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Results for “Tuberous Sclerosis Complex 2 Protein”

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PubMed1999

Loss of the TSC2 product tuberin in subependymal giant-cell tumors.

We investigated immunocytochemically the expression of tuberin, the TSC2 gene product, in brain resections from children with and without tuberous sclerosis, to characterize the phenotype of balloon and tumor cells, and to elucidate the relationship between tuberin and formation of subependymal giant-cell tumors. In cortical tubers, tuberin was expressed in processes and cell bodies of balloon cells, which also showed consistent vimentin and nestin immunoreactivity, but no glial fibrillary acidic protein, neurofilament, or galactocerebroside positivity by immunofluorescence confocal microscopy. The majority of balloon cells in white matter showed weaker tuberin immunoreactivity than similar cells in cortical tubers. In subependymal giant-cell tumors, there was minimal to no immunoreactivity. Why tuberin is expressed in tubers but not in subependymal giant-cell tumors is not known. If tuberin plays a role in tumor suppression, then lack of tuberin might be a marker for deletion of both alleles, leading to enhanced cellular growth in subependymal giant-cell hamartomas, eventually of sufficient size to cause clinical symptoms.

Adolescent↗
PubMed2000

Simultaneous loss of hamartin and tuberin from the cerebrum, kidney and heart with tuberous sclerosis.

Tuberous sclerosis (TSC) is caused by a mutation in either the TSC1 or TSC2 gene. The clinical manifestations of mutations of the two genes are hardly distinguishable, for reasons as yet unknown. In this study, we examined the expression of the products of these genes, hamartin and tuberin, in control and TSC tissues. Western blotting disclosed that hamartin and tuberin are both abundant in the cerebral gray matter and that they have similar subcellular distributions and developmental patterns of expression. Immunohistochemical localizations of hamartin and tuberin were also similar, with high levels of expression being localized to the cerebral neurons and glial cells, renal uriniferous and collecting tubules, and cardiac muscles. In the cerebrum with TSC, both hamartin and tuberin were simultaneously reduced in the cortical tubers and subependymal giant cell astrocytomas, and from the normal-appearing cortex. The renal angiomyolipomas and cardiac rhabdomyomas also showed a loss of both the proteins. These results provide evidence for the co-localization and interaction of hamartin and tuberin in vivo, and suggest that a mutation in one TSC gene may secondarily affect the expression of the other in some TSC lesions.

Adolescent↗
PubMed2001

Cells derived from tuberous sclerosis show a prolonged S phase of the cell cycle and increased apoptosis.

Tuberous sclerosis complex (TSC) is a multisystemic disorder characterized by systemic hamartomas. Although the disease-determining genes TSC1 and TSC2 have been isolated, the molecular pathogenesis of the disease is not understood. We examined cell cycle abnormalities in skin specimens and cultured cells derived from specific lesions of TSC patients with confirmed TSC1 or TSC2 mutations. None of the specimens used in this study showed loss of heterozygosity (LOH). We detected more cells positive for PCNA and fewer cells positive for MPP2 in the epidermis of TSC patients than in the epidermis of control patients without TSC. Incorporation of 5-bromo-2-deoxyuridine (BrdU) was similar in fibroblasts derived from TSC lesions and in normal human fibroblasts. These results suggest that the cell cycle of TSC cells shows a prolonged S phase. Flow cytometric analysis confirmed S phase prolongation in TSC cells. Many apoptotic cells were detected by a nick end labeling assay in both skin tissue and cultured fibroblasts derived from specific TSC lesions. Examination of cyclin levels showed increased nuclear cyclin A and cytoplasmic cyclin B and decreased nuclear cdc2 levels. We conclude that suppression of either TSC1 or TSC2 may change cyclin levels, prolong S phase and induce apoptotic cell death.

Adult↗
PubMed2002

An unusual renal angiomyolipoma with morphological lymphangioleiomyomatosis features and coexpression of oestrogen and progesterone receptors.

