Contrasting effects of IG20 and its splice isoforms, MADD and DENN-SV, on tumor necrosis factor alpha-induced apoptosis and activation of caspase-8 and -3

Male Reproduction in Spinal Muscular Atrophy (SMA) and the Potential Impact of Oral Survival of Motor Neuron 2 (SMN2) Pre-mRNA Splicing Modifiers

Spinal muscular atrophy (SMA) is a neuromuscular disease caused by deletions or mutations in the survival of motor neuron 1 (SMN1) gene resulting in reduced levels of SMN protein. SMN protein is produced by cells throughout the body, and evidence suggests that low SMN protein can have systemic implications, including in male reproductive organs. However, a paucity of research exists on this important topic. This article will discuss findings from non-clinical studies on the role of SMN in the male reproductive system; additionally, real-world observational reports of individuals with SMA will be examined. Furthermore, we will review the non-clinical reproductive findings of risdiplam, a small-molecule SMN2 splicing modifier approved for the treatment of SMA, which has widespread distribution in both the central nervous system and peripheral organs. Specifically, the available non-clinical evidence of the effect of risdiplam on male reproductive organs and spermatogenesis is examined. Lastly, the article will highlight available capabilities to assess male fertility as well as the advanced reproductive technologies utilized to treat male infertility. This article demonstrates the need for further research to better understand the impacts of SMA on male fertility and reproduction.

New insights into the clinical and molecular spectrum of the MADD-related neurodevelopmental disorder

Biallelic pathogenic variants in MADD lead to a very rare neurodevelopmental disorder which is phenotypically pleiotropic grossly ranging from severe neonatal hypotonia, failure to thrive, multiple organ dysfunction, and early lethality to a similar but milder phenotype with better survival. Here, we report 5 patients from 3 unrelated Egyptian families in whom 4 patients showed the severe end of the spectrum displaying neonatal respiratory distress, hypotonia and chronic diarrhea while one patient presented with the mild form displaying moderate intellectual disability and myopathy. In addition, we observed distal arthrogryposis and nonspecific structural brain anomalies in all our patients. Interestingly, cerebellar and brainstem hypoplasia were noted in one patient. Whole exome sequencing identified three novel homozygous variants in the MADD gene: two likely pathogenic [c.4321delC p.(Gln1441ArgfsTer46) and c.2620 C > T p.(Arg874Ter)] and one variant of uncertain significance (c.4307 G > A, p.Arg1436Gln). The variants segregated with the disease in all available family members. Our findings confirm that arthrogryposis, genital, cardiac and structural brain anomalies are manifestations of MADD which expand the spectrum of MADD-related neurodevelopmental disorder. Moreover, they further highlight the convergence of MADD variants on different organ systems leading to complex phenotypes.

A splice site variant in MADD affects hormone expression in pancreatic β cells and pituitary gonadotropes

MAPK activating death domain (MADD) is a multifunctional protein regulating small GTPases RAB3 and RAB27, MAPK signaling, and cell survival. Polymorphisms in the MADD locus are associated with glycemic traits, but patients with biallelic variants in MADD manifest a complex syndrome affecting nervous, endocrine, exocrine, and hematological systems. We identified a homozygous splice site variant in MADD in 2 siblings with developmental delay, diabetes, congenital hypogonadotropic hypogonadism, and growth hormone deficiency. This variant led to skipping of exon 30 and in-frame deletion of 36 amino acids. To elucidate how this mutation causes pleiotropic endocrine phenotypes, we generated relevant cellular models with deletion of MADD exon 30 (dex30). We observed reduced numbers of β cells, decreased insulin content, and increased proinsulin-to-insulin ratio in dex30 human embryonic stem cell-derived pancreatic islets. Concordantly, dex30 led to decreased insulin expression in human β cell line EndoC-βH1. Furthermore, dex30 resulted in decreased luteinizing hormone expression in mouse pituitary gonadotrope cell line LβT2 but did not affect ontogeny of stem cell-derived GnRH neurons. Protein-protein interactions of wild-type and dex30 MADD revealed changes affecting multiple signaling pathways, while the GDP/GTP exchange activity of dex30 MADD remained intact. Our results suggest MADD-specific processes regulate hormone expression in pancreatic β cells and pituitary gonadotropes.

Mechanisms of Drug Resistance in Ovarian Cancer and Associated Gene Targets

In the United States, over 100,000 women are diagnosed with a gynecologic malignancy every year, with ovarian cancer being the most lethal. One of the hallmark characteristics of ovarian cancer is the development of resistance to chemotherapeutics. While the exact mechanisms of chemoresistance are poorly understood, it is known that changes at the cellular and molecular level make chemoresistance challenging to treat. Improved therapeutic options are needed to target these changes at the molecular level. Using a precision medicine approach, such as gene therapy, genes can be specifically exploited to resensitize tumors to therapeutics. This review highlights traditional and novel gene targets that can be used to develop new and improved targeted therapies, from drug efflux proteins to ovarian cancer stem cells. The review also addresses the clinical relevance and landscape of the discussed gene targets.

Phenotype and genotype spectrum of variants in guanine nucleotide exchange factor genes in a broad cohort of Iranian patients

Background

Guanine nucleotide exchange factors (GEFs) play pivotal roles in neuronal cell functions by exchanging GDP to GTP nucleotide and activation of GTPases. We aimed to determine the genotype and phenotype spectrum of GEF mutations by collecting data from a large Iranian cohort with intellectual disability (ID) and/or developmental delay (DD).

Methods

We collected data from nine families with 20 patients extracted from Iranian cohort of 640 families with ID and/or DD. Next‐generation sequencing (NGS) was used to identify the causing variants in recruited families. We also compared our clinical and molecular findings with previously reported patients carrying mutations in these GEF genes in the literature published until mid‐2021.

Results

We identified disease‐causing variants in eight GEF genes including ALS2, IQSEC2, MADD, RAB3GAP1, RAB3GAP2, TRIO, ITSN1, and DENND2A. The major clinical manifestations in 203 previously reported cases along with our 20 patients with disease causing variants in eight GEF genes were as follow; speech disorder (85.2%), ID (81.6%), DD (81.1%), inability to walk (71.3%), facial dysmorphisms features (52.4%), abnormalities in skull morphology (55.6%), hypotonia and muscle weakness (47%), and brain MRI abnormalities (43.4%).

Conclusion

Our study provides new insights into the genotype and phenotype spectrum of mutations in GEF genes.

Homozygous variant in MADD, encoding a Rab guanine nucleotide exchange factor, results in pleiotropic effects and a multisystemic disorder

Rab proteins coordinate inter-organellar vesicle-mediated transport, facilitating intracellular communication, protein recycling, and signaling processes. Dysfunction of Rab proteins or their direct interactors leads to a wide range of diseases with diverse manifestations. We describe seven individuals from four consanguineous Arab Muslim families with an infantile-lethal syndrome, including failure to thrive (FTT), chronic diarrhea, neonatal respiratory distress, variable pituitary dysfunction, and distal arthrogryposis. Exome sequencing analysis in the independent families, followed by an internal gene-matching process using a local exome database, identified a homozygous splice-site variant in MADD (c.2816 + 1 G > A) on a common haplotype. The variant segregated with the disease in all available family members. Determination of cDNA sequence verified single exon skipping, resulting in an out-of-frame deletion. MADD encodes a Rab guanine nucleotide exchange factor (GEF), which activates RAB3 and RAB27A/27B and is thus a crucial regulator of neuromuscular junctions and endocrine secretory granule release. Moreover, MADD protects cells from caspase-mediated TNF-α-induced apoptosis. The combined roles of MADD and its downstream effectors correlate with the phenotypic spectrum of disease, and call for additional studies to confirm the pathogenic mechanism and to investigate possible therapeutic avenues through modulation of TNF-α signaling.

