The third member of the transforming acidic coiled coil-containing gene family, TACC3, maps in 4p16, close to translocation breakpoints in multiple myeloma, and is upregulated in various cancer cell lines

Characterization and localization of expression of an erythropoietin-induced gene, ERIC-1/TACC3, identified in erythroid precursor cells

Gene expression profiles during erythropoietin (Epo)-induced differentiation of erythroid progenitor cells derived from the Friend virus anaemia (FVA) and phenylhydrazine (PHZ) murine models have been examined using differential display polymerase chain reaction (PCR). Ten cDNA fragments upregulated by Epo were isolated. The ribonuclease protection assay confirmed differential expression between Epo-stimulated and Epo-deprived cells for one of these, provisionally named ERIC-1. Sequencing of the full-length cDNA predicted a protein of 558 amino acids, 17 amino acids longer than mTACC3, the third member of a novel family of proteins that contain a coiled-coil domain. The human homologue, cloned using rapid amplification of cDNA ends (RACE)-PCR, encodes a larger protein of 838 amino acids that is identical to hTACC3. In addition to erythroid precursor cells, ERIC-1/TACC3 is expressed at high levels in the testes, at moderate levels in the thymus and peripheral leucocytes, and at lower levels in the spleen and intestinal tissue. Immunohistochemical analysis using an antibody to a GST fusion product of the C-terminus of hERIC-1/TACC3 revealed that it is localized to Sertoli cells in the human testes. Confocal microscopy demonstrated hERIC-1/TACC3 protein concentrated in the perinuclear vesicles of dermal microvascular endothelial cells. Although ERIC-1/TACC3 is expressed in a wide range of tissues, its upregulation by Epo in erythroid progenitors implies that it has a role in terminal erythropoiesis.

Cloning and structural characterization of ECTACC, a new member of the transforming acidic coiled coil (TACC) gene family: cDNA sequence and expression analysis in human microvascular endothelial cells

Erythropoietin (Epo) transduces mitogenic and chemoattractant signals to human endothelial cells. Identifications of Epo-responsive genes are important for understanding the molecular nature of Epo signaling in endothelial cells. The effects of Epo on differential expression of various genes were examined in human microvascular endothelial cells (HMVEC) by differential display reverse transcriptase polymerase chain reaction (RT-PCR). In the current study we obtained from Epo-treated HMVEC a cDNA fragment with characteristics of the 3' end of mRNA. Using the cDNA fragment, we then selectively isolated a full-length clone by screening an unamplified endothelial cell cDNA library followed by 5' rapid amplification of cDNA ends by polymerase chain reaction (RACE-PCR). The nucleotide sequence of the longest cDNA revealed an open reading frame of 3311 nucleotides that encodes a protein consisting of approximately 906 amino acids with a predicted MW of approximately 100 kDa. The nucleotide sequence of the cDNA is nearly identical to that of transforming acidic coiled coil-containing (TACC2) and anti-zuai-1 (AZU-1) cDNA clones except at the 5'- and 3'-ends. Northern blot analysis showed an increase in endothelial-TACC-related mRNA levels in Epo-treated cells in comparison to that of the control cells. Endothelial-TACC-related mRNA was highly expressed in heart and skeletal muscle tissue. Placenta and brain tissue exhibited low levels of expression of endothelial-TACC-related gene. Southern blot analysis of genomic DNA from somatic cell hybrids showed that endothelial-TACC-related cDNA maps to chromosome 10. Immunofluorescence microscopy and the occurrence of several putative phosphorylation and SH3 binding sites on the deduced protein suggest that endothelial-TACC-related protein may be involved in Epo signaling cascades in endothelial cells.

The TACC domain identifies a family of centrosomal proteins that can interact with microtubules

We recently showed that the Drosophila transforming acidic coiled-coil (D-TACC) protein is located in the centrosome, interacts with microtubules, and is required for mitosis in the Drosophila embryo. There are three known human TACC proteins that share a conserved, C-terminal, coiled-coil region with D-TACC. These proteins have all been implicated in cancer, but their normal functions are unknown. We show that all three human TACC proteins are concentrated at centrosomes, but with very different characteristics: TACC1 is weakly concentrated at centrosomes during mitosis; TACC2 is strongly concentrated at centrosomes throughout the cell cycle; and TACC3 is strongly concentrated in a more diffuse region around centrosomes during mitosis. When the C-terminal TACC domain is overexpressed in HeLa cells, it forms large polymers in the cytoplasm that can interact with both microtubules and tubulin. The full-length TACC proteins form similar polymers when overexpressed, but their interaction with microtubules and tubulin is regulated during the cell cycle. At least one of the human TACC proteins appears to increase the number and/or stability of centrosomal microtubules when overexpressed during mitosis. Thus, the TACC domain identifies a family of centrosomal proteins that can interact with microtubules. This may explain the link between the TACC genes and cancer.