Angiomyolipoma is the most common mesenchymal renal tumour, the clonal origin of which has recently been demonstrated. It is composed of varying amounts of blood vessels, smooth muscle and fat. In this report, we describe a renal angiomyolipoma, which is unusual owing to the presence of a lymphangioleiomyomatosis-like component, occurring in a 41-year-old woman suffering from sporadic lymphangioleiomyomatosis. The diagnosis was based on histopathological and immunohistochemical findings. The tumour consisted of an intimate admixture of two components: one was typical of a classical angiomyolipoma and the other was reminiscent of lymphangioleiomyomatosis. HMB45 positivity was found on 5% of the cells of the angiomyolipoma component. Ten percent of the nuclei of the lymphangioleiomyomatosis and angiomyolipoma components expressed oestrogen receptors and 5% progesterone receptors. This case illustrates a very unusual pattern of a renal angiomyolipoma containing a lymphangioleiomyomatosis-like component. The oestrogen and progesterone immunoreactivity suggests that angiomyolipoma could be hormonally dependent. Therefore, we have emphasised the morphological and immunohistochemical similarities between angiomyolipoma and lymphangioleiomyomatosis.

Adult↗
PubMed2000

Molecular genetic advances in tuberous sclerosis.

Over the past decade, there has been considerable progress in understanding the molecular genetics of tuberous sclerosis, a disorder characterised by hamartomatous growths in numerous organs. We review this progress, from cloning and characterising TSC1 and TSC2, the genes responsible for the disorder, through to gaining insights into the functions of their protein products hamartin and tuberin, and the identification and engineering of animal models. We also present the first comprehensive compilation and analysis of all reported TSC1 and TSC2 mutations, consider their diagnostic implications and review genotype/phenotype relationships.

Alternative Splicing↗
PubMed2000

Molecular analysis of the TSC1 and TSC2 tumour suppressor genes in sporadic glial and glioneuronal tumours.

Reduced expression of the TSC2 tumour suppressor gene product, tuberin, has been reported in sporadic astrocytomas, suggesting that the TSC genes may play a role in formation of sporadic glial or glioneuronal tumours. We studied paired constitutional and tumour DNA samples from 100 patients with sporadic glial and glioneuronal tumours for loss of heterozygosity (LOH) at the TSC1 and TSC2 loci using a combination of seven previously reported and seven novel polymorphic markers. LOH was seen in 1/16 astrocytomas, 3/15 ependymomas, 5/16 gangliogliomas, 2/14 glioblastoma multiforme, 0/7 oligodendrogliomas, 0/7 tumours of mixed oligodendrocytic/astrocytic histology, 2/11 pilocytic astrocytomas and 0/1 subependymal giant cell astrocytomas informative at both loci. However, SSCP screening of all coding exons of the TSC1 or TSC2 genes in the tumours displaying LOH, and of both genes in 21 gangliogliomas, revealed no intragenic mutations. The lack of demonstrable inactivation of both alleles of either TSC gene in any of the tumours investigated suggests that they do not play a frequent role in the aetiology of sporadic glial or glioneuronal tumours.

Alleles↗
PubMed2005

Tuberous sclerosis and the kidney: from mesenchyme to epithelium, and beyond.

The renal manifestations of tuberous sclerosis complex (TSC) are remarkably diverse, including polycystic kidney disease, oncocytomas, renal cell carcinomas, and both benign and malignant angiomyolipomas. All of these occur in children as well as adults with TSC. Benign angiomyolipomas, which can cause spontaneous life-threatening hemorrhage, are by far the most prevalent and the greatest source of morbidity. What is particularly unusual about TSC, setting it apart from virtually all other inherited forms of renal disease, is the abnormalities of both mesenchymal cells (angiomyolipomas) and epithelial cells (cysts, oncocytomas, and carcinomas). Recently, the TSC1/TSC2 protein complex was shown to inhibit the kinase mTOR (mammalian target of rapamycin). This places TSC1/TSC2 at center stage in signaling pathways that regulate cell growth. Furthermore, recent advances in TSC1/TSC2 signaling open the door for targeted therapy for TSC patients. Here, we will address the genetic, cellular and biochemical mechanisms that may contribute to the unusually broad spectrum of renal disease in cells with TSC1 or TSC2 mutations, and consider how the TSC signaling pathways may be linked to other renal diseases such as polycystic kidney disease and renal cell carcinoma.

