SEARCH · PubMed Health

Results for “Tuberous Sclerosis Complex 2 Protein”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources

PubMed2001

Hamartin and tuberin interaction with the G2/M cyclin-dependent kinase CDK1 and its regulatory cyclins A and B.

Tuberous sclerosis (TSC) is a multi-system disorder characterized by hamartomatous tumors and abnormal brain development, with multiple foci of disrupted neuronal migration and giant dysmorphic neurons within cortical tubers. TSC is associated with mutations in 2 genes, TSC1 and TSC2, which encode hamartin and tuberin, respectively. The functions of these proteins have yet to be determined. Recently, the Drosophila homologue of TSC2, gigas, has been shown to be required for the G2/M transition of the cell cycle. However, the mechanism of this action remains unknown. Because the cyclin-dependent kinase CDK1 forms a complex with cyclin B1 to trigger the G2/M transition, we hypothesized that tuberin interacts with CDK1 to regulate its activity. In the study reported in this paper, we have used co-immunoprecipitation and confocal microscopy to demonstrate that tuberin interacts with and co-localizes with CDK1 and its binding partner cyclin B1 in multiple cell types. We also demonstrate that hamartin interacts with CDK1 and cyclin B1. We further present evidence that tuberin interacts with the other regulatory subunit of CDK1, cyclin A. These findings suggest a direct role for tuberin and hamartin in modulating the activity of CDK1 during G2 and the G2/M transition. This is the first description of a role for both tuberin and hamartin in a common cellular function, providing a potential mechanism for the identical clinicopathologic manifestations that result when either of these proteins are inactivated.

Antibody Specificity↗

PubMed2003

[Analysis of gene mutation in patients with tuberous sclerosis complex with polymerase chain reaction-single strand conformation polymorphism].

OBJECTIVE: Tuberous sclerosis complex (TSC) is an autosomal dominant disease characterized by unusual tumor-like growth, termed hamartomas that develop in a variety of tissues and organs. Clinical findings characteristic of TSC include facial angiofibroma, epilepsy and mental retardation. In the last decade, two genes (TSC1 and TSC2) responsible for this disease were identified and both of them are speculated to be a kind of tumor suppressor gene. TSC1 and TSC2 are located on 9q34 and 16p13.3, respectively. This study was designed to detect gene mutations in patients with TSC. METHODS: All the exons of TSC1 and TSC2 were analyzed by using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) in DNA separated from peripheral blood of 28 patients with TSC and 100 normal controls. Of the 28 patients, 17 were male and 11 were female, the age of the patients was 1 - 48 years. RESULTS: The mutations were not clustered on a particular exon in either of the genes. Four TSC1 mutations found in 28 cases were on exons (1 nonsense, 2 missense and 1 frameshift); 13 mutations were found in TSC2 gene (2 nonsense, 2 frameshift, 1 deletion and 8 missense). Both TSC1 and TSC2 mutations were detected in 2 cases respectively. The same missense mutation (Q654E) was found in 2 unrelated patients. There was no obvious relationship between the location of the mutation and the clinical symptoms. CONCLUSION: Mutations found in this study were distributed on various exons and there was no clustering of the mutations, the widespread distribution of TSC1/TSC2 mutations hinders the development of a simple diagnostic test, and the identification of individual mutations does not provide prediction of prognosis.

Adolescent↗

PubMed2003

Insulin activation of Rheb, a mediator of mTOR/S6K/4E-BP signaling, is inhibited by TSC1 and 2.

Tumor suppressor genes evolved as negative effectors of mitogen and nutrient signaling pathways, such that mutations in these genes can lead to pathological states of growth. Tuberous sclerosis (TSC) is a potentially devastating disease associated with mutations in two tumor suppressor genes, TSC1 and 2, that function as a complex to suppress signaling in the mTOR/S6K/4E-BP pathway. However, the inhibitory target of TSC1/2 and the mechanism by which it acts are unknown. Here we provide evidence that TSC1/2 is a GAP for the small GTPase Rheb and that insulin-mediated Rheb activation is PI3K dependent. Moreover, Rheb overexpression induces S6K1 phosphorylation and inhibits PKB phosphorylation, as do loss-of-function mutations in TSC1/2, but contrary to earlier reports Rheb has no effect on MAPK phosphorylation. Finally, coexpression of a human TSC2 cDNA harboring a disease-associated point mutation in the GAP domain, failed to stimulate Rheb GTPase activity or block Rheb activation of S6K1.

