PubMed Health⌕ Search

Biomedical subjects

M Hengstschläger

Publications and source records attributed to M Hengstschläger.

At least 19 recordsLinked to original sources
PubMed2006

Akt regulates nuclear/cytoplasmic localization of tuberin.

The autosomal dominantly inherited disease tuberous sclerosis (TSC) affects approximately 1 in 6000 individuals and is characterized by the development of tumors, named hamartomas, in different organs. TSC1, encoding hamartin, and TSC2, encoding tuberin are tumor suppressor genes responsible for TSC. Hamartin and tuberin form a complex, of which tuberin is assumed to be the functional component. The TSC proteins have been implicated in the control of cell cycle by activating the cyclin-dependent kinase inhibitor p27 and in cell size regulation by inhibiting the mammalian target of rapamycin (mTOR)/p70S6K cascade. Phosphorylation of S939 and T1462 by Akt downregulates tuberin's potential to inhibit mTOR/p70S6K. Here, we show that this tuberin phosphorylation by Akt does not affect tuberin-mediated control of p27 protein amounts. This demonstrates that regulating p27 protein amounts and mTOR/p70S6K are separable functions of tuberin. Furthermore, we found that phosphorylation by Akt triggers upregulation of cytoplasmic and downregulation of nuclear tuberin. In cycling cells with high Akt activity, tuberin is predominantly localized to the cytoplasm. In arrested G0 cells with downregulated Akt activity, a significant proportion of tuberin is localized to the nucleus. Upon re-entry into the normal ongoing cell cycle, nuclear localization of tuberin is downregulated parallel to the activation of Akt. Recently, the mTOR/p70S6K cascade has been demonstrated to exist in both the cytoplasm and nucleus. We here also found that tuberin harbors the potential to regulate p70S6K activity in both the cytoplasm and nucleus. This description of functional tuberin in the cytoplasm and the nucleus together with our observation of Akt-controlled and cell cycle-regulated tuberin localization are of particular interest for a further understanding of tuberin's function as a gate keeper of the G0 cell status as well as of Akt's activity to control cell proliferation.

Animals↗
PubMed2006

Tuberin negatively affects BCL-2's cell survival function.

Uncontrolled cell cycle progression and cell growth are key properties of tumor cells. The tumor suppressor genes responsible for the autosomal dominantly inherited disease tuberous sclerosis (TSC) have been demonstrated to control both, cell cycle and cell size regulation. Hamartin, encoded by TSC1, and tuberin, encoded by TSC2, form a complex, of which tuberin is assumed to be the functional component. Loss of TSC genes function triggers hamartoma development in TSC patients. However, in vivo mostly tumor cell development is rapidly terminated via apoptosis. BCL-2, the founding member of the BCL-2 family of proteins, is well known for its anti-apoptotic properties. Here we show that pro-apoptotic actinomycin D cannot interfere with BCL-2's cell survival functions. However, we found tuberin to negatively regulate BCL-2's anti-apoptotic effects on low serum-induced apoptosis. These findings warrant further investigations to elucidate the molecular mechanism underlying tuberin's negative effects on cell survival.

Animals↗
PubMed2006

Tuberin activates the proapoptotic molecule BAD.

TSC1, encoding hamartin, and TSC2, encoding tuberin, are tumor suppressor genes responsible for the autosomal dominantly inherited disease tuberous sclerosis (TSC). TSC affects approximately 1 in 6000 individuals and is characterized by the development of tumors, named hamartomas, in different organs. Hamartin and tuberin form a complex, of which tuberin is assumed to be the functional component. The TSC proteins have been implicated in the control of cell cycle and cell size. In addition to enhanced growth, reduced death rates can lead to tumor development. Therefore, defects in the apoptosis-inducing pathways contribute to neoplastic cell expansion. Here, we show that tuberin triggers apoptosis, accompanied by downregulation of p70S6K activity and of phosphorylation of BAD on residue Ser136, and by upregulation of the interaction of BAD/BCL-2 and BAD/BCL-XL. AKT phosphorylation negatively regulates tuberin's potential to trigger apoptosis. Experiments with BAD-/- cells demonstrate BAD to be a mediator of tuberin's effects on the regulation of apoptosis. Tuberin interferes with insulin-like growth factor-1-induced BAD Ser136 phosphorylation and cell survival. Our work proposes a model in which tuberin-mediated inhibition of p70S6K activates BAD to heterodimerize with BCL-2 and BCL-XL to promote apoptosis. A mutation of TSC2--as it occurs in TSC patients--attenuates this proapoptotic potential, underscoring the relevance of our findings for human pathophysiology.

