Fragile X syndrome, a common form of inherited mental retardation, is caused by the absence of the fragile X mental retardation protein (FMRP) due to a mutation in the FMR1 gene. We investigated the differentiation of neural stem cells generated from the brains of fmr1-knockout (KO) mice and from postmortem tissue of a fragile X fetus. Mouse and human FMRP-deficient neurospheres generated more TuJ1-positive cells (3-fold and 5-fold, respectively) than the control neurospheres generated from normal mouse and human brains, and these cells showed morphological alterations with fewer and shorter neurites and a smaller cell body volume. The number of cells expressing glial fibrillary acidic protein and generated by these neurospheres was reduced because of increased apoptotic cell death. Furthermore, there was an increase in a population of cells with intense oscillatory Ca 2؉ responses to neurotransmitters in differentiated cells lacking FMRP. In addition, the number of cells in a cohort of bromodeoxyuridine-labeled newborn cells was increased in the subventricular zone of the telencephalon of the fmr1-KO mouse in vivo. These results demonstrate substantial alterations in the early maturation of FMRPdeficient neural stem cells in fragile X syndrome and in the fmr1-KO mice.fmr1 gene ͉ fragile X mental retardation protein ͉ neurogenesis ͉ oscillations F ragile X syndrome is a common form of inherited mental retardation with an incidence of one in every 4,000 males (1). Many patients exhibit attention deficits, hyperactivity, autistic-like behavior, unusual responses to sensory stimuli, and epileptic seizures (for a review, see ref.2). The syndrome is caused by the absence or dysfunction of the fragile X mental retardation protein (FMRP), most often due to a mutation in the FMR1 gene leading to transcriptional silencing of the gene (2). FMRP is an RNA-binding protein that associates with polyribosomes and acts as a translational repressor of specific mRNAs at synaptic sites, and in that way it can regulate synapse growth and function (3-8). FMRP is highly expressed in the human central nervous system (9, 10). The absence of FMRP results in abnormalities of dendritic spines in fragile X patients (11)(12)(13)(14). The phenotype of the fmr1-knockout (KO) mice exhibits similarities with human fragile X syndrome (15,16). Abnormalities in synaptogenesis, synaptic structures and functions have been observed in the KO mice in vivo (17-21). One particularly interesting finding has been the augmentation of metabotropic glutamate receptor (mGluR)-dependent long-term depression in the fmr1-KO mice (22).Neural stem cells (NSCs) are multipotent, self-renewing cells that can be propagated in culture. Human NSCs provide a source of cells for in vitro studies attempting to elucidate neural mechanisms in the pathogenesis of human neurological disorders (23,24). In the present study, we exploited mouse and human NSCs to study the pathogenesis of fragile X syndrome and the cellular mechanisms leading to cognitive impairment and epilepsy. ...

Oncogenic transcription factor Myc deregulates the cell cycle and simultaneously reprograms cellular metabolism to meet the biosynthetic and bioenergetic needs of proliferation. Myc also sensitizes cells to mitochondria-dependent apoptosis. Although metabolic reprogramming has been circumstantially connected to vulnerability to apoptosis, the connecting molecular pathways have remained poorly defined. Here, we show that Myc-induced altered glutamine metabolism involves ATP depletion and activation of the energy sensor AMP-activated protein kinase (AMPK), which induces stabilizing phosphorylation of p53 at Ser15. Under influence of Myc, AMPK-stabilized tumor suppressor protein p53 accumulates in the mitochondria and interacts with the protein complex comprised of B-cell lymphoma 2 (Bcl-2) antagonist/killer (BAK) and Bcl2-like 1 (Bcl-xL). Mitochondrial p53 induces conformational activation of proapoptotic Bak without disrupting the Bak-Bcl-x L interaction. Further liberation of Bak specifically from the p53-activated Bak-Bcl-x L complex leads to spontaneous oligomerization of Bak and apoptosis. Thus, Myc-induced metabolic changes are coupled via AMPK and phospho-p53 to the mitochondrial apoptosis effector Bak, demonstrating a cell-intrinsic mechanism to counteract uncontrolled proliferation.oncogene | cell death | cancer metabolism

Although loss of epithelial integrity is a hallmark of advanced cancer, it remains poorly understood whether genetic alterations corrupting this integrity causally facilitate tumorigenesis. We show that conditional deletion of tumor suppressor gene Lkb1 (Par-4) in the mammary gland compromises epithelial integrity manifested by mislocalization of cell polarity markers, lateralization of tight junctions, deterioration of desmosomes and basement membrane (BM), and hyperbranching of the mammary ductal tree. We identify the desmosomal BM remodelling serine protease Hepsin as a key factor mediating Lkb1 loss-induced structural alterations in mammary epithelium and BM fragmentation. Although loss of Lkb1 alone does not promote mammary tumorigenesis, combination of Lkb1 deficiency with oncogenic c-Myc leads to dramatic acceleration in tumor formation. The results coupling Lkb1 loss-mediated epithelial integrity defects to mislocalization of serine protease Hepsin and to oncogenic synergy with c-Myc imply that Lkb1 loss facilitates oncogenic proliferation by releasing epithelial cells from structural BM boundaries.breast cancer | mouse model

No abstract

Hepsin belongs to a family of cell-surface serine proteases, which have sparked interest as therapeutic targets because of the accessibility of extracellular protease domain for inhibitors. Hepsin is frequently amplified and/or overexpressed in epithelial cancers, but it is not clear how enhanced hepsin expression confers a potential for oncogenicity. We show that hepsin is consistently overexpressed in more than 40% of examined breast cancers, including all major biological subtypes. The effects of doxycycline-induced hepsin overexpression were examined in mammary epithelial organoids, and we found that induced hepsin acutely downmodulates its cognate inhibitor, hepatocyte growth factor (HGF) activator inhibitor type 1 (HAI-1). Hepsin-induced depletion of cellular HAI-1 led to a sharp increase in pericellular serine protease activity. The derepressed hepsin proteolytically activated downstream serine proteases, augmented HGF/MET signalling and caused deterioration of desmosomes and hemidesmosomes; structures important for cell cohesion and cell-basement membrane interaction. Moreover, chronic induction of hepsin considerably shortened the latency of Myc-dependent tumourigenesis in the mouse mammary gland. The serine protease and uPA system inhibitor WX-UK1, identified as a micromolar range hepsin inhibitor, prevented hepsin from augmenting HGF/MET signalling and disrupting desmosomes and hemidesmosomes. The findings suggest that the oncogenic activity of hepsin arises not only from elevated expression level but also from depletion of HAI-1, events which together trigger gain-of-function activity impacting HGF/MET signalling and epithelial cohesion. Thus, hepsin overexpression is a major oncogenic conferrer to a serine protease activity involved in breast cancer dissemination.