A Combinatorial Code for CPEB-Mediated c-myc Repression

During early embryonic development, the RNA-binding protein CPEB mediates cytoplasmic polyadenylation and translational activation through a combinatorial code defined by the cy-toplasmic polyadenylation element (CPE) present in maternal mRNAs. However, in non-neuronal somatic cells, CPEB accelerates deadenylation to repress translation of the target, including c-myc mRNA, through an ill-defined cis-regulatory mechanism. Using RNA mutagenesis and electrophoretic mobility shift assays, we demonstrated that a combination of tandemly arranged consensus (cCPE) and non-consensus (ncCPE) cytoplasmic polyadenylation elements (CPEs) constituted a combinatorial code for CPEB-mediated c-myc mRNA decay. CPEB binds to cCPEs with high affinity (Kd = ~250 nM), whereas it binds to ncCPEs with low affinity (Kd > ~900 nM). CPEB binding to a cCPE enhances CPEB binding to the proximal ncCPE. In contrast, while a cCPE did not activate mRNA degradation, an ncCPE was essential for the induction of degradation, and a combination of a cCPE and ncCPEs further promoted degradation. Based on these findings, we propose a model in which the high-affinity binding of CPEB to the cCPE accelerates the binding of the second CPEB to the ncCPEs, resulting in the recruitment of deadenylases, acceleration of deadenylation, and repression of c-myc mRNAs.

TUG1-mediated R-loop resolution at microsatellite loci as a prerequisite for cancer cell proliferation

Oncogene-induced DNA replication stress (RS) and consequent pathogenic R-loop formation are known to impede S phase progression. Nonetheless, cancer cells continuously proliferate under such high-stressed conditions through incompletely understood mechanisms. Here, we report taurine upregulated gene 1 (TUG1) long noncoding RNA (lncRNA), which is highly expressed in many types of cancers, as an important regulator of intrinsic R-loop in cancer cells. Under RS conditions, TUG1 is rapidly upregulated via activation of the ATR-CHK1 signaling pathway, interacts with RPA and DHX9, and engages in resolving R-loops at certain loci, particularly at the CA repeat microsatellite loci. Depletion of TUG1 leads to overabundant R-loops and enhanced RS, leading to substantial inhibition of tumor growth. Our data reveal a role of TUG1 as molecule important for resolving R-loop accumulation in cancer cells and suggest targeting TUG1 as a potent therapeutic approach for cancer treatment.

Protocol for analyzing intact mRNA poly(A) tail length using nanopore direct RNA sequencing

Poly(A) tail metabolism contributes to post-transcriptional regulation of gene expression. Here, we present a protocol for analyzing intact mRNA poly(A) tail length using nanopore direct RNA sequencing, which excludes truncated RNAs from the measurement. We describe steps for preparing recombinant eIF4E mutant protein, purifying m7G- capped RNAs, library preparation, and sequencing. Resulting data can be used not only for expression profiling and poly(A) tail length estimation but also for detecting alternative splicing and polyadenylation events and RNA base modification. For complete details on the use and execution of this protocol, please refer to Ogami et al. (2022).¹.

Systematic characterization of seed overlap microRNA cotargeting associated with lupus pathogenesis

BACKGROUND

Combinatorial gene regulation by multiple microRNAs (miRNAs) is widespread and closely spaced target sites often act cooperatively to achieve stronger repression ("neighborhood" miRNA cotargeting). While miRNA cotarget sites are suggested to be more conserved and implicated in developmental control, the pathological significance of miRNA cotargeting remains elusive.

RESULTS

Here, we report the pathogenic impacts of combinatorial miRNA regulation on inflammation in systemic lupus erythematosus (SLE). In the SLE mouse model, we identified the downregulation of two miRNAs, miR-128 and miR-148a, by TLR7 stimulation in plasmacytoid dendritic cells. Functional analyses using human cell lines demonstrated that miR-128 and miR-148a additively target KLF4 via extensively overlapping target sites ("seed overlap" miRNA cotargeting) and suppress the inflammatory responses. At the transcriptome level, "seed overlap" miRNA cotargeting increases susceptibility to downregulation by two miRNAs, consistent with additive but not cooperative recruitment of two miRNAs. Systematic characterization further revealed that extensive "seed overlap" is a prevalent feature among broadly conserved miRNAs. Highly conserved target sites of broadly conserved miRNAs are largely divided into two classes-those conserved among eutherian mammals and from human to Coelacanth, and the latter, including KLF4-cotargeting sites, has a stronger association with both "seed overlap" and "neighborhood" miRNA cotargeting. Furthermore, a deeply conserved miRNA target class has a higher probability of haplo-insufficient genes.

CONCLUSIONS

Our study collectively suggests the complexity of distinct modes of miRNA cotargeting and the importance of their perturbations in human diseases.

Nuclear RNA Exosome and Pervasive Transcription: Dual Sculptors of Genome Function

The genome is pervasively transcribed across various species, yielding numerous non-coding RNAs. As a counterbalance for pervasive transcription, various organisms have a nuclear RNA exosome complex, whose structure is well conserved between yeast and mammalian cells. The RNA exosome not only regulates the processing of stable RNA species, such as rRNAs, tRNAs, small nucleolar RNAs, and small nuclear RNAs, but also plays a central role in RNA surveillance by degrading many unstable RNAs and misprocessed pre-mRNAs. In addition, associated cofactors of RNA exosome direct the exosome to distinct classes of RNA substrates, suggesting divergent and/or multi-layer control of RNA quality in the cell. While the RNA exosome is essential for cell viability and influences various cellular processes, mutations and alterations in the RNA exosome components are linked to the collection of rare diseases and various diseases including cancer, respectively. The present review summarizes the relationships between pervasive transcription and RNA exosome, including evolutionary crosstalk, mechanisms of RNA exosome-mediated RNA surveillance, and physiopathological effects of perturbation of RNA exosome.

Widespread transcript shortening through alternative polyadenylation in secretory cell differentiation

Most eukaryotic genes produce alternative polyadenylation (APA) isoforms. Here we report that, unlike previously characterized cell lineages, differentiation of syncytiotrophoblast (SCT), a cell type critical for hormone production and secretion during pregnancy, elicits widespread transcript shortening through APA in 3'UTRs and in introns. This global APA change is observed in multiple in vitro trophoblast differentiation models, and in single cells from placentas at different stages of pregnancy. Strikingly, the transcript shortening is unrelated to cell proliferation, a feature previously associated with APA control, but instead accompanies increased secretory functions. We show that 3'UTR shortening leads to transcripts with higher mRNA stability, which augments transcriptional activation, especially for genes involved in secretion. Moreover, this mechanism, named secretion-coupled APA (SCAP), is also executed in B cell differentiation to plasma cells. Together, our data indicate that SCAP tailors the transcriptome during formation of secretory cells, boosting their protein production and secretion capacity.