Biallelic MADD variants cause a phenotypic spectrum ranging from developmental delay to a multisystem disorder

In pleiotropic diseases, multiple organ systems are affected causing a variety of clinical manifestations. Here, we report a pleiotropic disorder with a unique constellation of neurological, endocrine, exocrine, and haematological findings that is caused by biallelic MADD variants. MADD, the mitogen-activated protein kinase (MAPK) activating death domain protein, regulates various cellular functions, such as vesicle trafficking, activity of the Rab3 and Rab27 small GTPases, tumour necrosis factor-α (TNF-α)-induced signalling and prevention of cell death. Through national collaboration and GeneMatcher, we collected 23 patients with 21 different pathogenic MADD variants identified by next-generation sequencing. We clinically evaluated the series of patients and categorized the phenotypes in two groups. Group 1 consists of 14 patients with severe developmental delay, endo- and exocrine dysfunction, impairment of the sensory and autonomic nervous system, and haematological anomalies. The clinical course during the first years of life can be potentially fatal. The nine patients in Group 2 have a predominant neurological phenotype comprising mild-to-severe developmental delay, hypotonia, speech impairment, and seizures. Analysis of mRNA revealed multiple aberrant MADD transcripts in two patient-derived fibroblast cell lines. Relative quantification of MADD mRNA and protein in fibroblasts of five affected individuals showed a drastic reduction or loss of MADD. We conducted functional tests to determine the impact of the variants on different pathways. Treatment of patient-derived fibroblasts with TNF-α resulted in reduced phosphorylation of the extracellular signal-regulated kinases 1 and 2, enhanced activation of the pro-apoptotic enzymes caspase-3 and -7 and increased apoptosis compared to control cells. We analysed internalization of epidermal growth factor in patient cells and identified a defect in endocytosis of epidermal growth factor. We conclude that MADD deficiency underlies multiple cellular defects that can be attributed to alterations of TNF-α-dependent signalling pathways and defects in vesicular trafficking. Our data highlight the multifaceted role of MADD as a signalling molecule in different organs and reveal its physiological role in regulating the function of the sensory and autonomic nervous system and endo- and exocrine glands.

Circular RNA circ_0074027 indicates a poor prognosis for NSCLC patients and modulates cell proliferation, apoptosis, and invasion via miR-185-3p mediated BRD4/MADD activation

Circular RNAs play an imperative role in cancer development and metastasis by regulating oncogenic and tumor-suppressive pathways. However, the role and mechanism of circ_0074027 in non-small-cell lung cancer (NSCLC) have not been elucidated. The expression levels of circ_0074027 were detected by qRT-PCR. The link between circ_0074027 expression and clinicopathologic parameters was analyzed by Fisher's exact test. The prognostic role of circ_0074027 was investigated by Kaplan-Meier and Cox regression analysis. Cell counting kit-8 and flow cytometric assays were utilized to evaluate NSCLC cell proliferation and apoptosis, respectively. Wound scratch and Transwell tests were applied to detect cell migratory and invasive capacities. The interaction potential of circ_0074027 and miR-185-3p was analyzed by the circBank database, and verified by dual-luciferase reporter assay. The downstream gene of miR-185-3p was also investigated. Circ_0074027 was elevated in NSCLC specimens and cell lines. Overexpressed circ_0074027 was related to more advanced TNM stages, poorer differentiation grade, and worse overall survival. Upregulated circ_0074027 increased the proliferation of H1299 cells by inhibiting cell apoptosis. Cell migration and invasion were enhanced after circ_0074027 overexpression. Silenced circ_0074027 caused the opposite effects in the A549 cell line. For mechanism investigation, circ_0074027 directly sponges miR-185-3p to enhance bromodomain-containing protein 4 (BRD4) and MAPK-activating death domain-containing protein (MADD) expression levels at the posttranscriptional level. Furthermore, we found the oncogenic function of circ_0074027 is attributed to its modulation of BRD4 and MADD. Collectively, upregulated circ_0074027 in NSCLC accelerates cell progression via miR-185-3p/BRD4/MADD pathway as a competing endogenous RNA.

MADD silencing enhances anti-tumor activity of TRAIL in anaplastic thyroid cancer

ATC is an aggressive disease with limited therapeutic options due to drug resistance. TRAIL is an attractive anti-cancer therapy that can trigger apoptosis in a cancer cell-selective manner. However, TRAIL resistance is a major clinical obstacle for its use as a therapeutic drug. Previously, we demonstrated that MADD is a cancer cell pro-survival factor that can modulate TRAIL resistance. However, its role, if any, in overcoming TRAIL resistance in ATC is unknown. First, we characterized ATC cell lines as either TRAIL resistant, TRAIL sensitive or moderately TRAIL sensitive and evaluated MADD expression/cellular localization. We determined the effect of MADD siRNA on cellular growth and investigated its effect on TRAIL treatment. We assessed the effect of combination treatment (MADD siRNA and TRAIL) on mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) levels. The effect of combination treatment on tumor growth was assessed in vivo. We found increased levels of MADD in ATC cells relative to Nthy-ori 3-1. MADD protein localizes in the cytosol (endoplasmic reticulum and Golgi body) and membrane. MADD knockdown resulted in spontaneous cell death that was synergistically enhanced when combined with TRAIL treatment in otherwise resistant ATC cells. Combination treatment resulted in a significant reduction in MMP and enhanced generation of ROS indicating the putative mechanism of action. In an orthotopic mouse model of TRAIL-resistant ATC, treatment with MADD siRNA alone reduced tumor growth that, when combined with TRAIL, resulted in significant tumor regressions. We demonstrated the potential clinical utility of MADD knockdown in sensitizing cells to TRAIL-induced apoptosis in ATC.

Loss of MADD expression inhibits cellular growth and metastasis in anaplastic thyroid cancer

Anaplastic Thyroid Cancer (ATC) is an aggressive malignancy with limited therapeutic options and dismal patient survival. We have previously shown MADD to be differentially overexpressed in multiple cancer histologies and to contribute to tumor cell growth and survival. Therefore, we targeted MADD by gene silencing, explored its effect on cellular proliferation and metastases and examined its therapeutic potential in an orthotopic ATC model in athymic nude mice. When compared to untreated control and scramble siRNA, MADD siRNA treatment inhibited the proliferative capacity of 8505C, C643 and HTH7 cells in vitro and 8505C-derived-orthotopic tumor growth in vivo. MADD ablation caused a significant reduction in cellular migration and invasion potential; clonogenic capacity; as well as, mitochondrial length and potential in vitro. This MADD siRNA-induced anti-migratory/invasive effect corresponded with inhibition of epithelial–mesenchymal transition (EMT) and Wnt signaling. Mechanistically, MADD siRNA inhibited TNFα induced activation of pERK, pGSK3β and β-catenin, suggesting that MADD knockdown might exert its anti-migratory/invasive effects, by blocking TNFα/ERK/GSK3β axis. MADD siRNA can inhibit β-catenin nuclear translocation and consequently, the expression of its target genes in ATC cells. In in vivo experiments, along with tumor regression, MADD siRNA treatment also decreased evidence of lung metastases. Immunohistochemically, MADD siRNA-treated tumor tissues exhibited a reduction in Ki67 and N-Cadherin expression, and an increase in E-Cadherin expression. In conclusion, we show the crucial role of MADD in ATC tumorigenesis and metastasis and its potential implications as a molecular target for ATC therapy.

Epigenetic silencing of tumor suppressor miR-3151 contributes to Chinese chronic lymphocytic leukemia by constitutive activation of MADD/ERK and PIK3R2/AKT signaling pathways

We hypothesize that miR-3151, localized to a GWAS-identified chronic lymphocytic leukemia (CLL) risk locus (8q22.3), is a tumor suppressor miRNA silenced by promoter DNA methylation in CLL. The promoter of miR-3151 was methylated in 5/7 (71%) CLL cell lines, 30/98 (31%) diagnostic primary samples, but not normal controls. Methylation of miR-3151 correlated inversely with expression. Treatment with 5-Aza-2′-deoxycytidine led to promoter demethylation and miR-3151 re-expression. Luciferase assay confirmed MAP-kinase activating death domain (MADD) and phosphoinositide-3-kinase, regulatory subunit 2 (PIK3R2) as direct targets of miR-3151. Moreover, restoration of miR-3151 resulted in inhibition of cellular proliferation and enhanced apoptosis, repression of MADD and PIK3R2, downregulation of MEK/ERK and PI3K/AKT signaling, and repression of MCL1. Lastly, miR-3151 methylation was significantly associated with methylation of miR-203 and miR-34b/c in primary CLL samples. Therefore, this study showed that miR-3151 is a tumor suppressive miRNA frequently hypermethylated and hence silenced in CLL. miR-3151 silencing by DNA methylation protected CLL cells from apoptosis through over-expression of its direct targets MADD and PIK3R2, hence constitutive activation of MEK/ERK and PI3K/AKT signaling respectively, and consequently over-expression of MCL1.

