Sequence analysis reveals that the BTG1 anti-proliferative gene is conserved throughout evolution in its coding and 3' non-coding regions

Exogenous insulin promotes the expression of B-cell translocation gene 1 and 2 in chicken pectoralis

B-cell translocation genes (BTG) have been proved to play important roles in carbohydrate metabolism through modifying insulin homeostasis and glucose metabolism. This study, therefore, was conducted to investigate the effects of exogenous insulin on the expression of BTG1 and BTG2 in chickens. Twenty-four-day-old broilers and layers were fasted for 16 h and randomly assigned to insulin treatment group (subcutaneously injected with 5 IU/kg body weight) or control group (received an equivalent volume of phosphate-buffered saline). Blood glucose concentration was measured, and it showed that the blood glucose concentrations in the layers were significantly (P < 0.05) higher than that in the broilers under fasting state. Response to exogenous insulin, the blood glucose concentrations were greatly reduced in both breeds. Of note, the blood glucose concentration restored to 62% of the basal state at 240 min (P < 0.05) after insulin stimulation in layers, whereas it was still in low level until 240 min in broilers (under fast state). Tissue profiling revealed that both BTG1 and BTG2 were abundantly expressed in the skeletal muscles of broilers. A negative correlation was observed between blood glucose and BTG1 (ρ = −0.289, P = 0.031) /BTG2 (ρ = −0.500, P < 0.001) in pectoralis, and BTG1 (ρ = −0.462, P < 0.001) in pancreas. As blood glucose decreased due to exogenous insulin administration (under fast state), the expression of both BTG1 and BTG2 notably upregulated in birds’ pectoralis at 120 min and/or 240 min, meanwhile pancreas BTG1 was also upregulated. Re-feeding at 120 min elevated the blood glucose and reduced the expression of BTG genes in pectoralis generally. In addition, the change of BTG1 and BTG2 expression showed distinct difference between layers and broilers at 120 min and 240 min after insulin stimulation in pectoralis, pancreas and heart tissue; even after re-feeding at 120 min, BTG2 expression at 240 min after insulin injection was downregulated in the pectoralis of layers, while it was upregulated in that broilers. Collectively, these results indicated that response to exogenous insulin, chicken blood glucose exhibited breed-specific dynamic change, and meanwhile the expressions of both BTG1 and BTG2 genes in chickens were significantly altered by exogenous insulin in a breed- and tissue-specific manner. BTG1 and BTG2 genes may negatively regulate bird's blood glucose by promoting the glucose uptake corporately in pectoralis, and through regulating the insulin secretion in pancreas (especially BTG1).

Conserved non-coding elements: developmental gene regulation meets genome organization

Comparative genomics has revealed a class of non-protein-coding genomic sequences that display an extraordinary degree of conservation between two or more organisms, regularly exceeding that found within protein-coding exons. These elements, collectively referred to as conserved non-coding elements (CNEs), are non-randomly distributed across chromosomes and tend to cluster in the vicinity of genes with regulatory roles in multicellular development and differentiation. CNEs are organized into functional ensembles called genomic regulatory blocks–dense clusters of elements that collectively coordinate the expression of shared target genes, and whose span in many cases coincides with topologically associated domains. CNEs display sequence properties that set them apart from other sequences under constraint, and have recently been proposed as useful markers for the reconstruction of the evolutionary history of organisms. Disruption of several of these elements is known to contribute to diseases linked with development, and cancer. The emergence, evolutionary dynamics and functions of CNEs still remain poorly understood, and new approaches are required to enable comprehensive CNE identification and characterization. Here, we review current knowledge and identify challenges that need to be tackled to resolve the impasse in understanding extreme non-coding conservation.

The Philadelphia chromosome in leukemogenesis

The truncated chromosome 22 that results from the reciprocal translocation t(9;22)(q34;q11) is known as the Philadelphia chromosome (Ph) and is a hallmark of chronic myeloid leukemia (CML). In leukemia cells, Ph not only impairs the physiological signaling pathways but also disrupts genomic stability. This aberrant fusion gene encodes the breakpoint cluster region-proto-oncogene tyrosine-protein kinase (BCR-ABL1) oncogenic protein with persistently enhanced tyrosine kinase activity. The kinase activity is responsible for maintaining proliferation, inhibiting differentiation, and conferring resistance to cell death. During the progression of CML from the chronic phase to the accelerated phase and then to the blast phase, the expression patterns of different BCR-ABL1 transcripts vary. Each BCR-ABL1 transcript is present in a distinct leukemia phenotype, which predicts both response to therapy and clinical outcome. Besides CML, the Ph is found in acute lymphoblastic leukemia, acute myeloid leukemia, and mixed-phenotype acute leukemia. Here, we provide an overview of the clinical presentation and cellular biology of different phenotypes of Ph-positive leukemia and highlight key findings regarding leukemogenesis.