Efficient differentiation and purification of human induced pluripotent stem cell-derived endothelial progenitor cells and expansion with the use of inhibitors of ROCK, TGF-β, and GSK3β

Endothelial cells (ECs) and endothelial progenitor cells (EPCs) play crucial roles in maintaining vascular health and homeostasis. Both cell types have been used in regenerative therapy as well as in various in vitro models; however, the properties of primary human ECs and EPCs are dissimilar owing to differences in genetic backgrounds and sampling techniques. Human induced pluripotent stem cells (hiPSCs) are an alternative cell source of ECs and EPCs. However, owing to the low purity of differentiated cells from hiPSCs, purification via an antigen–antibody reaction, which damages the cells, is indispensable. Besides, owing to limited expandability, it is difficult to produce these cells in large numbers. Here we report the development of relatively simple differentiation and purification methods for hiPSC-derived EPCs (iEPCs). Furthermore, we discovered that a combination of three small molecules, that is, Y-27632 (a selective inhibitor of Rho-associated, coiled-coil containing protein kinase [ROCK]), A 83–01 (a receptor-like kinase inhibitor of transforming growth factor beta [TGF-β]), and CHIR-99021 (a selective inhibitor of glycogen synthase kinase-3β [GSK3β] that also activates Wnt), dramatically stimulated protein synthesis-related pathways and enhanced the proliferative capacity of iEPCs. These findings will help to establish a supply system of EPCs at an industrial scale.

The RNA-binding protein QKI-7 recruits the poly(A) polymerase GLD-2 for 3' adenylation and selective stabilization of microRNA-122

MicroRNA-122 (miR-122) is highly expressed in hepatocytes, where it plays an important role in regulating cholesterol and fatty acid metabolism, and it is also a host factor required for hepatitis C virus replication. miR-122 is selectively stabilized by 3' adenylation mediated by the cytoplasmic poly(A) polymerase GLD-2 (also known as PAPD4 or TENT2). However, it is unclear how GLD-2 specifically stabilizes miR-122. Here, we show that QKI7 KH domain-containing RNA binding (QKI-7), one of three isoforms of the QKI proteins, which are members of the signal transduction and activation of RNA (STAR) family of RNA-binding proteins, is involved in miR-122 stabilization. QKI down-regulation specifically decreased the steady-state level of mature miR-122, but did not affect the pre-miR-122 level. We also found that QKI-7 uses its C-terminal region to interact with GLD-2 and its QUA2 domain to associate with the RNA-induced silencing complex protein Argonaute 2 (Ago2), indicating that the GLD-2-QKI-7 interaction recruits GLD-2 to Ago2. QKI-7 exhibited specific affinity to miR-122 and significantly promoted GLD-2-mediated 3' adenylation of miR-122 in vitro Taken together, our findings indicate that miR-122 binds Ago2-interacting QKI-7, which recruits GLD-2 for 3' adenylation and stabilization of miR-122.

A novel method for stabilizing microRNA mimics

MicroRNAs (miRNAs) are a class of small non-coding RNAs that negatively regulate gene expression at post-transcriptional level via translational repression and/or mRNA degradation. miRNAs are associated with many cellular processes, and down-regulation of miRNAs causes numerous diseases including cancer, neurological disorders, inflammation, and cardiovascular diseases, for which miRNA replacement therapy has emerged as a promising approach. This approach aims to restore down-regulated miRNAs using synthetic miRNA mimics. However, it remains a critical issue that miRNA mimics are unstable and transient in cells. Here, we first show that miRNA mimics are rapidly degraded by a mechanism different from Tudor-staphylococcal/micrococcal-like nuclease (TSN)-mediated miRNA decay, which degrades endogenous miRNAs, and newly identified 2'-5'-oligoadenylate synthetase (OAS)/RNase L as key factors responsible for the degradation of miRNA mimics in human cells. Our results suggest that the OAS1 recognizes miRNA mimics and produces 2'-5'-oligoadenylates (2-5A), which leads to the activation of latent endoribonuclease RNase L to degrade miRNA mimics. A small-molecule inhibitor that blocks RNase L can stabilize miRNA mimics. These findings provide a promising method for the stabilization of miRNA mimics, as well as for the efficient miRNA replacement therapy.

NRDE-2, the human homolog of fission yeast Nrl1, prevents DNA damage accumulation in human cells

The RNA helicase Mtr4 is a versatile protein that is a crucial component of several distinct RNA surveillance complexes. Here we describe a novel complex that contains Mtr4, but has a role distinct from any of those previously described. We found that Mtr4 association with the human homolog of fission yeast Nrl1, NRDE-2, defines a novel function for Mtr4 in the DNA damage response pathway. We provide biochemical evidence that Mtr4 and NRDE-2 are part of the same complex and show that both proteins play a role in the DNA damage response by maintaining low DNA double-strand break levels. Importantly, the DNA damage response function of the Mtr4/NRDE-2 complex does not depend on the formation of R loops. We show however that NRDE-2 and Mtr4 can affect R-loop signals at a subset of distinct genes, possibly regulating their expression. Our work not only expands the wide range of Mtr4 functions, but also elucidates an important role of the less characterized human NRDE-2 protein.

MicroRNP-mediated translational activation of nonadenylated mRNAs in a mammalian cell-free system

MicroRNAs are small noncoding RNAs that regulate translation and mRNA stability by binding target mRNAs in complex with Argonaute (AGO) proteins. AGO interacts with a member of the TNRC6 family proteins to form a microRNP complex, which recruits the CCR4-NOT complex to accelerate deadenylation and inhibits translation. MicroRNAs primarily repress translation of target mRNAs but have been shown to enhance translation of a specific type of target reporter mRNAs in various experimental systems: G0 quiescent mammalian cells, Xenopus laevis oocytes, Drosophila embryo extracts, and HeLa cells. In all of the cases mentioned, a common feature of the activated target mRNAs is the lack of a poly(A) tail. Here, we show let-7-microRNP-mediated translational activation of nonadenylated target mRNAs in a mammalian cell-free system, which contains over-expressed AGO2, TNRC6B, and PAPD7 (TUTase5, TRF4-1). Importantly, translation of nonadenylated mRNAs was activated also by tethered TNRC6B silencing domain (SD), in the presence of PAPD7. Deletion of the poly(A)-binding protein (PABP) interacting motif (PAM2) from the TNRC6B-SD abolished the translational activation, suggesting the involvement of PABP in the process. Similar results were also obtained in cultured HEK293T cells. This work may provide novel insights into microRNP-mediated mRNA regulation.

RBBP6 isoforms regulate the human polyadenylation machinery and modulate expression of mRNAs with AU-rich 3' UTRs

Campigli Di Giammartino et al. find that RBBP6 is a component of a large multisubunit protein complex that mediates polyadenylation of mRNA precursors. Genome-wide analyses following RBBP6 knockdown revealed decreased transcript levels, especially of mRNAs with AU-rich 3′ UTRs such as c-Fos and c-Jun, and increased usage of distal poly(A) sites.