Animals↗
PubMed2006

Cytoskeleton changes following differentiation of N1E-115 neuroblastoma cell line.

No systematic approach to detect expression of differentiation-related elements was published so far. The undifferentiated N1E-115 neuroblastoma cell line was switched into a neuronal phenotype by DMSO treatment and used for proteomic experiments. We used two-dimensional gel electrophoresis followed by unambiguous mass spectrometrical identification of proteins to generate a map of cytoskeleton proteins (CPs), i.e., to search for differentiation-related structures. Alpha-actin, actin-like protein 6A, gamma-tubulin complex component 2, tubulin alpha 3/alpha 7, CLIP associating protein 2, B4 integrin interactor homolog were detectable in the undifferentiated cell line exclusively and neuron-specific CPs drebrin and presynaptic density protein 95, actin-related protein 2/3, alpha and beta-centractin, PDZ-domain actin binding protein, actinin alpha 1, profilin II, ezrin, coactosin-like protein, transgelin 2, myosin light polypeptide 6, tubulin alpha 2, 6 and 7, beta tubulin (94% similar with tubulin beta-2), tubulin beta 3, tubulin tyrosine ligase-like protein 1, lamin B1 and keratin 20 were observed in the differentiated cell line only. We herein identified differentiation-related expressional patterns thus providing new evidence for the role of CPs in the process of neuronal differentiation.

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↗
PubMed2005

The neuronal differentiation process involves a series of antioxidant proteins.

Involvement of individual antioxidant proteins (AOXP) and antioxidants in the differentiation process has been already reported. A systematic search strategy for detecting differentially regulated AOXP in neuronal differentiation, however, has not been published so far. The aim of this study was to provide an analytical tool identifying AOXP and to generate a differentiation-related AOXP expressional pattern. The undifferentiated N1E-115 neuroblastoma cell line was switched into a neuronal phenotype by DMSO treatment and used for proteomic experiments: We used two-dimensional gel electrophoresis followed by unambiguous mass spectrometrical (MALDI-TOF-TOF) identification of proteins to generate a map of AOXP. 16 AOXP were unambiguously determined in both cell lines; catalase, thioredoxin domain-containing protein 4 and hypothetical glutaredoxin/glutathione S-transferase C terminus-containing protein were detectable in the undifferentiated cells only. Five AOXP were observed in both, undifferentiated and differentiated cells and thioredoxin, thioredoxin-like protein p19, thioredoxin reductase 1, superoxide dismutases (Mn and Cu-Zn), glutathione synthetase, glutathione S-transferase P1 and Mu1 were detected in differentiated cells exclusively. Herein a differential expressional pattern is presented that reveals so far unpublished antioxidant principles involved in neuronal differentiation by a protein chemical approach, unambiguously identifying AOXP. This finding not only shows concomitant determination of AOXP but also serves as an analytical tool and forms the basis for design of future studies addressing AOXP and differentiation per se.

Animals↗
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↗
PubMed2003

Stem cell marker expression in human trisomy 21 amniotic fluid cells and trophoblasts.

Down Syndrome is the most frequent genetic cause of mental retardation. Deregulation of specific differentiation processes is a major cause for the neuropathological cell features typical for this syndrome. The molecular mechanisms leading to Down Syndrome are likely to be operative from the very earliest time of embryonic/fetal development. We therefore analysed human amniotic fluid cell samples and cytotrophoblastic cells from placental biopsies, both with normal karyotypes and with trisomy 21, for the mRNA expression of stem cell marker genes. Here we describe for the first time that these human primary cell sources contain cells that express telomerase reverse transcriptase, leukemia inhibitory factor receptor, and bone morphogenetic protein receptor II. A specific difference between aneuploid and normal cells could not be detected. These data provide evidence that human amniotic fluid and cytotrophoblastic cell cultures might provide a new source for research on primary cell systems expressing these stem cell markers. In addition, it is suggested that early deregulation of the expression of these genes in the here analysed cell sources does not contribute to the molecular development of Down Syndrome.

