The need to build a tool to facilitate the quick creation and editing of models encoded in the Systems Biology Markup language (SBML) has been growing with the number of users and the increased complexity of the language. SBMLeditor tries to answer this need by providing a very simple, low level editor of SBML files. Users can create and remove all the necessary bits and pieces of SBML in a controlled way, that maintains the validity of the final SBML file.

Regulatory T cells (Tregs) are relatively autoreactive yet, paradoxically, have been found to display normal sensitivity to thymic deletion. The relationship between self-avidity, apoptosis, and the selection of Tregs therefore remains unclear. We show that thymic Tregs develop efficiently, even at low self-avidity, and are moderately resistant to apoptosis in comparison to conventional thymocytes. Consistent with this, although conventional self-reactive T cell populations undergo chronic peripheral deletion, self-reactive Tregs are largely spared removal. Similarly, the distribution of Tregs among peripheral CD4(+) cells exhibits a linear inverse relationship with CD45RB expression, indicating relative apoptosis resistance of Tregs in chronic responses to environmental Ags. We also show that appropriate controls for CD45RB levels are important for comparisons of Treg and conventional T cell activity. When thus controlled, and contrary to previous reports, Tregs exhibit normal sensitivity to cell death through TCR-independent stimuli, such as the purinergic receptor, P2X(7). Finally, although absence of CD45 in gene-targeted mice results in profound T cell hyporesponsiveness, there is little or no effect on thymic Treg frequency. In summary, the data support a model in which signal strength plays little part in Treg lineage specification, though moderate resistance of self-reactive Tregs to apoptosis may result in progressive biasing of peripheral Treg TCRs toward autoreactivity in comparison to those of conventional T cells.

Neurodegenerative disorders involve death of cell bodies, axons, dendrites and synapses, but it is surprisingly difficult to determine the spatiotemporal sequence of events and the causal relationships among these events. Neuronal compartments often crucially depend upon one another for survival, and molecular defects in one compartment can trigger cellular degeneration in distant parts of the neuron. Here, we consider the novel approaches used to understand these biologically complex and technically challenging questions in amyotrophic lateral sclerosis, spinal muscular atrophy, glaucoma, Alzheimer's disease, Parkinson's disease and polyglutamine disorders. We conclude that there is partial understanding of what degenerates first and why, but that controversy remains the rule not the exception. Finally, we highlight strategies for resolving these fundamental issues.

Processing of the amyloid precursor protein (APP) by beta- and gamma-secretases leads to the generation of amyloid-beta (Abeta) peptides with varying lengths. Particularly Abeta42 contributes to cytotoxicity and amyloid accumulation in Alzheimer's disease (AD). However, the precise molecular mechanism of Abeta42 generation has remained unclear. Here, we show that an amino-acid motif GxxxG within the APP transmembrane sequence (TMS) has regulatory impact on the Abeta species produced. In a neuronal cell system, mutations of glycine residues G29 and G33 of the GxxxG motif gradually attenuate the TMS dimerization strength, specifically reduce the formation of Abeta42, leave the level of Abeta40 unaffected, but increase Abeta38 and shorter Abeta species. We show that glycine residues G29 and G33 are part of a dimerization site within the TMS, but do not impair oligomerization of the APP ectodomain. We conclude that gamma-secretase cleavages of APP are intimately linked to the dimerization strength of the substrate TMS. The results demonstrate that dimerization of APP TMS is a risk factor for AD due to facilitating Abeta42 production.

Ribosome display is a cell-free technology for the in vitro selection and evolution of proteins encoded by DNA libraries, in which individual nascent proteins (phenotypes) are linked physically to their corresponding mRNA (genotypes) in stable protein-ribosome-mRNA (PRM) complexes. Formation of the complexes can be achieved through deletion of the stop codon of the mRNA, stalling the ribosome at the end of translation; the nascent protein is extended by a spacer such as the immunoglobulin Ckappa domain or others to allow exit through the ribosome tunnel. Through affinity for a ligand, the protein-mRNA coupling permits simultaneous isolation of a functional nascent protein and its translated mRNA; the latter is then converted into cDNA by reverse transcription and amplified for further manipulation, repeated cycles or soluble protein expression. Through the use of PCR-generated libraries, avoiding the need for cloning, ribosome display can be used to both screen very large populations and continuously search for new diversity during subsequent rounds of selection. Additionally, the use of cell-free systems allows the selection of proteins that are toxic or unstable in cells, and proteins with chemical modifications. Ribosome display systems using both prokaryotic and eukaryotic cell extracts have been developed. Examples of the application of eukaryotic systems include the selection and evolution of antibody fragments, DNA binding domains, enzymes, interacting proteins and peptides among others. Here we describe the step-by-step procedure to perform our previously described eukaryotic ribosome display method, which has the distinctive feature of an in situ reverse transcription-PCR (RT-PCR) procedure for DNA recovery from ribosome-bound mRNA. We also introduce a recent, previously unpublished improvement to the procedure in which in situ reverse transcription is combined with sensitive single-primer PCR technology.

