carried out immunohistochemical analysis to evaluate the expression of p53, p63, and p73 in 60 samples of OC, including dentigerous cysts, radicular cysts, orthokeratinized OC, and odontogenic keratocysts (OKC). The epithelial expression of p53-family members was evaluated both in the basal-parabasal and in the superficial layers, measuring the percentage of positive cells and the value of expression intensity. The expression of p53-family members showed a significant difference between the "OKC" and "non-OKC" groups. In particular, p53 positivity in the basal-parabasal layers, as well as p63 positivity in the superficial layers, were more common in OKC (P<0.0001; P=0.0237). p73 expression in the superficial layers was significantly more expressed in the "non-OKC" group (P<0.0001). No significant differences of staining intensity scores were reported between the groups. The Spearman test showed a positive correlation between p53 and p73 expression at the basal-parabasal level in all cysts (r=0.6626; P<0.0001). These results showed a significantly different expression of p53-family members in OC groups, in particular between the "OKC" and "non-OKC" groups, suggesting the existence of a p53-family pathway in the epithelial lining of OC.

Transcript profiling in the testes and prostates of postnatal day 30 Sprague-Dawley rats exposed prenatally and lactationally to 2-hydroxy-4-methoxybenzophenone

2-hydroxy-4-methoxybenzophenone (HMB) is an ultraviolet light-absorbing compound that is used in sunscreens, cosmetics and plastics. HMB has been reported to have weak estrogenic activity by in vivo and in vitro studies, making it a chemical with potential reproductive concern. To explore if prenatal and lactational HMB exposure alters gene expression profiles of the developing reproductive organs, we performed microarray analysis using the prostate and testis of postnatal day (PND) 30 male Sprague-Dawley rats offspring exposed to 0, 3000, or 30,000 ppm of HMB from gestational day 6 through PND 21. Gene expression profiles of the prostate and testis were differentially affected by HMB dose with significant alterations observed at the 30,000 ppm HMB group. Tissue-specific gene expression was also identified. These genes, whose expression was altered by HMB exposure, may be considered as candidate biomarker(s) for testicular or prostatic toxicity; however, further studies are necessary to explore this potential.

Manic Fringe deficiency imposes Jagged1 addiction to intestinal tumor cells

Delta ligands regulate Notch signaling in normal intestinal stem cells, while Jagged1 activates Notch in intestinal adenomas carrying active β-catenin. We used the Apc^Min/+ mouse model, tumor spheroid cultures, and patient-derived orthoxenografts to address this divergent ligand-dependent Notch function and its implication in disease. We found that intestinal-specific Jag1 deletion or antibody targeting Jag1 prevents tumor initiation in mice. Addiction to Jag1 is concomitant with the absence of Manic Fringe (MFNG) in adenoma cells, and its ectopic expression reverts Jag1 dependence. In 239 human colorectal cancer patient samples, MFNG imposes a negative correlation between Jag1 and Notch, being high Jag1 in the absence of MFNG predictive of poor prognosis. Jag1 antibody treatment reduces patient-derived tumor orthoxenograft growth without affecting normal intestinal mucosa. Our data provide an explanation to Jag1 dependence in cancer, and reveal that Jag1-Notch1 interference provides therapeutic benefit in a subset of colorectal cancer and FAP syndrome patients.

A data mining paradigm for identifying key factors in biological processes using gene expression data

A large volume of biological data is being generated for studying mechanisms of various biological processes. These precious data enable large-scale computational analyses to gain biological insights. However, it remains a challenge to mine the data efficiently for knowledge discovery. The heterogeneity of these data makes it difficult to consistently integrate them, slowing down the process of biological discovery. We introduce a data processing paradigm to identify key factors in biological processes via systematic collection of gene expression datasets, primary analysis of data, and evaluation of consistent signals. To demonstrate its effectiveness, our paradigm was applied to epidermal development and identified many genes that play a potential role in this process. Besides the known epidermal development genes, a substantial proportion of the identified genes are still not supported by gain- or loss-of-function studies, yielding many novel genes for future studies. Among them, we selected a top gene for loss-of-function experimental validation and confirmed its function in epidermal differentiation, proving the ability of this paradigm to identify new factors in biological processes. In addition, this paradigm revealed many key genes in cold-induced thermogenesis using data from cold-challenged tissues, demonstrating its generalizability. This paradigm can lead to fruitful results for studying molecular mechanisms in an era of explosive accumulation of publicly available biological data.

