SEDLIN forms homodimers: characterisation of SEDLIN mutations and their interactions with transcription factors MBP1, PITX1 and SF1

Functional analysis of a novel nonsense variant c.91A>T of the TRAPPC2 gene in a Chinese family with X-linked recessive autosomal spondyloepiphyseal dysplasia tarda

Spondyloepiphyseal dysplasia tarda (SEDT) is a condition involving late-onset, X-linked recessive skeletal dysplasia caused by mutations in the TRAPPC2 gene. In this paper, we identified a novel nonsense variant in a SEDT pedigree and analyzed the function of the variant in an attempt to explain the new pathogenesis of the TRAPPC2 protein in SEDT. Briefly, DNA and RNA samples from the peripheral blood of SEDT individuals were prepared. The causative variant in the Chinese SEDT family was identified by clinic whole-exome sequencing analysis. Then, we observed the mRNA expression of TRAPPC2 in patients and the mutant TRAPPC2 level in vitro and analyzed the protein stability and subcellular distribution by cell fluorescence and Western blotting. We also investigated the effect of TRAPPC2 knockdown on the expression and secretion of COL2A1 in SW1353 cells or primary human chondrocytes. Herein, we found a nonsense variant, c.91A>T, of the TRAPPC2 gene in the pedigree. TRAPPC2 mRNA expression levels were significantly decreased in the available peripheral blood cell samples of two affected patients. An in vitro study showed that the mutant plasmid exhibited significantly lower mRNA and protein of TRAPPC2, and the mutant protein changed its membrane distribution. TRAPPC2 knockdown resulted in decreased COL2A1 expression and collagen II secretions. Our data indicate that the novel nonsense variant, c.91A>T, of the TRAPPC2 gene is the cause of SEDT in this pedigree. The variant results in a lowered expression of TRAPPC2 and then affects the COL2A1 expression and collagen II secretions, which may explain the mechanism of loss of function of the variant.

A novel missense variant in TRAPPC2 causes X-linked spondyloepiphyseal dysplasia tarda: A case report

RATIONALE

X-linked spondyloepiphyseal dysplasia tarda (X-linked SEDT) is a rare hereditary cause in childhood short stature due to mutations in trafficking protein particle complex subunit 2 (TRAPPC2) gene located on chromosome Xp22. Several pathogenic variants in TRAPPC2 have been reported, but missense variants are rare.

PATIENT CONCERNS

A 13-year, 8-month-old Chinese Han boy presenting with short stature for the past 7 years.

DIAGNOSIS

X-linked SEDT was established by a combination of clinical and radiographic features, confirmed by targeted next-generation sequencing. Genetic testing of the TRAPPC2 gene revealed a novel missense variant with c.260A>C (p.H87P) hemizygote in exon5. The mother was found to be a heterozygous TRAPPC2 carrier, whereas the father was normal.

INTERVENTIONS

Patient was treated with recombinant human growth hormone daily. Patient's height, glucose level, and possible progressive joint and back pain with osteoarthritis were under intensive observation regularly.

OUTCOMES

The patient achieved 2.1 cm height gain over the first 3 months' recombinant human growth hormone treatment without joint or back pain. However, the therapy was terminated because of increased glucose level on follow-up.

LESSONS

The short stature is a noteworthy problem for X-linked SEDT cases. We report a novel missense variant site in TRAPPC2 treated with growth hormone in the literature. We do not recommend the use of recombinant human growth hormone on patients with X-linked SEDT for the concern of glucose homeostasis.

A novel deletion variant in TRAPPC2 causes spondyloepiphyseal dysplasia tarda in a five-generation Chinese family

Background

Spondyloepiphyseal dysplasia tarda (SEDT) is a rare X-linked recessive inherited osteochondrodysplasia caused by mutations in the TRAPPC2 gene. It is clinically characterized by disproportionate short stature and early onset of degenerative osteoarthritis. Clinical diagnosis can be challenging due to the late-onset of the disease and lack of systemic metabolic abnomalites. Genetic diagnosis is critical in both early diagnosis and management of the disease. Here we reported a five-generation Chinese SEDT family and described the novel molecular findings.

