Epigenetic silencing of the candidate tumor suppressor gene PROX1 in sporadic breast cancer

Molecular expression of Forkhead Box C2 gene (FOXC2) and Prospero homeobox gene (PROX-1) in oral squamous carcinoma and their correlation with clinicopathological parameters: A prospective cohort study

Background

Forkhead box C2 gene (FOXC2) acts as an epithelial-mesenchymal transition (EMT) inducer while Prospero homeobox 1 gene (PROX-1) function as a regulator of lymphangiogenesis and angiogenesis in oral squamous cell carcinoma (OSCC). It is presumed that PROX-1 has both tumour-suppressive and oncogenic effects. The main aim of this study is to evaluate the role of PROX-1 and FOXC2 in the invasion and progression of OSCC cases and to correlate their expression with various histopathological parameters.

Materials and Methods

A prospective cohort study was conducted in a total sample size of 52 OSCC tissues and histologically tumour-free margins of 20. mRNA expression and protein levels of FOXC2 and PROX-1 were evaluated using real-time PCR and sandwich enzyme-linked immunosorbent assay techniques. Chi-square analysis and correlation analysis were done. Kaplan-Meier analysis evaluated the survival rate.

Results

Mean Ct values of FOXC2 were 1.915 ± 0.519 and PROX-1 was 0.061 ± 0.173. There was a significant 2-fold increase in the FOXC2 expression and a 0.5-fold decrease in the PROX-1 expression in OSCC tissue. Increased levels of FOXC2 protein and decreased levels of PROX-1 with a mean difference of 1.64 ± 0.73 ng/ml and 1.27 ± 0.33 ng/ml were observed in OSCC compared to histologically tumour-free margins. A significant positive correlation was found between the FOXC2 expression and clinicopathological parameters such as staging, perineural invasion (PNI) and lymphovascular invasion (LVI) whereas PROX-1 showed a significant negative correlation with histopathological parameters such as staging, PNI, LVI and tumour staging. There was a significant positive correlation between the PROX-1 and histologically tumour-free margins in disease-free survival patients (P-value = 0.03).

Conclusion

FOXC2 and PROX-1 expressions were correlated with lymphovascular invasion, OSCC tumour staging and PNI. Thus, FOXC2 and PROX-1 could be possible therapeutic targets in the treatment of OSCC that can inhibit the EMT in OSCC and thereby favouring a better prognosis.

Prox1 Suppresses the Proliferation of Breast Cancer Cells via Direct Inhibition of c-Myc Gene Expression

Breast cancer is one of the most lethal malignancies in women worldwide and is characterized by rapid growth and low survival rates, despite advances in tumor biology and therapies. Novel therapeutic approaches require new insights into the molecular mechanisms of malignant transformation and progression. To this end, here, we identified Prox1 as a negative regulator of proliferation and tumor-related metabolism in breast cancer. In particular, we showed that breast tumors from human patients exhibited reduced levels of Prox1 expression, while high expression levels of Prox1 were associated with a favorable prognosis in breast cancer patients. Moreover, we experimentally demonstrated that Prox1 was sufficient to strongly suppress proliferation, migration, and the Warburg effect in human breast cancer cells without inducing apoptosis. Most importantly, over-expression of Prox1 inhibited breast tumor growth in vivo in both heterotopic and orthotopic xenograft mouse models. The anti-tumorigenic effect of Prox1 was mediated by the direct repression of c-Myc transcription and its downstream target genes. Consistently, c-Myc over-expression from an artificial promoter that was not targeted by Prox1 reversed Prox1's anti-tumor effects. These findings suggest that Prox1 has a tumor suppressive role via direct transcriptional regulation of c-Myc, making it a promising therapeutic gene for breast cancer.

Homeobox Protein PROX1 Expression is Negatively Regulated by Histone Deacetylase 1 and c-JUN Complex in MDA-MB-231 Human Breast Cancer Cells

Prospero homeobox 1 (PROX1) is a member of the homeobox transcription factor family that plays a critical role in the development of multiple tissues and specification of cell fate. PROX1 expression is differentially regulated based on the cellular context and plays an antagonistic role as a tumour promoter or suppressor in different tumour types. In human breast cancer, PROX1 expression is suppress-ed; however, the molecular mechanism by which it is down-regulated remains poorly understood. Here, we show that ectopic expression of PROX1 reduces the motility and invasiveness of MDA-MB-231 human breast cancer cells, suggesting that PROX1 functions as a negative regulator of tumour invasion in MDA-MB-231 cells. Treatment with histone deacetylase (HDAC) inhibitors up-regulates PROX1 mRNA and protein expression levels. Knockdown of HDAC1 using short hairpin RNA also up-regulates PROX1 mRNA and protein expression levels. We found that HDAC1 interacted with c-JUN at the activator protein (AP)-1-binding site located at -734 to -710 in the PROX1 promoter region to suppress PROX1 expression. In addition, c-JUN N-terminal kinase-mediated c-JUN phosphorylation was found to be crucial for silencing PROX1 expression. In conclusion, PROX1 expression can be silenced by the epigenetic mechanism involved in the complex formation of HDAC1 and c-JUN at the AP-1 site in the PROX1 promoter region in MDA-MB-231 human breast cancer cells. Therefore, this study revealed the epigenetic regulatory mechanism involved in the suppression of PROX1 expression in breast cancer cells.

The Role of PROX1 in Neoplasia: A Key Player Often Overlooked

The human PROX1 gene (Prospero homeobox gene 1) is a member of the homeobox transcription factor family. PROX1 plays a key role in the development of the lymphatic system and is primarily used as a lymphatic vessel marker. However, as the accumulating evidence indicates that PROX1 is also implicated in the tumorigenesis of various cancer types, the scientific community has attempted to elucidate its complicated function in neoplasia pathogenesis, as well as its utility in cancer diagnosis, prognosis, and therapy. PROX1 has been shown to participate in the complex molecular mechanisms affecting tumorigenesis and has been associated with a plethora of clinicopathological parameters, including tumor stage and patients’ overall survival. Depending on the specific organ affected, PROX1 has exhibited both tumor-promoting and tumor-suppressing properties, with its inhibition and reactivation representing possible novel therapeutic interventions, respectively. Moreover, researchers have reported PROX1 as a useful tool in the fields of diagnosis and prognosis assessment. The current study aims to summarize and present the existing data that render PROX1 a novel and useful diagnostic and prognostic biomarker, as well as a possible therapeutic target.

Prox1 inhibits neurite outgrowth during central nervous system development

During central nervous system (CNS) development, proper and timely induction of neurite elongation is critical for generating functional, mature neurons, and neuronal networks. Despite the wealth of information on the action of extracellular cues, little is known about the intrinsic gene regulatory factors that control this developmental decision. Here, we report the identification of Prox1, a homeobox transcription factor, as a key player in inhibiting neurite elongation. Although Prox1 promotes acquisition of early neuronal identity and is expressed in nascent post-mitotic neurons, it is heavily down-regulated in the majority of terminally differentiated neurons, indicating a regulatory role in delaying neurite outgrowth in newly formed neurons. Consistently, we show that Prox1 is sufficient to inhibit neurite extension in mouse and human neuroblastoma cell lines. More importantly, Prox1 overexpression suppresses neurite elongation in primary neuronal cultures as well as in the developing mouse brain, while Prox1 knock-down promotes neurite outgrowth. Mechanistically, RNA-Seq analysis reveals that Prox1 affects critical pathways for neuronal maturation and neurite extension. Interestingly, Prox1 strongly inhibits many components of Ca2+ signaling pathway, an important mediator of neurite extension and neuronal maturation. In accordance, Prox1 represses Ca2+ entry upon KCl-mediated depolarization and reduces CREB phosphorylation. These observations suggest that Prox1 acts as a potent suppressor of neurite outgrowth by inhibiting Ca2+ signaling pathway. This action may provide the appropriate time window for nascent neurons to find the correct position in the CNS prior to initiation of neurites and axon elongation.

The Impact of Transcription Factor Prospero Homeobox 1 on the Regulation of Thyroid Cancer Malignancy

Transcription factor Prospero homeobox 1 (PROX1) is continuously expressed in the lymphatic endothelial cells, playing an essential role in their differentiation. Many reports have shown that PROX1 is implicated in cancer development and acts as an oncoprotein or suppressor in a tissue-dependent manner. Additionally, the PROX1 expression in many types of tumors has prognostic significance and is associated with patient outcomes. In our previous experimental studies, we showed that PROX1 is present in the thyroid cancer (THC) cells of different origins and has a high impact on follicular thyroid cancer (FTC) phenotypes, regulating migration, invasion, focal adhesion, cytoskeleton reorganization, and angiogenesis. Herein, we discuss the PROX1 transcript and protein structures, the expression pattern of PROX1 in THC specimens, and its epigenetic regulation. Next, we emphasize the biological processes and genes regulated by PROX1 in CGTH-W-1 cells, derived from squamous cell carcinoma of the thyroid gland. Finally, we discuss the interaction of PROX1 with other lymphatic factors. In our review, we aimed to highlight the importance of vascular molecules in cancer development and provide an update on the functionality of PROX1 in THC biology regulation.

