Canonical TGF-β Pathway Activity Is a Predictor of SHH-Driven Medulloblastoma Survival and Delineates Putative Precursors in Cerebellar Development
ABSTRACT Medulloblastoma (MB) is the most common malignant brain tumor of childhood. Very little is known about aggressive forms of this disease, such as metastatic or recurrent MBs. In order to identify pathways involved in aggressive MB pathophysiology, we performed unbiased, whole genome microarrays on MB tumors at both the human and murine levels. Primary human MBs were compared, transcriptomically, to their patient-matched recurrent or metastatic tumors. Expression profiling was also performed on murine tumors from two spontaneously developing MB mouse models (Ptch+/- and Smo/Smo) that present with differing clinical severities. At both the human and murine levels we identified transforming growth factor-beta (TGF-β) as a potential contributor to MB progression/metastasis. Smad3, a major downstream component of the TGF-β pathway, was also evaluated using immunohistochemistry in malignant human tissues and was shown to correlate with MB metastasis and survival. Similarly, Smad3 expression during development identified a subset of cerebellar neuronal precursors as putative cells of origin for the Smad3-positive MBs. To our knowledge, this is the first study that links TGF-β to MB pathogenesis. Our research suggests that canonical activation of this pathway leads to better prognosis for patients.
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ABSTRACT: Pancreatic adenocarcinoma, one of the worst malignancies of exocrine pancreas, is a solid tumor with increasing incidence and mortality in industrialized countries. It is usually driven by oncogenic Kras point mutations and evolves into a highly aggressive metastatic carcinoma due to secondary gene mutations and specific signaling pathways unbalance. To examine in vivo the effects of Kras(G12D) during pancreatic cancer progression and time correlation with cancer signaling pathways activities, we have generated a zebrafish model of Pancreatic adenocarcinoma in which eGFP-Kras(G12D) expression was specifically driven to the pancreatic tissue by using the GAL4/UAS conditional expression system. Outcrossing the inducible oncogenic Kras(G12D) line with transgenic zebrafish reporters harboring specific signaling responsive elements of transcriptional effectors, we were able to follow TGFβ, Notch, Bmp and Shh activities during tumor development. Zebrafish transgenic lines expressing eGFP-Kras(G12D) showed normal exocrine pancreas development till 3 weeks post fertilization (wpf). From 4 to 24 wpf we observed several degree of acinar lesions, characterized by an increase of mesenchymal cells and mixed acinar/ductal features followed by progressive bowel and liver infiltrations finally bringing to highly aggressive carcinoma. Moreover, live imaging analysis of the exocrine pancreatic tissue revealed an increasing number of Kras positive cells and progressive activation of TGFβ; and Notch pathways. Increase of TGFβ, following Kras(G12D) activation, was confirmed in a concomitant model of medulloblastoma (MDB). Notch and Shh signaling activities during tumor onset were different between MDB and pancreatic adenocarcinoma indicating a tissue specific regulation of cell signaling pathways. Moreover, our results shows that a living model of pancreatic adenocarcinoma joined with cell signaling reporters is a suitable tool to describe in vivo the signaling cascades and molecular mechanisms involved in tumor development and a potential platform to screen for novel oncostatic drugs.Disease Models and Mechanisms 05/2014; 7(7). DOI:10.1242/dmm.014969 · 5.54 Impact Factor
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ABSTRACT: Medulloblastoma (MB) is one of the most common pediatric cancers, likely originating from abnormal development of cerebellar progenitor neurons. MicroRNA (miRNA) has been shown to play an important role in the development of the central nervous system. Microarray analysis was used to investigate miRNA expression in desmoplastic MB from patients diagnosed at a young age (1 or 2 years old). Normal fetal or newborn cerebellum was used as control. A total of 84 differentially expressed miRNAs (64 downregulated and 20 upregulated) were found. Most downregulated miRNAs (32/64) were found to belong to the cluster of miRNAs at the 14q32 locus, suggesting that this miRNA locus is regulated as a module in MB. Possible mechanisms of 14q32 miRNAs downregulation were investigated by the analysis of publicly available gene expression data sets. First, expression of estrogen-related receptor-γ (ESRRG), a reported positive transcriptional regulator of some 14q32 miRNAs, was found downregulated in desmoplastic MB. Second, expression of the parentally imprinted gene MEG3 was lower in MB in comparison to normal cerebellum, suggesting a possible epigenetic silencing of the 14q32 locus. miR-129-5p (11p11.2/7q32.1), miR-206 (6p12.2), and miR-323-3p (14q32.2), were chosen for functional studies in DAOY cells. Overexpression of miR-129-5p using mimics decreased DAOY proliferation. No effect was found with miR-206 or miR-323 mimics.Frontiers in Oncology 09/2013; 3:254. DOI:10.3389/fonc.2013.00254
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ABSTRACT: Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) is silenced by promoter methylation in many types of tumors, yet ASC's role in most cancers remains unknown. Here, we show that ASC is highly expressed in a model of medulloblastoma, the most common malignant pediatric brain cancer; ASC is also expressed in human medulloblastomas. Importantly, while ASC deficiency did not affect normal cerebellar development, ASC knockout mice on the Smoothened (ND2:SmoA1) transgenic model of medulloblastoma exhibited a profound reduction in medulloblastoma incidence and a delayed tumor onset. A similar decrease in tumorigenesis with ASC deficiency was also seen in the hGFAP-Cre:SmoM2 mouse model of medulloblastoma. Interestingly, hyperproliferation of the external granule layer (EGL) was comparable at P20 in both wild-type and ASC-deficient SmoA1 mice. However, while the apoptosis and differentiation markers remained unchanged at this age, proliferation makers were decreased, and the EGL was reduced in thickness and area by P60. This reduction in proliferation with ASC deficiency was also seen in isolated SmoA1 cerebellar granule precursor cells in vitro, indicating that the effect of ASC deletion on proliferation was cell autonomous. Interestingly, ASC-deficient SmoA1 cerebella exhibited disrupted expression of genes in the transforming growth factor-β pathway and increased level of nuclear Smad3. Taken together, these results demonstrate an unexpected role for ASC in Sonic hedgehog-driven medulloblastoma tumorigenesis, thus identifying ASC as a promising novel target for antitumor therapy.Oncogene advance online publication, 27 January 2014; doi:10.1038/onc.2013.577.Oncogene 01/2014; 34(3). DOI:10.1038/onc.2013.577 · 8.56 Impact Factor