Methods

Detailed family history and clinical data were collected. Genomic DNA was extracted from venous blood samples of family members. The exons of genes known to be associated with skeletal disorders were captured and deep sequenced. Variants were annotated by ANNOVAR and associated with multiple databases. Putative variants were confirmed by Sanger sequencing. The identified variant was classified according to the American College of Medical Genetics (ACMG) criteria.

Results

The proband was a 27-year-old Chinese male who presented with short-trunk short stature and joint pain. His radiographs showed platyspondyly with posterior humping, narrow hip-joint surfaces, and pelvic osteosclerosis. A pedigree analysis of 5 generations with 6 affected males revealed an X-linked recessive mode of inheritance. Affected males were diagnosed as SEDT according to the clinical and radiological features. Next-generation sequencing identified a novel variant of c.216_217del in the exon 4 of TRAPPC2 gene in the proband and other affected males. This variant resulted in the shift of reading frame and early termination of protein translation (p.S73Gfs*15). The mother and maternal female relatives of the proband were heterozygous carriers of the same variant, while no variations were detected in this gene of his father and other unaffected males. Based on the ACMG criteria, the novel c.216_217del variant of the TRAPPC2 gene was the pathogenic variant of this SEDT family.

Conclusion

In this study we identified the novel pathogenic variant of of c.216_217del in the gene of TRAPPC2 in this five-generation Chinese SEDT family. Our findings expand the clinical and molecular spectrum of SEDT and helps the genetic diagnosis of SEDT patients.

Clinical Diagnosis of X-Linked Spondyloepiphyseal Dysplasia Tarda and a Novel Missense Mutation in the Sedlin Gene (SEDL)

OBJECTIVE

Spondyloepiphyseal dysplasia tarda (SEDT) is a rare hereditary bone disease characterized by spinal and epiphyseal anomalies. We identified the disease by gene sequencing in a Chinese pedigree with SEDT.

METHODS

We extracted genomic DNA from five members of a four-generation Chinese SEDT kindred with three affected males and then analyzed the genetic mutation by PCR and DNA sequencing.

RESULTS

DNA sequencing showed that the genetic missense mutation occurred one bp upstream of exon 6 in the SEDL gene in two families, and a heterozygous mutation was found in a female carrier. In addition, no mutation was found in the other members of the family.

CONCLUSION

SEDT in this family was caused by a G/C missense mutation in exon 6 of the SEDL gene, previously not shown to be associated with X-linked SEDT.

TRAPPC13 modulates autophagy and the response to Golgi stress

Tether complexes play important roles in endocytic and exocytic trafficking of lipids and proteins. In yeast, the multisubunit transport protein particle (TRAPP) tether regulates endoplasmic reticulum (ER)-to-Golgi and intra-Golgi transport and is also implicated in autophagy. In addition, the TRAPP complex acts as a guanine nucleotide exchange factor (GEF) for Ypt1, which is homologous to human Rab1a and Rab1b. Here, we show that human TRAPPC13 and other TRAPP subunits are critically involved in the survival response to several Golgi-disrupting agents. Loss of TRAPPC13 partially preserves the secretory pathway and viability in response to brefeldin A, in a manner that is dependent on ARF1 and the large GEF GBF1, and concomitant with reduced caspase activation and ER stress marker induction. TRAPPC13 depletion reduces Rab1a and Rab1b activity, impairs autophagy and leads to increased infectivity to the pathogenic bacterium Shigella flexneri in response to brefeldin A. Thus, our results lend support for the existence of a mammalian TRAPPIII complex containing TRAPPC13, which is important for autophagic flux under certain stress conditions.

