Relationship between radiation dose reduction and image quality change in photostimulable phosphor luminescence X-ray imaging systems

OBJECTIVES

The aim of the study was to clarify the change in image quality upon X-ray dose reduction and to re-analyse the possibility of X-ray dose reduction in photostimulable phosphor luminescence (PSPL) X-ray imaging systems. In addition, the study attempted to verify the usefulness of multiobjective frequency processing (MFP) and flexible noise control (FNC) for X-ray dose reduction.

METHODS

Three PSPL X-ray imaging systems were used in this study. Modulation transfer function (MTF), noise equivalent number of quanta (NEQ) and detective quantum efficiency (DQE) were evaluated to compare the basic physical performance of each system. Subjective visual evaluation of diagnostic ability for normal anatomical structures was performed. The NEQ, DQE and diagnostic ability were evaluated at base X-ray dose, and 1/3, 1/10 and 1/20 of the base X-ray dose.

RESULTS

The MTF of the systems did not differ significantly. The NEQ and DQE did not necessarily depend on the pixel size of the system. The images from all three systems had a higher diagnostic utility compared with conventional film images at the base and 1/3 X-ray doses. The subjective image quality was better at the base X-ray dose than at 1/3 of the base dose in all systems. The MFP and FNC-processed images had a higher diagnostic utility than the images without MFP and FNC.

CONCLUSIONS

The use of PSPL imaging systems may allow a reduction in the X-ray dose to one-third of that required for conventional film. It is suggested that MFP and FNC are useful for radiation dose reduction.

Prior treatment with vitamin K(2) significantly improves the efficacy of risedronate

Prior 8-week treatment with menatetrenone, MK-4, followed by 8-week risedronate prevented the shortcomings of individual drugs and significantly increased the strength of ovariectomized ICR mouse femur compared to the ovariectomized (OVX) controls. Neither MK-4 following risedronate nor the concomitant administration may be recommended because they brought the least beneficial effect.

INTRODUCTION

The objective of this study was to determine the best combinatory administration of risedronate at 0.25 mg/kg/day (R) with vitamin K(2) at approximately 100 microg MK-4/kg/day (K) to improve strength of osteoporotic mouse bone.

METHODS

Thirteen-week-old ICR mice, ovariectomized at 9-week, were treated for 8 weeks with R, K, or R plus K (R/K), and then, either the treatment was withdrawn (WO) or switched to K or R in the case of R and K. After another 8 weeks, the mice were killed, and mechanical tests and analyses of femur properties by peripheral quantitative computed tomography, microfocus X-ray tube computed tomography, and confocal laser Raman microspectroscopy were carried out.

RESULTS

The K to R femur turned out superior in parameters tested such as material properties, bone mineral density, BMC, trabecular structure, and geometry of the cortex. The increased cross-sectional moment of inertia, which occurred after K withdrawal, was prevented by risedronate in K to R. In addition to K to R, some properties of R to WO diaphysis and K to WO epiphysis were significantly better than OVX controls.

CONCLUSION

Prior treatment with MK-4 followed by risedronate significantly increased femur strength in comparison to the OVX controls.

Molecular cloning and characterization of a KRAB-containing zinc finger protein, ZNF317, and its isoforms

To identify zinc finger genes in human primary cultured erythroid progenitor cells, RT-PCR was performed using primers specific for the conserved sequence in zinc finger domains of mouse Friend of GATA-1. We identified a novel Krüppel-associated box (KRAB) zinc finger gene, ZNF317. Evaluation of full-length cDNA obtained by RACE showed that it encoded a protein composed of 13 Krüppel-like zinc fingers and a KRAB domain. RT-PCR analysis revealed four alternatively splicing products (ZNF317-1 through ZNF317-4). The ZNF317 gene has seven exons and is located in human chromosome 19p13. Northern analysis revealed that ZNF317-1 and ZNF317-2 transcripts were ubiquitously expressed, whereas ZNF317-3 and ZNF317-4 transcripts were detected only in lymphocytes, spleen, and lung. Competitive RT-PCR analysis showed that the expression of ZNF317 mRNA significantly decreased during erythroid maturation. In lymphocytes, ZNF317 expression was reduced in response to mitogenic stimulation. We propose that ZNF317 may play an important role in erythroid maturation and lymphoid proliferation.

Thrombopoietin and interleukin-2 induce association of CRK with STAT5

Crk (Crk I and II) proteins and closely related CrkL are adapters which are commonly involved in various signaling processes in various cells, and these proteins share many ligands. Whether they have redundant or distinct physiologic roles is unclear. By coprecipitation and far Western blotting analysis, we demonstrate that Crk (I/II) binds to tyrosine phosphorylated STAT5 in cells stimulated by cytokines such as thrombopoietin (TPO) and interleukin-2 (IL-2). The association did not require nuclear elements and can be observed in primary cells as this was also demonstrated in TPO-stimulated platelets. Using a beta-casein promoter STAT5 binding site as a probe, we have also demonstrated that CrkL (a close relative of Crk) antiserum, but not Crk antiserum, supershifted the STAT5-DNA complex by an electrophoretic mobility shift assay, suggesting that CrkL, but not Crk, is the major component of the complex. Thus, Crk and CrkL may have distinct roles in the regulation of STAT5.

Increased D-type cyclin expression together with decreased cdc2 activity confers megakaryocytic differentiation of a human thrombopoietin-dependent hematopoietic cell line

At the late phase of megakaryocytopoiesis, megakaryocytes undergo endomitosis, which is characterized by DNA replication without cell division. Although a number of cell cycle regulatory molecules have been identified, the precise roles of these molecules in megakaryocytic endomitosis are largely unknown. In a human interleukin-3-dependent cell line transfected with the thrombopoietin (TPO) receptor c-mpl (F-36P-mpl), either treatment with TPO or the overexpression of activated ras (Ha-Ras(G12V)) induced megakaryocytic maturation with polyploid formation. We found that TPO stimulation or Ha-Ras(G12V) expression led to up-regulation of cyclin D1, cyclin D2, and cyclin D3 expression. In addition, expression levels of cyclin A and cyclin B were reduced during the total course of both TPO- and Ha-Ras(G12V)-induced megakaryocytic differentiation, thereby leading to decreased cdc2 kinase activity. Neither the induced expression of cyclin D1, cyclin D2, or cyclin D3 nor the expression of a dominant negative form of cdc2 alone could induce megakaryocytic differentiation of F-36P-mpl cells. In contrast, overexpression of dominant negative cdc2 together with cyclin D1, cyclin D2, or cyclin D3 facilitated megakaryocytic differentiation in the absence of TPO. These results suggest that both D-type cyclin expression and decreased cdc2 kinase activity may participate in megakaryocytic differentiation.

