The role of human endogenous retroviruses (HERVs) in disease pathogenesis is unclear. We show that HERV-K is activated in a subpopulation of patients with sporadic amyotrophic lateral sclerosis (ALS) and that its envelope (env) protein may contribute to neurodegeneration. The virus was expressed in cortical and spinal neurons of ALS patients, but not in neurons from control healthy individuals. Expression of HERV-K or its env protein in human neurons caused retraction and beading of neurites. Transgenic animals expressing the env gene developed progressive motor dysfunction accompanied by selective loss of volume of the motor cortex, decreased synaptic activity in pyramidal neurons, dendritic spine abnormalities, nucleolar dysfunction, and DNA damage. Injury to anterior horn cells in the spinal cord was manifested by muscle atrophy and pathological changes consistent with nerve fiber denervation and reinnervation. Expression of HERV-K was regulated by TAR (trans-activation responsive) DNA binding protein 43, which binds to the long terminal repeat region of the virus. Thus, HERV-K expression within neurons of patients with ALS may contribute to neurodegeneration and disease pathogenesis.

The Notch family of proteins plays an integral role in determining cell fates, such as proliferation, differentiation, and apoptosis. We show that Notch-1 and its ligands, Deltalike-1 and Jagged-1, are overexpressed in many glioma cell lines and primary human gliomas. Immunohistochemistry of a primary human glioma tissue array shows the presence in the nucleus of the Notch-1 intracellular domain, indicating Notch-1 activation in situ. Down-regulation of Notch-1, Deltalike-1, or Jagged-1 by RNA interference induces apoptosis and inhibits proliferation in multiple glioma cell lines. In addition, pretreatment of glioma cells with Notch-1 or Delta-like-1 small interfering RNA significantly prolongs survival in a murine orthotopic brain tumor model. These results show, for the first time, the dependence of cancer cells on a single Notch ligand; they also suggest a potential Notch juxtacrine/autocrine loop in gliomas. Notch-1 and its ligands may present novel therapeutic targets in the treatment of glioma. (Cancer Res 2005; 65(6): 2353-63)

Summary Selective autophagy recycles damaged organelles and clears intracellular pathogens to prevent their aberrant accumulation. How ULK1 kinase is targeted and activated during selective autophagic events remains to be elucidated. In this study, we used chemically inducible dimerization (CID) assays in tandem with CRISPR KO lines to systematically analyze the molecular basis of selective autophagosome biogenesis. We demonstrate that ectopic placement of NDP52 on mitochondria or peroxisomes is sufficient to initiate selective autophagy by focally localizing and activating the ULK1 complex. The capability of NDP52 to induce mitophagy is dependent on its interaction with the FIP200/ULK1 complex, which is facilitated by TBK1. Ectopically tethering ULK1 to cargo bypasses the requirement for autophagy receptors and TBK1. Focal activation of ULK1 occurs independently of AMPK and mTOR. Our findings provide a parsimonious model of selective autophagy, which highlights the coordination of ULK1 complex localization by autophagy receptors and TBK1 as principal drivers of targeted autophagosome biogenesis.

Mutations in DJ-1, PINK1 (PTEN-induced putative kinase 1) and parkin all cause recessive parkinsonism in humans, but the relationships between these genes are not clearly defined. One event associated with loss of any of these genes is altered mitochondrial function. Recent evidence suggests that turnover of damaged mitochondria by autophagy might be central to the process of recessive parkinsonism. Here, we show that loss of DJ-1 leads to loss of mitochondrial polarization, fragmentation of mitochondria and accumulation of markers of autophagy (LC3 punctae and lipidation) around mitochondria in human dopaminergic cells. These effects are due to endogenous oxidative stress, as antioxidants will reverse all of them. Similar to PINK1 and parkin, DJ-1 also limits mitochondrial fragmentation in response to the mitochondrial toxin rotenone. Furthermore, overexpressed parkin will protect against loss of DJ-1 and, although DJ-1 does not alter PINK1 mitochondrial phenotypes, DJ-1 is still active against rotenone-induced damage in the absence of PINK1. None of the three proteins complex together using size exclusion chromatography. These data suggest that DJ-1 works in parallel to the PINK1/parkin pathway to maintain mitochondrial function in the presence of an oxidative environment.

