Biomedical subjects

Stephan M Tanner

Publications and source records attributed to Stephan M Tanner.

13 recordsLinked to original sources

PubMed2006

Differential gene expression in patients genetically predisposed to pancreatic cancer.

BACKGROUND: Nearly 10% of all pancreatic cancer (PCA) results from genetic predisposition. Although abnormalities in sporadic PCA have been described, little is known about the genetics of heritable PCA. The purpose of this study was to identify novel genes expressed in patients with a presumed genetic predisposition or "familial" PCA. PATIENTS AND METHODS: We defined "familial" PCA as patients having one or more first-degree relatives with biopsy-proven adenocarcinoma of the pancreas. Using a PCR-based subtractive and enrichment procedure, representational difference analysis (RDA), pancreatic tumor cDNA was reverse-transcribed from pooled poly(A)+ mRNA from six such patients (tester) and compared to pooled cDNA from five normal pancreata (driver). Tumor-specific gene fragments were identified and confirmed to be overexpressed in familial PCA by comparative RT-PCR. Six PCA cell lines, 11 sporadic tumors, 5 neuroendocrine tumors, and 3 chronic pancreatitis tissues were screened to determine the specificity of these genes. RESULTS: Sequence analysis revealed several sequences of unknown significance and six genes previously described in neoplasia/carcinogenesis: Apolipoprotein A4, CEA, Keratin 19, Stratifin (14-3-3 sigma), Trefoil Factor, and Calcium Binding Protein S100 A6. Screening of cell lines and pancreatic tissue types showed varying degrees of specificity for familial and sporadic PCA. The APO-A4 gene was up-regulated in familial PCA. CONCLUSIONS: The pattern of frequency in all screened tissue suggests that these genes are associated with conditions that produce significant desmoplastic responses and are difficult to differentiate from chronic inflammatory processes. Apolipoprotein A4 is preferentially expressed in familial patients, suggesting that the importance of fatty acid synthesis in carcinogenesis be investigated further.

Adenocarcinoma↗

PubMed2006

Imerslund-Grasbeck syndrome associated with recurrent aphthous stomatitis and defective neutrophil function.

Vitamin B(12) deficiency is a well-known cause of recurrent aphthous stomatitis (RAS). However, the mechanism by which this deficiency causes the stomatitis is not well understood. Imerslund-Grasbeck syndrome (IGS) causes vitamin B(12) deficiency and proteinuria due to a defect in the vitamin B(12) receptor. We sought to determine whether the RAS observed in IGS patients is associated with neutrophil dysfunction. We report 3 infants with vitamin B(12) deficiency due to IGS, who presented with borderline or normal hemoglobin concentrations, RAS, and a neutrophil function defect. All 3 patients were homozygous for a splice site mutation affecting exon 4 of the AMN gene. A direct correlation was observed between low serum vitamin B12 levels and defective neutrophil function (low chemotaxis and elevated superoxide production) in the patients. Vitamin B(12) therapy led to an immediate resolution of aphthous stomatitis and full correction of neutrophil function. We demonstrated that serum vitamin B(12) deficiency is associated with a neutrophil chemotactic defect and RAS in IGS patients. We suggest that the RAS observed in these patients is due to this defect.

Anemia, Megaloblastic↗

PubMed2005

Amnionless function is required for cubilin brush-border expression and intrinsic factor-cobalamin (vitamin B12) absorption in vivo.