Repurposing L-Menthol for Systems Medicine and Cancer Therapeutics? L-Menthol Induces Apoptosis through Caspase 10 and by Suppressing HSP90

The objective of the present study was to repurpose L-menthol, which is frequently used in oral health and topical formulations, for cancer therapeutics. In this article, we argue that monoterpenes such as L-menthol might offer veritable potentials in systems medicine, for example, as cheaper anti-cancer compounds. Other monoterpenes such as limonene, perillyl alcohol, and geraniol have been shown to induce apoptosis in various cancer cell lines, but their mechanisms of action are yet to be completely elucidated. Earlier, we showed that L-menthol modulates tubulin polymerization and apoptosis to inhibit cancer cell proliferation. In the present report, we used an apoptosis-related gene microarray in conjunction with proteomics analyses, as well as in silico interpretations, to study gene expression modulation in human adenocarcinoma Caco-2 cell line in response to L-menthol treatment. The microarray analysis identified caspase 10 as the important initiator caspase, instead of caspase 8. The proteomics analyses showed downregulation of HSP90 protein (also corroborated by its low transcript abundance), which in turn indicated inhibition of AKT-mediated survival pathway, release of pro-apoptotic factor BAD from BAD and BCLxL complex, besides regulation of other factors related to apoptosis. Based on the combined microarray, proteomics, and in silico data, a signaling pathway for L-menthol-induced apoptosis is being presented for the first time here. These data and literature analysis have significant implications for "repurposing" L-menthol beyond oral medicine, and in understanding the mode of action of plant-derived monoterpenes towards development of cheaper anticancer drugs in future.

MADD is a downstream target of PTEN in triggering apoptosis

Mitogen-activated kinase activating death domain containing protein (MADD) is abundantly expressed in cancer cells and necessary for maintaining cancer cell survival. However, this survival function of MADD is dependent upon its phosphorylation by protein kinase B (Akt). The tumour suppressor PTEN (phosphatase and tensin homolog deleted on chromosome 10) is a lipid phosphatase that negatively regulates the phosphatidylinositol 3-kinase (PI3K)-Akt signaling pathway. The downstream targets of PTEN in triggering apoptosis have not yet been completely identified. Here, we report that MADD can act as a pro-apoptotic factor to initiate TRAIL-induced apoptosis when its phosphorylation is attenuated by PTEN. Our data show that tumor necrosis factor α-related apoptosis-inducing ligand (TRAIL) induced a reduction in MADD phosphorylation with a concomitant up-regulation of PTEN. Knock down of PTEN using a specific siRNA prevented TRAIL-induced reduction in pMADD levels. Surprisingly, Akt non-phosphorylated MADD translocated from the plasma membrane to cytoplasm where it bound to 14-3-3 and displaced 14-3-3 associated Bax, which translocated to mitochondria resulting in cytochrome c release. Taken together, our data reveal that PTEN can convey the death signal by preventing MADD phosphorylation by Akt.

IG20/MADD plays a critical role in glucose-induced insulin secretion

Pancreatic β-cell dysfunction is a common feature of type 2 diabetes. Earlier, we had cloned IG20 cDNA from a human insulinoma and had shown that IG20/MADD can encode six different splice isoforms that are differentially expressed and have unique functions, but its role in β-cell function was unexplored. To investigate the role of IG20/MADD in β-cell function, we generated conditional knockout (KMA1ko) mice. Deletion of IG20/MADD in β-cells resulted in hyperglycemia and glucose intolerance associated with reduced and delayed glucose-induced insulin production. KMA1ko β-cells were able to process insulin normally but had increased insulin accumulation and showed a severe defect in glucose-induced insulin release. These findings indicated that IG20/MADD plays a critical role in glucose-induced insulin release from β-cells and that its functional disruption can cause type 2 diabetes. The clinical relevance of these findings is highlighted by recent reports of very strong association of the rs7944584 single nucleotide polymorphism (SNP) of IG20/MADD with fasting hyperglycemia/diabetes. Thus, IG20/MADD could be a therapeutic target for type 2 diabetes, particularly in those with the rs7944584 SNP.

Aberrant splicing in neurological diseases

Splicing of precursor messenger RNA (pre-mRNA) removes the intervening sequences (introns) and joins the expressed regions (exons) in the nucleus, before an intron-containing eukaryotic mRNA transcript can be exported and translated into proteins in the cytoplasm. While some sequences are always included or excluded (constitutive splicing), others can be selectively used (alternative splicing) in this process. Particularly by alternative splicing, up to tens of thousands of variant transcripts can be produced from a single gene, which contributes greatly to the proteomic diversity for such complex cellular functions as 'wiring' neurons in the nervous system. Disruption of this process leads to aberrant splicing, which accounts for the defects of up to 50% of mutations that cause certain human genetic diseases. In this review, we describe the different mechanisms of aberrant splicing that cause or have been associated with neurological diseases.

MADD promotes the survival of human lung adenocarcinoma cells by inhibiting apoptosis

MAPK-activating death domain protein (MADD) binds to the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor and acts as a key downstream mediator in the TRAIL-induced apoptosis pathway. The aim of this study was to evaluate the expression of MADD in normal human and adenocarcinoma tissues of the lungs and its influence on proliferation and apoptosis of A549 human lung adenocarcinoma cells. Immunohistochemistry was carried out to detect the expression of MADD in normal and tumor tissues of the lungs. Expression of the MADD gene in A549 cells was measured by reverse transcription-polymerase chain reaction. A549 cells were transfected with plasmids carrying the DNA fragment encoding MADD and lentiviral vectors used for RNA interference, respectively. MADD expression in the transfected A549 cells was determined by western blotting. Proliferation and apoptosis were detected using MTT assay and flow cytometry, respectively. It was found that non-small cell lung cancer tissues expressed MADD at higher levels compared to normal lung tissues, and the level of MADD in lung adenocarcinoma was higher compared to that in lung squamous cell carcinoma. MADD was expressed in A549 cells. Both introduction of the DNA fragment encoding MADD and RNA interference targeting MADD effectively altered levels of MADD in the A549 cells. Overexpression of MADD in the A549 cells inhibited apoptosis and increased survival whereas abrogation of MADD promoted apoptosis and reduced cell proliferation. These results suggest that MADD may be a potential therapeutic target for lung adenocarcinoma therapy involving the TRAIL-induced apoptosis pathway.

MADD knock-down enhances doxorubicin and TRAIL induced apoptosis in breast cancer cells

The Map kinase Activating Death Domain containing protein (MADD) isoform of the IG20 gene is over-expressed in different types of cancer tissues and cell lines and it functions as a negative regulator of apoptosis. Therefore, we speculated that MADD might be over-expressed in human breast cancer tissues and that MADD knock-down might synergize with chemotherapeutic or TRAIL-induced apoptosis of breast cancer cells. Analyses of breast tissue microarrays revealed over-expression of MADD in ductal and invasive carcinomas relative to benign tissues. MADD knockdown resulted in enhanced spontaneous apoptosis in human breast cancer cell lines. Moreover, MADD knockdown followed by treatment with TRAIL or doxorubicin resulted in increased cell death compared to either treatment alone. Enhanced cell death was found to be secondary to increased caspase-8 activation. These data indicate that strategies to decrease MADD expression or function in breast cancer may be utilized to increase tumor cell sensitivity to TRAIL and doxorubicin induced apoptosis.

