Wnt-beta-catenin Pathway Research Articles

Abstract 1273: RASSF1 promoter hypermethylation is associated with activated CTNNB1 pathways in hepatocellular carcinoma

Abstract BACKGROUND: The promoter-region of the Ras association domain family member 1 (RASSF1) gene is frequently hypermethylated in several solid tumors, including hepatocellular carcinoma (HCC). Wnt-pathway deregulation and increased accumulation of nuclear catenin-beta-1 (CTNNB1) has been associated with RASSF1 inactivation, and more recently, with diminished response to immune checkpoint blockade in HCC. There is limited data from clinical tumor and liquid biopsy samples on the relationship between RASSF1 promoter methylation and Wnt beta-catenin pathway activation status in HCC. METHODS: Pyrosequencing was performed to assess RASSF1 promoter methylation in DNA from paired HCC tumor/adjacent-liver tissues as well as cell-free DNA (cfDNA) and buffy coat DNA from blood samples collected in Streck cfDNA tubes from 40 patients with surgically-resectable HCC participating in an IRB-approved diagnostic clinical trial (NCT01395030). All blood samples were collected pre-operatively while all tissue samples were collected upon surgical tumor resection. The DNA methylation analysis results from tumors were compared to a CTNNB1 pathway activation gene expression signature obtained from the same tumor samples. Targeted next-generation DNA sequencing (NGS) was also performed on a limited number of cfDNA samples using a 56 gene Oncology Panel (56G v2, Swift Bioscience) to obtain mutational profiles (including CTNNB1 mutation status) from each HCC case. Allele variant detection was performed using the ERASE-Seq algorithm (Fluxion Biosciences). RESULTS: RASSF1 promoter hypermethylation was detected in 35/40 tumor samples. Levels of RASSF1 promoter methylation were significantly higher in tumor as compared to liver tissue DNA (55.2% vs. 23.5%, p < 0.0001). Methylation levels in the RASSF1 promoter were also significantly higher in cfDNA as compared to buffy-coat DNA (7.5% vs. 0.4%, p < 0.0001). Tumors enriched for genes associated with Wnt beta-catenin pathway activation demonstrated significantly higher RASSF1 promoter methylation as compared to tumors enriched for immune/interferon-related genes (63% vs. 20%, Tukey p = 0.0004). Pilot liquid biopsy studies involving DNA NGS and methylation analysis in a subset of pre-operative blood samples also revealed higher RASSF1 promoter methylation among the cell-free DNA samples carrying activating CTNNB1 exon 3 mutations as compared to p53 mutations (23.4% vs. 1.4%, Tukey p = 0.009) and PIK3 mutations (23.4% vs. 1.5%, Tukey p = 0.031). RASSF1 promoter methylation in tumor tissue DNA was also significantly higher in patients with liquid biopsy detected CTNNB1-mutations as compared to p53-mutations (65.5% versus 37%, p = 0.030). CONCLUSION: CTNNB1 mutations and related gene expression patterns may be associated with RASSF1 promoter hypermethylation in HCC. The clinical implications for immunotherapy and the mechanisms underlying these associations deserve further investigation. Citation Format: Sandi Alexander Kwee, Karolina Peplowska, Christine Farrar, Linda Wong, Min-ae Song, Maarit Tiirikainen. RASSF1 promoter hypermethylation is associated with activated CTNNB1 pathways in hepatocellular carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1273.

Abstract P6-08-07: Gain and amplification of RAC1 GTP-ase in BC: Explaining alterations in patients by experiments using TNBC model