High frequency of BTG1 deletions in patients with BCR-ABL1-positive acute leukemia

Deletions affecting the B-cell translocation gene 1 (BTG1) have recently been reported in 9% of patients with B-cell precursor acute lymphoblastic leukemia (BCP-ALL), and occur even more frequently in ETV6-RUNX1-positive and BCR-ABL1-positive subgroups. To investigate whether the BTG1 deletions occur in other BCR-ABL1-positive acute leukemias besides BCP-ALL, we analyzed 44 leukemia cases harboring the BCR-ABL1 transcript [32 BCP-ALL, six mixed-phenotype acute leukemia (MPAL), and six chronic myeloid leukemia in B-lineage blast crisis (CML-BC)] by array-based comparative genomic hybridization and reverse transcription-PCR. BTG1 deletions were present in 31.8% of BCR-ABL1-positive acute leukemia patients, including 31.3% of BCP-ALL (10/32), 33.3% of MPAL (2/6), and 33.3% of CML-BC (B-lineage) (2/6) patients. Of note, the intragenic deletion breakpoints, mapping to 5 different positions at the proximal end of the breakpoint, clustered tightly within exon 2 of BTG1, which were located within a stretch of 20 bp from nucleotide 284 to nucleotide 304 and led to truncated BTG1 transcripts. There were no significant differences in the median white blood cell count, hemoglobin concentration, platelet count, bone marrow blast count, sex, age, or overall complete remission rate between patients with and without BTG1 deletions. Taken together, our data suggest that BTG1 deletions might play a role in leukemogenesis of BCP-ALL as well as of BCR-ABL1-positive MPAL and CML-BC (B-lineage).

Second cistron in CACNA1A gene encodes a transcription factor mediating cerebellar development and SCA6

The CACNA1A gene, encoding the voltage-gated calcium channel subunit α1A, is involved in pre- and postsynaptic Ca(2+) signaling, gene expression, and several genetic neurological disorders. We found that CACNA1A coordinates gene expression using a bicistronic mRNA bearing a cryptic internal ribosomal entry site (IRES). The first cistron encodes the well-characterized α1A subunit. The second expresses a transcription factor, α1ACT, which coordinates expression of a program of genes involved in neural and Purkinje cell development. α1ACT also contains the polyglutamine (polyQ) tract that, when expanded, causes spinocerebellar ataxia type 6 (SCA6). When expressed as an independent polypeptide, α1ACT-bearing an expanded polyQ tract-lacks transcription factor function and neurite outgrowth properties, causes cell death in culture, and leads to ataxia and cerebellar atrophy in transgenic mice. Suppression of CACNA1A IRES function in SCA6 may be a potential therapeutic strategy.

Tumor growth suppression by adenovirus-mediated introduction of a cell-growth-suppressing gene tob in a pancreatic cancer model

TOB (transducer of ErbB-2) is a tumor suppressor that interacts with protein-tyrosine kinase receptors, including ErbB-2. Introduction of the tob gene into NIH3T3 cells results in cell growth suppression. In this study, we evaluated the effect of tob expression in pancreatic cell lines (AsPC-1, BxPC-3, SOJ) and discuss the tumor-suppressing effects of adenoviral vector expressing tob cDNA. We first measured the levels of endogenous tob mRNA being expressed in all pancreatic cancer cell lines. Then, we examined the effect of adenoviral vector containing tob cDNA (Ad-tob vector) on cancer cell lines. The viral vector was expanded with transfection in 293 cells. The titer of the vector was 350x10(6) pfu/ml. These cancer cells were able to be transfected with MOI 20 without adenoviral toxicity. The transfection of Ad-tob vector results in growth suppression of SOJ and AsPC-1 cell lines. The magnitude of the expression of the Ad-tob gene in cancer is correlated to tumor suppressive activity. We prepared pancreatic cancer peritonitis models using a peritoneal injection of AsPC-1 cells. In this model, bloody ascites and multiple tumor nodules were seen at the mesentery after 16 days. AdCAtob (50x10(6) pfu/day) was administered from day 5 to day 9 after 4 days of peritoneal injection of 2x10(6) AsPC-1 cells. Tumor growth suppression occurred 10 days after peritoneal injection of AdCAtob compared with the control group. There were no tumor nodules in the abdomen and no bloody ascites. These results suggest that the peritoneal injection of AdCAtob has potential to suppress the formation of pancreatic cancer peritonitis, and can be applied for chemotherapy-resistant cancer peritonitis.