Alternative Pre-mRNA Splicing, Cell Death, and Cancer

Alternative splicing is one of the most powerful mechanisms for generating functionally distinct products from a single genetic loci and for fine-tuning gene activities at the post-transcriptional level. Alternative splicing plays important roles in regulating genes critical for cell death. These cell death genes encode death ligands, cell surface death receptors, intracellular death regulators, signal transduction molecules, and death executor enzymes such as caspases and nucleases. Alternative splicing of these genes often leads to the formation of functionally different products, some of which have antagonistic effects that are either cell death-promoting or cell death-preventing. Differential alternative splicing can affect expression, subcellular distribution, and functional activities of the gene products. Molecular defects in splicing regulation of cell death genes have been associated with cancer development and resistance to treatment. Studies using molecular, biochemical, and systems-based approaches have begun to reveal mechanisms underlying the regulation of alternative splicing of cell death genes. Systematic studies have begun to uncover the multi-level interconnected networks that regulate alternative splicing. A global picture of the complex mechanisms that regulate cell death genes at the pre-mRNA splicing level has thus begun to emerge.

Down-modulation of expression, or dephosphorylation, of IG20/MADD in tumor necrosis factor-related apoptosis-inducing ligand-resistant thyroid cancer cells makes them susceptible to treatment with this ligand

BACKGROUND

The IG20/MADD gene is overexpressed in thyroid cancer tissues and cell lines, and can contribute to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) resistance. The ability of the MADD protein to resist TRAIL-induced apoptosis is dependent upon its phosphorylation by Akt. Interestingly, while TRAIL induces a significant reduction in the levels of phospho-Akt (pAkt) and phospho-MADD (pMADD) in TRAIL-sensitive cells, it fails to do so in TRAIL-resistant cells. In this study, we investigated if MADD phosphorylation by Akt was contributing to TRAIL resistance in thyroid cancer cells.

METHODS

We determined the susceptibility of different thyroid cancer cell lines to TRAIL-induced apoptosis by fluorescence-activated cell sorting (FACS) analysis. We tested for various TRAIL resistance factors by FACS analyses or for IG20/MADD expression by quantitative reverse transcription-polymerase chain reaction. We determined the levels of pAkt and pMADD upon TRAIL treatment in thyroid cancer cells by Western blotting. We tested if down-modulation of IG20/MADD gene expression using shRNA or phosphorylation using a dominant negative Akt (DN-Akt) or pretreatment with LY294002, a PI3 kinase inhibitor, could help overcome TRAIL resistance.

RESULT

BCPAP and TPC1 cells were susceptible, while KTC1 and FTC133 cells were resistant, to TRAIL-induced apoptosis. The differential susceptibility to TRAIL was not related to the levels of expression of death receptors, decoy receptors, or TRAIL. KTC1 and FTC133 cells showed higher levels of IG20/MADD expression relative to BCPAP and TPC1, and were rendered susceptible to TRAIL treatment upon IG20/MADD knockdown. Interestingly, upon TRAIL treatment, the pAkt and pMADD levels were reduced in TRAIL-sensitive BCPAP and TPC1 cells, while they remained unchanged in the resistant KTC1 and FTC133 cells. While expression of a constitutively active Akt in BCPAP and TPC1 cells rendered them resistant to TRAIL, pretreating KTC1 and FTC133 cells with LY294002 rendered them TRAIL-sensitive. Moreover, expression of a DN-Akt in KTC1 and FTC133 cells reduced the levels of pAkt and pMADD and sensitized them to TRAIL-induced apoptosis.

CONCLUSION

Our results show that pMADD is an important TRAIL resistance factor in certain thyroid cancer cells and suggest that down-modulation of either IG20/MADD expression or phosphorylation can render TRAIL-resistant thyroid cancer cells sensitive to TRAIL.

Bcl-x pre-mRNA splicing regulates brain injury after neonatal hypoxia-ischemia

The bcl-x gene appears to play a critical role in regulating apoptosis in the developing and mature CNS and following CNS injury. Two isoforms of Bcl-x are produced as a result of alternative pre-mRNA splicing: Bcl-x(L) (the long form) is anti-apoptotic, while Bcl-x(S) (short form) is pro-apoptotic. Despite the antagonistic activities of these two isoforms, little is known about how regulation of alternative splicing of bcl-x may mediate neural cell apoptosis. Here, we report that apoptotic stimuli (staurosporine or C2-ceramide) reciprocally altered Bcl-x splicing in neural cells, decreasing Bcl-x(L) while increasing Bcl-x(S). Specific knockdown of Bcl-x(S) attenuated apoptosis. To further define regulatory elements that influenced Bcl-x splicing, a Bcl-x minigene was constructed. Deletional analysis revealed several consensus sequences within intron 2 that altered splicing. We found that the splicing factor, CUG-binding-protein-1 (CUGBP1), bound to a consensus sequence close to the Bcl-x(L) 5' splice site, altering the Bcl-x(L)/Bcl-x(S) ratio and influencing cell death. In vivo, neonatal hypoxia-ischemia reciprocally altered Bcl-x pre-mRNA splicing, similar to the in vitro studies. Manipulation of the splice isoforms using viral gene transfer of Bcl-x(S) shRNA into the hippocampus of rats before neonatal hypoxia-ischemia decreased vulnerability to injury. Moreover, alterations in nuclear CUGBP1 preceded Bcl-x splicing changes. These results suggest that alternative pre-mRNA splicing may be an important regulatory mechanism for cell death after acute neurological injury and may potentially provide novel targets for intervention.

The impact of genomics on pediatric research and medicine

In this review, we discuss some of the most recent developments in genomics research and their relevance to the field of pediatrics. In particular, we examine 3 major approaches that are being used to identify genetic correlates of disease: genome-wide association studies, copy number variation studies, and next-generation sequencing. In the past few years, these approaches have yielded major insights into the causes and pathophysiology of a wide range of diseases but are also constrained by certain limitations. This review provides an overview of the genomic landscape in complex pediatric disorders and sets the stage for translating new discoveries into clinical practice, the future of genomic medicine.

Knockdown of MADD and c-FLIP overcomes resistance to TRAIL-induced apoptosis in ovarian cancer cells

OBJECTIVE

The clinical utility of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in the treatment of established human malignancies is limited by the development of resistance to TRAIL. We hypothesized that knockdown of map-kinase activating death domain containing protein (MADD), a TRAIL-resistance factor, may overcome TRAIL resistance in ovarian cancer cells.

STUDY DESIGN

MADD expression in resected ovarian cancer specimens and cell lines was quantified with the use of polymerase chain reaction. Sensitivity of ovarian cancer cell lines to TRAIL, with or without MADD knockdown, was assessed.

RESULTS

MADD is expressed at relatively higher levels in human malignant ovarian cancer tissues and cell lines, compared with normal ovarian tissues. The cell lines OVCA429 and OVCAR3 were susceptible, and cell lines CAOV-3 and SKOV-3 were resistant to TRAIL. MADD knockdown in CAOV-3 cells, but not in SKOV-3 cells, conferred TRAIL sensitivity. Knockdown of cellular Fas-associated death domain-like interleukin-1 beta-converting enzyme-inhibitory protein (c-FLIP) in SKOV-3 cells increased spontaneous and TRAIL-induced apoptosis, which was further increased on MADD knockdown.

CONCLUSION

MADD/c-FLIP(L) knockdown can render TRAIL-resistant ovarian cancer cells susceptible to TRAIL.

Splicing factor hnRNPH drives an oncogenic splicing switch in gliomas

This study reveals two alternative splicing events that contribute to the development of glioma. HnRNPH is shown to control production of a pro-survival splice variant of the death-domain adaptor protein IG20-MADD and the motility-enhancing isoform of the RON receptor tyrosine kinase.