Comparative structural analysis of haemagglutinin proteins from type A influenza viruses: conserved and variable features

Background

Genome variation is very high in influenza A viruses. However, viral evolution and spreading is strongly influenced by immunogenic features and capacity to bind host cells, depending in turn on the two major capsidic proteins. Therefore, such viruses are classified based on haemagglutinin and neuraminidase types, e.g. H5N1. Current analyses of viral evolution are based on serological and primary sequence comparison; however, comparative structural analysis of capsidic proteins can provide functional insights on surface regions possibly crucial to antigenicity and cell binding.

Results

We performed extensive structural comparison of influenza virus haemagglutinins and of their domains and subregions to investigate type- and/or domain-specific variation. We found that structural closeness and primary sequence similarity are not always tightly related; moreover, type-specific features could be inferred when comparing surface properties of haemagglutinin subregions, monomers and trimers, in terms of electrostatics and hydropathy. Focusing on H5N1, we found that variation at the receptor binding domain surface intriguingly relates to branching of still circulating clades from those ones that are no longer circulating.

Conclusions

Evidence from this work suggests that integrating phylogenetic and serological analyses by extensive structural comparison can help in understanding the ‘functional evolution’ of viral surface determinants. In particular, variation in electrostatic and hydropathy patches can provide molecular evolution markers: intriguing surface charge redistribution characterizing the haemagglutinin receptor binding domains from circulating H5N1 clades 2 and 7 might have contributed to antigenic escape hence to their evolutionary success and spreading.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-014-0363-5) contains supplementary material, which is available to authorized users.

The role of protein structural analysis in the next generation sequencing era

Proteins are macromolecules that serve a cell’s myriad processes and functions in all living organisms via dynamic interactions with other proteins, small molecules and cellular components. Genetic variations in the protein-encoding regions of the human genome account for >85% of all known Mendelian diseases, and play an influential role in shaping complex polygenic diseases. Proteins also serve as the predominant target class for the design of small molecule drugs to modulate their activity. Knowledge of the shape and form of proteins, by means of their three-dimensional structures, is therefore instrumental to understanding their roles in disease and their potentials for drug development. In this chapter we outline, with the wide readership of non-structural biologists in mind, the various experimental and computational methods available for protein structure determination. We summarize how the wealth of structure information, contributed to a large extent by the technological advances in structure determination to date, serves as a useful tool to decipher the molecular basis of genetic variations for disease characterization and diagnosis, particularly in the emerging era of genomic medicine, and becomes an integral component in the modern day approach towards rational drug development.

Mutation or knock-down of 17β-hydroxysteroid dehydrogenase type 10 cause loss of MRPP1 and impaired processing of mitochondrial heavy strand transcripts

17β-Hydroxysteroid dehydrogenase type 10 (HSD10) is multifunctional protein coded by the X-chromosomal HSD17B10 gene. Mutations in this gene cause HSD10 disease characterized by progressive neurological abnormalities and cardiomyopathy. Disease progression and severity of symptoms is unrelated to the protein's dehydrogenase activity. Recently, it was shown that HSD10 is an essential component of mitochondrial Ribonuclease P (RNase P), an enzyme required for mitochondrial tRNA processing, but little is known about the role of HSD10 in RNase P function. RNase P consists of three different proteins MRPP1, MRPP2 (HSD10) and MRPP3, each of which is essential for RNase P function. Here, we show that HSD10 protein levels are significantly reduced in fibroblasts from patients carrying the HSD17B10 mutation p.R130C. A reduction in HSD10 levels was accompanied by a reduction in MRPP1 protein but not MRPP3 protein. In HSD10 knock-down cells, MRPP1 protein content was also reduced, indicating that HSD10 is important for the maintenance of normal MRPP1 protein levels. Ectopic expression of HSD10 partially restored RNA processing in HSD10 knock-down cells and fibroblasts, and also expression of MRPP1 protein was restored to values comparable to controls. In both, patient fibroblasts and HSD10 knock-down cells, there was evidence of impaired processing of precursor tRNA transcripts of the mitochondrial heavy strand but not the light strand compared with controls. Our findings indicate that HSD10 is important for the maintenance of the MRPP1-HSD10 subcomplex of RNase P and that loss of HSD10 causes impaired mitochondrial precursor transcript processing which may explain mitochondrial dysfunction observed in HSD10 disease.

