Meningiomas are common primary brain tumours frequently presenting with deleted and/or mutated NF2 gene located on 22q.1p has been reported as the second most commonly deleted chromosomal region in these neoplasms.
Merlin is thought to play a crucial role as a tumor suppressor not only in hereditary NF2-related tumors, but also in sporadic tumors such as schwannomas, meningiomas and gliomas.
All VS and many meningiomas result from loss of the neurofibromatosis type 2 (NF2) gene product merlin, with ensuing PAK hyperactivation and increased cell proliferation/survival.
Allelic loss on 22q also is characteristic for meningiomas, however most of these alterations are considered to be associated with mutations of the NF2 gene.
Alterations in the NF2 gene coding for merlin cause all tumours that occur in patients suffering from neurofibromatosis type 2, all spontaneous schwannomas and the majority of meningiomas.
Analogous to merlin, we show that DAL-1 loss is an early event in meningioma tumorigenesis, suggesting that these two protein 4.1 family members are critical growth regulators in the pathogenesis of meningiomas.
Analysis of 40 CpG sites distributed within 750 bp of the promoter region suggests that NF2 promoter methylation does not play a major role in meningioma development.
As the molecular pathogenesis of meningiomas and schwannomas, characterized by NF2 gene alterations, remains unclear and suitable molecular targets need to be identified, we used low density cDNA microarrays to establish expression patterns of 96 cancer-related genes on 23 schwannomas, 42 meningiomas and 3 normal cerebral meninges.
Because group I p21-activated kinases (Paks) bind to and are inhibited by the NF2-encoded protein Merlin, we assessed the signaling and anti-tumor effects of three group-I specific Pak inhibitors - Frax597, 716 and 1036 - in NF2-/- meningiomas in vitro and in an orthotopic mouse model.
Cell lines Ben-Men-1 (benign), IOMM-Lee and KT21 (malignant), and pairs of merlin-positive or -negative meningioma cells were used to assess sensitivity toward mTORC1 inhibitors in methyl-tetrazolium and bromodeoxyuridine (BrdUrd) assays.
Chromosome 22q carries the locus of a tumor suppressor gene, the neurofibromatosis 2 (NF2) gene, which has been shown to be lost or mutated in some NF2-related tumors, sporadic meningiomas, and vestibular schwannomas, as well as a few other tumors.
Consequently, the disruptions due to merlin inactivation in the progression of malignant mesothelioma may represent a tumor suppressor role operating by a different pathway than that in schwannoma or meningioma.
Current data indicate that meningioma initiation is closely linked to the inactivation of one or more members of the highly conserved protein 4.1 superfamily, including the neurofibromatosis type 2 gene product merlin/schwannomin, protein 4.IB (DAL-1) and protein 4.1R.
Defects caused by mutations of the NF2 gene give rise to NF2 disease, which is generally characterized by the formation of bilateral vestibular schwannomas and, to a lesser extent, meningiomas and ependymomas.