A homeobox gene related to Drosophila distal-less promotes ovarian tumorigenicity by inducing expression of vascular endothelial growth factor and fibroblast growth factor-2

Single-Cell Transcriptome Analysis Reveals Development-Specific Networks at Distinct Synchronized Antral Follicle Sizes in Sheep Oocytes

The development of the ovarian antral follicle is a complex, highly regulated process. Oocytes orchestrate and coordinate the development of mammalian ovarian follicles, and the rate of follicular development is governed by a developmental program intrinsic to the oocyte. Characterizing oocyte signatures during this dynamic process is critical for understanding oocyte maturation and follicular development. Although the transcriptional signature of sheep oocytes matured in vitro and preovulatory oocytes have been previously described, the transcriptional changes of oocytes in antral follicles have not. Here, we used single-cell transcriptomics (SmartSeq2) to characterize sheep oocytes from small, medium, and large antral follicles. We characterized the transcriptomic landscape of sheep oocytes during antral follicle development, identifying unique features in the transcriptional atlas, stage-specific molecular signatures, oocyte-secreted factors, and transcription factor networks. Notably, we identified the specific expression of 222 genes in the LO, 8 and 6 genes that were stage-specific in the MO and SO, respectively. We also elucidated signaling pathways in each antral follicle size that may reflect oocyte quality and in vitro maturation competency. Additionally, we discovered key biological processes that drive the transition from small to large antral follicles, revealing hub genes involved in follicle recruitment and selection. Thus, our work provides a comprehensive characterization of the single-oocyte transcriptome, filling a gap in the mapping of the molecular landscape of sheep oogenesis. We also provide key insights into the transcriptional regulation of the critical sizes of antral follicular development, which is essential for understanding how the oocyte orchestrates follicular development.

FOXM1: A small fox that makes more tracks for cancer progression and metastasis

Transcription factors (TFs) are indispensable for the modulation of various signaling pathways associated with normal cell homeostasis and disease conditions. Among cancer-related TFs, FOXM1 is a critical molecule that regulates multiple aspects of cancer cells, including growth, metastasis, recurrence, and stem cell features. FOXM1 also impact the outcomes of targeted therapies, chemotherapies, and immune checkpoint inhibitors (ICIs) in various cancer types. Recent advances in cancer research strengthen the cancer-specific role of FOXM1, providing a rationale to target FOXM1 for developing targeted therapies. This review compiles the recent studies describing the pivotal role of FOXM1 in promoting metastasis of various cancer types. It also implicates the contribution of FOXM1 in the modulation of chemotherapeutic resistance, antitumor immune response/immunotherapies, and the potential of small molecule inhibitors of FOXM1.

Role of Basic Fibroblast Growth Factor in Cancer: Biological Activity, Targeted Therapies, and Prognostic Value

Cancer is the leading cause of death worldwide; thus, it is necessary to find successful strategies. Several growth factors, such as vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF, FGF2), and transforming growth factor beta (TGF-β), are involved in the main processes that fuel tumor growth, i.e., cell proliferation, angiogenesis, and metastasis, by activating important signaling pathways, including PLC-γ/PI3/Ca2+ signaling, leading to PKC activation. Here, we focused on bFGF, which, when secreted by tumor cells, mediates several signal transductions and plays an influential role in tumor cells and in the development of chemoresistance. The biological mechanism of bFGF is shown by its interaction with its four receptor subtypes: fibroblast growth factor receptor (FGFR) 1, FGFR2, FGFR3, and FGFR4. The bFGF–FGFR interaction stimulates tumor cell proliferation and invasion, resulting in an upregulation of pro-inflammatory and anti-apoptotic tumor cell proteins. Considering the involvement of the bFGF/FGFR axis in oncogenesis, preclinical and clinical studies have been conducted to develop new therapeutic strategies, alone and/or in combination, aimed at intervening on the bFGF/FGFR axis. Therefore, this review aimed to comprehensively examine the biological mechanisms underlying bFGF in the tumor microenvironment, the different anticancer therapies currently available that target the FGFRs, and the prognostic value of bFGF.

DNA methylation-mediated differential expression of DLX4 isoforms has opposing roles in leukemogenesis

Background

Previously, we reported the expression of DLX4 isoforms (BP1 and DLX7) in myeloid leukemia, but the functional role of DLX4 isoforms remains poorly understood. In the work described herein, we further determined the underlying role of DLX4 isoforms in chronic myeloid leukemia (CML) leukemogenesis.

Methods

The expression and methylation of DLX4 isoforms were detected by real-time quantitative PCR (RT-qPCR) and real-time quantitative methylation-specific PCR (RT-qMSP) in patients with CML. The functional role of DLX4 isoforms was determined in vitro and in vivo. The molecular mechanism of DLX4 isoforms in leukemogenesis was identified based on chromatin immunoprecipitation with high-throughput sequencing (ChIP-Seq)/assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-Seq) and RNA sequencing (RNA-Seq).