Arap3 is a phosphoinositide (PI) 3 kinase effector that serves as a GTPase activating protein (GAP) for both Arf and Rho G-proteins. The protein has multiple pleckstrin homology (PH) domains that bind preferentially phosphatidyl-inositol-3,4,5-trisphosphate (PI(3,4,5,)P3) to induce translocation of Arap3 to the plasma membrane upon PI3K activation. Arap3 also contains a Ras association (RA) domain that interacts with the small G-protein Rap1 and a sterile alpha motif (SAM) domain of unknown function. In a yeast two-hybrid screen for new interaction partners of Arap3, we identified the PI 5'-phosphatase SHIP2 as an interaction partner of Arap3. The interaction between Arap3 and SHIP2 was observed with endogenous proteins and shown to be mediated by the SAM domain of Arap3 and SHIP2. In vitro, these two domains show specificity for a heterodimeric interaction. Since it was shown previously that Arap3 has a higher affinity for PI(3,4,5,)P3 than for PI(3,4)P2, we propose that the SAM domain of Arap3 can function to recruit a negative regulator of PI3K signaling into the effector complex.

Drosophila Muscleblind (Mbl) proteins control terminal muscle and neural differentiation, but their molecular function has not been experimentally addressed. Such an analysis is relevant as the human Muscleblind-like homologs (MBNL1-3) are implicated in the pathogenesis of the inherited muscular developmental and degenerative disease myotonic dystrophy. The Drosophila muscleblind gene expresses four protein coding splice forms (mblA to mblD) that are differentially expressed during the Drosophila life cycle, and which vary markedly in their ability to rescue the embryonic lethal phenotype of muscleblind mutant flies. Analysis of muscleblind mutant embryos reveals misregulated alternative splicing of the transcripts encoding Z-band component alpha-Actinin, which can be replicated in human cells expressing a Drosophilaalpha-actinin minigene and epitope-tagged Muscleblind isoforms. MblC appreciably altered alpha-actinin splicing in this assay, whereas other isoforms had only a marginal or no effect, demonstrating functional specialization among Muscleblind proteins. To further analyze the molecular basis of these differences, we studied the subcellular localization of Muscleblind isoforms. Consistent with the splicing assay results, MblB and MblC were enriched in the nucleus while MblA was predominantly cytoplasmic. In myotonic dystrophy, transcripts bearing expanded non-coding CUG or CCUG repeats interfere with the function of human MBNL proteins. Co-expression of CUG repeat RNA with the alpha-actinin minigene altered splicing compared with that seen in muscleblind mutant embryos, indicating that CUG repeat expansion RNA also interferes with Drosophila muscleblind function. Moreover MblA, B, and C co-localize with CUG repeat RNA in nuclear foci in cell culture. Our observations indicate that Muscleblind isoforms perform different functions in vivo, that MblC controls muscleblind-dependent alternative splicing events, and establish the functional conservation between Muscleblind and MBNL proteins both over a physiological target (alpha-actinin) and a pathogenic one (CUG repeats).

The plasticity of chromatin is governed by multi-subunit protein complexes that enzymatically regulate chromosomal structure and activity. Such complexes include ATP-dependent chromatin remodelling factors that are involved in many fundamental processes such as transcription, DNA repair, replication and chromosome structure maintenance. Because ATP-dependent chromatin remodelling factors play important roles, it is not surprising to find that their functions are regulated in a plethora of ways, including post-translational modifications of their subunits and subunit composition changes. The activity of these enzymes is modulated by many factors, including linker histones, histone variants, histone chaperones, non-histone chromatin constituents such as HMG-proteins and secondary messengers, such as inositolpolyphosphates. Additionally, specific histone modifications and interaction with site-specific transcriptional regulators direct the targeting of these activities. Understanding the network of mechanisms that control ATP-dependent chromatin remodelling will constitute an important challenge towards our understanding of chromatin dynamics.