Prolactin enhances CCAAT enhancer-binding protein-beta (C/EBP beta) and peroxisome proliferator-activated receptor gamma (PPAR gamma) messenger RNA expression and stimulates adipogenic conversion of NIH-3T3 cells

Extracellular stimuli trigger adipocyte differentiation by inducing the complex cascades of transcription. Transcription factors CCAAT enhancer-binding proteins (C/EBPs) and peroxisome proliferator-activated receptor gamma (PPARgamma) play crucial roles in this process. Although ectopic expression of these factors in NIH-3T3 cells, a multipotential mesenchymal stem cell line, results in adipogenic conversion, little is known as to hormonal factors that regulate adipogenesis in these cells. In this report we demonstrate that PRL, a lactogenic hormone, enhances C/EBPbeta and PPARbeta mRNA expression and augments adipogenic conversion of NIH-3T3 cells. Moreover, we show that ectopic expression of the PRL receptor in NIH-3T3 cells results in efficient adipocyte conversion when stimulated with PRL and a PPARgamma ligand, as evidenced by expression of the adipocyte differentiation-specific genes as well as the presence of fat-laden cells. We further demonstrate that signal transducer and activator of transcription 5 (Stat5), a PRL signal transducer, activates aP2 promoter in a PRL-dependent manner. These results suggest that PRL acts as an adipogenesis-enhancing hormone in NIH-3T3 cells.

Differential regulation of immediate early gene expression in preadipocyte cells through multiple signaling pathways

Using digoxigenin (DIG)-based differential hybridization, a series of immediate early genes (IEG) was identified following the adipogenic stimulation in 3T3-L1 preadipocyte cells. Most of the known IEGs were identified as well as new members such as zf9 and Stra13. To delineate possible signaling pathways accounting for these gene expression, a subset of specific kinase inhibitors, SB203580, PD98059, rapamycin, LY294002, and Ro-32-0432, which inhibit p38 (HOG), MEK (MAPKK), S6 kinase, PI3 kinase, and protein kinase C (PKC), respectively, were employed. The IEGs were classified into three categories according to their susceptibility to the inhibitors. Expression of the first group (c-fos, jun-B, egr-1, tis11, tis21, thrombospondin-1, erp, thyroid hormone receptor [N-10], cyr61, and zf9) was mainly dependent on PKC and MEK pathways, while that of the second class (gene33 and tis10) exhibited an additional dependence on PI3 kinase pathways. The third one (Id-3, gly96, and Stra13) was characterized in that none of these inhibitors interfered with gene expression. Our results suggest that the induction of IEGs by the adipogenic stimuli is mediated by common as well as distinct signaling pathways.

Human SOX11, an upregulated gene during the neural differentiation, has a long 3' untranslated region

To obtain essential genes for neuronal development, we have performed a molecular indexing method using a human teratocarcinoma cell line, NTera-2. We isolated a cDNA fragment, designated B18, as an upregulated gene during the neural differentiation. From the complete cDNA sequence of B18 it was revealed that this cDNA was the human SOX11 gene. While a previous report has determined only a approximately 2 kb of the SOX11 cDNA including the entire open reading frame, our full length cDNA was 8743 bp possessing a long 3' untranslated region. Human SOX11 cDNA was mapped to chromosome region 2p25.3 between markers AFMA070WC9 and WI-1412 by radiation hybrid mapping.

cDNA cloning and expression analysis of mouse zf9, a Krüppel-like transcription factor gene that is induced by adipogenic hormonal stimulation in 3T3-L1 cells

Using a differential hybridization method, we have cloned a zinc finger transcription factor gene whose expression was enhanced by adipogenic hormones in preadipocyte 3T3-L1 cells. Cloning of this gene revealed that it encodes a mouse homologue of rat Zf9 and human CPBP/GBF, previously identified as a wound-induced transcription factor and GC-rich binding protein, respectively. The mRNA for this clone consisted of 0.9 kb coding region and 3.2 kb long 3' untranslated region. Northern blot analysis revealed that it was ubiquitously expressed, among adult tissues, in which abundant expression was observed in lung, ovary and thymus. The transcript was transiently induced by different stimuli such as serum, cAMP and 12-O-tetradecanoylphorbol 13-acetate. Nuclear run-on and RNA synthesis inhibitor chase experiments indicated that the transient induction of the mRNA was regulated both at transcriptional and post-transcriptional levels.

Human T-cell leukemia virus type 1 Tax protein induces the expression of STAT1 and STAT5 genes in T-cells

Human T-cell leukemia virus type 1 (HTLV-1) Tax transforms normal T-cells in the presence of interleukin (IL)-2 in vitro. STAT is a family of transcription factors that play a pivotal role in cytokine-induced functions of a various type of cells. We investigated the involvement of STATs in the transformation of T-cells by HTLV-1. HTLV-1-transformed T-cell lines expressed higher amounts of STAT1, STAT3 and STAT5 RNA and proteins than virus-negative T cells. The expression of STAT1 and STAT5 in a human T-cell line was induced by Tax. IL-2 induced the DNA binding activity of STAT3 and STAT5 of a HTLV-1-transformed cell line and then stimulated its proliferation. In contrast, IL-2 did neither in a cell line lacking STAT3 and STAT5. The expression of STAT1, STAT3 and STAT5 mRNAs were also induced by a T-cell mitogen in normal human peripheral blood mononuclear cells. Our results suggest that the induction of STAT1 and STAT5 by Tax enhances cytokine-induced functions of virus-infected T-cells, hence the induction may play a role in IL-2-dependent transformation steps of T-cells by HTLV-1.

Transcriptional regulation of the cyclin D1 promoter by STAT5: its involvement in cytokine-dependent growth of hematopoietic cells

STAT5 is a member of a family of transcription factors that participate in the signal transduction pathways of many hormones and cytokines. Although STAT5 is suggested to play a crucial role in the biological effects of cytokines, its downstream target(s) associated with cell growth control is largely unknown. In a human interleukin-3 (IL-3)-dependent cell line F-36P-mpl, the induced expression of dominant-negative (dn)-STAT5 and of dn-ras led to inhibition of IL-3-dependent cell growth, accompanying the reduced expression of cyclin D1 mRNA. Also, both constitutively active forms of STAT5A (1*6-STAT5A) and ras (H-rasG12V) enabled F-36P-mpl cells to proliferate without added growth factors. In NIH 3T3 cells, 1*6-STAT5A and H-rasG12V individually and cooperatively transactivated the cyclin D1 promoter in luciferase assays. Both dn-STAT5 and dn-ras suppressed IL-3-induced cyclin D1 promoter activities in F-36P-mpl cells. Using a series of mutant cyclin D1 promoters, 1*6-STAT5A was found to transactivate the cyclin D1 promoter through the potential STAT-binding sequence at -481 bp. In electrophoretic mobility shift assays, STAT5 bound to the element in response to IL-3. Furthermore, the inhibitory effect of dn-STAT5 on IL-3-dependent growth was restored by expression of cyclin D1. Thus STAT5, in addition to ras signaling, appears to mediate transcriptional regulation of cyclin D1, thereby contributing to cytokine-dependent growth of hematopoietic cells.