Amniotic Fluid↗
PubMed2003

Cell cycle and cell size regulation in Down syndrome cells.

Although the neuropathological features typical for Down Syndrome obviously result from deregulation of both, cell cycle control and differentiation processes, so far research focused on the latter. Considering the known similarities between the neuropathology of Down Syndrome and Alzheimer's disease and the knowledge, that in Alzheimer's disease neuronal degeneration is associated with the activation of mitogenic signals and cell cycle activation, it is tempting to investigate the consequences of an additional chromosome 21 on mammalian cell cycle regulation. We analysed the distribution of cells in different cell cycle phases on the flowcytometer and the cell size of human amniotic fluid cells with normal karyotypes and with trisomy 21. We could not detect any significant differences suggesting that the presence of an additional copy of the about 225 genes on human chromosome 21 does not trigger cell cycle effects in amniotic fluid cells. These data provide new insights into the cell biology of trisomy 21 cells.

Amniotic Fluid↗
PubMed2002

Prenatal diagnosis of a supernumerary aberrant chromosome 9.

For counselling of parents, as well as to basically understand how chromosome aneuploidies affect embryonic or fetal development, it is of great importance to analyse and collect genotypes of fetuses with clinical anomalies. This report describes the first prenatal diagnosis of a supernumerary chromosome 9 with deletion of the chromosome region 9q34. Ultrasound examination in the 13th week of gestation detected increased nuchal translucency of 6.9 mm, fetal ascites and a pronounced facial anomaly. Hysteroscopic examination before curettage made it possible to describe this facial anomaly as a double-sided, median defect of the superior lip with protrusion of parts of intersegments. This report provides evidence that the absence of trisomy 9 in 9q34 does not prevent abnormal facial development.

Abnormalities, Multiple↗
PubMed2002

Prenatal diagnosis of a de novo inversion of chromosome (2)(p21q11).

Prenatal diagnosis of "apparently balanced" chromosomal rearrangements, if not inherited from a parent, are problematic for genetic counsellors and families. Although the parents need to be informed about the increased risk of multiple congenital anomalies, the anomalies that the fetus is at risk can not be discussed unless a similar breakpoint and accompanying phenotype have been reported in the literature. In the reported case prenatal ultrasound examination revealed a massive hydrocephalus internus and IUGR. The karyotype of the fetus was inv(2)(p21q11) de novo. Postmortem examination revealed short palpebral fissures, hypertelorism, atypical nasiolabial configuration, microgenia, extended position of the fingers, atypical proximal inserted first toe, hydrocephalus internus, hypoplasia of the cerebellum and bulbi olfactorii, bilateral hypoplastic lungs, atrial septal defect II, small right ventricle, dysplasia of the pulmonary valve, hypoplastic pulmonary artery, right proximal ureterostenosis, hypoplastic gall bladder. This is the first description of a de novo inversion (2)(p21q11) in a fetus with multiple malformations.

Abnormalities, Multiple↗
PubMed2002

Dandy-Walker malformation as sonographic marker for fetal triploidy.

Fetal triploidy is a frequent reason for early abortion, and only few fetuses survive into the second trimester of pregnancy. Common sonographic markers for triploidy in the second trimester are severe asymmetric growth restriction (triploidy of maternal origin) and partial molar changes of the placenta (triploidy of paternal origin), together with structural fetal malformations. We report prenatal sonographic findings of thirteen triploid fetuses between 18 and 34 weeks' gestational age (eleven fetuses with 69, XXX, and two fetuses with 69, XXY). Intrauterine growth restriction (11/13 fetuses), oligohydramnios (8/13), bilateral cerebral ventriculomegaly (6/13), structural heart defects (4/13), and Dandy-Walker malformation or Dandy-Walker variant (4/13) were the most frequent findings. We conclude that the Dandy-Walker malformation and Dandy-Walker variant should be considered as additional sonographic markers for fetal triploidy.

