PAX6 is expressed in pancreatic adenocarcinoma and is downregulated during induction of terminal differentiation

The PAX Genes: Roles in Development, Cancer, and Other Diseases

Since their 1986 discovery in Drosophila, Paired box (PAX) genes have been shown to play major roles in the early development of the eye, muscle, skeleton, kidney, and other organs. Consistent with their roles as master regulators of tissue formation, the PAX family members are evolutionarily conserved, regulate large transcriptional networks, and in turn can be regulated by a variety of mechanisms. Losses or mutations in these genes can result in developmental disorders or cancers. The precise mechanisms by which PAX genes control disease pathogenesis are well understood in some cases, but much remains to be explored. A deeper understanding of the biology of these genes, therefore, has the potential to aid in the improvement of disease diagnosis and the development of new treatments.

Investigation of the Expression and Regulation of SCG5 in the Context of the Chromogranin-Secretogranin Family in Malignant Tumors

The SCG5 gene has been demonstrated to play an essential role in the development and progression of a range of malignant neoplasms. The regulation of SCG5 expression involves multiple biological pathways. According to relevant studies, SCG5 is differentially expressed in different cancers, and its up- or down-regulation may even affect tumour growth, invasion, and migration, which caught our attention. Therefore, we summarise the regulatory roles played by the SCG5 gene in a variety of cancers and the biological regulatory mechanisms associated with its possible promotion or inhibition of tumour biological behavior, to further explore the potential of SCG5 as a new tumour marker and hopefully provide theoretical guidance for subsequent disease research and treatment.

Induction of Apoptosis in Human Pancreatic Cancer Stem Cells by the Endoplasmic Reticulum-Targeted Alkylphospholipid Analog Edelfosine and Potentiation by Autophagy Inhibition

Pancreatic cancer is one of the most lethal malignancies with a poor and gloomy prognosis and the highest mortality-to-incidence ratio. Pancreatic cancer remains an incurable malignancy, and current therapies are ineffective. We isolated cancer stem cells (CSCs) from the human PANC-1 pancreatic cancer cell line as CD44⁺CD24⁺EpCAM⁺ cells. These CSCs form pancreatic cancer spheres or spheroids and develop tumors in SCID mice after subcutaneous injection of as few as 100 cells per mouse. Here, we found that the alkylphospholipid analog edelfosine inhibited CSC pancreatic cancer spheroid formation and induced cell death, as assessed by an increase in the percentage of cells in the sub-G₀/G₁ region by means of flow cytometry, indicative of DNA breakdown and apoptosis. This correlated with an increase in caspase-3 activity and PARP breakdown, as a major substrate of caspase-3, following PANC-1 CSC treatment with edelfosine. The antitumor ether lipid edelfosine colocalized with the endoplasmic reticulum in both PANC-1 cells as well as PANC-1 CSCs by using a fluorescent edelfosine analog, and induced an endoplasmic reticulum stress response in both PANC-1 cells and PANC-1 CSCs, with a potent CHOP/GADD153 upregulation. Edelfosine elicited a strong autophagy response in both PANC-1 cells and PANC-1 CSCs, and preincubation of CSCs with autophagy inhibitors, chloroquine or bafilomycin A1, enhanced edelfosine-induced apoptosis. Primary cultures from pancreatic cancer patients were sensitive to edelfosine, as well as their respective isolated CSCs. Nontumorigenic pancreatic human cell line HPNE and normal human fibroblasts were largely spared. These data suggest that pancreatic CSCs isolated from established cell lines and pancreatic cancer patients are sensitive to edelfosine through its accumulation in the endoplasmic reticulum and induction of endoplasmic reticulum stress.