Abstract INTRODUCTION: RAC1-GTPase which transduces signals from cell surface integrins, have been implicated in metastasis. We reported that Wnt-beta-catenin pathway (WP) that signals metastasis (BMC Cancer, 2013), is one of the salient genetic features of Triple-Negative Breast Cancer (TNBC) (PlosOne, 2013).AIM: We demonstrated that TNBC cells acquire integrin-directed metastasis-associated (ID-MA) phenotypes following an upregulation of the WP (Oncotarget, In Press). Here we examined how WP signals are transduced in the context of ID-MA phenotypes in TNBC.METHOD: We documented gain and amplification of RAC1 gene in Breast Invasive Carcinoma subtypes from cBioPortal. The outcome for RFS was studied in the Hungarian ER-ve BC cohort.Mechanistically, we studied fibronectin-directed (1) migration, (2) matrigel- invasion, (3) RAC1 activation, (4) actin dynamics (confocal microscopy) and (5) podia-parameters using pharmacological agents (sulindac sulfide), genetic tools (beta-catenin siRNA), WP modulators (Wnt-C59, XAV939), RAC1 inhibitors (NSC23766, W56) and WP stimulations (LWnt3ACM, Wnt3A recombinant) in a panel of 6-7 TNBC cell lines, RESULTS: The collective percentage of gain and amplification of RAC1 were (1) 31% of total 1105 breast invasive carcinoma samples, (2) 29% of total 594 ER+ve samples, (3) 39% of total 174 ER-ve samples, (4) 38% of total 120 HER2+ve samples and (4)35% of total 82 TNBC samples (brca/tcga/pub2015; Cell 2015).In invasive ductal BC subtypes, gain and amplification of RAC1 were (1) 32% of total 201 Luminal A samples, (2) 37% of total 122 PAM50 Luminal B samples, (3) 47% of total 51 PAM50 Her2-enriched samples and (4) 33% of total 107 PAM50 Basal-like samples. In invasive lobular cancers, gain and amplification of RAC1 were 24% of total 127 samples.Involvement of WP in different TNBC cells was tested following stimulation by LWnt3ACM and Wnt3Arecombinant protein and different inhibitors of WP by both qRT-PCR and WB for beta-catenin, active beta-catenin, cMYC, cyclin D1and WP specific several stem cell markers. The WP attenuation, which (a) decreased cellular levels of beta-catenin, as well as its nuclear active-form, (b) decreased fibronectin-induced migration & invasion, (c) altered actin dynamics and (d) decreased podia-parameters was successful in blocking fibronectin-mediated RAC1/Cdc42 activity. Both Wnt-antagonists and RAC1 inhibitors blocked fibronectin-induced RAC1 activation and inhibited fibronectin-induced ID-MA phenotypes following WP stimulation by LWnt3ACM and Wnt3Arecombinant protein. High expression of RAC1 was associated with poor outcome for RFS with HR=1.48 [CI: 1.15-1.9] p=0.0019 in the Hungarian ER-veBC cohort.CONCLUSION:In TNBC model, the activation of RAC1 signals downstream of WP mediated ID-MA phenotypes. The identification of the functional relationship between RAC1 signaling and the WP activation in the control of ID-MA mechanistically explains how the activation of WP in TNBC is associated with the high metastatic incidences and a dismal outcome. Citation Format: Dey N, Carlson JH, Jepperson T, Willis S, De P, Leyland-Jones B. Gain and amplification of RAC1 GTP-ase in BC: Explaining alterations in patients by experiments using TNBC model [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-08-07.

RAC1 GTP-ase signals Wnt-beta-catenin pathway mediated integrin-directed metastasis-associated tumor cell phenotypes in triple negative breast cancers.

The acquisition of integrin-directed metastasis-associated (ID-MA) phenotypes by Triple-Negative Breast Cancer (TNBC) cells is caused by an upregulation of the Wnt-beta-catenin pathway (WP). We reported that WP is one of the salient genetic features of TNBC. RAC-GTPases, small G-proteins which transduce signals from cell surface proteins including integrins, have been implicated in tumorigenesis and metastasis by their role in essential cellular functions like motility. The collective percentage of alteration(s) in RAC1 in ER+ve BC was lower as compared to ER-ve BC (35% vs 57%) (brca/tcga/pub2015). High expression of RAC1 was associated with poor outcome for RFS with HR=1.48 [CI: 1.15-1.9] p=0.0019 in the Hungarian ER-veBC cohort. Here we examined how WP signals are transduced via RAC1 in the context of ID-MA phenotypes in TNBC. Using pharmacological agents (sulindac sulfide), genetic tools (beta-catenin siRNA), WP modulators (Wnt-C59, XAV939), RAC1 inhibitors (NSC23766, W56) and WP stimulations (LWnt3ACM, Wnt3A recombinant) in a panel of 6-7 TNBC cell lines, we studied fibronectin-directed (1) migration, (2) matrigel invasion, (3) RAC1 and Cdc42 activation, (4) actin dynamics (confocal microscopy) and (5) podia-parameters. An attenuation of WP, which (a) decreased cellular levels of beta-catenin, as well as its nuclear active-form, (b) decreased fibronectin-induced migration, (c) decreased invasion, (d) altered actin dynamics and (e) decreased podia-parameters was successful in blocking fibronectin-mediated RAC1/Cdc42 activity. Both Wnt-antagonists and RAC1 inhibitors blocked fibronectin-induced RAC1 activation and inhibited the fibronectin-induced ID-MA phenotypes following specific WP stimulation by LWnt3ACM as well as Wnt3A recombinant protein. To test a direct involvement of RAC1-activation in WP-mediated ID-MA phenotypes, we stimulated brain-metastasis specific MDA-MB231BR cells with LWnt3ACM. LWnt3ACM-stimulated fibronectin-directed migration was blocked by RAC1 inhibition in MDA-MB231BR cells. In the light of our previous report that WP upregulation causes ID-MA phenotypes in TNBC tumor cells, here we provide the first mechanism based evidence to demonstrate that WP upregulation signals ID-MA tumor cell phenotypes in a RAC1-GTPase dependent manner involving exchange-factors like TIAM1 and VAV2. Our study demonstrates for the first time that beta-catenin-RAC1 cascade signals integrin-directed metastasis-associated tumor cell phenotypes in TNBC.