Polyadenylation of mRNA precursors is mediated by a large multisubunit protein complex. Here we show that RBBP6 (retinoblastoma-binding protein 6), identified initially as an Rb- and p53-binding protein, is a component of this complex and functions in 3′ processing in vitro and in vivo. RBBP6 associates with other core factors, and this interaction is mediated by an unusual ubiquitin-like domain, DWNN (“domain with no name”), that is required for 3′ processing activity. The DWNN is also expressed, via alternative RNA processing, as a small single-domain protein (isoform 3 [iso3]). Importantly, we show that iso3, known to be down-regulated in several cancers, competes with RBBP6 for binding to the core machinery, thereby inhibiting 3′ processing. Genome-wide analyses following RBBP6 knockdown revealed decreased transcript levels, especially of mRNAs with AU-rich 3′ untranslated regions (UTRs) such as c-Fos and c-Jun, and increased usage of distal poly(A) sites. Our results implicate RBBP6 and iso3 as novel regulators of 3′ processing, especially of RNAs with AU-rich 3′ UTRs.

Antiproliferative protein Tob directly regulates c-myc proto-oncogene expression through cytoplasmic polyadenylation element-binding protein CPEB

The regulation of mRNA deadenylation constitutes a pivotal mechanism of the post-transcriptional control of gene expression. Here we show that the antiproliferative protein Tob, a component of the Caf1-Ccr4 deadenylase complex, is involved in regulating the expression of the proto-oncogene c-myc. The c-myc mRNA contains cis elements (CPEs) in its 3'-untranslated region (3'-UTR), which are recognized by the cytoplasmic polyadenylation element-binding protein (CPEB). CPEB recruits Caf1 deadenylase through interaction with Tob to form a ternary complex, CPEB-Tob-Caf1, and negatively regulates the expression of c-myc by accelerating the deadenylation and decay of its mRNA. In quiescent cells, c-myc mRNA is destabilized by the trans-acting complex (CPEB-Tob-Caf1), while in cells stimulated by the serum, both Tob and Caf1 are released from CPEB, and c-Myc expression is induced early after stimulation by the stabilization of its mRNA as an 'immediate-early gene'. Collectively, these results indicate that Tob is a key factor in the regulation of c-myc gene expression, which is essential for cell growth. Thus, Tob appears to function in the control of cell growth at least, in part, by regulating the expression of c-myc.

Thrombopoietin stimulates proliferation and megakaryocytic differentiation of mouse pro-B cell line BF-TE22

We have isolated and characterized a thrombopoietin (TPO)-dependent BF-TE22 cell line endogenously expressing murine Mpl, which is a subclone of murine pro-B Ba/F3 cells. TPO stimulated the proliferation of BF-TE22 cells in a dose-dependent manner, and also induced the expression of megakaryocyte lineage-specific AP-51 and CD61 cell surface antigens. The results indicate that the murine Mpl on BF-TE22 cells can transmit both proliferation and megakaryocyte lineage-specific differentiation signals to cells. Furthermore, it was shown that IL-3 inhibits the TPO-induced differentiation signals of BF-TE22 cells. These results suggest that the signals mediated by IL-3 predominate over those of TPO in BF-TE22 cells. Thus, BF-TE22 cells will be useful for the biological and biochemical studies of the TPO-Mpl signal transduction mechanism.

Reduction of osteocalcin expression in aged human dental pulp

AIM

To investigate the expression of osteocalcin mRNA in young and in aged human dental pulp tissue to determine the characteristics of osteocalcin expression.

METHODOLOGY

Human dental pulp tissues of the third molars were obtained from healthy young (17-23 years) and aged (>50 years) subjects, and total RNA was extracted. Osteocalcin mRNA expression was determined by RT-PCR and by quantitative real-time RT-PCR (QRT-PCR). The threshold cycle (Ct) value, which reflects the amount of PCR, was calculated and the difference between the value in young and aged pulp was statistically analysed.

RESULTS

Osteocalcin mRNA was detected in all samples of human dental pulp tissue homogenates by RT-PCR analysis. Osteocalcin mRNA was expressed in young adult dental pulp but was decreased in aged human dental pulp. QRT-PCR analysis also showed a reduced expression of osteocalcin mRNA in aged human pulp. Expression of osteocalcin in young human pulp was significantly higher (about sixfold) than in aged pulp (P<0.01, Mann-Whitney U-test).

CONCLUSION

Reduction of osteocalcin expression may be associated with the loss of viability in human dental pulp tissue, and may be a characteristic of aged human dental pulps.

Reduction of connexin 43 expression in aged human dental pulp

AIM

To investigate the expression of connexin 43 (CX43) mRNA in young and old human dental pulp tissues to determine the characteristics of CX43 expression.

METHODOLOGY

Samples were obtained from human dental pulp of healthy young (17-23 years) and aged (>50 years) subjects. CX43 expression was determined by RT-PCR and by quantitative real-time RT-PCR (QRT-PCR). The threshold cycle (Ct) value, which reflects the amount of PCR, was calculated and the difference between value in the young pulp and that in the aged pulp was statistically analysed.

RESULTS

RT-PCR analysis of human dental pulp tissue detected CX43 mRNA in all the samples. CX43 was abundantly expressed in young adult dental pulp, but expression of CX43 mRNA was dramatically decreased in aged human dental pulp. QRT-PCR analysis also showed the reduced expression of CX43 in aged pulp, and expression of CX43 in young pulp was significantly higher (about 10-fold, P < 0.01, Mann-Whitney U-test).

CONCLUSION

Reduction of CX43 expression may be associated with the loss of viability in human dental pulp, and is considered as one characteristic of aged pulp.

A method of measuring salivary flow rate in the lower labial mucosal region

To measure resting whole saliva, draining and spitting methods have been commonly used. However, these methods require the patients' understanding and cooperation. The aim of this study was to establish a method for measuring the salivary flow rate that does not rely on patient's cooperation or the state of the mouth and does not cause any discomfort to patients when performing the measurements. The salivary flow rate in the lower labial mucosal region was measured by means of strips that incorporated the iodo-starch reaction. The salivary flow rate was then calculated on the basis of the number of spots and area of discoloration on the strip. In order to test the validity of these methods, the correlation between these results and resting whole saliva measured by the draining method was also investigated. A positive correlation was found between the salivary flow rate estimated from the area of discoloration on the strip and the resting whole saliva (r=0.678, P=0.01). Therefore, these findings indicate that this is a valid method of measuring the salivary flow rate in the lower labial mucosal region.

