Learning that Ptc1 is a medulloblastoma tumor suppressor led directly to the identification of the Ptc1 ligand, Sonic hedgehog, as a powerful mitogen for cerebellar granule cell precursors.
Constitutive activation of hedgehog signaling, often caused by PTCH1 inactivation and leading to inappropriate activation of GLI target genes, is crucial for the development of several human tumors including basal cell carcinoma of the skin and medulloblastoma.
Mutations of the human Patched gene ( PTCH ) have been identified in individuals with the nevoid basal cell carcinoma syndrome (NBCCS) as well as in sporadic basal cell carcinomas and medulloblastomas.
In immunohistochemistry assays, anti-GAB1 antibody expression is positive in tumors showing SHH pathway activation or PTCH mutation, while positive immunoexpression for YAP1 antibody can be only found in WNT-activated and SHH-activated MDB.
Novel PTCH1 mutations in Japanese Nevoid basal cell carcinoma syndrome patients: two familial and three sporadic cases including the first Japanese patient with medulloblastoma.
Each SUFU-positive family included a single case of medulloblastoma, whereas only two (1.7%) of 115 individuals with Gorlin syndrome and a PTCH1 mutation developed medulloblastoma.
Eight genetic variants annotating three genes in the sonic hedgehog signaling pathway; CCND2, PTCH1, and GLI2, were found to be associated with the risk of medulloblastoma (P(combined) < 0.05).
This is supported by the observation that human medulloblastomas with PTCH1 mutations displayed more similarities to PTCH1 wild-type tumors of the same age group than to PTCH1-mutated tumors of the other age group.
Genetic analyses revealed recurrent somatic inactivations of the tumor suppressor gene Ptch1 and a recapitulation of the sonic hedgehog subgroup of human medulloblastomas.
In mice, Ptc1 haploinsufficiency and disruption of DNA repair (DNA ligase IV inactivation) or cell cycle regulation (Kip1, Ink4d, or Ink4c inactivation), in conjunction with p53 dysfunction, predispose to medulloblastoma.
Primary tumor cells derived from two models of murine medulloblastoma (Ptch1(+/-);Ink4c(-/-) and p53(FL/FL);Nestin-Cre(+); Ink4c(-/-)) that retain and lack p53 function, respectively, displayed a dependence on functional p53 to engage 17-DMAG-induced apoptosis.
Orthotopic transplantation of NES cells generated from Gorlin syndrome patients, who are predisposed to medulloblastoma due to germline-mutated PTCH1, also generated medulloblastoma.
Here we have used Ptc1(+/-); p53(-/-) mice which develop medulloblastoma to test the ability of cyclopamine to inhibit endogenous tumor growth in vivo after tumor initiation through intraperitoneal delivery, which avoids the brain damage associated with direct injection.
Shh-associated MBs originate postnatally, from dysregulated hyperproliferation of GCPs in developing cerebellum's external granular layer (EGL), as shown in heterozygous Ptch1<sup>+/-</sup> knock-out mouse strains that model human MB occurrence and progression.
These findings demonstrate an indispensable role for astrocytes in MB tumorigenesis and reveal a novel Ptch1-independent Shh pathway involved in MB progression.<i></i>.
To study the role of Ptc1 in cerebellar tumor development and to create a preclinical therapeutic platform, we have generated a conditional Ptc1 haploinsufficiency model of medulloblastoma by inactivating Ptc1 in Pax7-expressing cells of the cerebellum.
Using Ptch1(+/-) mice to study medulloblastoma progression, we found that Ptch1 loss of heterozygosity (LOH) is an early event that is associated with high levels of cell senescence in preneoplasia.
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.