EYA1 phosphatase function is essential to drive breast cancer cell proliferation through cyclin D1

Methylation of the phosphatase-transcription activator EYA1 by protein arginine methyltransferase 1: mechanistic, functional, and structural studies

The eyes absent (EYA) family proteins are conserved transcriptional coactivators with intrinsic protein phosphatase activity. They play an essential role in the development of various organs in metazoans. These functions are associated with a unique combination of phosphatase and transactivation activities. However, it remains poorly understood how these activities and the consequent biologic functions of EYA are regulated. Here, we demonstrate that 2 conserved arginine residues, R304 and R306, of EYA1 are essential for its in vitro phosphatase activity and in vivo function during Drosophila eye development. EYA1 physically interacts with protein arginine methyltransferase 1, which methylates EYA1 at these residues both in vitro and in cultured mammalian and insect cells. Moreover, we show that wild-type, but not methylation-defective, EYA1 associates with γ-H2A.X in response to ionizing radiation. Taken together, our results identify the conserved arginine residues of EYA1 that play an important role for its activity, thus implicating arginine methylation as a novel regulatory mechanism of EYA function.-Li, X., Eberhardt, A., Hansen, J. N., Bohmann, D., Li, H., Schor, N. F. Methylation of the phosphatase-transcription activator EYA1 by protein arginine methyltransferase 1: mechanistic, functional, and structural studies.

EYA1's Conformation Specificity in Dephosphorylating Phosphothreonine in Myc and Its Activity on Myc Stabilization in Breast Cancer

EYA1 is known to be overexpressed in human breast cancer, in which the Myc protein is also accumulated in association with decreased phospho-T58 (pT58) levels. We have recently reported that EYA1 functions as a unique protein phosphatase to dephosphorylate Myc at pT58 to regulate Myc levels. However, it remains unclear whether EYA1-mediated Myc dephosphorylation on T58 is a critical function in regulating Myc protein stability in breast cancer. Furthermore, EYA1's substrate specificity has remained elusive. In this study, we have investigated these questions, and here, we report that depletion of EYA1 using short hairpin RNA (shRNA) in breast cancer cells destabilizes the Myc protein and increases pT58 levels, leading to an increase in the doubling time and impairment of cell cycle progression. In correlation with EYA1-mediated stabilization of cMyc and reduced levels of pT58, EYA1 greatly reduced cMyc-FBW7 binding and cMyc ubiquitination, thus providing novel insight into how EYA1 acts to regulate the FBW7-mediated Myc degradation machinery. We found that the conserved C-terminal haloacid dehalogenase domain of EYA1, which has been reported to have only tyrosine phosphatase activity, has dual phosphatase activities, and both the N- and C-terminal domains interact with substrates to increase the catalytic activity of EYA1. Enzymatic assay and nuclear magnetic resonance (NMR) analysis demonstrated that EYA1 has a striking conformation preference for phospho-T58 of Myc. Together, our results not only provide novel structural evidence about the conformation specificity of EYA1 in dephosphorylating phosphothreonine in Myc but also reveal an important mechanism contributing to Myc deregulation in human breast cancer.

SIX1 is overexpressed in endometrial carcinoma and promotes the malignant behavior of cancer cells through ERK and AKT signaling

The sineoculis homeobox homolog 1 (SIX1) protein has been found to be important for cancer progression. However, its biological role in human endometrial carcinomas remains unexplored. The potential mechanism of SIX1-induced cancer progression remains unclear. In the present study, SIX1 protein expression was examined in 84 cases of endometrial carcinoma tissues using immunohistochemisty, and SIX1 was found to be overexpressed in 51.1% (43/84) of cervical cancer cells. Small interfering RNA (siRNA) knockdown of SIX1 was also performed in Ishikawa cells with high endogenous SIX1 expression, and SIX1 was overexpressed in the HEC1B cell line with low endogenous expression. SIX1 overexpression promoted cell growth rate and colony formation ability, whereas SIX1 depletion inhibited cell growth and colony formation. Further analysis showed that SIX1 knockdown downregulated, and SIX1 overexpression upregulated, cyclin D1, cyclin E, phosphorylated (p-)extracellular signal-regulated kinase (ERK), and p-protein kinase B (AKT) expression. The ERK inhibitor, U0126, and AKT inhibitor treatments blocked the effect of SIX1 on proliferation. In conclusion, the present study found that SIX1 overexpression promotes cancer cell growth in endometrial carcinoma, possibly through ERK- and AKT-mediated pathways.

