Coordinated regulation of gene expression relies on transcription factors (TFs) binding to specific DNA sites. Our large-scale information-theoretical analysis of>> 950 TF-binding motifs demonstrates that prokaryotes and eukaryotes use strikingly different strategies to target TFs to specific genome locations. Although bacterial TFs can recognize a specific DNA site in the genomic background, eukaryotic TFs exhibit widespread, nonfunctional binding and require clustering of sites to achieve specificity. We find support for this mechanism in a range of experimental studies and in our evolutionary analysis of DNA-binding domains. Our systematic characterization of binding motifs provides a quantitative assessment of the differences in transcription regulation in prokaryotes and eukaryotes.

Endocytosis and intracellular processing of transferrin (Tf) and Tf receptors were examined in rat reticulocytes. Subcellular fractionation revealed that Tf enters a non-lysosomal endocytic compartment with a density between those of plasma membrane and lysosomes. After 20 min of uptake at (37 degrees C) 35 to 40% of cell-associated Tf was contained in this intermediate-density compartment. To test the fidelity of colloidal gold-Tf (AuTf) as a probe for Tf processing, reticulocytes were fractionated after uptake of 131I-Tf and 125I-AuTf. The subcellular distributions of the two ligands were indistinguishable by this method, a result suggesting that AuTf is processed similarly to Tf. Electron microscopy revealed that AuTf entered multivesicular endosomes (MVEs) as well as various small vesicles and tubular structures. In addition MVE exocytosis was observed with discharge of inclusion vesicles and associated AuTf. AuTf was bound to the outside of these vesicles both before and after exocytosis. These data suggest that Tf receptors are shed from developing reticulocytes by incorporation into the limiting membrane of inclusion vesicles, followed by discharge of these vesicles by MVE exocytosis. As further evidence of this process, we isolated inclusion vesicles after their discharge and found them to contain Tf receptors. Moreover, the rate of Tf receptor shedding by inclusion vesicle discharge matches Tf receptor loss rates closely enough to suggest that this is the primary path of receptor loss during reticulocyte development.

BACKGROUND

Environmental conditions, such as water supply, temperature and salinity, strongly affect plant growth and development. Extremes of these conditions (abiotic stresses) adversely affect many different mechanisms associated with plant responses and adaptation to stress: photosynthetic mechanisms, e.g. stomatal control of CO(2) diffusion, photosystem II repair, ribulose bisphosphate carboxylase/oxygenase (Rubisco) activity and scavenging of reactive oxygen species (ROS), are susceptible to damage, and photosynthetic efficiency can be greatly decreased. Responses and adaptations require differential gene expression, which is regulated by specific transcription factors (TFs).

METHODS

The role and regulation of several TFs involved in abiotic stress response pathways are considered, with emphasis on new findings regarding expression of genes related to both stomatal and non-stomatal limitations to CO(2) photosynthetic assimilation.

CONCLUSIONS

Many TFs, belonging to different families (e.g. MYB, bZIP and DREB), have been related to abiotic stress responses; however, only a few are known to regulate the expression of photosynthesis-related genes in response to stress. Several TFs belonging to the MYB family play an important role in both stomatal and non-stomatal responses by regulation of stomatal numbers and sizes, and metabolic components, respectively. To obtain more insight into this area of potentially large agronomic impact, it is essential to identify and functionally characterize new TFs that mediate the stress responses regulating the expression of genes associated with photosynthesis and related metabolism.

The yeast retroviruslike element Ty3 inserts at the transcription initiation sites of genes transcribed by RNA polymerase III (Pol III). An in vitro integration assay was developed with the use of Ty3 viruslike particles and a modified SUP2 tyrosine transfer RNA (tRNA(Tyr)) gene target. Integration was position-specific and required Ty3 integrase, Pol III transcription factor (TF) IIIB-, TFIIIC-, and Pol III-containing fractions showed that TFIIIB and TFIIIC, together, were sufficient for position-specific Ty3 integration, but not for transcription. This report demonstrates that in vitro integration of a retroelement can be targeted by cellular proteins.