Results

BP1 expression was increased in patients with CML with unmethylated promoter, but DLX7 expression was decreased with hypermethylated promoter. Functionally, overexpression of BP1 increased the proliferation rate of K562 cells with S/G2 promotion, whereas DLX7 overexpression reduced the proliferation rate of K562 cells with G1 arrest. Moreover, K562 cells with BP1 overexpression increased the tumorigenicity in NCG mice, whereas K562 cells with DLX7 overexpression decreased the tumorigenicity. Mechanistically, a total of 91 genes including 79 messenger RNAs (mRNAs) and 12 long noncoding RNAs (lncRNAs) were discovered by ChIP-Seq and RNA-Seq as direct downstream targets of BP1. Among the downstream genes, knockdown of RREB1 and SGMS1-AS1 partially revived the proliferation caused by BP1 overexpression in K562 cells. Similarly, using ATAC-Seq and RNA-Seq, a total of 282 genes including 151 mRNA and 131 lncRNAs were identified as direct downstream targets of DLX7. Knockdown of downstream genes PTPRB and NEAT1 partially revived the proliferation caused by DLX7 overexpression in K562 cells. Finally, we also identified and validated a SGMS1-AS1/miR-181d-5p/SRPK2 competing endogenous RNA (ceRNA) network caused by BP1 overexpression in K562 cells.

Conclusions

The current findings reveal that DNA methylation-mediated differential expression of DLX4 isoforms BP1 and DLX7 plays opposite functions in leukemogenesis. BP1 plays an oncogenic role in leukemia development, whereas DLX7 acts as a tumor suppressor gene. These results suggest DLX4 as a therapeutic target for antileukemia therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11658-022-00358-0.

Evaluating the Expression of Candidate Homeobox Genes and Their Role in Local-Site Inflammation in Mucosal Tissue Obtained from Children with Non-Syndromic Cleft Lip and Palate

Craniofacial development including palatogenesis is a complex process which requires an orchestrated and spatiotemporal expression of various genes and factors for proper embryogenesis and organogenesis. One such group of genes essential for craniofacial development is the homeobox genes, transcriptional factors that are commonly associated with congenital abnormalities. Amongst these genes, DLX4, HOXB3, and MSX2 have been recently shown to be involved in the etiology of non-syndromic cleft lip and palate. Hence, we investigated the gene and protein expression of these genes in normal and cleft affected mucosal tissue obtained from 22 children, along with analyzing their role in promoting local-site inflammation using NF-κB. Additionally, we investigated the role of PTX3, which plays a critical role in tissue remodeling and wound repair. We found a residual gene and protein expression of DLX4 in cleft mucosa, although no differences in gene expression levels of HOXB3 and MSX2 were noted. However, a significant increase in protein expression for these genes was noted in the cleft mucosa (p < 0.05), indicating increased cellular proliferation. This was coupled with a significant increase in NF-κB protein expression in cleft mucosa (p < 0.05), highlighting the role of these genes in promotion of pro-inflammatory environment. Finally, no differences in gene expression of PTX3 were noted.

A Gene Signature of Survival Prediction for Kidney Renal Cell Carcinoma by Multi-Omic Data Analysis

Kidney renal cell carcinoma (KIRC), which is the most common subtype of kidney cancer, has a poor prognosis and a high mortality rate. In this study, a multi-omics analysis is performed to build a multi-gene prognosis signature for KIRC. A combination of a DNA methylation analysis and a gene expression data analysis revealed 863 methylated differentially expressed genes (MDEGs). Seven MDEGs (BID, CCNF, DLX4, FAM72D, PYCR1, RUNX1, and TRIP13) were further screened using LASSO Cox regression and integrated into a prognostic risk score model. Then, KIRC patients were divided into high- and low-risk groups. A univariate cox regression analysis revealed a significant association between the high-risk group and a poor prognosis. The time-dependent receiver operating characteristic (ROC) curve shows that the risk group performs well in predicting overall survival. Furthermore, the risk group is contained in the best multivariate model that was obtained by a multivariate stepwise analysis, which further confirms that the risk group can be used as a potential prognostic biomarker. In addition, a nomogram was established for the best multivariate model and shown to perform well in predicting the survival of KIRC patients. In summary, a seven-MDEG signature is a powerful prognosis factor for KIRC patients and may provide useful suggestions for their personalized therapy.

Overexpression of BP1, an isoform of Homeobox Gene DLX4, promotes cell proliferation, migration and predicts poor prognosis in endometrial cancer

The expression of homeobox gene DLX4 has been verified in some tumors, but not in endometrial cancer. We found that expression of DLX7, a splicing isoform of DLX4, did not show any significant difference in expression between endometrial cancer and endometrium. However, BP1, another splicing isoform of DLX4, was highly expressed in endometrial cancer, and its expression was positively correlated with patient prognosis, cancer pathological grade, tumor invasion and metastasis. Lentiviral-mediated expression of BP1 in HEC-1-B cells accelerated the cell cycle progression from G0/G1 into S phase, and promoted cell proliferation and migration both in vitro and in vivo. Real-time PCR and western blotting showed that the expression levels of p15, p21 and E-cadherin significantly decreased, and levels of cyclinD1 and MMP-2 increased in endometrial cancer cells. In conclusion, our results demonstrate that high expression of BP1 is associated with poor prognosis in patients with endometrial cancer and promotes cell proliferation and migration.