XBtg2 is required for notochord differentiation during early Xenopus development

The notochord is essential for normal vertebrate development, serving as both a structural support for the embryo and a signaling source for the patterning of adjacent tissues. Previous studies on the notochord have mostly focused on its formation and function in early organogenesis but gene regulation in the differentiation of notochord cells itself remains poorly defined. In the course of screening for genes expressed in developing notochord, we have isolated Xenopus homolog of Btg2 (XBtg2). The mammalian Btg2 genes, Btg2/PC3/TIS21, have been reported to have multiple functions in the regulation of cell proliferation and differentiation but their roles in early development are still unclear. Here we characterized XBtg2 in early Xenopus laevis embryogenesis with focus on notochord development. Translational inhibition of XBtg2 resulted in a shortened and bent axis phenotype and the abnormal structures in the notochord tissue, which did not undergo vacuolation. The XBtg2-depleted notochord cells expressed early notochord markers such as chordin and Xnot at the early tailbud stage, but failed to express differentiation markers of notochord such as Tor70 and 5-D-4 antigens in the later stages. These results suggest that XBtg2 is required for the differentiation of notochord cells such as the process of vacuolar formation after determination of notochord cell fate.

Identification and characterization of ameloblastin gene in an amphibian, Xenopus laevis

Ameloblastin (AMBN) is an enamel sheath protein that presumably has a role in determining the prismatic structure of growing enamel crystals. To investigate the relationship between the molecular evolution of the AMBN gene and development of enamel prismatic structures, it is considered to be of great significance in the identification of homologues of the AMBN genes in nonmammals whose teeth lack an enamel prismatic structure. Several clones containing AMBN cDNA were isolated from an African clawed toad tooth cDNA library by screening with a polymerase chain reaction (PCR) method. Sequence analysis of the clones revealed that they were derived from different genes (toad-A and toad-B), which were found to contain ORFs encoding 408- and 352-amino-acid proteins, respectively. The N-terminal part of the toad AMBN proteins and the phosphorylation motif for casein kinase II, as well as several features, were found to be highly conserved throughout the evolution of tetrapods. Exon-intron boundaries were shared by toad and caiman genes with the exception of exons 6, 7 and 10 while human and caiman genes shared them exclusive of exons 8 and 9 which have been found only in the human. As for exon 7, it was absent in both toad genes. Moreover, the AMBN genes were transcribed only in the upper jaw, presumably in teeth. These results may provide useful information for investigation of the evolution of enamel.

In search of a function for the TIS21/PC3/BTG1/TOB family

The Btg family of anti-proliferative gene products includes Pc 3/Tis 21/Btg 2, Btg 1, Tob, Tob2, Ana/Btg3, Pc3k and others. These proteins are characterized by similarities in their amino-terminal region: the Btg1 homology domain. However, the pleiotropic nature of these family proteins has been observed and no common physiological function among family members was suggested from the history of their identification. Recent progress in the search for Btg family functions has come from the analysis of cell regulation and of cell differentiation. It is now emerging that every member of this family has a potential to regulate cell growth. We would like to propose here to use a nomenclature APRO as a new term for the family.

Cloning of PC3B, a novel member of the PC3/BTG/TOB family of growth inhibitory genes, highly expressed in the olfactory epithelium

We identified in the EST database murine and human sequences similar, but not identical, to the members of the PC3/BTG/TOB family of cell cycle inhibitors. A conserved domain (aa 50-68) of the PC3 protein, the prototype member of the family, was used as a query. That domain has been shown by us to be necessary for the antiproliferative activity of PC3. A murine EST clone and a highly homologous human EST clone, containing the entire ORF, were chosen for sequencing. Comparison to databases and a phylogenetic tree analysis indicated that these EST clones are the mouse and human homologues of a gene that represents a novel member of the PC3/BTG/TOB family. This gene, named PC3B, is endowed with marked antiproliferative activity, being able to induce G(1) arrest, and is highly expressed in testis, in oocyte, and in preimplantation embryos. Analysis of its expression during murine development indicated a specific localization in the olfactory epithelium at midgestation, suggesting that PC3B might be involved in the differentiation of this neuronal structure. Human PC3B mapped to chromosome 11q23, as indicated by radiation hybrid analysis.

