Search

The L1 syndrome, a genetic disease that affects 1/30 000 newborn males, is sustained by numerous missense mutations of L1 cell adhesion molecule (L1CAM), an adhesion surface protein active also in transmembrane signaling, essential for the development and function of neurons. To investigate the cell biology of L1CAM, we employed a high RE1-silencing transcription (factor) clone of the pheochromocytoma PC12 line, defective in L1CAM expression and neurite outgrowth. The clone was transfected with wild-type L1CAM and four missense, disease-inducing point mutants encoding proteins distributed to the cell surface. The mutant-expressing cells, defective in adhesion to extracellular matrix proteins and in migration, exhibited unchanged proliferation. The nerve growth factor (NGF)-induced neurite outgrowth was re-established in defective clone cells transfected with the wild-type and the H210Q and I219T L1CAMs mutants, but not in the others. The stimulated outgrowth was confirmed in a second defective PC12 clone over-expressing the NGF receptor TrkA, treated with NGF and/or a recombinant L1CAM chimera. These results revealed a new function of L1CAM, a positive, robust and dose-dependent modulation of the TrkA receptor activated spontaneously or by NGF. The variable effects observed with the different L1CAM mutants suggest that this function contributes to the marked heterogeneity of symptoms and severity observed in the patients affected by the L1 syndrome., (© 2012 The Authors Journal of Neurochemistry © 2012 International Society for Neurochemistry.)

Dihydroceramides, the precursors of ceramides in the de novo sphingolipid synthesis, have been recently implicated in active signalling. We previously demonstrated that dihydroceramide accumulation, in response to treatment with the dihydroceramide desaturase inhibitor XM462, induced autophagy with no sign of cell death in the gastric carcinoma HCG27 cell line. Here we show that XM462 treatment induces a transient early increase in dihydroceramides that are successively metabolized into other sphingolipids. Dihydroceramides accumulation is associated with cyclin D1 expression modulation, delayed G1/S transition of cell cycle and increased autophagy. Moreover, XM462 treatment induces ER stress via the activation of the translation inhibitor eIF2α and the pro-survival transcriptional factor Xbp1. Exogenous addition of a short chain dihydroceramide analog reproduces the effects of endogenous accumulation of dihydroceramides, causing cell cycle delay of the G1/S transition, autophagy enhancement, eIF2α activation and Xbp1 splicing. Blocking autophagy with 3-methyladenine abrogates the effect of XM462 on cell cycle and reduces cell survival to XM462 treatment. Furthermore, the XM462-induced survival response is able to reduce etoposide toxicity in HCG27 and HCT116 cancer cells. Our data suggest a role of dihydroceramide in regulating cell proliferation and survival., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Background: Low oxygen (O2) availability, a condition called hypoxia, has different and profound consequences in tissues and organs. Besides the hypoxia-inducible response, mammalian cells induce a coordinated cytoprotective pathway called Unfolded Protein Response (UPR). We studied the molecular basis of UPR and apoptosis in animal models exposed to different hypoxic stresses and assessed the ability of liver and myocardium to respond to low oxygen by activating different arms of the UPR according to the severity of the insults in a tissue specific manner., Methods: We assessed the levels of several UPR markers in hypoxic animals by Real Time PCR and Western blotting., Results: While the hepatocytes activate the apoptotic pathway mediated, in part, by CHOP and p-JNK, we could not detect an UPR-dependent apoptosis in myocytes. Moreover, severe hypoxia results in ATF4 translation, and induction of CHOP and GADD34 transcripts in liver, by contrast in the myocardium, the ATF4-CHOP-GADD34 signaling pathway is not detectably activated., General Significance: Comparison of several UPR markers in liver and myocardium enabled to underscore the ability of hepatocytes and myocites to selectively activate and fine tune the UPR signaling pathway during hypoxia in vivo., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The cellular pathways activated by mutant prion protein (PrP) in genetic prion diseases, ultimately leading to neuronal dysfunction and degeneration, are not known. Several mutant PrPs misfold in the early secretory pathway and reside longer in the endoplasmic reticulum (ER) possibly stimulating ER stress-related pathogenic mechanisms. To investigate whether mutant PrP induced maladaptive responses, we checked key elements of the unfolded protein response (UPR) in transgenic mice, primary neurons and transfected cells expressing two different mutant PrPs. Because ER stress favors the formation of untranslocated PrP that might aggregate in the cytosol and impair proteasome function, we also measured the activity of the ubiquitin proteasome system (UPS). Molecular, biochemical and immunohistochemical analyses found no increase in the expression of UPR-regulated genes, such as Grp78/Bip, CHOP/GADD153, or ER stress-dependent splicing of the mRNA encoding the X-box-binding protein 1. No alterations in UPS activity were detected in mutant mouse brains and primary neurons using the Ub(G76V)-GFP reporter and a new fluorogenic peptide for monitoring proteasomal proteolytic activity in vivo. Finally, there was no loss of proteasome function in neurons in which endogenous PrP was forced to accumulate in the cytosol by inhibiting cotranslational translocation. These results indicate that neither ER stress, nor perturbation of proteasome activity plays a major pathogenic role in prion diseases.

