Identification of Pax protein inhibitors that suppress target gene expression and cancer cell proliferation.

The Pax family of developmental control genes are frequently deregulated in human disease. In the kidney, Pax2 is expressed in developing nephrons but not in adult proximal and distal tubules, whereas polycystic kidney epithelia or renal cell carcinoma continues to express high levels. Pax2 reduction in mice or cell culture can slow proliferation of cystic epithelial cells or renal cancer cells. Thus, inhibition of Pax activity may be a viable, cell-type-specific therapy. We designed an unbiased, cell-based, high-throughput screen that identified triazolo pyrimidine derivatives that attenuate Pax transactivation ability. We show that BG-1 inhibits Pax2-positive cancer cell growth and target gene expression but has little effect on Pax2-negative cells. Chromatin immunoprecipitation suggests that these inhibitors prevent Pax protein interactions with the histone H3K4 methylation complex at Pax target genes in renal cells. Thus, these compounds may provide structural scaffolds for kidney-specific inhibitors with therapeutic potential.

Reduced PAX2 expression in murine fallopian tube cells enhances estrogen receptor signaling.

High-grade serous ovarian cancer (HGSOC) is thought to progress from a series of precursor lesions in the fallopian tube epithelium (FTE). One of the preneoplastic lesions found in the FTE is called a secretory cell outgrowth (SCOUT), which is partially defined by a loss of paired box 2 (PAX2). In the present study, we developed PAX2-deficient murine cell lines in order to model a SCOUT and to explore the role of PAX2 loss in the etiology of HGSOC. Loss of PAX2 alone in the murine oviductal epithelium (MOE) did not induce changes in proliferation, migration and survival in hypoxia or contribute to resistance to first line therapies, such as cisplatin or paclitaxel. RNA sequencing of MOE PAX2shRNA cells revealed significant alterations in the transcriptome. Silencing of PAX2 in MOE cells produced a messenger RNA expression pattern that recapitulated several aspects of the transcriptome of previously characterized human SCOUTs. RNA-seq analysis and subsequent qPCR validation of this SCOUT model revealed an enrichment of genes involved in estrogen signaling and an increase in expression of estrogen receptor α. MOE PAX2shRNA cells had higher estrogen signaling activity and higher expression of putative estrogen responsive genes both in the presence and absence of exogenous estrogen. In summary, loss of PAX2 in MOE cells is sufficient to transcriptionally recapitulate a human SCOUT, and this model revealed an enrichment of estrogen signaling as a possible route for tumor progression of precursor lesions in the fallopian tube.

Pseudolaric acid B inhibits PAX2 expression through Wnt signaling and induces BAX expression, therefore promoting apoptosis in HeLa cervical cancer cells.

OBJECTIVES: Pseudolaric acid B (PAB) has been shown to inhibit the growth of various tumor cells, but the molecular details of its function are still unknown. This study investigated the molecular mechanisms by which PAB induces apoptosis in HeLa cells. METHODS: The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were performed to investigate the effect of PAB treatment in various cervical cancer cell lines. Annexin V/propidium iodide staining combined with flow cytometry and Hoechst 33258 staining were used to assess PAB-induced apoptosis. Additionally, we performed bioinformatics analyses and identified a paired box 2 (PAX2) binding site on the BAX promoter. We then validated the binding using luciferase and chromatin immunoprecipitation assays. Finally, western blotting assays were used to investigate PAB effect on the Wnt signaling and the involved signaling molecules. RESULTS: PAB promotes apoptosis and downregulates PAX2 expression in HeLa cells in a time- and concentration-dependent manner. PAX2 binds to the promoter of BAX and inhibits its expression; therefore, PAX2 inhibition is associated with increased levels of BAX, which induces apoptosis of HeLa cells via the mitochondrial pathway. Additionally, PAB inhibits classical Wnt signaling. CONCLUSION: PAB effectively inhibits Wnt signaling and PAX2 expression, and increases BAX levels, which induce apoptosis in HeLa cells. Therefore, PAB is a promising natural molecule for the treatment of cervical cancer.

Pax2 is essential for proliferation and osteogenic differentiation of mouse mesenchymal stem cells via Runx2.

Mesenchymal stem cells (MSCs) have been widely studied in the field of regenerative medicine with the potential to solve osteoporosis. Paired box 2 (Pax2), as a transcription factor, is the master regulator of embryogenesis and oncogenesis. However, the function of Pax2 in osteogenesis is unknown. Here, we reported for the first time that the expression of Pax2 gradually increased during osteogenic differentiation of mouse MSCs, and osteoprogenitor cells. However, detected in osteoblastic cells of mouse tibia, the expression of Pax2 in the embryonic stage was higher than that in adulthood. In C3H/10/T1/2 cells and compact bone-derived mouse MSCs (mMSCs), Pax2 knock-down inhibited the proliferation of these cells, down-regulated the expression of osteogenic marker genes, as well as repressed the ALP activity and mineralization. In addition, Pax2 enhanced the transcriptional activity of Runx2, and activated the MAPK pathway genes (ERK, JNK and p38). Furthermore, knock-down of Pax2 repressed the mMSCs-mediated bone regeneration in an ectopic bone formation model. In conclusion, Pax2 promotes osteogenesis of mouse MSCs, suggesting that Pax2 has a role in the pathophysiology of bone related diseases, and has potential application in bone tissue regeneration.