Conservation of the 3'-untranslated region of the Rab1a gene in amniote vertebrates: exceptional structure in marsupials and possible role for posttranscriptional regulation

The YPT1/RAB1 protein, a key regulator of the intracellular vesicle transport in eukaryotes, is highly conserved in function and amino acid sequence. Here we report that the most highly conserved nucleotide sequence of the Rab1a gene of amniote vertebrates corresponds to the 3'-untranslated region (3'-UTR) of the mRNA. Sequences of 27 species ranging from mammals to sauropsida are >91% identical in this region. Secondary structure prediction procedures applied to the 3'-UTR sequences between positions 750 and 984 and 1428 (mouse cDNA: Y00094), respectively, of the RAB1a mRNAs revealed families of alternative structures around nucleotide position 800 as recurrent features. The two hairpin loops are also predicted for marsupials, despite of their exceptional extension of the A-rich sequence in between. Yet, sequence conservation is much higher than required to conserve secondary structure. Implications for posttranscriptional regulation and protein binding are discussed.

Expression of rat BTG(3) gene, Rbtg3, is regulated by redox changes

The Rbtg3 gene was isolated by PCR (polymerase chain reaction) cloning from the cDNA library of Rat1 fibroblasts that were stimulated with TPA (12-O-tetradecanoylphorbol-13-acetate) or various growth factors for 3h and was found to be a rat homologue of mouse BTG3 and human ANA genes. The Rbtg3 gene had unique DNA sequences in the 5'-UTR and 3'-UTR that contained four ATTTA and one TTATTTA(T/A)(T/A) nonamer motif, and also a polyA addition site. Nucleotide homology of Rbtg3 with BTG3 and ANA was 88.5 and 76.6%, respectively. Expression of Rbtg3 was investigated in SD rats as well as cell lines derived from mouse--SW3T3, NIH3T3 fibroblasts--and rat--Rat1, 3Y1 fibroblasts and PC12--cells. Rbtg3 was highly expressed in brain but barely in lung, kidney, thymus and spleen. The constitutive expression level was high in SW3T3, Rat1 and 3Y1 fibroblasts, but very low in NIH3T3 fibroblast and PC12 cells. However, in all cells tested, Rbtg3 was proved to be one of the primary response genes superinduced by TPA (50ng/ml)+cycloheximide (CHX, 10 microgram/ml). Expression of Rbtg3 was induced by H(2)O(2) (500mM) up to fourfold in PC12 cells and was blocked by pretreatment of NAC (N-acetyl-L-cysteine, 10mM). The induction was ninefold in 3Y1 fibroblasts by menadione (25mM) treatment for 1h, whereas it was reduced to a third of the control level in SW3T3 fibroblast by the same treatment. Rbtg3 was not expressed in NIH3T3 cells but minimally regulated by redox changes as compared with rapid and strong induction of TIS21/BTG2 mRNAs after TPA or H(2)O(2) stimulation. The above results indicate that Rbtg3 is one of many redox-regulated genes as well as a primary response gene.

RNase treatment of yeast and mammalian cell extracts affects in vitro substrate methylation by type I protein arginine N-methyltransferases

Type I protein arginine N-methyltransferases catalyze the formation of omega-NG-monomethylarginine and asymmetric omega-NG, NG-dimethylarginine residues using S-adenosyl-l-methionine as the methyl donor. In vitro these enzymes can modify a number of soluble methyl-accepting substrates in yeast and mammalian cell extracts including several species that interact with RNA. We treated normal and hypomethylated Saccharomyces cerevisiae and RAT1 cell extracts with RNase prior to in vitro methylation by recombinant protein N-arginine methyltransferases and found that the methylation of certain polypeptides is enhanced up to 12-fold whereas that of others is diminished. 2-D gel electrophoresis of RNase-treated yeast extracts allowed us to tentatively identify the glycine- and arginine-rich (GAR) domain-containing proteins Gar1, Nop1, Sbp1, and Npl3 as major methyl-acceptors based on their known isoelectric points and apparent molecular weights. These results suggest that the methylation and RNA-binding of GAR domain-containing proteins in vivo may regulate protein-nucleic acid or protein-protein interactions.