EYA4 functions as tumor suppressor gene and prognostic marker in pancreatic ductal adenocarcinoma through β-catenin/ID2 pathway

Eye absent homolog 4 (EYA4) was initially found as key gene in controlling eye development in Drosophila. We recently found that EYA4 was an independent prognostic factor in hepatocellular carcinoma. Its biological functions in malignancies remained unknown. The present study aimed at investigating its biological functions, molecular mechanisms and prognostic values in pancreatic ductal adenocarcinoma (PDAC). Overexpression of EYA4 in PDAC cells inhibited proliferation and invasion in vitro and tumor growth in vivo. Depletion of EYA4 in PDAC cells enhanced proliferation and invasion in vitro and tumor growth in vivo. Mechanistically, armed with the serine/threonine-specific protein phosphatase activity, EYA4 dephosphorylated β-catenin at Ser675, blocked β-catenin nuclear translocation and inhibited ID2 transactivation. Consistently, EYA4 expression inversely correlated with the levels of p-Ser675-β-catenin and ID2 in tissues. EYA4 expression in PDAC tissues was significantly reduced as compared with adjacent non-tumoral tissues. EYA4 expression was an independent prognostic factor in PDAC, with a lower EYA4 level in association with shorter long-term survival and disease-free time. We showed that EYA4 functioned as tumor suppressor gene in PDAC via repressing β-catenin/ID2 activation, and was an independent prognostic factor in PDAC.

EYA1 expression and subcellular localization in neuroblastoma and its association with prognostic markers

Neuroblastoma, the most frequently occurring extracranial solid tumor of childhood, arises from neural crest-derived cells that are arrested at an early stage of differentiation in the developing sympathetic nervous system. There is an urgent need to identify clinically relevant biomarkers for better prognosis and treatment of this aggressive malignancy. Eyes Absent 1 (EYA1) is an essential transcriptional coactivator for neuronal developmental programs during organogenesis. Whether or not EYA1 is implicated in neuroblastoma and subcellular localization of EYA1 is relevant to clinical behaviour of neuroblastoma is not known. We studied EYA1 expression and subcellular localization by immunohistochemistry in tissue microarrays containing tumor specimens from 98 patients, 66 of which were characterized by known clinical prognostic markers of neuroblastoma. Immunostaining results were evaluated and statistically correlated with the degree of histologic differentiation and with neuroblastoma risk stratification group characteristics, including stage of disease, patient age, tumor histology and mitosis-karyorrhexis index (MKI), respectively. We found that EYA1 levels were significantly higher in neuroblastomas than in ganglioneuromas and ganglioneuroblastomas. EYA1 was more highly expressed in stage 1,2,3 or 4S tumors as compared to stage 4 tumors (P<0.01). Tumors with high levels of nuclear EYA1 were more frequently associated with high nuclear MYCN levels. These results suggest that modulation of expression and intracellular localization of EYA1 in neural crest cells may provide a novel direction for therapeutic strategies.

MicroRNA-101 inhibits cell proliferation and induces apoptosis by targeting EYA1 in breast cancer