Are Pax proteins potential therapeutic targets in kidney disease and cancer?

Pax genes encode developmental regulators that are expressed in a variety of tissues and control critical events in morphogenesis. In the kidney, Pax2 and Pax8 are expressed in embryonic development and in specific renal diseases associated with aberrant epithelial cell proliferation. Prior genetic and cell biological studies suggest that reducing the activity of Pax proteins in renal cancer or in polycystic kidney disease can slow the progression of these conditions. The Pax proteins may be critical for providing tissue and locus specificity to recruit epigenetic modifiers that control gene expression and chromatin structure. Although they are nuclear, targeting Pax proteins to inhibit function may be feasible with small molecules. Such inhibition of Pax protein function may provide novel therapies for subsets of renal disorders that are tissue- and cell type-specific and avoid systemic effects on non-Pax-expressing cells and tissues. Given the paucity of effective treatments for renal cancer and cystic disease, the Pax family of proteins represents new pharmaceutical targets that merit exploration and further development.

Inhibition of Pax2 Transcription Activation with a Small Molecule that Targets the DNA Binding Domain.

The Pax gene family encodes DNA binding transcription factors that control critical steps in embryonic development and differentiation of specific cell lineages. Often, Pax proteins are re-expressed or ectopically expressed in cancer and other diseases of abnormal proliferation, making them attractive targets for tissue specific inhibition by small molecules. In this report, we used a homology model of the Pax2 paired domain and a virtual screen to identify small molecules that can inhibit binding of the paired domain to DNA and Pax2 mediated transcription activation. Candidates from the virtual screen were then confirmed in a cell based Pax2 transactivation assay. Subsequently, we tested analogs of these hits to identify a single compound that effectively blocked Pax2 activity and DNA binding with a Kd of 1.35-1.5 µM. The compound, termed EG1, was used to inhibit embryonic kidney development, a process directly dependent on Pax2 activity. Furthermore, we show that EG1 can inhibit proliferation of Pax2 positive renal and ovarian cancer cell lines but has little effect on Pax2 negative cancer cells. These data confirm that small molecules targeting the DNA binding paired domain can be identified and may be good lead compounds for developing tissue and cell-type specific anticancer therapies.

PAX2 function, regulation and targeting in fallopian tube-derived high-grade serous ovarian cancer.

The fallopian tube epithelium (FTE) is one of the progenitor populations for high-grade serous ovarian cancer (HGSC). Loss of PAX2 is the earliest known molecular aberration in the FTE occurring in serous carcinogenesis followed by a mutation in p53. Pathological studies report consistent loss of PAX2 in benign lesions as well as serous tumors. In the current study, the combined loss of PAX2 and expression of the R273H p53 mutant protein in murine oviductal epithelial (MOE) cells enhanced proliferation and growth in soft agar in vitro but was insufficient to drive tumorigenesis in vivo. A serially passaged model was generated to investigate the role of aging, but was also insufficient to drive tumorigenesis. These models recapitulate early benign lesions and suggest that a latency period exists between loss of PAX2, p53 mutation and tumor formation. Stathmin and fut8 were identified as downstream targets regulated by loss of PAX2 and mutation of p53 in MOE cells. Re-expression of PAX2 in PAX2-null human HGSC cells reduced cell survival via apoptosis. Phosphatase and tensin homolog (PTEN)shRNA negatively regulated PAX2 expression and stable re-expression of PAX2 in MOE:PTENshRNA cells significantly reduced proliferation and peritoneal tumor formation in athymic nude mice. PAX2 was determined to be a direct transcriptional target that was activated by wild-type p53, whereas mutant p53 inhibited PAX2 transcription in MOE cells. A small molecule screen using the proximal PAX2 promoter driving luciferase identified four small molecules that were able to enhance PAX2 mRNA expression in MOE cells. PAX2 re-expression in HGSC cells and PTEN-deficient oviductal tumors may have the potential to induce apoptosis. In summary, mutant p53 and PTEN loss negatively regulated PAX2 and PAX2 re-expression in HGSC cells induced cell death.

Involvement of pax2 in ovarian development and recrudescence of catfish: a role in steroidogenesis.