It is now widely recognized that a strong correlation exists between cancer and aberrant hemostasis. Patients with various types of cancers, including pancreatic, colorectal, and gastric cancer, often develop thrombosis, a phenomenon commonly referred to as Trousseau syndrome. Reciprocally, components from the coagulation cascade also influence cancer progression. The primary initiator of coagulation, the transmembrane receptor tissue factor (TF), has gained considerable attention as a determinant of tumor progression. On complex formation with its ligand, coagulation factor VIIa, TF influences protease-activated receptor-dependent tumor cell behavior, and regulates integrin function, which facilitate tumor angiogenesis both in vitro and in mouse models. Furthermore, evidence exists that an alternatively spliced isoform of TF also affects tumor growth and tumor angiogenesis. In patient material, TF expression and TF cytoplasmic domain phosphorylation correlate with disease outcome in many, but not in all, cancer subtypes, suggesting that TF-dependent signal transduction events are a potential target for therapeutic intervention in selected types of cancer. In this review, we summarize our current understanding of the role of TF in tumor growth and metastasis, and speculate on anticancer therapy by targeting TF.

Transcription factors (TFs) bind specific sequences in promoter-proximal and -distal DNA elements to regulate gene transcription. RNA is transcribed from both of these DNA elements, and some DNA binding TFs bind RNA. Hence, RNA transcribed from regulatory elements may contribute to stable TF occupancy at these sites. We show that the ubiquitously expressed TF Yin-Yang 1 (YY1) binds to both gene regulatory elements and their associated RNA species across the entire genome. Reduced transcription of regulatory elements diminishes YY1 occupancy, whereas artificial tethering of RNA enhances YY1 occupancy at these elements. We propose that RNA makes a modest but important contribution to the maintenance of certain TFs at gene regulatory elements and suggest that transcription of regulatory elements produces a positive-feedback loop that contributes to the stability of gene expression programs.

The YEASTRACT (http://www.yeastract.com) information system is a tool for the analysis and prediction of transcription regulatory associations in Saccharomyces cerevisiae. Last updated in June 2013, this database contains over 200,000 regulatory associations between transcription factors (TFs) and target genes, including 326 DNA binding sites for 113 TFs. All regulatory associations stored in YEASTRACT were revisited and new information was added on the experimental conditions in which those associations take place and on whether the TF is acting on its target genes as activator or repressor. Based on this information, new queries were developed allowing the selection of specific environmental conditions, experimental evidence or positive/negative regulatory effect. This release further offers tools to rank the TFs controlling a gene or genome-wide response by their relative importance, based on (i) the percentage of target genes in the data set; (ii) the enrichment of the TF regulon in the data set when compared with the genome; or (iii) the score computed using the TFRank system, which selects and prioritizes the relevant TFs by walking through the yeast regulatory network. We expect that with the new data and services made available, the system will continue to be instrumental for yeast biologists and systems biology researchers.

Tissue factor (TF) is an essential enzyme activator that forms a catalytic complex with FVII(a) and initiates coagulation by activating FIX and FX, ultimately resulting in thrombin formation. TF is found in adventitia of blood vessels and the lipid core of atherosclerotic plaques. In unstable coronary syndromes, plaque rupture initiates coagulation by exposing TF to blood. Biologically active TF has been detected in vessel walls and circulating blood. Elevated intravascular TF has been reported in diverse pro-thrombotic syndromes such as myocardial infarction, sepsis, anti-phospholipid syndrome and sickle-cell disease. It is unclear how TF circulates, although it may be present in pro-coagulant microparticles. We now report identification of a form of human TF generated by alternative splicing. Our studies indicate that alternatively spliced human tissue factor (asHTF) contains most of the extracellular domain of TF but lacks a transmembrane domain and terminates with a unique peptide sequence. asHTF is soluble, circulates in blood, exhibits pro-coagulant activity when exposed to phospholipids, and is incorporated into thrombi. We propose that binding of asHTF to the edge of thrombi contributes to thrombus growth by creating a surface that both initiates and propagates coagulation.