Severe autoimmune thrombocytopenia after allogeneic bone marrow transplantation for aplastic anemia

Autoimmune thrombocytopenia (AITP) after bone marrow transplantation (BMT) was suggested to occur by immune dysregulation mainly in association with graft-versus-host disease (GVHD). Here we present a patient who developed severe AITP after BMT. A 40-year-old woman with severe aplastic anemia received a BMT from a partially HLA-matched brother. Despite myeloid and erythroid engraftments, platelet recovery was delayed. All bone marrow cells were 46,XY and were derived from the donor. Grade I acute GVHD involving skin developed from day 34 posttransplantation, but promptly responded to prednisolone in addition to a prophylactic dose of tacrolimus. With the tapering of prednisolone, thrombocytopenia progressed without substantial changes in the white blood cell count, hemoglobin concentration, or reticulocyte count. On day 188, the patient developed chronic GVHD involving skin and liver, which promptly responded to the readministration of prednisolone and increased tacrolimus. However, the patient's platelet count decreased to 9 x 10(9) cells/L on day 222. The platelet-associated immunoglobulin G (PAIgG) values were elevated. Bone marrow examination showed hypercellularity with plentiful megakaryocytes. The number of colony-forming units-megakaryocyte was within the normal range. The elevated PAIgG values and a correlation between thrombocytopenia and the intensity of the immunosuppressive agents strongly suggested a causative role of the autoimmune mechanisms for thrombocytopenia in this patient.

Native thrombopoietin: structure and function

Thrombopoietin (TPO), the c-Mpl ligand, is produced constitutively in liver and other organs, circulates in the bloodstream, and is delivered to bone marrow, where it stimulates the early development of multiple hematopoietic lineages and megakaryocytopoiesis. The concentration of TPO in blood is regulated by c-Mpl mass on platelets and megakaryocytes. In addition to regulation by the number of TPO molecules, including the possible modulation of TPO mRNA abundance in bone marrow, megakaryocytopoiesis and platelet production may be regulated as a result of modulation of TPO activity by proteolytic processing that generates truncated forms of the molecule. Characterization of TPO partially purified from human plasma, however, revealed that the full-length molecule was the predominant form in the blood of both normal individuals and thrombocytopenic patients, although small amounts of truncated species were detected. Thus, truncation of TPO, at least that in the circulation examined, does not appear to contribute to the direct regulation of platelet production in response to increased demand. Given that native TPO isolated from the plasma of thrombocytopenic animals comprises truncated forms, the truncation of TPO is likely of physiological importance in the life history of this molecule.

Gene expression and transcriptional regulation of thrombopoietin

Thrombopoietin (TPO) is predominantly expressed in the liver among various tissues that express TPO transcripts. To investigate the transcriptional regulation of the human TPO gene in the liver, we determined the major transcription initiation site by means of 5'-RACE and Northern blotting. From these analyses, we concluded that TPO gene transcription started at various points, and the transcription initiation sites of the human TPO gene were localized downstream, close to a point we determined by S1 nuclease mapping. The human TPO promoter region contains consensus sequences of GATA, Evi-1, and Ets binding sites. We used the hepatocellular carcinoma cell line, HepG2, that expresses TPO mRNA to analyze its promoter activity by transfecting various reporter plasmids containing a sequentially 5'-deleted human TPO promoter. Although GATA binding factors increased the promoter activity, their effect was independent of the GATA binding consensus sequence. On the other hand, Evi-1 did not affect transcription. Moreover, we defined the core promoter region, in which an Ets binding consensus sequence was located. The deletion or mutation of the Ets binding site resulted in a loss of the promoter activity. These results suggested that TPO is regulated by the Ets family of transcription factors.

Stressful delivery influences circulating thrombopoietin (TPO) levels in newborns: possible role for cortisol in TPO-mpl binding

The regulation mechanism of circulating thrombopoietin (TPO) level in human newborns remains unknown. In the present study, we examined whether the TPO concentrations in cord blood were influenced by the difference in the delivery method and the presence or absence of maternal/fetal complications. Cortisol levels were simultaneously measured to assess the adrenal response of fetuses. Both the TPO level and the cortisol level were substantially greater in the neonates delivered vaginally with and without the complications than in those delivered by cesarean section without the complications. The binding assay showed that the incubation of mpl(+)/BaF3 cells with cortisol gave rise to a significant decrease in the binding sites of TPO. These results suggest that the stress to the fetuses near the time of delivery affects the cord blood TPO levels, which may be mediated in part by the action of cortisol on the TPO-mpl binding system.

Functional analysis of the C-terminal region of recombinant human thrombopoietin. C-terminal region of thrombopoietin is a "shuttle" peptide to help secretion

Thrombopoietin (TPO) is a cytokine that primarily stimulates megakaryocytopoiesis and thrombopoiesis. TPO has a unique C-terminal tail peptide of about 160 amino acids that consists mostly of hydrophilic residues and contains six N-linked sugar chains. In order to investigate the biological function of the C-terminal domain, two series of mutations were performed. One is systematic truncation from the C terminus. Another is elimination of N-glycosylation sites in the C-terminal domain by Asn to Gln mutations. After the mutant proteins were expressed by mammalian cells, it was found that the elimination of the N-linked sugar sites did not affect the biological activity, whereas truncation of the C-terminal domain resulted in elevation of in vitro activity up to 4-fold. The C-terminal peptide itself was found to inhibit the in vitro activity. Moreover, both the C-terminal truncation and the elimination of the N-glycosylation sites decreased the secretion level progressively down to (1)/(10) that of wild type, and the amount of the mutant left in the cell increased. The N-glycosylation in the C-terminal region was found to be important for secretion of TPO. Among six N-glycosylation sites in the C-terminal region, two locations, Asn-213 and Asn-234, were found to be critical for secretion, and two other locations, Asn-319 and Asn-327, did not affect the secretion.

The effect of granulocyte colony-stimulating factor administration in healthy donors before bone marrow harvesting

To investigate whether granulocyte colony-stimulating factor (G-CSF) administration to donors before harvest may lighten the burden imposed on them and accelerate the bone marrow (BM) recovery, we administered 2 microgram/kg/d of G-CSF for five consecutive days before the marrow harvest. All of the donors tolerated the G-CSF administration well without severe adverse events. After 5 d of G-CSF treatment, CD34+ cells and granulocyte-macrophage colony-forming units (GM-CFU) in the donors' BM exceeded baseline values by 4.2-fold (range 0.71-316) and 1.6-fold (0.28-118) respectively. The concentration of total nucleated cells (x 107/ml) in the graft increased from 1.61 (0.95-3.23) to 2.44 (1.27-4.01). Although we collected 1020 ml of BM and obtained 1.50 x 1010 nucleated cells from unprimed donors, 940 ml of BM were sufficient to obtain 2.14 x 1010 nucleated cells from primed donors. However, G-CSF-primed BM did not shorten the time to tri-lineage engraftment and the duration of hospitalization compared with unprimed BM, although primed BM contained more CD34+ cells than baseline values. We consider that the advantages of BM priming are not the acceleration of BM recovery but rather the reduction of blood loss during BM harvesting.