Transcription Factor Prospero Homeobox 1 (PROX1) as a Potential Angiogenic Regulator of Follicular Thyroid Cancer Dissemination

It is well known that Prospero homeobox 1 (PROX1) is a crucial regulator of lymphangiogenesis, that reprograms blood endothelial cells to lymphatic phenotype. However, the role of PROX1 in tumor progression, especially in angiogenesis remains controversial. Herein, we studied the role of PROX1 in angiogenesis in cell lines derived from follicular thyroid cancer (FTC: FTC-133) and squamous cell carcinoma of the thyroid gland (SCT: CGTH-W-1) upon PROX1 knockdown. The genes involved in angiogenesis were selected by RNA-seq, and the impact of PROX1 on vascularization potential was investigated using human umbilical vein endothelial cells (HUVECs) cultured in conditioned medium collected from FTC- or SCT-derived cancer cell lines after PROX1 silencing. The angiogenic phenotype was examined in connection with the analysis of focal adhesion and correlated with fibroblast growth factor 2 (FGF2) levels. Additionally, the expression of selected genes involved in angiogenesis was detected in human FTC tissues. As a result, we demonstrated that PROX1 knockdown resulted in upregulation of factors associated with vascularization, such as metalloproteinases (MMP1 and 3), FGF2, vascular endothelial growth factors C (VEGFC), BAI1 associated protein 2 (BAIAP2), nudix hydrolase 6 (NUDT6), angiopoietin 1 (ANGPT1), and vascular endothelial growth factor receptor 2 (KDR). The observed molecular changes resulted in the enhanced formation of capillary-like structures by HUVECs and upregulated focal adhesion in FTC-133 and CGTH-W-1 cells. The signature of selected angiogenic genes' expression in a series of FTC specimens varied depending on the case. Interestingly, PROX1 and FGF2 showed opposing expression levels in FTC tissues and seven thyroid tumor-derived cell lines. In summary, our data revealed that PROX1 is involved in the spreading of thyroid cancer cells by regulation of angiogenesis.

Long non-coding RNA LINC00968 reduces cell proliferation and migration and angiogenesis in breast cancer through up-regulation of PROX1 by reducing hsa-miR-423-5p

Background: Breast cancer (BC) is a common invasive malignancy in women with unclear etiology. A recent study suggested that long non-coding RNA (lncRNA), LINC00968 had a tumor-promoting effect in cancer. However, the role of LINC00968 in BC remains unclear. Therefore, we conducted the present study to determine the effect of LINC00968 in BC and its underlying mechanism. Methods: The expression of LINC00968 and hsa-miR-423-5p in BC tissues and cells was determined using reverse transcription quantitative polymerase chain reaction and western blot analysis. Dual luciferase reporter, RNA pull-down and RNA immunoprecipitation assays were used to determine the relationship among LINC00968, PROX1 and hsa-miR-423-5p. Gain- and loss-function approaches were utilized to examine the effects of LINC00968, PROX1 and hsa-miR-423-5p on cell proliferation, migration, tube formation in vitro; and tumor growth and angiogenesis in vivo. Results: LINC00968 expression reduced while hsa-miR-423-5p increased in BC tissues relative to adjacent normal tissues. Overexpression of LINC00968 was observed to inhibit BC cell proliferation, migration and tube formation abilities in vitro as well as tumor growth in vivo through inhibition of hsa-miR-423-5p. And hsa-miR-423-5p mediated BC cellular functions and tumor growth through down-regulating PROX1. LINC00968 was identified as a competing endogenous RNA to upregulate PROX1 by downregulating hsa-miR-423-5p. More importantly, it was found that LINC00968 increased PROX1 expression in vivo in a concentration-dependent manner. Conclusion: Taken together, this study suggests that LINC00968 inhibits the progression of BC through impeding hsa-miR-423-5p-mediated PROX1 inhibition. LINC00968 may be a potential therapeutic target for BC therapy that warrants further studies.

Molecular Signature of Prospero Homeobox 1 (PROX1) in Follicular Thyroid Carcinoma Cells

The prospero homeobox 1 (PROX1) transcription factor is a product of one of the lymphangiogenesis master genes. It has also been suggested to play a role in carcinogenesis, although its precise role in tumour development and metastasis remains unclear. The aim of this study was to gain more knowledge on the PROX1 function in thyroid tumorigenesis. Follicular thyroid cancer-derived cells—CGTH-W-1—were transfected with PROX1-siRNA (small interfering RNA) and their proliferation, cell cycle, apoptosis and motility were then analysed. The transcriptional signature of PROX1 depletion was determined using RNA-Sequencing (RNA-Seq) and the expression of relevant genes was further validated using reverse transcriptase quantitative PCR (RT-qPCR), Western blot and immunocytochemistry. PROX1 depletion resulted in a decreased cell motility, with both migratory and invasive potential being significantly reduced. The cell morphology was also affected, while the other studied cancer-related cell characteristics were not significantly altered. RNA-seq analysis revealed significant changes in the expression of transcripts encoding genes involved in both motility and cytoskeleton organization. Our transcriptional analysis of PROX1-depleted follicular thyroid carcinoma cells followed by functional and phenotypical analyses provide, for the first time, evidence that PROX1 plays an important role in the metastasis of thyroid cancer cells by regulating genes involved in focal adhesion and cytoskeleton organization in tumour cells.

PROX1 is a transcriptional regulator of MMP14

The transcription factor PROX1 is essential for development and cell fate specification. Its function in cancer is context-dependent since PROX1 has been shown to play both oncogenic and tumour suppressive roles. Here, we show that PROX1 suppresses the transcription of MMP14, a metalloprotease involved in angiogenesis and cancer invasion, by binding and suppressing the activity of MMP14 promoter. Prox1 deletion in murine dermal lymphatic vessels in vivo and in human LECs increased MMP14 expression. In a hepatocellular carcinoma cell line expressing high endogenous levels of PROX1, its silencing increased both MMP14 expression and MMP14-dependent invasion in 3D. Moreover, PROX1 ectopic expression reduced the MMP14-dependent 3D invasiveness of breast cancer cells and angiogenic sprouting of blood endothelial cells in conjunction with MMP14 suppression. Our study uncovers a new transcriptional regulatory mechanism of cancer cell invasion and endothelial cell specification.

Lymphatics-associated genes are downregulated at transcription level in non-small cell lung cancer

The present study aimed to verify a possibility of ongoing lymphangiogenesis in non-small cell lung cancer (NSCLC) via examination of mRNA levels of a number of lymphangiogenesis-associated genes in tumors. It was hypothesized that transcriptional activation of these genes would occur in tumors that stimulate new lymphatic vessel formation. The study was performed on 140 pairs of fresh-frozen surgical specimens of cancer and unaffected lung tissues derived from NSCLC stage I-IIIA patients. mRNA levels were evaluated with the reverse transcription-quantitative polymerase chain reaction method and expressed as fold change differences between the tumor and normal tissues. Possible associations between expression and patient clinicopathological characteristics and survival were analyzed. In the NSCLC tissue samples, vascular endothelial growth factor (VEGF) C, VEGFD, VEGFR3, VEGFR2, VEGFR1, lymphatic vessel endothelial hyaluronan receptor 1, integrin subunit α 9, FOX2, neuropilin 2, fibroblast growth factor 2 genes were significantly downregulated (P<0.001 for all) compared with matched normal lung tissues, whereas mRNA levels for VEGFA, spleen associated tyrosine kinase, podoplanin, and prospero homeobox 1 genes were similar in both tissues. Neither lymph node status, nor disease pathological stage influenced expression, whereas more profound suppression of gene activities appeared to occur in squamous cell carcinomas compared with adenocarcinomas. The VEGFR1 mRNA expression level was significantly connected with patient survival in the univariate analysis, and was an independent prognostic factor for overall survival in the multivariate Cox's proportional hazards model (HR 2.103; 95% confidence interval: 1.005-4.401; P=0.049). The results support a hypothesis of absence of new lymphatic vessel formation inside growing NSCLC tumor mass, however do not exclude a possibility of lymphangiogenesis in narrow marginal tumor parts.

High Expression of Prospero-Related Homeobox-1 (PROX1) Is Associated With Poor Prognosis in Patients With Salivary Adenoid Cystic Carcinoma

PURPOSE

Prospero-related homeobox-1 (PROX1) plays an important role in the invasion and metastasis of many human cancers. However, the expression pattern of PROX1 in salivary adenoid cystic carcinoma (SACC) remains unclear. The aim of this study was to investigate PROX1 expression and its prognostic value in SACC.