Adaptor Proteins, Signal Transducing↗

PubMed1999

Optimal temperature selection for mutation detection by denaturing HPLC and comparison to single-stranded conformation polymorphism and heteroduplex analysis.

BACKGROUND: Denaturing HPLC (DHPLC) is a semi-automated method for detecting unknown DNA sequence variants. The sensitivity of the method is dependent on the temperature at which the analysis is undertaken, the selection of which is dependent on operator experience. To circumvent this, software has been developed for predicting the optimal temperature for DHPLC analysis. We examined the utility of this software. METHODS: To maximize the relevance of our data for other investigators, we have screened 42 different amplimers from CFTR, TSC1, and TSC2. The samples consisted of 103 unique sequence heterozygotes and 126 wild-type homozygous controls. RESULTS: At the temperature recommended by the software, 96% (99 of 103) of heterozygotes and all of the wild-type controls were correctly classified. This compares favorably with sensitivities of 85% for single-stranded conformation polymorphism and 82% for gel-based heteroduplex analyses of the same fragments. CONCLUSIONS: Software-optimized DHPLC is a highly sensitive method for mutation detection. However, where sensitivity >96% is required, our data suggest that in addition to the recommended temperature, fragments should also be run at the recommended temperature plus 2 degrees C.

Chromatography, High Pressure Liquid↗

PubMed2002

14-3-3beta binds to and negatively regulates the tuberous sclerosis complex 2 (TSC2) tumor suppressor gene product, tuberin.

TSC2, or tuberin, is the product of the tuberous sclerosis tumor suppressor gene TSC2 and acts downstream of the phosphatidylinositol 3-kinase-Akt signaling pathway to negatively regulate cellular growth. One mechanism underlying its function is to assemble into a heterodimer with the TSC1 gene product TSC1, or hamartin, resulting in a reduction in phosphorylation, and hence activation, of the ribosomal subunit S6 kinase (S6K). We identified a novel interaction between TSC2 and 14-3-3beta. We found that 14-3-3beta does not interfere with TSC1-TSC2 binding and can form a ternary complex with these two proteins. Association between 14-3-3beta and TSC2 requires phosphorylation of TSC2 at a unique residue that is not a known Akt phosphorylation site. The overexpression of 14-3-3beta compromises the ability of the TSC1-TSC2 complex to reduce S6K phosphorylation. The antagonistic activity of 14-3-3beta toward TSC is dependent on the 14-3-3beta-TSC2 interaction, since a mutant of TSC2 that is not recognized by 14-3-3beta is refractory to 14-3-3beta. We suggest that 14-3-3 proteins interact with the TSC1-TSC2 complex and negatively regulate the function of the TSC proteins.

14-3-3 Proteins↗

PubMed1998

[The results of recent research in neurocutaneous syndromes].

Identification of NF1, TSC2 and TSC1 genes has enabled us to focus on their function and regulation. Evidence suggests that these genes are tumor suppressor genes. Malignant tissues in NF1 and hamartomatous tissues in TSC show "loss of heterozygosity" in NF1 and TSC1, 2 genes, respectively. In addition, in the Eker rat with hereditary renal carcinoma, a mutation in the TSC2 gene has been identified. In this review I mentioned briefly several issues to be clarified in the near future.

Animals↗

PubMed1998

Development of high-grade renal cell carcinomas in rats independently of somatic mutations in the Tsc2 and VHL tumor suppressor genes.

Ferric nitrilotriacetate (Fe-NTA) induces renal proximal tubular damage that ultimately leads to a high incidence of renal cell carcinoma (RCC) in rats. The RCCs are characterized by 1) high incidence of pulmonary metastasis and peritoneal invasion, 2) high incidence of tumor-associated mortality and 3) possible involvement of reactive oxygen species in carcinogenesis. The present study investigated the possible role of Tsc2 and VHL tumor suppressor genes in this model. Thirty-four Fe-NTA-induced primary RCCs and 20 other primary or metastatic tumors of rats were searched for genetic alteration in all the coding exons of both genes by polymerase chain reaction-single-strand-conformation polymorphism analysis and sequencing in conjunction with morphological evaluation. In the Fe-NTA-induced RCCs, frequency of metastasis or invasion was proportionally associated with the nuclear grade of the tumor (grades 1-3). Only one Fe-NTA-induced RCC of grade 1 revealed missense mutations with loss of heterozygosity in exon 10 of the Tsc2 gene (codons 334, GTG (Val) to GCG (Ala), and 336, TAT (Tyr) to CAT (His). No mutation was found in the VHL gene. The results suggest that 1) high-grade RCCs can develop in the absence of mutations in the Tsc2 and VHL genes in rats, and that 2) Tsc2 gene somatic mutation can nonetheless be one of the causes of non-Eker rat RCCs.