In tumours, aberrant splicing generates variants that contribute to multiple aspects of tumour establishment, progression and maintenance. We show that in glioblastoma multiforme (GBM) specimens, death-domain adaptor protein Insuloma-Glucagonoma protein 20 (IG20) is consistently aberrantly spliced to generate an antagonist, anti-apoptotic isoform (MAP-kinase activating death domain protein, MADD), which effectively redirects TNF-α/TRAIL-induced death signalling to promote survival and proliferation instead of triggering apoptosis. Splicing factor hnRNPH, which is upregulated in gliomas, controls this splicing event and similarly mediates switching to a ligand-independent, constitutively active Recepteur d′Origine Nantais (RON) tyrosine kinase receptor variant that promotes migration and invasion. The increased cell death and the reduced invasiveness caused by hnRNPH ablation can be rescued by the targeted downregulation of IG20/MADD exon 16- or RON exon 11-containing variants, respectively, using isoform-specific knockdown or splicing redirection approaches. Thus, hnRNPH activity appears to be involved in the pathogenesis and progression of malignant gliomas as the centre of a splicing oncogenic switch, which might reflect reactivation of stem cell patterns and mediates multiple key aspects of aggressive tumour behaviour, including evasion from apoptosis and invasiveness.

Regulating TRAIL receptor-induced cell death at the membrane : a deadly discussion

The use of TRAIL/APO2L and monoclonal antibodies targeting TRAIL receptors for cancer therapy holds great promise, due to their ability to restore cancer cell sensitivity to apoptosis in association with conventional chemotherapeutic drugs in a large variety of tumors. TRAIL-induced cell death is tightly regulated right from the membrane and at the DISC (Death-Inducing Signaling Complex) level. The following patent and literature review aims to present and highlight recent findings of the deadly discussion that determines tumor cell fate upon TRAIL engagement.

Akt-phosphorylated mitogen-activated kinase-activating death domain protein (MADD) inhibits TRAIL-induced apoptosis by blocking Fas-associated death domain (FADD) association with death receptor 4

MADD plays an essential role in cancer cell survival. Abrogation of endogenous MADD expression results in significant spontaneous apoptosis and enhanced susceptibility to tumor necrosis factor alpha-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. However, the regulation of MADD function is largely unknown. Here, we demonstrate that endogenous MADD is phosphorylated at three highly conserved sites by Akt, and only the phosphorylated MADD can directly interact with the TRAIL receptor DR4 thereby preventing Fas-associated death domain recruitment. However, in cells susceptible to TRAIL treatment, TRAIL induces a reduction in MADD phosphorylation levels resulting in MADD dissociation from, and Fas-associated death domain association with DR4, which allows death-inducing signaling complex (DISC) formation leading to apoptosis. Thus, the pro-survival function of MADD is dependent upon its phosphorylation by Akt. Because Akt is active in most cancer cells and phosphorylated MADD confers resistance to TRAIL-induced apoptosis, co-targeting Akt-MADD axis is likely to increase efficacy of TRAIL-based therapies.

Apoptosis and Autoimmune Disorders

Apoptosis or programmed cell death plays a central role in regulating not only the development of lymphocytes but also in their homeostasis. A breakdown in apoptosis related signaling mechanisms could result in the development of autoimmune disorders. The past decade has witnessed an explosive increase in knowledge with respect to various apoptotic signaling pathways and their aberrant behavior in autoimmune disorders. Although Fas/FasL mediated signaling appears to be a common paradigm that has emerged from studies in various autoimmune disorders, examples suggesting a role for other cell death pathways have also surfaced. Understanding the definitive role of apoptosis in various autoimmune disorders is likely to define novel targets for future therapeutic intervention.

MADD, a splice variant of IG20, is indispensable for MAPK activation and protection against apoptosis upon tumor necrosis factor-alpha treatment

We investigated the physiological role of endogenous MAPK-activating death domain-containing protein (MADD), a splice variant of the IG20 gene, that can interact with TNFR1 in tumor necrosis factor-alpha (TNFalpha)-induced activation of NF-kappaB, MAPK, ERK1/2, JNK, and p38. Using exon-specific short hairpin RNAs expressing lentiviruses, we knocked down the expression of all IG20 splice variants or MADD, which is overexpressed in cancer cells. Abrogation of MADD expression rendered cells highly susceptible to TNFalpha-induced apoptosis in the absence of cycloheximide. It also resulted in a dramatic loss in TNFalpha-induced activation of MAPK without any apparent effect on NF-kappaB activation. This observation was substantiated by an accompanying loss in the activation of p90RSK, a key downstream target of MAPK, whereas the NF-kappaB-regulated interleukin 6 levels remained unaffected. Endogenous MADD knockdown, however, did not affect epidermal growth factor-induced MAPK activation thereby demonstrating the specific requirement of MADD for TNF receptor-mediated MAPK activation. Re-expression of short hairpin RNA-resistant MADD in the absence of endogenous IG20 expression rescued the cells from TNFalpha-induced apoptosis. The requirement for MADD was highly specific for TNFalpha-induced activation of MAPK but not the related JNK and p38 kinases. Loss of MADD expression resulted in reduced Grb2 and Sos1/2 recruitment to the TNFR1 complex and decreased Ras and MEKK1/2 activation. These results demonstrate the essential role of MADD in protecting cancer cells from TNFalpha-induced apoptosis by specifically activating MAPKs through Grb2 and Sos1/2 recruitment, and its potential as a novel cancer therapeutic target.

Knockdown of IG20 gene expression renders thyroid cancer cells susceptible to apoptosis

AIM

The aim of the study was to investigate the expression and function of the IG20 gene in thyroid cancer cell survival, proliferation, and apoptosis.

METHODS

We determined the expression levels of the major isoforms of IG20 by quantitative RT-PCR in normal and thyroid tumor tissues/cell lines. We evaluated the functional consequence of IG20 knockdown in WRO (follicular carcinoma) and FRO (anaplastic carcinoma) thyroid cancer cell lines by measuring spontaneous, TNFalpha-related apoptosis-inducing ligand (TRAIL), and TNFalpha-induced apoptosis.

RESULTS

The IG20 gene expression levels were higher in benign and malignant thyroid tumors and in WRO and FRO cells relative to normal tissues. Predominantly, MADD and DENN-SV isoforms of IG20 gene were expressed. IG20 knockdown resulted in increased spontaneous, TRAIL-, and TNFalpha-induced apoptosis in WRO, but not FRO, cells. FRO cell resistance to apoptosis is likely due to caspase-8 deficiency.

CONCLUSION

IG20 knockdown renders WRO cells more susceptible to spontaneous, TRAIL-, and TNFalpha-induced apoptosis and thus demonstrates the prosurvival function of the IG20 gene in thyroid cancer. These observations, combined with overexpression of IG20 noted in thyroid tumor tissues, may suggest a potential role in thyroid cancer survival and growth and indicate that IG20 may be targeted either alone or in conjunction with TRAIL or TNFalpha treatment in certain thyroid cancers.

Regulation of apoptosis and caspase-8 expression in neuroblastoma cells by isoforms of the IG20 gene

The IG20 gene undergoes alternative splicing resulting in the differential expression of six putative splice variants. Four of these (IG20pa, MADD, IG20-SV2, and DENN-SV) are expressed in virtually all human tissues. However, investigations examining alternative splicing of the IG20 gene to date have been largely limited to nonneural malignant and nonmalignant cells. In this study, we investigated the expression of alternative splice isoforms of the IG20 gene in human neuroblastoma cells. We found that six IG20 splice variants (IG20-SVs) were expressed in two human neuroblastoma cell lines (SK-N-SH and SH-SY5Y), highlighted by the expression of two unique splice isoforms (i.e., KIAA0358 and IG20-SV4). Similarly, we found enriched expression of these two IG20-SVs in human neural tissues derived from cerebral cortex, hippocampus, and, to a lesser extent, spinal cord. Using gain-of-function studies and siRNA technology, we determined that these "neural-enriched isoforms" exerted significant and contrasting effects on vulnerability to apoptosis in neuroblastoma cells. Specifically, expression of KIAA0358 exerted a potent antiapoptotic effect in both the SK-N-SH and SH-SY5Y neuroblastoma cell lines, whereas expression of IG20-SV4 had proapoptotic effects directly related to the activation of caspase-8 in these cells, which have minimal or absent constitutive caspase-8 expression. These data indicate that the pattern of expression of these neural-enriched IG20-SVs regulates the expression and activation of caspase-8 in certain neuroblastoma cells, and that manipulation of IG20-SV expression pattern may represent a potent therapeutic strategy in the therapy of neuroblastoma and perhaps other cancers.