Angiomyolipoma↗
PubMed2004

Proteins interacting with the tuberous sclerosis gene products.

Tuberous sclerosis (TSC) is an autosomal dominant tumor suppressor gene syndrome affecting about 1 in 6000 to 10000 individuals. The genes, TSC1, encoding hamartin, and TSC2, encoding tuberin are responsible for TSC. Since their identification 1997 and 1993 respectively, a variety of different functions have been described for the TSC gene products. Hamartin and tuberin form a complex, providing a tentative explanation for the similar disease phenotype in TSC patients with mutations in either of these genes. In addition, associations of hamartin or tuberin with several different proteins have been demonstrated. In this review, we summarize the current knowledge on hamartin- and tuberin-interacting proteins and discuss their role for the understanding of the functions of the TSC gene products.

Animals↗
PubMed2005

14-3-3 proteins are involved in the regulation of mammalian cell proliferation.

The 14-3-3 proteins are a family of abundant, widely expressed acidic polypeptides. The seven isoforms interact with over 70 different proteins. 14-3-3 isoforms have been demonstrated to be involved in the control of positive as well as negative regulators of mammalian cell proliferation. Here we used the approach of inactivating 14-3-3 protein functions via overexpression of dominant negative mutants to analyse the role of 14-3-3 proteins in mammalian cell proliferation. We found 14-3-3 dominant negative mutants to downregulate the proliferation rates of HeLa cells. Overexpression of these dominant negative mutants triggers upregulation of the protein levels of the cyclin-dependent kinase inhibitor p27, a major negative cell cycle regulator. In addition, they downregulate the protein levels of the important cell cycle promoter cyclin D1. These data provide new insights into mammalian cell proliferation control and allow a better understanding of the functions of 14-3-3 proteins.

14-3-3 Proteins↗
PubMed2002

Tuberous sclerosis in a 19-week fetus: immunohistochemical and molecular study of hamartin and tuberin.

Tuberous sclerosis complex (TSC) is a genetically heterogeneous disease caused by mutations of TSC1 or TSC2 genes. It involves multiple organ systems resulting in mild to lethal hamartoma formation due to gene mutation in the germ line and loss of heterozygosity (LOH) in somatic cells. Hamartin (TSC1) and tuberin (TSC2) are expressed broadly. However, little is known about tissue susceptibility to hamartomas when equal or similar amounts of TSC gene expression are present. In this study, we present a 19-week gestational age fetus with pathological features of TSC, which was confirmed by finding LOH of TSC2 in a cardiac rhabdomyoma. Developmental expression of hamartin and tuberin in the TSC fetus, an age-matched non-TSC fetus, and a 26-week gestational age non-TSC fetus were analyzed by immunohistochemistry. We found that in addition to the differential expression of the TSC genes in some normal tissues compared with that in the TSC-affected fetus, the cellular localization and distribution of hamartin and tuberin were dramatically different in different tissues. In general, hamartin and tuberin are mainly expressed in epithelial cells, myocytes, and neural tissues. By comparing the incidence of the hamartomas in early childhood and gene expression in tissues, it appears that tissues with co-expression of hamartin and tuberin are prone to a higher incidence of hamartomas than those expressing only one protein, or two proteins but in different patterns of cellular localization.

Adult↗
PubMed2006

Giant cells: contradiction to two-hit model of tuber formation?