Synbindin in extracellular signal-regulated protein kinase spatial regulation and gastric cancer aggressiveness

BACKGROUND

The molecular mechanisms that control the aggressiveness of gastric cancer (GC) remain poorly defined. Here we show that synbindin contributes to the aggressiveness of GC by activating extracellular signal-regulated protein kinase (ERK) signaling on the Golgi apparatus.

METHODS

Expression of synbindin was examined in normal gastric mucosa (n = 44), intestinal metaplastic gastric mucosa (n = 66), and GC tissues (n=52), and the biological effects of synbindin on tumor growth and ERK signaling were detected in cultured cells, nude mice, and human tissue samples. The interaction between synbindin and mitogen-activated protein kinase kinase (MEK1)/ERK was determined by immunofluorescence and fluorescence resonance energy transfer assays. The transactivation of synbindin by nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) was detected using luciferase reporter assay and chromatin immunoprecipitation.

RESULTS

High expression of synbindin was associated with larger tumor size (120.8 vs 44.8 cm(3); P = .01), advanced tumor node metastasis (TNM) stage (P = .003), and shorter patient survival (hazard ratio = 1.51; 95% confidence interval [CI] = 1.01 to 2.27; P = .046). Synbindin promotes cell proliferation and invasion by activating ERK2 on the Golgi apparatus, and synbindin is directly transactivated by NF-κB. Synbindin expression level was statistically significantly higher in human GCs with activated ERK2 than those with low ERK2 activity (intensity score of 11.5, 95% CI = 10.4 to 12.4 vs intensity score of 4.6, 95% CI 3.9 to 5.3; P < .001). Targeting synbindin in xenograft tumors decreased ERK2 phosphorylation and statistically significantly reduced tumor volume (451.2mm(3), 95% CI = 328.3 to 574.1 vs 726.1mm(3), 95% CI = 544.2 to 908.2; P = .01).

CONCLUSIONS

Synbindin contributes to malignant phenotypes of GC by activating ERK on the Golgi, and synbindin is a potential biomarker and therapeutic target for GC.

MIP-2A is a novel target of an anilinoquinazoline derivative for inhibition of tumour cell proliferation

We recently identified a novel anilinoquinazoline derivative, Q15, as a potent apoptosis inducer in a panel of human cancer cell lines and determined that Q15 targets hCAP-G2, a subunit of condensin II complex, leading to abnormal cell division. However, whether the defect in normal cell division directly results in cell death remains unclear. Here, we used an mRNA display method on a microfluidic chip to search for other Q15-binding proteins. We identified an additional Q15-binding protein, MIP-2A (MBP-1 interacting protein-2A), which has been reported to interact with MBP-1, a repressor of the c-Myc promoter. Our results indicate that Q15 inhibits the interaction between MIP-2A and MBP-1 as well as the expression of c-Myc protein, thereby inducing cell death. This study suggests that the simultaneous targeting of hCAP-G2 and MIP-2A is a promising strategy for the development of antitumor drugs as a treatment for intractable tumours.

Whole exome sequencing and functional studies identify an intronic mutation in TRAPPC2 that causes SEDT

Skeletal dysplasias are challenging to diagnose because of their phenotypic variability, genetic heterogeneity, and diverse inheritance patterns. We conducted whole exome sequencing of a Turkish male with a suspected X-linked skeletal dysplasia of unknown etiology as well as his unaffected mother and maternal uncle. Bioinformatic filtering of variants implicated in skeletal system development revealed a novel hemizygous mutation, c.341-(11_9)delAAT, in an intron of TRAPPC2, the causative locus of spondyloepiphyseal dysplasia tarda (SEDT). We show that this deletion leads to the loss of wild-type TRAPPC2 and the generation of two functionally impaired mRNAs in patient cells. These consequences are predicted to disrupt function of SEDLIN/TRAPPC2. The clinical and research data were returned, with appropriate caveats, to the patient and informed his disease status and reproductive choices. Our findings expand the allelic repertoire of SEDT and show how prior filtering of the morbid human genome informed by inheritance pattern and phenotype, when combined with appropriate functional tests in patient-derived cells, can expedite discovery, overcome issues of missing data and help interpret variants of unknown significance. Finally, this example shows how the return of a clinically confirmed mutational finding, supported by research allele pathogenicity data, can assist individuals with inherited disorders with life choices.