Transcriptional regulation of the cyclin D1 promoter by STAT5: its involvement in cytokine-dependent growth of hematopoietic cells

STAT5 is a member of a family of transcription factors that participate in the signal transduction pathways of many hormones and cytokines. Although STAT5 is suggested to play a crucial role in the biological effects of cytokines, its downstream target(s) associated with cell growth control is largely unknown. In a human interleukin-3 (IL-3)-dependent cell line F-36P-mpl, the induced expression of dominant-negative (dn)-STAT5 and of dn-ras led to inhibition of IL-3-dependent cell growth, accompanying the reduced expression of cyclin D1 mRNA. Also, both constitutively active forms of STAT5A (1*6-STAT5A) and ras (H-rasG12V) enabled F-36P-mpl cells to proliferate without added growth factors. In NIH 3T3 cells, 1*6-STAT5A and H-rasG12V individually and cooperatively transactivated the cyclin D1 promoter in luciferase assays. Both dn-STAT5 and dn-ras suppressed IL-3-induced cyclin D1 promoter activities in F-36P-mpl cells. Using a series of mutant cyclin D1 promoters, 1*6-STAT5A was found to transactivate the cyclin D1 promoter through the potential STAT-binding sequence at -481 bp. In electrophoretic mobility shift assays, STAT5 bound to the element in response to IL-3. Furthermore, the inhibitory effect of dn-STAT5 on IL-3-dependent growth was restored by expression of cyclin D1. Thus STAT5, in addition to ras signaling, appears to mediate transcriptional regulation of cyclin D1, thereby contributing to cytokine-dependent growth of hematopoietic cells.

Thrombopoietin induces association of Crkl with STAT5 but not STAT3 in human platelets

Crkl, a 39-kD SH2, SH3 domain-containing adapter protein, is constitutively tyrosine phosphorylated in hematopoietic cells from chronic myelogenous leukemia (CML) patients. We recently reported that thrombopoietin induces tyrosine phosphorylation of Crkl in normal platelets. In this study, we demonstrate that thrombopoietin induces association of Crkl with a tyrosine phosphorylated 95- to 100-kD protein in platelets and in UT7/TPO cells, a thrombopoietin-dependent megakaryocytic cell line. With specific antibodies against STAT5, we demonstrate that the 95- to 100-kD protein in Crkl immunoprecipitates is STAT5. This coimmunoprecipitation was specific in that Crkl immunoprecipitates do not contain STAT3, although STAT3 becomes tyrosine phosphorylated in thrombopoietin-stimulated platelets. The coimmunoprecipitaion of Crkl with STAT5 was inhibited by the immunizing peptide for Crkl antisera or phenyl phosphate (20 mmol/L). After denaturing of Crkl immunoprecipitates, Crkl was still immunoprecipitated by Crkl antisera. However, coimmunoprecipitation of STAT5 was not observed. Coincident with STAT5 tyrosine phosphorylation, thrombopoietin induces activation of STAT5 DNA-binding activity as demonstrated by electrophoretic mobility shift assays (EMSA). Using a beta-casein promoter STAT5 binding site as a probe, we have also demonstrated that Crkl antisera supershift the STAT5-DNA complex, suggesting that Crkl is a component of the complex in the nucleus. Furthermore, interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and erythropoietin also induce Crkl-STAT5 complex formation in responding cells in a stimulation-dependent manner. In vitro, glutathione S-transferase (GST)-Crkl bound to STAT5 inducibly through its SH2 domain. These results indicate that thrombopoietin, IL-3, GM-CSF, and erythropoietin commonly induce association of STAT5 and Crkl and that the complex translocates to the nucleus and binds to DNA. Interestingly, such association between STAT5 and Crkl was not observed in cytokine-stimulated murine cells, suggesting an intriguing possibility that components of the human STAT5-DNA complex may be different from those of the murine counterpart.

Transcriptional regulation of the beta-casein gene by cytokines: cross-talk between STAT5 and other signaling molecules

The beta-casein promoter has been widely used to monitor the activation of STAT (signal transducer and activator of transcription)5 since STAT5 was originally found as a mediator of PRL-inducible beta-casein expression. However, not only is expression of the beta-casein gene regulated by STAT5 but it is also affected by other molecules such as glucocorticoid and Ras. In this report, we describe the transcriptional regulation of the beta-casein gene by cytokines in T cells. We have found that the beta-casein gene is expressed in a cytotoxic T cell line, CTLL-2, in response to interleukin-2 (IL-2), which activates STAT5. While IL-4 does not activate STAT5, it induces expression of STAT5-regulated genes in CTLL-2, i.e. beta-casein, a cytokine-inducible SH2-containing protein (CIS), and oncostatin M (OSM), suggesting that STAT6 activated by IL-4 substitutes for the function of STAT5 in T cells. IL-2-induced beta-casein expression was enhanced by dexamethasone, and this synergistic effect of Dexamethasone requires the sequence between -155 and -193 in the beta-casein promoter. Coincidentally, a deletion of this region enhanced the IL-2-induced expression of beta-casein. Expression of an active form of Ras, Ras(G12V), suppressed the IL-2-induced beta-casein and OSM gene expression, and the negative effect of Ras is mediated by the region between -105 and -193 in the beta-casein promoter. In apparent contradiction, expression of a dominant negative form of Ras, RasN17, also inhibited IL-2-induced activation of the promoter containing the minimal beta-casein STAT5 element as well as the promoters of CIS and OSM. In addition, Ras(G12V) complemented signaling by an erythropoietin receptor mutant defective in Ras activation and augmented the activation of the beta-casein promoter by the mutant erythropoietin receptor signaling, suggesting a possible role of Ras in Stat5-mediated gene expression. These results collectively reveal a complex interaction of STAT5 with other signaling pathways and illustrate that regulation of gene expression requires integration of opposing signals.