Congenital Abnormalities↗
PubMed2001

Tuberous sclerosis causing mutants of the TSC2 gene product affect proliferation and p27 expression.

The autosomal dominant disease tuberous sclerosis (TSC) is caused by mutations in either TSC1 on chromosome 9q34, encoding hamartin, or TSC2 on chromosome 16p13.3, encoding tuberin. TSC is characterized by hamartomas that occur in many organs of affected patients and these have been considered to likely result from defects in proliferation control. Although the true biochemical functions of the two TSC proteins have not been clarified, a series of independent investigations demonstrated that modulated hamartin or tuberin expression cause deregulation of proliferation/cell cycle in human, rodent and Drosophila cells. In support of tuberin acting as a tumor suppressor, ectopic overexpression of TSC2 has been shown to decrease proliferation rates of mammalian cells. Furthermore, overexpression of TSC2 has been demonstrated to trigger upregulation of the cyclin-dependent kinase inhibitor p27. We report that three different naturally occurring and TSC causing mutations within the TSC2 gene eliminate neither the anti-proliferative capacity of tuberin nor tuberin's effects on p27 expression. For the first time these data provide strong evidence that deregulation of proliferation and/or upregulation of p27 are not likely to be the primary/only mechanisms of hamartoma development in TSC. These results demand reassessment of previous hypotheses of the pathogenesis of TSC.

Animals↗
PubMed2001

Prenatal diagnosis of a de novo supernumerary marker derived from chromosome 16.

Marker chromosomes are supernumerary chromosomes of unknown origin and are seldom found in prenatal diagnosis. Application of fluorescent in situ hybridization (FISH) allows the identification of the chromosomal origin of markers. Estimation of the risk of an abnormal phenotype outcome can be enabled by collecting data on phenotypes associated with markers of the same chromosomal origin. So far only very few cases of prenatal diagnosis of de novo supernumerary markers derived from chromosome 16 have been reported. Here the prenatal diagnosis of a de novo supernumerary marker chromosome 16 is described and the relevant literature discussed.

Abortion, Induced↗
PubMed2001

Tuberous sclerosis gene products in proliferation control.

Two genes, TSC1 and TSC2, have been shown to be responsible for tuberous sclerosis (TSC). The detection of loss of heterozygosity of TSC1 or TSC2 in hamartomas, the growths characteristically occurring in TSC patients, suggested a tumor suppressor function for their gene products hamartin and tuberin. Studies analyzing ectopically modulated expression of TSC2 in human and rodent cells together with the finding that a homolog of TSC2 regulates the Drosophila cell cycle suggest that TSC is a disease of proliferation/cell cycle control. We discuss this question including very recent data obtained from analyzing mice expressing a modulated TSC2 transgene, and from studying the effects of deregulated TSC1 expression. Elucidation of the cellular functions of these proteins will form the basis of a better understanding of how mutations in these genes cause the disease and for the development of new therapeutic strategies.

Active Transport, Cell Nucleus↗
PubMed2000

The TSC1 gene product, hamartin, negatively regulates cell proliferation.

Tuberous sclerosis is an autosomal dominant hereditary disease caused by mutations in either the TSC1 or the TSC2 tumor suppressor gene. The TSC1 gene on chromosome 9q34 encodes a 130 kDa protein named hamartin, and the TSC2 gene on chromosome 16p13.3 codes for tuberin, a 200 kDa protein. Here we show that expression of hamartin, assayed by immunoblot analyses, is high in G(0)-arrested cells and hamartin is expressed throughout the entire ongoing cell cycle. An interaction of hamartin and tuberin can be detected in every phase of the cell cycle. Ectopic expression of high levels of hamartin attenuates cellular proliferation. We provide evidence that this effect could depend on a coiled-coil region earlier proposed to be involved in binding of hamartin to tuberin. Further investigations revealed that hamartin affects cell proliferation via deregulation of G(1) phase. Our data have a clear impact on understanding the role of hamartin during development of this disease.

Animals↗