Tuberous sclerosis (TSC) is an autosomal dominant disease characterized by the formation of hamartomatous lesions in many organs, including brain, heart or kidneys. It has been found that TSC is caused by the mutation in one of the two tumor suppressor genes: TSC1 or TSC2, encoding hamartin and tuberin, respectively. According to Knudson's two-hit model of tumorigenesis, second-hit mutation and resulting loss of heterozygosity (LOH) of a tumor suppressor gene is necessary for tumor formation. In fact, LOH is commonly found in several types of hamartomas formed in the process of tuberous sclerosis, but, interestingly, not in brain lesions, containing characteristic giant cells. In this paper, we review literature covering origination of giant cells and present several hypotheses explaining why in spite of the presence of hamartin and tuberin, brain lesions form in TSC patients.

Giant Cells↗
PubMed2006

Hamartin and tuberin modulate gene transcription via beta-catenin.

Tuberous sclerosis, neurological genetic disorder characterized by the formation of benign tumors or hamartomas in multiple organ systems, is recently getting much attention. Numerous papers describe still-not-fully-explained pathogenesis of the disease. Studies on tuberous sclerosis allowed identification of two tumor suppressor genes, TSC1 and TSC2, encoding proteins implicated in the disease: hamartin and tuberin, respectively. The importance of these proteins is confirmed by their ubiquitous character and by the fact that TSC1/TSC2 complex is involved in the regulation of the activity of mTOR, a master controller of protein translation. Thus, the meaning of hamartin and tuberin goes far beyond tuberous sclerosis. As far as the influence of the TSC1/TSC2 complex on protein translation is well described in numerous reviews, little attention is drawn to the recently discovered role of the TSC1/TSC2 complex in gene transcription via the WNT signaling pathway. The present paper focuses on recent developments documenting the role of hamartin and tuberin in the WNT pathway.

Animals↗
PubMed2003

Tuberous sclerosis genes regulate cellular 14-3-3 protein levels.

The genes TSC1, encoding hamartin, and TSC2, encoding tuberin are responsible for tuberous sclerosis. This autosomal dominant tumor suppressor gene syndrome affects about 1 in 6000 individuals. A variety of tumors characteristically occur in different organs of tuberous sclerosis patients and are believed to result from defects in cell cycle/cell size control. We performed a proteomics approach of two-dimensional gel electrophoresis with subsequent mass spectrometrical identification of protein spots after ectopic overexpression of human TSC1 or TSC2. We found the cellular levels of four isoforms of the 14-3-3 protein family, 14-3-3 gamma, 14-3-3, 14-3-3 sigma, and 14-3-3 zeta, to be regulated by the two tuberous sclerosis gene products. In the same experiments the protein levels of keratin 7, capZ alpha-1 subunit, ezrin, and nedasin were not affected by ectopic TSC1 or TSC2. Western blot analyses confirmed the deregulation of 14-3-3 proteins upon ectopic overexpression of TSC1 and TSC2. A TSC1 mutant not encoding the transmembrane domain and the tuberin-binding domain but harbouring most of the coiled-coil region and the ERM protein interaction domain of hamartin did not affect 14-3-3 protein levels. The here presented findings suggest that deregulation of 14-3-3 protein amounts might contribute to the development of tumors in tuberous sclerosis patients. These data provide important new insights into the molecular development of this disease especially since both, the TSC genes and the 14-3-3 proteins, are known to be involved in mammalian cell cycle control.

14-3-3 Proteins↗
PubMed2005

Phosphorylation and binding partner analysis of the TSC1-TSC2 complex.

Tuberous sclerosis complex (TSC) is an autosomal dominant benign tumour syndrome caused by mutations to either the TSC1 or TSC2 tumour suppressor gene. The TSC1 and TSC2 gene products, TSC1 and TSC2, form a protein complex that integrates inputs from multiple signalling cascades to inactivate the small GTPase rheb, and thereby inhibit mTOR-dependent cell growth. We have used matrix-assisted laser desorption/ionisation time-of-flight and Fourier transform mass spectrometry to identify TSC1 and TSC2 phosphorylation sites and candidate TSC1 and TSC2 interacting proteins. We identified three sites of TSC2 phosphorylation and a novel site of TSC1 phosphorylation, and investigated the roles of these sites in regulating the activity of the TSC1-TSC2 complex. In addition, we identified three TSC1-TSC2 interacting proteins, including DOCK7 a putative rhebGEF.