The PAX6-ZEB2 axis promotes metastasis and cisplatin resistance in non-small cell lung cancer through PI3K/AKT signaling

Paired-box 6 (PAX6) is an important transcription factor required for the function of human neuroectodermal epithelial tissues. Previous studies have suggested that it is also expressed in several types of tumors and has an oncogenic role. However, little is known about its role in non-small cell lung cancer (NSCLC). Here, we found that PAX6 expression levels were upregulated in human lung cancer tissues and correlated with poor clinical outcomes. PAX6 overexpression significantly promoted NSCLC epithelial-to-mesenchymal transition (EMT) and metastasis, whereas its knockdown inhibited these processes. PAX6 is commonly correlated with EMT-mediated stem cell transformation, thereby inducing cisplatin resistance. Using the RT² Profiler PCR Array, we found that WNT5A, EGFR, and ZEB2 were differentially regulated in response to PAX6 modulation. In addition, PAX6 directly bound to the promoter region of ZEB2. ZEB2 knockdown significantly reduced the expression and function of PAX6. ZEB2 was upregulated upon PAX6 overexpression and downregulated upon PAX6 knockdown, whereas E-cadherin expression negatively correlated with PAX6 levels. Moreover, p-PI3K and p-AKT were significantly enhanced by PAX6, which was reversed by the addition of the PI3K-AKT inhibitor, LY294002. These data suggest that PAX6 can mediate E-cadherin downregulation through the PI3K/AKT signaling pathway by directly binding the promoter region of ZEB2, thereby mediating cell migration, stem cell transformation, and cisplatin resistance; and ultimately, affecting survival in NSCLC patients.

Gene expression analysis of embryonic pancreas development master regulators and terminal cell fate markers in resected pancreatic cancer: A correlation with clinical outcome

BACKGROUND

Despite the recent introduction of new drugs and the development of innovative multi-target treatments, the prognosis of pancreatic ductal adenocarcinoma (PDAC) remains very poor. Even when PDAC is resectable, the rate of local or widespread disease recurrence remains particularly high. Currently, reliable prognostic biomarkers of recurrence are lacking. We decided to explore the potential usefulness of pancreatic developmental regulators as biomarkers of PDAC relapse.

METHODS

We analyzed by quantitative real-time PCR the mRNA of selected factors involved either in pancreatic organogenesis (ISL1, NEUROD1, NGN3, NKX2.2, NKX6.1, PAX4, PAX6, PDX1 and PTF1α) or associated with terminally committed pancreatic cells (CHGA, CHGB, GAD2, GCG, HNF6α, INS, KRT19, SYP) in 17 PDAC cell lines and in frozen tumor samples from 41 PDAC patients.

RESULTS

High baseline levels of the ISL1, KRT19, PAX6 and PDX1 mRNAs in PDAC cell lines, were risk factors for time-dependent xenograft appearance after subcutaneous injection in CD1-Nude mice. Consistently, in human PDAC samples, high levels of KRT19 mRNA were associated with reduced overall survival and earlier recurrence. Higher levels of PDX1 or PAX6 mRNAs were instead associated with a higher frequency of local recurrence.

CONCLUSIONS

Our findings suggest that selected factors associated with pancreas development or its terminal differentiation might be implicated in mechanisms of PDAC progression and/or metastatic spread and that the measurement of their mRNA in tumors might be potentially used to improve patient prognostic stratification and prediction of the relapse site.

Epigenetically regulated PAX6 drives cancer cells toward a stem-like state via GLI-SOX2 signaling axis in lung adenocarcinoma

It remains unclear whether PAX6 acts as a crucial transcription factor for lung cancer stem cell (CSC) traits. We demonstrate that PAX6 acts as an oncogene responsible for induction of cancer stemness properties in lung adenocarcinoma (LUAD). Mechanistically, PAX6 promotes GLI transcription, resulting in SOX2 upregulation directly by the binding of GLI to the proximal promoter region of the SOX2 gene. The overexpressed SOX2 enhances the expression of key pluripotent factors (OCT4 and NANOG) and suppresses differentiation lineage factors (HOPX and NKX2-1), driving cancer cells toward a stem-like state. In contrast, in the differentiated non-CSCs, PAX6 is transcriptionally silenced by its promoter methylation. In human lung cancer tissues, the positive linear correlations of PAX6 expression with GLI and SOX2 expression and its negative correlations with HOPX and NKX2-1 expression were observed. Therapeutically, the blockade of the PAX6-GLI-SOX2 signaling axis elicits a long-lasting therapeutic efficacy by limiting CSC expansion following chemotherapy. Furthermore, a methylation panel including the PAX6 gene yielded a sensitivity of 79.1% and specificity of 83.3% for cancer detection using serum DNA from stage IA LUAD. Our findings provide a rationale for targeting the PAX6-GLI-SOX2 signaling axis with chemotherapy as an effective therapeutic strategy and support the clinical utility of PAX6 gene promoter methylation as a biomarker for early lung cancer detection.

