Abnormal activation of components of the Hedgehog pathway--specifically, resulting from mutations in the Patched 1 gene--is associated with the development of basal cell carcinoma, as well as several other cancers, including medulloblastoma.
In contrast, mice lacking one or two functional Ink4c alleles and one copy of Patched (Ptc1) encoding the Shh receptor rapidly developed MBs that retained wild-type p53.
Conversely, patients with PTCH1 germline mutations experience Shh overstimulation resulting in Gorlin (Nevoid Basal Cell Carcinoma) syndrome and an increased incidence of malignant transformation of CGNPs leading to medulloblastoma formation.
Here we provide evidence that a discrete subtype of medulloblastoma that contains activating mutations in the WNT pathway effector CTNNB1 (hereafter, WNT subtype) arises outside the cerebellum from cells of the dorsal brainstem.
We report a series of 72 paediatric medulloblastomas evaluated for beta-catenin protein expression, CTNNB1 mutations, and comparative genomic hybridization.
Taken together, these data suggest that activating mutations in the beta-catenin gene may be involved in the development of a subset of medulloblastomas.
We identified no PTCH1 mutations and two SUFU mutations that cause premature protein truncating in the series of sporadic non-familial medulloblastomas.
TP53 mutation status was not associated with unfavorable prognosis (P = .63) and was not linked to 17p allelic loss but was over-represented in the prognostically favorable WNT subgroup of MB as defined by CTNNB1 mutation (seven of 35 TP53-mutated tumors v 14 of 271 TP53 wild-type tumors; P = .005) and in tumors carrying high-level MYCN amplification (seven of 21 TP53-mutated tumors v 14 of 282 TP53 wild-type tumors; P = .001).
Several recurrent mutations were identified, both in known medulloblastoma-related genes (CTNNB1, PTCH1, MLL2, SMARCA4) and in genes not previously linked to this tumour (DDX3X, CTDNEP1, KDM6A, TBR1), often in subgroup-specific patterns.
β-catenin is an integral component of the canonical Wnt signaling pathway, and its mutations are an autosomal recessive cause of colorectal cancer (CRC), medulloblastoma (MDB), and ovarian cancer.
Disruption of these proteins could result in upregulation of the Wnt signaling and accumulation of beta-catenin, followed by cell proliferation and medulloblastoma oncogenesis.
Components of these two developmental and cancer-associated pathways, including (Patched) PTCH, SMOH, adenomatous polyposis coli (APC), beta-catenin and AXIN1 show somatic mutations in sporadic MBs.
Gorlin syndrome is associated with germline mutations in components of the Sonic Hedgehog pathway, including Patched1 (<i>PTCH1)</i> and Suppressor of fused (<i>SUFU)</i><i>SUFU</i> mutation carriers appear to have an especially high risk of early-onset medulloblastoma.
Previous genetic studies in MBs have identified mutations in genes coding for beta-catenin and its partners, APC and AXIN1, which cause activation of Wnt signaling.
Together with the previous report describing three cases of non-NBCCS medulloblastoma carrying a germline mutation in this gene, individuals with a SUFU germline mutation are expected to have a markedly high risk of developing medulloblastoma and probably meningioma.
WNT-activated MDB is associated to monosomy 6, CTNNB1, DDX3X and TP53 mutations, beta-catenin nuclear immunoexpression, and a better prognosis than SHH-activated MDB.