MicroRNAs (miRNAs or miRs) regulate gene expression by negatively modulating the stability or translational efficiency of their target genes by targeting the 3'-untranslated region (3'-UTR). Aberrant miRNA expression has been reported in various types of cancer; miRNAs can function as either oncogenes or tumor suppressor genes in cancer. In this study, we examined the expression level of miR‑101 in breast cancer tissues and cell lines by RT-qPCR, and found that miR‑101 expression was downregulated in breast cancer tissues and cell lines; indeed, in 6 of the 28 tissue samples, miR‑101 could not be detected. Furthermore, miR‑101, when transfected into SKBR3 cells, inhibited cell proliferation and promoted apoptosis, while miR‑101 inhibitor had the opposite effect. A dual-luciferase reporter assay revealed that miR‑101 targeted the 3'-UTR of eyes absent homolog 1 (Drosophila) (EYA1). Western blot analysis demonstrated a significantly decreased protein level of EYA1 in the SKBR3 cells transfected with miR‑101 mimic, whereas transfection with miR‑101 inhibitor led to an increased level of EYA1. Moreover, an increased expression of EYA1 was also found in breast cancer tissues and cell lines. The silencing of EYA1 using siRNA targeting EYA1 (EYA1‑siRNA) significantly inhibited SKBR3 cell proliferation and promoted apoptosis, and also suppressed the increased proliferation induced by transfection with miR‑101 inhibitor. The protein expression levels of Notch signaling components (jagged1, Hes1 and Hey1) were significantly decreased by transfection with miR‑101 mimic and EYA1-siRNA, and were increased by transfection with miR‑101 inhibitor. Furthermore, the elevated protein expression levels of jagged1, Hes1 and Hey1 induced by transfection with miR‑101 inhibitor in the SKBR3 cells were significantly decreased by transfection with EYA1-siRNA. Taken together, these results suggest that miR‑101 is down-regulated in breast cancer, and can inhibit cell proliferation and promote apoptosis by targeting EYA1 through the Notch signaling pathway.

Let-7c blocks estrogen-activated Wnt signaling in induction of self-renewal of breast cancer stem cells

Let-7 miRNAs are involved in carcinogenesis and tumor progression through their roles in maintaining differentiation and normal development. However, there is little research focusing on the effects of let-7 on Wnt-activated self-renewal of breast cancer stem cells. By analyzing the expression levels of let-7 family members in clinical tissues, we found that higher expression levels of let-7b and let-7c were correlated with better clinical prognosis of patients with estrogen receptor (ER)α-positive breast tumor. Further, we found that only let-7c was inversely correlated with ERα expression, and there is corelationship between let-7c and Wnt signaling in clinical tissues. Aldehyde dehydrogenase (ALDH)1 sorting and mammosphere formation assays showed that let-7c inhibited the self-renewal of stem cells in ERα-positive breast cancer. Let-7c decreased ERα expression through directly binding to the 3'UTR (untranslated region), and let-7c inhibited the estrogen-induced activation of Wnt signaling. Depletion of ERα abolished let-7c functions in stem cell signatures, which further confirmed that let-7c inhibited estrogen-induced Wnt activity through decreasing ERα expression. Taken together, our findings identified a biochemical and functional link between let-7c with ERα/Wnt signaling in breast cancer stem cells.

Enrichment of CD44 in basal-type breast cancer correlates with EMT, cancer stem cell gene profile, and prognosis

Cluster of differentiation 44 (CD44) is a transmembrane glycoprotein that serves as the receptor for the extracellular matrix component hyaluronic acid. CD44 has been reported to play key roles in cell proliferation, motility, and survival, but its role in breast cancer remains controversial. In this study, we conducted a meta-analysis. A total of 23 published Gene Expression Omnibus databases were included to evaluate the association between CD44 mRNA expression and clinicopathological characteristics or prognosis of the patients with breast cancer. Our analysis revealed that CD44 expression was associated with clinicopathological features, including the histological grade, estrogen receptor status, progesterone receptor status, and human epidermal growth factor receptor-2 status. Higher levels of CD44 expression were observed in the basal subtype of breast cancer both at the mRNA and protein levels (odds ratio [OR] =2.08, 95% confidence interval [CI]: 1.72–2.52; OR =2.11, 95% CI: 1.67–2.68). Patients with CD44 overexpression exhibited significantly worse overall survival (hazard ratio =1.27; 95% CI: 1.04–1.55). Whole gene profile analysis revealed that CD44 expression was enriched in basal-type breast cancer and correlated with epithelial–mesenchymal transition and cancer stem cell gene profiles. In summary, our analyses indicated that CD44 potentially might be a prognostic marker for breast cancer and thus can serve as a therapeutic target for basal-type breast cancer.