MATERIALS AND METHODS

PROX1 expression was determined by immunohistochemistry (IHC) in SACC tissue specimens. Correlations between PROX1 expression and clinicopathologic features were investigated. The Kaplan-Meier method was used to analyze the correlation between PROX1 expression and survival. Independent prognostic factors associated with overall survival (OS) were analyzed using Cox regression analysis.

RESULTS

The IHC data showed that the PROX1 positivity rate in SACC tissue specimens was significantly higher than that in normal salivary gland tissues (71.1 vs 13.3%; P < .05). PROX1 expression was detected mainly in the nucleolus. In addition, PROX1 expression was correlated with perineural invasion, local regional recurrence, and distant metastasis of patients with SACC (P < .05), and no significant association was found between PROX1 expression and other clinicopathologic parameters. Data indicated that patients with positive PROX1 expression had poor OS compared with those with negative PROX1 expression (P = .0005). Multivariate analysis showed that PROX1 expression, local regional recurrence, and distant metastasis were independent prognostic factors for OS.

CONCLUSIONS

These findings showed that PROX1 expression was statistically higher in SACC specimens. Positive expression of PROX1 might serve as a potential predictor of prognosis in SACC.

The role of prospero homeobox 1 (PROX1) expression in follicular thyroid carcinoma cells

The prospero homeobox 1 (Prox1) transcription factor is a key player during embryogenesis and lymphangiogenesis. Altered Prox1 expression has been found in a variety of human cancers, including papillary thyroid carcinoma (PTC). Interestingly, Prox1 may exert tumor suppressive or tumor promoting effect, depending on the tissue context. In this study, we have analyzed Prox1 expression in normal and malignant human thyroid carcinoma cell lines. Moreover, we determined the effect of Prox1 silencing and overexpression on the cellular processes associated with the metastatic potential of tumor cells: proliferation, migration, invasion, apoptosis and anchorage-independent growth, in the follicular thyroid carcinoma (FTC) FTC-133 cell line. We found that Prox1 expression was significantly higher in FTC-derived cells than in PTC-derived cells and normal thyroid, and it was associated with the PI3K/Akt signaling pathway. In the FTC-133 cells, it was associated with cell invasive potential, motility and wound closure capacities, but not with proliferation or apoptosis. Modifying Prox1 expression also induced substantial changes in the cytoskeleton structure and cell morphology. In conclusion, we have shown that Prox1 plays an important role in the development of FTC and that its suppression prevents, whereas its overexpression promotes, the malignant behavior of thyroid follicular cancer cells.

Genome-Wide Association Study to Identify Susceptibility Loci That Modify Radiation-Related Risk for Breast Cancer After Childhood Cancer

Background

Childhood cancer survivors treated with chest-directed radiotherapy have substantially elevated risk for developing breast cancer. Although genetic susceptibility to breast cancer in the general population is well studied, large-scale evaluation of breast cancer susceptibility after chest-directed radiotherapy for childhood cancer is lacking.

Methods

We conducted a genome-wide association study of breast cancer in female survivors of childhood cancer, pooling two cohorts with detailed treatment data and systematic, long-term follow-up: the Childhood Cancer Survivor Study and St. Jude Lifetime Cohort. The study population comprised 207 survivors who developed breast cancer and 2774 who had not developed any subsequent neoplasm as of last follow-up. Genotyping and subsequent imputation yielded 16 958 466 high-quality variants for analysis. We tested associations in the overall population and in subgroups stratified by receipt of lower than 10 and 10 or higher gray breast radiation exposure. We report P values and pooled per-allele risk estimates from Cox proportional hazards regression models. All statistical tests were two-sided.

Results

Among survivors who received 10 or higher gray breast radiation exposure, a locus on 1q41 was associated with subsequent breast cancer risk (rs4342822, nearest gene PROX1 , risk allele frequency in control subjects [RAF controls ] = 0.46, hazard ratio = 1.92, 95% confidence interval = 1.49 to 2.44, P = 7.09 × 10 -9 ). Two rare variants also showed potentially promising associations (breast radiation ≥10 gray: rs74949440, 11q23, TAGLN , RAF controls = 0.02, P = 5.84 × 10 -8 ; <10 gray: rs17020562, 1q32.3, RPS6KC1 , RAF controls = 0.0005, P = 6.68 × 10 -8 ). Associations were restricted to these dose subgroups, with consistent findings in the two survivor cohorts.

Conclusions

Our study provides strong evidence that germline genetics outside high-risk syndromes could modify the effect of radiation exposure on breast cancer risk after childhood cancer.

High PROX1 expression in gastric cancer predicts better survival

BACKGROUND

PROX1 is a transcription factor involved in the development of various organs. It has also an important function in colorectal cancer progression. The aim of this study was to investigate the prognostic role of PROX1 expression in gastric cancer.

METHODS

We evaluated PROX1 expression in gastric cancer by immunohistochemistry of tumor-tissue microarrays including tumor specimens from 283 patients who underwent surgery at Helsinki University Hospital. We investigated the association of PROX1 expression with clinicopathologic variables and patient survival.

RESULTS

Cytoplasmic PROX1 reactivity was high in 56 (20.5%) and low in 217 (79.5%) cases. Low PROX1 immunostaining associated with diffuse cancer type (p = 0.002). In subgroup analysis, PROX1 was a significant marker of better prognosis in patients aged under 66 (p = 0.007), in those with intestinal cancer (p = 0.025), among men (p = 0.019), and in tumors of less than 5 cm diameter (p = 0.030). Patients with high PROX1 expression had a cancer-specific 5-year survival of 65.6% (95% CI 52.7-78.5), compared to 37.1% (95% CI 30.2-44.0) for those with low expression (p = 0.004, log-rank test). This result remained significant in multivariable analysis (HR = 0.56; 95% CI 0.35-0.90; p = 0.017).

CONCLUSION

In gastric cancer, high cytoplasmic PROX1 expression is an independent marker of better prognosis.

Aberrant gene-specific DNA methylation signature analysis in cervical cancer

Multicomponent molecular modifications such as DNA methylation may offer sensitive and specific cervical intraepithelial neoplasia and cervical cancer biomarkers. In this study, we tested cervical tissues at various stages of tumor progression for 5-methylcytosine and 5-hydroxymethylcytosine levels and also DNA promoter methylation profile of a panel of genes for its diagnostic potential. In total, 5-methylcytosine, 5-hydroxymethylcytosine, and promoter methylation of 33 genes were evaluated by reversed-phase high-performance liquid chromatography, enzyme-linked immunosorbent assay based technique, and bisulfate-based next generation sequencing. The 5-methylcytosine and 5-hydroxymethylcytosine contents were significantly reduced in squamous cell carcinoma and receiver operating characteristic curve analysis showed a significant difference in (1) 5-methylcytosine between normal and squamous cell carcinoma tissues (area under the curve = 0.946) and (2) 5-hydroxymethylcytosine levels among normal, squamous intraepithelial lesions and squamous cell carcinoma. Analyses of our next generation sequencing results and data from five independent published studies consisting of 191 normal, 10 low-grade squamous intraepithelial lesions, 21 high-grade squamous intraepithelial lesions, and 335 malignant tissues identified a panel of nine genes ( ARHGAP6, DAPK1, HAND2, NKX2-2, NNAT, PCDH10, PROX1, PITX2, and RAB6C) which could effectively discriminate among the various groups with sensitivity and specificity of 80%-100% (p < 0.05). Furthermore, 12 gene promoters (ARHGAP6, HAND2, LHX9, HEY2, NKX2-2, PCDH10, PITX2, PROX1, TBX3, IKBKG, RAB6C, and DAPK1) were also methylated in one or more of the cervical cancer cell lines tested. The global and gene-specific methylation of the panel of genes identified in our study may serve as useful biomarkers for the early detection and clinical management of cervical cancer.

MicroRNA-181a inhibits tumor proliferation, invasiveness, and metastasis and is downregulated in gastric cancer

MicroRNAs (miRNAs) play crucial roles in the development and progression of human cancers, including gastric cancer. The discovery of miRNAs may provide a new and powerful tool for studying the mechanism, diagnosis, and treatment of gastric cancer. Here we show that miR-181a levels were significantly downregulated in gastric cancer tissues compared with the adjacent normal regions in 80 paired samples. Moreover, the lower levels of miR-181a were associated with the pM or pTNM stage in clinical gastric cancer patients. In addition, the ectopic expression of miR-181a in the gastric cancer cell line HGC-27 inhibited cell proliferation, cell migration, and invasion by directly interacting with the mRNA encoding the oncogenic factor Prox1. Taken together, our results indicate that miR-181a might act as a tumor suppressor in gastric cancer, which may provide a novel diagnostic and therapeutic option for human gastric cancer in the near future.