Animals↗

PubMed1995

Hereditary renal cell carcinoma in the Eker rat: a unique animal model for the study of cancer susceptibility.

A class of genes, the so-called tumor suppressor genes or anti-oncogenes, was originally identified as being responsible for germ-line transmission of cancer susceptibility in humans. Tumor suppressor genes are recessive at the cellular level with respect to oncogenesis but often manifest as dominantly inherited familial cancer syndromes. This type of cancer syndrome arises in the Eker rat due to a genetic defect in the tuberous sclerosis 2 (Tsc2) gene. The Eker rat familial cancer syndrome serves as a unique animal model in which to study the molecular pathways of renal tubular epithelial carcinogenesis as well as a valuable tool for studies that examine how chemical carcinogens interact with cancer susceptibility genes.

Animals↗

PubMed2002

Cell proliferation is insufficient, but loss of tuberin is necessary, for chemically induced nephrocarcinogenicity.

Although 2,3,5-tris-(glutathion-S-yl)hydroquinone (TGHQ; 2.5 micromol/kg ip) markedly increased cell proliferation within the outer stripe of the outer medulla (OSOM) of the kidney in both wild-type (Tsc2(+/+)) and mutant Eker rats (Tsc2(EK/+)), only TGHQ-treated Tsc2(EK/+) rats developed renal tumors, indicating that cell proliferation per se was not sufficient for tumor development. Tuberin expression was initially induced within the OSOM after TGHQ treatment but was lost within TGHQ-induced renal tumors. High extracellular signal-regulated kinase (ERK) activity occurred in the OSOM of Tsc2(EK/+) rats at 4 mo and in TGHQ-induced renal tumors. Cyclin D1 was also highly expressed in TGHQ-induced renal tumors. Reexpression of Tsc2 in tuberin-negative cells decreased ERK activity, consistent with the growth-suppressive effects of this tumor suppressor gene. Thus 1) stimulation of cell proliferation after toxicant insult is insufficient for tumor formation; 2) tuberin induction after acute tissue injury suggests that Tsc2 is an acute-phase response gene, limiting the proliferative response after injury; and 3) loss of Tsc2 gene function is associated with cell cycle deregulation.

Animals↗

PubMed2000

Novel cerebral lesions in the Eker rat model of tuberous sclerosis: cortical tuber and anaplastic ganglioglioma.

The Eker rat is a model for human tuberous sclerosis (TSC) caused by a mutation in the Tsc2 gene. We describe here histological and immunohistochemical findings of the brain lesions in Eker rats, with emphasis on 2 novel lesions found in this study: a cortical tuber and an anaplastic ganglioglioma. The rat cortical tuber resembled those of humans, and further confirmed the value of this animal model as a tool for investigating the molecular pathology of tuberous sclerosis. On the other hand, the rat anaplastic ganglioglioma had features of a malignant neoplasm that are absent from human subependymal giant cell astrocytomas.

Animals↗

PubMed2002

SNP identification, haplotype analysis, and parental origin of mutations in TSC2.

Inactivating mutations in the TSC2 gene, consisting of 41coding exons in 40 kb on 16p13, cause the hamartoma syndrome tuberous sclerosis. During TSC2 mutational analysis we identified ten SNPs that occur within or close to exon boundaries at minor allele frequencies greater than 5%. We determined the haplotypes for six of these SNPs and the microsatellite marker kg8 in the 3' region of TSC2 in a set of 40 parent-child trios. The most common haplotypes accounted for 53%, 11%, 6%, and 5% of chromosomes. Thirty-eight TSC2 mutation-bearing haplotypes had a similar distribution, indicating that there was no haplotype that predisposed to mutation in this region of TSC2. Family analysis was possible in 12 sporadic cases, and indicated that the mother was the parent of origin in 7 cases (3 point mutations, 2 small deletions, 2 large deletions), while the father was in 5 cases (2 point mutations, 3 small deletions). We conclude that TSC2 mutations occur at substantial frequency on both the maternally and paternally derived TSC2 alleles, in contrast to many other genetic diseases including NF1. The observations have implications for genetic counseling in TSC.

Adult↗

PubMed1997

Dynamic molecular combing: stretching the whole human genome for high-resolution studies.