PAX2, a member of paired box family, is an essential transcription factor for the organ development in vertebrates including teleosts, yet no evidence has been shown for its involvement in reproduction. To study this, partial- and/or full-length cDNA of pax2 was isolated from the ovary of catfish, Clarias batrachus, along with its other Pax family members, pax1 and pax9 Tissue distribution and ontogeny expression analysis indicated the prevalence of pax2 but not pax1 and pax9 in ovary. Varied phase-wise expression during ovarian cycle and elevation of pax2 after human chorionic gonadotropin induction showed probable regulation by gonadotropins. Pax2 could be localized in various stages of oocytes and in follicular layer of vitellogenic and post-vitellogenic oocytes. To assess the functional significance of pax2, transient RNA silencing was performed using primary catfish ovarian follicle culture, in vitro, and in catfish, in vivo, through ovary-targeted injection of PEI-esiRNA. Pax2 siRNA treatment reduced the expression of various transcripts related to ovarian development like signaling molecules such as wnt4 and wnt5, estrogen receptors, several steroidogenic enzymes and transcription factors. These transitions in transcript levels might have been mediated by Pax2 acting upstream of wnt4/5 that may play a role in steroidogenesis and/or ovarian development along with ad4bp/sf-1 or by direct or indirect interaction with steroidogenic enzyme genes, which is evident from the change in the levels of serum estradiol-17ß but not 17α,20ß-dihydroxy-4-pregnen-3-one. Taken together, it seems that pax2 has a plausible role during ovarian development and/or recrudescence of catfish either directly or indirectly through Wnt signaling pathway.

PAX2 is activated by estradiol in breast cancer cells of the luminal subgroup selectively, to confer a low invasive phenotype.

BACKGROUND: Metastasis is the leading cause of death among breast cancer patients. Identifying key cellular factors controlling invasion and metastasis of breast cancer cells should pave the way to new therapeutic strategies efficiently interfering with the metastatic process. PAX2 (paired box 2) transcription factor is expressed by breast cancer cells in vivo and recently, it was shown to negatively regulate the expression of ERBB2 (erythroblastic leukemia viral oncogene homolog 2, HER-2/neu), a well-documented pro-invasive and pro-metastastic gene, in luminal/ERalpha-positive (ERα+) breast cancer cells. The objective of the present study was to investigate a putative role for PAX2 in the control of luminal breast cancer cells invasion, and to begin to characterize its regulation. RESULTS: PAX2 activity was higher in cell lines from luminal compared to non-luminal subtype, and activation of PAX2 by estradiol was selectively achieved in breast cancer cell lines of the luminal subtype. This process was blocked by ICI 182780 and could be antagonized by IGF-1. Knockdown of PAX2 in luminal MCF-7 cells completely abrogated estradiol-induced downregulation of ERBB2 and decrease of cell invasion, whereas overexpression of PAX2 in these cells enhanced estradiol effects on ERBB2 levels and cell invasion. CONCLUSIONS: The study demonstrates that PAX2 activation by estradiol is selectively achieved in breast cancer cells of the luminal subtype, via ERα, and identifies IGF-1 as a negative regulator of PAX2 activity in these cells. Further, it reveals a new role for PAX2 in the maintenance of a low invasive behavior in luminal breast cancer cells upon exposure to estradiol, and shows that overexpression and activation of PAX2 in these cells is sufficient to reduce their invasive ability.

The transcription factor PAX2 regulates ADAM10 expression in renal cell carcinoma.

ADAM10 is a metalloprotease that plays an important role in the progression and metastasis of various cancers. In the present study, we present compelling evidence that PAX2 can bind to the promotor of ADAM10 and regulate ADAM10 protein expression in renal cancer cells. We further show that ADAM10 is the major sheddase for the constitutive cleavage of L1-CAM and c-Met, two important proteins involved in the progression of renal cancer. The downregulation of ADAM10 led to a more scattered cell phenotype, which was accompanied by the induction of Slug and the loss of E-cadherin, which is observed during epithelial-to-mesenchymal transition (EMT). In addition, the downregulation of ADAM10 reduced the proliferation but induced the migration of renal cancer cells. Notably, the downregulation of PAX2 led to an increased L1-CAM expression, which was accompanied by a massive metalloprotease-mediated release of soluble L1-CAM. Importantly, soluble L1-CAM induced the proliferation of endothelial cells and the migration of renal cancer cells. Finally, we can demonstrate that the silencing of PAX2 led to an L1-CAM-dependent activation of the PI3K/Akt pathway, one important pathway mediating cancer cell survival. In summary, we identified PAX2 as a regulator of L1-CAM and ADAM10, which play crucial roles in the progression of various cancers including renal cell carcinoma and the downregulation of ADAM10 maybe an earlier step in renal cancer development as it seems to be involved in processes of EMT.

Prolyl hydroxylase domain protein 3 targets Pax2 for destruction.