Abstract 4605: Metastasis-associated tumor cell phenotypes in TNBC is regulated by Wnt-beta-catenin pathway signals

Abstract Introduction: Acquisitions of metastasis-associated phenotypes (MA) by Triple Negative Breast Cancer (TNBC) cells are imparted by genetic alterations which cause deregulation of different signaling pathways associated to those phenotypes. We have recently reported that an upregulation of the Wnt-beta-catenin pathway (WP) is one of the salient genetic features of TNBC and demonstrated that the WP signaling in TNBC is associated with poor prognosis and metastasis (Dey et al., 2013). We have also identified that the functional upregulation of secreted-MMP7, a transcriptional target of WP in TNBC is associated to the functional loss/absence of PTEN gene (Dey et al., 2013), the most common first event associated with basal-like subtype (Martins et al., 2012). Aim: In order to understand the relevance of WP pathway in the biology of metastasizing TNBC tumor cells, here we have undertaken a study in which the involvement of WP is tested in the context of MA phenotypes including (1) integrin-directed migration, (2) matrigel-invasion and (3) clonogenic growth and proliferation in 15 TNBC cell lines. Methods: CHIR9902, Wnt-C59, XAV939, sulindac sulfide, beta-catenin SiRNA as well as physiological stimulation of the WP (LWnt3A CM) were used for the study. Podia-parameters were studied using confocal microscopy for architecture of filamentous actin while matrigel invasion was studied by MMP7 specific caesin-zymography. Results: The collective% of alterations in CTNNB1, APC and DVL1 genes among total breast invasive carcinomas (TCGA 2012) were 17% in contrast to 46% breast invasive carcinomas, PAM50 Basal. A similar trend was observed among subtypes of BC from brca/tcga/pub2015 (cBioPortal). Wnt-C59, XAV939, sulindac sulfide and beta-catenin SiRNA (1) inhibited fibronectin-directed migration (2) decreased maximum relative distance from the origin and average velocity of the movement by real-time video microscopy, (3) altered cytoskeletal organization of the filamentous-actin and decreased the podia parameters, (4) decreased matrigel-invasion, and (6) inhibited cell proliferation and 3D colony formation. Mechanistically the treatment with sulindac sulfide and beta-catenin SiRNA decreased cellular levels of beta-catenin, active beta-catenin and MMP7 in the same TNBC cell lines wherein fibronectin-directed migration, invasion, and colony formation were found inhibited. LWnt3ACM stimulated cell proliferation, clonogenicity, migration and invasion was perturbed by WP modulators, sulindac sulfide and PI3K pathway inhibitor in brain-metastasis specific TNBC cells. Conclusion: Here we present the first conclusive evidence to demonstrate that the WP activation is functionally responsible for MA phenotypes in TNBC. Our data explains the why different components of the WP is upregulated in TNBC and how WP activation is associated with poor prognosis and metastasis in this subtype. Citation Format: Nandini Dey, Jennifer H. Carlson, Pradip De, Brian R. Leyland-Jones. Metastasis-associated tumor cell phenotypes in TNBC is regulated by Wnt-beta-catenin pathway signals. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4605.

Wnt-beta-catenin pathway signals metastasis-associated tumor cell phenotypes in triple negative breast cancers.