Oncogenic Metabolism Acts as a Prerequisite Step for Induction of Cancer Metastasis and Cancer Stem Cell Phenotype

Metastasis is a major obstacle to the efficient and successful treatment of cancer. Initiation of metastasis requires epithelial-mesenchymal transition (EMT) that is regulated by several transcription factors, including Snail and ZEB1/2. EMT is closely linked to the acquisition of cancer stem cell (CSC) properties and chemoresistance, which contribute to tumor malignancy. Tumor suppressor p53 inhibits EMT and metastasis by negatively regulating several EMT-inducing transcription factors and regulatory molecules; thus, its inhibition is crucial in EMT, invasion, metastasis, and stemness. Metabolic alterations are another hallmark of cancer. Most cancer cells are more dependent on glycolysis than on mitochondrial oxidative phosphorylation for their energy production, even in the presence of oxygen. Cancer cells enhance other oncogenic metabolic pathways, such as glutamine metabolism, pentose phosphate pathway, and the synthesis of fatty acids and cholesterol. Metabolic reprogramming in cancer is regulated by the activation of oncogenes or loss of tumor suppressors that contribute to tumor progression. Oncogenic metabolism has been recently linked closely with the induction of EMT or CSC phenotypes by the induction of several metabolic enzyme genes. In addition, several transcription factors and molecules involved in EMT or CSCs, including Snail, Dlx-2, HIF-1α, STAT3, TGF-β, Wnt, and Akt, regulate oncogenic metabolism. Moreover, p53 induces metabolic change by directly regulating several metabolic enzymes. The collective data indicate the importance of oncogenic metabolism in the regulation of EMT, cell invasion and metastasis, and adoption of the CSC phenotype, which all contribute to malignant transformation and tumor development. In this review, we highlight the oncogenic metabolism as a key regulator of EMT and CSC, which is related with tumor progression involving metastasis and chemoresistance. Targeting oncometabolism might be a promising strategy for the development of effective anticancer therapy.

Establishment of a nine-gene prognostic model for predicting overall survival of patients with endometrial carcinoma

Endometrial carcinoma (EC) is the most common malignant tumor of the female genital tract in developed countries. The prognosis of early stage EC is favorable, but a subset faces high risk of cancer progression or recurrence. EC has a poor prognosis upon progression to advanced or metastatic stages. Therefore, our goal is to build a robust prognostic model for predicting overall survival (OS) in EC patients. In this study, 1571 genes were identified as being associated with OS based on genomewide expression profiles using a training dataset. Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that these genes were involved in various cancer-related signaling pathways. Nine signature genes were further selected using stepwise selection, and their potential role in the development of EC was demonstrated by performing differential expression analysis between EC and normal uterine tissues. A prognostic model that aggregated these nine signature genes was ultimately established and effectively divided EC patients into two risk groups. OS for patients in the high-risk group was significantly poorer compared with that of the low-risk group. This nine-gene model was subsequently validated and evaluated using the TCGA dataset and shown to have a high discriminating power to distinguish EC patients with an elevated risk of mortality based on the FIGO staging system and other prognostic factors. This study provides a novel prognostic model for the identification of EC patients with elevated risk of mortality and will help to improve our understanding of the underlying mechanisms involved in prognostic EC 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.

DLX1 acts as a crucial target of FOXM1 to promote ovarian cancer aggressiveness by enhancing TGF-β/SMAD4 signaling

Recent evidence from a comprehensive genome analysis and functional studies have revealed that FOXM1 is a crucial metastatic regulator that drives cancer progression. However, the regulatory mechanism by which FOXM1 exerts its metastatic functions in cancer cells remains obscure. Here, we report that DLX1 acts as a FOXM1 downstream target, exerting pro-metastatic function in ovarian cancers. Both FOXM1 isoforms (FOXM1B or FOXM1C) could transcriptionally upregulate DLX1 through two conserved binding sites, located at +61 to +69bp downstream (TFBS1) and −675 to −667bp upstream (TFBS2) of the DLX1 promoter, respectively. This regulation was further accentuated by the significant correlation between the nuclear expression of FOXM1 and DLX1 in high-grade serous ovarian cancers. Functionally, the ectopic expression of DLX1 promoted ovarian cancer cell growth, cell migration/invasion and intraperitoneal dissemination of ovarian cancer in mice, whereas small interfering RNA-mediated DLX1 knockdown in FOXM1-overexpressing ovarian cancer cells abrogated these oncogenic capacities. In contrast, depletion of FOXM1 by shRNAi only partially attenuated tumor growth and exerted almost no effect on cell migration/invasion and the intraperitoneal dissemination of DLX1-overexpressing ovarian cancer cells. Furthermore, the mechanistic studies showed that DLX1 positively modulates transforming growth factor-β (TGF-β) signaling by upregulating PAI-1 and JUNB through direct interaction with SMAD4 in the nucleus upon TGF-β1 induction. Taken together, these data strongly suggest that DLX1 has a pivotal role in FOXM1 signaling to promote cancer aggressiveness through intensifying TGF-β/SMAD4 signaling in high-grade serous ovarian cancer cells.