Trs20 is required for TRAPP II assembly

The modular TRAPP complexes act as nucleotide exchangers to activate the Golgi Ypt/Rab GTPases, Ypt1 and Ypt31/Ypt32. In yeast, TRAPP I acts at the cis-Golgi and its assembly and structure are well characterized. In contrast, TRAPP II acts at the trans-Golgi and is poorly understood. Especially puzzling is the role of Trs20, an essential TRAPP I/II subunit required neither for the assembly of TRAPP I nor for its Ypt1-exchange activity. Mutations in Sedlin, the human functional ortholog of Trs20, cause the cartilage-specific disorder SEDT. Here we show that Trs20 interacts with the TRAPP II-specific subunit Trs120. Furthermore, the Trs20-Trs120 interaction is required for assembly of TRAPP II and for its Ypt32-exchange activity. Finally, Trs20-D46Y, with a single-residue substitution equivalent to a SEDT-causing mutation in Sedlin, interacts with TRAPP I, but the resulting TRAPP complex cannot interact with Trs120 and TRAPP II cannot be assembled. These results indicate that Trs20 is crucial for assembly of TRAPP II, and the defective assembly caused by a SEDT-linked mutation suggests that this role is conserved.

Discovery of new Longin and Roadblock domains that form platforms for small GTPases in Ragulator and TRAPP-II

Guanine nucleotide exchange factors (GEFs) control the site and extent of GTPase activity. Longin domains (LDs) are found in many Rab-GEFs, including DENNs, MON1/CCZ1, BLOC-3 and the TRAPP complex. Other GEFs, including Ragulator, contain roadblock domains (RDs), the structure of which is closely related to LDs. Other GTPase regulators, including mglB, SRX and Rags, use LDs or RDs as platforms for GTPases. Here, we review the conserved relationship between GTPases and LD/RDs, showing how LD/RD dimers act as adaptable platforms for GTPases. To extend our knowledge of GEFs, we used a highly sensitive sequence alignment tool to predict the existence of new LD/RDs. We discovered two yeast Ragulator subunits, and also a new LD in TRAPPC10 that may explain the Rab11-GEF activity ascribed to TRAPP-II.

Biomedical and social aspects of spondyloepiphyseal dysplasia tarda cases from bengkulu district of indonesia

BACKGROUND

Although short stature male (SSM) cases are often found in South Bengkulu, no management reports about their existence are available. This paper summarizes the researches of biomedical and social aspects for the human genetic disorders.

CASE PRESENTATION

Field survey results indicated that SSM community was located in Kedurang area, and 67 persons with SSM were successfully sampled from a population of 17,357 persons (one of 260). Anthropometric comparative studies, history of the pattern of X-linked inheritance, as well as the study of anatomy through radiology and ultrasound confirmed that SSM is spondyloepiphyseal dysplasia tarda (SEDT). Genomic studies through characterisation of mutations of the SEDL gene revealed that point mutations on SEDT Kedurang are different from the results of previous similar studies, and these people are predicted to come from the same ancestors. It is necessary to notice that persons with SEDT have normal intellectual ability, but the physical conditions make their socio-economic competitiveness very low. Furthermore premature joint pains make persons with SEDT become old faster than the ordinary people by the age of 40 years. Realizing that they are marginalized, some of them try to come together to establish a foundation designed to make a better life.

CONCLUSION

It can be concluded that the appropriate management of SEDT should be done by integrating to improve their nutritional status, reduce the suffering of joint pain, develop labelled molecular markers for early detection, and increase their socio-economic competitiveness.