Protecting Pax6 3' UTR from MicroRNA-7 Partially Restores PAX6 in Islets from an Aniridia Mouse Model

Aniridia is a rare congenital syndrome that is associated with reduced visual acuity and progressive loss of vision. Aniridia patients may also develop systemic health issues associated with defects in the pancreas, digestive, and central nervous systems. The spectrum of symptoms associated with aniridia is due to haploinsufficiency of the paired box 6 gene (PAX6) and its role in the development and maintenance of the affected tissues. Here, we isolated pancreatic islets from mice heterozygous for Pax6 to test whether a Pax6-specific miRNA suppression (target protector) strategy can restore PAX6 protein levels. We show that miR-7 and miR-375 target specific sites within the Pax6 3' UTR in a mouse pancreatic β-insulinoma cell line. Tough decoys (Tuds) against miR-7 and miR-375 increase expression of a mouse Pax6 3' UTR luciferase reporter and increase PAX6 protein levels in these cells. Finally, we demonstrate that the shielding of the miR-7 binding site with a target protector restores PAX6 protein levels in the Pax6 heterozygous islets. The data presented here represent a proof of concept for RNA-based therapy for the progressive defects associated with aniridia and suggest the target protector approach may be a useful therapeutic strategy for other haploinsufficiency diseases.

Elimination of cancer stem cells and reactivation of latent HIV-1 via AMPK activation: Common mechanism of action linking inhibition of tumorigenesis and the potential eradication of HIV-1

Although promising treatments are currently in development to slow disease progression and increase patient survival, cancer remains the second leading cause of death in the United States. Cancer treatment modalities commonly include chemoradiation and therapies that target components of aberrantly activated signaling pathways. However, treatment resistance is a common occurrence and recent evidence indicates that the existence of cancer stem cells (CSCs) may underlie the limited efficacy and inability of current treatments to effectuate a cure. CSCs, which are largely resistant to chemoradiation therapy, are a subpopulation of cancer cells that exhibit characteristics similar to embryonic stem cells (ESCs), including self-renewal, multi-lineage differentiation, and the ability to initiate tumorigenesis. Interestingly, intracellular mechanisms that sustain quiescence and promote self-renewal in adult stem cells (ASCs) and CSCs likely also function to maintain latency of HIV-1 in CD4⁺ memory T cells. Although antiretroviral therapy is highly effective in controlling HIV-1 replication, the persistence of latent but replication-competent proviruses necessitates the development of compounds that are capable of selectively reactivating the latent virus, a method known as the "shock and kill" approach. Homeostatic proliferation in central CD4⁺ memory T (T_CM) cells, a memory T cell subset that exhibits limited self-renewal and differentiation and is a primary reservoir for latent HIV-1, has been shown to reinforce and stabilize the latent reservoir in the absence of T cell activation and differentiation. HIV-1 has also been found to establish durable and long-lasting latency in a recently discovered subset of CD4⁺ T cells known as T memory stem (T_SCM) cells. T_SCM cells, compared to T_CM cells, exhibit stem cell properties that more closely match those of ESCs and ASCs, including self-renewal and differentiation into all memory T cell subsets. It is our hypothesis that activation of AMPK, a master regulator of cellular metabolism that plays a critical role in T cell activation and differentiation of ESCs and ASCs, will lead to both T cell activation-induced latent HIV-1 reactivation, facilitating virus destruction, as well as "activation", differentiation, and/or apoptosis of CSCs, thus inhibiting tumorigenesis. We also propose the novel observation that compounds that have been shown to both facilitate latent HIV-1 reactivation and promote CSC differentiation/apoptosis (e.g. bryostatin-1, JQ1, metformin, butyrate, etc.) likely do so through a common mechanism of AMPK activation.