Beta protein 1 homeoprotein induces cell growth and estrogen-independent tumorigenesis by binding to the estrogen receptor in breast cancer

Expression of Beta Protein 1 (BP1), a homeotic transcription factor, increases during breast cancer progression and may be associated with tumor aggressiveness. In our present work, we investigate the influence of BP1 on breast tumor formation and size in vitro and in vivo. Cells overexpressing BP1 showed higher viability when grown in the absence of serum (p < 0.05), greater invasive potential (p < 0.05) and formed larger colonies (p < 0.004) compared with the controls. To determine the influence of BP1 overexpression on tumor characteristics, MCF-7 cells transfected with either empty vector (V1) or overexpressor plasmids (O2 and O4) were injected into the fat pads of athymic nude mice. Tumors grew larger in mice receiving O2 or O4 cells than in mice receiving V1 cells. Moreover, BP1 mRNA expression levels were positively correlated with tumor size in patients (p = 0.01). Interestingly, 20% of mice injected with O2 or O4 cells developed tumors in the absence of estrogen, while no mice receiving V1 cells developed tumors. Several mechanisms of estrogen independent tumor formation related to BP1 were established. These data are consistent with the fact that expression of breast cancer anti-estrogen resistance 1 (BCAR1) was increased in O2 compared to V1 cells (p < 0.01). Importantly, O2 cells exhibited increased proliferation when treated with tamoxifen, while V1 cells showed growth inhibition. Overall, BP1 overexpresssion in MCF-7 breast cancer cells leads to increased cell growth, estrogen-independent tumor formation, and increased proliferation. These findings suggest that BP1 may be an important biomarker and therapeutic target in ER positive breast cancer.

The homeoprotein DLX4 stimulates NF-κB activation and CD44-mediated tumor-mesothelial cell interactions in ovarian cancer

Ovarian cancers often highly express inflammatory cytokines and form implants throughout the peritoneal cavity. However, the mechanisms that drive inflammatory signaling and peritoneal metastasis of ovarian cancer are poorly understood. We previously identified that high expression of DLX4, a transcription factor encoded by a homeobox gene, is associated with reduced survival of ovarian cancer patients. In this study, we identified that DLX4 stimulates attachment of ovarian tumor cells to peritoneal mesothelial cells in vitro and increases the numbers of peritoneal implants in xenograft models. DLX4 induced expression of the cell surface molecule CD44 in ovarian tumor cells, and inhibition of CD44 abrogated the ability of DLX4 to stimulate tumor-mesothelial cell interactions. The induction of CD44 by DLX4 was attributed to increased activity of NF-κB that was stimulated by the inflammatory cytokine IL-1β, a transcriptional target of DLX4. The stimulatory effects of DLX4 on CD44 levels and tumor-mesothelial cell interactions were abrogated when IL-1β or NF-κB was inhibited in tumor cells. Furthermore, DLX4 expression levels strongly correlated with NF-κB activation and disease stage in clinical specimens of ovarian cancer. Collectively, these findings indicate that DLX4 induces CD44 by stimulating IL-1β-mediated NF-κB activity, thereby promoting peritoneal metastasis of ovarian cancer.

Expression of long non-coding RNA DLX6-AS1 in lung adenocarcinoma

Background

Lung adenocarcinoma (LAC), the primary histological type of non-small cell lung cancer (NSCLC), has displayed an increasing incidence and mortality worldwide. However, therapeutic approaches were limited. Dysregulation of some lncRNAs has been shown in various types of cancers including LAC. The aim of the present study was to vertify lncRNA DLX6-AS1 expression in LAC.

Methods

Microarray assay revealed expression profile of lncRNAs in LAC. qRT-PCR ( quantitative reverse transcription PCR) was performed to identify lncRNA DLX6-AS1 expression level in 72 paired LAC and adjacent normal lung tissues. qRT-PCR and Western blotting were used to verify that down-regulation lncRNA DLX6-AS1 decreased DLX6 (distal-less homeobox 6) mRNA and protein expression.

Results

Microarray analysis identified up-regulation of 272 lncRNAs and down-regulation of 635 lncRNAs in LAC tissues. The expression level of lncRNA DLX6-AS1 in LAC tissues was significantly higher compared to paired adjacent normal lung tissues (P< 0.05). In addition, its expression level was closed correlated with both histological differentiation (P = 0.004) and TNM stage (P = 0.033). qRT-PCR and Western blotting analysis showed that DLX6 mRNA and protein levels were lower in si-LncRNA group than in the NC (negative control) and Blank groups.

Conclusions

Microarray analysis identified that lncRNA DLX6-AS1 was up-regulated in LAC tissues. High DLX6-AS1 expression levels were significantly associated with both histological differentiation and TNM stage. Down-regulation of lncRNA DLX6-AS1 expression decreased the DLX6 mRNA and protein levels.