Characterization of native human thrombopoietin in the blood of normal individuals and of patients with haematologic disorders

Thrombopoietin (TPO) isolated from thrombocytopenic plasma of various animal species has previously been shown to comprise only truncated forms of the molecule, presumably generated by proteolysis. Native TPO has now been partially purified from normal human plasma by immunoaffinity chromatography and was confirmed to be biologically active. Gel filtration in the presence of SDS revealed that TPO eluted in two peaks: a major peak corresponding to the elution position of fully glycosylated recombinant human TPO (rhTPO) consisting of 332 amino acid residues, and a minor peak corresponding to a smaller molecular size. Immunoblot analysis also revealed that most plasma-derived TPO migrated at the same position as fully glycosylated rhTPO, corresponding to a molecular size of approximately 80 to 100 kDa. Furthermore, the size distribution of circulating TPO in patients with various haematologic disorders did not differ markedly from that of plasma-derived TPO from healthy individuals. These results indicate that the truncation of circulating TPO is not related to disease pathophysiology, and that the predominant form of TPO in blood is a biologically active approximately 80- to 100-kDa species. The size distribution of TPO extracted from normal platelets was similar to that of TPO in plasma; the proportion of truncated TPO was decreased by prior incubation of platelets with hirudin. indicating that the endogenous truncated TPO, at least in platelet extract, was generated by thrombin-mediated cleavage.

Apoptosis of erythroid precursors under stimulation with thrombopoietin: contribution to megakaryocytic lineage choice

Although the effect of thrombopoietin (TPO) on megakaryocyte production is well established, its role in the commitment of multipotential hematopoietic progenitors to the megakaryocytic lineage remains to be determined. In the present study, we attempted to clarify the determination process of megakaryocytic lineage as a terminal differentiation pathway under stimulation with TPO. Day 7 cultured cells grown by TPO derived from cord blood CD34+ cells were divided into four subpopulations on the basis of CD34 and CD41 expression. The CD34-/CD41- cells showed the labeling pattern of anti-CD42b and anti-CD9 antibodies closer to that of the CD34+/CD41- cells than the CD34+/CD41+ cells. Replating experiments revealed that approximately 40% of the CD34-/CD41- cells proliferated in response to a combination of growth factors, and more than 80% of them were pure erythroid precursors. However, this subpopulation failed to grow/survive and fell into apoptosis in the presence of TPO alone. In contrast, the CD34+/CD41+ cells, which predominantly contained megakaryocytic precursors, exerted a low but significant proliferative potential in the presence of TPO. The insufficient response to TPO of the CD34-/CD41- cells may result from the apparently low expression of c-MpI, as determined by flow cytometric analysis and reverse transcription-polymerase chain reaction analysis. Therefore, these results suggest that the apoptosis of hematopoietic precursors other than megakaryocytic precursors is related to the determination of the terminal differentiation under the influence of TPO.

IL-2/LAK therapy for refractory acute monoblastic leukemia relapsing after unrelated allogeneic bone marrow transplantation

Leukemia relapse is a major cause of treatment failure after allogeneic bone marrow transplantation. We administered recombinant interleukin-2 (rIL-2) to a patient who relapsed after unrelated allogeneic bone marrow transplantation (uBMT). While the number of peripheral blood monoblastic leukemia cells increased after administration of rIL-2, the patient achieved durable remission for 5 months after low-dose chemotherapy followed by adoptive transfer of engrafted graft-derived lymphokine-activated killer (LAK) cells. Following the disappearance of the blast cells, however, both cutaneous and liver GVHD were exacerbated. Administration of rIL-2 and adoptive transfer of graft-derived LAK cells are considered to be possible choices for the treatment of acute leukemia relapsing after uBMT when donor leukocyte transfusion is not available.

Mobilization of primitive haemopoietic progenitor cells and stem cells with long-term repopulating ability into peripheral blood in mice by pegylated recombinant human megakaryocyte growth and development factor

We investigated in detail the effect of pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) on peripheral blood progenitor cell (PBPC) mobilization in male BDF1 mice. Treatment with PEG-rHuMGDF for 5 d stimulated a striking expansion of the circulating levels of multiple types of colony-forming units in culture (CFU-c), including CFU-granulocyte-macrophage, CFU-megakaryocyte, burst-forming units-erythroid, and multipotent CFU-c, and primitive day-12 CFU-spleen. All of these progenitors were mobilized into the peripheral blood (PB) with similar kinetics; their numbers peaked after the cessation of treatment and then declined earlier than platelet numbers peaked. The maximal increase in any of the four CFU-c in the PB was attained with at least 300 microg/kg/d of PEG-rHuMGDF, whereas peripheral platelet counts plateaued at 30 microg/kg/d. Adoptive transfer with PB from PEG-rHuMGDF-treated donor mice resulted in greater survival of lethally irradiated recipients. The majority of the recipients that survived at 187 d after transplantation with PEG-rHuMGDF-mobilized PB showed significant donor engraftment at the progenitor cell level. The combined administration of appropriate doses of PEG-rHuMGDF and recombinant human granulocyte colony-stimulating factor induced a synergistic increase in the circulating levels of the four CFU-c compared to either factor alone. These results indicate that PEG-rHuMGDF as a single agent can mobilize a full spectrum of PBPCs in mice.

Native thrombopoietin: structure and function

Thrombopoietin (TPO), the c-Mpl ligand, is produced constitutively in liver and other organs, circulates in the bloodstream, and is delivered to bone marrow, where it stimulates the early development of multiple hematopoietic lineages and megakaryocytopoiesis. The concentration of TPO in blood is regulated by c-Mpl mass on platelets and megakaryocytes. In addition to regulation by the number of TPO molecules, including the possible modulation of TPO mRNA abundance in bone marrow, megakaryocytopoiesis and platelet production may be regulated as a result of modulation of TPO activity by proteolytic processing that generates truncated forms of the molecule. Characterization of TPO partially purified from human plasma, however, revealed that the full-length molecule was the predominant form in the blood of both normal individuals and thrombocytopenic patients, although small amounts of truncated species were detected. Thus, truncation of TPO, at least that in the circulation examined, does not appear to contribute to the direct regulation of platelet production in response to increased demand. Given that native TPO isolated from the plasma of thrombocytopenic animals comprises truncated forms, the truncation of TPO is likely of physiological importance in the life history of this molecule.