Molecular Programs Underlying Asymmetric Stem Cell Division and Their Disruption in Malignancy

Asymmetric division of stem cells is a highly conserved and tightly regulated process by which a single stem cell produces two unequal daughter cells. One retains its stem cell identity while the other becomes specialized through a differentiation program and loses stem cell properties. Coordinating these events requires control over numerous intra- and extracellular biological processes and signaling networks. In the initial stages, critical events include the compartmentalization of fate determining proteins within the mother cell and their subsequent passage to the appropriate daughter cell in order to direct their destiny. Disturbance of these events results in an altered dynamic of self-renewing and differentiation within the cell population, which is highly relevant to the growth and progression of cancer. Other critical events include proper asymmetric spindle assembly, extrinsic regulation through micro-environmental cues, and non-canonical signaling networks that impact cell division and fate determination. In this review, we discuss mechanisms that maintain the delicate balance of asymmetric cell division in normal tissues and describe the current understanding how some of these mechanisms are deregulated in cancer.

Prospero homeobox 1 mediates the progression of gastric cancer by inducing tumor cell proliferation and lymphangiogenesis

BACKGROUND

Prospero homeobox 1 (PROX1) functions as a tumor suppressor gene or an oncogene in various cancer types. However, the distinct function of PROX1 in gastric cancer is unclear. We determined whether PROX1 affected the oncogenic behavior of gastric cancer cells and investigated its prognostic value in patients with gastric cancer.

METHODS

A small interfering RNA against PROX1 was used to silence PROX1 expression in gastric cancer cell lines AGS and SNU638. Expression of PROX1 in gastric cancer tissues was investigated by performing immunohistochemistry. Apoptosis, proliferation, angiogenesis, and lymphangiogenesis were determined by performing the TUNEL assay and immunohistochemical staining for Ki-67, CD34, and D2-40.

RESULTS

PROX1 knockdown induced apoptosis by activating cleaved caspase-3, caspase-7, caspase-9, and poly(ADP-ribose) polymerase, and by decreasing the expression of anti-apoptotic proteins Bcl-2 and Bcl-xL. PROX1 knockdown also suppressed tumor cell proliferation. In addition, PROX1 knockdown decreased lymphatic endothelial cell invasion and tube formation and the expression of vascular endothelial growth factor (VEGF)-C and -D and cyclooxygenase (COX)-2. However, PROX1 knockdown only decreased umbilical vein endothelial cell invasion, not tube formation. The mean Ki-67 labeling index and lymphatic vessel density value of PROX1-positive tumors were significantly higher than those of PROX1-negative tumors. However, no significant difference was observed between PROX1 expression and apoptotic index or microvessel density. PROX1 expression was significantly associated with age, cell differentiation, lymph node metastasis, cancer stage, and poor survival.

CONCLUSIONS

These results indicate that PROX1 mediates the progression of gastric cancer by inducing tumor cell proliferation and lymphangiogenesis.

Methylation status of homeobox genes in common human cancers

Approximately 300 homeobox loci were identified in the euchromatic regions of the human genome, of which 235 are probable functional genes and 65 are likely pseudogenes. Many of these genes play important roles in embryonic development and cell differentiation. Dysregulation of homeobox gene expression is a frequent occurrence in cancer. Accumulating evidence suggests that as genetics disorders, epigenetic modifications alter the expression of oncogenes and tumor suppressor genes driving tumorigenesis and perhaps play a more central role in the evolution and progression of this disease. Here, we described the current knowledge regarding homeobox gene DNA methylation in human cancer and describe its relevance in the diagnosis, therapeutic response and prognosis of different types of human cancers.

PROX1 and β-catenin are prognostic markers in pancreatic ductal adenocarcinoma

Background

The Wnt/β-catenin pathway has a key role in regulating cellular processes and its aberrant signaling can lead to cancer development. The role of β-catenin expression in pancreatic ductal adenocarcinoma is somewhat controversial. Transcription factor PROX1 is a target of Wnt/β-catenin signaling and it is involved in carcinogenesis through alterations in its expression. The actions can be either oncogenic or tumor suppressive depending on the tissue. The aim of this study was to investigate PROX1 and β-catenin expression in pancreatic ductal adenocarcinoma (PDAC).

Methods

Expression of PROX1 and β-catenin were evaluated in 156 patients by immunohistochemistry of tissue microarrays. Associations between tumor marker expression and clinicopathological parameters were assessed by the Fischer’s exact-test or the linear-by-linear association test. The Kaplan-Meier method and log-rank test were used for survival analysis. Uni- and multivariate survival analyses were carried out by the Cox regression proportional hazard model.

Results

High PROX1 expression was seen in 74 (48 %) tumors, and high β-catenin expression in 100 (65 %). High β-catenin expression was associated with lower tumor grade (p = 0.025). High PROX1 and β-catenin expression associated significantly with lower risk of death from PDAC in multivariate analysis (HR = 0.63; 95 % CI 0.42–0.95, p = 0.026; and HR = 0.54; 95 % CI 0.35–0.82, p = 0.004; respectively). The combined high expression of PROX1 and β-catenin also predicted lower risk of death from PDAC (HR = 0.46; 95 % CI 0.28–0.76, p = 0.002).

Conclusion

In conclusion, high PROX1 and β-catenin expression were independent factors for better prognosis in pancreatic ductal adenocarcinoma.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2497-5) contains supplementary material, which is available to authorized users.

Expression and methylation patterns partition luminal-A breast tumors into distinct prognostic subgroups

Background

Breast cancer is a heterogeneous disease comprising several biologically different types, exhibiting diverse responses to treatment. In the past years, gene expression profiling has led to definition of several “intrinsic subtypes” of breast cancer (basal-like, HER2-enriched, luminal-A, luminal-B and normal-like), and microarray based predictors such as PAM50 have been developed. Despite their advantage over traditional histopathological classification, precise identification of breast cancer subtypes, especially within the largest and highly variable luminal-A class, remains a challenge. In this study, we revisited the molecular classification of breast tumors using both expression and methylation data obtained from The Cancer Genome Atlas (TCGA).

Methods

Unsupervised clustering was applied on 1148 and 679 breast cancer samples using RNA-Seq and DNA methylation data, respectively. Clusters were evaluated using clinical information and by comparison to PAM50 subtypes. Differentially expressed genes and differentially methylated CpGs were tested for enrichment using various annotation sets. Survival analysis was conducted on the identified clusters using the log-rank test and Cox proportional hazards model.

Results

The clusters in both expression and methylation datasets had only moderate agreement with PAM50 calls, while our partitioning of the luminal samples had better five-year prognostic value than the luminal-A/luminal-B assignment as called by PAM50. Our analysis partitioned the expression profiles of the luminal-A samples into two biologically distinct subgroups exhibiting differential expression of immune-related genes, with one subgroup carrying significantly higher risk for five-year recurrence. Analysis of the luminal-A samples using methylation data identified a cluster of patients with poorer survival, characterized by distinct hyper-methylation of developmental genes. Cox multivariate survival analysis confirmed the prognostic significance of the two partitions after adjustment for commonly used factors such as age and pathological stage.

Conclusions

Modern genomic datasets reveal large heterogeneity among luminal breast tumors. Our analysis of these data provides two prognostic gene sets that dissect and explain tumor variability within the luminal-A subgroup, thus, contributing to the advancement of subtype-specific diagnosis and treatment.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-016-0724-2) contains supplementary material, which is available to authorized users.

The identification of age-associated cancer markers by an integrative analysis of dynamic DNA methylation changes

As one of the most widely studied epigenetic modifications, DNA methylation has an important influence on human traits and cancers. Dynamic variations in DNA methylation have been reported in malignant neoplasm and aging; however, the mechanisms remain poorly understood. By constructing an age-associated and cancer-related weighted network (ACWN) based on the correlation of the methylation level and the protein-protein interaction, we found that DNA methylation changes associated with age were closely related to the occurrence of cancer. Additional analysis of 102 module genes mined from the ACWN revealed discrimination based on two main patterns. One pattern involved methylation levels that increased with aging and were higher in cancer patients compared with normal controls (HH pattern). The other pattern involved methylation levels that decreased with aging and were lower in cancer compared with normal (LL pattern). Upon incorporation with gene expression levels, 25 genes were filtered based on negative regulation by DNA methylation. These genes were regarded as potential cancer risk markers that were influenced by age in the process of carcinogenesis. Our results will facilitate further studies regarding the impact of the epigenetic effects of aging on diseases and will aid in the development of tailored cancer preventive strategies.

MiR-670-5p induces cell proliferation in hepatocellular carcinoma by targeting PROX1

MiRNAs, as oncogenes or as anti-oncogenes, play critically regulated roles in human cancers at posttranscriptional level. A number of dysregulated miRNAs has been observed in HCC. However, the expression and function of miR-670-5p have not been evaluated in HCC to date. In this study, we examined and confirmed the over-expression of miR-670-5p in HCC and in hepatoma-derived cells Hep3B. At least 60% of HCC tissues showed a greater than three-fold enhance in the expression of miR-670-5p compared with paired adjacent non-cancerous tissues. Knockdown studies for miR-670-5p showed that the expression of miR-670-5p promoted cellular proliferation. In tissues and cells with high expression of miR-670-5p, decreased expression of PROX1, a miR-670-5p predicated target, was detected. It confirmed that PROX1 expression was obviously affected by the expression of miR-670-5p. Furthermore, overexpression of PROX1 greatly inhibitted cellular proliferation. Therefore, it was inferred that miR-670-5p may play important roles in enhancing proliferation activity that is associated with HCC by modulating PROX1 expression at posttranscriptional level.