The homeoprotein DLX4 controls inducible nitric oxide synthase-mediated angiogenesis in ovarian cancer

Background

Homeobox genes encode transcription factors that control patterning of virtually all organ systems including the vasculature. Tumor angiogenesis is stimulated by several homeobox genes that are overexpressed in tumor cells, but the mechanisms of these genes are poorly understood. In this study, we investigated the mechanisms by which DLX4, a homeobox gene that is associated with increased tumor microvessel density, stimulates ovarian tumor angiogenesis.

Methods

Expression of DLX4 and nitric oxide synthases was analyzed in publicly available transcriptional profiles of ovarian cancer clinical specimens. Levels of inducible nitric oxide synthase (iNOS) were evaluated by quantitative RT-PCR, flow cytometry and nitric oxide assays using ovarian cancer cell lines in which DLX4 was overexpressed or knocked down. Signal Transducer and Activator of Transcription 1 (STAT1) expression and activity were evaluated by luciferase reporter assays, immunofluorescence staining, Western blot and immunoprecipitation. Endothelial cell growth and tumor angiogenesis were evaluated in in vitro assays and xenograft models.

Results

We identified that DLX4 induces expression of iNOS, an enzyme that stimulates angiogenesis by generating nitric oxide. Analysis of datasets of two independent patient cohorts revealed that high DLX4 expression in ovarian cancer is strongly associated with elevated expression of iNOS but not of other nitric oxide synthases. Studies using STAT1-expressing and STAT1-deficient cells revealed that DLX4 interacts with STAT1 and induces iNOS expression in part by stimulating STAT1 activity. Expression of DLX4 in ovarian cancer cells stimulated endothelial cell growth in vitro and increased microvessel density in xenograft models, and these stimulatory effects of DLX4 were abrogated when its induction of iNOS was inhibited.

Conclusion

These findings indicate that DLX4 promotes ovarian tumor angiogenesis in part by stimulating iNOS expression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0368-3) contains supplementary material, which is available to authorized users.

Regulation of the oncogenic function of distal-less 4 by microRNA-122 in hepatocellular carcinoma

Distal-less 4 (DLX4) is a member of the DLX family of homeobox genes. Recent reports have suggested that abnormal expression of DLX4 is present in several types of human tumors, including breast cancer, leukemia and colon cancer. However, the function and the mechanistic regulation of DLX4 in hepatocellular carcinoma (HCC) are elusive. In the present study, a proportion of hepatocellular carcinomas were identified to exhibit upregulated DLX4 expression. This study proposed that the overexpression of DLX4 is associated with the downregulation of miR-122, an underexpressed miRNA in human HCC. Functional studies have demonstrated that the downregulation of DLX4 in hepatocellular carcinoma cell lines is regulated by miR-122 through binding to its 3'UTR. Furthermore, a DLX4 overexpression vector lacking the 3'UTR was shown to abolish miR-122-induced inhibition of proliferation in the HCC cell line Hep3B. These results gave new insight into the mechanism of the miR-122/DLX4 axis in HCC.

Increased copy number of the DLX4 homeobox gene in breast axillary lymph node metastasis

DLX4 is a homeobox gene strongly implicated in breast tumor progression and invasion. Our main objective was to determine the DLX4 copy number status in sentinel lymph node (SLN) metastasis to assess its involvement in the initial stages of the axillary metastatic process. A total of 37 paired samples of SLN metastasis and primary breast tumors (PBT) were evaluated by fluorescence in situ hybridization, quantitative polymerase chain reaction and array comparative genomic hybridization assays. DLX4 increased copy number was observed in 21.6% of the PBT and 24.3% of the SLN metastasis; regression analysis demonstrated that the DLX4 alterations observed in the SLN metastasis were dependent on the ones in the PBT, indicating that they occur in the primary tumor cell populations and are maintained in the early axillary metastatic site. In addition, regression analysis demonstrated that DLX4 alterations (and other DLX and HOXB family members) occurred independently of the ones in the HER2/NEU gene, the main amplification driver on the 17q region. Additional studies evaluating DLX4 copy number in non-SLN axillary lymph nodes and/or distant breast cancer metastasis are necessary to determine if these alterations are carried on and maintained during more advanced stages of tumor progression and if could be used as a predictive marker for axillary involvement.

Homeobox Gene Deregulation: Impact on the Hallmarks of Cancer

Homeobox genes comprise a super-family of evolutionarily conserved genes that play essential roles in controlling body plan specification and cell fate determination. Substantial evidence indicates that leukemogenesis is driven by abnormal expression of homeobox genes that control hematopoiesis. In solid tumors, aberrant expression of homeobox genes has been increasingly found to modulate diverse processes such as cell proliferation, cell death, metastasis, angiogenesis and DNA repair. This review discusses how homeobox genes are deregulated in solid tumors and the functional significance of this deregulation in the hallmarks of cancer.