Histone deacetylase inhibitors (HDACIs) are promising antineoplastic agents for the treatment of cancer. Here we report that the lipid peroxidation end product 4-hydroxynonenal (HNE) significantly potentiates the anti-tumor effects of the HDAC inhibitor panobinostat (LBH589) in the PC3 prostate cancer cell model. Panobinostat and HNE inhibited proliferation of PC3 cells and the combination of the two agents resulted in a significant combined effect. Cell cycle analysis revealed that both single agents and, to a greater extent, their combined treatment induced G2/M arrest, but cell death occurred in the combined treatment only. Furthermore, HNE and, to a greater extent, the combined treatment induced dephosphorylation of Cdc2 leading to progression into mitosis as confirmed by α-tubulin/DAPI staining and phospho-histone H3 (Ser10) analysis. To evaluate possible induction of DNA damage we utilized the marker phosphorylated histone H2A.X. Results showed that the combination of panobinostat and HNE induced significant DNA damage concomitant with the mitotic arrest. Then, by using androgen receptor (AR)-expressing PC3 cells we observed that the responsiveness to HNE and panobinostat was independent of the expression of functional AR. Taken together, our data suggest that HNE potentiates the antitumoral effect of the HDACI panobinostat in prostate cancer cells., (Copyright © 2010 Elsevier Inc. All rights reserved.)

After few days of intense immunoglobulin (Ig) secretion, most plasma cells undergo apoptosis, thus ending the humoral immune response. We asked whether intrinsic factors link plasma cell lifespan to Ig secretion. Here we show that in the late phases of plasmacytic differentiation, when antibody production becomes maximal, proteasomal activity decreases. The excessive load for the reduced proteolytic capacity correlates with accumulation of polyubiquitinated proteins, stabilization of endogenous proteasomal substrates (including Xbp1s, IkappaBalpha, and Bax), onset of apoptosis, and sensitization to proteasome inhibitors (PI). These events can be reproduced by expressing Ig-mu chain in nonlymphoid cells. Our results suggest that a developmental program links plasma cell death to protein production, and help explaining the peculiar sensitivity of normal and malignant plasma cells to PI.

Deficiency in coagulation factor VIII leads to the bleeding disorder hemophilia A. Previous studies demonstrated that factor VIII secretion is limited due to an ATP-requiring step early in the secretory pathway. In this report, we identified that this ATP-dependent rate-limiting step involves the dissociation of non-disulfide-linked aggregates within the endoplasmic reticulum (ER). In contrast to the numerous examples of interchain disulfide-linked aggregates, factor VIII is the first protein characterized to form non-disulfide-linked high molecular weight aggregates within the ER. Approximately a third of newly synthesized factor VIII was detected in high molecular weight aggregates. These aggregates disappeared over time as functional factor VIII appeared in the medium. The aggregated complexes did not require proteasomal degradation for clearance. Aggregate formation was enhanced by ATP depletion, and upon restoration of metabolic energy, these aggregates were dissociated and secreted. With the coexpression of von Willebrand factor (vWF), a small portion of vWF coaggregated with factor VIII. However, vWF dissociated from the aggregates more rapidly than factor VIII, supporting that these aggregates are dynamic. An increase in the factor VIII expression level elicited a corresponding increase in the fraction of factor VIII that was aggregated. In addition, a 110 amino acid sequence containing a hydrophobic beta-sheet within factor VIII was identified that may predispose factor VIII to aggregation. These data show that formation and ATP-dependent dissolution of nondisulfide-linked factor VIII aggregates is a dynamic, rate-limiting step during the folding process in the early secretory pathway. In summary, we have identified an unprecedented requirement for protein transport out of the ER that involves an ATP-dependent dissociation of non-disulfide-linked aggregates within the ER.