Multiple Functions of the Eya Phosphotyrosine Phosphatase

Eyes absent (Eya), a protein conserved from plants to humans and best characterized as a transcriptional coactivator, is also the prototype for a novel class of eukaryotic aspartyl protein tyrosine phosphatases. This minireview discusses recent breakthroughs in elucidating the substrates and cellular events regulated by Eya's tyrosine phosphatase function and highlights some of the complexities, new questions, and surprises that have emerged from efforts to understand how Eya's unusual multifunctionality influences developmental regulation and signaling.

The DACH/EYA/SIX gene network and its role in tumor initiation and progression

The functional abnormality of developmental genes is a common phenomenon in cancer initiation and progression. The retinal determination gene network (RDGN) is a key signal in Drosophila eye specification, and this conservative pathway is also required for the development of multiple organs in mammalian species. Recent studies demonstrated that aberrant expressions of RDGN components in vertebrates, mainly Dach, Six, and Eya, represent a novel tumor signal. RDGN regulates proliferation, apoptosis, tumor growth and metastasis through interactions with multiple signaling pathways in a co-ordinated fashion; Dach acts as a tumor suppressor, whereas Six and Eya function as oncogenes. Clinical analyses demonstrated that the expression levels of RDGN correlate with tumor stage, metastasis and survival, suggesting that combinational detection of this pathway might be used as a promising biomarker for the stratification of therapy and for the prediction of the prognosis of cancer patients.

Interplay of retinal determination gene network with TGF-β signaling pathway in epithelial-mesenchymal transition

As a fundamental event in the generation of tissues and organs during embryogenesis, the epithelial-mesenchymal transition (EMT) has also been implicated in cancer progression by its ability to alter the plasticity of epithelial cells to acquire invasive properties. Evidence is mounting that ectopic activation of transforming growth factors β (TGF-β)/bone morphogenetic protein (BMP) superfamily members to enhance tumorigenesis and metastasis. In this respect, the Retinal Determination Gene Network (RDGN), which was identified to govern the normal initiation of the morphogenetic furrow in Drosophila, has now been found to be de-regulated in various types of cancers, and the key members of this network, DACH, SIX, and EYA, have emerged as novel co-regulators of TGF- signaling during EMT. Understanding the molecular mechanism by which RDGN regulates TGF-β/BMP signaling to influence EMT may lead to novel strategies for targeted therapies.

The Eya1 phosphatase promotes Shh signaling during hindbrain development and oncogenesis

Sonic hedgehog (Shh) signaling is critical in development and oncogenesis, but the mechanisms regulating this pathway remain unclear. Although protein phosphorylation clearly affects Shh signaling, little is known about phosphatases governing the pathway. Here, we conducted a small hairpin RNA (shRNA) screen of the phosphatome and identified Eya1 as a positive regulator of Shh signaling. We find that the catalytically active phosphatase Eya1 cooperates with the DNA-binding protein Six1 to promote gene induction in response to Shh and that Eya1/Six1 together regulate Gli transcriptional activators. We show that Eya1, which is mutated in a human deafness disorder, branchio-oto-renal syndrome, is critical for Shh-dependent hindbrain growth and development. Moreover, Eya1 drives the growth of medulloblastoma, a Shh-dependent hindbrain tumor. Together, these results identify Eya1 and Six1 as key components of the Shh transcriptional network in normal development and in oncogenesis.

DICER1 regulated let-7 expression levels in p53-induced cancer repression requires cyclin D1

Let-7 miRNAs act as tumour suppressors by directly binding to the 3′UTRs of downstream gene products. The regulatory role of let-7 in downstream gene expression has gained much interest in the cancer research community, as it controls multiple biological functions and determines cell fates. For example, one target of the let-7 family is cyclin D1, which promotes G0/S cell cycle progression and oncogenesis, was correlated with endoribonuclease DICER1, another target of let-7. Down-regulated let-7 has been identified in many types of tumours, suggesting a feedback loop may exist between let-7 and cyclin D1. A potential player in the proposed feedback relationship is Dicer, a central regulator of miRNA expression through sequence-specific silencing. We first identified that DICER1 is the key downstream gene for cyclin D1-induced let-7 expression. In addition, we found that let-7 miRNAs expression decreased because of the p53-induced cell death response, with deregulated cyclin D1. Our results also showed that cyclin D1 is required for Nutlin-3 and TAX-induced let-7 expression in cancer repression and the cell death response. For the first time, we provide evidence that let-7 and cyclin D1 form a feedback loop in regulating therapy response of cancer cells and cancer stem cells, and importantly, that alteration of let-7 expression, mainly caused by cyclin D1, is a sensitive indicator for better chemotherapies response.