Dual functions of the homeoprotein DLX4 in modulating responsiveness of tumor cells to topoisomerase II-targeting drugs

Topoisomerase II (TOP2)-targeting poisons such as anthracyclines and etoposide are commonly used for cancer chemotherapy and kill tumor cells by causing accumulation of DNA double-strand breaks (DSB). Several lines of evidence indicate that overexpression of TOP2A, the gene encoding topoisomerase IIα, increases sensitivity of tumor cells to TOP2 poisons, but it is not clear why some TOP2A-overexpressing (TOP2A-High) tumors respond poorly to these drugs. In this study, we identified that TOP2A expression is induced by DLX4, a homeoprotein that is overexpressed in breast and ovarian cancers. Analysis of breast cancer datasets revealed that TOP2A-high cases that also highly expressed DLX4 responded more poorly to anthracycline-based chemotherapy than TOP2A-high cases that expressed DLX4 at low levels. Overexpression of TOP2A alone in tumor cells increased the level of DSBs induced by TOP2 poisons. In contrast, DLX4 reduced the level of TOP2 poison-induced DSBs irrespective of its induction of TOP2A. DLX4 did not stimulate homologous recombination-mediated repair of DSBs. However, DLX4 interacted with Ku proteins, stimulated DNA-dependent protein kinase activity, and increased erroneous end-joining repair of DSBs. Whereas DLX4 did not reduce levels of TOP2 poison-induced DSBs in Ku-deficient cells, DLX4 stimulated DSB repair and reduced the level of TOP2 poison-induced DSBs when Ku was reconstituted in these cells. Our findings indicate that DLX4 induces TOP2A expression but reduces sensitivity of tumor cells to TOP2 poisons by stimulating Ku-dependent repair of DSBs. These opposing activities of DLX4 could explain why some TOP2A-overexpressing tumors are not highly sensitive to TOP2 poisons.

Genes regulated in metastatic osteosarcoma: evaluation by microarray analysis in four human and two mouse cell line systems

Osteosarcoma (OS) is a rare bone neoplasm that affects mainly adolescents. It is associated with poor prognosis in case of metastases formation. The search for metastasis predicting markers is therefore imperative to optimize treatment strategies for patients at risk and important for the search of new drugs for the treatment of this devastating disease. Here, we have analyzed by microarray the differential gene expression in four human and two mouse OS cell line systems consisting of parental cell lines with low metastatic potential and derivatives thereof with increased metastatic potential. Using two osteoblastic cell line systems, the most common OS phenotype, we have identified forty-eight common genes that are differentially expressed in metastatic cell lines compared to parental cells. The identified subset of metastasis relevant genes in osteoblastic OS overlapped only minimally with differentially expressed genes in the other four preosteoblast or nonosteoblastic cell line systems. The results imply an OS phenotype specific expression pattern of metastasis regulating proteins and form a basis for further investigation of gene expression profiles in patients' samples combined with survival analysis with the aim to optimize treatment strategies to develop new drugs and to consequently improve the survival of patients with the most common form of osteoblastic OS.

DLX4 upregulates TWIST and enhances tumor migration, invasion and metastasis

The distal-less homeobox gene 4 (DLX4) is a member of the DLX family of homeobox genes. Although absent from most normal adult tissues, DLX4 is widely expressed in leukemia, lung, breast, ovarian and prostate cancers. However the molecular targets, mechanisms and pathways that mediate the role of DLX4 in tumor metastasis are poorly understood. In this study, we found that DLX4 induces cancer cells to undergo epithelial to mesenchymal transition (EMT) through TWIST. Overexpression of DLX4 increased expression of TWIST expression in cancer cell lines, resulting in increased migratory and invasive capacity. Likewise, knocking down expression of DLX4 decreased TWIST expression and the migration ability of cancer cell lines. DLX4 bound to regulatory regions of the TWIST gene. Both western blotting and immunohistochemistry staining showed that the expression of DLX4 and TWIST are correlated in most of breast tumors. Taken together, these data from both cell models and tumor tissues demonstrate that DLX4 not only upregulates TWIST expression but also induces EMT and tumor metastasis. Altogether, we propose a new pathway in which DLX4 drives expression of TWIST to promote EMT, cancer migration, invasion and metastasis.

HOXA9 promotes ovarian cancer growth by stimulating cancer-associated fibroblasts

Epithelial ovarian cancers (EOCs) often exhibit morphologic features of embryonic Müllerian duct-derived tissue lineages and colonize peritoneal surfaces that overlie connective and adipose tissues. However, the mechanisms that enable EOC cells to readily adapt to the peritoneal environment are poorly understood. In this study, we show that expression of HOXA9, a Müllerian-patterning gene, is strongly associated with poor outcomes in patients with EOC and in mouse xenograft models of EOC. Whereas HOXA9 promoted EOC growth in vivo, HOXA9 did not stimulate autonomous tumor cell growth in vitro. On the other hand, expression of HOXA9 in EOC cells induced normal peritoneal fibroblasts to express markers of cancer-associated fibroblasts (CAFs) and to stimulate growth of EOC and endothelial cells. Similarly, expression of HOXA9 in EOC cells induced normal adipose- and bone marrow-derived mesenchymal stem cells (MSCs) to acquire features of CAFs. These effects of HOXA9 were due in substantial part to its transcriptional activation of the gene encoding TGF-β2 that acted in a paracrine manner on peritoneal fibroblasts and MSCs to induce CXCL12, IL-6, and VEGF-A expression. These results indicate that HOXA9 expression in EOC cells promotes a microenvironment that is permissive for tumor growth.