Disseminated intravascular thrombosis is a frequent complication of endotoxic shock, and modulation of endothelial cell hemostatic properties has been proposed to play a role in its pathogenesis based on studies of endothelial cells in culture. This study examined the in vivo expression of tissue factor (TF) and thrombomodulin (TM) in a baboon model of lethal Escherichia coli sepsis using immunohistochemistry with monospecific antibodies. Expression of E-selectin (E-sel) was also determined as a marker of endothelial cell activation. Correlation of immunoreactivity with procoagulant activity in lipopolysaccharide-stimulated cultured human endothelial cells showed that immunohistochemistry was sufficiently sensitive to detect as little as 5% of the maximum in vitro endothelial cell TF response. Vascular endothelium of control animals expressed TM but had no detectable TF or E-sel. Following E. coli infusion, widespread E-sel expression and microvascular fibrin deposition was evident within 6 hours. However, expression of TF by endothelial cells became detectable only in the splenic microvasculature, where endothelial specificity of TF expression was confirmed by dual immunofluorescence of TF with von Willebrand's factor and with TM. In the spleen, there was a dissociation of expression of TF and E-sel, with marginal zone vessels being TF-positive and E-sel-negative, whereas sinusoidal endothelium was E-sel-positive but TF-negative. TM expression was unchanged from controls. Additionally, expression of TF by lung alveolar epithelial cells, splenic macrophages, and epithelial cells of the renal glomeruli was observed to be enhanced in septic animals. This study documents endothelial cell expression of TF in vivo in a relevant pathological setting. At the same time, compared with endothelial cells in culture, there is in vivo both significantly greater control of TF expression than expected, given the strong positive stimuli present in lethal E. coli septic shock and an unpredicted heterogeneity of activation responses.

Transcription factors (TFs) are major players in gene regulatory networks and interactions between TFs and their target genes furnish spatiotemporal patterns of gene expression. Establishing the architecture of regulatory networks requires gathering information on TFs, their targets in the genome, and the corresponding binding sites. We have developed GRASSIUS (Grass Regulatory Information Services) as a knowledge-based Web resource that integrates information on TFs and gene promoters across the grasses. In its initial implementation, GRASSIUS consists of two separate, yet linked, databases. GrassTFDB holds information on TFs from maize (Zea mays), sorghum (Sorghum bicolor), sugarcane (Saccharum spp.), and rice (Oryza sativa). TFs are classified into families and phylogenetic relationships begin to uncover orthologous relationships among the participating species. This database also provides a centralized clearinghouse for TF synonyms in the grasses. GrassTFDB is linked to the grass TFome collection, which provides clones in recombination-based vectors corresponding to full-length open reading frames for a growing number of grass TFs. GrassPROMDB contains promoter and cis-regulatory element information for those grass species and genes for which enough data are available. The integration of GrassTFDB and GrassPROMDB will be accomplished through GrassRegNet as a first step in representing the architecture of grass regulatory networks. GRASSIUS can be accessed from www.grassius.org.

BACKGROUND

Target genes of a transcription factor (TF) Pou5f1 (Oct3/4 or Oct4), which is essential for pluripotency maintenance and self-renewal of embryonic stem (ES) cells, have previously been identified based on their response to Pou5f1 manipulation and occurrence of Chromatin-immunoprecipitation (ChIP)-binding sites in promoters. However, many responding genes with binding sites may not be direct targets because response may be mediated by other genes and ChIP-binding site may not be functional in terms of transcription regulation.