Insulin-like growth factor-I augments erythropoietin-induced proliferation through enhanced tyrosine phosphorylation of STAT5

Insulin-like growth factor (IGF-I) is known to synergistically stimulate the proliferation of hematopoietic cells in combination with other hematopoietic growth factors. However, the precise mechanism underlying the cooperative effects of IGF-I is unknown. In a human interleukin-3 or erythropoietin (EPO)-dependent cell line, F-36P, IGF-I alone failed to stimulate DNA synthesis but did augment the EPO-dependent DNA synthesis of F-36P cells. The treatment of F-36P cells with a combination of EPO and IGF-I (EPO/IGF-I) was found to enhance EPO-induced tyrosine phosphorylation of STAT5, whereas IGF-I alone did not. Furthermore, c-CIS mRNA expression, one of the target molecules of STAT5, was more effectively induced by EPO/IGF-I than by EPO alone. To examine the mechanisms of the EPO- and EPO/IGF-I-induced proliferation of F-36P cells, we expressed dominant negative (dn) mutants of STAT5 and Ras in an inducible system. The EPO-induced DNA synthesis and the cooperative effect of EPO/IGF-I were significantly inhibited by the inducible expression of dn-STAT5 or dn-Ras. In addition, the inducible expression of dn-Ras abolished the IGF-I-enhanced tyrosine phosphorylation of STAT5. These results suggest that IGF-I may augment EPO-induced proliferation by enhancing tyrosine phosphorylation of STAT5 and raise the possibility that Ras may be involved in the augmentation of STAT5 tyrosyl phosphorylation.

Involvement of prolonged ras activation in thrombopoietin-induced megakaryocytic differentiation of a human factor-dependent hematopoietic cell line

Thrombopoietin (TPO) is a hematopoietic growth factor that plays fundamental roles is both megakaryopoiesis and thrombopoiesis through binding to its receptor, c-mpl. Although TPO has been shown to activate various types of intracellular signaling molecules, such as the Janus family of protein tyrosine kinases, signal transducers and activators of transcription (STATs), and ras, the precise mechanisms underlying TPO-induced proliferation and differentiation remain unknown. In an effort to clarify the mechanisms of TPO-induced proliferation and differentiation, c-mpl was introduced into F-36P, a human interleukin-3 (IL-3)-dependent erythroleukemia cell line, and the effects of TPO on the c-mpl-transfected F-36P (F-36P-mpl) cells were investigated. F-36P-mpl cells were found to proliferate and differentiate at a high rate into mature megakaryocytes in response to TPO. Dominant-negative (dn) forms of STAT1, STAT3, STAT5, and ras were inducibly expressed in F-36P-mpl cells, and their effects on TPO-induced proliferation and megakaryocytic differentiation were analyzed. Among these dn molecules, both dn ras and dn STAT5 reduced TPO- or IL-3-induced proliferation of F-36P-mpl cells by approximately 30%, and only dn ras could inhibit TPO-induced megakaryocytic differentiation. In accord with this result, overexpression of activated ras (H-rasG12V) for 5 days led to megakaryocytic differentiation of F-36P-mpl cells. In a time course analysis on H-rasG12V-induced differentiation, activation of the ras pathway for 24 to 28 h was required and sufficient to induce megakaryocytic differentiation. Consistent with this result, the treatment of F-36P-mpl cells with TPO was able to induce prolonged activation of ras for more than 24 h, whereas IL-3 had only a transient effect. These results suggest that prolonged ras activation may be involved in TPO-induced megakaryocytic differentiation.

Differential constitutive activation between STAT-related proteins and MAP kinase in primary acute myelogenous leukaemia

Many cytokines and growth factors stimulate multiple signal transduction pathways essential for proliferation in human acute leukaemia cells, including a mitogen-activated protein (MAP) kinase pathway and a Janus kinase (JAK)-STAT (signal transducers and activators of transcription) pathway. We have previously shown constitutive activation of MAP kinase in approximately 50% of acute myelogenous leukaemia (AML) samples. Recently, STAT proteins have been reported to be constitutively activated in 10-20% of AML cases. STAT3 and STAT5 are the main STAT proteins activated in haemopoietic progenitors in response to cytokines such as IL-3, GM-CSF, erythropoietin and thrombopoietin. Although the possibility of STAT1 protein as a substrate for MAP kinase at a serine residue has been suggested, the cross-talk between STATs and MAP kinase pathways in vivo, especially in leukaemia cells, remains unknown. We examined the phosphorylation of STAT 3 and STAT 5 at the tyrosine residues in AML samples in which MAP kinase activity had already been found. 40/50 primary AML cases (80%) exhibited constitutive tyrosine phosphorylation of STAT5. Electrophoretic mobility shift assay showed DNA binding activity of STAT5 correlated with tyrosine phosphorylation of STAT5. Similarly, with respect to STAT3, 17/23 cases examined (74%) showed constitutive tyrosine phosphorylation of STAT3. In addition, we examined the tyrosyl-phosphorylation of STAT5 isoforms, STAT5A and STAT5B, in 20 AML cases, and found selective STAT5B phosphorylation in the absence of STAT5A phosphorylation in three cases. Furthermore, in certain AML cases, constitutive activation of MAP kinase and STAT proteins occurred independently. No significant correlation of MAP kinase activation was observed with either tyrosine phosphorylation of STAT3/STAT5 or positive DNA binding of STAT proteins. These results suggest that constitutive activation of STAT proteins occurs commonly and that the causes of constitutive activation of these two major cascades are heterogeneous in AML.

Identification of the critical portions of the human IL-4 receptor alpha chain for activation of STAT6

Interleukin-4 (IL-4) has been shown to activate Janus kinase (Jak)-1 and Jak-3, followed by activation of STAT (signal transducers and activators of transcription) 6. This Jak-STAT pathway is central to the initiation of IL-4 activities. In this study, we identified the essential region for the proliferation signal and activation of Jak-1, Jak-3, and STAT6 in the cytoplasmic domain of the human IL-4 receptor alpha chain (hIL-4R alpha) using a mouse T cell line CTLL-2. We found that the region between amino acid 353 and 393 is critical for the proliferation signal and activation of STAT6, but not for tyrosine phosphorylation of Jaks. These results suggest that in addition to the "Box-1" portion, which is known to be essential for Jak-1 activation, the more membrane-distal region of hIL-4R alpha is also necessary for activation of STAT6.