Gene expression differences among different MSI statuses in colorectal cancer

Colorectal cancer is the third most common cancer in males and second in females. This disease can be caused by genetic and acquired/environmental factors. Microsatellite instability (MSI) is one of the major mechanisms in colorectal cancer. This mechanism is a specific condition of genetic hyper mutability that results from incompetent DNA mismatch repair. MSI has been applied to classify different colorectal cancer subtypes. However, the effects of MSI status on gene expression are largely unknown. In our study, we integrated the gene expression profile and MSI status of all CRC samples from the TCGA database, and then categorized the CRC samples into three subgroups, namely, MSI-stable, MSI-low, and MSI-high, according to the MSI status. We applied a novel computational method based on machine learning and screened the genes specifically expressed for the different colorectal cancer subtypes. The results showed the distinct mechanisms of the different colorectal cancer subtypes with MSI status and provided the genes that may be the optimal standards to further classify the various molecular subtypes of colorectal cancer with distinct MSI status.

DLX3-Dependent STAT3 Signaling in Keratinocytes Regulates Skin Immune Homeostasis

Epidermal-specific deletion of the homeobox transcription regulator DLX3 disrupts keratinocyte differentiation and results in an IL-17-linked psoriasis-like skin inflammation. To identify the epidermal initiating signals produced by DLX3-null keratinocytes, we performed acute deletion of DLX3 in adult epidermis using a tamoxifen-inducible Krt14-cre/ERT system. K14CreERT;DLX3fl/fl skin exhibited dysregulated expression of differentiation-associated genes, upregulation of proinflammatory cytokines, and accumulation of Langerhans cells and macrophages within 3 days of tamoxifen-induced DLX3 ablation. We also observed increased accumulation of IL-17A-secreting Vγ4 γδ T cells and heightened levels of IL-17 and IL-36 family of cytokines starting 1 week after DLX3 deletion. Interestingly, transcriptome profiling of K14CreERT;DLX3fl/fl epidermis at 3 days identified activated STAT3 as a transcriptional regulator and revealed differential expression of STAT3 signaling-related genes. Furthermore, activation of STAT3 was strongly increased in K14CreERT;DLX3fl/fl skin, and topical treatment with an inhibitor of STAT3 activation attenuated the immune phenotype. RNA-seq analysis of vehicle and STAT3 inhibitor treated K14CreERT;DLX3fl/fl skin identified differentially expressed genes associated with inhibition of leukocyte infiltration. Collectively, our results show that DLX3 is a critical regulator of STAT3 signaling network that maintains skin homeostasis.

Role of FGFR2b expression and signaling in keratinocyte differentiation: sequential involvement of PKCδ and PKCα

The tumor suppressor epithelial isoform of the fibroblast growth factor receptor 2 (FGFR2b) induces human keratinocyte early differentiation. Moreover, protein kinases C (PKCs) are known to regulate the differentiation program in several cellular contexts, including keratinocytes. Therefore, in this paper we propose to clarify if FGFR2b could play a role also in the late steps of keratinocyte differentiation and to assess if this receptor-induced process would sequentially involve PKCδ and PKCα isoforms. Immunofluorescence, biochemical, and molecular approaches, performed on 2D cultures or 3D organotypic rafts of human keratinocytes overexpressing FGFR2b by stable transduction, showed that receptor signaling induced the precocious onset and an accelerated progression of keratinocyte differentiation, indicating that FGFR2b is a crucial regulator of the entire program of keratinocyte differentiation. In addition, the use of specific inhibitors and gene silencing approaches through specific siRNA demonstrated that PKCδ controls the onset of FGFR2b-triggered differentiation, while PKCα plays a role restricted to the terminal stages of the process. Molecular analysis revealed that the two PKC isoforms sequentially act via induction of KLF4 and DLX3, two transcription factors linked by negative loops to p63, suggesting that p63 would represent the hub molecule at the crossroad of an intricate signaling network downstream FGFR2b, involving multiple PKC-induced transcription factors.

Homeobox transcription factor DLX4 is not necessary for skin development and homeostasis

Dlx4 is a member of a family of homeobox genes with homology to Drosophila distal-less (dll) gene. We show that Dlx4 expression pattern partially overlaps with its cis-linked gene Dlx3 during mouse development as well as in neonatal and adult skin. In mice, Dlx4 is expressed in the branchial arches, embryonic limbs, digits, nose, hair follicle and in the basal and suprabasal layers of mouse interfollicular epidermis. We show that inactivation of Dlx4 in mice did not result in any overtly gross pathology. Skin development, homeostasis and response to TPA treatment were similar in mice with loss of Dlx4 compared to wild-type counterparts.