RESULTS

To reduce the number of false positives, we propose to separate responding genes into groups according to direction, magnitude, and time of response, and to apply the false discovery rate (FDR) criterion to each group individually. Using this novel algorithm with stringent statistical criteria (FDR < 0.2) to a compendium of published and new microarray data (3, 6, 12, and 24 hr after Pou5f1 suppression) and published ChIP data, we identified 420 tentative target genes (TTGs) for Pou5f1. The majority of TTGs (372) were down-regulated after Pou5f1 suppression, indicating that the Pou5f1 functions as an activator of gene expression when it binds to promoters. Interestingly, many activated genes are potent suppressors of transcription, which include polycomb genes, zinc finger TFs, chromatin remodeling factors, and suppressors of signaling. Similar analysis showed that Sox2 and Nanog also function mostly as transcription activators in cooperation with Pou5f1.

CONCLUSIONS

We have identified the most reliable sets of direct target genes for key pluripotency genes - Pou5f1, Sox2, and Nanog, and found that they predominantly function as activators of downstream gene expression. Thus, most genes related to cell differentiation are suppressed indirectly.

The afferent cortical connections of individual cytoarchitectonic areas within the superior temporal sulcus (STS) of the rhesus monkey were studied by retrograde tracer techniques, including double tracer experiments. Rostral superior temporal polysensory (STP) cortex (area TPO-1) receives input from the rostral superior temporal gyrus (STG), cortex of the circular sulcus, and parahippocampal gyrus (PHG) (areas 35, TF, and TL). Mid-STP cortex (areas TPO-2 and -3) has input from the mid-STG, cortex of the mid-circular sulcus, caudal inferior parietal lobule (IPL), cingulate gyrus (areas, 23, 24, retrosplenial cortex), and mid-PHG (areas 28, TF, TH, and TL). Caudal STP cortex (area TPO-4) has afferent connections with the caudal STG, cortex of the caudal insula and caudal circular sulcus, caudal IPL, lower bank of the intraparietal sulcus (IPS), medial parietal lobe, cingulate gyrus, and mid- and caudal PHG (areas TF, TH, TL; prostriate area). The most rostral cortex of the lower bank of the STS (areas TEa and TEm), a presumed visual association area, receives input from the rostral inferotemporal (IT) region; more caudal portions of areas TEa and TEm have afferent connections with the caudal IT region, PHG, preoccipital gyrus, and cortex of the lower bank of the IPS.

Hemostasis initiates angiogenesis-dependent wound healing, and thrombosis is frequently associated with advanced cancer. Although activation of coagulation generates potent regulators of angiogenesis, little is known about how this pathway supports angiogenesis in vivo. Here we show that the tissue factor (TF)-VIIa protease complex, independent of triggering coagulation, can promote tumor and developmental angiogenesis through protease-activated receptor-2 (PAR-2) signaling. In this context, the TF cytoplasmic domain negatively regulates PAR-2 signaling. Mice from which the TF cytoplasmic domain has been deleted (TF Delta CT mice) show enhanced PAR-2-dependent angiogenesis, in synergy with platelet-derived growth factor BB (PDGF-BB). Ocular tissue from diabetic patients shows PAR-2 colocalization with phosphorylated TF specifically on neovasculature, suggesting that phosphorylation of the TF cytoplasmic domain releases its negative regulatory control of PAR-2 signaling in angiogenesis. Targeting the TF-VIIa signaling pathway may thus enhance the efficacy of angiostatic treatments for cancer and neovascular eye diseases.

Severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2) is an emergent pathogen responsible for the coronavirus disease 2019 (COVID-19). Since its emergence, the novel coronavirus has rapidly achieved pandemic proportions causing remarkably increased morbidity and mortality around the world. A hypercoagulability state has been reported as a major pathologic event in COVID-19, and thromboembolic complications listed among life-threatening complications of the disease. Platelets are chief effector cells of hemostasis and pathological thrombosis. However, the participation of platelets in the pathogenesis of COVID-19 remains elusive. This report demonstrates that increased platelet activation and platelet-monocyte aggregates formation is observed in severe COVID-19 patients, but not in patients presenting mild COVID-19 syndrome. In addition, exposure to plasma from severe COVID-19 patients increased the activation of control platelets ex vivo. In our cohort of COVID-19 patients admitted to the ICU, platelet-monocyte interaction was strongly associated with TF expression by the monocytes. Platelet activation and monocyte TF expression were associated with markers of coagulation dysfunction as fibrinogen and D-dimers, and were increased in patients requiring invasive mechanical ventilation or patients that evolved with in-hospital mortality. Finally, platelets from severe COVID-19 patients were able to induce TF expression ex vivo in monocytes from healthy volunteers, a phenomenon that was inhibited by platelet P-selectin neutralization or integrin αIIb/β3 blocking with the aggregation inhibitor abciximab. Altogether, these data shed light on new pathological mechanisms involving platelet activation and platelet-dependent monocyte TF expression, which were associated with COVID-19 severity and mortality.

Mapping transcriptional regulatory networks is difficult because many transcription factors (TFs) are activated only under specific conditions. We describe a generic strategy for identifying genes and pathways induced by individual TFs that does not require knowledge of their normal activation cues. Microarray analysis of 55 yeast TFs that caused a growth phenotype when overexpressed showed that the majority caused increased transcript levels of genes in specific physiological categories, suggesting a mechanism for growth inhibition. Induced genes typically included established targets and genes with consensus promoter motifs, if known, indicating that these data are useful for identifying potential new target genes and binding sites. We identified the sequence 5'-TCACGCAA as a binding sequence for Hms1p, a TF that positively regulates pseudohyphal growth and previously had no known motif. The general strategy outlined here presents a straightforward approach to discovery of TF activities and mapping targets that could be adapted to any organism with transgenic technology.

Transposable elements and their remnants constitute a substantial fraction of eukaryotic genomes. Host genomes have evolved defence mechanisms, including chromatin modifications and RNA interference, to regulate transposable elements. Here we describe a genome surveillance mechanism for retrotransposons by transposase-derived centromeric protein CENP-B homologues of the fission yeast Schizosaccharomyces pombe. CENP-B homologues of S. pombe localize at and recruit histone deacetylases to silence TfTfTf' bodies, the organization of which depends on CENP-Bs that display discrete nuclear structures. Furthermore, CENP-Bs prevent an 'extinct' TfTfTfTf bodies. Our results reveal a probable ancient retrotransposon surveillance pathway important for host genome integrity, and highlight potential conflicts between DNA transposons and retrotransposons, major transposable elements believed to have greatly moulded the evolution of genomes.

Two novel and related C(2)H(2) zinc finger proteins that are highly expressed in the brain, CTIP1 and CTIP2 (COUP TF-interacting proteins 1 and 2, respectively), were isolated and shown to interact with all members of the chicken ovalbumin upstream promoter transcription factor (COUP-TF) subfamily of orphan nuclear receptors. The interaction of CTIP1 with ARP1 was studied in detail, and CTIP1 was found to harbor two independent ARP1 interaction domains, ID1 and ID2, whereas the putative AF-2 of ARP1 was required for interaction with CTIP1. CTIP1, which exhibited a punctate staining pattern within the nucleus of transfected cells, recruited cotransfected ARP1 to these foci and potentiated ARP1-mediated transcriptional repression of a reporter construct. However, transcriptional repression mediated by ARP1 acting through CTIP1 did not appear to involve recruitment of a trichostatin A-sensitive histone deacetylase(s) to the template, suggesting that this repression pathway may be distinct from that utilized by several other nuclear receptors.