The SIX1-EYA transcriptional complex as a therapeutic target in cancer

INTRODUCTION

The SIX homeodomain proteins and the eyes absent (EYA) family of co-activators form a bipartite transcription factor complex that promotes the proliferation and survival of progenitor cells during organogenesis and is down-regulated in most adult tissues. Abnormal over-expression of SIX1 and EYA in adult tissue is associated with the initiation and progression of diverse tumor types. Importantly, SIX1 and EYA are often co-overexpressed in tumors, and the SIX1-EYA2 interaction has been shown to be critical for metastasis in a breast cancer model. The EYA proteins also contain protein tyrosine phosphatase activity, which plays an important role in breast cancer growth and metastasis as well as directing cells to the repair pathway upon DNA damage.

AREAS COVERED

This review provides a summary of the SIX1/EYA complex as it relates to development and disease and the current efforts to therapeutically target this complex.

EXPERT OPINION

Recently, there have been an increasing number of studies suggesting that targeting the SIX1/EYA transcriptional complex will potently inhibit tumor progression. Although current attempts to develop inhibitors targeting this complex are still in the early stages, continued efforts toward developing better compounds may ultimately result in effective anti-cancer therapies.

Pin1-based diagnostic and therapeutic strategies for breast cancer

Pin1 is the only known cis-to-trans isomerase that recognizes the phosphorylated pThr/pSer-Pro motifs in many signaling molecules, playing unique roles in the pathogenesis of breast cancer. First, Pin1 is prevalently over-expressed in kinds of breast cancer cell lines and tissues, such as MDA-MB-231 cell, MCF-7 cell, Her2+, ERα+, and basal-like breast cancer subtypes. Second, Pin1 amplifies many oncogenic signaling pathways, inhibits multiple tumor suppressors, promotes the angiogenesis and metastasis of breast cancer cells, and enhances the resistance of breast cancer cells to anti-tumor medicines. Third, inhibiting Pin1 blocks most of these detrimental effects in a great number of breast cancer cell lines. These findings suggest Pin1 as a promising diagnostic biomarker as well as an efficient therapeutic target for breast cancer. It is strongly expected that a Pin1-positive subtype of breast cancers should be extremely concerned and that the therapeutic efficacy of Pin1 inhibitors on breast cancer patients should be evaluated as soon as possible. Nonetheless, Pin1-based therapeutic strategies for breast cancer still deserve some debates. Hence, we give the predictions of several important issues, such as application precondition, side effects, and personalized medication, when Pin1 inhibitors are used in the breast cancer therapy. These proposals are meaningful for the further development of Pin1-based diagnostic and therapeutic strategies in order to conquer breast cancer.

Eya1 interacts with Six2 and Myc to regulate expansion of the nephron progenitor pool during nephrogenesis

Self-renewal and proliferation of nephron progenitor cells and the decision to initiate nephrogenesis are crucial events directing kidney development. Despite recent advancements in defining lineage and regulators for the progenitors, fundamental questions about mechanisms driving expansion of the progenitors remain unanswered. Here we show that Eya1 interacts with Six2 and Myc to control self-renewing cell activity. Cell fate tracing reveals a developmental restriction of the Eya1(+) population within the intermediate mesoderm to nephron-forming cell fates and a common origin shared between caudal mesonephric and metanephric nephrons. Conditional inactivation of Eya1 leads to loss of Six2 expression and premature epithelialization of the progenitors. Six2 mediates translocation of Eya1 to the nucleus, where Eya1 uses its threonine phosphatase activity to control Myc phosphorylation/dephosphorylation and function in the progenitor cells. Our results reveal a functional link between Eya1, Six2, and Myc in driving the expansion and maintenance of the multipotent progenitors during nephrogenesis.