Nuclear PROX1 is Associated with Hypoxia-Inducible Factor 1α Expression and Cancer Progression in Esophageal Squamous Cell Carcinoma

BACKGROUND

Transcription factor prospero homeobox 1 (PROX1) has been identified as a master regulator of lymphangiogenesis associated with metastasis. Although PROX1 expression has been investigated in several cancers, its clinical significance remains controversial and needs further validation. In this study, we investigated the clinical and functional significance of PROX1 and PROX1 regulator hypoxia-inducible factor 1α (HIF1α) in esophageal squamous cell carcinoma (ESCC).

METHODS

A total of 117 samples from ESCC patients were analyzed for PROX1, HIF1α, and E-cadherin expression by immunohistochemistry; correlation with clinicopathological characteristics was determined. PROX1 function was evaluated in PROX1 small interfering RNA (siRNA)-transfected human ESCC cells in vitro by assessing cell proliferation and migration.

RESULTS

PROX1 expression was higher in ESCC than in normal tissues. Patients with higher PROX1 expression (n = 26) had increased nuclear accumulation of HIF1α (p = 0.004) and more advanced metastasis, both lymph node (N factor; p = 0.09) and hematogenous (M factor; p = 0.04), than those with lower PROX1 expression (n = 91). In addition, high PROX1 and HIF1α expression correlated with low levels of E-cadherin, an epithelial cell marker. Analysis of overall and cancer-specific survival indicated that elevated PROX1 expression was significantly correlated with poor prognosis (p = 0.0064). PROX1 downregulation in ESCC cells inhibited cellular proliferation and migration (p < 0.05). Hypoxia restored PROX1 levels that were reduced by PROX1-specific siRNA.

CONCLUSION

Our data suggest that high expression of PROX1 in ESCC could be used as an indicator of poor prognosis, and that PROX1 is a promising candidate molecular target for ESCC treatment.

Cancer stem cell division: when the rules of asymmetry are broken

Asymmetric division of stem cells is a highly conserved and tightly regulated process by which a single stem cell produces two daughter cells and simultaneously directs the differential fate of both: one retains its stem cell identity while the other becomes specialized and loses stem cell properties. Coordinating these events requires control over numerous intra- and extracellular biological processes and signaling networks. In the initial stages, critical events include the compartmentalization of fate determining proteins within the mother cell and their subsequent passage to the appropriate daughter cell. Disturbance of these events results in an altered dynamic of self-renewing and differentiation within the cell population, which is highly relevant to the growth and progression of cancer. Other critical events include proper asymmetric spindle assembly, extrinsic regulation through micro-environmental cues, and noncanonical signaling networks that impact cell division and fate determination. In this review, we discuss mechanisms that maintain the delicate balance of asymmetric cell division in normal tissues and describe the current understanding how some of these mechanisms are deregulated in cancer. The universe is asymmetric and I am persuaded that life, as it is known to us, is a direct result of the asymmetry of the universe or of its indirect consequences. The universe is asymmetric. -Louis Pasteur.

PROX1 gene is differentially expressed in oral cancer and reduces cellular proliferation

Homeobox genes are a family of transcription factors that play a pivotal role in embryogenesis. Prospero homeobox 1 (PROX1) has been shown to function as a tumor suppressor gene or oncogene in various types of cancer, including oral squamous cell carcinoma (OSCC). We have previously identified PROX1 as a downregulated gene in OSCC. The aim of this study is to clarify the underlying mechanism by which PROX1 regulates tumorigenicity of OSCC cells. PROX1 mRNA and protein expression levels were first investigated in 40 samples of OSCC and in nontumor margins. Methylation and amplification analysis was also performed to assess the epigenetic and genetic mechanisms involved in controlling PROX1 expression. OSCC cell line SCC9 was also transfected to stably express the PROX1 gene. Next, SCC9-PROX1-overexpressing cells and controls were subjected to proliferation, differentiation, apoptosis, migration, and invasion assays in vitro. OSCC samples showed reduced PROX1 expression levels compared with nontumor margins. PROX1 amplification was associated with better overall survival. PROX1 overexpression reduces cell proliferation and downregulates cyclin D1. PROX1-overexpressing cells also exhibited reduced CK18 and CK19 expression and transcriptionally altered the expression of WISP3, GATA3, NOTCH1, and E2F1. Our results suggest that PROX1 functions as a tumor suppressor gene in oral carcinogenesis.

Impact of an altered PROX1 expression on clinicopathology, prognosis and progression in renal cell carcinoma

The transcription factor PROX1 (prospero homeobox 1) has a critical role in the development of various organs, and has been implicated in both oncogenic and tumor-suppressive functions in human cancers. However, the role of PROX1 in the development of renal cell carcinomas (RCCs) has not yet been studied. Here, we reported that PROX1 expression was decreased in human RCC tissues compared with adjacent normal tissues. In RCC tissues, however, poorly differentiated RCC expressed higher PROX1 levels compared with well-differentiated RCC. In addition, the PROX1 immunostaining levels were positively correlated with tumor nuclear grade and lymph node metastasis. Further, high PROX1 expression indicated poor survival for patients. These findings imply that in the different developmental stages of RCC, PROX1 may exert distinct functions according to the specific microenvironment of tumor. Moreover, in vitro experiments revealed that PROX1 overexpression enhanced the proliferation and migration of RCC cells; conversely, PROX1 depletion by siRNA attenuated the proliferation and migration of RCC cells. Collectively, these observations suggest that PROX1 plays an important role in RCC development and progression, and PROX1 may be a novel target for prevention and treatment of RCC.

Prox1 and FOXC2 act as regulators of lymphangiogenesis and angiogenesis in oral squamous cell carcinoma

Prospero homeobox 1 (Prox1) and forkhead box (FOX) C2 regulate angiogenesis and/or lymphangiogenesis. However, the detailed role and function of Prox1 and FOXC2 in cancer remains controversial. In the present study, we examined the expression of Prox1 and FOXC2 proteins in specimens from 163 cases with oral squamous cell carcinoma (OSCC). Furthermore, the role of Prox1 and FOXC2 in cancer cell growth and invasion was evaluated in cultured OSCC cells. Prox1 expression was significantly associated with local progression of the tumor (P = 0.0023), clinical stage (P<0.0001), lymphovessel density (LVD) (P<0.0001), nodal metastasis (P<0.0001), and worse prognosis (P<0.0001). Immunoreactivity of FOXC2 was strongly correlated with microvessel density (MVD) (P<0.0001) and poor prognosis (P = 0.0076). In vitro analysis demonstrated that Prox1 regulates cell growth, proliferation, invasion, and lymphangiogenesis by activating vascular endothelial growth factor (VEGF)-C expression. Furthermore, FOXC2 enhanced the expression level of Prox1 and promoted angiogenesis by enhancement of VEGF-A expression. Our results suggested that Prox1 and FOXC2 play key roles in OSCC progression and that further studies focusing on these proteins may yield useful insights for diagnosis and therapy of OSCC.

Transcription factor PROX1: its role in development and cancer

The homeobox gene PROX1 is critical for organ development during embryogenesis. The Drosophila homologue, known as prospero has been shown to act as a tumor suppressor by controlling asymmetric cell division of neuroblasts. Likewise, alterations in PROX1 expression and function are associated with a number of human cancers including hematological malignancies, carcinomas of the pancreas, liver and the biliary system, sporadic breast cancer, Kaposiform hemangioendothelioma, colon cancer, and brain tumors. PROX1 is involved in cancer development and progression and has been ascribed both tumor suppressive and oncogenic properties in a variety of different cancer types. However, the exact mechanisms through which PROX1 regulates proliferation, migration, and invasion of cancer cells are by large unknown. This review provides an update on the role of PROX1 in organ development and on its emerging functions in cancer, with special emphasis on the central nervous system and glial brain tumors.