Stems of dicotyledonous plants consist of an outer epidermis, a cortex, a ring of secondarily thickened vascular bundles and interfascicular cells, and inner pith parenchyma cells with thin primary walls. It is unclear how the different cell layers attain and retain their identities. Here, we show that WRKY transcription factors are in part responsible for the parenchymatous nature of the pith cells in dicotyledonous plants. We isolated mutants of Medicago truncatula and Arabidopsis thaliana with secondary cell wall thickening in pith cells associated with ectopic deposition of lignin, xylan, and cellulose, leading to an ∼50% increase in biomass density in stem tissue of the Arabidopsis mutants. The mutations are caused by disruption of stem-expressed WRKY transcription factor (TF) genes, which consequently up-regulate downstream genes encoding the NAM, ATAF1/2, and CUC2 (NAC) and CCCH type (C3H) zinc finger TFs that activate secondary wall synthesis. Direct binding of WRKY to the NAC gene promoter and repression of three downstream TFs were confirmed by in vitro assays and in planta transgenic experiments. Secondary wall-bearing cells form lignocellulosic biomass that is the source for second generation biofuel production. The discovery of negative regulators of secondary wall formation in pith opens up the possibility of significantly increasing the mass of fermentable cell wall components in bioenergy crops.

Chromatin immunoprecipitation (ChIP) is a powerful technique to study interactions between transcription factors (TFs) and DNA in vivo. For genome-wide de novo discovery of TF-binding sites, the DNA that is obtained in ChIP experiments needs to be processed for sequence identification. The sequences can be identified by direct sequencing (ChIP-SEQ) or hybridization to microarrays (ChIP-CHIP). Given the small amounts of DNA that are usually obtained in ChIP experiments, successful and reproducible sample processing is challenging. Here we provide a detailed procedure for ChIP of plant TFs, as well as protocols for sample preparation for ChIP-SEQ and for ChIP-CHIP. Our ChIP procedure is optimized for high signal-to-noise ratio starting with tissue fixation, followed by nuclei isolation, immunoprecipitation, DNA amplification and purification. We also provide a guide for primary data analysis of ChIP-SEQ data. The complete protocol for ChIP-SEQ/ChIP-CHIP sample preparation starting from plant harvest takes approximately 7 d.

The chicken ovalbumin upstream promoter-transcription factors (COUP-TFI and II) make up the most conserved subfamily of nuclear receptors that play key roles in angiogenesis, neuronal development, organogenesis, cell fate determination, and metabolic homeostasis. Although the biological functions of COUP-TFs have been studied extensively, little is known of their structural features or aspects of ligand regulation. Here we report the ligand-free 1.48 A crystal structure of the human COUP-TFII ligand-binding domain. The structure reveals an autorepressed conformation of the receptor, where helix alpha10 is bent into the ligand-binding pocket and the activation function-2 helix is folded into the cofactor binding site, thus preventing the recruitment of coactivators. In contrast, in multiple cell lines, COUP-TFII exhibits constitutive transcriptional activity, which can be further potentiated by nuclear receptor coactivators. Mutations designed to disrupt cofactor binding, dimerization, and ligand binding, substantially reduce the COUP-TFII transcriptional activity. Importantly, retinoid acids are able to promote COUP-TFII to recruit coactivators and activate a COUP-TF reporter construct. Although the concentration needed is higher than the physiological levels of retinoic acids, these findings demonstrate that COUP-TFII is a ligand-regulated nuclear receptor, in which ligands activate the receptor by releasing it from the autorepressed conformation.

Two fundamental aspects of plant development are the maturation phase of embryo development in seed plants and totipotency via somatic embryogenesis (SE). The LEAFY COTYLEDON (LEC) transcription factors (TFs) establish environments that promote cellular processes characteristic of the maturation phase and the initiation of somatic embryo formation. Based on recent studies, we and others propose that specific target genes activated by the LEC TFs underlie, in part, their roles in the maturation phase and SE. We also propose that the effect of LEC TFs on the balance of abscisic acid to gibberellic acid might link their roles in totipotency and the maturation phase.