Lyn physically associates with the erythropoietin receptor and may play a role in activation of the Stat5 pathway

Protein tyrosine phosphorylation plays a crucial role in signaling from the receptor for erythropoietin (Epo), although the Epo receptor (EpoR) lacks the tyrosine kinase domain. We have previously shown that the Jak2 tyrosine kinase couples with the EpoR to transduce a growth signal. In the present study, we demonstrate that Lyn, a Src family tyrosine kinase, physically associates with the EpoR in Epo-dependent hematopoietic cell lines, 32D/EpoR-Wt and F36E. Coexpression experiments in COS7 cells further showed that Lyn induces tyrosine phosphorylation of the EpoR and that both LynA and LynB, alternatively spliced forms of Lyn, bind with the membrane-proximal 91-amino acid region of the EpoR cytoplasmic domain. In vitro binding studies using GST-Lyn fusion proteins further showed that the Src homology (SH)-2 domain of Lyn specifically binds with the tyrosine-phosphorylated EpoR in lysate from Epo-stimulated cells, whereas the tyrosine kinase domain of Lyn binds with the unphosphorylated EpoR. Far-Western blotting and synthetic phosphopeptide competition assays further indicated that the Lyn SH2 domain directly binds to the tyrosine-phosphorylated EpoR, most likely through its interaction with phosphorylated Y-464 or Y-479 in the carboxy-terminal region of the EpoR. In vitro binding studies also demonstrated that the Lyn SH2 domain directly binds to tyrosine-phosphorylated Jak2. In vitro reconstitution experiments in COS7 cells further showed that Lyn induces tyrosine phosphorylation of Stat5, mainly on Y-694, and activates the DNA-binding and transcription-activating abilities of Stat5. In agreement with this, Lyn enhanced the Stat5-dependent transcriptional activation when overexpressed in 32D/EpoR-Wt cells. In addition, Lyn was demonstrated to phosphorylate the EpoR and Stat5 on tyrosines in vitro. These results suggest that Lyn may play a role in activation of the Jak2/Stat5 and other signaling pathways by the EpoR.

Differentiation inducers modulate cytokine signaling pathways in a murine erythroleukemia cell line

Hexamethylenebisacetamide (HMBA) is a potent differentiation inducer of murine erythroleukemia cells. Immunoprecipitation followed by Western blotting with an anti-phosphotyrosine (P-Tyr) antibody revealed that HMBA increased P-Tyr levels and/or amounts of several proteins containing P-Tyr in F5-5, a murine erythroleukemia cell line. Among these proteins, we identified a Mr 130,000 protein to be Janus-activated kinase 2 (JAK2). HMBA induced tyrosine phosphorylation of JAK2 and signal transducers and activators of transcription 5 (STAT5) but not other JAKs or STATs. This phosphorylation was apparent 12 h after treatment, maximal at 24 h, and persisted for at least 96 h. Consistently, HMBA increased STAT5 DNA-binding activities. Other chemical inducers, DMSO and butyrate, also induced a sustained activation of JAK2/STAT5, whereas fetal calf serum and erythropoietin induced transient activation but not differentiation. Furthermore, overexpression of a dominant-negative form of STAT5 inhibited the chemically induced differentiation. These results suggest that persistent activation of the signaling pathway plays a significant role in the inducer-mediated differentiation. Our data also suggest that molecular mechanisms for the inducer-mediated activation of JAK2 are independent of cytokine receptor-mediated activation mechanisms. We tentatively conclude that cytokine signaling is an important target of chemical inducers in these cells.

Erythropoietin induces tyrosine phosphorylation of the interleukin-3 receptor beta subunit (betaIL3) and recruitment of Stat5 to possible Stat5-docking sites in betaIL3

The receptors for erythropoietin (Epo) and interleukin-3 (IL-3) both induce the ligand-dependent activation of the Jak2 tyrosine kinase. Activated Jak2 then phosphorylates these receptors and thereby recruits various signaling molecules containing the Src homology (SH)-2 domain, including Stat5, to the tyrosine phosphorylated receptors. In the present study, we demonstrate that Epo stimulation induces unidirectional cross-phosphorylation of the IL-3 receptor beta subunit (betaIL3) on tyrosines and its rapid and transient association with Stat5 in murine IL-3-dependent cell lines engineered to express the Epo receptor (EpoR). Using cell lines expressing various EpoR mutants, it was demonstrated that the Epo-induced tyrosine phosphorylation of betaIL3 is dependent on the membrane-proximal EpoR cytoplasmic region involved in the activation of Jak2, but not on the extracellular and transmembrane regions or on the carboxy-terminal 145 amino acid region containing all the intracellular tyrosine residues. It was also shown that IL-3 induces rapid and dose-dependent association of Jak2 with betaIL3. However, Epo failed to induce any detectable association of betaIL3 with Jak2 or the EpoR. The present study also demonstrates that in IL-3-stimulated cells, an ovine Stat5 mutant harboring a substitution of Tyr694 to Phe, which abolishes the tyrosine phosphorylation required for activation, fails to dimerize with endogenous Stat5, shows sustained binding with tyrosine-phosphorylated betaIL3, and inhibits the tyrosine phosphorylation of endogenous Stat5. These results suggest that betaIL3 may have Stat5 docking sites, similar to those found in the EpoR, that facilitate the activation of Stat5 by Jak2 and raise the possibility that Epo may cross-activate or transmodulate the IL-3 receptor signaling pathways.

[Simplified analytical method of 99mTc-labeled phosphonate]

A simplified and rapid analytical method of 99mTc-labeled phosphonates was tested using a mini-column based on an anion-exchange type of cartridge. Free 99mTcO4- in the prepared solutions of 99mTc-labeled phosphonate was eluted from the column by a neutral phosphate buffer solution. Partly components of the 99mTc-labeled phosphonates was eluted from the column by a 100 mM sodium phosphonate solution, while the residual components were not eluted from the mini-column. In addition, for analysis of 99mTc-labeling rate in 99mTc-MDP solution, this method requires much less time than thin layer chromatography (TLC). Therefore, the method is more suitable for analysis of 99mTc-labeled phosphonates than TLC now in use, particularly rapid analysis for 99mTc-labeling rate of the compounds and the stability.

A possible involvement of Stat5 in erythropoietin-induced hemoglobin synthesis

Erythropoietin (EPO) and its cell surface receptor (EPOR) play central roles in the proliferation and differentiation of mammalian erythroid progenitor cells. Recently both the tyrosine residues in the EPOR responsible for the activation of Stat5 and the role of Stat5 for EPO-dependent cell proliferation have been shown. Here, we describe the roles of Stat5 and of these tyrosine residues in the EPOR in the erythroid differentiation of murine hematopoietic cell line SKT6 which produces hemoglobin in response to EPO. Chimeric receptors carrying the extracellular domain of the EGF receptor and the intracellular domain of the EPOR were introduced into SKT6 cells. Like EPO, EGF equally activated Stat5 and induced hemoglobin. Activation of Stat5 and hemoglobin expression by EGF were markedly impaired in cells expressing the tyrosine mutated chimeric receptors. In addition, ectopic expression of the prolactin receptor, another cytokine receptor that activates Stat5, led to hemoglobin synthesis. Finally, hemoglobin synthesis was severely inhibited by overexpressing a dominant negative form of Stat5. These results collectively suggest that Stat5 plays a role in EPO-mediated hemoglobin synthesis in SKT6 cells.