DACH1 inhibits cyclin D1 expression, cellular proliferation and tumor growth of renal cancer cells

Background

Renal cell carcinoma (RCC) is a complex with diverse biological characteristics and distinct molecular signature. New target therapies to molecules that drive RCC initiation and progression have achieved promising responses in some patients, but the total effective rate is still far from satisfaction. Dachshund (DACH1) network is a key signaling pathway for kidney development and has recently been identified as a tumor suppressor in several cancer types. However, its role in renal cell carcinoma has not been fully investigated.

Methods

Immunohistochemical staining for DACH1, PCNA and cyclin D1 was performed on human renal tissue microaraays and correlation with clinic-pathological characteristics was analyzed. In vitro proliferation, apoptosis and in vivo tumor growth were evaluated on human renal cancer cell lines with decitabine treatment or ectopic expression of DACH1. Downstream targets and potential molecular mechanism were investigated through western blot, immunoprecipitation and reporter gene assays.

Results

Expression of DACH1 was significantly decreased in human renal carcinoma tissue. DACH1 protein abundance was inversely correlated with the expression of PCNA and cyclin D1, tumor grade, and TNM stage. Restoration of DACH1 function in renal clear cell cancer cells inhibited in vitro cellular proliferation, S phase progression, clone formation, and in vivo tumor growth. In mechanism, DACH1 repressed cyclin D1 transcription through association with AP-1 protein.

Conclusion

Our results indicated that DACH1 was a novel molecular marker of RCC and it attributed to the malignant behavior of renal cancer cells. Re-activation of DACH1 may represent a potential therapeutic strategy.

Cyclin D1 induction of Dicer governs microRNA processing and expression in breast cancer

Cyclin D1 encodes the regulatory subunit of a holoenzyme that phosphorylates the pRB protein and promotes G₁/S cell cycle progression and oncogenesis. Dicer is a central regulator of miRNA maturation, encoding an enzyme that cleaves double strand RNA or stem-loop-stem RNA into 20–25 nucleotide long small RNA, governing sequence specific gene silencing and heterochromatin methylation. The mechanism by which the cell cycle directly controls the non-coding genome is poorly understood. Here we show that cyclin D1^−/− cells are defective in pre-miRNA processing which is restored by cyclin D1a rescue. Cyclin D1 induces Dicer expression in vitro and in vivo. Dicer is transcriptionally targeted by cyclin D1, via a cdk-independent mechanism. Cyclin D1 and Dicer expression significantly correlates in luminal A and basal-like subtypes of human breast cancer. Cyclin D1 and Dicer maintain heterochromatic histone modification (Tri-m-H3K9). Cyclin D1-mediated cellular proliferation and migration is Dicer-dependent. We conclude that cyclin D1 induction of Dicer coordinates microRNA biogenesis.

The PI3K/Akt signal hyperactivates Eya1 via the SUMOylation pathway

Eya1 is a conserved critical regulator of organ-specific stem cells. Ectopic Eya1 activities, however, promote transformation of mammary epithelial cells. Signals that instigate Eya1 oncogenic activities remain to be determined. Here, we show that Akt1 kinase physically interacts with Eya1 and phosphorylates a conserved consensus site of the Akt kinase. PI3K/Akt signaling enhances Eya1 transcription activity, which largely attributes to the phosphorylation-induced reduction of Eya1 SUMOylation. Indeed, SUMOylation inhibits Eya1 transcription activity; and pharmacologic and genetic activation of PI3K/Akt robustly reduces Eya1 SUMOylation. Wild type but not Akt phosphorylation site mutant Eya1 variant rescues the cell migratory phenotype of EYA1-silenced breast cancer cells, highlighting the importance of Eya1 phosphorylation. Furthermore, knockdown EYA1 sensitizes breast cancer cells to the PI3K/Akt1 inhibitor and irradiation treatments. Thus, the PI3K/Akt signal pathway activates Eya1. These findings further suggest that regulation of SUMOylation by PI3K/Akt signaling is likely an important aspect of tumorigenesis.