Expression of the antiproliferative gene TIS21 at the onset of neurogenesis identifies single neuroepithelial cells that switch from proliferative to neuron-generating division

At the onset of mammalian neurogenesis, neuroepithelial (NE) cells switch from proliferative to neuron-generating divisions. Understanding the molecular basis of this switch requires the ability to distinguish between these two types of division. Here we show that in the mouse ventricular zone, expression of the mRNA of the antiproliferative gene TIS21 (PC3, BTG2) (i) starts at the onset of neurogenesis, (ii) is confined to a subpopulation of NE cells that increases in correlation with the progression of neurogenesis, and (iii) is not detected in newborn neurons. Expression of the TIS21 mRNA in the NE cells occurs transiently during the cell cycle, i.e., in the G1 phase. In contrast to the TIS21 mRNA, the TIS21 protein persists through the division of NE cells and is inherited by the neurons, where it remains detectable during neuronal migration and the initial phase of differentiation. Our observations indicate that the TIS21 gene is specifically expressed in those NE cells that, at their next division, will generate postmitotic neurons, but not in proliferating NE cells. Using TIS21 as a marker, we find that the switch from proliferative to neuron-generating divisions is initiated in single NE cells rather than in synchronized neighboring cells.

Human carbon catabolite repressor protein (CCR4)-associative factor 1: cloning, expression and characterization of its interaction with the B-cell translocation protein BTG1

The human BTG1 protein is thought to be a potential tumour suppressor because its overexpression inhibits NIH 3T3 cell proliferation. However, little is known about how BTG1 exerts its anti-proliferative activity. In this study, we used the yeast 'two-hybrid' system to screen for interacting protein partners and identified human carbon catabolite repressor protein (CCR4)-associative factor 1 (hCAF-1), a homologue of mouse CAF-1 (mCAF-1) and Saccharomyces cerevisiae yCAF-1/POP2. In vitro the hCAF-1/BTG1 complex formation was dependent on the phosphorylation of a putative p34cdc2 kinase site on BTG1 (Ser-159). In yeast, the Ala-159 mutant did not interact with hCAF-1. In addition, phosphorylation of Ser-159 in vitro showed specificity for the cell cycle kinases p34CDK2/cyclin E and p34CDK2/cyclin A, but not for p34CDK4/cyclin D1 or p34cdc2/cyclin B. Cell synchrony experiments with primary cultures of rat aortic smooth-muscle cells (RSMCs) demonstrated that message and protein levels of rat CAF-1 (rCAF-1) were up-regulated under conditions of cell contact, as previously reported for BTG1 [Wilcox, Scott, Subramanian, Ross, Adams-Burton, Stoltenborg and Corjay (1995) Circulation 92, I34-I35]. Western blot and immunohistochemical analysis showed that rCAF-1 localizes to the nucleus of contact-inhibited RSMCs, where it was physically associated with BTG1, as determined by co-immunoprecipitation with anti-hCAF-1 antisera. Overexpression of hCAF-1 in NIH 3T3 and osteosarcoma (U-2-OS) cells was itself anti-proliferative with colony formation reduced by 67% and 90% respectively. Taken together, these results indicate that formation of the hCAF-1/BTG1 complex is driven by phosphorylation at BTG1 (Ser-159) and implicates this complex in the signalling events of cell division that lead to changes in cellular proliferation associated with cell-cell contact.

RNA and protein interactions modulated by protein arginine methylation

This review summarizes the current status of protein arginine N-methylation reactions. These covalent modifications of proteins are now recognized in a number of eukaryotic proteins and their functional significance is beginning to be understood. Genes that encode those methyltransferases specific for catalyzing the formation of asymmetric dimethylarginine have been identified. The enzyme modifies a number of generally nuclear or nucleolar proteins that interact with nucleic acids, particularly RNA. Postulated roles for these reactions include signal transduction, nuclear transport, or a direct modulation of nucleic acid interactions. A second methyltransferase activity that symmetrically dimethylates an arginine residue in myelin basic protein, a major component of the axon sheath, has also been characterized. However, a gene encoding this activity has not been identified to date and the cellular function for this methylation reaction has not been clearly established. From the analysis of the sequences surrounding known arginine methylation sites, we have determined consensus methyl-accepting sequences that may be useful in identifying novel substrates for these enzymes and may shed further light on their physiological role.