Adenoviral vectors provide a promising gene therapy system for the treatment of hemophilia A. Potent vectors encoding a human factor VIII (FVIII) cDNA were developed that mediated sustained FVIII expression in normal and hemophiliac mice and complete phenotypic correction of the bleeding disorder in hemophiliac mice and dogs (Connelly and Kaleko, Haemophilia 1998; 4: 380-8). However, these studies utilized vectors encoding a truncated version of the human FVIII cDNA lacking the B-domain (BDD FVIII). In this work, an adenoviral vector encoding the human full-length (FL) FVIII cDNA was generated and characterized. While functional FL FVIII was secreted in vitro, expression of the FL protein was not detected in the plasma of vector-treated hemophiliac mice. Unexpectedly, the FL FVIII vector-treated animals demonstrated phenotypic correction of the bleeding defect as measured by a tail-clip survival study. FL FVIII protein was visualized in the mouse livers using human FVIII-specific immunohistochemical analyses. These data demonstrate that adenoviral vector-mediated in vivo expression of BDD FVIII is more efficient than that of the FL protein and that phenotypic correction can occur in the absence of detectable levels of FVIII.

Factor VIII is a large complex glycoprotein that is deficient in hemophilia A. It has a domain organization consisting of A1-A2-B-A3-C1-C2 where the B domain is a heavily glycosylated region that is dispensable for procoagulant activity. Factor VIII expression is 10-to 20-fold lower than the homologous coagulation factor V. Factor VIII expression is limited due to a low level of steady-state messenger RNA in the cytoplasm and inefficient transport of the primary translation product from the endoplasmic reticulum to the Golgi apparatus. Within the secretory pathway, factor VIII is processed to a heterodimer of the heavy chain (domains A1-A2-B) in a metal ion association with the light chain (domains A3-C1-C2). Upon secretion from the cell, von Willebrand factor binds the light chain of factor VIII and stabilizes the factor, preventing degradation. Protein folding within the mammalian secretory pathway is facilitated by molecular chaperones. Within the endoplasmic reticulum, factor VIII exhibits stable interaction with protein chaperones identified as the immunoglobulin-binding protein (BiP), calnexin and calreticulin. BiP is a peptide-dependent ATPase that interacts with exposed hydrophobic surfaces on unfolded proteins or unassembled protein subunits. A potential BiP binding site within factor VIII has been identified. Mutation of a single amino acid residue in the potential BiP binding site increased the secretion efficiency of factor VIII by threefold. Interestingly, the proposed BiP binding site is adjacent to a type-1 copper binding site within the A1 domain that is required for interaction between the factor VIII A1 domain and the A3 domain. We propose that Cu(I) binds the type-1 copper ion-binding site in the A1 domain and provides the essential requirement for a stable interaction between the heavy and light chains. Calnexin and calreticulin are transmembrane and lumenal proteins, respectively, localized to the endoplasmic reticulum, which associate transiently with many soluble and membrane glycoproteins during folding and subunit assembly. The calnexin and calreticulin interaction with factor VIII occurs primarily through amino-terminal linked oligosaccharides within the heavily glycosylated factor VIII B domain and this interaction appears to be required for factor VIII secretion. The findings suggest that factor VIII cycles through interactions with BiP, calnexin and calreticulin. Although the interaction with BiP does not appear to be required for factor VIII secretion, data suggest that the calnexin and/or calreticulin interaction is required for secretion. The observations suggest a unique requirement for carbohydrate processing and calnexin/calreticulin interaction that may limit the productive secretion of factor VIII and have implications for approaches towards somatic cell gene therapy for hemophilia A.

