The Tumor Suppressor Function of LGI1

Several evidences supporting the tumor suppressor role of LGI1 have been presented here. The discovery of chromosomal rearrangements leading to loss of LGI1 expression in glioblastoma cells, mutations in LGI1 gene specifically associated with gliobastoma and the downregulation of LGI1 expression in several tumors all point out a role of LGI1 in tumor suppression. Furthermore the findings that re-expression of LGI1 in glioblastoma cells impaired cell growth and migration ability through inhibition of the ERK1/2 pathway, with consequent downregulation of MMPs expression, support a role in the suppression of metastasis formation and tumor vascularization. This is in line with the downregulation of LGI1 expression observed in the malignant progression of gliomas. The findings that increased expression of LGI1 impaired growth and survival of neuroblastoma cells further strengthen the tumor suppressor role of LGI1. The involvement of LGI1 in the negative regulation of the PI3K/AKT pathway supporting cell proliferation and survival explains the mechanism of spontaneous cell death triggered by the elevation of LGI1 levels in neuroblatoma cells. The activation of intrinsic apoptosis triggered by LGI1 is consistent with a blockage of AKT activity, which regulates Bcl-2 family members involved in the control of mitochondrial membrane permeability. Furthermore, the interaction of LGI1 protein with voltage gated potassium channels (Kv1.1) shown to prevent channel inactivation by Kv1b subunit, provides an additional link with apoptosis since these channels are important regulators of cell survival. Because suppression of apoptosis in cancer cells is one of the main strategies to achieve the survival advantage required for malignant progression, it is feasible that alterations of LGI1 gene or downregulation of expression often observed in cancer cells might be required to suppress apoptosis through the inhibition of survival pathways linked to growth factor receptors and of Kv channels activity

Organization and structure of the genes for the cytochrome b/c1 complex in purple photosynthetic bacteria. A phylogenetic study describing the homology of the b/c1 subunits between prokaryotes, mitochondria, and chloroplasts.

The cytochrome b/c1 complex is an ubiquitous energy transducing enzyme, part of the electron transport chain of prokaryotes, mitochondria, and chloroplasts (b6/f). In the ancient purple photosynthetic bacteria, the b/c1 complex occupies a central metabolic role, being part of their photosynthetic and respiratory electron transport chain. In Rhodobacter the three subunits of the b/c1 complex are FeS protein, cytochrome b, and cytochrome c1, and they are encoded by a constitutively expressed operon named fbc. The organization of the genes for the cytochrome b/c1 complex, the modality of transcription, and the biogenesis of the encoded polypeptides will be described. The Rhodobacter species used to isolate the fbc genes, previously reported as R. sphaeroides was identified as R. capsulatus. Further biochemical characterization of the prokaryotic b/c1 complex indicated that the three polypeptides encoded by the fbc operon comprise the entire catalytic structure: ubiquinol-cytochrome-c reductase. The amino acid sequences of the three b/c1 subunits from the photosynthetic bacterium Rhodobacter capsulatus were compared with the corresponding sequences from yeast mitochondria and spinach chloroplasts. The high homology found between the sequences of all three redox polypeptides from R. capsulatus and yeast mitochondria (cytochrome b 41%, FeS protein 46%, cytochrome c1 31%) provided further evidence that mitochondria arose from the phylogenetic line of purple bacteria. The structure of cytochrome b also exhibited considerable homology to chloroplast cytochrome b6 plus subunit IV (26%). The amino acid sequence of the Rieske FeS protein from R. capsulatus and chloroplasts were found to be conserved only in the C-terminal part (14% total identity), whereas the homology between cytochrome c1 and cytochrome f is very weak (12%), despite similar topology of the two polypeptides. Analysis of the homology suggested that the catalytic sites quinol oxidase (Q0) and quinone reductase (Qi) arose monophonetically, whereas cytochrome c and plastocyanin reductase sites are not homologous and could derive from diverse ancestral genes by convergent evolution

Transcriptional regulation by cAMP and Ca2+ links the Na/Ca2+ exchanger 3 to memory and sensory pathways

The signaling cascades triggered by neurotrophins such as BDNF and by several neurotransmitters and hormones lead to the rapid induction of gene transcription by increasing the intracellular concentration of cAMP and Ca2+. This review examines the mechanisms by which these second messengers control transcriptional initiation at CRE promoters via transcription factor CREB, as well as at DRE sites via transcriptional repressor DREAM. The regulation of the SLC8A3 gene encoding the Na+/Ca2+ exchanger 3 (NCX3) is taken as an example to illustrate both mechanisms since it includes a CRE site in the promoter and several DRE sites in the exon 1 sequence. The upregulation of the NCX3 by Ca2+ signals may be specifically required to establish the Ca2+ balance that regulates several physiological and pathological processes in neurons. The regulatory features and the expression pattern of SLC8A3 gene suggest that NCX3 activity could be crucial in neuronal functions such as memory formation and sensory processing

NTRK2 (Neurotrophic Tyrosine Kinase, Receptor, Type 2) Atlas Genet Cytogenet Oncol Haematol.,

Gene chart for Atlas of Genetics and Cytogenetics in Oncology and Haematology of the NTRK2 (Neurotrophic tyrosine kinase, receptor, type 2

Structural homologies in the b/c1 complex from Rhodobacter.