Glycogen synthase kinase 3 (GSK3), a serine/threonine kinase, is involved in diverse cellular processes ranging from nutrient and energy homeostasis to proliferation and apoptosis. Its role in glioblastoma multiforme has yet to be elucidated. We identified GSK3 as a regulator of glioblastoma multiforme cell survival using microarray analysis and small-molecule and genetic inhibitors of GSK3 activity. Various molecular and genetic approaches were then used to dissect out the molecular mechanisms responsible for GSK3 inhibitioninduced cytotoxicity. We show that multiple small molecular inhibitors of GSK3 activity and genetic down-regulation of GSK3A/B significantly inhibit glioma cell survival and clonogenicity. The potency of the cytotoxic effects is directly correlated with decreased enzyme activity-activating phosphorylation of GSK3A/B Y276/Y216 and with increased enzyme activity inhibitory phosphorylation of GSK3A S21. Inhibition of GSK3 activity results in c-MYC activation, leading to the induction of Bax, Bim, DR4/DR5, and tumor necrosis factor-related apoptosis-inducing ligand expression and subsequent cytotoxicity. Additionally, down-regulation of GSK3 activity results in alteration of intracellular glucose metabolism resulting in dissociation of hexokinase II from the outer mitochondrial membrane with subsequent mitochondrial destabilization. Finally, inhibition of GSK3 activity causes a dramatic decrease in intracellular nuclear factor-KB activity. Inhibition of GSK3 activity results in c-MYC-dependent glioma cell death through multiple mechanisms, all of which converge on the apoptotic pathways. GSK3 may therefore be an important therapeutic target for gliomas. Future studies will further define the optimal combinations of GSK3 inhibitors and cytotoxic agents for use in gliomas and other cancers. [Cancer Res 2008;68(16):6643-51]

Chronic immune activation is a major complication of antiretroviral therapy (ART) for HIV infection and can cause a devastating immune reconstitution inflammatory syndrome (IRIS) in the brain. The mechanism of T-cell activation in this population is not well understood. We found HIV-Tat protein and IL-17-expressing mononuclear cells in the brain of an individual with IRIS. Tat was also present in the CSF of individuals virologically controlled on ART. Hence we examined if Tat protein could directly activate T cells. Tat transcriptionally dysregulated 94 genes and induced secretion of 11 cytokines particularly activation of IL-17 signaling pathways supporting the development of a proinflammatory state. Tat increased IL-17 transcription and secretion in T cells. Tat entered the T cells rapidly by clathrin-mediated endocytosis and localized to both the cytoplasm and the nucleus. Tat activated T cells through a nonclassical pathway dependent upon vascular endothelial growth factor receptor-2 and downstream secondary signaling pathways but independent of the T-cell receptor. However, Tat stimulation of T cells did not induce T-cell proliferation but increased viral infectivity. This study demonstrates Tat's role as a virulence factor, by driving T-cell activation and contributing to IRIS pathophysiology. This supports the necessity of an anti-Tat therapy in conjunction with ART and identifies multiple targetable pathways to prevent Tat-mediated T-cell activation.

Disorders of pain neural systems are frequently chronic and, when recalcitrant to treatment, can severely degrade the quality of life. The pain pathway begins with sensory neurons in dorsal root or trigeminal ganglia and the neuronal subpopulations that express the TRPV1 ion channel transduce sensations of painful heat and inflammation, and play a fundamental role in clinical pain arising from cancer and arthritis. In the present study we elucidate the complete transcriptomes of neurons from the TRPV1 lineage and a non-TRPV1 neuro-glial population in sensory ganglia through the combined application of next-gen deep RNA-Seq, genetic neuronal labeling with fluorescence-activated cell sorting, or neuron-selective chemoablation. RNA-Seq accurately quantitates gene expression, a difficult parameter to determine with most other methods especially for very low and very high expressed genes. Differentially expressed genes are present at every level of cellular function from the nucleus to the plasma membrane. We identified many ligand receptor pairs in the TRPV1 population suggesting that autonomous presynaptic regulation maybe a major regulatory mechanism in nociceptive neurons. The data define, in a quantitative, cell population specific fashion, the molecular signature of a distinct and clinically important group of pain-sensing neurons and provide an overall framework for understanding the transcriptome of TRPV1 nociceptive neurons.

Autosomal-dominant missense mutations in leucine-rich repeat kinase 2 (LRRK2) are a common genetic cause of Parkinson's disease (PD). LRRK2 is a multidomain protein with kinase and GTPase activities. Dominant mutations are found in the domains that have these two enzyme activities including the common G2019S mutation that increases kinase activity by 2-3 fold. However, there is also a genetic variant in some populations, G2385R, that lies in a C-terminal WD40 domain of LRRK2 and acts as a risk factor for PD. In this study we show that the G2385R mutation causes a partial loss of the kinase function of LRRK2 and deletion of the C-terminus completely abolishes kinase activity. This effect is strong enough to overcome the kinase activating effects of the G2019S mutation in the kinase domain. Hsp90 has an increased affinity to G2385R variant compare to wild type LRRK2 and inhibition of the chaperone binding combined with proteasome inhibition leads to association of mutant LRRK2 with high molecular weight native fractions that likely represent proteasome degradation pathways. The loss of function of G2385R correlates with several cellular phenotypes that have been proposed to be kinase dependent. These results suggest that the C-terminus of LRRK2 plays an important role in maintaining enzymatic function of the protein and that G2385R may be associated with PD in a way that is different from kinase activating mutations. These results may be important in understanding the differing mechanism(s) by which mutations in LRRK2 act and may also have implications for therapeutic strategies for PD.