Analysis of mRNA in two haemophilic monozygotic twins offers novel information on the organisation of expressed sequences distal to the coagulation factor VIII gene. These patients show an inversion that, in contrast to the common inversions responsible for 1/5 of all haemophilia A, affects the first rather than intron 22 of the gene. This displaces the most telomeric of the factor VIII exons (exon 1) by approximately 100 kb towards the telomere, and close to the region of the C6.1A gene. This novel inversion creates two hybrid transcription units: one formed by the promoter and first exon of the factor VIII gene followed by a widely expressed sequence; the other by the promoter and coding region of the C6.1A gene plus most of the factor VIII gene (part of intron 1 and exons 2-26). Investigation of this transcription unit reveals that the C6.1A gene has an unsuspected intron in the region coding for the previously described 3'-untranslated tail of the message. Furthermore, exons located beyond the known C6.1A sequence and present in normal transcripts precede exons 2-26 of the factor VIII gene in the hybrid mRNA of the haemophilic twins. The factor VIII sequences in this hybrid mRNA are not expected to be expressed because they lack the first exon, encoding the prepeptide, and follow a translation stop in the C6.1A gene. Leukaemia-related translocations in the C6.1A region suggest that this region may be somewhat unstable.

Since direct diagnosis based on detection of factor IX mutations by direct sequencing is currently performed in a few laboratories only, restriction fragment length polymorphisms are still useful for carrier detection and prenatal diagnosis of hemophilia B. We analyzed 29 women from 20 families at risk of hemophilia B with three intragenic (MnlI, DdeI, TaqI) and two extragenic (HhaI, BamHI) restriction fragment length polymorphisms, all by the polymerase chain reaction. This analysis confirmed 10 possible carriers and excluded 16 as carriers. The diagnosis was made in 17 of the 20 families (85%). The combination of three polymorphisms indicated that MnlI/DdeI/HhaI and TaqI/DdeI/HhaI were the most informative (15/20 families, 75% and 14/20 families, 70%). For carrier detection with the most useful polymorphism combination (TaqI/DdeI/HhaI) we devised a multiplex polymerase chain reaction that uses two or three sets of primers, allowing carrier diagnosis in one step with 99% reliability. Our results indicate that the combination of five restriction fragment length polymorphisms makes carrier detection and prenatal diagnosis possible for 85% of families at risk of hemophilia B, with 99% reliability. With multiplex polymerase chain reaction such diagnoses can be obtained faster.

The identification of carriers and the prenatal diagnosis of hemophilia A have greatly improved with knowledge of the structure of the factor VIII gene. This has permitted the defect to be traced in families by using restriction fragment length polymorphisms. This study summarizes 5 years' experience at A. Bianchi Bonomi Hemophilia and Thrombosis Center and the problems encountered. One hundred and forty-four women at risk of hemophilia A from 93 families were referred to our center for DNA analysis. Carrier detection was performed in 95 women, including 11 who were pregnant. Prenatal diagnosis was performed at 7-14 weeks' gestation in 56 pregnant women. We employed two intragenic restriction fragment length polymorphisms (XbaI and BclI) and the two extragenic restriction fragment length polymorphisms (TaqI and BglII). Combining the results of intra and extragenic restriction fragment length polymorphisms with pedigree analysis, a diagnosis was reached in approximately 90% of cases. Of the 33 male fetuses, 11 were affected and 19 not affected. Two cases of recombination between extragenic restriction fragment length polymorphisms and the factor VIII locus were found.

Treatment of GD1a [alpha-Neu5Ac-(2----3)-beta-GalNAc-(1----4)-[alpha- Neu5Ac-(2----3)]-beta-Gal-(1----4)-beta-Glc-(1----1)-Cer] with dicyclohexylcarbodi-imide in anhydrous methyl sulfoxide affords 94-98% of GD1a-dilactone. The involvement of the carboxyl groups of the two sialic acid residues in the lactone rings was proved by ammoniolysis and reduction experiments, which gave ganglioside derivatives containing the amide of sialic acid and N-acetylneuraminulose, respectively. 1H-N.m.r. spectroscopy showed that the lactone rings involved position 2 of each galactose residue in the ester linkages.