Canonical and alternative transcript expression of PAX6 and CXCR4 in pancreatic cancer

Pancreatic cancer is a lethal disease with a propensity for invading and metastasizing into the surrounding tissues, including the liver and intestines. A number of factors are aberrantly overexpressed in this tumor type and actively promote cancer progression and metastasis. The present study demonstrates that paired box transcription factor 6 (PAX6) and C-X-C chemokine receptor 4 (CXCR4) are frequently co-expressed in primary pancreatic adenocarcinoma tumors and established cell lines. Expression analysis methods used in the present study included evaluation of protein expression by western blot analysis and immunofluorescence, transcript expression levels by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and luciferase assays utilizing regulatory elements from the CXCR4 gene locus. Canonical PAX6 and alternative splice variant PAX6(5a) proteins are expressed in pancreatic cancer and can drive gene expression through a conserved enhancer element within the first intron of the CXCR4 gene. As demonstrated by the introduction of an exogenous reporter construct with or without the intronic enhancer, loss of this element inhibited gene expression within numerous pancreatic cancer cell lines including Panc1, MIA-PaCa2 and BxPC3. All of the pancreatic cancer cell lines expressed the canonical CXCR4B transcript in addition to the alternatively spliced variant CXCR4A as determined by RT-qPCR experiments. The discovery of variant transcripts in pancreatic cancer cells may provide new candidates for future targeted therapies.

Targeting pancreatic expressed PAX genes for the treatment of diabetes mellitus and pancreatic neuroendocrine tumors

INTRODUCTION

Four members of the PAX family, PAX2, PAX4, PAX6 and PAX8 are known to be expressed in the pancreas. Accumulated evidences indicate that several pancreatic expressed PAX genes play a significant role in pancreatic development/functionality and alterations in these genes are involved in the pathogenesis of pancreatic diseases. Areas covered: In this review, we summarize the ongoing research related to pancreatic PAX genes in diabetes mellitus and pancreatic neuroendocrine tumors. We dissect the current knowledge at different levels; from mechanistic studies in cell lines performed to understand the molecular processes controlled by pancreatic PAX genes, to in vivo studies using rodent models that over-express or lack specific PAX genes. Finally, we describe human studies associating variants on pancreatic-expressed PAX genes with pancreatic diseases. Expert opinion: Based on the current literature, we propose that future interventions to treat pancreatic neuroendocrine tumors and diabetes mellitus could be developed via the modulation of PAX4 and/or PAX6 regulated pathways.

Pax6 regulates the expression of Dkk3 in murine and human cell lines, and altered responses to Wnt signaling are shown in FlpIn-3T3 cells stably expressing either the Pax6 or the Pax6(5a) isoform

Pax6 is a transcription factor important for early embryo development. It is expressed in several cancer cell lines and tumors. In glioblastoma, PAX6 has been shown to function as a tumor suppressor. Dickkopf 3 (Dkk3) is well established as a tumor suppressor in several tumor types, but not much is known about the regulation of its expression. We have previously found that Pax6 and Pax6(5a) increase the expression of the Dkk3 gene in two stably transfected mouse fibroblast cell lines. In this study the molecular mechanism behind this regulation is looked at. Western blot and reverse transcriptase quantitative PCR (RT-qPCR) confirmed higher level of Dkk3 expression in both Pax6 and Pax6(5a) expressing cell lines compared to the control cell line. By the use of bioinformatics and electrophoretic mobility shift assay (EMSA) we have mapped a functional Pax6 binding site in the mouse Dkk3 promoter. The minimal Dkk3 promoter fragment required for transcriptional activation by Pax6 and Pax6(5a) was a 200 bp region just upstream of the transcriptional start site. Mutation of the evolutionary conserved binding site in this region abrogated transcriptional activation and binding of Pax6/Pax6(5a) to the mouse Dkk3 promoter. Since the identified Pax6 binding site in this promoter is conserved, RT-qPCR and Western blot were used to look for regulation of Dkk3/REIC expression in human cell lines. Six of eight cell lines tested showed changes in Dkk3/REIC expression after PAX6 siRNA knockdown. Interestingly, we observed that the Pax6/Pax6(5a) expressing mouse fibroblast cell lines were less responsive to canonical Wnt pathway stimulation than the control cell line when TOP/FOP activity and the levels of active β-catenin and GSK3-β Ser9 phosphorylation were measured after LiCl stimulation.

Downregulation of PAX6 by shRNA inhibits proliferation and cell cycle progression of human non-small cell lung cancer cell lines

Background

The transcription factor PAX6 is primarily expressed in embryos. PAX6 is also expressed in several tumors and plays an oncogenic role. However, little is known about the role of PAX6 in lung cancer.