Role of IG20 splice variants in TRAIL resistance

Tumor necrosis factor receptor-related apoptosis-inducing ligand (TRAIL) can induce apoptosis primarily in cancer cells with little or no effect on normal cells; therefore, it has the potential for use in cancer therapy. TRAIL binding to death receptors DR4 and DR5 triggers the death-inducing signal complex formation and activation of procaspase-8, which in turn activates caspase-3, leading to cell death. Like FasL, TRAIL can trigger type 1 (caspase-8 --> caspase-3) or type 2 (caspase-8 --> Bid cleavage --> capsase-9 --> caspase-3) apoptotic pathways depending on the cell type. Some cancers are resistant to TRAIL treatment because most molecules in the TRAIL signaling pathway, including FLIPs and IAPs, can contribute to resistance. In addition, we have identified an essential role for splice variants of the IG20 gene in TRAIL resistance.

Changes in glucose metabolism and gene expression after transfer of anti-angiogenic genes in rat hepatoma

PURPOSE

Human troponin I (TROP), the soluble receptor for vascular endothelial growth factor (sFLT) and angiostatin (ASTAT) are potent inhibitors of endothelial cell proliferation, angiogenesis and tumour growth in vivo. Transfer of these genes into tumours may induce changes not only in perfusion, but also more general ones such as changes in metabolism. The aim of this study was to assess these reactions using FDG-PET and high-throughput methods such as gene profiling.

METHODS

We established Morris hepatoma (MH3924A) cell lines expressing TROP, sFLT or ASTAT and quantified (18)F-fluorodeoxyglucose ((18)FDG) uptake by dynamic positron emission tomography (PET) after tumour inoculation in ACI rats. Furthermore, expression of glucose transporter-1 and -3 (GLUT-1 and GLUT-3) as well as hexokinase-1 and -2 were investigated by RT-PCR and immunohistomorphometry. In addition, gene array analyses were performed.

RESULTS

(18)FDG uptake, vascular fraction and distribution volume were significantly higher in all genetically modified tumours. Immunohistomorphometry showed an increased percentage of hexokinase-1 and -2 as well as GLUT-1 and -3 immunoreactive (ir) cells. Using gene arrays and comparing all three groups of genetically modified tumours, we found upregulated expression of 36 genes related to apoptosis, signal transduction, stress or metabolism.

CONCLUSION

TROP-, sFLT- or ASTAT-expressing MH3924A tumours show enhanced influx of (18)FDG, which seems to be caused by several factors: enhanced exchange of nutrients between blood and tumour, increased amounts of glucose transporters and hexokinases, and increased expression of genes related to apoptosis, matrix and stress, which induce an increased demand for glucose.

MADD/DENN Splice Variant of the IG20 Gene Is a Negative Regulator of Caspase-8 Activation

The MADD variant of the IG20 gene is necessary and sufficient for cancer cell survival. Abrogation of MADD, but not the other IG20 splice variants, can render cancer cells more susceptible to spontaneous as well as TRAIL (tumor necrosis factor alpha-related apoptosis-inducing ligand)-induced apoptosis. Both types of apoptosis in cells devoid of MADD can be inhibited by expression of CrmA or dominant-negative FADD, thereby suggesting that endogenous MADD may be targeting caspase-8 activation. Immunoprecipitation studies showed that MADD down-modulation could lead to caspase-8 activation at the death receptors without an apparent increase in the recruitment of death-inducing signaling complex components such as FADD. Further, we found that MADD can directly interact with death receptors, but not with either caspase-8 or FADD, and can inhibit caspase-8 activation. These results clearly demonstrate the importance of MADD in the control of cancer cell survival/death and in conferring significant resistance to TRAIL-induced apoptosis. In addition, our results indicate the therapeutic potential of MADD abrogation in enhancing TRAIL-induced selective apoptosis of cancer cells.

(Peri)vascular production and action of pro-inflammatory cytokines in brain pathology

In response to tissue injury or infection, the peripheral tissue macrophage induces an inflammatory response through the release of IL-1β (interleukin-1β) and TNFα (tumour necrosis factor α). These cytokines stimulate macrophages and endothelial cells to express chemokines and adhesion molecules that attract leucocytes into the peripheral site of injury or infection. The aims of the present review are to (i) discuss the relevance of brain (peri)vascular cells and compartments to bacterial meningitis, HIV-1-associated dementia, multiple sclerosis, ischaemic and traumatic brain injury, and Alzheimer's disease, and (ii) to provide an overview of the production and action of pro-inflammatory cytokines by (peri)vascular cells in these pathologies of the CNS (central nervous system). The brain (peri)vascular compartments are highly relevant to pathologies affecting the CNS, as infections are almost exclusively blood-borne. Insults disrupt blood and energy flow to neurons, and active brain-to-blood transport mechanisms, which are the bottleneck in the clearance of unwanted molecules from the brain. Perivascular macrophages are the most reactive cell type and produce IL-1β and TNFα after infection or injury to the CNS. The main cellular target for IL-1β and TNFα produced in the brain (peri)vascular compartment is the endothelium, where these cytokines induce the expression of adhesion molecules and promote leucocyte infiltration. Whether this and other effects of IL-1 and TNF in the brain (peri)vascular compartments are detrimental or beneficial in neuropathology remains to be shown and requires a clear understanding of the role of these cytokines in both damaging and repair processes in the CNS.

MADD/DENN splice variant of the IG20 gene is necessary and sufficient for cancer cell survival

The IG20 gene is overexpressed in human tumors and cancer cell lines, and encodes at least four splice variants (SVs) namely, IG20pa, MADD, IG20-SV2 and DENN-SV. Earlier, gain-of-function studies showed that IG20-SVs can exhibit diverse functions and play a critical role in cell proliferation and apoptosis. Expression of exogenous IG20pa or DENN-SV rendered cells either susceptible or resistant to induced apoptosis, respectively, whereas MADD and IG20-SV2 had no apparent effect. In order to understand the contrasting effects of the IG20-SVs in a physiologically more relevant system, we expressed exon-specific small hairpin RNAs (shRNAs) to selectively knockdown specific IG20-SVs. Consistent with an earlier study, knockdown of all IG20-SVs resulted in spontaneous apoptosis of HeLa and PA-1 cells. In addition, we unambiguously demonstrated that knockdown of MADD can render cells susceptible to spontaneous apoptosis but had no discernible effect on cell proliferation, colony size or cell cycle progression. Moreover, expression of MADD alone, and not DENN-SV, in the absence of endogenous IG20-SVs was sufficient to prevent spontaneous apoptosis. Our results show the utility of shRNAs for selective knockdown of particular IG20-SVs and their potential therapeutic value in cancer. Further, they demonstrate that MADD alone is sufficient and necessary for cancer cell survival.

The IA-2 interactome

AIMS/HYPOTHESIS

Islet antigen-2 (IA-2), a major autoantigen in type 1 diabetes, is an enzymatically inactive member of the transmembrane protein tyrosine phosphatase (PTP) family. IA-2 is located in dense-core secretory vesicles and is involved in the regulation of insulin secretion. The present experiments were initiated to identify those proteins that interact with IA-2 (i.e. the IA-2 interactome) as a first step towards elucidating the mechanism(s) by which IA-2 influences insulin secretion and serves as an autoantigen.

MATERIALS AND METHODS

To determine the proteins with which IA-2 interacts, a yeast two-hybrid system was used to screen a human foetal library, and deletion mutants were used to determine the binding sites. Positive interactions were confirmed by immunoprecipitation pull-down experiments using cell lysate from transfected mammalian cell lines.