Amnionless (AMN) and cubilin gene products appear to be essential functional subunits of an endocytic receptor called cubam. Mutation of either gene causes autosomal recessive Imerslund-Gräsbeck syndrome (I-GS, OMIM no. 261100) in humans, a disorder characterized by selective intestinal malabsorption of cobalamin (vitamin B12) and urinary loss of several specific low-molecular-weight proteins. Vital insight into the molecular pathology of I-GS has been obtained from studies of dogs with a similar syndrome. In this work, we show that I-GS segregates in a large canine kindred due to an in-frame deletion of 33 nucleotides in exon 10 of AMN. In a second, unrelated I-GS kindred, affected dogs exhibit a homozygous substitution in the AMN translation initiation codon. Studies in vivo demonstrated that both mutations abrogate AMN expression and block cubilin processing and targeting to the apical membrane. The essential features of AMN dysfunction observed in vivo are recapitulated in a heterologous cell-transfection system, thus validating the system for analysis of AMN-cubilin interactions. Characterization of canine AMN mutations that cause I-GS establishes the canine model as an ortholog of the human disorder well suited to studies of AMN function and coevolution with cubilin.

Animals↗

PubMed2005

Hereditary juvenile cobalamin deficiency caused by mutations in the intrinsic factor gene.

Hereditary juvenile megaloblastic anemia due to vitamin B12 (cobalamin) deficiency is caused by intestinal malabsorption of cobalamin. In Imerslund-Grasbeck syndrome (IGS), cobalamin absorption is completely abolished and not corrected by the administration of intrinsic factor (IF); if untreated, the disease is fatal. Biallelic mutations either in the cubilin (CUBN) or amnionless (AMN) gene cause IGS. In a series of families clinically diagnosed with likely IGS, at least six displayed no evidence of mutations in CUBN or AMN. A genome-wide search for linkage followed by mutational analysis of candidate genes was performed in five of these families. A region in chromosome 11 showed evidence of linkage in four families. The gastric IF (GIF) gene located in this region harbored homozygous nonsense and missense mutations in these four families and in three additional families. The disease in these cases therefore should be classified as hereditary IF deficiency. Clinically, these patients resembled those with typical IGS; radiocobalamin absorption tests had been inconclusive regarding the nature of the defect. In the diagnosis of juvenile cobalamin deficiency, mutational analysis of the CUBN, AMN, and GIF genes provides a molecular characterization of the underlying defect and may be the diagnostic method of choice.

Chromosome Mapping↗

PubMed2005

Baalc, a marker of mesoderm and muscle.

Transcripts of the Brain and Acute Leukemia, Cytoplasmic (BAALC) gene are expressed in human neuroectodermal tissues and in CD34-positive bone marrow cells. High transcript levels occur in leukemic blasts from some patients with acute myeloid leukemia (AML), where high expression is an independent marker of poor prognosis. To gain insight into the hitherto unknown function of BAALC/Baalc, we studied its protein expression in embryonic and adult mouse tissue by immunohistochemical analysis. Baalc protein was mainly expressed in developing and mature muscle cells (cardiac, skeletal, and smooth) beginning on day E9 (heart). Signal was seen in the pre-muscle mesodermal cells of the dermatomyotome regions, and the derivatives of the lateral plate and intermediate mesoderm such as smooth muscle wall of the esophagus, stomach, the gut tube, bronchi, small blood vessels, and urinary bladder. This pattern continued through the late embryonic stages into adulthood. Baalc appeared to localize in the cytoplasm, adjacent to the cell membrane. This is distinctly observed in adult skeletal muscle cells. Baalc co-localized with known muscle-associated proteins but not with neural crest or neuronal markers. Scattered expression in adult bone marrow hematopoietic cells and weak expression in the brain neuropil also occurred. In conclusion, BAALC/Baalc is a marker of the mesodermal lineage, especially muscle.

Animals↗

PubMed2005

Homozygous AMN mutation in hereditary selective intestinal malabsorption of vitamin B12 in Jordan.