The pre-B-cell receptor (pre-BCR) is composed of two immunoglobulin mu heavy chains and two surrogate light chains, which associate with the signaling molecules Igalpha and Igbeta (Igalpha/beta). The production of a functional pre-BCR is the first checkpoint in the current model of B-cell development. The pre-BCR mediates signals resulting in heavy chain allelic exclusion, down-regulation of the recombination machinery, developmental progression, V(H) repertoire selection, proliferation and down-regulation of the surrogate light chain genes. Recent studies suggest that some of these processes could take place at an earlier stage in B-cell development than previously thought, and might not result from signals mediated by the pre-BCR.

The development and maintenance of regulatory T (T-reg) cells is crucial for determining the level of reactivity in the immune system. Until recently, however, surprisingly little was known about the factors involved in the development of these cells in the thymus or the mechanisms that maintain them in the periphery. Studies have now demonstrated that thymic development of T-reg cells is facilitated by TCRs with increased affinity for self-peptide-MHC complexes. Increased TCR affinity alone, however, is not sufficient to support the development of T-reg cells, and external factors such as CD80 and CD86, ligands for co-stimulatory receptor CD28, and interleukin 2 are required. These factors are also needed to maintain the T-reg cell subset in the periphery.

Exposure to excess androgens in utero induces irreversible changes in gonadotrophin secretion and results in disrupted reproductive endocrine and ovarian function in adulthood, in a manner reminiscent of the common clinical endocrinopathy of polycystic ovary syndrome (PCOS). We have recently identified an abnormality in early follicle development in PCOS which we suggested might be an androgenic effect. We propose that altered ovarian function in androgenized ewes is due to prenatal androgens not only causing an abnormality of gonadotrophin secretion, but also exerting a direct effect on the early stages of folliculogenesis. Therefore, in this study, we explored the possible differences between small preantral follicles in the ovarian cortex of androgenized female lambs with those of normal lambs. At 8 months of age, small ovarian cortical biopsies (approximately 5 mm3) were obtained at laparotomy from nine female lambs that had been exposed to androgens in utero from embryonic days 30 to 90 of a 147-day pregnancy, and 11 control female lambs. Further, ovarian tissue was obtained at 20 months of age from ten androgenized and nine control animals. Tissue was either fixed immediately for histology or cultured for up to 15 days prior to fixing. The number of follicles in haematoxylin and eosin-stained sections was counted and recorded along with the stage of development. Before culture, the total follicle density (follicles/mm3 tissue) was not statistically significantly different between the two types of ovary at either 8 or 20 months of age. Furthermore, there were no statistically significant differences in the density of follicles at each stage of development. However, there was a lower percentage of primordial follicles, but a higher percentage of primary follicles, in biopsies taken at 8 months from androgenized lambs when compared with controls. At 20 months, the proportions of follicles at the primordial and primary stages were not significantly different between the two groups, but this was mainly attributable to an increase in the proportion of growing follicles in biopsies from control animals. Culture of ovarian cortex from 8-month-old lambs resulted in a progressive increase in the proportion of growing follicles when compared with tissue fixed on the day of surgery. However, there was no difference between androgenized and control tissue in the percentage of growing follicles. The increase in the proportion of growing follicles in the cortex of androgenized animals is reminiscent of similar observations in human polycystic ovaries and suggests that excess exposure to androgen in early life plays a part in the accelerated progression of follicle development from the primordial to the primary stage in polycystic ovaries.

3BP2 is a pleckstrin homology domain- and Src homology 2 (SH2) domain-containing adapter protein that is mutated in the rare human bone disorder cherubism and which has also been implicated in immunoreceptor signaling. However, a function for this protein has yet to be established. Here we show that mice lacking 3BP2 exhibited a perturbation in the peritoneal B1 and splenic marginal-zone B-cell compartments and diminished thymus-independent type 2 antigen response. 3BP2(-/-) B cells demonstrated a proliferation defect in response to antigen receptor cross-linking and a heightened sensitivity to B-cell receptor-induced death via a caspase-3-dependent apoptotic pathway. We show that 3BP2 binds via its SH2 domain to the CD19 signaling complex and is required for optimum Syk phosphorylation and calcium flux.