Sequence and developmental expression of AmphiTob, an amphioxus homolog of vertebrate Tob in the PC3/BTG1/Tob family of tumor suppressor genes

Tob is a member of the PC3/ BTG1/Tob family of vertebrate tumor suppressor genes; its expression is known to inhibit proliferation of cells in vitro, but its possible roles during normal development have not been investigated previously. The present study concerns the structure and developmental expression of AmphiTob in an invertebrate chordate, amphioxus. This is the first investigation of any Tob gene during embryological development. The 311 amino acid AmphiTob protein is similar to vertebrate Tob but lacks the C-terminal PQ-rich domain of the latter. In early embryos of amphioxus, in situ hybridization first reveals AmphiTob expression in the hypoblast at the gastrula stage on the likely dorsal side of the embryo. During subsequent development, expression is seen in several tissues of the ectoderm, mesoderm, and endoderm. The most striking expression domains are in the developing somitic musculature and dorsal nerve cord. In the medial wall of each somite, AmphiTob is expressed strongly by cells destined to differentiate into the axial trunk muscles; this pattern persists until late in the larval stage, evidently because undifferentiated cells are continually becoming myogenic as the muscles grow. Nerve cord cells conspicuously transcribe AmphiTob from the late neurula until the early larval stage: Expression occurs in a few cells scattered along the nerve cord and in a group of cells located in the cerebral vesicle (in a region presumably homologous to the vertebrate diencephalic forebrain). During development, an intense and transitory transcription of AmphiTob may be an early event in cells exiting the cell cycle in preparation for differentiation.

Enhancement of B-cell translocation gene-1 expression by prostaglandin E2 in macrophages and the relationship to proliferation

Although prostaglandin (PG) E2 is known to suppress various macrophage functions, the molecular mechanisms by which that occurs are largely unknown. To understand better those mechanisms, differential screening of a cDNA library from PGE2-treated macrophages was performed. Subsequently, the DNA sequence of a differentially expressed cDNA clone was determined and the cDNA was identified as B-cell translocation gene-1 (BTG1), a recently cloned antiproliferative gene. A two-to threefold increase in macrophage BTG1 expression was observed after PGE2 treatment. PGE1 and platelet-activating factor, but not leukotrienes B4, and C4, or lipopolysaccharide, also enhanced BTG1 expression. Furthermore, this effect ws mimicked by dibutyryl cAMP which indicated the involvement of elevated cAMP in the PGE2-mediated enhancement of BTG1. Moreover, there was an inverse correlation between BTG1 mRNA expression and macrophage proliferation; however, BTG1 alteration was not associated with macrophage tumoricidal activation. Thus, BTG1 may play a role in PGE2-mediated inhibition of macrophage proliferation and not activation.

Induction of tetradecanoyl phorbol acetate-inducible sequence (TIS) genes by electroconvulsive shock in rat brain

We studied the induction of tetradecanoyl phorbol acetate-inducible sequences (TIS)1, 7, 8, 11, and 21 in rat cerebral cortex, hippocampus, and cerebellum after electroconvulsive shock (ECS). These genes were reported to be induced by depolarization in PC-12 cells. Single ECS induced TIS1, 8, 11, and 21, but not TIS7 genes in the rat brain regions examined. In cerebral cortex and hippocampus, induction of TIS1, TIS8, and TIS21 reached peak at 30 or 45 min after ECS. The induced mRNA of TIS1 and 21 decreased rapidly and returned almost to the basal level by 90 min after ECS, whereas those of TIS8 and 11 lasted longer. In cerebellum, TIS genes were induced and disappeared more rapidly than in the other two regions. The 10 and 20 daily ECSs did not affect the inducibility of TIS1, 11, and 21 in cerebellum, but the induction of TIS8 was attenuated by 35% after 20 daily ECSs. Our study indicated that ECS could induce some of the TIS genes in various rat brain regions, but the induction patterns were different depending on the TIS genes and brain regions. Our study also suggested that chronic ECS could not attenuate the induction of some immediate early genes.