OBJECTIVE: Juvenile megaloblastic anemia is a rare and often hereditary disorder of cobalamin absorption, transport or intracellular metabolism. Several syndromes present with megaloblastic anemia such as congenital megaloblastic anemia due to intrinsic factor defect and juvenile megaloblastic anemia with proteinuria due to defects in the cubilin or the amnionless protein. METHODS: We identified a large kindred with juvenile megaloblastic anemia. Four genes, GIF, CUBN, TCN1, and TCN2, was previously excluded from being responsible for the syndrome of this family who was discovered in Irbid, Jordan, during the year 1999. At that time, the amnionless (AMN) gene was not yet known to implicate in megaloblastic anemia. In this study, we screened the AMN for mutations in the Ohio State University, Iowa, United States of America. In addition, follow-up testing was carried out in the University of Iowa in 2004. RESULTS: We identified a homozygous splice site mutation in the patients. This mutation was previously detected in families from Turkey and Tunisia. It is suspected to be a founder mutation of Middle Eastern origin. CONCLUSION: Molecular testing for this specific mutation in cases of Middle Eastern origin is a valuable tool for presymptomatic diagnosis, carrier identification and perhaps prenatal diagnosis.

Anemia, Megaloblastic↗

PubMed2004

Acute myeloid leukemia with complex karyotypes and abnormal chromosome 21: Amplification discloses overexpression of APP, ETS2, and ERG genes.

Molecular mechanisms of leukemogenesis have been successfully unraveled by studying genes involved in simple rearrangements including balanced translocations and inversions. In contrast, little is known about genes altered in complex karyotypic abnormalities. We studied acute myeloid leukemia (AML) patients with complex karyotypes and abnormal chromosome 21. High-resolution bacterial artificial chromosome (BAC) array-based comparative genomic hybridization disclosed amplification predominantly in the 25- to 30-megabase (MB) region that harbors the APP gene (26.3 MB) and at position 38.7-39.1 MB that harbors the transcription factors ERG and ETS2. Using oligonucleotide arrays, APP was by far the most overexpressed gene (mean fold change 19.74, P = 0.0003) compared to a control group of AML with normal cytogenetics; ERG and ETS2 also ranked among the most highly expressed chromosome 21 genes. Overexpression of APP and ETS2 correlated with genomic amplification, but high APP expression occurred even in a subset of AML patients with normal cytogenetics (10 of 64, 16%). APP encodes a glycoprotein of unknown function previously implicated in Alzheimer's disease, but not in AML. We hypothesize that APP and the transcription factors ERG and ETS2 are altered by yet unknown molecular mechanisms involved in leukemogenesis. Our results highlight the value of molecularly dissecting leukemic cells with complex karyotypes.

Acute Disease↗

PubMed2004

Genetically heterogeneous selective intestinal malabsorption of vitamin B12: founder effects, consanguinity, and high clinical awareness explain aggregations in Scandinavia and the Middle East.

Selective intestinal malabsorption of vitamin B(12) causing juvenile megaloblastic anemia (MGA; MIM# 261100) is a recessively inherited disorder that is believed to be rare except for notable clusters of cases in Finland, Norway, and the Eastern Mediterranean region. The disease can be caused by mutations in either the cubilin (CUBN; MGA1; MIM# 602997) or the amnionless (AMN; MIM# 605799) gene. To explain the peculiar geographical distribution, we hypothesized that mutations in one of the genes would mainly be responsible for the disease in Scandinavia, and mutations in the other gene in the Mediterranean region. We studied 42 sibships and found all cases in Finland to be due to CUBN (three different mutations) and all cases in Norway to be due to AMN (two different mutations), while in Turkey, Israel, and Saudi Arabia, there were two different AMN mutations and three different CUBN mutations. Haplotype evidence excluded both CUBN and AMN conclusively in five families and tentatively in three families, suggesting the presence of at least one more gene locus that can cause MGA. We conclude that the Scandinavian cases are typical examples of enrichment by founder effects, while in the Mediterranean region high degrees of consanguinity expose rare mutations in both genes. We suggest that in both regions, physician awareness of this disease causes it to be more readily diagnosed than elsewhere; thus, it may well be more common worldwide than previously thought.

Anemia, Megaloblastic↗

PubMed2003

The functional cobalamin (vitamin B12)-intrinsic factor receptor is a novel complex of cubilin and amnionless.