The homeobox transcription factor Prox1 inhibits proliferation of hepatocellular carcinoma cells by inducing p53-dependent senescence-like phenotype

The homeobox transcription factor Prox1 is highly expressed in adult hepatocytes and is involved in the regulation of bile acid synthesis and gluconeogenesis in the liver by interacting with other transcriptional activators or repressors. Recent studies showed that Prox1 could inhibit proliferation of hepatocellular carcinoma (HCC) cells and reduced Prox1 expression was associated with poor prognosis of HCC patients. However, the underlying mechanism by which Prox1 attenuates HCC growth is still unclear. In this study, we demonstrated that Prox1 induced senescence-like phenotype of HCC cells to reduce cell proliferation. Our results indicated that the tumor suppressor p53 is a key mediator of Prox1-induced growth suppression because Prox1 only induced senescence-like phenotype in HCC cells harboring wild type p53. In addition, knockdown of p53 by shRNA reversed the effect of Prox1. However, chromatin immunoprecipitation assay did not demonstrate the direct binding of Prox1 to proximal promoter of human p53 gene suggesting Prox1 might not directly activate p53 transcription. We found that Prox1 suppressed Twist expression in HCC cells and subsequently relieved its inhibition on p53 gene transcription. The involvement of Twist in the regulation of p53 by Prox1 was supported by the following evidence: (1) Prox1 inhibited Twist expression and promoter activity; (2) knockdown of Twist in SK-HEP-1 cells upregulated p53 expression and (3) ectopic expression of Twist counteracted Prox1-induced p53 transcription and senescence-like phenotype. We also indentified an E-box located at p53 promoter which is required for Twist to inhibit p53 expression. Finally, our animal experiment confirmed that Prox1 suppressed HCC growth in vivo. Collectively, we conclude that Prox1 suppresses proliferation of HCC cells via inhibiting Twist to trigger p53-dependent senescence-like phenotype.

Mechanisms of asymmetric progenitor divisions in the Drosophila central nervous system

The Drosophila central nervous system develops from polarised asymmetric divisions of precursor cells, called neuroblasts. Decades of research on neuroblasts have resulted in a substantial understanding of the factors and molecular events responsible for fate decisions of neuroblasts and their progeny. Furthermore, the cell-cycle dependent mechanisms responsible for asymmetric cortical protein localisation, resulting in the unequal partitioning between daughters, are beginning to be exposed. Disruption to the appropriate partitioning of proteins between neuroblasts and differentiation-committed daughters can lead to supernumerary neuroblast-like cells and the formation of tumours. Many of the factors responsible for regulating asymmetric division of Drosophila neuroblasts are evolutionarily conserved and, in many cases, have been shown to play a functionally conserved role in mammalian neurogenesis. Recent genome-wide studies coupled with advancements in live-imaging technologies have opened further avenues of research into neuroblast biology. We review our current understanding of the molecular mechanisms regulating neuroblast divisions, a powerful system to model mammalian neurogenesis and tumourigenesis.

Epigenome remodelling in breast cancer: insights from an early in vitro model of carcinogenesis

Epigenetic gene regulation has influence over a diverse range of cellular functions, including the maintenance of pluripotency, differentiation, and cellular identity, and is deregulated in many diseases, including cancer. Whereas the involvement of epigenetic dysregulation in cancer is well documented, much of the mechanistic detail involved in triggering these changes remains unclear. In the current age of genomics, the development of new sequencing technologies has seen an influx of genomic and epigenomic data and drastic improvements in both resolution and coverage. Studies in cancer cell lines and clinical samples using next-generation sequencing are rapidly delivering spectacular insights into the nature of the cancer genome and epigenome. Despite these improvements in technology, the timing and relationship between genetic and epigenetic changes that occur during the process of carcinogenesis are still unclear. In particular, what changes to the epigenome are playing a driving role during carcinogenesis and what influence the temporal nature of these changes has on cancer progression are not known. Understanding the early epigenetic changes driving breast cancer has the exciting potential to provide a novel set of therapeutic targets or early-disease biomarkers or both. Therefore, it is important to find novel systems that permit the study of initial epigenetic events that potentially occur during the first stages of breast cancer. Non-malignant human mammary epithelial cells (HMECs) provide an exciting in vitro model of very early breast carcinogenesis. When grown in culture, HMECs are able to temporarily escape senescence and acquire a pre-malignant breast cancer-like phenotype (variant HMECs, or vHMECs). Cultured HMECs are composed mainly of cells from the basal breast epithelial layer. Therefore, vHMECs are considered to represent the basal-like subtype of breast cancer. The transition from HMECs to vHMECs in culture recapitulates the epigenomic phenomena that occur during the progression from normal breast to pre-malignancy. Therefore, the HMEC model system provides the unique opportunity to study the very earliest epigenomic aberrations occurring during breast carcinogenesis and can give insight into the sequence of epigenomic events that lead to breast malignancy. This review provides an overview of epigenomic research in breast cancer and discusses in detail the utility of the HMEC model system to discover early epigenomic changes involved in breast carcinogenesis.

Prospero homeobox 1 promotes epithelial-mesenchymal transition in colon cancer cells by inhibiting E-cadherin via miR-9

PURPOSE

Prospero homeobox 1 (PROX1) has been shown to function as a tumor suppressor in various types of cancer. However, it promotes colon cancer progression. The aim of this study is to clarify the underlying mechanism by which PROX1 regulates tumorigenicity of colon cancer.

EXPERIMENTAL DESIGN

Association of PROX1 and clinicopathological features was studied by immunohistochemical staining. Pri-miR-9-2 and miR-9 were detected by quantitative real-time PCR. Assays of cell invasion, adhesion, and matrix metalloproteinase activity were used to study PROX1-mediated epithelial-mesenchymal transition (EMT).

RESULTS

PROX1 was overexpressed in 43% (59/136) of colon cancer tissues and its expression was correlated with E-cadherin downregulation (P = 0.00005), advanced tumor staging (P = 0.005), and lymph node metastasis (P = 0.000009). Enforced expression of PROX1 in DLD-1 cells caused downregulation of E-cadherin and integrins and attenuated cell adhesion. These cells showed increase of matrix metalloproteinase activity and invasive ability. Conversely, knockdown of PROX1 in SW620 cells restored E-cadherin protein expression and reduced invasiveness. Unexpectedly, repression of E-cadherin by PROX1 was not mediated by transcriptional inhibition. We found that PROX1 bound to miR-9-2 promoter and triggered its expression to suppress E-cadherin 3'UTR reporter activity and protein expression. Anti-miR-9 restored E-cadherin in SW620 cells, whereas precursor miR-9 inhibited E-cadherin in PROX1-knockdown cells. The miR-9 level was higher in tumor tissues with high PROX1/low E-cadherin than that of tumor tissues with low PROX1/high E-cadherin.

CONCLUSIONS

Our results provide mechanistic insights by which PROX1 promotes EMT and colon cancer progression. Targeting of PROX1-mediated oncogenic activity may be helpful for the treatment of colon cancer.

PROX1 overexpression inhibits protein kinase C beta II transcription through promoter DNA methylation

Prospero-related homeobox 1 (PROX1) is important for embryonic organ formation and differentiation, and changes in PROX1 activity were recently associated with cancer. To address the PROX1 roles in tumorigenesis, we established cells stably overexpressing PROX1 using the human cervical cancer cell line, HeLa. Overexpression of PROX1 reduced cell proliferation and the rate of tumor formation as compared with controls. Comparison of gene expression profiles between PROX1-overexpressing and mock-transfected cells revealed that the expression of protein kinase C βII (PRKCB2) is down-regulated in PROX1-overexpressing cells. A PRKCB inhibitor suppressed cell growth of control cells more than PROX1-expressing cells. Analysis of the 5'-promoter of PRKCB revealed that a region between -110 bp and the first exon contains two Sp1 binding sites and is important for transcriptional regulation of PRKCB. The inhibition of Sp1 transcription factor resulted in down-regulation of PRKCB2 protein levels. Treatment with a demethylating agent, 5-aza-2'-deoxycytidine, restored PRKCB2 mRNA expression in PROX1-expressing cells, suggesting that the 5'-promoter of PRKCB is methylated in these cells. Actually, it was found that a CpG island in this region, in particular a CpG site overlapping with the distal Sp1 site, was hypermethylated and direct Sp1 binding to this region was inhibited in PROX1-overexpressing cells. Thus, the suppressive effect of PROX1 on cell growth and tumor formation might be partially mediated by PRKCB2 via altered methylation of its promoter.

Methylcap-seq reveals novel DNA methylation markers for the diagnosis and recurrence prediction of bladder cancer in a Chinese population

PURPOSE

There is a need to supplement or supplant the conventional diagnostic tools, namely, cystoscopy and B-type ultrasound, for bladder cancer (BC). We aimed to identify novel DNA methylation markers for BC through genome-wide profiling of BC cell lines and subsequent methylation-specific PCR (MSP) screening of clinical urine samples.

EXPERIMENTAL DESIGN

The methyl-DNA binding domain (MBD) capture technique, methylCap/seq, was performed to screen for specific hypermethylated CpG islands in two BC cell lines (5637 and T24). The top one hundred hypermethylated targets were sequentially screened by MSP in urine samples to gradually narrow the target number and optimize the composition of the diagnostic panel. The diagnostic performance of the obtained panel was evaluated in different clinical scenarios.

