An ABC Transporter Drives Medulloblastoma Pathogenesis by Regulating Sonic Hedgehog Signaling

Mutations in Sonic hedgehog (SHH) signaling promote aberrant proliferation and tumor growth. SHH-medulloblastoma (MB) is among the most frequent brain tumors in children less than 3 years of age. Although key components of the SHH pathway are well-known, we hypothesized that new disease-modifying targets of SHH-MB might be identified from large-scale bioinformatics and systems biology analyses. Using a data-driven systems biology approach, we built a MB-specific interactome. The ATP-binding cassette transporter ABCC4 was identified as a modulator of SHH-MB. Accordingly, increased ABCC4 expression correlated with poor overall survival in patients with SHH-MB. Knockdown of ABCC4 expression markedly blunted the constitutive activation of the SHH pathway secondary to Ptch1 or Sufu insufficiency. In human tumor cell lines, ABCC4 knockdown and inhibition reduced full-length GLI3 levels. In a clinically relevant murine SHH-MB model, targeted ablation of Abcc4 in primary tumors significantly reduced tumor burden and extended the lifespan of tumor-bearing mice. These studies reveal ABCC4 as a potent SHH pathway regulator and a new candidate to target with the potential to improve SHH-MB therapy. SIGNIFICANCE: These findings identify ABCC4 transporter as a new target in SHH-MB, prompting the development of inhibitors or the repurporsing of existing drugs to target ABCC4.

Novel role of Giα2 in cell migration: Downstream of PI3-kinase-AKT and Rac1 in prostate cancer cells

Tumor cell motility is the essential step in cancer metastasis. Previously, we showed that oxytocin and epidermal growth factor (EGF) effects on cell migration in prostate cancer cells require Giα2 protein. In the current study, we investigated the interactions among G-protein coupled receptor (GPCR), Giα2, PI3-kinase, and Rac1 activation in the induction of migratory and invasive behavior by diverse stimuli. Knockdown and knockout of endogenous Giα2 in PC3 cells resulted in attenuation of transforming growth factor β1 (TGFβ1), oxytocin, SDF-1α, and EGF effects on cell migration and invasion. In addition, knockdown of Giα2 in E006AA cells attenuated cell migration and overexpression of Giα2 in LNCaP cells caused significant increase in basal and EGF-stimulated cell migration. Pretreatment of PC3 cells with Pertussis toxin resulted in attenuation of TGFβ1- and oxytocin-induced migratory behavior and PI3-kinase activation without affecting EGF-induced PI3-kinase activation and cell migration. Basal- and EGF-induced activation of Rac1 in PC3 and DU145 cells were not affected in cells after Giα2 knockdown. On the other hand, Giα2 knockdown abolished the migratory capability of PC3 cells overexpressing constitutively active Rac1. The knockdown or knockout of Giα2 resulted in impaired formation of lamellipodia at the leading edge of the migrating cells. We conclude that Giα2 protein acts at two different levels which are both dependent and independent of GPCR signaling to induce cell migration and invasion in prostate cancer cells and its action is downstream of PI3-kinase-AKT-Rac1 axis.

Mouse medulloblastoma driven by CRISPR activation of cellular Myc

MYC-driven Group 3 (G3) medulloblastoma (MB) is the most aggressive of four molecular subgroups classified by transcriptome, genomic landscape and clinical outcomes. Mouse models that recapitulate human G3 MB all rely on retroviral vector-induced Myc expression driven by viral regulatory elements (Retro-Myc tumors). We used nuclease-deficient CRISPR/dCas9-based gene activation with combinatorial single guide RNAs (sgRNAs) to enforce transcription of endogenous Myc in Trp53-null neurospheres that were orthotopically transplanted into the brains of naïve animals. Three combined sgRNAs linked to dCas9-VP160 induced cellular Myc expression and large cell anaplastic MBs (CRISPR-Myc tumors) which recapitulated the molecular characteristics of mouse and human G3 MBs. The BET inhibitor JQ1 suppressed MYC expression in a human G3 MB cell line (HD-MB03) and CRISPR-Myc, but not in Retro-Myc MBs. This G3 MB mouse model in which Myc expression is regulated by its own promoter will facilitate pre-clinical studies with drugs that regulate Myc transcription.