The role of erythropoietin receptor tyrosine phosphorylation in erythropoietin-induced proliferation

Although studies with truncated erythropoietin receptors (EpoRs) have suggested the tyrosine phosphorylation (Yphos) of the EpoR may not play a significant role in Epo-induced proliferation, we found, using a full length EpoR mutant designed Null, in which all 8 of the intracellular tyrosines (Ys) were substituted with phenylalanines (Fs), that Null cells required 5-10 fold more Epo than wild type (WT) EpoR containing cells in order to proliferate as well. Moreover, a comparison of Epo-induced proliferation with Epo-induced Yphos patterns, using DA-3 cells expressing WT, Null and various Y to F EpoR point mutants revealed that Stat5 Yphos and activation correlated directly with proliferation and was mediated primarily throuhg the most membrane proximal Y, i.e., Y343, although other tyrosines (most likely Y401 and Y431) within the EpoR could activate Stat5 in its absence. We also found that EpoR Yphos was essential for the Yphos of Shc and for the Yphos and association of a 145 kDa protein with Shc. We purified and cloned this Shc-associated 145 kDa protein and found that it was a unique SH2 containing inositol polyphosphate-5-phosphatase. This novel enzyme, which we have called SHIP for SH2-containing inositol-phosphatase, may modulate both Ras and inositol signaling pathways.

Roles of the N and C terminal domains of the interleukin-3 receptor alpha chain in receptor function

The interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor, and IL-5 receptor alpha chains are each composed of three extracellular domains, a transmembrane domain and a short intracellular region. Domains 2 and 3 constitute the cytokine receptor module (CRM), typical of the cytokine receptor superfamily; however, the function of the N-terminal domain is not known. We have investigated the functions of the N-terminal and C-terminal domains of the IL-3 receptor (IL-3R) alpha chain. We find that cells transfected with the receptor beta chain (h beta c) and a truncated IL-3R alpha that is devoid of the intracellular region fail to proliferate or to activate STAT5 in response to human IL-3, despite binding the IL-3 with affinity indistinguishable from that of full-length receptor. In addition, IL-3-induced phosphorylation of h beta c was not detected. Thus, the IL-3R alpha intracellular region does not contribute detectably to stabilization of the receptor/ligand complex, but is essential for signal propagation. In contrast, a truncated IL-3R alpha with the N-terminal domain deleted interacts functionally with the beta chain; mouse cells transfected with these receptor chains proliferate in response to human IL-3 and STAT5 transcription factor is activated. High- and low-affinity binding sites are retained, although the affinity for IL-3 is decreased 15-fold, indicating a significant role for the N-terminal domain in IL-3 binding.

Suppression of interleukin-3-induced gene expression by a C-terminal truncated Stat5: role of Stat5 in proliferation

Interleukin-3 (IL3) was shown recently to utilize the transcription factor Stat5, but the genes regulated by this pathway and the biological consequence of Stat5 activation remained to be determined. In order to study the role of Stat5 in IL3 signalling, we constructed a dominant-negative Stat5 protein by C-terminal truncation, and inducibly expressed it in an IL3-dependent cell line. The effect of dominant-negative Stat5 induction on expression of IL3 early response genes was examined, and expression of several genes, including cis, osm and pim-1 was inhibited profoundly. The expression of c-fos was also reduced, but to a lesser extent. While activated Ras alone (though not Stat5 alone) could induce c-fos, maximal expression required the action of both Ras and Stat5. Interestingly, although the membrane-proximal region of the IL3 receptor beta-chain is responsible for both Jak2-Stat5 activation and c-myc induction, c-myc levels were not affected by the dominant-negative Stat5. Thus, the signals directed by this membrane-proximal domain, which is essential for transducing a DNA synthesis signal, can be separated further into Stat5 or c-myc pathways. The net effect of dominant-negative Stat5 expression was partial inhibition of IL3-dependent growth. This provides the first direct evidence that Stat5 is involved in regulation of cell proliferation.

Topography of the Escherichia coli initiation factor 2/fMet-tRNA(f)(Met) complex as studied by cross-linking

trans-Diamminedichloroplatinum(II) was used to induce reversible cross-links between Escherichia coli initiation factor 2 (IF-2) and fMet-tRNA(f)(Met). Two distinct cross-links between IF-2 and the initiator tRNA were produced. Analysis of the cross-linking regions on both RNA and protein moieties reveals that the T arm of the tRNA is in the proximity of a region of the C-terminal domain of IF-2 (residues Asn611-Arg645). This cross-link is well-correlated with the fact that the C-domain of IF-2 contains the fMet-tRNA binding site and that the cross-linked RNA fragment precisely maps in a region which is protected by IF-2 from chemical modification and enzymatic digestion. Rather unexpectedly, a second cross-link was characterized which involves the anticodon arm of fMet-tRNA(f)(Met) and the N-terminal part of IF-2 (residues Trp215-Arg237).

Critical proline residues of the cytoplasmic domain of the IL-5 receptor alpha chain and its function in IL-5-mediated activation of JAK kinase and STAT5

The high-affinity receptor (R) for IL-5 consists of a unique alpha chain (IL-5R alpha) and a beta chain (beta c) that is shared with the receptors for IL-3 and granulocyte macrophage colony stimulating factor (GM-CSF). We defined two regions of IL-5R alpha for the IL-5-induced proliferative response, the expression of nuclear proto-oncogenes, and the tyrosine phosphorylation of cellular proteins including beta c, SH2/SH3-containing proteins and JAK2 kinase. In the studies described here, we demonstrate that IL-5, IL-3 or GM-CSF stimulation induces the tyrosine phosphorylation of JAK2, and to a lesser extent JAK1, and of STAT5. Mutational analysis revealed that one of the proline residues, particularly Pro352 and Pro355, in the membrane-proximal proline-rich sequence (Pro352-Pro353-X-Pro355) of the cytoplasmic domain of IL-5R alpha is required for cell proliferation, and for both JAK1 and JAK2 activation. In addition, transfectants expressing chimeric receptors which consist of the extracellular domain of IL-5R alpha and the cytoplasmic domain of beta c responded to IL-5 for proliferation and tyrosine phosphorylation of JAK1. Intriguingly, electrophoretic mobility shift assay analysis revealed that STAT5 was activated in cells showing either JAK1 or JAK2 tyrosine phosphorylation. These results indicate that activation of JAK1, JAK2 and STAT5 is critical to coupling IL-5-induced tyrosine phosphorylation and ultimately mitogenesis, and that Pro352 and Pro355 in the proline-rich sequence appear to play more essential roles in cell growth and in both JAK1/STAT5 and JAK2/STAT5 activation than Pro353 does.