DLX3 promotes bone marrow mesenchymal stem cell proliferation through H19/miR-675 axis

The underlying molecular mechanism of the increased bone mass phenotype in Tricho-dento-osseous (TDO) syndrome remains largely unknown. Our previous study has shown that the TDO point mutation c.533A>G, Q178R in DLX3 could increase bone density in a TDO patient and transgenic mice partially through delaying senescence in bone marrow mesenchymal stem cells (BMSCs). In the present study, we provided a new complementary explanation for TDO syndrome: the DLX3 (Q178R) mutation increased BMSCs proliferation through H19/miR-675 axis. We found that BMSCs derived from the TDO patient (TDO-BMSCs) had stronger proliferation ability than controls by clonogenic and CCK-8 assays. Next, experiments of overexpression and knockdown of wild-type DLX3 via lentiviruses in normal BMSCs confirmed the results by showing its negative role in cell proliferation. Through validated high-throughput data, we found that the DLX3 mutation reduced the expression of H19 and its coexpression product miR-675 in BMSCs. Function and rescue assays suggested that DLX3, long noncoding RNA H19, and miR-675 are negative factors in modulation of BMSCs proliferation as well as NOMO1 expression. The original higher proliferation rate and the expression of NOMO1 in TDO-BMSCs were suppressed after H19 restoration. Collectively, it indicates that DLX3 regulates BMSCs proliferation through H19/miR-675 axis. Moreover, the increased expression of NOMO1 and decreased H19/miR-675 expression in DLX3 (Q178R) transgenic mice, accompanying with accrual bone mass and density detected by micro-CT, further confirmed our hypothesis. In summary, we, for the first time, demonstrate that DLX3 mutation interferes with bone formation partially through H19/miR-675/NOMO1 axis in TDO syndrome.

DLX3 interacts with GCM1 and inhibits its transactivation-stimulating activity in a homeodomain-dependent manner in human trophoblast-derived cells

The placental transcription factors Distal-less 3 (DLX3) and Glial cell missing-1 (GCM1) have been shown to coordinate the specific regulation of PGF in human trophoblast cell lines. While both factors independently have a positive effect on PGF gene expression, when combined, DLX3 acts as an antagonist to GCM. Despite this understanding, potential mechanisms accounting for this regulatory interaction remain unexplored. We identify physical and functional interactions between specific domains of DLX3 and GCM1 in human trophoblast-derived cells by performing immunoprecipitation and mammalian one hybrid assays. Studies revealed that DLX3 binding reduced the transcriptional activity of GCM1, providing a mechanistic explanation of their functional antagonism in regulating PGF promoter activity. The DLX3 homeodomain (HD) was essential for DLX3-GCM1 interaction, and that the HD together with the DLX3 amino- or carboxyl-terminal domains was required for maximal inhibition of GCM1. Interestingly, a naturally occurring DLX3 mutant that disrupts the carboxyl-terminal domain leading to tricho-dento-osseous syndrome in humans displayed activities indistinguishable from wild type DLX3 in this system. Collectively, our studies demonstrate that DLX3 physically interacts with GCM1 and inhibits its transactivation activity, suggesting that DLX3 and GCM1 may form a complex to functionally regulate placental cell function through modulation of target gene expression.

Dlx3 and GCM-1 functionally coordinate the regulation of placental growth factor in human trophoblast-derived cells

Placental growth factor (PGF) is abundantly expressed by trophoblast cells within human placentae and is important for trophoblast development and placental vascularization. Circulating maternal serum levels of PGF are dynamically upregulated across gestation in normal pregnancies, whereas low circulating levels and placental production of PGF have been implicated in the pathogenesis of preeclampsia and other gestational diseases. However, the underlying molecular mechanism of regulating PGF expression in the human placenta remains poorly understood. In this study, we demonstrated that transcription factors Distal-less 3 (DLX3) and Glial cell missing-1 (GCM1) were both sufficient and required for PGF expression in human trophoblast-derived cells by overexpression and knockdown approaches. Surprisingly, while DLX3 and GCM1 were both positive regulators of PGF, co-overexpression of DLX3 and GCM1 led to an antagonist effect on PGF expression on the endogenous gene and a luciferase reporter. Further, deletion and site-directed mutagenesis studies identified a novel regulatory element on the PGF promoter mediating both DLX3- and GCM1-dependent PGF expression. This regulatory region was also found to be essential for the basal activity of the PGF promoter. Finally, Chromatin-immunoprecipitation (ChIP) assays revealed colocalization of DLX3 and GCM1 at the identified regulatory region on the PGF promoter. Taken together, our studies provide important insights into intrinsic regulation of human placental PGF expression through the functional coordination of DLX3 and GCM1, and are likely to further the understanding of pathogenesis of PGF dysregulation in preeclampsia and other disease conditions.