Amino Acid Sequence↗
PubMed2006

Mutational analysis of TSC1 and TSC2 in Korean patients with tuberous sclerosis complex.

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by a broad phenotypic spectrum that includes seizures, mental retardation, renal dysfunction and dermatological abnormalities. TSC is caused by mutations affecting either of the tumor-suppressor genes TSC1 and TSC2. At least 495 mutations of TSC1 and TSC2 have been reported. Twenty-two males and 22 females who were diagnosed with TSC at the Seoul National University Children's Hospital between 1982 and 2002 were enrolled in the study. Forty-four patients were from different families and included nine familial cases and 35 sporadic cases. Denaturing high performance liquid chromatography and DNA sequencing analysis of TSC1 and TSC2 revealed 13 types of mutations (30%). One novel mutation of TSC1 and nine novel mutations of TSC2 were identified. The TSC1 mutation and one of the nine TSC2 mutations were missense mutations and seven of the nine TSC2 mutations caused truncation of proteins. One novel single nucleotide substitution was identified at the consensus splicing donor site of exon 39 (c.5,069-1G>A). This mutation is predicted to cause a splicing error. Of the TSC2 mutation loci, the correlation with cardiac rhabdomyoma was more significant when the mutation was in the C-terminal part of tuberin than the N-terminal part. This is the first extensive mutational analysis of TSC1 and TSC2 in Korean TSC patients.

Child, Preschool↗
PubMed2006

Essential role of tuberous sclerosis genes TSC1 and TSC2 in NF-kappaB activation and cell survival.

The TSC1-TSC2 complex has recently been implicated in cell survival responses. We observed that NF-kappaB signaling is attenuated in TSC1- and TSC2-deficient MEFs concomitant with reduced survival following DNA damage or TNFalpha stimulation. Reconstitution of TSC2 expression in TSC2(-/-) MEFs rescued survival in an NF-kappaB activity-dependent manner. Furthermore, in TSC2(-/-) MEFs, the rapamycin-mediated inhibition of deregulated mTOR activity restored NF-kappaB activation and survival. This rapamycin-mediated effect was reversed by inhibition of NF-kappaB transcriptional activation or by inhibition of ERK1/2 MAP kinase or PI-3K pathways, which lie on signaling cascades that lead to NF-kappaB activation. These results provide evidence for a crosstalk between the TSC/Rheb/mTOR pathway and the NF-kappaB induction pathways and indicate that NF-kappaB functions as an important survival factor that regulates TSC2-dependent cell survival.

Animals↗
PubMed2005

Phosphorylation and functional inactivation of TSC2 by Erk implications for tuberous sclerosis and cancer pathogenesis.

Tuberous sclerosis (TSC) is a tumor syndrome caused by mutation in TSC1 or TSC2 genes. TSC tumorigenesis is not always accompanied by loss of heterozygosity (LOH). Recently, extracellular signal-regulated kinase (Erk) has been found activated in TSC lesions lacking TSC1 or TSC2 LOH. Here, we show that Erk may play a critical role in TSC progression through posttranslational inactivation of TSC2. Erk-dependent phosphorylation leads to TSC1-TSC2 dissociation and markedly impairs TSC2 ability to inhibit mTOR signaling, cell proliferation, and oncogenic transformation. Importantly, expression of an Erk nonphosphorylatable TSC2 mutant in TSC2+/- tumor cells where Erk is constitutively activated blocks tumorigenecity in vivo, while wild-type TSC2 is ineffective. Our findings position the Ras/MAPK pathway upstream of the TSC complex and suggest that Erk may modulate mTOR signaling and contribute to disease progression through phosphorylation and inactivation of TSC2.

Amino Acid Sequence↗