JunD Is Required for Proliferation of Prostate Cancer Cells and Plays a Role in Transforming Growth Factor-β (TGF-β)-induced Inhibition of Cell Proliferation

TGF-β inhibits proliferation of prostate epithelial cells. However, prostate cancer cells in advanced stages become resistant to inhibitory effects of TGF-β. The intracellular signaling mechanisms involved in differential effects of TGF-β during different stages are largely unknown. Using cell line models, we have shown that TGF-β inhibits proliferation in normal (RWPE-1) and prostate cancer (DU145) cells but does not have any effect on proliferation of prostate cancer (PC3) cells. We have investigated the role of Jun family proteins (c-Jun, JunB, and JunD) in TGF-β effects on cell proliferation. Jun family members were expressed at different levels and responded differentially to TGF-β treatment. TGF-β effects on JunD protein levels, but not mRNA levels, correlated with its effects on cell proliferation. TGF-β induced significant reduction in JunD protein in RWPE-1 and DU145 cells but not in PC3 cells. Selective knockdown of JunD expression using siRNA in DU145 and PC3 cells resulted in significant reduction in cell proliferation, and forced overexpression of JunD increased the proliferation rate. On the other hand, knockdown of c-Jun or JunB had little, if any, effect on cell proliferation; overexpression of c-Jun and JunB decreased the proliferation rate in DU145 cells. Further studies showed that down-regulation of JunD in response to TGF-β treatment is mediated via the proteasomal degradation pathway. In conclusion, we show that specific Jun family members exert differential effects on proliferation in prostate cancer cells in response to TGF-β, and inhibition of cell proliferation by TGF-β requires degradation of JunD protein.

The Interaction of Myc with Miz1 Defines Medulloblastoma Subgroup Identity

Four distinct subgroups of cerebellar medulloblastomas (MBs) differ in their histopathology, molecular profiles, and prognosis. c-Myc (Myc) or MycN overexpression in granule neuron progenitors (GNPs) induces Group 3 (G3) or Sonic Hedgehog (SHH) MBs, respectively. Differences in Myc and MycN transcriptional profiles depend, in part, on their interaction with Miz1, which binds strongly to Myc but not MycN, to target sites on chromatin. Myc suppresses ciliogenesis and reprograms the transcriptome of SHH-dependent GNPs through Miz1-dependent gene repression to maintain stemness. Genetic disruption of the Myc/Miz1 interaction inhibited G3 MB development. Target genes of Myc/Miz1 are repressed in human G3 MBs but not in other subgroups. Therefore, the Myc/Miz1 interaction is a defining hallmark of G3 MB development.

Abstract 2977: Myc and Miz1 in medulloblastoma

Medulloblastoma (MB) is the most common malignant pediatric brain tumor, which arises in the cerebellum. Human MBs are classified into four subgroups: Wingless (WNT), Sonic Hedgehog (SHH), Group 3 (G3) and Group 4 (G4). In 2012, we developed a mouse model of the most aggressive and least curable G3 MB, by overexpressing MYC but not MYCN, in Trp53-null cerebellar granule neuron progenitors (GNPs), which were implanted into the cortices of recipient CD-1 nu/nu mice. Remarkably, enforced expression of MYCN in Trp53-null GNPs induced a SHH MB. This was unexpected since MYC and MYCN bind to the same E-box DNA binding sequences. We hypothesized that the difference between MYC- and MYCN-induced MBs might be due to their interaction with different partners in GNPs. Human G3 MBs are distinguished by MYC overexpression. The MYC proto-oncogene encodes a bHLH/leucine-zipper transcription factor that forms heterodimers with MAX to drive transcription. However, MYC can repress transcription when the MYC/MAX heterodimer is recruited to core promoter sequences by MIZ1, a member of the POZ-domain/zinc-finger transcription factor. MIZ1, ubiquitously expressed during embryonic development, can either be a transcription activator or repressor depending on its binding partners.