FGF-2 regulates cell proliferation, migration, and angiogenesis through an NDY1/KDM2B-miR-101-EZH2 pathway

The histone H3K27 methyltransferase EZH2 plays an important role in oncogenesis, by mechanisms that are incompletely understood. Here, we show that the JmjC domain histone H3 demethylase NDY1 synergizes with EZH2 to silence the EZH2 inhibitor miR-101. NDY1 and EZH2 repress miR-101 by binding its promoter in concert, via a process triggered by upregulation of NDY1. Whereas EZH2 binding depends on NDY1, the latter binds independently of EZH2. However, both are required to repress transcription. NDY1 and EZH2 acting in concert upregulate EZH2 and stabilize the repression of miR-101 and its outcome. NDY1 is induced by FGF-2 via CREB phosphorylation and activation, downstream of DYRK1A, and mediates the FGF-2 and EZH2 effects on cell proliferation, migration, and angiogenesis. The FGF-2-NDY1/EZH2-miR-101-EZH2 axis described here was found to be active in bladder cancer. These data delineate an oncogenic pathway that functionally links FGF-2 with EZH2 via NDY1 and miR-101.

Homeobox gene Dlx-2 is implicated in metabolic stress-induced necrosis

BACKGROUND

In contrast to tumor-suppressive apoptosis and autophagic cell death, necrosis promotes tumor progression by releasing the pro-inflammatory and tumor-promoting cytokine high mobility group box 1 (HMGB1), and its presence in tumor patients is associated with poor prognosis. Thus, necrosis has important clinical implications in tumor development; however, its molecular mechanism remains poorly understood.

RESULTS

In the present study, we show that Distal-less 2 (Dlx-2), a homeobox gene of the Dlx family that is involved in embryonic development, is induced in cancer cell lines dependently of reactive oxygen species (ROS) in response to glucose deprivation (GD), one of the metabolic stresses occurring in solid tumors. Increased Dlx-2 expression was also detected in the inner regions, which experience metabolic stress, of human tumors and of a multicellular tumor spheroid, an in vitro model of solid tumors. Dlx-2 short hairpin RNA (shRNA) inhibited metabolic stress-induced increase in propidium iodide-positive cell population and HMGB1 and lactate dehydrogenase (LDH) release, indicating the important role(s) of Dlx-2 in metabolic stress-induced necrosis. Dlx-2 shRNA appeared to exert its anti-necrotic effects by preventing metabolic stress-induced increases in mitochondrial ROS, which are responsible for triggering necrosis.

CONCLUSIONS

These results suggest that Dlx-2 may be involved in tumor progression via the regulation of metabolic stress-induced necrosis.

Up-regulation of homeodomain genes, DLX1 and DLX2, by FLT3 signaling

BACKGROUND

Activating mutations in fms-like tyrosine kinase-3 (FLT3) are frequent in acute myeloid leukemia and represent both a poor prognostic feature and a therapeutic target. We have identified a previously unrecognized downstream effect of FLT3 activation, namely up-regulation of the homeodomain genes, DLX1 and DLX2.

DESIGN AND METHODS

MV4;11 cells with FLT3-internal tandem duplication mutation, RS4;11 cells with wild-type FLT3 and blasts from patients with acute myeloid leukemia were used to pursue the relation between FLT3, DLX1/2 and transforming growth factor-β (TGFβ). Real-time quantitative reverse transcriptase polymerase chain reaction, western blot and reverse-phase protein array were performed to detect changes in gene and protein expression. RNA interference and MTS assays were used to study the interaction of PKC412, FLT3 inhibitor and TGFβ1.

RESULTS

A direct relationship between FLT3 activity and DLX1/2 expression was revealed by both inhibition and up-regulation of FLT3 signaling in MV4;11 and RS4;11 cell lines, respectively, in isolated blast cells from patients with acute myeloid leukemia, and in reverse-phase protein array assays of samples from patients with acute myeloid leukemia. Mechanistically, the link between FLT3 and DLX1 expression appears to involve MAPK signaling through the ERK and JNK pathways. To determine whether elevated DLX1 had a functional consequence, we explored the reported inhibition by DLX1 on TGFβ/Smad signaling. Indeed, TGFβ responses were blunted by FLT3 activation in a DLX1-dependent manner and FLT3 inhibition resulted in a time-dependent increase in nuclear phospho-Smad2.

CONCLUSIONS

These findings suggest that alterations in DLX1/2 contribute to the biological consequences of FLT3 activation.