CPEB, maskin, and cyclin B1 mRNA at the mitotic apparatus: implications for local translational control of cell division

In Xenopus development, the expression of several maternal mRNAs is regulated by cytoplasmic polyadenylation. CPEB and maskin, two factors that control polyadenylation-induced translation are present on the mitotic apparatus of animal pole blastomeres in embryos. Cyclin B1 protein and mRNA, whose translation is regulated by polyadenylation, are colocalized with CPEB and maskin. CPEB interacts with microtubules and is involved in the localization of cyclin B1 mRNA to the mitotic apparatus. Agents that disrupt polyadenylation-induced translation inhibit cell division and promote spindle and centrosome defects in injected embryos. Two of these agents inhibit the synthesis of cyclin B1 protein and one, which has little effect on this process, disrupts the localization of cyclin B1 mRNA and protein. These data suggest that CPEB-regulated mRNA translation is important for the integrity of the mitotic apparatus and for cell division.

Molecular aspects of multiple myeloma

Multiple myeloma (MM) is a B-cell neoplasm characterized by bone marrow infiltration with malignant plasma cells, which synthesize and secrete monoclonal immunoglobulin (Ig) fragments. Despite the considerable progress in the understanding of MM biology, the molecular basis of the disease remains elusive. The initial transformation is thought to occur in a postgerminal center B-lineage cell, carrying a somatically hypermutated Ig heavy chain (IGH) gene. This plasmablastic precursor cell colonizes the bone marrow, propagates clonally and differentiates into a slowly proliferating myeloma cell population, all under the influence of specific cell adhesion molecules and cytokines. Production of interleukin-6 by stromal cells, osteoblasts and, in some cases, neoplastic cells is an essential element of myeloma cell growth, with the cytokine stimulus being delivered intracellularly via the Jack-STAT and ras signaling pathways. While karyotypic changes have been identified in up to 50% of MM patients, recent molecular cytogenetic techniques have revealed chromosomal abnormalities in the vast majority of examined cases. Translocations mostly involve illegal switch rearrangements of the IGH locus with various partner genes (CCND1, FGFR3, c-maf). Such events have been assigned a critical role in MM development. Mutations in coding and regulatory regions, as well as aberrant expression patterns of several oncogenes (c-myc, ras) and tumor suppressor genes (p16, p15) have been reported. Key regulators of programmed cell death (BCL-2, Fas), tumor expansion (metalloproteinases) and drug responsiveness (topoisomerase II alpha) have also been implicated in the pathogenesis of this hematologic malignancy. A tumorigenic role for human herpesvirus 8 (HHV8) was postulated recently, following the detection of viral sequences in bone marrow dendritic cells of MM patients. However, since several research groups were unable to confirm this observation, the role of HHV8 remains unclear. Translation of the advances in MM molecular biology into novel therapeutic strategies is essential in order to improve disease prognosis.

Isolation and characterization of AINT: a novel ARNT interacting protein expressed during murine embryonic development

Basic helix-loop-helix-PER-ARNT-SIM (bHLH-PAS) proteins form dimeric transcription factors to mediate diverse biological functions including xenobiotic metabolism, hypoxic response, circadian rhythm and central nervous system midline development. The Ah receptor nuclear translocator protein (ARNT) plays a central role as a common heterodimerization partner. Herein, we describe a novel, embryonically expressed, ARNT interacting protein (AINT) that may be a member of a larger coiled-coil PAS interacting protein family. The AINT C-terminus mediates interaction with the PAS domain of ARNT in yeast and interacts in vitro with ARNT and ARNT2 specifically. AINT localizes to the cytoplasm and overexpression leads to non-nuclear localization of ARNT. A dynamic pattern of AINT mRNA expression during embryogenesis and cerebellum ontogeny supports a role for AINT in development.