To investigate whether the MYC/MIZ1 complex contributed to G3 MBs, we used a mutant of MYC which no longer binds to MIZ1 in which a Valine is substituted for an Aspartic acid amino acid at position 394 (MYCV394D). We enforced the expression of MYC or MYCV394D in GNPs purified from seven-day-old Trp53-null mouse pups using retroviral transduction, and implanted transduced GNPs into the cerebral cortices of recipient mice. MYCV394D-induced tumors developed later than MYC-induced G3 MBs. Histopathological analysis revealed that MYC-induced tumors exhibited a large cell/anaplastic (LCA) phenotype and were classified as G3 MBs; however, MYCV394D-induced tumors were described as unclassified primitive neuroectodermal tumors. In vitro, MYCV394D-induced tumors formed tumorspheres that were highly apoptotic and less proliferative compared to MYC tumorspheres. Global gene expression of MYCV394D tumors was distinct from murine G3 and SHH subgroup MBs. Particularly, genes needed for neuronal differentiation and which are strongly repressed by MYC in G3 MBs, were no longer repressed by the MYCV394D mutant, indicating that the MYC/MIZ1 complex was responsible for their repression.

To analyze whether the MYC/MIZ1 complex was present on chromatin in G3 MBs, we performed ChIP-Seq for MYC and MIZ1. In contrast to Trp53-null GNPs, where MIZ1 only binds 140 promoters, 11.549 promoters were occupied by MIZ1 in G3 MBs, 9.353 of which were co-occupied by MYC (81%). Because as many of the joined binding sites neither contained a canonical E-box sequence nor a bona fide MIZ1 binding motif, we speculate that cooperative binding of oncogenic MYC with MIZ1 is necessary for binding.

Our data suggest that the MYC-MIZ1 interaction is critical for the development of G3 MBs.

Citation Format: BaoHan T. Vo, Elmar Wolf, Daisuke Kawauchi, Jerold Rehg, David Finkelstein, Brian Murphy, Martin Eilers, Martine F. Roussel. Myc and Miz1 in medulloblastoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2977. doi:10.1158/1538-7445.AM2014-2977

Abstract 4073: Proteasomal degradation of JunD is required for TGF-β induced inhibition of proliferation in prostate cancer cells

Transforming growth factor-β (TGF-β) inhibits proliferation of prostate epithelial cells. However, prostate cancer cells in advanced stages become resistant to TGF-β effects on proliferation. In this study, we have investigated the role of AP-1 family of transcription factors, specifically the Jun family members (c-Jun, JunB and JunD) in TGF-β1 effects on prostate cancer cell proliferation. Basal expression of individual Jun family members was determined by RT-PCR and Western blot analysis in four prostate cell lines: RWPE1, LNCaP, DU145 and PC3 cells. Jun levels were also examined in response to TGF-β1. c-Jun was expressed in all cell lines and its expression was up-regulated by TGF-β1. Levels of JunB were higher in normal cells compared to those in cancer cells and TGF-β1caused an increase in JunB levels. JunD levels were higher in all cell lines; TGF-β1 had differential effects on JunD protein levels. While it caused a significant decrease in JunD levels in RWPE-1 and DU145 cells, it did not affect JunD levels in PC3 cells. These differential effects on JunD levels correlated with differential effects of TGF-β on cell proliferation. Individual Jun family members were overexpressed in DU145 cells and effects on cell proliferation were determined. Over-expression of c-Jun and JunB decreased proliferation rate in DU145 cells; however, overexpression of JunD increased proliferation in these cells. Interestingly, cells over-expressing JunD still succumb to inhibitory effect of TGF-β1 after six to eight days of incubation. Furthermore, silencing JunD by siRNA decreased proliferation in both DU145 and PC3 cells. To determine the molecular mechanism of TGF-β-induced down-regulation of JunD, we pretreated cells over-expressing JunD with a proteosomal inhibitor, MG132. Pretreatment of MG132 blocked the degradation of JunD in in DU145 cells over-expressing JunD. In conclusion, our studies show that specific Jun family exerts differential effects on proliferation in prostate cancer cells in response to TGF-β1. While c-Jun and Jun B mediate the inhibitory effects of TGF-β1 on proliferation, JunD counteracts these effects. TGF-β1 causes inhibition in proliferation by degrading JunD via proteasomal degradation.