Tumor cells acquire metastasis-associated (MA) phenotypes following genetic alterations in them which cause deregulation of different signaling pathways. Earlier, we reported that an upregulation of the Wnt-beta-catenin pathway (WP) is one of the genetic salient features of triple-negative breast cancer (TNBC), and WP signaling is associated with metastasis in TNBC. Using cBioPortal, here we found that collective % of alteration(s) in WP genes, CTNNB1, APC and DVL1 among breast-invasive-carcinomas was 21% as compared to 56% in PAM50 Basal. To understand the functional relevance of WP in the biology of heterogeneous/metastasizing TNBC cells, we undertook this comprehensive study using 15 cell lines in which we examined the role of WP in the context of integrin-dependent MA-phenotypes. Directional movement of tumor cells was observed by confocal immunofluorescence microscopy and quantitative confocal-video-microscopy while matrigel-invasion was studied by MMP7-specific casein-zymography. WntC59, XAV939, sulindac sulfide and beta-catenin siRNA (1) inhibited fibronectin-directed migration, (2) decreased podia-parameters and motility-descriptors, (3) altered filamentous-actin, (4) decreased matrigel-invasion and (5) inhibited cell proliferation as well as 3D clonogenic growth. Sulindac sulfide and beta-catenin siRNA decreased beta-catenin/active-beta-catenin and MMP7. LWnt3ACM-stimulated proliferation, clonogenicity, fibronection-directed migration and matrigel-invasion were perturbed by WP-modulators, sulindac sulfide and GDC-0941. We studied a direct involvement of WP in metastasis by stimulating brain-metastasis-specific MDA-MB231BR cells to demonstrate that LWnt3ACM-stimulated proliferation, clonogenicity and migration were blocked following sulindac sulfide, GDC-0941 and beta-catenin knockdown. We present the first evidence showing a direct functional relationship between WP activation and integrin-dependent MA-phenotypes. By proving the functional relationship between WP activation and MA-phenotypes, our data mechanistically explains (1) why different components of WP are upregulated in TNBC, (2) how WP activation is associated with metastasis and (3) how integrin-dependent MA-phenotypes can be regulated by mitigating the WP.

Abstract 3443: Wnt-beta-catenin-Rac1 signaling axis regulates metastasis-associated phenotypes in TNBC

Abstract Background: RAC1-GTPase controls many cellular phenotypes including integrin-directed migration via its control over the actin-cytoskeleton. We and others have established the upregulation of Wnt-beta-catenin pathway (WP) in triple negative breast cancer (TNBC), the most aggressive subtype of breast cancer (Dey et al., 2013, BMC Cancer; Dey et al., 2013, PLOS ONE). Here we report for the first time that metastasis-associated phenotypes in TNBC are controlled by Wnt-beta-catenin-RAC1signaling axis. Methodology: The involvement of WP was tested using (1) WP modulators (CHIR99021, Wnt-C59, XAV939), (2) sulindac sulfide and (3) beta-catenin SiRNA. We studied metastasis-associated phenotypes including, (1) proliferation (CelltiterGLO) (2) clonogenic growth (3D On-TOP assay) (3) fibronectin-directed migration (4) matrigel invasion (5) vascular mimicry (6) actin dynamics (confocal-microscopy and podia-parameters) (7) protein expression (WB) (8) real-time imaging for migration and vascular mimicry and (9) adhesion in the context of RAC1 activation in a panel of 3-4 TNBC cell lines. Results: Sulindac sulfide as well as transient transfection of beta-catenin SiRNA (1) decreased cellular levels of beta-catenin, inhibited proliferation, attenuated metastasis-associated different phenotypes and blocked fibronectin-mediated RAC1 as well as Cdc42 activities and (2) altered actin dynamics and inhibited podia-parameters (lamellopodia and fillopodia). Both Wnt-antagonists and RAC1 inhibitor (NSC23766) blocked fibronectin-induced RAC1 activation and inhibited the metastasis-associated phenotypes, while Wnt-activator enhanced phenotypes like vascular mimicry. Conclusion: Results of our experiments show that upregulation of WP regulates metastasis-associated phenotypes in TNBC via activation of RAC1 GTP-ase. The functional link between WP, metastasis and the activation of RAC1 is being currently worked out using RAC1SiRNA and pharmacological inhibitor of RAC1 in brain metastasizing MDA-MB231BR cells to specifically address the role of Wnt-beta-catenin-RAC1 signaling axis in the context of distant metastasis, the results of which will be presented at the meeting. Citation Format: Nandini Dey, Jennifer Carlson, Pradip De, Brian Leyland-Jones. Wnt-beta-catenin-Rac1 signaling axis regulates metastasis-associated phenotypes in TNBC. [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 3443. doi:10.1158/1538-7445.AM2014-3443

Wnt-β-Catenin Pathway Regulates Vascular Mimicry in Triple Negative Breast Cancer

