Activation of Akt independent of PTEN and CTMP tumor-suppressor gene mutations in epilepsy-associated Taylor-type focal cortical dysplasias

Abstract

Focal cortical dysplasias (FCD) with Taylor-type balloon cells (FCD(IIb)) are frequently observed in biopsy specimens of patients with pharmacoresistant focal epilepsies. The molecular pathogenesis of FCD(IIb), which lack familial inheritance, is only poorly understood. Due to their highly differentiated, malformative nature and glioneuronal phenotype, FCD(IIb) share neuropathological characteristics with lesions observed in familial disorders such as cortical tubers present in patients with autosomal dominant tuberous sclerosis complex (TSC), related to mutations in the TSC1 or TSC2 genes, and dysplastic gangliocytomas of the cerebellum found in Cowden disease. Current data have indicated distinct allelic variants of TSC1 to accumulate in FCD(IIb). TSC1 represents a tumor suppressor operating in the phosphatidylinositol 3-kinase (PI3K)/insulin pathway. The tumor-suppressor gene PTEN is mutated in Cowden disease. Like PTEN, also carboxyl-terminal modulator protein (CTMP) modulates PI3K-pathway signaling, both via inhibition of Akt/PKB, a kinase inactivating the TSC1/TSC2 complex. Here, we have analyzed alterations of Akt, PTEN and CTMP relevant for insulin signaling upstream of TSC1/TSC2 in FCD(IIb). Immunohistochemistry with antibodies against phosphorylated Akt (phospho-Akt; Ser 473) in FCD(IIb) (n=23) showed strong phospho-Akt expression in dysplastic FCD(IIb) components. We have further studied sequence alterations of PTEN (n=34 FCD(IIb)) and CTMP (n=20 FCD(IIb)) by laser microdissection/single-strand conformation polymorphism analysis. We observed a somatic mutation in an FCD(IIb), i.e., amino-acid exchange at nucleotide position 834 (PTEN cDNA, GenBank AH007803.1) in exon 8 with replacement of phenylalanine by leucine (F278L). We also found several silent polymorphisms of PTEN in exon 2 and exon 8 as well as silent and coding polymorphisms but no mutations in CTMP. No loss of heterozygosity in FCD(IIb) (n=6) at 10q23 was observed. To our knowledge, we here report on the first somatic mutation of a tumor-suppressor gene, i.e., PTEN, in FCD(IIb). However, our study also demonstrates that mutational alterations of PTEN and CTMP do not play major pathogenetic roles for activation of Akt in FCD(IIb). Future studies need to determine the origin of insulin pathway activation upstream of TSC1/TSC2 in FCD(IIb).

Co-expression of cyclin D1 and phosphorylated ribosomal S6 proteins in hemimegalencephaly

“…Interestingly, mutations in PTEN, which negatively regulates both mTOR and -catenin signaling [15], have been demonstrated in HMEG associated with Proteus syndrome [19]. Non-synonymous polymorphisms have been reported in PTEN and TSC1 in CDBC [2,17]; however, no functional PTEN or TSC gene polymorphisms or mutations were detected in our sample of sporadic HMEG cases. These data suggest that sporadic HMEG is genetically distinct from HMEG associated with a and b, 500 microns).…”

“…The association between phosphorylation of ribosomal S6 protein and enhanced protein synthesis, increased cell size, and expansive tissue growth has been clearly demonstrated in TSC [1,17]. Interestingly, mutations in PTEN, which negatively regulates both mTOR and -catenin signaling [15], have been demonstrated in HMEG associated with Proteus syndrome [19].…”

PI3K-AKT pathway polymerase chain reaction (PCR) array analysis of epilepsy induced by type II focal cortical dysplasia

“…Therefore, changes in TCL1A protein levels in type II FCD lesions, along with cellular distribution, and abnormal expression mechanisms are worth further study. Finally, consistent with the experimental results of Schick et al (2006), we found no change in PTEN expression, indicating that the abnormal activation of AKT in type II FCD lesions might not be associated with PTEN regulatory mutations.…”

An Investigation of the Expression of G1-Phase Cell Cycle Proteins in Focal Cortical Dysplasia Type IIB

“…Recent studies in FCD have confirmed activation of pathways, including phosphatidylinositol 3-kinase PIK3 and mTor (9,10,27,28), which have regulatory effects on cell growth and protein synthesis and are implicated in the observed cytomegaly in both neurons and BCs in these lesions. In addition, altered expression of molecules in BCs and DNs, as pAKT (28), in addition to A-catenin (11) in the wnt signaling pathway, have been previously reported in FCD series and may have influence on cell cycle regulation as they are also involved in the regulation and/or degradation of cyclins D and E (21). Based on these observations, the possibility of late G 1 arrest occurring in BCs also merited further exploration.…”