Prolyl hydroxylase domain proteins (PHDs) hydroxylate HIFα in the presence of oxygen, leading to HIFα proteasomal destruction. The PHDs family comprises PHD1, 2, and 3. Recent studies indicate that, in addition to HIFα, PHDs have other substrates. Paired box (Pax) 2, a transcription factor, was found aberrantly expressed in a variety of cancers. However, the underlying mechanisms remain unknown. Here we demonstrate that PHD3 is a negative regulator of expression of Pax2. We found that PHD3 bound to Pax2 and mediated Pax2 destruction directly. Inhibition of PHD3 hydroxylase activity led to upregulation of Pax2 protein but not mRNA level. We found that Pax2 protein was increased and PHD3 protein was decreased in colorectal cancer, and the increased Pax2 was associated with decreased PHD3. Our results suggest that PHD3 targets Pax2 for destruction. The findings may disclose a mechanism for the regulation of Pax2 expression in cancer cells.

Inhibition of PAX2 expression results in alternate cell death pathways in prostate cancer cells differing in p53 status.

Inhibition of apoptosis is a critical pathophysiological factor that contributes to the development of prostate cancer. Recently, PAX2, a transcriptional regulator implicated in oncogenesis, has been demonstrated to be expressed by prostate cancer. However, its downstream molecular pathways for suppression of apoptosis, other than the tumor suppressor gene p53, have yet to be elucidated. Here, we examine the effects of inhibiting PAX2 expression by prostate cancer cells that differ in p53 gene status. These data collectively demonstrate that PAX2 inhibition results in cell death independent of p53, and that additional tumor suppressors or cell death pathways may be inhibited by PAX2 in prostate cancer cells.

PAX2 inactivation enhances cisplatin-induced apoptosis in renal carcinoma cells.

Renal cell carcinoma (RCC) is the most common kidney malignancy and has a poor prognosis owing to its resistance to chemotherapy. RCC cells overexpress the transcription factor, PAX2, normally expressed in fetal kidney but downregulated at birth. Since Pax2 suppresses apoptosis during renal development, we reasoned that PAX2 may confer resistance to cisplatin-induced apoptosis in RCC. Here, we show that PAX2 confers resistance to cisplatin-induced apoptosis in normal kidney cells and fetal kidney explants. Human embryonic kidney 293 cells transfected with a PAX2 expression vector and exposed to cisplatin (40 microM) exhibited 45 +/- 15% as much caspase-3 cleavage compared to control cells. Conversely, murine collecting duct cells stably transfected with PAX2 antisense cDNA had twofold increase in cisplatin-induced apoptosis. Murine fetal (embryonic day 15) kidney explants from PAX2(1Neu)+/- mice exposed to cisplatin (25 microM x 24 h) had 50% increased apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling staining). We then show that RCC cells (CAKI-1 (human, Caucasian, kidney, carcinoma) and ACHN (human, Caucasian, kidney, adenocarcinoma)) express PAX2 protein. PAX2-small interfering RNA (100 nM) reduces endogenous PAX2 protein (10% of baseline) and induces apoptosis (Annexin-V staining). Pax2 knockdown sensitized RCC cells to cisplatin-induced apoptosis, killing 50-60% of cisplatin-resistant ACHN and CAKI-1 cells. These findings suggest that PAX2 confers resistance to cisplatin-induced apoptosis in non-transformed kidney cells and fetal kidney explants. Similarly, Pax2 overexpression in RCC cells contributes to cisplatin resistance. Conceivably, a therapeutic strategy that inactivates Pax2 in vivo might enhance the efficacy of conventional cytotoxic drugs against RCC.

Expression of Pax2 in human renal tumor-derived endothelial cells sustains apoptosis resistance and angiogenesis.

The transcription factor Pax2 is known to play a key role during renal development and to act as an oncogene favoring renal tumor growth. We recently showed that endothelial cells derived from human renal carcinomas display abnormal characteristics of survival and angiogenic properties. In the present study we found that renal tumor-derived endothelial cells, but not normal endothelial cells, expressed Pax2 protein and mRNA. To down-regulate Pax2 expression, we transfected tumor-derived endothelial cells with an anti-sense PAX2 vector whereas we transfected normal human microvascular endothelial cells with a sense PAX2 vector to induce Pax2 expression. The inhibition of Pax2 expression in tumor-derived endothelial cells induced an increase in tumor suppressor PTEN expression and a decrease in Akt phosphorylation. In addition, decreased apoptosis resistance, adhesion, invasion, and in vitro and in vivo angiogenesis were observed. Conversely, Pax2 induction in normal endothelial cells conferred to these cells a proinvasive, proangiogenic phenotype similar to that of tumor-derived endothelial cells. These results indicate that Pax2 is involved in renal tumor angiogenesis and its expression may antagonize that of the PTEN tumor suppressor gene, affecting the Akt-survival pathway and promoting angiogenesis.