RESULTS

Six new interacting proteins were identified by this approach: mitogen-activated protein kinase-activating death domain (MADD), the MADD isoform IG20, PTPrho, PTPsigma, sorting nexin 19 (SNX19) and cyclophilin A. Using a series of IA-2 deletion mutants, we identified the regions on the IA-2 molecule to which five of the interacting proteins bound. Amino acids 744-979 of IA-2 were required for the maximum binding of MADD, IG20 and SNX19, whereas amino acids 602-907 of IA-2 were required for the maximum binding of PTPrho and PTPsigma. Pull-down experiments with cell lysate from transfected mammalian cells confirmed the binding of the interacting proteins to IA-2.

CONCLUSIONS/INTERPRETATION

The IA-2 interactome based on, pull-down experiments, currently consists of 12 proteins. The identification of these interacting proteins provides clues as to how IA-2 exerts its biological functions.

A simplified probe preparation for ELISA-based NF-κB activity assay

Nuclear factor-kappaB (NF-kappaB) is critically involved in the transcriptional regulation of many genes and multiple biological and pathobiological processes. To efficiently monitor and to rapidly screen NF-kappaB transcriptional activity, an ELISA-based assay has been increasingly and successfully employed as a new method in a variety of cell lines and experimental models since its first demonstration and recent development. In the ELISA-based assay, NF-kappaB is captured by a double-stranded DNA probe pre-linked on multi-well plates. Typically, the DNA probe contains the double-stranded consensus binding sequence for active NF-kappaB and another double-stranded sequence linking the consensus binding sequence with the plate (linker sequence). Since nuclear factor has no binding activity with single-stranded DNA, we modified the probe construction as containing the double-stranded consensus binding sequence and a single-stranded-linker sequence. Our results show that this kind of probe is highly sensitive and specific for NF-kappaB activity assay, whereas the preparation of this kind of probe is much more convenient. A single-stranded-linker sequence may largely decrease nonspecific protein binding and thus increase the sensitivity of this assay.

IG20 (MADD splice variant-5), a proapoptotic protein, interacts with DR4/DR5 and enhances TRAIL-induced apoptosis by increasing recruitment of FADD and caspase-8 to the DISC

Recently, we identified Insulinoma-Glucagonoma clone 20 (IG20) that can render cells more susceptible to tumor necrosis factor-alpha (TNF-alpha)-induced apoptosis. In addition, it can slow cell proliferation, and enhance drug- and radiation-induced cell death. TNF-related apoptosis-inducing ligand (TRAIL) can selectively induce apoptosis in some cancer cells and render others susceptible to cotreatment with drugs and irradiation, with little or no effect on most normal cells. In this study, we investigated the potential of IG20 to enhance TRAIL-induced apoptosis and found that it can render cells more susceptible to TRAIL treatment through enhanced activation of caspases. Further, we showed that this effect can be suppressed by caspase inhibitors, p35 and CrmA, and a dominant-negative Fas-associated death domain-containing protein (DN-FADD). Results from colocalization and immunoprecipitation studies showed that IG20 can interact with TRAIL death receptors (DR), DR4 and DR5 and increase recruitment of FADD and caspase-8 into the TRAIL death-inducing signaling complex (DISC). These results indicate that IG20 is a novel protein that can enhance TRAIL-induced apoptosis by facilitating DISC formation.

A complete genetic analysis of neuronal Rab3 function

Rab3A, Rab3B, Rab3C, and Rab3D are closely related GTP-binding proteins of synaptic vesicles that may function in neurotransmitter release. We have produced knock-out (KO) mice for Rab3B and Rab3C and crossed them with previously generated Rab3A and 3D knock-out mice to generate double, triple, and quadruple Rab3 knock-out mice. We have found that all single and double Rab3 knock-out mice are viable and fertile. Most triple Rab3 knock-out mice perish whenever Rab3A is one of the three deleted proteins, whereas all triple knock-out mice that express Rab3A are viable and fertile. Finally, all quadruple knock-out mice die shortly after birth. Quadruple Rab3 KO mice initially develop normally and are born alive but succumb to respiratory failure. Rab3-deficient mice display no apparent changes in synapse structure or brain composition except for a loss of rabphilin, a Rab3-binding protein. Analysis of cultured hippocampal neurons from quadruple knock-out mice uncovered no significant change in spontaneous or sucrose-evoked release but an approximately 30% decrease in evoked responses. This decrease was caused by a decline in the synaptic and the vesicular release probabilities, suggesting that Rab3 proteins are essential for the normal regulation of Ca2+-triggered synaptic vesicle exocytosis but not for synaptic vesicle exocytosis as such. Our data show that Rab3 is required for survival in mice and that the four Rab3 proteins are functionally redundant in this role. Furthermore, our data demonstrate that Rab3 is not in itself essential for synaptic membrane traffic but functions to modulate the basic release machinery.

Dual role of DENN/MADD (Rab3GEP) in neurotransmission and neuroprotection

DENN/MADD is a component of a signalling protein complex that is localized to the cytosol and exerts multiple functions by using different binding partners. Human DENN/MADD is physically the same death-domain protein as rat Rab3 GDP/GTP exchange protein (Rab3GEP). DENN/MADD regulates the recycling of Rab3 small G proteins under normal conditions and has an essential role in Ca(2+)-dependent neurotransmitter release and exocytosis. It is also involved in blocking the apoptosis of neuronal cells under conditions of cytotoxic stress. Recent research supports an important role for DENN/MADD in neuroprotection: reduced endogenous DENN/MADD expression and enhanced pro-apoptotic signalling has been found in brains affected by Alzheimer's disease.

Epidemiology and molecular pathology at crossroads to establish causation: molecular mechanisms of malignant transformation

Epidemiology is a very reliable science for the identification of carcinogens. Epidemiological studies require that the effect, cancer in this case, has already occurred, when of course it would be more desirable to identify potential carcinogenic substances at an earlier stage before they have caused a large number of malignancies and thus become identifiable by epidemiological studies. In the past 30 years, molecular pathology (which includes chemistry, biochemistry, molecular biology, molecular virology, molecular genetics, epigenetics, genomics, proteomics, and other molecular-based approaches) has identified some key alterations that are required for cellular transformation and malignancy. Agents that specifically interfere with some of these mechanisms are suspected human carcinogens. It can be stated that tumor formation requires the following steps: (1) inactivation of Rb and p53 cellular pathways; (2) activation of Ras and/or other growth promoting pathways; (3) inactivation of phosphatase 2A that causes changes in the phosphorylation and activity of several cellular proteins; (4) evasion of apoptosis; (5) telomerase activation or alternative mechanisms of cellular immortalization; (6) angiogenic activity; and (7) the ability to invade surrounding tissues and to metastasize. Here, we review the molecular mechanisms of cellular transformation. The integration of this knowledge with classical epidemiology and animal studies should permit a more rapid and accurate identification of human carcinogens.

Down-regulation of DENN/MADD, a TNF receptor binding protein, correlates with neuronal cell death in Alzheimer's disease brain and hippocampal neurons

Tumor necrosis factor (TNF) alpha and mitogen-activated protein kinase/c-Jun N-terminal kinase (MAPK/JNK) pathways are both implicated in Alzheimer's disease (AD) pathogenesis. Increased expression of several members of the TNF pathway and JNK activation of c-Jun ultimately result in neuronal apoptosis. DENN/MADD, a multifunctional domain protein expressed in neurons, interacts with both the p55 TNF receptor (TNFR) type 1 and JNK3, placing it at a critical juncture in regulating signaling of neurodegeneration. We examined expression and interactions of the TNFR1 binding proteins, DENN/MADD, and TNFR-associated death domain (TRADD) protein in AD-affected tissues and cell cultures. We found reduced DENN/MADD and increased TRADD expression immunohistochemically in the hippocampus in areas of AD pathology compared to normal controls but little intraneuronal colocalization. In brain homogenates, DENN/MADD protein and mRNA expression was significantly reduced in AD compared to controls. Conversely, TRADD, TNFR1, and activated JNK were increased. Murine neuroblastoma and rat hippocampal cultures stressed with Abeta1-42 and the cortices of AD transgenic mice (Tg2576Swe) each showed decreased DENN/MADD expression and TRADD up-regulation in the mice, compared to controls. DENN/MADD antisense treatment of cultured rat hippocampal neurons reduced endogenous DENN/MADD and promoted neuronal cell death. DENN/MADD and TRADD competitively bound to TNFR1 when overexpressed in N(2)A cells, with DENN/MADD abrogating TNFR1 binding to TRADD. DENN/MADD may therefore be protective by inhibiting TRADD-induced apoptotic cell death. Reduction of DENN/MADD may affect long-term neuronal viability in AD by allowing TRADD mediation of TNFR1 signaling in response to oxidative or cytokine-promoted stresses.