Thrombopoietin enhances the production of myeloid cells, but not megakaryocytes, in juvenile chronic myelogenous leukemia

We previously reported the aberrant growth of granulocyte-macrophage (GM) progenitors induced by a combination of stem cell factor (SCF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) in juvenile chronic myelogenous leukemia (JCML). We examined here the effects of thrombopoietin (TPO) on the proliferation and differentiation of hematopoietic progenitors in JCML. In serum-deprived single-cell cultures of normal bone marrow (BM) CD34+CD38high cells, the addition of TPO to the culture containing SCF + GM-CSF resulted in an increase in the number and size of GM colonies. In the JCML cultures, in contrast, the number of SCF + GM-CSF-dependent GM colonies was not increased by the addition of TPO. However, the TPO addition caused an enlargement of GM colonies in cultures from the JCML patients to a significantly greater extent compared with the normal controls. There was no difference in the type of the constituent cells of GM colonies with or without TPO grown by JCML BM cells. A flow cytometric analysis showed that the c-Mpl expression was found on CD13+ myeloid cells generated by CD34+CD38high BM cells from JCML patients, but was at an undetectable level in normal controls. The addition of TPO to the culture containing SCF or SCF + GM-CSF caused a significant increase in the production of GM colony-forming cells by JCML CD34+CD38neg/low population, indicating the stimulatory effects of TPO on JCML primitive hematopoietic progenitors. Normal BM cells yielded a significant number of megakaryocytes as well as myeloid cells in response to a combination of SCF, GM-CSF, and/or TPO. In contrast, megakaryocytic cells were barely produced by the JCML progenitors. Our results may provide a fundamental insight that the administration of TPO enhances the aberrant growth of GM progenitors rather than the recovery of megakaryocytopoiesis.

A combination of stem cell factor and granulocyte colony-stimulating factor enhances the growth of human progenitor B cells supported by murine stromal cell line MS-5

We have developed a long-term culture system using the murine bone marrow stromal cells MS-5 to support the growth of progenitor B cells with CD34-, CD10+, CD19+, and cytoplasmic mu chain (C mu)-negative surface phenotype from human CD34+ cells purified from umbilical cord blood (CB). When 10(3) CD34+ cells/well were seeded on MS-5 stromal cells at the beginning of culture in the absence of exogenously added cytokines, progenitor B cells first appeared after 14 days, and the maximal cell production was achieved during the 6th week of culture. Intriguingly, the addition of recombinant human stem cell factor (rhSCF) and granulocyte colony-stimulating factor (rhG-CSF), but not rhIL-7, strikingly enhanced the growth of progenitor B cells from CB CD34+ population cultured on MS-5 stromal cells. The culture of progenitor B cells could be maintained until the 6th week of culture when some cells were revealed to have a C mu phenotype, and a small number of cells had immunoglobulin mu chain on their cell surface in the presence of both rhSCF and rhG-CSF. When CD34+ cells were cultured physically separated from the stromal layer by membrane, supportive effects of MS-5 stromal cells for the growth of progenitor B cells were not observed. These results suggest that the present culture system could generate progenitor B cells to proliferate from CB CD34+ cells, that some of these progenitor B cells could differentiate into immature B cells in conjunction with rhSCF and rhG-CSF, and that a species-cross-reactive membrane-bound factor(s), which stimulates early human B lymphopoiesis, may exist in MS-5 stromal cells. Further studies are required to investigate the mechanism how rhG-CSF acts on progenitor B cells to allow their proliferation and differentiation.

Neutralization of biological activity and inhibition of receptor binding by antibodies against human thrombopoietin

Thrombopoietin (TPO) is a recently isolated cytokine that primarily regulates megakaryocytopoiesis and thrombopoiesis. We recently reported the development of a variety of antibodies (Abs) to synthetic peptides of human (h)TPO and to recombinant human TPO (rhTPO). In this study, we characterized the Abs and mapped immunologically distinct areas of the molecule. Among the five different antipeptide polyclonal Abs, only one, raised against synthetic peptide D8 to Q28, neutralized the TPO-dependent growth of FDCP-2 cells expressing human Mpl (FDCP-hMpl5 cells). One out of seven anti-rhTPO monoclonal Abs, designated as TN1, also showed neutralizing activity. TN1 was found to be specifically reactive with two proteolytic fragments, residues S1 to R117 and A60 to K122 of hTPO, indicating that the epitope(s) of TN1 is localized in residues A60 to R117 of the molecule. These two neutralizing Abs inhibited the binding of biotinylated rhTPO to FDCP-hMpl5 cells. On the other hand, the other Abs, which reacted with five polypeptides of S47 to D62, L108 to A126, N172 to A190, S262 to T284, and P306 to G332 of hTPO, did not show either the neutralizing activity or the ability to inhibit the binding of biotinylated rhTPO to the cell surface hMpl. These findings indicate that two regions, residues D8 to Q28 and A60 to R117 of hTPO, may contain the domains associated with its receptor, C-Mpl. These Abs characterized here are valuable for studying the structural analysis and the biological function of hTPO mediated by its receptor.

Cellular localization of thrombopoietin mRNA in the liver by in situ hybridization

The expression of thrombopoietin (TPO) mRNA is observed in several tissues, including liver, kidney, brain, skeletal muscle, intestine, spleen, and bone marrow. Among these organs, the highest expression of TPO mRNA is detected in the liver. We identified cells producing TPO by means of in situ hybridization of adult rat liver using digoxigenin-11-UTP-labeled cRNA probes. We found that the cells expressing TPO mRNA also expressed serum albumin mRNA. TPO mRNA was detected in parenchymal cells (hepatocytes) but not in non-parenchymal cells (including endothelial cells, epithelial cells, and so forth). To determine the location of TPO expression in embryogenesis, sections of fetal mice were further analyzed by in situ hybridization. TPO mRNA was detected only in hepatocytes of fetal liver, which was also the major site of hematopoiesis. The expression of TPO mRNA in fetal liver was observed from 12.5 days postcoitus. Northern blot analysis showed that mouse liver transcribed the same size of TPO mRNA in the fetus and in the adult. These results clearly demonstrate that hepatocytes are the primary site of TPO production in the liver from fetus to adult.

Action of thrombopoietin at the megakaryocyte progenitor level is critical for the subsequent proplatelet production

Formation of proplatelets from megakaryocytes is believed to be the first step of platelet production in vitro. In this study, we evaluated the effects of recombinant human thrombopoietin (hTPO) on the development of proplatelets from a GpIIb/IIIa+ population of rat bone marrow cells highly enriched for late megakaryocyte progenitors (GpIIb/IIIa+ CFU-MK) that we recently found to be a primary target population of TPO. Quantitative measurement of hTPO-induced proplatelet formation was performed in liquid cultures. Proplatelet formation from megakaryocytes derived from GpIIb/IIIa+ CFU-MK in the presence of hTPO began on day 4 of culture and peaked the following day. On day 5 of culture, lower concentrations of hTPO expanded the number of megakaryocytes, increased the number of proplatelets and the percentage of proplatelet-developing megakaryocytes. Increasing hTPO concentrations resulted in a modest decrease in proplatelet development. We next used hTPO to derive immature or mature megakaryocytes from GpIIb/IIIa+ CFU-MK. These populations of cultured megakaryocytes spontaneously formed proplatelets when recultured in the absence of exogenous hTPO. The addition of hTPO at higher concentrations modestly augmented proplatelet production from immature megakaryocytes derived from 2-day liquid cultures. However, either murine interleukin-6 (IL-6) or human IL-11, but not rat IL-3, was more potent than hTPO in augmenting proplatelet formation from immature megakaryocytes. Each of these four cytokines had an inhibitory effect on proplatelet formation from more differentiated megakaryocytes derived from 3-day liquid cultures. These results indicate that TPO enhances proplatelet production primarily by stimulating CFU-MK to increase the number of proplatelet-forming megakaryocytes and that its action is clearly different from those of other cytokines that also stimulate megakaryocytopoiesis.