Imerslund-Gräsbeck syndrome (I-GS, megaloblastic anemia 1) is an autosomal recessive disorder characterized by intestinal cobalamin (vitamin B(12)) malabsorption and proteinuria. I-GS-causing mutations are found in either of 2 genes encoding the epithelial proteins: cubilin and amnionless (AMN). Cubilin recognizes intrinsic factor (IF)-cobalamin and various other proteins to be endocytosed in the intestine and kidney, respectively, whereas the function of AMN is unknown. Here we show that cubilin and AMN colocalize in the endocytic apparatus of polarized epithelial cells and copurify as a tight complex during IF-cobalamin affinity and nondenaturing gel filtration chromatography. In transfected cells expressing either AMN or a truncated IF-cobalamin-binding cubilin construct, neither protein alone conferred ligand endocytosis. In cubilin transfectants, cubilin accumulated in early biosynthetic compartments. However, in cells cotransfected with AMN and the cubilin construct, cubilin trafficked to the cell surface and endosomes, and the cells exhibited IF-cobalamin endocytosis and lysosomal degradation of IF. These data indicate that cubilin and AMN are subunits of a novel cubilin/AMN (cubam) complex, where AMN binds to the amino-terminal third of cubilin and directs subcellular localization and endocytosis of cubilin with its ligand. Therefore, mutations affecting either of the 2 proteins may abrogate function of the cubam complex and cause IG-S.

Amino Acid Sequence↗

PubMed2003

BAALC expression predicts clinical outcome of de novo acute myeloid leukemia patients with normal cytogenetics: a Cancer and Leukemia Group B Study.

Cytogenetic aberrations are important prognostic factors in acute myeloid leukemia (AML). Of adults with de novo AML, 45% lack cytogenetic abnormalities, and identification of predictive molecular markers might improve therapy. We studied the prognostic impact of BAALC (Brain And Acute Leukemia, Cytoplasmic), a novel gene involved in leukemia, in 86 de novo AML patients with normal cytogenetics who were uniformly treated on Cancer and Leukemia Group B 9621. BAALC expression was determined by comparative real-time reverse transcriptase-polymerase chain reaction in pretreatment blood samples, and patients were dichotomized at BAALC's median expression into low and high expressers. Low expressers had higher white counts (P =.03) and more frequent French-American-British M5 morphology (P =.007). Compared to low expressers, high BAALC expressers showed significantly inferior overall survival (OS; median, 1.7 vs 5.8 years, P =.02), event-free survival (EFS; median, 0.8 vs 4.9 years, P =.03), and disease-free survival (DFS; median, 1.4 vs 7.3 years, P =.03). Multivariable analysis confirmed high BAALC expression as an independent risk factor. For high BAALC expressers the hazard ratio of an event for OS, EFS, and DFS was respectively 2.7, 2.6, and 2.2. We conclude that high BAALC expression predicts an adverse prognosis and may define an important risk factor in AML with normal cytogenetics.

Acute Disease↗

PubMed2003

Amnionless, essential for mouse gastrulation, is mutated in recessive hereditary megaloblastic anemia.

The amnionless gene, Amn, on mouse chromosome 12 encodes a type I transmembrane protein that is expressed in the extraembryonic visceral layer during gastrulation. Mice homozygous with respect to the amn mutation generated by a transgene insertion have no amnion. The embryos are severely compromised, surviving to the tenth day of gestation but seem to lack the mesodermal layers that normally produce the trunk. The Amn protein has one transmembrane domain separating a larger, N-terminal extracellular region and a smaller, C-terminal cytoplasmic region. The extracellular region harbors a cysteine-rich domain resembling those occurring in Chordin, found in Xenopus laevis embryos, and Sog, found in Drosophila melanogaster. As these cysteine-rich domains bind bone morphogenetic proteins (Bmps), it has been speculated that the cysteine-rich domain in Amn also binds Bmps. We show that homozygous mutations affecting exons 1-4 of human AMN lead to selective malabsorption of vitamin B12 (a phenotype associated with megaloblastic anemia 1, MGA1; OMIM 261100; refs. 5,6) in otherwise normal individuals, suggesting that the 5' end of AMN is dispensable for embryonic development but necessary for absorption of vitamin B12. When the 5' end of AMN is truncated by mutations, translation is initiated from alternative downstream start codons.