The mammalian immediate-early TIS21 protein and the leukemia-associated BTG1 protein interact with a protein-arginine N-methyltransferase

The TIS21 immediate-early gene and leukemia-associated BTG1 gene encode proteins with similar sequences. Two-hybrid analysis identified a protein that interacts with TIS21 and BTG1. Sequence motifs associated with S-adenosyl-L-methionine binding suggested this protein might have methyltransferase activity. A glutathione S-transferase (GST) fusion of the putative methyltransferase modifies arginine residues, in appropriate protein substrates, to form NG-monomethyl and NG,NG-dimethylarginine (asymmetric). We term the protein- arginine N-methyltransferase (EC 2.1.1.23) gene "PRMT1, " for protein-arginine methyltransferase 1. GST-TIS21 and GST-BTG1 fusion proteins qualitatively and quantitatively modulate endogenous PRMT1 activity, using control and hypomethylated RAT1 cell extracts as methyl-accepting substrates. PRMT1 message appears ubiquitous, and is constitutive in mitogen-stimulated cells. Modulation of PRMT1 activity by transiently expressed regulatory subunits may be an additional mode of signal transduction following ligand stimulation.

Differential expression of TIS21 and TIS1 genes in the various organs of Balb/c mice, thymic carcinoma tissues and human cancer cell lines

As a part of a series of investigations on the functions of TIS21 and TIS1 genes, we measured in vivo 12-O-tetradecanoylphorbol-13-acetate (TPA) inducibility of primary response genes (TIS21, TIS8 and TIS1) in the Balb/c mice and the changes of TIS gene expression in thymic carcinoma tissues and A549 and NCIH69 human lung cancer cell lines. In vivo induction of the TIS genes (TIS21, -8 and -1) by intraperitoneal injection of TPA was dramatic only at the needle contact site, i.e. in the abdominal muscle, not in the thigh muscle. Expression of TIS21 and TIS1 in the Balb/c mice thymus, lung, stomach and spleen was very strong (Lim IK et al. 1994a), regardless of TPA injection. Thymic carcinoma tissues developed in SV40-T-antigen-containing transgenic mice did not express TIS21 and TIS1, and expressed TIS8 weakly. Interestingly, induction of TIS21 expression was obliterated in the human lung cancer cells; A549 cells completely lost the ability to express TIS21 after a combined treatment of TPA and cycloheximide. We also measured the induction of TIS genes by TPA and/or cycloheximide in Raw264.7 mouse macrophage cells and U937 human histiocytic lymphoma cells. However, the induction profile was quite different; repressed and deregulated expression in the U937 cells as compared to rapid and transient induction of TIS genes in the Raw264.7 cells. These data may suggest a repressed expression of TIS21 and TIS1 in the cancer tissues and cells derived from the organs that constitutively express TIS21 in mice and in human cancer cells.

Preferential primary-response gene expression in promotion-resistant versus promotion-sensitive JB6 cells

The 12-O-tetradecanoylphorbol-13-acetate (TPA)-inducible sequence (TIS) genes are a set of primary response genes induced in Swiss 3T3 cells by TPA. They include three transcription factors, a prostaglandin synthase, and three proteins of unknown function. To ascertain which, if any TIS genes might be involved in tumor promotion, we examined the expression of these genes in response to tumor promoters in transformation promotion-sensitive (P+) and -resistant (P-) JB6 murine epidermal cells, a model used to identify events relevant to promotion. A subset of TIS genes (TIS1, TIS10, and TIS21) was preferentially induced by TPA in P-cells. In addition, TIS1 and TIS21 mRNAs were preferentially induced in P-cells by epidermal growth factor, another transformation promoter that distinguishes P+ from P-cells. TIS1 and TIS21 protein levels were also greater in TPA-treated P-cells than P+ cells. Forskolin, a cAMP-elevating anti-promoter, increased TPA-induced levels of TIS1, TIS10, and TIS21 mRNAs in P+ cells, ruling in potential roles for these genes in modulating tumor promotion. The anti-promoters fluocinolone acetonide, retinoic acid, and superoxide dismutase did not enhance TPA-induced levels of TIS1 and TIS21 mRNAs in P+ cells, suggesting that these inhibitors may act on other promotion-relevant genes. TIS1 encodes a member of the steroid receptor superfamily. TIS1 encodes a protein of unknown function with strong sequence similarity to BTG1, a proposed "anti-proliferative gene" (Rouault JP, Rimokh R, Tessa C, et al., EMBO J 11:1663-1670, 1992). Preferential induction by multiple promoters of these TIS genes in P-cells and enhancement of their induction in P+ cells by the anti-promoter forskolin make TIS1 and TIS21 candidates for promotion suppressor genes.