A trapper keeper for TRAPP, its structures and functions

During biosynthesis many membrane and secreted proteins are transported from the endoplasmic reticulum, through the Golgi and on to the plasma membrane in small transport vesicles. These transport vesicles have to undergo budding, movement, tethering, docking, and fusion at each organelle of the biosynthetic pathway. The transport protein particle (TRAPP) complex was initially identified as the tethering factor for endoplasmic reticulum (ER)-derived COPII vesicles, but the functions of TRAPP may extend to other areas of biology. Three forms of TRAPP complexes have been discovered to date, and recent advances in research have provided new insights on the structures and functions of TRAPP. Here we provide a comprehensive review of the recent findings in TRAPP biology.

The adaptor function of TRAPPC2 in mammalian TRAPPs explains TRAPPC2-associated SEDT and TRAPPC9-associated congenital intellectual disability

BACKGROUND

The TRAPP (Transport protein particle) complex is a conserved protein complex functioning at various steps in vesicle transport. Although yeast has three functionally and structurally distinct forms, TRAPPI, II and III, emerging evidence suggests that mammalian TRAPP complex may be different. Mutations in the TRAPP complex subunit 2 (TRAPPC2) cause X-linked spondyloepiphyseal dysplasia tarda, while mutations in the TRAPP complex subunit 9 (TRAPPC9) cause postnatal mental retardation with microcephaly. The structural interplay between these subunits found in mammalian equivalent of TRAPPI and those specific to TRAPPII and TRAPPIII remains largely unknown and we undertook the present study to examine the interaction between these subunits. Here, we reveal that the mammalian equivalent of the TRAPPII complex is structurally distinct from the yeast counterpart thus leading to insight into mechanism of disease.

PRINCIPAL FINDINGS

We analyzed how TRAPPII- or TRAPPIII- specific subunits interact with the six-subunit core complex of TRAPP by co-immunoprecipitation in mammalian cells. TRAPPC2 binds to TRAPPII-specific subunit TRAPPC9, which in turn binds to TRAPPC10. Unexpectedly, TRAPPC2 can also bind to the putative TRAPPIII-specific subunit, TRAPPC8. Endogenous TRAPPC9-positive TRAPPII complex does not contain TRAPPC8, suggesting that TRAPPC2 binds to either TRAPPC9 or TRAPPC8 during the formation of the mammalian equivalents of TRAPPII or TRAPPIII, respectively. Therefore, TRAPPC2 serves as an adaptor for the formation of these complexes. A disease-causing mutation of TRAPPC2, D47Y, failed to interact with either TRAPPC9 or TRAPPC8, suggesting that aspartate 47 in TRAPPC2 is at or near the site of interaction with TRAPPC9 or TRAPPC8, mediating the formation of TRAPPII and/or TRAPPIII. Furthermore, disease-causing deletional mutants of TRAPPC9 all failed to interact with TRAPPC2 and TRAPPC10.

CONCLUSIONS

TRAPPC2 serves as an adaptor for the formation of TRAPPII or TRAPPIII in mammalian cells. The mammalian equivalent of TRAPPII is likely different from the yeast TRAPPII structurally.

A yeast two hybrid screen identifies SPATA4 as a TRAPP interactor

The TRAPP vesicle-tethering complex consists of more than 10 distinct polypeptides and is involved in protein transport. Using the C2 subunit as bait we identified SPATA4, a spermatocyte-specific protein of unknown function, as an interacting partner in a yeast two hybrid screen. Further studies indicate SPATA4 interacts with the C2 portion of the TRAPP complex. SPATA4 fractionates with both cytosolic and nuclear fractions suggesting it may have several distinct functions. SPATA4 is one of only three human proteins that contain a DUF1042 domain and we show that C2 does not interact with another one of the DUF1042 domain-containing proteins. Our results suggest a role for SPATA4 in membrane traffic and a specialized function for TRAPP in spermatocytes.