The BCR serves to both signal cellular activation and enhance uptake and presentation of Ags by B cells; however, the intracellular signaling mechanisms linking the BCR to Ag presentation functions have been controversial. PI3Ks are critical signaling enzymes controlling many cellular processes, with the p110delta isoform playing a critical role in BCR signaling. In this study, we used pharmacological and genetic approaches to evaluate the role of p110delta signaling in Ag presentation by primary B lymphocytes. It was found that activation of allogeneic T cells is significantly reduced when B cells are pretreated with global PI3K inhibitors, but was intact when p110delta signaling was specifically inactivated. In contrast, inactivation of p110delta significantly impaired the ability of B cells to activate T cells in a BCR-mediated Ag uptake and presentation model. Prestimulation of p110delta-inactivated B cells with anti-CD40 or LPS could not rescue their BCR-mediated Ag presentation ability to normal levels. p110delta signaling was required for efficient presentation of either anti-Ig or protein Ag via a lysozyme-specific BCR. p110delta-inactivated B cells were able to internalize Ag normally, and no defects in association of Ag with lysosome-associated membrane protein 1(+) late endosomes were observed; however, these cells were less effective in forming polarized conjugates with Ag-specific T cells. Our data demonstrate a role for p110delta signaling in B cell Ag presentation function, implicating 3-phosphoinositides and their targets in the latter stages of this process.

At the immature B cell stage the BCR signals the down-regulation of the RAG genes and Ig L chain (LC) allelic and isotype exclusion. The signaling pathway that regulates these events is poorly characterized. We demonstrate that immature B cells from mice deficient in the PI3K catalytic subunit p110delta fail to suppress RAG expression and inappropriately recombine kappa and lambda LC loci. In addition, in the presence of the autoantigen, clonal deletion and receptor editing still takes place, demonstrating that these processes are independent of p110delta. These results demonstrate a role for p110delta in the regulation of RAG gene expression and thereby LC allelic/isotype exclusion.

Epigenetic modifications of nucleosomal histones are thought to mediate transcriptional states and impose heritable instructions upon differentiation. In a paper of Torres-Padilla and colleagues in Nature, protein modification at arginine residues, namely of core histones, is correlated with cell fate determination at the 4-cell stage in the mouse embryo. This represents the first link of global epigenetic instructions associated with specification of early cell lineages.

Diabetes is associated with endothelial dysfunction and platelet activation, both of which may contribute to increased cardiovascular risk. We investigated whether the hydroxy-3-methyl-glutaryl CoA reductase inhibitor rosuvastatin improves endothelial function and reduces platelet activation in diabetic rats. Therefore, male Wistar rats were injected with streptozotocin (STZ, 50mg/kg i.v.) to induce insulin-deficient diabetes. Treatment with rosuvastatin (20mg/[kg day]) or vehicle was initiated 2 weeks after injection of STZ and continued for 2 weeks. Thereafter, platelet activation was assessed in fresh whole blood and vascular function was characterized in isolated aortic segments in organ bath chambers. Endothelium-dependent relaxation induced by acetylcholine was significantly attenuated in diabetic rats and improved by treatment with rosuvastatin (maximum relaxation, % of precontraction-control: 99.8+/-0.2, STZ-vehicle: 80.7+/-2.9, STZ-rosuvastatin: 98.9+/-0.7; p<0.01). Similarly, treatment with rosuvastatin significantly reduced fibrinogen-binding to activated GPIIb/IIIa (mean fluorescence-control: 161.0+/-6.9, STZ-vehicle: 207.8+/-15.9, rosuvastatin: 173.6+/-5.3; p<0.05) and P-Selectin surface expression on platelets (mean fluorescence-control: 76.5+/-7.3, STZ-vehicle: 92.1+/-5.5, rosuvastatin: 75.2+/-6.5; p<0.05), while both markers of platelet activation were increased in diabetic rats. Therefore, rosuvastatin treatment normalizes endothelial function and reduces platelet activation in diabetic rats. These effects may contribute to the reduction of cardiovascular events by statins in diabetic patients.