The Wnt-beta-catenin pathway (WP) regulates different aspects of cell fate, migration and polarity. Inappropriate deregulation of this pathway leads to oncogenic and metastatic changes. The Triple Negative (TN) subset of BC (the absence of hormone receptors and absence of amplification/overexpression of HER2 receptors) exhibits aggressive clinical behavior and has poor clinical outcome. We have recently identified WP as one of the key signature pathways in TNBC associated with metastasis [1,2]. Here we report for the first time that WP controls metastasis-associated phenotype of Vascular Mimicry (VM) in TNBC. We have established 2D and 3D models to study VM in this subset of BC and characterized different TNBC cell lines in terms of VM and identified the role of WP in the regulation of VM. To establish the role of WP in the regulation of VM in TNBC, we have used (1) a pharmacological inhibitor of beta-catenin which is a functional readout of WP and (2) signaling modulators of WP. Since PI3K-pathway is an upstream regulator of WP, we have also used inhibitors of PI3K-pathway to test our hypothesis. Mechanistically (1) sulindac sulfide (pharmacological inhibitor of beta-catenin) and XAV939 (modulator of WP) mediated decrease in beta-catenin, (2) XAV939 mediated increase in axin and (3) LY294002 or SF1126 (pan PI3K inhibitors) mediated decrease in pGSK3beta caused an abrogation of VM in various TNBC cell lines including BT20, HCC1937, SUM149, MDA-MB231 and MDA-MB468. Finally we obtained genetic proof-of-concept using beta-catenin SiRNA. SiRNAmediated downregulation of WP abrogated VM demonstrating the involvement of WP in VM. Functionally, our data show that VM in brain specific metastatic TNBC cells is mediated via activation of WP.

377 Selective Inhibition of AKT Protein Isoforms Augments Gefitinib Response in EGFR Mutated NSCLC Cells

Introduction: Genetic changes occurring in the triple negative (TN) subset of breast tumors (BT) contribute to different phenotypes in the tumor cells via deregulation of specific signaling-pathways. We identified a differential upregulation of the Wnt-beta-catenin pathway in TNBT (Barwick etal, 2008; Dey etal. 2009), and reported that in TNBT, the poor prognosis and the higher incidence of metastasis are associated with an activation of this pathway (Barwick etal., 2009). We also reported a role of the pathway in the control of migration and invasion of tumor cells (Dey etal. 2009, 2010). Since integrin-directed migration and invasion of the tumor cells are instrumental for the metastasis, and TN tumor cells are highly invasive in nature, we hypothesized that the upregulation of this pathway in TNBT is functionally connected to the control of metastasis-associated phenotypes. This hypothesis is further strengthened by our identification of MMP7 as a selective-biomarker of TNBT (Abramovitz etal, 2009). Purpose: We studied the involvement of the pathway in the control of metastasis-associated phenotypes in TN breast cancer (BC) cells. Methods: We tested the effects of (1) different chemical modulators of the Wnt signaling, and (2) downregulation of beta-catenin on the (a) cell signaling marker(s), (b) cell proliferation, (c) clonogenic growth, (d) migration, (e) invasion, and (f) vascular mimicry (VM) using a panel of six TNBT cells. Results: (1) CHIR99021 (selective GSK3b inhibitor which activates Wnt signaling) enhanced clonogenic growth, and VM while WntC59 (palmitylates Wnt proteins and blocks the Wnt secretion/activity), as well as XAV939 (tankyrase inhibitor that blocks beta-catenin-mediated transcription via axin stabilization) blocked clonogenic growth, cell proliferation, fibronectindirected migration, and VM in TNBT cells. (2) Sulindac sulfide (decreases cellular levels of total and active beta-catenin) inhibited migration, invasion, VM, actin cytoskeleton, podia-parameters, RAC1/Cdc42 activation, and MMP7 in TNBC cells. (3) SiRNA mediated downregulation of betacatenin protein in TNBC cells inhibited cell proliferation, clonogenic growth, migration, invasion, c-MYC, and VM. Conclusion: Wnt-beta-catenin pathway activates cellular signaling for the metastasis-associated phenotypes like proliferation, clonogenic growth, migration, invasion and VM in TNBT cells and this function is directly mediated by via cellular levels of beta-catenin. An inhibition of the Wntbeta-catenin pathway might be an effective combination treatment strategy in TNBC.