DNA in amounts representative of hundreds of eukaryotic genomes was extended on silanized surfaces by dynamic molecular combing. The precise measurement of hybridized DNA probes was achieved directly without requiring normalization. This approach was validated with the high-resolution mapping of cosmid contigs on a yeast artificial chromosome (YAC) within yeast genomic DNA. It was extended to human genomic DNA for precise measurements ranging from 7 to 150 kilobases, of gaps within a contig, and of microdeletions in the tuberous sclerosis 2 gene on patients' DNA. The simplicity, reproducibility, and precision of this approach makes it a powerful tool for a variety of genomic studies.

Calpain↗

PubMed2003

Human bladder tumors with 2-hit mutations of tumor suppressor gene TSC1 and decreased expression of p27.

PURPOSE: Because loss of chromosome 9 is known to be the most common finding in human bladder tumors, we studied the mutation of the tumor suppressor gene TSC1 (chromosome 9q34) in bladder tumors. Since another tumor suppressor gene, TSC2 (chromosome 16p13.3), is reported to interact with TSC1 in the pathway that modulates tumor suppression, we assessed loss of heterozygosity (LOH) at 16p13.3. Furthermore, we also examined the expression of p27 because the TSC1 product is reported to influence the level of p27. MATERIALS AND METHODS: Microsatellite markers were used to evaluate LOH at 9q34 or 16p13.3. Mutations of TSC1 were screened by single strand conformation polymorphism analysis and verified by direct sequencing. The expression of p27 was examined by reverse transcriptase-polymerase chain reaction and immunohistochemical examination. RESULTS: We identified LOH at 9q34 in 12 of 37 bladder tumors (32.4%) but no LOH at 16p13.3 was observed. Furthermore, on single strand conformational polymorphism analysis we identified tumor specific mutations of TSC1 in 4 cases, of which all had LOH at 9q34, demonstrating the 2-hit mutations of TSC1. The expression of p27 was suppressed in all 4 cases with the 2-hit mutations of TSC1. Unexpectedly p27 suppression was detected at the transcription level, although its mechanism is unknown. CONCLUSIONS: Our data suggest that the TSC1 mutation possibly has a causative role in the initiation or progression of some bladder tumors and this process is possibly related to the functional loss of p27.

Carcinoma, Transitional Cell↗

PubMed1999

A comparison of cell phenotypes in hemimegalencephaly and tuberous sclerosis.

Hemimegalencephaly, an uncommon sporadic nonfamilial congenital dysplastic abnormality of the central nervous system, constitutes a pathological spectrum of neuronal migration disorders, but consistently includes abnormal large neurons similar to those in the cortical tubers of tuberous sclerosis. Microscopically, there are also cells with homogeneous and weakly eosinophilic cytoplasm with a single eccentric nucleus, sometimes called balloon cells (likewise prominent in tuberous sclerosis). We looked for immunohistochemical and ultrastructural differences in the large neurons and balloon cells between hemimegalencephaly and tuberous sclerosis. Microtubule-associated protein 1B and 2, phosphorylated and non-phosphorylated neurofilament and synaptophysin identify the large neurons and distinguish them from balloon cells in both entities. Balloon cells in hemimegalencephaly showed no immunoreactivity for TSC2 gene product, tuberin, and vimentin, but similar cells in tuber tissue showed consistent immunoreactivity. Balloon cells in hemimegalencephaly showed no immunoreactivity for glial fibrillary acidic protein, but some cells in tubers showed such immunoreactivity. Ultrastructurally, balloon cells in hemimegalencephaly contained very few lysosomes, microfilaments, and microtubules, but abundant lipofuscin granules. Similar cells in tubers had prominent lysosomes, more microfilaments and microtubules, and very few lipofuscin granules. The resemblance between abnormal cells in hemimegalencephaly and tuberous sclerosis is superficial; their immunohistochemistry and electron microscopic profiles show distinct differences.

Adolescent↗

PubMed2002

[A case of intractable epilepsy: diagnosis of tuberous sclerosis based on histopathological findings and immunohistochemical expression of hamartin and tuberin].

We report here a 14-year-old boy suffering from intractable epilepsy since the age of 2. Neuroimaging showed a lesion in the left temporal lobe. He underwent resection of the left temporal lobe and multiple subpial transection of the left frontal lobe at the age of 8. Histopathological findings of surgical specimens were similar to those of tubers of tuberous sclerosis (TSC), although he had no other TSC stigmata. To discriminate from cortical dysplasia grade III, we examined the immunohistochemical expression of hamartin and tuberin, the TSC1 and TSC2 gene products. Based on results, we diagnosed this case as having TSC. He has been seizure free since the operation. Although lower than preoperatively, his intelligence quotient has not been declining progressively.