Activating mutations in PTPN3 promote cholangiocarcinoma cell proliferation and migration and are associated with tumor recurrence in patients

BACKGROUND & AIMS

The pathogenesis of intrahepatic cholangiocarcinoma (ICC), the second most common hepatic cancer, is poorly understood, and the incidence of ICC is increasing worldwide. We searched for mutations in human ICC tumor samples and investigated how they affect ICC cell function.

METHODS

We performed whole exome sequencing of 7 pairs of ICC tumors and their surrounding nontumor tissues to detect somatic alterations. We then screened 124 pairs of ICC and nontumor samples for these mutations, including 7 exomes. We compared mutations in PTPN3 with tumor recurrence in 124 patients and PTPN3 expression levels with recurrence in 322 patients (the combination of both in 86 patients). The functional effects of PTPN3 variations were determined by RNA interference and transgenic expression in cholangiocarcinoma cell lines (RBE, HCCC-9810, and Huh28).

RESULTS

Based on exome sequencing, pathways that regulate protein phosphorylation were among the most frequently altered in ICC samples and genes encoding protein tyrosine phosphatases (PTPs) were among the most frequently mutated. We identified mutations in 9 genes encoding PTPs in 4 of 7 ICC exomes. In the prevalence screen of 124 paired samples, 51.6% of ICCs contained somatic mutations in at least 1 of 9 PTP genes; 41.1% had mutations in PTPN3. Transgenic expression of PTPN3 in cell lines increased cell proliferation, colony formation, and migration. PTPN3(L232R) and PTPN3(L384H), which were frequently detected in ICC samples, were found to be gain-of-function mutations; their expression in cell lines further increased cell proliferation, colony formation, and migration. ICC-associated variants of PTPN3 altered phosphatase activity. Patients whose tumors contained activating mutations or higher levels of PTPN3 protein than nontumor tissues had higher rates of disease recurrence than patients whose tumors did not have these characteristics.

CONCLUSIONS

Using whole exome sequencing of ICC samples from patients, we found that more than 40% contain somatic mutations in PTPN3. Activating mutations in and high expression levels of PTPN3 were associated with tumor recurrence.

Allosteric inhibitors of the Eya2 phosphatase are selective and inhibit Eya2-mediated cell migration

Eya proteins are essential co-activators of the Six family of transcription factors and contain a unique tyrosine phosphatase domain belonging to the haloacid dehalogenase family of phosphatases. The phosphatase activity of Eya is important for the transcription of a subset of Six1-target genes, and also directs cells to the repair rather than apoptosis pathway upon DNA damage. Furthermore, Eya phosphatase activity has been shown to mediate transformation, invasion, migration, and metastasis of breast cancer cells, making it a potential new drug target for breast cancer. We have previously identified a class of N-arylidenebenzohydrazide compounds that specifically inhibit the Eya2 phosphatase. Herein, we demonstrate that these compounds are reversible inhibitors that selectively inhibit the phosphatase activity of Eya2, but not Eya3. Our mutagenesis results suggest that this class of compounds does not bind to the active site and the binding does not require the coordination with Mg(2+). Moreover, these compounds likely bind within a site on the opposite face of the active site, and function as allosteric inhibitors. We also demonstrate that this class of compounds inhibits Eya2 phosphatase-mediated cell migration, setting the foundation for these molecules to be developed into chemical probes for understanding the specific function of the Eya2 phosphatase and to serve as a prototype for the development of Eya2 phosphatase specific anti-cancer drugs.

The canonical wnt signal restricts the glycogen synthase kinase 3/fbw7-dependent ubiquitination and degradation of eya1 phosphatase

Haploinsufficiency of Eya1 causes the branchio-oto-renal (BOR) syndrome, and abnormally high levels of Eya1 are linked to breast cancer progression and poor prognosis. Therefore, regulation of Eya1 activity is key to its tissue-specific functions and oncogenic activities. Here, we show that Eya1 is posttranslationally modified by ubiquitin and that its ubiquitination level is self-limited to prevent premature degradation. Eya1 has an evolutionarily conserved CDC4 phosphodegron (CPD) signal, a target site of glycogen synthase kinase 3 (GSK3) kinase and Fbw7 ubiquitin ligase, which is required for Eya1 ubiquitination. Genetic deletion of Fbw7 and pharmacological inhibition of GSK3 significantly decrease Eya1 ubiquitination. Conversely, activation of the phosphatidylinositol 3-kinase (PI3K)/Akt and the canonical Wnt signal suppresses Eya1 ubiquitination. Compound Eya1(+/-); Wnt9b(+/-) mutants exhibit an increased penetrance of renal defect, indicating that they function in the same genetic pathway in vivo. Together, these findings reveal that the canonical Wnt and PI3K/Akt signal pathways restrain the GSK3/Fbw7-dependent Eya1 ubiquitination, and they further suggest that dysregulation of this novel axis contributes to tumorigenesis.