Effects and mechanisms of angiotensin II receptor blockade with telmisartan in a normotensive model of mesangioproliferative nephritis

Renoprotective actions of angiotensin receptor blockers are not well established in normotensive, low-grade proteinuric glomerular diseases. We examined the effect of low-dose telmisartan (LT) and high-dose telmisartan (HT) versus conventional antihypertensive therapy in the rat anti-Thy1.1 model of glomerulonephritis. Rats were randomized on Day 4 after disease induction to no treatment (CT, control), LT or HT or hydrochlorothiazide + hydralazine (HCT + H). All rats remained normotensive: HT and HCT + H reduced blood pressure by 15-20%. LT, HT and HCT + H reduced glomerular endothelial cell proliferation and glomerular and interstitial matrix deposition on Day 14. Only HT reduced podocyte damage and tubular cell dedifferentiation on Day 9 and mesangial cell activation on Day 14. By gene expression analysis arrays, we identified discs-large homolog 1 and angiopoietin-like 4 as potential mediators of the HT effects. In addition, we identified several pathways possibly related to the pleiotropic effects of HT, including growth factor signalling, mammalian target of rapamycin signalling, protein ubiquitination, the Wnt-beta catenin pathway and hypoxia signaling. In summary, treatment with HT, initiated after the induction of disease, ameliorates glomerular and tubulointerstitial damage. We provide the first comprehensive insight into the mechanisms underlying the renoprotective effect of high-dose angiotensin II receptor blockers (ARBs). Our study lays the basis for future investigations on novel pathways affected by ARBs in renal disease.

Wnt signaling through canonical and non-canonical pathways: Recent progress

The Wnt–beta-catenin pathway regulates cell adhesion, morphology, proliferation, migration and structural remodeling. The aspects of the canonical and non-canonical pathways are reviewed here. The major components of this network are the Wnt ligands which bind to frizzled receptors at the cell surface. Activation of Wnt signaling down regulates the intracellular beta-catenin degradation component, allowing beta-catenin levels to accumulate within the cell. At normal levels, beta-catenin associates at the intracellular side of the membrane with cadherins to promote cell adhesion and with the actin microfilament cytoskeletal network to control cell shape. If beta-catenin levels become elevated, it can begin to accumulate within the cell nucleus and activate transcription in conjunction with co-transcription factors Lefs/Tcfs.Cell populations can regulate neighboring populations via the paracrine action of growth factors and through the action of cell adhesion molecules. Many examples of these interactions exist. The major players in Wnt signaling and its downstream canonical and non-canonical partners are reviewed here. For more details visit the World Wide Web Wnt Homepage (http://www.stanford.edu/∼ rnusse/wntwindow.html).

Effects on the serotoninergic system in sub-acute transmissible spongiform encephalopathies: current data, hypotheses, suggestions for experimentation

Sub-acute transmissible spongiform encephalopathies (TSEs), or prion diseases, are affections in which little is known of their etiology. The predominant theory stipulates that an abnormal protease-resistant prion protein (PrPres) would be infectious by directly inducing its defective conformation to the normal native protein (PrPC). The function of PrPC remains unknown. The preferred localization of PrPC at the level of the synapses supposes a function in neuronal transmission. Several neurotransmitter systems (acetylcholine, GABA, dopamine, etc.) are damaged in TSEs, mainly the serotonin (5-HT) system. At a hypothetical level, PrPC would play a trophic and functional role by regulating the capture of amino acid precursors of neurotransmitters and the functions of neuroreceptors, in particular regarding tryptophan and 5-HT receptors. By comparison with the modes of action of Ras proteins and of the envelope glycoprotein of jaagsiekte sheep retrovirus, the adaptation of an oncogenic model is suggested for the mode of action of PrPres. The sequence of events could be the following: capture of PrPres and forming of an abnormal receptor, chronic disturbance of transduction pathways, more particularly of the phosphatidylinositol-3 kinase (PI-3K)/protein kinase B (Akt)/glycogen synthetase kinase 3 (GSK 3)/Wnt-beta catenin pathway, deregulation of the PrP gene and infrequent and transitory forming of abnormal RNA messengers and, finally, the forming of abnormal proteins and the deterioration of the serotoninergic system. The involvement of endogenous nucleic acids is supposed. The infectious agent of TSEs could be an ancestral form of retrovirus, such as a retrotransposon using the prion protein as an envelope glycoprotein. Pharmacological tests, by comparison with a rare disease of unknown etiology in cattle, bovine spastic paresis, are suggested with the amino acid precursors of neuromediators (tryptophan, tyrosine, glutamic acid, etc.) and with lithium, neuroprotector and regulator of the serotonergic system.