A novel DLX3-PKC integrated signaling network drives keratinocyte differentiation

Epidermal homeostasis relies on a well-defined transcriptional control of keratinocyte proliferation and differentiation, which is critical to prevent skin diseases such as atopic dermatitis, psoriasis or cancer. We have recently shown that the homeobox transcription factor DLX3 and the tumor suppressor p53 co-regulate cell cycle-related signaling and that this mechanism is functionally involved in cutaneous squamous cell carcinoma development. Here we show that DLX3 expression and its downstream signaling depend on protein kinase C α (PKCα) activity in skin. We found that following 12-O-tetradecanoyl-phorbol-13-acetate (TPA) topical treatment, DLX3 expression is significantly upregulated in the epidermis and keratinocytes from mice overexpressing PKCα by transgenic targeting (K5-PKCα), resulting in cell cycle block and terminal differentiation. Epidermis lacking DLX3 (DLX3cKO), which is linked to the development of a DLX3-dependent epidermal hyperplasia with hyperkeratosis and dermal leukocyte recruitment, displays enhanced PKCα activation, suggesting a feedback regulation of DLX3 and PKCα. Of particular significance, transcriptional activation of epidermal barrier, antimicrobial peptide and cytokine genes is significantly increased in DLX3cKO skin and further increased by TPA-dependent PKC activation. Furthermore, when inhibiting PKC activity, we show that epidermal thickness, keratinocyte proliferation and inflammatory cell infiltration are reduced and the PKC-DLX3-dependent gene expression signature is normalized. Independently of PKC, DLX3 expression specifically modulates regulatory networks such as Wnt signaling, phosphatase activity and cell adhesion. Chromatin immunoprecipitation sequencing analysis of primary suprabasal keratinocytes showed binding of DLX3 to the proximal promoter regions of genes associated with cell cycle regulation, and of structural proteins and transcription factors involved in epidermal differentiation. These results indicate that Dlx3 potentially regulates a set of crucial genes necessary during the epidermal differentiation process. Altogether, we demonstrate the existence of a robust DLX3–PKCα signaling pathway in keratinocytes that is crucial to epidermal differentiation control and cutaneous homeostasis.

Senescence: novel insight into DLX3 mutations leading to enhanced bone formation in Tricho-Dento-Osseous syndrome

The homeodomain transcription factor distal-less homeobox 3 gene (DLX3) is required for hair, tooth and skeletal development. DLX3 mutations have been found to be responsible for Tricho-Dento-Osseous (TDO) syndrome, characterized by kinky hair, thin-pitted enamel and increased bone density. Here we show that the DLX3 mutation (c.533 A>G; Q178R) attenuates osteogenic potential and senescence of bone mesenchymal stem cells (BMSCs) isolated from a TDO patient, providing a molecular explanation for abnormal increased bone density. Both DLX3 mutations (c.533 A>G and c.571_574delGGGG) delayed cellular senescence when they were introduced into pre-osteoblastic cells MC3T3-E1. Furthermore, the attenuated skeletal aging and bone loss in DLX3 (Q178R) transgenic mice not only reconfirmed that DLX3 mutation (Q178R) delayed cellular senescence, but also prevented aging-mediated bone loss. Taken together, these results indicate that DLX3 mutations act as a loss of function in senescence. The delayed senescence of BMSCs leads to increased bone formation by compensating decreased osteogenic potentials with more generations and extended functional lifespan. Our findings in the rare human genetic disease unravel a novel mechanism of DLX3 involving the senescence regulation of bone formation.

Multiple functions of p21 in cell cycle, apoptosis and transcriptional regulation after DNA damage

An appropriate control over cell cycle progression depends on many factors. Cyclin-dependent kinase (CDK) inhibitor p21 (also known as p21(WAF1/Cip1)) is one of these factors that promote cell cycle arrest in response to a variety of stimuli. The inhibitory effect of P21 on cell cycle progression correlates with its nuclear localization. P21 can be induced by both p53-dependent and p53-independent mechanisms. Some other important functions attributed to p21 include transcriptional regulation, modulation or inhibition of apoptosis. These functions are largely dependent on direct p21/protein interactions and also on p21 subcellular localizations. In addition, p21 can play a role in DNA repair by interacting with proliferating cell nuclear antigen (PCNA). In this review, we will focus on the multiple functions of p21 in cell cycle regulation, apoptosis and gene transcription after DNA damage and briefly discuss the pathways and factors that have critical roles in p21 expression and activity.