Bone scintigraphy in detection of bone invasion by oral carcinoma

Detecting osseous involvement is clinically important in the management of oral carcinoma. Thirty-one patients with osseous involvement due to oral carcinoma who underwent panoramic radiography and bone scintigraphy were evaluated retrospectively. Bone scintigraphy confirmed osseous involvement in all 31 (100%) of these patients. In 27 (87%) of 31 patients with osseous involvement, both the panoramic radiogram and bone scintigram were positive. In the remaining four patients (13%), bone scintigram was positive for mandibular or maxillary invasion, while panoramic radiogram was negative. There were no instances of an abnormal radiogram with a normal bone scintigram. These findings strongly suggest that bone scintigraphy is more sensitive than panoramic radiography in detecting osseous involvement of the mandible and maxilla due to oral carcinoma. Furthermore, bone scintigraphy was a critical pre-surgical in determining the extent of the osseous involvement.

Tyrosine 343 in the erythropoietin receptor positively regulates erythropoietin-induced cell proliferation and Stat5 activation

While previous studies with truncated erythropoietin receptors (EpRs) have suggested that the tyrosine phosphorylation of the EpR does not play a role in Ep-induced proliferation, we have found, using a more subtle, full length EpR mutant, designated Null, in which all eight of the intracellular tyrosines have been substituted with phenylalanine residues, that Null cells require substantially more Ep than wild-type cells in order to proliferate as efficiently. A comparison of Ep-induced proliferation with Ep-induced tyrosine phosphorylation patterns, using wild-type and Null EpR-expressing cells, revealed that Stat5 tyrosine phosphorylation and activation correlated directly with proliferation. Moreover, studies with a Y343F EpR point mutant and various EpR deletion mutants revealed that both Ep-induced proliferation and Stat5 activation were mediated primarily through Y343, but that other tyrosines within the EpR could activate Stat5 in its absence.

Interleukin 2 and erythropoietin activate STAT5/MGF via distinct pathways

Signal transducers and activators of transcription (STAT) proteins play an important role in cytokine signal transduction in conjunction with Janus kinases (JAKs). MGF/STAT5 is known as prolactin regulated STAT. Here we demonstrate that interleukin 2 (IL-2) as well as erythropoietin (EPO) stimulate STAT5 and induce tyrosine phosphorylation of STAT5. These IL-2- and EPO-induced STATs have an identical DNA binding specificity and immunoreactivity. We also show that IL-4 induces a DNA binding factor which possesses similar, but distinct, DNA binding specificity from that of STAT5 and is immunologically different from STAT5. Analysis of two EPO receptor (EPOR) transfected CTLL-2 cell lines discloses that IL-2 activates JAK1 and JAK3 as well as STAT5, while EPO stimulates STAT5 and JAK2 in EPO-responsive CTLL-2 cells (ERT/E2). On the contrary, EPO activates neither JAK2 nor STAT5 in other cell lines that failed to respond to EPO (ERT cells). EPOR and JAK2 associate with each other regardless of EPO presence in ERT/E2 cells, however, such an interaction is not present in ERT cells. Thus, EPOR and JAK2 association seems to be important for EPO responsiveness in CTLL-2 cells.

Prolactin, growth hormone, erythropoietin and granulocyte-macrophage colony stimulating factor induce MGF-Stat5 DNA binding activity

The molecular components which mediate cytokine signaling from the cell membrane to the nucleus were studied. Upon the interaction of cytokines with their receptors, members of the janus kinase (Jak) family of cytoplasmic protein tyrosine kinases and of the signal transducers and activators of transcription (Stat) family of transcription factors are activated through tyrosine phosphorylation. It has been suggested that the Stat proteins are substrates of the Jak protein tyrosine kinases. MGF-Stat5 is a member of the Stat family which has been found to confer the prolactin response. MGF-Stat5 can be phosphorylated and activated in its DNA binding activity by Jak2. The activation of MGF-Stat5 is not restricted to prolactin. Erythropoietin (EPO) and growth hormone (GH) stimulate the DNA binding activity of MGF-Stat5 in COS cells transfected with vectors encoding EPO receptor and MGF-Stat5 or vectors encoding GH receptor and MGF-Stat5. The activation of DNA binding by prolactin, EPO and GH requires the phosphorylation of tyrosine residue 694 of MGF-Stat5. The transcriptional induction of a beta-casein promoter luciferase construct in transiently transfected COS cells is specific for the prolactin activation of MGF-Stat5; it is not observed in EPO- and GH-treated cells. In the UT7 human hematopoietic cell line, EPO and granulocyte-macrophage colony stimulating factor activate the DNA binding activity of a factor closely related to MGF-Stat5 with respect to its immunological reactivity, DNA binding specificity and molecular weight. These results suggest that MGF-Stat5 regulates physiological processes in mammary epithelial cells, as well as in hematopoietic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-3, granulocyte-macrophage colony-stimulating factor, and interleukin-5 transduce signals through two forms of STAT5

Recently, JAK2 kinase was found to be one of the tyrosine kinases activated by interleukin-3 (IL-3) in target cells. JAK2 belongs to a family of kinases that act upstream of transcription factors called STATs. STATs exist in the cytoplasm as latent, transcriptionally inactive forms until, in response to extracellular signals, they become phosphorylated on tyrosine residues, translocate to the nucleus, and bind to specific DNA elements. Because IL-3 activates JAK2, we searched for the STAT(s) that might transduce IL-3 signals. Several lines of evidence suggest that IL-3 uses the murine homologue of STAT5, a factor originally purified from sheep. Unexpectedly, during isolation of the murine homologue, we found two highly related molecules that we have designated STAT5A and STAT5B.

Mediation of growth hormone-dependent transcriptional activation by mammary gland factor/Stat 5

Previous observations have shown that binding of growth hormone to its receptor leads to activation of transcription factors via a mechanism involving phosphorylation on tyrosine residues. In order to establish whether the prolactin-activated transcription factor Stat 5 (mammary gland factor) is also activated by growth hormone, nuclear extracts were prepared from COS-7 cells transiently expressing transfected Stat 5 and growth hormone receptor cDNA. Gel electrophoresis mobility shift analyses revealed the growth hormone-dependent presence of specific DNA-binding proteins in these extracts. The complexes formed could be supershifted by polyclonal anti-Stat 5 antiserum. In other experiments nuclear extracts from growth hormone-treated Chinese hamster ovary cells stably expressing transfected growth hormone receptor cDNA and liver from growth hormone-treated hypophysectomized rats were used for gel electrophoresis mobility shift analyses. These also revealed the presence of specific DNA-binding proteins sharing antigenic determinants with Stat 5. Stat 5 cDNA was shown to be capable of complementing the growth hormone-dependent activation of transcription of a reporter gene in the otherwise unresponsive COS-7 cell line. This complementation was dependent on the presence of Stat 5 tyrosine 694, suggesting a role for phosphorylation of this residue in growth hormone-dependent activation of DNA-binding and transcription.