A high-resolution radiation hybrid map of the proximal portion of mouse chromosome 5

Radiation hybrid (RH) mapping of the mouse genome provides a useful tool in the integration of existing genetic and physical maps, as well as in the ongoing effort to generate a dense map of expressed sequence tags. To facilitate functional analysis of mouse Chromosome 5, we have constructed a high-resolution RH map spanning 75 cM of the chromosome. During the course of these studies, we have developed RHBase, an RH data management program that provides data storage and an interface to several RH mapping programs and databases. We have typed 95 markers on the T31 RH panel and generated an integrated map, pooling data from several sources. The integrated RH map ranges from the most proximal marker, D5Mit331 (Chromosome Committee offset, 3 cM), to D5Mit326, 74.5 cM distal on our genetic map (Chromosome Committee offset, 80 cM), and consists of 138 markers, including 89 simple sequence length polymorphic markers, 11 sequence-tagged sites generated from BAC end sequence, and 38 gene loci, and represents average coverage of approximately one locus per 0.5 cM with some regions more densely mapped. In addition to the RH mapping of markers and genes previously localized on mouse Chromosome 5, this RH map places the alpha-4 GABA(A) receptor subunit gene (Gabra4) in the central portion of the chromosome, in the vicinity of the cluster of three other GABA(A) receptor subunit genes (Gabrg1-Gabra2-Gabrb1). Our mapping effort has also defined a new cluster of four genes in the semaphorin gene family (Sema3a, Sema3c, Sema3d, and Sema3e) and the Wolfram syndrome gene (Wfs1) in this region of the chromosome.

AZU-1: a candidate breast tumor suppressor and biomarker for tumor progression

To identify genes misregulated in the final stages of breast carcinogenesis, we performed differential display to compare the gene expression patterns of the human tumorigenic mammary epithelial cells, HMT-3522-T4-2, with those of their immediate premalignant progenitors, HMT-3522-S2. We identified a novel gene, called anti-zuai-1 (AZU-1), that was abundantly expressed in non- and premalignant cells and tissues but was appreciably reduced in breast tumor cell types and in primary tumors. The AZU-1 gene encodes an acidic 571-amino-acid protein containing at least two structurally distinct domains with potential protein-binding functions: an N-terminal serine and proline-rich domain with a predicted immunoglobulin-like fold and a C-terminal coiled-coil domain. In HMT-3522 cells, the bulk of AZU-1 protein resided in a detergent-extractable cytoplasmic pool and was present at much lower levels in tumorigenic T4-2 cells than in their nonmalignant counterparts. Reversion of the tumorigenic phenotype of T4-2 cells, by means described previously, was accompanied by the up-regulation of AZU-1. In addition, reexpression of AZU-1 in T4-2 cells, using viral vectors, was sufficient to reduce their malignant phenotype substantially, both in culture and in vivo. These results indicate that AZU-1 is a candidate breast tumor suppressor that may exert its effects by promoting correct tissue morphogenesis.

D-TACC: a novel centrosomal protein required for normal spindle function in the early Drosophila embryo

We identify Drosophila TACC (D-TACC) as a novel protein that is concentrated at centrosomes and interacts with microtubules. We show that D-TACC is essential for normal spindle function in the early embryo; if D-TACC function is perturbed by mutation or antibody injection, the microtubules emanating from centrosomes in embryos are short and chromosomes often fail to segregate properly. The C-terminal region of D-TACC interacts, possibly indirectly, with microtubules, and can target a heterologous fusion protein to centrosomes and microtubules in embryos. This C-terminal region is related to the mammalian transforming, acidic, coiled-coil-containing (TACC) family of proteins. The function of the TACC proteins is unknown, but the genes encoding the known TACC proteins are all associated with genomic regions that are rearranged in certain cancers. We show that at least one of the mammalian TACC proteins appears to be associated with centrosomes and microtubules in human cells. We propose that this conserved C-terminal 'TACC domain' defines a new family of microtubule-interacting proteins.

Maskin is a CPEB-associated factor that transiently interacts with elF-4E

In Xenopus, the CPE is a bifunctional 3' UTR sequence that maintains maternal mRNA in a dormant state in oocytes and activates polyadenylation-induced translation during oocyte maturation. Here, we report that CPEB, which binds the CPE and stimulates polyadenylation, interacts with a new factor we term maskin. Maskin contains a peptide sequence that is conserved among elF-4E-binding proteins. Affinity chromatography demonstrates that CPEB, maskin, and elF-4E reside in a complex in oocytes, and yeast two-hybrid analyses indicate that CPEB and maskin bind directly, as do maskin and elF-4E. While CPEB and maskin remain together during oocyte maturation, the maskin-elF-4E interaction is substantially reduced. The dissolution of this complex may result in the binding of elF-4E to elF-4G and the translational activation of CPE-containing mRNAs.