Diabetes is associated with endothelial dysfunction and platelet activation, both of which may contribute to increased cardiovascular risk. We investigated whether the hydroxy-3-methyl-glutaryl CoA reductase inhibitor rosuvastatin improves endothelial function and reduces platelet activation in diabetic rats. Therefore, male Wistar rats were injected with streptozotocin (STZ, 50mg/kg i.v.) to induce insulin-deficient diabetes. Treatment with rosuvastatin (20mg/[kg day]) or vehicle was initiated 2 weeks after injection of STZ and continued for 2 weeks. Thereafter, platelet activation was assessed in fresh whole blood and vascular function was characterized in isolated aortic segments in organ bath chambers. Endothelium-dependent relaxation induced by acetylcholine was significantly attenuated in diabetic rats and improved by treatment with rosuvastatin (maximum relaxation, % of precontraction-control: 99.8+/-0.2, STZ-vehicle: 80.7+/-2.9, STZ-rosuvastatin: 98.9+/-0.7; p<0.01). Similarly, treatment with rosuvastatin significantly reduced fibrinogen-binding to activated GPIIb/IIIa (mean fluorescence-control: 161.0+/-6.9, STZ-vehicle: 207.8+/-15.9, rosuvastatin: 173.6+/-5.3; p<0.05) and P-Selectin surface expression on platelets (mean fluorescence-control: 76.5+/-7.3, STZ-vehicle: 92.1+/-5.5, rosuvastatin: 75.2+/-6.5; p<0.05), while both markers of platelet activation were increased in diabetic rats. Therefore, rosuvastatin treatment normalizes endothelial function and reduces platelet activation in diabetic rats. These effects may contribute to the reduction of cardiovascular events by statins in diabetic patients.

Vascular adhesion protein-1 (VAP-1) is an adhesion molecule and amine oxidase that is expressed at high levels in the human liver. It promotes leukocyte adhesion to the liver in vivo and drives lymphocyte transmigration across hepatic sinusoidal endothelial cells in vitro. We report that in addition to supporting leukocyte adhesion, provision of specific substrate to VAP-1 results in hepatic endothelial cell activation, which can be abrogated by treatment with the enzyme inhibitor semicarbazide. VAP-1-mediated activation was rapid; dependent upon nuclear factor-kappaB, phosphatidylinositol-3 kinase, and mitogen-activated protein kinase pathways; and led to upregulation of the adhesion molecules E-selectin, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 and secretion of the chemokine CXCL8. This response resulted in enhanced lymphocyte adhesion, was restricted to hepatic endothelial cells that expressed VAP-1, and was not observed in human umbilical vein endothelial cells.

The Kcnq1 imprinted domain encodes a paternally expressed noncoding RNA Kcnq1ot1 and several paternally repressed protein-coding genes. Transcriptional regulation is controlled by the Kcnq1ot1 gene whose maternal germline methylation imprint overlaps with the Kcnq1ot1 promoter. The domain can be divided into two groups of genes. One group is imprinted in all lineages and is reliant on DNA methylation for its imprinting. The other group contains genes that are imprinted specifically in the placenta and retain their imprinting in the absence of Dnmt1, the primary DNA maintenance methylase. In the placenta paternal Kcnq1ot1 expression is associated with the acquisition of repressive histone modifications throughout the domain. Using the Dnmt1o knockout, we have analyzed the effect of removing DNA maintenance methylation at the eight-cell stage on the Kcnq1 imprinted domain. In the placenta the expression of the normally silent maternal Kcnq1ot1 allele leads to reduced expression of the surrounding maternally expressed genes. This repression is seen in both the placental-specific imprinted genes and the ubiquitously imprinted genes. Conversely, reduction of functional Dnmt1 results solely in reduced expression of the ubiquitously imprinted genes in the placenta. This suggests that Kcnq1ot1 expression can epigenetically silence placentally imprinted genes in the cluster only during a specific developmental window. This highlights the possibility that Kcnq1ot1-mediated repression is temporally regulated leading to epigenetic silencing of placental-specific genes. We show that allele-specific histone modifications are still present in the Dnmt1 ( -/- ) trophoblast at placental-specific imprinted loci and are likely responsible for maintaining the imprinting of these genes in the absence of DNA methylation.

Antiendothelial cell antibodies (AECAs) are commonly detectable in diseases associated with vascular injury, including systemic lupus erythematosus (SLE), systemic sclerosis, Takayasu arteritis, Wegener granulomatosis, Behçet syndrome, and transplant arteriosclerosis. Here, we explore the hypothesis that these antibodies might augment polymorphonuclear leukocyte (PMN) adhesion to endothelium in inflammation. Initially, we established that a mouse IgG mAb bound to endothelial cells (ECs) significantly increased PMN adhesion to cytokine-stimulated endothelium in an FcgammaRIIa-dependent manner. Neutralizing antibodies, and adenoviral transduction of resting ECs, demonstrated that the combination of E-selectin, CXCR1/2, and beta(2) integrins is both necessary and sufficient for this process. We observed an identical mechanism using AECA IgG isolated directly from patients with SLE. Assembled immune complexes also enhanced PMN adhesion to endothelium, but, in contrast to adhesion because of AECAs, this process did not require CXCR1/2, was not inhibited by pertussis toxin, and was FcgammaRIIIb rather than FcgammaRIIa dependent. These data are the first to demonstrate separate nonredundant FcgammaRIIa and FcgammaRIIIb-mediated mechanisms by which EC-bound monomeric IgG and assembled immune complexes amplify leukocyte adhesion under dynamic conditions. Furthermore, the observation that FcgammaRIIa and CXCR1/2 cooperate to enhance PMN recruitment in the presence of AECAs suggests a mechanism whereby AECAs may augment tissue injury during inflammatory responses.

