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ASC deficiency suppresses proliferation and prevents medulloblastoma incidence

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.

ORGANISM(S): Mus musculus

PROVIDER: GSE48682 | GEO | 2014/05/23

SECONDARY ACCESSION(S): PRJNA211222

REPOSITORIES: GEO

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Project description:Deregulated developmental processes in the cerebellum cause medulloblastoma, the most common malignant tumor of the central nervous system. About 20-30% of cases are caused by mutations increasing the activity of the Sonic hedgehog (Shh) pathway, a critical mitogen in cerebellar development. The proto-oncogene Smoothened is a key transducer of the Shh pathway. Activating mutations in Smoothened that lead to constitutive activity of the Shh pathway have been identified in human medulloblastoma. To understand the molecular and cellular effects of Smoothened variants in normal development and medulloblastoma genesis, we generated the SmoA2 transgenic mouse model which expresses the transgene exclusively in granule neuron precursors. In this study, we demonstrate how two point mutations in a single molecule can produce starkly different phenotypes as seen in comparison to our previous model, ND2:SmoA1. The SmoA2 mice have severe aberrations in cerebellar development whereas the SmoA1 mice are largely normal during development. Medulloblastomas in the SmoA2 mice develop in the dysplastic cerebellar milieu. Intriguingly, despite disruptions in the stereotypic organization of the cerebellum, the SmoA2 mice do not exhibit any overt abnormalities in motor coordination. The differences in the global transcriptional profiles downstream of SmoA1 and SmoA2 further demonstrate the distinctiveness of the two oncogenic Smoothened mutations. The SmoA2 model serves as a unique spatiotemporal tool to investigate the functional significance of the reiterative cerebellar circuitry as well as to further understand Shh pathway mechanics in cerebellar development and oncogenesis. We previously generated a SmoA1 transgenic mouse medulloblastoma model, which expresses the SmoA1 transgene driven by the GNP-specific fragment of the promoter of ND2 transcription factor leading to constitutively active Shh signaling exclusively in the cerebellum. In this study, we characterize the ND2:SmoA2 transgenic mouse model with a similarly designed transgene expressing the SmoA2 mutation. To assess transcriptional changes downstream of SmoA1 and SmoA2, we evaluated global gene expression profiles of P5 SmoA1, SmoA2 and Wt age-matched cerebella. We chose this specific developmental stage because (1) the phenotypes of SmoA1 and SmoA2 are robust and distinct at P5; (2) at P5 GNPs undergo proliferation, migration and differentiation and therefore expression profiling could capture key differences in multiple processes.

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ASC deficiency suppresses proliferation and prevents medulloblastoma incidence

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