Methods

The function of PAX6 in lung cancer cells was evaluated by small interfering RNA-mediated depletion of the protein followed by analyses of cell proliferation, anchorage-independent growth, and cell cycle arrest. The changes of cyclin D1, pRB, ERK1/2, p38 expression caused by PAX6 inhibition were detected using western-blotting. The PAX6 mRNA level in 52 pairs of tumors and corresponding matched adjacent normal tissues from non-small cell lung cancer patients and lung cancer cell lines was detected by real-time PCR.

Results

Suppression of PAX6 expression inhibited cell growth and colony formation in A549 and H1299 cells. The percentage of cells in G1-phase increased when PAX6 expression was inhibited. The cyclin D1 protein level, as well as the pRB phosphorylation level, decreased as a result of PAX6 down-regulation. The activity of ERK1/2 and p38 was also suppressed in PAX6 knock-down cells. The PAX6 mRNA was highly expressed in lung cancer tissue and lung cancer cell lines. In most patients (about 65%), the relative ratio of PAX6 mRNA in primary NSCLC versus adjacent tissues exceeded 100.

Conclusions

Our data implicated that PAX6 accelerates cell cycle progression by activating MAPK signal pathway. PAX6 mRNA levels were significantly elevated in primary lung cancer tissues compared to their matched adjacent tissues.

PAX Genes in Cancer; Friends or Foes?

PAX genes have been shown to be critically required for the development of specific tissues and organs during embryogenesis. In addition, PAX genes are expressed in a handful of adult tissues where they are thought to play important roles, usually different from those in embryogenesis. A common theme in adult tissues is a requirement for PAX gene expression in adult stem cell maintenance or tissue regeneration. The connections between adult stem cell PAX gene expression and cancer are intriguing, and the literature is replete with examples of PAX gene expression in either situation. Here we systematically review the literature and present an overview of postnatal PAX gene expression in normal and cancerous tissue. We discuss the potential link between PAX gene expression in adult tissue and cancer. In addition, we discuss whether persistent PAX gene expression in cancer is favorable or unfavorable.

Effects of parathyroid hormone-related protein and macrophage inflammatory protein-1α in Jurkat T-cells on tumor formation in vivo and expression of apoptosis regulatory genes in vitro

Parathyroid hormone-related protein (PTHrP) and macrophage inflammatory protein-1α (MIP-1α) have been implicated in the pathogenesis of adult T-cell leukemia/lymphoma, but their effects on T-cells have not been well studied. Here we analyzed the functions of PTHrP and MIP-1α on T-cell growth and death both in vitro and in vivo by overexpressing either factor in human Jurkat T-cells. PTHrP or MIP-1α did not affect Jurkat cell growth in vitro, but PTHrP increased their sensitivity to apoptosis. Importantly, PTHrP and MIP-1α decreased both tumor incidence and growth in vivo. To investigate possible mechanisms, polymerase chain reaction (PCR) arrays and real-time reverse transcription (RT)-PCR assays were performed. Both PTHrP and MIP-1α increased the expression of several factors including signal transducer and activator of transcription 4, tumor necrosis factor α, receptor activator of nuclear factor κB ligand and death-associated protein kinase 1, and decreased the expression of inhibitor of DNA binding 1, interferon γ and CD40 ligand in Jurkat cells. In addition, MIP-1α also increased the expression of transcription factor AP-2α and PTHrP increased expression of the vitamin D3 receptor. These data demonstrate that PTHrP and MIP-1α exert a profound antitumor effect presumably by increasing the sensitivity to apoptotic signals through modulation of transcription and apoptosis factors in T-cells.

Isoform- and dose-sensitive feedback interactions between paired box 6 gene and delta-catenin in cell differentiation and death