Acknowledgements: These studies were supported by the NIH/NIMHD/RCMI grant #G12MD007590, NIH/NIMHD #5P20MD002285, and DOD grant # W8I-08-1-0077.

Citation Format: Ana C. Millena, BaoHan T. Vo, Nicole Strong, Lindsey Walker, Yang Cao, Natalya Klueva, Curt Pfarr, Shafiq Khan. Proteasomal degradation of JunD is required for TGF-β induced inhibition of proliferation in prostate cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4073. doi:10.1158/1538-7445.AM2013-4073

The essential role of Giα2 in prostate cancer cell migration

Cell- and receptor-specific regulation of cell migration by Gi/oα-proteins remains unknown in prostate cancer cells. In the present study, oxytocin (OXT) receptor was detected at the protein level in total cell lysates from C81 (an androgen-independent subline of LNCaP), DU145 and PC3 prostate cancer cells, but not in immortalized normal prostate luminal epithelial cells (RWPE1), and OXT-induced migration of PC3 cells. This effect of OXT has been shown to be mediated by Gi/oα-dependent signaling. Accordingly, OXT inhibited forskolin-induced luciferase activity in PC3 cells that were transfected with a luciferase reporter for cyclic AMP activity. Although mRNAs for all three Giα isoforms were present in PC3 cells, Giα2 was the most abundant isoform that was detected at the protein level. Pertussis toxin (PTx) inhibited the OXT-induced migration of PC3 cells. Ectopic expression of the PTx-resistant Giα2-C352G, but not wild-type Giα2, abolished this effect of PTx on OXT-induced cell migration. The Giα2-targeting siRNA was shown to specifically reduce Giα2 mRNA and protein in prostate cancer cells. The Giα2-targeting siRNA eliminated OXT-induced migration of PC3 cells. These data suggest that Giα2 plays an important role in the effects of OXT on PC3 cell migration. The Giα2-targeting siRNA also inhibited EGF-induced migration of PC3 and DU145 cells. Expression of the siRNA-resistant Giα2, but not wild type Giα2, restored the effects of EGF in PC3 cells transfected with the Giα2-targeting siRNA. In conclusion, Giα2 plays an essential role in OXT and EGF signaling to induce prostate cancer cell migration.

Differential role of Sloan-Kettering Institute (Ski) protein in Nodal and transforming growth factor-beta (TGF-β)-induced Smad signaling in prostate cancer cells

Transforming growth factor-beta (TGF-β) signaling pathways contain both tumor suppressor and tumor promoting activities. We have demonstrated that Nodal, another member of the TGF-β superfamily, and its receptors are expressed in prostate cancer cells. Nodal and TGF-β exerted similar biological effects on prostate cells; both inhibited proliferation in WPE, RWPE1 and DU145 cells, whereas neither had any effect on the proliferation of LNCaP or PC3 cells. Interestingly, Nodal and TGF-β induced migration in PC3 cells, but not in DU145 cells. TGF-β induced predominantly phosphorylation of Smad3, whereas Nodal induced phosphorylation of only Smad2. We also determined the expression and differential role of Ski, a corepressor of Smad2/3, in Nodal and TGF-β signaling in prostate cancer cells. Similar levels of Ski mRNA were found in several established prostate cell lines; however, high levels of Ski protein were only detected in prostate cancer cells and prostate cancer tissue samples. Exogenous Nodal and TGF-β had no effects on Ski mRNA levels. On the other hand, TGF-β induced a rapid degradation of Ski protein mediated by the proteasomal pathway, whereas Nodal had no effect on Ski protein. Reduced Ski levels correlated with increased basal and TGF-β-induced Smad2/3 phosphorylation. Knockdown of endogenous Ski reduced proliferation in DU145 cells and enhanced migration of PC3 cells. We conclude that high levels of Ski expression in prostate cancer cells may be responsible for repression of TGF-β and Smad3 signaling, but Ski protein levels do not influence Nodal and Smad2 signaling.