Homeodomain protein DLX4 counteracts key transcriptional control mechanisms of the TGF-β cytostatic program and blocks the antiproliferative effect of TGF-β

The antiproliferative activity of transforming growth factor-β (TGF-β) is essential for maintaining normal tissue homeostasis and is lost in many types of tumors. Gene responses that are central to the TGF-β cytostatic program include activation of the cyclin-dependent kinase inhibitors, p15(Ink4B) and p21(WAF1/Cip1), and repression of c-myc. These gene responses are tightly regulated by a repertoire of transcription factors that include Smad proteins and Sp1. The DLX4 homeobox patterning gene encodes a transcription factor that is absent from most normal adult tissues, but is expressed in a wide variety of malignancies, including lung, breast, prostate and ovarian cancers. In this study, we demonstrate that DLX4 blocks the antiproliferative effect of TGF-β. DLX4 inhibited TGF-β-mediated induction of p15(Ink4B) and p21(WAF1/Cip1) expression. DLX4 bound and prevented Smad4 from forming complexes with Smad2 and Smad3, but not with Sp1. However, DLX4 also bound and inhibited DNA-binding activity of Sp1. In addition, DLX4 induced expression of c-myc independently of TGF-β/Smad signaling. The ability of DLX4 to counteract key transcriptional control mechanisms of the TGF-β cytostatic program could explain, in part, the resistance of tumors to the antiproliferative effect of TGF-β.

Mutually exclusive expression of DLX2 and DLX5/6 is associated with the metastatic potential of the human breast cancer cell line MDA-MB-231

Background

The DLX gene family encodes for homeobox transcription factors involved in the control of morphogenesis and tissue homeostasis. Their expression can be regulated by Endothelin1 (ET1), a peptide associated with breast cancer invasive phenotype. Deregulation of DLX gene expression was found in human solid tumors and hematologic malignancies. In particular, DLX4 overexpression represents a possible prognostic marker in ovarian cancer. We have investigated the role of DLX genes in human breast cancer progression.

Methods

MDA-MB-231 human breast carcinoma cells were grown in vitro or injected in nude mice, either subcutaneously, to mimic primary tumor growth, or intravenously, to mimic metastatic spreading. Expression of DLX2, DLX5 and DLX6 was assessed in cultured cells, either treated or not with ET1, tumors and metastases by RT-PCR. In situ hybridization was used to confirm DLX gene expression in primary tumors and in lung and bone metastases. The expression of DLX2 and DLX5 was evaluated in 408 primary human breast cancers examining the GSE1456 and GSE3494 microarray datasets. Kaplan-Meier estimates for disease-free survival were calculated for the patients grouped on the basis of DLX2/DLX5 expression.

Results

Before injection, or after subcutaneous growth, MDA-MB-231 cells expressed DLX2 but neither DLX5 nor DLX6. Instead, in bone and lung metastases resulting from intravenous injection we detected expression of DLX5/6 but not of DLX2, suggesting that DLX5/6 are activated during metastasis formation, and that their expression is alternative to that of DLX2. The in vitro treatment of MDA-MB-231 cells with ET1, resulted in switch from DLX2 to DLX5 expression. By data mining in microarray datasets we found that expression of DLX2 occurred in 21.6% of patients, and was significantly correlated with prolonged disease-free survival and reduced incidence of relapse. Instead, DLX5 was expressed in a small subset of cases, 2.2% of total, displaying reduced disease-free survival and high incidence of relapse which was, however, non-significantly different from the other groups due to the small size of the DLX+ cohort. In all cases, we found mutually exclusive expression of DLX2 and DLX5.

Conclusions

Our studies indicate that DLX genes are involved in human breast cancer progression, and that DLX2 and DLX5 genes might serve as prognostic markers.

Upregulation of DLX5 promotes ovarian cancer cell proliferation by enhancing IRS-2-AKT signaling

The distal-less homeobox gene (dlx) 5 encodes a transcription factor that controls jaw formation and appendage differentiation during embryonic development. We had previously found that Dlx5 is overexpressed in an Akt2 transgenic model of T-cell lymphoma. To investigate if DLX5 is involved in human cancer, we screened its expression in the NCI 60 cancer cell line panel. DLX5 was frequently upregulated in cell lines derived from several tumor types, including ovarian cancer. We next validated its upregulation in primary ovarian cancer specimens. Stable knockdown of DLX5 by lentivirus-mediated transduction of short hairpin RNA (shRNA) resulted in reduced proliferation of ovarian cancer cells due to inhibition of cell cycle progression in connection with the downregulation of cyclins A, B1, D1, D2, and E, and decreased phosphorylation of AKT. Cell proliferation resumed following introduction of a DLX5 cDNA harboring wobbled mutations at the shRNA-targeting sites. Cell proliferation was also rescued by transduction of a constitutively active form of AKT. Intriguingly, downregulation of IRS-2 and MET contributed to the suppression of AKT signaling. Moreover, DLX5 was found to directly bind to the IRS-2 promoter and augmented its transcription. Knockdown of DLX5 in xenografts of human ovarian cancer cells resulted in markedly diminished tumor size. In addition, DLX5 was found to cooperate with HRAS in the transformation of human ovarian surface epithelial cells. Together, these data suggest that DLX5 plays a significant role in the pathogenesis of some ovarian cancers.