RESULTS

A total of 1,627 hypermethylated promoter targets in the BC cell lines was identified by Illumina sequencing. The top 104 hypermethylated targets were reduced to eight genes (VAX1, KCNV1, ECEL1, TMEM26, TAL1, PROX1, SLC6A20, and LMX1A) after the urine DNA screening in a small sample size of 8 normal control and 18 BC subjects. Validation in an independent sample of 212 BC patients enabled the optimization of five methylation targets, including VAX1, KCNV1, TAL1, PPOX1, and CFTR, which was obtained in our previous study, for BC diagnosis with a sensitivity and specificity of 88.68% and 87.25%, respectively. In addition, the methylation of VAX1 and LMX1A was found to be associated with BC recurrence.

CONCLUSIONS

We identified a promising diagnostic marker panel for early non-invasive detection and subsequent BC surveillance.

Prox1 suppresses the proliferation of neuroblastoma cells via a dual action in p27-Kip1 and Cdc25A

Neuroblastoma is a pediatric tumor that originates from precursor cells of the sympathetic nervous system with less than 40% long-term survival in children diagnosed with high-risk disease. These clinical observations underscore the need for novel insights in the mechanisms of malignant transformation and progression. Accordingly, it was recently reported that Prox1, a homeobox transcription regulator, is expressed in higher levels in human neuroblastoma with favorable prognosis. Consistently, we have recently shown that Prox1 exerts a strong antiproliferative effect on neural precursor cells during embryonic development. Thus, Prox1 is a candidate gene with a critical role in suppressing malignant neuroblastoma transformation. Here, we provide evidence that Prox1 strongly suppresses the proliferation of mouse and human neuroblastoma cell lines and blocks the growth of neuroblastoma tumors in SCID mice. Conversely, short hairpin RNA (shRNA) -mediated knockdown of basal Prox1 expression significantly induces proliferation, genomic instability and the ability of neuroblastoma cells to form tumors. Mechanistically, analysis of an inducible Prox1-overexpressing Neuro2A cell line indicates that Prox1 is sufficient to suppress CyclinD1, CyclinA and CyclinB1, consistent with a role in cell cycle arrest. Surprisingly, Prox1 strongly induces CyclinE1 expression in the same system despite its action on blocking cell cycle progression, which could account for the context dependent oncogenic function of Prox1. Most importantly, Prox1 was sufficient to decrease Cdc25A and induce p27-Kip1, but not p21-Cip1 or p53. By alleviating the Prox1 action in Cdc25A and p27-Kip1 expression, we were able to rescue its effect on cell cycle arrest. Together these data suggest that Prox1 negatively regulates neuroblastoma carcinogenesis through suppression of Cdc25A and induction of p27-Kip1 to counteract CyclinE1 overexpression and block cell cycle progression. Furthermore, these observations render Prox1 a candidate target for the treatment of neuroblastoma tumors.

Prox1 transcription factor as a marker for vascular tumors-evaluation of 314 vascular endothelial and 1086 nonvascular tumors

Prox1, a transcription factor important in the regulation and maintenance of the lymphatic endothelial phenotype, is consistently expressed in lymphangiomas and Kaposi sarcoma and has also been reported in Kaposiform hemangioendothelioma. However, information on its distribution in vascular tumors, such as angiosarcoma, is limited. In this study, we examined selected normal tissues and 314 vascular endothelial and 1086 nonvascular tumors to get an insight into the biology of these tumors and on potential diagnostic use of Prox1 as an immunohistochemical marker. In adult tissues, Prox1 was essentially restricted to lymphatic endothelia, with expression in subsets of pancreatic and gastrointestinal epithelia. However, it was also detected in embryonic liver and heart. Prox1 was consistently expressed in lymphangiomas, venous hemangiomas, Kaposi sarcoma, in endothelia of spindle cell hemangioma, Kaposiform hemangioendothelioma, and retiform hemangioendothelioma, and in half of epithelioid hemangioendotheliomas. It was present in most cutaneous angiosarcomas from different sites but was less commonly expressed in deep soft tissue and visceral angiosarcomas. In contrast, Prox1 was generally absent in capillary and cavernous hemangiomas. In positive hemangiomas and angiosarcomas it was coexpressed with podoplanin, another marker of the lymphatic endothelial phenotype. There was an inverse correlation with CD34 expression. The expression in mesenchymal nonendothelial neoplasm was limited. Prox1 was detected in 5 of 27 synovial sarcomas, specifically in the epithelia of biphasic tumors. Four of 16 Ewing sarcomas and 5 of 15 paragangliomas were also positive. All melanomas and undifferentiated sarcomas were negative. Among epithelial neoplasms, Prox1 was detected in 18 of 38 colonic carcinomas and 10 of 15 cholangiocarcinomas and in a minority of pulmonary, prostatic, and endometrial adenocarcinomas. The common Prox1 expression in angiosarcoma and its rare presence in nonvascular mesenchymal tumors make this marker suitable for the diagnosis of angiosarcoma and Kaposi sarcoma. However, the presence of Prox1 in some malignant epithelial tumors necessitates caution in applying Prox1 as a marker for vascular tumors. Common Prox1 expression in angiosarcoma may reflect the lymphatic endothelial phenotype in these tumors. Its patterns of expression in hemangiomas and angiosarcoma may be diagnostically useful and offer a new parameter in the biological classification of vascular tumors.

Characterization of a carcinogenesis-associated long non-coding RNA

A negative selection strategy was used in the present study to isolate long polyA-minus RNAs from the total transcriptome and a long non-coding RNA named Yiya was identified. Yiya is a 1.9 kb long intergenic ncRNA gene mapped to chromosome 1q41, a well-established cancer susceptibility locus. Expression profiling revealed a general and regulated expression pattern of Yiya in major tissues, and more interestingly, identified elevated mRNA levels in different cancers. Quantitative analysis further demonstrated a dynamic regulation of Yiya expression in cell cycle progression, suggesting that it was involved in cell cycle regulation. Supporting this, overexpression of Yiya promotes cell cycle progression at the G1/S transition, therefore identifying Yiya as a cell-cycle-associated long non-coding RNA.

Roles for MSI2 and PROX1 in hematopoietic stem cell activity

PURPOSE OF REVIEW

The MSI2 and PROX1 proteins are increasingly recognized for their critical roles in the biology of primitive hematopoietic cells and for their potential contributions to leukemic pathogenesis. Here we summarize the studies that have shed light on the hematopoietic-specific roles of MSI2 and PROX1 and give an overview of the molecular mechanisms underlying their function.

RECENT FINDINGS

In addition to a likely role in cell cycle restraint, the hematopoietic stem cell agonist MSI2 is essential for the maintenance of primitive cell fate through ensuring appropriate balance between self-renewal and differentiation. Overexpression of Msi2 can contribute to the progression of murine myeloid leukemia and in the human setting is associated with poor prognosis. Regulatory control imposed by MSI2 may be achieved partly through regulation of the Notch signaling pathway. Prox1 behaves in an opposing manner to Msi2, resulting in elevated stem cell numbers when depleted. It has a potential role in cell cycle control and may act at the level of primitive hematopoietic stem and progenitor cells as it does in other systems by directly promoting commitment and differentiation. PROX1 functions as a tumor suppressor in numerous tissue types and has been found mutated in hematopoietic cell lines and primary blood malignancies.

SUMMARY

Deciphering the molecular mechanisms through which MSI2 and PROX1 affect primitive hematopoietic cell fate will provide insight into the regulation of normal hematopoiesis and facilitate better understanding of the leukemic transformation process. This will be directly applicable to the development of effective regenerative therapies and targeted leukemia treatments.

PROX1 is a predictor of survival for gliomas WHO grade II

Background:

The clinical course of World Health Organisation grade II gliomas remains variable and their time point of transformation into a more malignant phenotype is unpredictable. Identification of biological markers that can predict prognosis in individual patients is of great clinical value. PROX1 is a transcription factor that has a critical role in the development of various organs. PROX1 has been ascribed both oncogenic and tumour suppressive functions in human cancers. We have recently shown that PROX1 may act as a diagnostic marker for high-grade gliomas. The aim of this study was to address the prognostic value of PROX1 in grade II gliomas.

Methods:

A total of 116 samples were evaluated for the presence of PROX1 protein. The number of immunopositive cells was used as a variable in survival analysis, together with established prognostic factors for this patient group.

Results:

Higher PROX1 protein was associated with poor outcome. In the multivariate analysis, PROX1 was identified as an independent factor for survival (P=0.024), together with the presence of mutated isocitrate dehydrogenase 1 R132H protein, and with combined losses of chromosomal arms 1p/19q in oligodendrocytic tumours.

Conclusion:

PROX1 is a novel predictor of survival for grade II gliomas.