Production of thrombopoietin (TPO) by rat hepatocytes and hepatoma cell lines

Recently, we purified rat thrombopoietin (TPO) from plasma of irradiated rats (XRP) by measuring its activity that stimulated the production of megakaryocytes from megakaryocyte progenitor cells (CFU-MK) in vitro. We then cloned the cDNAs for rat and human TPO. In this study, we found the production of TPO by hepatocytes isolated with the collagenase perfusion method from both normal and thrombocytopenic rats, by a two-step fractionation of hepatocyte culture medium (CM). Subsequently, CM of rat hepatoma cell lines was screened for the presence of TPO; three cell lines, H4-II-E, McA-RH8994, and HTC, were found to produce TPO. According to the purification procedure for TPO from XRP, TPO was partially purified from 2 L CM of each of three cell lines with a six-step procedure. In the final reverse-phase column, TPO from each cell line was eluted with the same retention time as that from XRP, and the TPO fraction exhibited megakaryocyte colony-stimulating activity (Meg-CSA). TPO-active fraction eluted from the final reverse-phase column was separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), extracted from the gel, and assayed. TPO activity from each cell line was found in the respective molecular weight region, indicating the heterogeneity of the TPO molecule. Using reverse transcriptase-polymerase chain reaction (RT-PCR), we detected the expression of TPO mRNA in hepatocytes, three hepatoma cell lines, normal rat liver, and X-irradiated rat liver. Northern blot analysis showed that TPO mRNA was expressed mainly in liver among the various organs tested. These data demonstrate that TPO is produced by rat hepatocytes and hepatoma cell lines and suggest that liver may be the primary organ that produces TPO.

Kinetics of 125I-PDGF binding and down-regulation of PDGF receptor in human arterial smooth muscle cell strains during cellular senescence in vitro

Platelet-derived growth factor (PDGF) is one of the major mitogens in serum to stimulate replication of human smooth muscle cells (SMCs) in culture. Previous studies using human fibroblasts failed to demonstrate changes in the receptor systems for growth factors during cellular senescence. We investigated the kinetics of 125I-PDGF(-BB) binding and down-regulation of the PDGF receptor in three human arterial SMC strains during cellular aging. The number of specific 125I-PDGF binding sites per cell increased slightly at a population doubling level (PDL) of 60%-80% of life span and then decreased at the PDL above 90%. The number of receptors per cell-surface area decreased with increasing in vitro age. The apparent Kd for the 125I-PDGF binding decreased with in vitro senescence. The internalization and degradation of 125I-PDGF per receptor were significantly reduced in senescent SMCs and the amount of 125I-PDGF that escaped degradation and was recycled back to the cell surface was significantly greater in senescent SMCs than young cells. Furthermore, down-regulation of the PDGF receptor was significantly greater in senescent SMCs than young cells. Immunoblot studies demonstrated that changes in beta-subunit of the PDGF receptor accounted for those in the studies using 125I-PDGF and that tyrosine phosphorylation of the PDGF receptor was significantly greater in young SMCs than aged cells. Our results suggest that age-related changes in the receptor systems for PDGF may be important contributors to the failure of DNA synthesis in senescent SMCs.

Purification and characterization of thrombopoietin

A thrombopoietic factor, termed thrombopoietin (TPO), was highly purified directly from the plasma of sublethally irradiated 1,100 rats by measuring the production of megakaryocytes from a highly enriched population of rat megakaryocyte progenitor cells (CFU-MK). The rat plasma TPO is a glycoprotein and strongly hydrophobic. The total activity and purification yields obtained were about 29% and 1.49 x 10(8), respectively. The amino acid sequences of the two peptide fragments prepared from the purified 19 kDa TPO were analyzed, and used for the cloning of rat and human TPO cDNAs. It was found that the 19 kDa TPO was truncated but comprised at least 163 amino acids. The sequence of human TPO cDNA revealed that the TPO was identical to the c-Mpl ligand. Both rat and human TPOs expressed in COS-1 cells exhibited significant activity toward the CFU-MK in vitro, and were active in stimulating platelet production in mice. These results indicate that a thrombopoietic factor originally found in the irradiated rat plasma is a ligand for the rat c-Mpl.

The sequence of a rat cDNA encoding thrombopoietin

Overlapping cDNA clones encoding rat thrombopoietin (TPO) were isolated from liver-derived cell line cDNA libraries and the nucleotide sequences were determined. The deduced 326-amino-acid rat TPO showed significant homology to the known TPO of other species, especially in the N-terminal sequence.

Cell-to-cell interaction of cytokine-dependent myeloblastic line constitutively expressing membrane-bound stem cell factor abrogates cytokine dependency partially through granulocyte-macrophage colony-stimulating factor production

Stem cell factor (SCF) is a cytokine for hematopoietic progenitor cells and plays an important role in megakaryocyte proliferation. The UT-7 cell line was established from a patient with megakaryoblastic leukemia, and its growth and survival are strictly dependent on interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), erythropoietin (Epo), or IL-6. In this study, we showed that SCF also supported the growth of UT-7 in the absence of other cytokines and downregulated the cell surface c-kit receptors. Constitutive expression of SCF by introducing SCF expression vector made UT-7 grow factor-independently in liquid medium, but not in semisolid medium. This SCF-expressing factor-independent UT-7 (UT-7scf9) expressed the membrane bound form of SCF on their surface, but did not secrete detectable amounts of soluble SCF. UT-7scf9 formed aggregates as they grew in the absence of cytokines, and this aggregation was inhibited by adding soluble SCF into the medium. UT-7 cultured with SCF and UT-7scf9 cultured without cytokines expressed GM-CSF, and anti-GM-CSF neutralizing antibody partially inhibited their growth. These results suggest that SCF stimulated UT-7 proliferation partially through the autocrine-loop of GM-CSF, and UT-7scf9 expressed SCF mostly as a membrane-bound form, which transduces its growth signal through c-kit receptor as they aggregate by cell-to-cell interaction.

Human leukocyte antigen in patients with moyamoya disease

BACKGROUND AND PURPOSE

Progressive stenosis or occlusion of bilateral internal carotid arteries by fibrocellular intimal thickening results in cerebral ischemia in moyamoya disease. In an attempt to elucidate the still-unknown etiologic factors in moyamoya disease, we assessed human leukocyte antigens in patients with this disease.