T cells in the thymus undergo opposing positive and negative selection processes so that the only T cells entering circulation are those bearing a T cell receptor (TCR) with a low affinity for self. The mechanism differentiating negative from positive selection is poorly understood, despite the fact that inherited defects in negative selection underlie organ-specific autoimmune disease in AIRE-deficient people and the non-obese diabetic (NOD) mouse strain

Phosphoinositide 3-kinases (PI3K) regulate immune activation via their roles in signal transduction of multiple classes of receptors. Here, we examined the effect of genetic inactivation of the hemopoietic cell-restricted PI3K isoform p110delta on systemic cytokine and chemokine responses and allergic airway inflammation. We found that type 2 cytokine responses (IL-4, IL-5 and IL-13) are significantly decreased in p110delta mutants, whereas type 1 cytokine responses (IFN-gamma and CXCL10) were robust. Elevated IFN-gamma production during the primary response to ovalbumin (OVA) was associated with reduced production of the regulatory cytokine IL-10. IFN-gamma and IL-10 production normalized after secondary OVA immunization; however, type 2 cytokine production was persistently reduced. Type 2 cytokine-dependent airway inflammation elicited by intranasal challenge with OVA was dramatically reduced, with reduced levels of eosinophil recruitment and mucus production observed in the lungs. Induction of respiratory hyper-responsiveness to inhaled methacholine, a hallmark of asthma, was markedly attenuated in p110delta-inactivated mice. Adoptive transfer of OVA-primed splenocytes from normal but not p110delta-inactivated mice could induce airway eosinophilia in naive, airway-challenged recipient mice. These data demonstrate a novel functional role for p110delta signaling in induction of type 2 responses in vivo and may offer a new therapeutic target for Th2-mediated airway disease.

Autophagy is a lysosome-dependent degradative pathway frequently activated in tumor cells treated with chemotherapy or radiation. Whether autophagy observed in treated cancer cells represents a mechanism that allows tumor cells to survive therapy or a mechanism for initiating a nonapoptotic form of programmed cell death remains controversial. To address this issue, the role of autophagy in a Myc-induced model of lymphoma generated from cells derived from p53ER(TAM)/p53ER(TAM) mice (with ER denoting estrogen receptor) was examined. Such tumors are resistant to apoptosis due to a lack of nuclear p53. Systemic administration of tamoxifen led to p53 activation and tumor regression followed by tumor recurrence. Activation of p53 was associated with the rapid appearance of apoptotic cells and the induction of autophagy in surviving cells. Inhibition of autophagy with either chloroquine or ATG5 short hairpin RNA (shRNA) enhanced the ability of either p53 activation or alkylating drug therapy to induce tumor cell death. These studies provide evidence that autophagy serves as a survival pathway in tumor cells treated with apoptosis activators and a rationale for the use of autophagy inhibitors such as chloroquine in combination with therapies designed to induce apoptosis in human cancers.

PTEN (phosphatase and tensin homologue deleted on chromosome 10) is a tumour suppressor that functions as a PtdIns(3,4,5)P3 3-phosphatase to inhibit cell proliferation, survival and growth by antagonizing PI3K (phosphoinositide 3-kinase)-dependent signalling. Recent work has begun to focus attention on potential biological functions of the protein phosphatase activity of PTEN and on the possibility that some of its functions are phosphatase-independent. We discuss here the structural and regulatory mechanisms that account for the remarkable specificity of PTEN with respect to its PtdIns substrates and how it avoids the soluble headgroups of PtdIns that occur commonly in cells. Secondly we discuss the concept of PTEN as a constitutively active enzyme that is subject to negative regulation both physiologically and pathologically. Thirdly, we review the evidence that PTEN functions as a dual specificity phosphatase with discrete lipid and protein substrates. Lastly we present a current model of how PTEN may participate in the control of cell migration.