Insulin like growth factor 2 regulation of aryl hydrocarbon receptor in MCF-7 breast cancer cells

Insulin like growth factor (IGF)-1 and IGF-2 stimulate normal growth, development and breast cancer cell proliferation. Cyclin D1 (CCND1) promotes cell cycle by inhibiting retinoblastoma protein (RB1). The aryl hydrocarbon receptor (AHR) is a major xenobiotic receptor that also regulates cell cycle. The purpose of this study was to investigate whether IGF-2 promotes MCF-7 breast cancer proliferation by inducing AHR. Western blot and quantitative real time PCR (Q-PCR) analysis revealed that IGF-2 induced an approximately 2-fold increase (P<.001) in the expression of AHR and CCND1. Chromatin immunoprecipitation (ChIP), followed by Q-PCR indicated that IGF-2 promoted (P<.001) a 7-fold increase in AHR binding on the CCND1 promoter. AHR knockdown significantly (P<.001) inhibited IGF-2 stimulated increases in CCND1 mRNA and protein. AHR knockdown cells were less (P<.001) responsive to the proliferative effects of IGF-2 than control cells. Collectively, our findings have revealed a new regulatory mechanism by which IGF-2 induction of AHR promotes the expression of CCND1 and the proliferation of MCF-7 cells. This previously uncharacterized pathway could be important for the proliferation of IGF responsive cancer cells that also express AHR.

Structure-activity relationships of benzbromarone metabolites and derivatives as EYA inhibitory anti-angiogenic agents

The tyrosine phosphatase activity of the phosphatase-transactivator protein Eyes Absent (EYA) is angiogenic through its roles in endothelial cell migration and tube formation. Benzbromarone, a known anti-gout agent, was previously identified as an inhibitor of EYA with anti-angiogenic properties. Here we show that the major metabolite of BBR, 6-hydroxy benzbromarone, is a significantly more potent inhibitor of cell migration, tubulogenesis and angiogenic sprouting. In contrast, other postulated metabolites of BBR such as 5-hydroxy benzbromaorne and 1’-hydroxy benzbromarone are less potent inhibitors of EYA tyrosine phosphatase activity as well as being less effective in cellular assays for endothelial cell migration and angiogenesis. Longer substituents at the 2 position of the benzofuran ring promoted EYA3 binding and inhibition, but were less effective in cellular assays, likely reflecting non-specific protein binding and a resulting reduction in free, bio-available inhibitor. The observed potency of 6-hydroxy benzbromarone is relevant in the context of the potential re-purposing of benzbromarone and its derivatives as anti-angiogenic agents. 6-hydroxy benzbromarone represents a metabolite with a longer half-life and greater pharmacological potency than the parent compound, suggesting that biotransformation of benzbromarone could contribute to its therapeutic activity.

CDK6 binds and promotes the degradation of the EYA2 protein

Cyclin-dependent kinase 6 (Cdk6) is a D-Cyclin-activated kinase that is directly involved in driving the cell cycle through inactivation of pRB in G₁ phase. Increasingly, evidence suggests that CDK6, while directly driving the cell cycle, may only be essential for proliferation of specialized cell types, agreeing with the notion that CDK6 also plays an important role in differentiation. Here, evidence is presented that CDK6 binds to and promotes degradation of the EYA2 protein. The EYA proteins are a family of proteins that activate genes essential for the development of multiple organs, regulate cell proliferation, and are misregulated in several types of cancer. This interaction suggests that CDK6 regulates EYA2 activity, a mechanism that could be important in development and in cancer.