Assessing combined methylation-sensitive high resolution melting and pyrosequencing for the analysis of heterogeneous DNA methylation

Heterogeneous DNA methylation leads to difficulties in accurate detection and quantification of methylation. Methylation-sensitive high resolution melting (MS-HRM) is unique among regularly used methods for DNA methylation analysis in that heterogeneous methylation can be readily identified, although not quantified, by inspection of the melting curves. Bisulfite pyrosequencing has been used to estimate the level of heterogeneous methylation by quantifying methylation levels present at individual CpG dinucleotides. Sequentially combining the two methodologies using MS-HRM to screen the amplification products prior to bisulfite pyrosequencing would be advantageous. This would not only replace the quality control step using agarose gel analysis prior to the pyrosequencing step but would also provide important qualitative information in its own right. We chose to analyze DAPK1 as it is an important tumor suppressor gene frequently heterogeneously methylated in a number of malignancies, including chronic lymphocytic leukemia (CLL). A region of the DAPK1 promoter was analyzed in ten CLL samples by MS-HRM. By using a biotinylated primer, bisulfite pyrosequencing could be used to directly analyze the samples. MS-HRM revealed the presence of various extents of heterogeneous DAPK1 methylation in all CLL samples. Further analysis of the biotinylated MS-HRM products by bisulfite pyrosequencing provided quantitative information for each CpG dinucleotide analyzed, and confirmed the presence of heterogeneous DNA methylation. Whereas each method could be used individually, MS-HRM and bisulfite pyrosequencing provided complementary information for the assessment of heterogeneous methylation.

Kaposin-B enhances the PROX1 mRNA stability during lymphatic reprogramming of vascular endothelial cells by Kaposi's sarcoma herpes virus

Kaposi's sarcoma (KS) is the most common cancer among HIV-positive patients. Histogenetic origin of KS has long been elusive due to a mixed expression of both blood and lymphatic endothelial markers in KS tumor cells. However, we and others discovered that Kaposi's sarcoma herpes virus (KSHV) induces lymphatic reprogramming of blood vascular endothelial cells by upregulating PROX1, which functions as the master regulator for lymphatic endothelial differentiation. Here, we demonstrate that the KSHV latent gene kaposin-B enhances the PROX1 mRNA stability and plays an important role in KSHV-mediated PROX1 upregulation. We found that PROX1 mRNA contains a canonical AU-rich element (ARE) in its 3′-untranslated region that promotes PROX1 mRNA turnover and that kaposin-B stimulates cytoplasmic accumulation of the ARE-binding protein HuR through activation of the p38/MK2 pathway. Moreover, HuR binds to and stabilizes PROX1 mRNA through its ARE and is necessary for KSHV-mediated PROX1 mRNA stabilization. Together, our study demonstrates that kaposin-B plays a key role in PROX1 upregulation during lymphatic reprogramming of blood vascular endothelial cells by KSHV.

Kaposi's sarcoma (KS) is the most common cancer in HIV-positive patients and KS-associated herpes virus (KSHV) was identified as its causing agent. We and others have discovered that when the virus infects endothelial cells of blood vessels, KSHV reprograms the cell type resembling endothelial cells in lymphatic vessels. Although endothelial cells of the blood vascular system and of the lymphatic system share functional similarities, the cell type-reprogramming does not occur under a normal physiological condition. Therefore, cell-fate reprogramming by the cancer-causing virus KSHV provides an important insight into the molecular mechanism for viral pathogenesis. Our current study investigates the molecular mechanism underlying the KSHV-mediated cell fate reprogramming. We identified that a KSHV latent gene kaposin-B plays an important role in KSHV-mediated regulation of PROX1 to promote PROX1 mRNA stability. This study will provide a better understanding on the tumorigenesis and pathogenesis of KS with a potential implication toward new KS therapy.

Homeobox transcription factor Prox1 in sympathetic ganglia of vertebrate embryos: correlation with human stage 4s neuroblastoma

Previously, we observed expression of the homeobox transcription factor Prox1 in neuroectodermal embryonic tissues. Besides essential functions during embryonic development, Prox1 has been implicated in both progression and suppression of malignancies. Here, we show that Prox1 is expressed in embryonic sympathetic trunk ganglia of avian and murine embryos. Prox1 protein is localized in the nucleus of neurofilament-positive sympathetic neurons. Sympathetic progenitors represent the cell of origin of neuroblastoma (NB), the most frequent solid extracranial malignancy of children. NB may progress to life-threatening stage 4, or regress spontaneously in the special stage 4s. By qRT-PCR, we show that Prox1 is expressed at low levels in 24 human NB cell lines compared with human lymphatic endothelial cells (LECs), whereas equal immunostaining of nuclei can be seen in embryonic LECs and sympathetic neurons. In NB stages 1, 2, 3, and 4, we observed almost equal expression levels, but significantly higher amounts in stage 4s NB. By immunohistochemistry, we found variable amounts of Prox1 protein in nuclei of NB cells, showing intra and interindividual differences. Because stage 4s NB are susceptible to postnatal apoptosis, we assume that high Prox1 levels are critical for their behavior.

Expression of PROX1 Is a common feature of high-grade malignant astrocytic gliomas

PROX1 is a prospero-related transcription factor that plays a critical role in the development of various organs including the mammalian lymphatic and central nervous systems; it controls cell proliferation and differentiation through different transcription pathwaysand has both oncogenic and tumor-suppressive functions. We investigated PROX1 expression patterns in 56 human astrocytic gliomas of different grades using immunohistochemistry. An average of 79% of cells in World Health Organization Grade IV (glioblastoma, n = 15) and 57% of cells in World Health Organization Grade III (anaplastic astrocytoma, n = 13) were strongly PROX1 positive; low-grade diffuse astrocytomas (Grade II, n = 13) had 21% of cells that were strongly positive; Grade I tumors (n = 15) had 1.5%; and non-neoplastic brain tissue (n = 15) had 3.7% of cells that were PROX1 positive. Double immunolabeling showed that PROX1+ cells in glioblastomas frequently coexpressed early neuronal proteins MAP2 and betaIII-tubulin but not the mature neuronal marker protein NeuN. Analyses of coexpression with proliferation markers suggest that PROX1+ cells have a marginally lower rate of proliferation than other tumor cells but are still mitotically active. We conclude that PROX1 may constitute a useful tool for the diagnosis and grading ofastrocytic gliomas and for distinguishing Grade III and Grade IV tumors from Grade I and Grade II tumors.

Epigenetic targeting in breast cancer: therapeutic impact and future direction

Breast carcinogenesis is a multistep process involving both genetic and epigenetic changes. Epigenetics is defined as a reversible and heritable change in gene expression that is not accompanied by alteration in gene sequence. DNA methylation and histone modifications are the two major epigenetic changes that influence gene expression in cancer. The interaction between methylation and histone modification is intricately orchestrated by the formation of repressor complexes. Several genes involved in proliferation, antiapoptosis, invasion and metastasis have been shown to be methylated in various malignant and premalignant breast neoplasms. The histone deacetylase inhibitors (HDi) have emerged as an important class of drugs to be used synergistically with other systemic therapies in the treatment of breast cancer. Since epigenetic changes are potentially reversible processes, much effort has been directed toward understanding this mechanism with the goal of finding novel therapies as well as more refined diagnostic and prognostic tools in breast cancer.

Ultradeep sequencing of a human ultraconserved region reveals somatic and constitutional genomic instability

Ultradeep sequencing of genomes permits the detection of very low-level genomic instability in non-neoplastic tissues of patients with the most common form of inherited colorectal cancer.

Early detection of cancer-associated genomic instability is crucial, particularly in tumour types in which this instability represents the essential underlying mechanism of tumourigenesis. Currently used methods require the presence of already established neoplastic cells because they only detect clonal mutations. In principle, parallel sequencing of single DNA filaments could reveal the early phases of tumour initiation by detecting low-frequency mutations, provided an adequate depth of coverage and an effective control of the experimental error. We applied ultradeep sequencing to estimate the genomic instability of individuals with hereditary non-polyposis colorectal cancer (HNPCC). To overcome the experimental error, we used an ultraconserved region (UCR) of the human genome as an internal control. By comparing the mutability outside and inside the UCR, we observed a tendency of the ultraconserved element to accumulate significantly fewer mutations than the flanking segments in both neoplastic and nonneoplastic HNPCC samples. No difference between the two regions was detectable in cells from healthy donors, indicating that all three HNPCC samples have mutation rates higher than the healthy genome. This is the first, to our knowledge, direct evidence of an intrinsic genomic instability of individuals with heterozygous mutations in mismatch repair genes, and constitutes the proof of principle for the development of a more sensitive molecular assay of genomic instability.

In hereditary non-polyposis colorectal cancer (HNPCC), a germline mutation in one allele of a gene responsible for repairing DNA damage predisposes the host to cancer, because subsequent somatic inactivation of the one wild-type allele leads to genomic instability that favours tumourigenesis. Nonneoplastic tissues of HNPCC individuals are believed to repair DNA normally, as they are heterozygous and thus are thought to be genomically stable. However, methods used to date are known to be incapable of detecting very low levels of genome instability. Here, we present a more sensitive procedure based on the resequencing of a HNPCC genomic region using next-generation sequencing technology. With this approach, we show that genomic instability is in fact detectable in nonneoplastic tissues of HNPCC patients compared with healthy donors. This constitutional instability may predispose them to acquiring the second somatic mutation event needed for cancer development.