The primary structure of the cytochrome b/c1 complex from photosynthetic bacteria that was deduced from the nucleotide sequence is discussed in relation with the homologies identified with the same complex of different organisms

A polymorphic GT repeat from the human cardiac Na+/Ca2+ exchanger intron 2 activates splicing

The sequence analysis of the human intron 2 from the Na+/Ca2+ exchanger 1 (NCX1) gene has revealed a GT repeat of variable length (10-16). The 5' sequence of intron 2 exhibited significant homology (65-70%) with other minisatellite sequences. DNA segments at the 5' end of intron 2 were inserted in the NCX1 cDNA (3.7 kb) to reconstruct the exon 2/intron 2 junction. Transient expression of these constructs in HEK293 cells generated shortened mRNAs ( approximately 2.5 kb). RT-PCR and ribonuclease protection analysis of the 3' end of the short transcripts indicated a splicing event at the intron 2/exon 2 junction (5' site) and in the vector sequence downstream of the NCX1 insert (3' site). Molecular dissection of the 5'-intron 2 sequence showed that the GT repeat was required for splicing activation, whereas the remainder of the 5'-intron 2 segment was completely inactive. The results indicate that the GT repeat is a strong intronic splicing enhancer that could be involved in the regulation of NCX1 expression, possibly mediating tissue-specific alternative splicing of the mutually exclusive exons 3 and 4, and/or exon-2 circularization

Gene transfer in cultured ganglion neurons by DNA/calcium phosphate co-precipitation and gene activation by NGF signal.

The co-precipitation of DNA with calcium phosphate has been successfully employed to transfect cultured chicken embryonic sensory neurons (DRG). Up to 90% of the cultured DRG neurons were transfected by this method. This has allowed a study of the intracellular second messengers involved in signal transduction and gene activation by NGF in DRG neurons. This method can be used to introduce foreign DNA also in rat DRG, striatal and hippocampal neurons in culture

LGI1 (Leucine-rich, Glioma Inactivated protein 1 precursor) Atlas Genet Cytogenet Oncol Haematol.

Gene chart of Atlas of Genetics and Cytogenetics in Oncology and Haematology of the LGI1 (Leucine-rich, Glioma Inactivated protein 1 precursor

Expression of LGI1 impairs proliferation and survival of HeLa cells

The LGI1 gene was suggested to function as tumor suppressor for its ability to reduce malignant features of glioblastoma cells. In support to this proposal was the findings that overexpression of LGI1 in neuroblastoma cells inhibited proliferation and induced apoptosis. In this study we performed stable LGI1 expression in HeLa cells to examine whether the noxious effect of LGI1 might be extended to cancer cells of diverse origin. HeLa cell clones stably expressing LGI1 exhibited a significant impairment of proliferation and a consistent increase of cell death when compared with control cells lacking expression of LGI1. Expression of LGI1 increased the activity of apoptosis effectors caspase \u20133/7, furthermore it downregulated the anti-apoptotic BCL2 gene and upregulated the pro-apoptotic BAX gene expression, suggesting that the cause of HeLa cells death might be an increased susceptibility to apoptosis induced by LGI1. The results suggested that LGI1 is capable to restrain growth and survival of adenocarcinoma cells such as HeLa

LGI1 Affects survival of neuroblastoma cells by inhibiting signalling through phosphoinositide 3-Kinase

Overexpression of the leucine-rich, glioma-inactivated 1 (LGI1) gene in neuroblastoma cells inhibited proliferation and efficiently induced apoptosis. Cell clones stably transfected with LGI1 cDNA showed greater mortality during a period of serum starvation in comparison with control cells stably transfected with empty vector. This observation suggested hindrance of the PI3K/Akt pathway, a central transducer of survival stimuli elicited by serum growth factors. Treatment with inhibitors of PI3K significantly increased the death of control cells but substantially failed to influence LGI1 cell death, which was greatest independently of the presence of inhibitors. Blockage of the PI3K/Akt pathway in LGI1 cells was confirmed by the lack of serum-induced Akt phosphorylation, in contrast with the strong response of control cells. Instead, serum-induced phosphorylation of ERK1/2 was not impaired by the expression of LGI1. This study showed that overexpression of LGI1 caused neuroblastoma cell death by blocking activation of the PI3K/Akt pathway. Thus, the possibility of upregulating LGI1 expression may be a novel strategy in suppressing oncogenesis and metastasis sustained by excessive activation of the PI3K/Akt pathway