Amnion↗

PubMed2003

Molecular cytogenetic characterization of the KG-1 and KG-1a acute myeloid leukemia cell lines by use of spectral karyotyping and fluorescence in situ hybridization.

The KG-1 cell line, established from bone marrow cells of a patient with erythroleukemia evolving to acute myelogenous leukemia, and its less differentiated variant, KG-1a, are widely used in research worldwide. However, to our knowledge, neither cell line was studied by use of molecular-cytogenetic techniques such as spectral karyotyping (SKY) and fluorescence in situ hybridization (FISH). Our G-banding, SKY, and FISH analyses revealed a complex karyotype with a pseudodiploid modal chromosome number in both the KG-1 and KG-1a cell lines. The lines shared several identical structural aberrations, including der(4)t(4;8), del(7q), der(8)t(8;12), idic(8)(p11), der(17)t(5;17), and der(20)t(12;20), but also differed with regard to other chromosome rearrangements. In contrast to KG-1, the KG-1a line lost one of the two copies of idic(8)(p11) present in KG-1 cells and gained a der(8;22)(q24;q13), an i(11)(q10), and a der(19)t(14;19)(q13;q13.4). Notably, we have shown that the KG-1 cells harbor a partial hexasomy of the long arm of chromosome 8, which may explain in part the previously reported significantly higher rate of formation of the AML1-ETO fusion gene in KG-1 cells subjected to high-dose gamma irradiation compared with the rates of formation of the BCR-ABL or the DEK-CAN fusion gene. Our detailed description of chromosome rearrangements in KG-1 and KG-1a will be useful for the cytogenetic authentication of the lines, and provide clues as to the regions of the genome that could be studied further to explain the differences in phenotypic properties between KG-1 and KG-1a cells.

Acute Disease↗

PubMed2003

BAALC, a novel marker of human hematopoietic progenitor cells.

OBJECTIVE: The gene BAALC (Brain And Acute Leukemia, Cytoplasmic), a novel molecular marker involved in leukemia, is highly expressed in a subset of patients with acute leukemia and predictive of clinical outcome in patients with acute myeloid leukemia and normal karyotype. The role of BAALC in hematopoiesis and leukemogenesis is unknown. MATERIAL AND METHODS: We used real-time RT-PCR to show that BAALC is strongly expressed in CD34(+) cells from the bone marrow and blood and only weakly expressed in total normal bone marrow and blood cells. RESULTS: Expression analyses of FACSorted cells revealed high BAALC transcript levels in CD34(+) bone marrow cells including CD34(+)/CD38(-), CD34(+)/CD33(+), as well as CD34(+)/CD19(+)/CD10(+), CD34(+)/CD7(+), and CD34(+)/CD71(+)/CD45(-) cell fractions. Expression was significantly lower in all CD34(-) fractions. In vitro differentiation of CD34(+) bone marrow cells showed downregulation of BAALC and CD34 transcripts as early as day 4 in suspension cultures supplemented with lineage-specific cytokines (G-CSF, M-CSF, or EPO). In cultures with only lineage-unspecific cytokines (IL-3, SCF, GM-CSF), BAALC transcripts persisted up to day 20, while CD34 transcripts disappeared earlier. These observations suggest that expression of BAALC is stage specific. CONCLUSIONS: BAALC expression is restricted to progenitor cells, and downregulation of BAALC occurs with cell differentiation. We postulate that BAALC represents a novel marker of an early progenitor cell common to the myeloid, lymphoid, and erythroid pathways.

Antigens, CD34↗