METHODS

We investigated 32 unrelated Japanese patients with moyamoya disease for typing of human leukocyte antigen A, B, C, and DR/DQ and compared the results with those from 178 unrelated control subjects.

RESULTS

We found a significant association of human leukocyte antigen B51 with moyamoya disease (corrected P < .05, chi 2 test). Although no significant associations were observed in DR/DQ typing, the frequency of the B51-DR4 combination was significantly higher in moyamoya patients than in control subjects (P < .002, Fisher's exact test).

CONCLUSIONS

These findings suggest that there may be a genetic predisposition for moyamoya disease and that host factors may play a role in the development of intimal thickening in early childhood.

Molecular cloning and chromosomal localization of the human thrombopoietin gene

The complete gene for human thrombopoietin (TPO) has been cloned by screening a human genomic library using human TPO cDNA as a probe. This gene is 6.2 kb in length and contains six exons and five introns. It is shown that the human genome contains a single copy of the human TPO gene according to Southern blotting analysis. The transcription initiation site was determined by S1 nuclease mapping. The human TPO gene expressed TPO activity when transfected into COS-1 cells. The human TPO gene has been mapped to chromosome 3q27 by in situ hybridization using a biotin-labeled probe.

Human arterial smooth muscle cell strains derived from patients with moyamoya disease: changes in biological characteristics and proliferative response during cellular aging in vitro

Moyamoya disease is a progressive cerebrovascular occlusive disease that occurs frequently in children. The etiology is unknown. We examined changes in biological characteristics and responsiveness to serum mitogens during the in vitro cellular aging of arterial smooth muscle cell strains derived from patients with moyamoya disease (HMSMC) and compared them with those of cells from age-matched control patients (HCSMC). HMSMC had a normal human diploid chromosome constitution. HMSMC and HCSMC had almost the same in vitro life span and the age-related patterns of biological parameters were essentially the same. However, the doubling time at the early passages was significantly longer in moyamoya SMC than control SMC, although there was no significant difference at the late passages. Furthermore, the poor responsiveness of moyamoya SMC to platelet-derived growth factor was retained throughout the life span in vitro. These results support the hypothesis that functional alterations in vascular cells are involved in the mechanism of development of intimal thickening in moyamoya disease.

Purification and characterization of a heat stable nuclear factor CIIIB1 involved in the regulation of the human ApoC-III gene

The apoC-III promoter region -86 to -74 is recognized by two nuclear factors designated CIIIB1 and CIIIB2 (NF-BA1) which are both activators of apoC-III gene transcription (Ogami, K., Hadzopoulou-Cladaras, M., Cladaras, C., and Zannis, V. I. (1990) J. Biol. Chem. 265, 9808-9815). In this communication we report the purification of factor CIIIB1 from rat liver nuclear extracts. The purification procedure included anion- and cation-exchange chromatography, DNA sequence-specific affinity chromatography, and heat treatment at 85 degrees C for 5 min. The ligand used for affinity chromatography was a mutated apoC-III -90 to -73 promoter sequence which binds only the CIIIB1 factor. The purified protein was identified as a poly-peptide of Mr 41,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and photoaffinity cross-linking. The binding site of CIIIB1, defined by DNase I footprinting and methylation interference assays, contains the octameric motif CAGGTGAC. Nucleotide substitutions within this sequence abolished the binding of the purified factor. DNase I footprinting analysis showed that purified CIIIB1 protein protects the apoA-II promoter region -65 to -48 which contains an identical octameric CAGGTGAC motif in the antisense strand suggesting that CIIIB1 may also play a role in apoA-II gene regulation.

Promoter elements and factors involved in hepatic transcription of the human ApoA-I gene positive and negative regulators bind to overlapping sites

DNase I footprinting analysis of the proximal apoA-I promoter sequences with rat liver nuclear extracts identified four protected regions: A, -22 to +17; B, -128 to -77; C, -175 to -148; and D, -220 to -190. Region D (-220 to -190) binds at least two distinct activities, designated AID1 and AID2, respectively, which can be separated by ion exchange chromatography. Region C (-175 to -148) forms five DNA protein complexes. Three of the complexes (2, 4, and 5) originate from the binding of more than one heat-stable nuclear factor, and two (1 and 3), from the binding of two heat-labile factors. The heat-stable factors bind in the -175 to -148 region and can be distinguished from C/EBP, which recognizes the same region, with DNA binding gel electrophoretic assays. Both factors 1 and 3 bind in the -168 to -148 apoA-I region. Despite the lack of a CCAAT motif in this region, the binding of factor 1 is competed out by oligonucleotides containing the binding sites of NFY and NFY*. Mutagenesis of the promoter region showed that mutations in the -171 to -166 and -158 to -153 regions diminished the binding of the heat-stable factors and reduced hepatic transcription to 14 and 8% of control, respectively. In contrast, a mutation in the -164 to -159 region abolished the binding of factor 1 and was associated with a 4.6-fold increase in hepatic transcription. These findings suggest that the heat-stable factors act as positive regulators, whereas factor 1 acts as a negative regulator in apoA-I gene transcription.

Promoter elements and factors required for hepatic and intestinal transcription of the human ApoCIII gene

We have mapped the promoter elements required for hepatic and intestinal transcription of the human apoCIII gene by deletion, nucleotide substitution, and DNase I footprinting analyses of the promoter region (nucleotides -1411 to +24). Deletion of the region -1020 to -871 increased 2-fold intestinal transcription without affecting hepatic transcription. Deletion of the region -890 to -686 decreased hepatic and intestinal transcription 34- and 13-fold respectively. Internal deletions of the -686 to -553 region increased intestinal transcription 2-fold and decreased hepatic transcription 9-fold. Finally, internal deletions in the region -408 to -163 decreased hepatic transcription 2- to 4-fold without affecting the intestinal transcription. Footprinting analysis using rat liver nuclear extracts identified 10 protected regions as follows: A, -32 to -25; B, -87 to -72; C, -138 to -119; D, -160 to -142; E, -414 to -403; F, -611 to -592; G, -669 to -648; H, -705 to -690; I, -766 to -726; and J, -792 to -779. The findings indicate that the region -890 to -686 is recognized by nuclear factors which promote both intestinal and hepatic transcription, whereas the region -686 to -553 is recognized by factors which promote only hepatic transcription. DNA binding and methylation interference assays indicated that the region -86 to -74 is recognized by two mutually exclusive nuclear factors with overlapping domains. One factor (CIIIB1) is unique to apoCIII and the other (CIIIB2) recognizes the regulatory elements of other apolipoprotein promoters. Binding of factor CIIIB2 is associated with normal transcription. In contrast, binding of factor CIIIB1 is associated with reduced transcription indicating that this factor may act as a modulator of transcription.