Antisense abrogation of DENN expression induces apoptosis of leukemia cells in vitro, causes tumor regression in vivo and alters the transcription of genes involved in apoptosis and the cell cycle

We previously reported that messenger RNA expression of DENN (differentially expressed in normal and neoplastic cells) is considerably higher in cancer cell lines than in normal cells. In our present study, we established that certain cancer cell lines express conspicuously higher levels of the 2 DENN isoforms in contrast to the 2 pro-apoptotic IG20 isoforms. Antisense DENN oligodeoxynucleotide treatment of K36 cells in vitro induced extensive apoptosis, while antisense DENN silencing of K36 tumor-bearing mice caused significant tumor regression in vivo. Compared to wild-type murine embryonic fibroblasts, antisense treatment of NFkappaB and TNFR1 KO cells resulted in markedly more pronounced cell death, whereas antisense-treated TNFalpha and TNFR2 knockouts exhibited less prominent apoptosis. Cell viability and apoptosis were authenticated by flow cytometry, membrane integrity, TUNEL, annexin V assays, histology and electron microscopy. Antisense abrogation of DENN expression culminated in upregulated expression of TNFR2, TRAIL and Fas, but downregulation of TNFalpha, TNFR1 and cyclin D3. Conversely, DENN overexpression stimulated cell proliferation and led to upregulated TRPM2 and cyclin B1, but diminished expression of Fas, TNFR2, TRAIL and Egr-1. The participation of TNFalpha, TNFR1, TNFR2 and Fas in the inhibition of DENN expression was also demonstrated. These data support the anti-apoptotic and cell survival role of DENN, especially in malignant cells, and its interaction with specific genes and proteins involved in the apoptotic and cell cycle pathways.

IG20, in contrast to DENN-SV, (MADD splice variants) suppresses tumor cell survival, and enhances their susceptibility to apoptosis and cancer drugs

We identified seven putative splice variants of the human IG20 gene. Four variants namely, IG20, MADD, IG20-SV2 and DENN-SV are expressed in human tissues. While DENN-SV is constitutively expressed in all tissues, expression of IG20 appears to be regulated. Interestingly, overexpression of DENN-SV enhanced cell replication and resistance to treatments with TNFalpha, vinblastine, etoposide and gamma-radiation. In contrast, IG20 expression suppressed cell replication and increased susceptibility to the above treatments. Moreover, cells that were resistant and susceptible to TNFalpha-induced apoptosis exclusively expressed endogenous DENN-SV and IG20, respectively. When PA-1 ovarian cancer cells that are devoid of endogenous IG20 variant, but express higher levels of DENN-SV, were transfected with IG20, they showed reduced cell proliferation and increased susceptibility to apoptosis induced by TNFalpha, TRAIL and gamma-radiation. This indicated that overexpression of IG20 can override endogenous DENN-SV function. CrmA reversed the effects of IG20, but not DENN-SV. In contrast, dominant-negative-I-kappa B reversed the effects of DENN-SV, but not IG20, and showed that DENN-SV most likely exerted its effects through NFkappaB activation. Together, our data show that IG20 gene can play a novel and significant role in regulating cell proliferation, survival and death through alternative mRNA splicing.

Genes trans-regulated by a novel hepatitis B virus preS2 antigen binding protein S2-29 by cDNA microarray

AIM: To study the biological functions of a novel hepatitis B virus preS2 antigen binding protein S2-29, and to analyze the gene expression profiles of HepG2 cell transfected with S2-29 gene.

METHODS: S2-29 gene was screened and identified by using yeast two-hybrid system 3 and coimmunoprecipita-tion technique. Full-length encoding frame S2-29 and its amino acid sequences were identified by using bioinformatics method and the recombined eukaryotic expression plasmid pcDNA3.1(-)-S2-29 was constructed and transfected into HepG2 cells. Total mRNA was isolated from the HepG2 cells transfected with pcDNA3.1(-) and pcDNA3.1(-)-S2-29, respectively. cDNA microarray was employed for detecting and analysing of mRNA from the HepG2 cells.

RESULTS: S2-29 cDNA sequence was obtained and identified by yeast two-hybrid screening and the bioinformatics analysis. Among 1 152 genes, there were 10 differences, of which 9 genes were upregulated and 1 gene were downregulated in HepG2 cells transfected with S2-29 protein expression plasmid. These genes differentially down-regulated by S2-29 protein included eukaryotic translation elongation factor 2, MAP-kinase activating death domain, glutathione peroxidase 5, gelsolin-like capping protein (actin filament), NDRG family member 2, prosaposin, SUMO-1 activating enzyme subunit 1, insulin receptor and a novel protein.

CONCLUSION: Microarray technique is successfully used to screen the genes trans-regulated by S2-29, which brings some new clues for studying the trans-regulation and biological function of S2-29.

DeltaBAFF, an alternate splice isoform that regulates receptor binding and biopresentation of the B cell survival cytokine, BAFF

The tumor necrosis family member BAFF is limiting for the survival of follicular B lymphocytes, but excessive BAFF signaling can lead to autoimmunity, suggesting that its activity must be tightly regulated. We have identified a conserved alternate splice isoform of BAFF, called deltaBAFF, which lacks 57 nt encoding the A-A1 loop and is co-expressed with BAFF in many mouse and human myeloid cells. Mouse deltaBAFF appears on the plasma membrane, but unlike BAFF it is inefficiently released by proteolysis. DeltaBAFF can associate with BAFF in heteromultimers and diminish BAFF bioactivity and release. Thus, alternative splicing of the BAFF gene suppresses BAFF B cell stimulatory function in several ways, and deltaBAFF may promote other functions as well.

Induction of apoptosis by 2,3,7,8-tetrachlorodibenzo-p-dioxin following endotoxin exposure

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent and persistent environmental toxin that induces hepatotoxicity and increases endotoxin-induced liver injury. The objective of this study was to evaluate whether TCDD could modulate apoptosis and cytokine-controlled apoptotic signaling pathways following lipopolysaccharide (LPS) exposure in female B6C3F1 mice. The effects of TCDD treatment were most dramatic late in the time course (10-14 days posttreatment). Serum enzyme activities were elevated at day 10 (100 microg TCDD/40 microg LPS treatment) and day 14 (100 microg TCDD/saline treatment), indicating peak liver damage occurred at those times. Histological examination of perfused livers showed an increase in apoptotic cells at day 14 in animals treated with 10 microg TCDD. Caspase-1 activity was suppressed at 14 days in mice treated with 100 microg TCDD/40 microg LPS and 100 microg TCDD/4 microg LPS compared to the respective corn oil (CO)/LPS-treated controls. Caspase-3 activity was suppressed at 14 days in 100 microg TCDD/saline-100 microg TCDD/40 microg LPS- and 100 microg TCDD/4 microg LPS-treated mice compared to respective CO/saline- or CO/LPS-treated control mice. At 40 microg LPS, caspase activity was stimulated in TCDD (100 microg)-exposed mice at 3 and 7 days and then suppressed at 10 and 14 days. Western blot analysis, electrophoretic mobility shift assay, and ELISA did not show any effect by TCDD (100 microg) on IkappaB-beta and IkappaB-alpha protein expression or on DNA binding activity of the nuclear NFkappaB protein. These data indicate that TCDD induces apoptosis 14 days posttreatment; however, we found no evidence of suppression of the antiapoptotic transcription factor NFkappaB.