Alternative splicing of the human gene SYBL1 modulates protein domain architecture of Longin VAMP7/TI-VAMP, showing both non-SNARE and synaptobrevin-like isoforms

Background

The control of intracellular vesicle trafficking is an ideal target to weigh the role of alternative splicing in shaping genomes to make cells. Alternative splicing has been reported for several Soluble N-ethylmaleimide-sensitive factor Attachment protein REceptors of the vesicle (v-SNAREs) or of the target membrane (t-SNARES), which are crucial to intracellular membrane fusion and protein and lipid traffic in Eukaryotes. However, splicing has not yet been investigated in Longins, i.e. the most widespread v-SNAREs. Longins are essential in Eukaryotes and prototyped by VAMP7, Sec22b and Ykt6, sharing a conserved N-terminal Longin domain which regulates membrane fusion and subcellular targeting. Human VAMP7/TI-VAMP, encoded by gene SYBL1, is involved in multiple cell pathways, including control of neurite outgrowth.

Results

Alternative splicing of SYBL1 by exon skipping events results in the production of a number of VAMP7 isoforms. In-frame or frameshift coding sequence modifications modulate domain architecture of VAMP7 isoforms, which can lack whole domains or domain fragments and show variant or extra domains. Intriguingly, two main types of VAMP7 isoforms either share the inhibitory Longin domain and lack the fusion-promoting SNARE motif, or vice versa. Expression analysis in different tissues and cell lines, quantitative real time RT-PCR and confocal microscopy analysis of fluorescent protein-tagged isoforms demonstrate that VAMP7 variants have different tissue specificities and subcellular localizations. Moreover, design and use of isoform-specific antibodies provided preliminary evidence for the existence of splice variants at the protein level.

Conclusions

Previous evidence on VAMP7 suggests inhibitory functions for the Longin domain and fusion/growth promoting activity for the Δ-longin molecule. Thus, non-SNARE isoforms with Longin domain and non-longin SNARE isoforms might have somehow opposite regulatory functions. When considering splice variants as "natural mutants", evidence on modulation of subcellular localization by variation in domain combination can shed further light on targeting determinants. Although further work will be needed to characterize identified variants, our data might open the route to unravel novel molecular partners and mechanisms, accounting for the multiplicity of functions carried out by the different members of the Longin proteins family.

Myc promoter-binding protein-1 (MBP-1) is a novel potential prognostic marker in invasive ductal breast carcinoma

BACKGROUND

Alpha-enolase is a glycolytic enzyme that catalyses the formation of phosphoenolpyruvate in the cell cytoplasm. α-Enolase and the predominantly nuclear Myc promoter-binding protein-1 (MBP-1) originate from a single gene through the alternative use of translational starting sites. MBP-1 binds to the P2 c-myc promoter and competes with TATA-box binding protein (TBP) to suppress gene transcription. Although several studies have shown an antiproliferative effect of MBP-1 overexpression on several human cancer cells, to date detailed observations of α-enolase and MBP-1 relative expression in primary tumors versus normal tissues and their correlation with clinicopathological features have not been undertaken.

METHODOLOGY AND FINDINGS

We analyzed α-enolase and MBP-1 expression in normal breast epithelium and primary invasive ductal breast carcinoma (IDC) from 177 patients by Western blot and immunohistochemical analyses, using highly specific anti-α-enolase monoclonal antibodies. A significant increase in the expression of cytoplasmic α-enolase was observed in 98% of the tumors analysed, compared to normal tissues. Nuclear MBP-1 was found in almost all the normal tissues while its expression was retained in only 35% of the tumors. Statistically significant associations were observed among the nuclear expression of MBP-1 and ErbB2 status, Ki-67 expression, node status and tumor grade. Furthermore MBP-1 expression was associated with good survival of patients with IDC.

CONCLUSIONS

MBP-1 functions in repressing c-myc gene expression and the results presented indicate that the loss of nuclear MBP-1 expression in a large number of IDC may be a critical step in the development and progression of breast cancer and a predictor of adverse outcome. Nuclear MBP-1 appears to be a novel and valuable histochemical marker with potential prognostic value in breast cancer.