Abstract 1064: Sloan-Kettering Institute (Ski) protein plays distant roles in activation of Smad proteins in response to nodal and TGF-β in prostate cancer cells

Transforming growth factor-β (TGF-β) acts as a tumor suppressor in the early stages of epithelial cancers by inhibiting proliferation and inducing apoptosis. However, in the later stages of the disease, TGF-β acts as a tumor promoter and is associated with aggressive forms of cancer due to its effects on angiogenesis, immune suppression, and metastasis. Previously, we have demonstrated that Nodal, another member of the TGF-β superfamily and its receptors are expressed in prostate cancer cell lines. Nodal and TGF-β exerted differential effects on prostate cancer cells; both inhibited proliferation in WPE, RWPE1, and DU145 cells while neither had effect on the proliferation of LNCaP and PC3 cells. On the other hand, Nodal and TGF-β induced migration in PC3 cells, but had no effect on cell migration in DU145 cells. Nodal primarily employs Smad2 for intracellular signaling while TGF-β is essential for both Smad2/3 phosphorylations. In the present study, we have determined the expression and role of Ski in Nodal and TGF-β signaling in prostate cancer cells. Ski is a co-repressor of the Smad-mediated TGF-β signaling. Ski was originally classified as an oncogene based on its ability to transform chicken and quail fibroblasts. RT-PCR analysis showed comparable mRNA levels of Ski in several established prostate cell lines; however, high levels of Ski protein were only detected in prostate cancer cell lines and Ski protein levels were very low or absent in normal cells. Ski protein levels were also high in prostate cancer tissue samples compared to normal prostate tissues. Treatment with Nodal and TGF-β had no effects on Ski mRNA levels; however, Nodal had no effect on Ski protein levels while TGF-β induced degradation of Ski protein levels mediated by the proteasome pathway. Reduced Ski levels correlated with increased basal and TGF-β-induced Smad2/3 phosphorylation. Knockdown of endogenous of Ski reduced proliferation in DU145 prostate cancer cells and enhanced migration of PC3 cells. We conclude that high level of Ski expression in prostate cancer cells may be responsible for repression of TGF-β and Smad2/3 signaling, but Ski protein levels do not influence Nodal effects.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1064. doi:1538-7445.AM2012-1064

Expression of nodal and nodal receptors in prostate stem cells and prostate cancer cells: autocrine effects on cell proliferation and migration

BACKGROUND

Nodal, a TGFβ like growth factor, functions as an embryonic morphogen that maintains the pluripotency of embryonic stem cells. Nodal has been implicated in cancer progression; however, there is no information on expression and functions of Nodal in prostate cancer. In this study, we have investigated the expression of Nodal, its receptors, and its effects on proliferation and migration of human prostate cells.

METHODS

RT-PCR, qPCR, and Western blot analyses were performed to analyze expression of Nodal and Nodal receptors and its effects on phosphorylation of Smad2/3 in prostate cells. The effects on proliferation and migration were determined by (3) H-Thymidine incorporation and cell migration assays in the presence or absence of Nodal receptor inhibitor (SB431542).

RESULTS

Nodal was highly expressed in WPE, DU145, LNCaP, and LNCaP-C81 cells with low expression in RWPE1 and RWPE2 cells, but not in PREC, PC3 and PC3M cells. Nodal receptors are expressed at varying levels in all prostate cells. Treatment with exogenous Nodal induced phosphorylation of Smad2/3 in WPE, DU145, and PC3 cells, which was blocked by SB431542. Nodal dose-dependently inhibited proliferation of WPE, RWPE1 and DU145 cells, but not LNCaP and PC3 cells. Nodal induced cell migration in PC3 cells, which was inhibited by SB431542; Nodal had no effect on cell migration in WPE and DU145 cells. The effects of Nodal on cell proliferation and migration are mediated via ALK4 and ActRII/ActRIIB receptors and Smad 2/3 phosphorylation.

CONCLUSIONS

Nodal may function as an autocrine regulator of proliferation and migration of prostate cancer cells.