Pax6, a mammalian homolog of the Drosophila paired box gene family member expressed in stem and progenitor cells, resides at the top of the genetic hierarchy in controlling cell fates and morphogenesis. While Pax6 activation can lead to mitotic arrest, premature neurogenesis, and apoptosis, the underlying molecular mechanisms have not been resolved. Here we report that either Pax6(+5a) or Pax6(-5a) was sufficient to promote, whereas their knockdown reduced the expression of delta-catenin (CTNND2), a neural specific member of the armadillo/beta-catenin superfamily. Pax6(+5a) elicited stronger effects on delta-catenin than Pax6(-5a). Inducible Pax6(+5a) expression demonstrated a biphasic and dose-dependent regulation of delta-catenin expression and cell fates. A moderate upregulation of Pax6(+5a) promoted delta-catenin expression and induced neurite-like cellular protrusions, but increasing expression of Pax6(+5a) reversed these processes. Furthermore, sustained high expression of Pax6(+5a) triggered apoptosis as determined by the reduction of phospho-Bad, Bcl-2, survivin and procaspases, as well as the increases in Bax and cleaved poly(ADP-ribose) polymerase. Importantly, re-introducing delta-catenin by ectopic expression elicited a feedback suppression on Pax6(+5a) expression and reduced Pax6(+5a) induced apoptosis. Therefore, delta-catenin expression is not only controlled by Pax6, but it also provides a feedback suppression mechanism for their functional interactions with important implications in cellular morphogenesis, apoptosis, and cancer.

PAX6 is expressed in pancreatic cancer and actively participates in cancer progression through activation of the MET tyrosine kinase receptor gene

Tumors of the exocrine pancreas have a poor prognosis. Several proteins are overexpressed in this cancer type, including the MET tyrosine kinase receptor and the transcription factor PAX6. In this report, we find that PAX6(5a), an alternately spliced variant form of PAX6, is expressed in pancreatic carcinoma cell lines at higher levels than the canonical PAX6 protein. Both protein forms of PAX6 bind directly to an enhancer element in the MET promoter and activate the expression of the MET gene. In addition, inhibition of PAX6 transcripts leads to a decline in cell growth and survival, differentiation, and a concurrent reduction of MET protein expression. These data support a model for a neoplastic pathway, where expression of a transcription factor from development activates the MET receptor, a protein that has been directly linked to protumorigenic processes of resisting apoptosis, tumor growth, invasion, and metastasis.

Increased nucleotide polymorphic changes in the 5'-untranslated region of delta-catenin (CTNND2) gene in prostate cancer

Cancer pathogenesis involves multiple genetic and epigenetic alterations, which result in oncogenic changes in gene expression. delta-Catenin (CTNND2) is overexpressed in cancer, although the mechanisms of its upregulation are highly variable. Here we report that in prostate cancer, the methylation of CpG islands in the delta-catenin promoter was not a primary regulatory event. There was also no delta-catenin gene amplification. However, using the single-strand conformation polymorphism analysis, we observed the increased nucleotide changes in the 5'-untranslated region of delta-catenin gene in human prostate cancer. At least one such change (-9 G>A) is a true somatic point mutation associated with a high Gleason's score, poorly differentiated prostatic adenocarcinoma. Laser capture microdissection coupled with PCR analyses detected the mutation only in cancerous but not in the adjacent benign prostatic tissues. Using chimeric genes encoding the luciferase reporter, we found that this mutation, but not a random mutation or a mutation that disrupts an upstream open reading frame, resulted in a remarkably higher expression and enzyme activity. This mutation did not affect transcriptional efficiency, suggesting that it promotes delta-catenin translation. This is the first report of delta-catenin gene mutation in cancer and supports the notion that multiple mechanisms contribute to its increased expression in carcinogenesis.

Pax genes in embryogenesis and oncogenesis

The paired box genes are a family of nine developmental control genes, which in human beings (PAX) and mice (Pax) encode nuclear transcription factors. The temporal and spatial expressions of these highly conserved genes are tightly regulated during foetal development including organogenesis. PAY/Paxgenes are switched off during the terminal differentiation of most structures. Specific mutations within a number of PAX/Pax genes lead to developmental abnormalities in both human beings and mice. Mutation in PAX3 causes Waardenburg syndrome, and craniofacial-deafness-hand syndrome. The Splotch phenotype in mouse exhibits defects in neural crest derivatives such as, pigment cells, sympathetic ganglia and cardiac neural crest-derived structures. The PAX family also plays key roles in several human malignancies. In particular, PAX3 is involved in rhabdomyosarcoma and tumours of neural crest origin, including melanoma and neuroblastoma. This review critically evaluates the roles of PAX/Pax in oncogenesis. It especially highlights recent advances in knowledge of how their genetic alterations directly interfere in the transcriptional networks that regulate cell differentiation, proliferation, migration and survival and may contribute to oncogenesis.