Tissue factor (TF) encryption is the post-translational suppression of TF procoagulant activity (PCA) on the cell surface. There is emerging evidence of encrypted TF in normal blood associated with monocytes and platelets. Expression of this latent TF PCA during the propagation phase of blood coagulation may contribute to hemostasis. One pathway leading to the decryption of TF PCA begins with an increase in cytosolic calcium. A large calcium influx triggers both the exposure of phosphatidylserine and the expression of TF PCA on cell surfaces. The connections between these events are reviewed along with evidence that lipid raft association may also contribute to TF encryption. The last step in the decryption of TF PCA is the proteolytic activation of zymogen factor VII. This event may be a key to understanding the different roles of intravascular and extravascular TF in the process of blood coagulation.

Aberrant expression of microRNAs has been recently associated with chronic lymphocytic leukemia (CLL) outcome. Although disease evolution can be predicted by several prognostic factors, a better outcome individualization in a given patient is still of utmost interest. Here, we showed that miR-29c and miR-223 expression levels decreased significantly with progression from Binet stage A to C were significantly lower in poor prognostic subgroups (defined by several prognostic factors) and could significantly predict treatment-free survival (TFS) and overall survival (OS). Furthermore, we developed a quantitative real-time polymerase chain reaction (qPCR) score combining miR-29c, miR-223, ZAP70, and LPL (from 0 to 4 poor prognostic markers) to stratify treatment and death risk in a cohort of 110 patients with a median follow-up of 72 months (range, 2-312). Patients with a score of 0/4, 1/4, 2/4, 3/4, and 4/4 had a median TFS of greater than 312, of 129, 80, 36, and 19 months, respectively (hazard ratio, HR(0/4 < 1/4 < 2/4 < 3/4 < 4/4) = 17.00, P < .001). Patients with a score of 0-1/4, 2-3/4, and 4/4 had a median OS of greater than 312, of 183 and 106 months, respectively (HR(0/4 < 1/4 < 2/4 < 3/4 < 4/4) = 13.69, P = .001). This score will help to identify, among the good and poor prognosis subgroups, patients who will need early therapy and thus will require a closer follow-up.

TRPM2 is a Ca(2+)-permeable channel that is activated by oxidative stress and confers susceptibility to cell death. Here, an isoform of TRPM2 was identified in normal human bone marrow that consists of the TRPM2 N terminus and the first two predicted transmembrane domains. Because of alternative splicing, a stop codon (TAG) is located at the splice junction between exons 16 and 17, resulting in deletion of the four C-terminal transmembrane domains, the putative calcium-permeable pore region, and the entire C terminus. This splice variant was found in other hematopoietic cells including human burst forming unit-erythroid-derived erythroblasts and TF-1 erythroleukemia cells. Endogenous expression of both the short form of TRPM2 (TRPM2-S) and the full length (TRPM2-L) was determined by reverse transcriptase-PCR, and localization of endogenous TRPM2 to the plasma membrane was demonstrated by confocal microscopy. Heterologous expression of TRPM2-S in HEK 293T cells demonstrated similar membrane localization as TRPM2-L, and coexpression of TRPM2-S did not alter the subcellular localization of TRPM2-L. The direct interaction of TRPM2-S with TRPM2-L was demonstrated with immunoprecipitation. H(2)O(2) induced calcium influx through TRPM2-L expressed in 293T cells. Coexpression of TRPM2-S suppressed H(2)O(2)-induced calcium influx through TRPM2-L. Furthermore, expression of TRPM2-S inhibited susceptibility to cell death and onset of apoptosis induced by H(2)O(2) in cells expressing TRPM2-L. These data demonstrate that TRPM2-S is an important physiologic isoform of TRPM2 and modulates channel activity and induction of cell death by oxidative stress through TRPM2-L.