Adolescent↗

PubMed1994

The molecular genetics of tuberous sclerosis.

Tuberous sclerosis (TSC) is an autosomal dominant trait characterized by the widespread development of benign tumours classified as hamartoma, and is often associated with seizures and mental retardation. The patchy distribution and focal nature of the growths suggests that they might result from inactivation of a tumour suppressor gene by a two-hit process. Over the last 2 years, studies designed to investigate both germline and somatic TSC mutations have lent support to this hypothesis. Analysis of TSC-associated hamartomas has shown loss of heterozygosity for the regions of chromosomes 9 and 16 known to harbour TSC genes, consistent with the occurrence of somatic 'second-hit' mutations. Parallel investigations using pulse field gel electrophoresis have identified constitutional deletions representing 'first-hit' mutations at 16p13.3, leading to the rapid identification of one of the causative genes, TSC2. Intriguingly, the TSC2 product, tuberin, has an area of sequence homology with the GTPase activating protein rap1GAP, suggesting a possible mechanism for its role in regulating cellular growth.

Chromosome Deletion↗

PubMed2006

TSC1/TSC2 and Rheb have different effects on TORC1 and TORC2 activity.

Target of rapamycin (TOR) plays a central role in cell growth regulation by integrating signals from growth factors, nutrients, and cellular energy levels. TOR forms two distinct physical and functional complexes, termed TOR complex 1 (TORC1) and TOR complex 2 (TORC2). TORC1, which is sensitive to rapamycin, regulates translation and cell growth, whereas TORC2, which is insensitive to rapamycin, regulates cell morphology and cell growth. The Ras homology enriched in brain (Rheb) small GTPase is known to be a key upstream activator of TORC1, although the mechanism of Rheb in TORC1 activation remains to be determined. However, the function of Rheb in the TORC2 regulation has not been elucidated. By measuring Akt and S6K phosphorylation as a functional assay for TORC1 and -2, here, we report that dRheb has an inhibitory effect on dTORC2 activity in Drosophila S2 cells. This negative effect of dRheb on dTORC2 is possibly due to a feedback mechanism involving dTORC1 and dS6K. We also observed that Rheb does not activate TORC2 in human embryonic kidney 293 cells, although it potently stimulates TORC1. Furthermore, tuberous sclerosis complex 1 (TSC1) and TSC2, which are negative regulators of Rheb, have negative and positive effects on TORC1 and -2, respectively. Our observations suggest that TSC1/2 and Rheb have different effects on the activity of TORC1 and -2, further supporting the complexity of TOR regulation.

Animals↗

PubMed2004

Involvement of G i/o proteins in nerve growth factor-stimulated phosphorylation and degradation of tuberin in PC-12 cells and cortical neurons.

Tuberin is a critical translation regulator whose role in nerve growth factor (NGF)-promoted neuronal survival has not been documented. In the present study, we examined the ability of NGF to regulate tuberin in PC-12 cells and primary cortical neurons. Incubation of serum-deprived cells with NGF stimulated tuberin phosphorylation and induced proteosome-mediated tuberin degradation. Inhibition of the phosphatidylinositol-3-kinase (PI3K) by wortmannin or overexpression of the kinase dead Akt mutant completely blocked the NGF-induced tuberin phosphorylation and degradation. It is interesting that the NGF-induced tuberin phosphorylation was partially blocked by pertussis toxin or overexpression of regulators of G protein signaling (regulator of G protein signaling Z1 and Galpha-interacting protein), suggesting the participation of G(i/o) proteins. The use of transducin as a Gbetagamma scavenger indicated that Gbetagamma subunits rather than Galpha(i/o) acted as the signal transducer. Epidermal growth factor can similarly induce tuberin phosphorylation and degradation via a PI3K/Akt pathway in PC-12 cells, but these responses were insensitive to pertussis toxin treatment. Treatment of PC-12 cells with a specific agonist to the G(i)-coupled alpha(2)-adrenoceptor also stimulated tuberin phosphorylation transiently, further demonstrating the involvement of G(i/o) signaling in tuberin regulation in PC-12 cells. Finally, overexpression of nonphosphorylable tuberin attenuated NGF-promoted survival of PC-12 cells, suggesting that the phosphorylation and degradation of tuberin are important for NGF-promoted cell survival. Together, this study demonstrates the regulatory effect of NGF and G(i/o) signaling on tuberin.

Animals↗