Interleukin-3, granulocyte-macrophage colony stimulating factor and interleukin-5 transduce signals through two STAT5 homologs

Interleukin-3 (IL-3) is an important regulator of hemopoiesis and considerable effort has been directed towards the study of its mechanism of signal transduction. In this paper, we describe the first molecular identification of a STAT transcription factor that is activated by IL-3. STATs exist in a cytoplasmic, transcriptionally inactive form which, in response to extracellular signals, become tyrosine phosphorylated and translocate to the nucleus where they bind to specific DNA elements. Several of these DNA elements were found which bind proteins in an IL-3-responsive manner. Analysis of these bandshift complexes with available antibodies to the known STATs suggests that IL-3 activates the DNA-binding ability of STAT5, a protein which was originally characterized as a prolactin-responsive transcription factor in sheep. IL-5 and granulocyte-macrophage colony stimulating factor (GM-CSF), which share a common signaling receptor subunit with IL-3, also activate STAT5. Unexpectedly, two murine STAT5 homologs, 96% identical to each other at the amino acid level, were isolated and IL-3-dependent GAS binding could be reconstituted in COS cells transfected with IL-3 receptor and either STAT5 cDNA. In IL-3-dependent hemopoietic cells, both forms of STAT5 are expressed and activated in response to IL-3.

[Development of helical CT and clinical application]

We applied helical CT to examinations of the clinical image diagnosis. Scanning was performed continuously while the couchtop of the CT scanner was shifted at a constant speed. The entire lung field could be scanned during a single holding of the breath when the couchtop speed was 20 mm/s. Tumors as small as 2 mm were detected. The diagnostic detectability and accuracy of helical CT were far superior to those conventional chest radiography. During abdominal examination, the target organ could be scanned at any specified phase (preferably arterial) during the injection of contrast medium. We detected very small hepatic tumors which could not be detected by conventional CT. Helical CT produced continuous data, which was reconstructed to display three-dimensional image. Helical CT could be used in mass screening for the detection of early lung cancer and in computer-aided diagnosis.

Prolactin induces phosphorylation of Tyr694 of Stat5 (MGF), a prerequisite for DNA binding and induction of transcription

Mammary gland factor (MGF) is a transcription factor discovered initially in the mammary epithelial cells of lactating animals. It confers the lactogenic hormone response to the milk protein genes. We reported recently the isolation of the cDNA encoding MGF. MGF is a novel member of the cytokine-regulated transcription factor gene family. Members of this gene family mediate interferon alpha/beta and interferon gamma induction of gene transcription, as well as the response to epidermal growth factor and interleukin-6, and have been named signal transducers and activators of transcription (Stat). The name Stat5 has been assigned to MGF. We studied the mechanisms involved in the prolactin activation of Stat5 in COS cells co-transfected with cDNA encoding Stat5 and the prolactin receptor. Prolactin treatment of the transfected cells caused activation of Stat5 within 5-10 min. This activation does not require ongoing protein synthesis. Tyrosine kinase inhibitors prevent Stat5 activation in transfected COS cells. Treatment of recombinant Stat5 with a tyrosine-specific protein phosphatase in vitro abolishes its DNA binding activity. Prolactin stimulation of transfected cells induces Stat5 phosphorylation on tyrosine. Phosphorylation of in vitro transcribed and translated Stat5 with the Jak2 tyrosine kinase, but not with fyn, lyn or lck, confers DNA binding activity. The prolactin response of the beta-casein milk protein gene promoter can be observed in COS cells transfected with cDNA vectors encoding Stat5 and the long form of the prolactin receptor. The short form of the prolactin receptor is unable to promote Stat5 phosphorylation and confer transcriptional induction in COS cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Mammary gland factor (MGF) is a novel member of the cytokine regulated transcription factor gene family and confers the prolactin response

Milk protein gene expression in mammary epithelial cells is regulated by the action of the lactogenic hormones insulin, glucocorticoids and prolactin. The mammary gland factor, MGF, has been shown to be a central mediator in the lactogenic hormone response. The DNA binding activity of MGF is hormonally regulated and essential for beta-casein promoter activity. We have used Red A Sepharose- and sequence-specific DNA affinity chromatography to purify MGF from mammary gland tissue of lactating sheep. Proteins of 84 and 92 kDa were obtained, proteolytically digested and the resulting peptides separated by reverse phase high pressure liquid chromatography. The 84 and 92 kDa proteins yielded very similar peptide patterns. The amino acid sequence of two peptides was determined. The sequence information was used to derive oligonucleotide probes. A cDNA library from the mRNA of mammary gland tissue of lactating sheep was screened and a molecular clone encoding MGF was isolated. MGF consists of 734 amino acids and has sequence homology with the 113 (Stat113) and 91 kDa (Stat91) components of ISGF3, transcription factors which are signal transducers of IFN-alpha/beta and IFN-gamma. Two species of MGF mRNA of 6.5 and 4.5 kb were detected in mammary gland tissue of lactating sheep. Lower mRNA expression was found in ovary, thymus, spleen, kidney, lung, muscle and the adrenal gland. MGF cDNA was incorporated into a eukaryotic expression vector and cotransfected with a vector encoding the long form of the prolactin receptor into COS cells. A strong MGF-specific bandshift was obtained with nuclear extracts of COS cells induced with prolactin. Treatment of activated MGF with a tyrosine-specific protein phosphatase resulted in the loss of DNA binding activity. Prolactin-dependent transactivation of a beta-casein promoter-luciferase reporter gene construct was observed in transfected cells.

Mammary gland-specific nuclear factor is present in lactating rodent and bovine mammary tissue and composed of a single polypeptide of 89 kDa

Mammary epithelial cells, under the regulation of the lactogenic hormones, produce high amounts of milk proteins during the lactation period. The caseins are the most abundant milk proteins. We have studied the regulation of beta-casein gene expression and found that the lactogenic hormones induce transcription of the beta-casein gene promoter. The hormonal regulation is mediated in part by a mammary gland-specific transcription factor (MGF). MGF is a specific DNA-binding protein which recognizes the sequence 5'-ACTTCT-TGGAATT-3'. This sequence is conserved with slight variations in the alpha- and beta-casein gene promoters of the cow and rodents at position -87 to -99. Bovine MGF and rodent MGF behaved identically when their DNA binding properties and migration in polyacrylamide gels as protein-DNA complexes were compared. MGF was purified to near homogeneity from nuclear extracts of mammary epithelial cells derived from lactating rats. The combination of Bio-Rex 70-, DNA-Sepharose-, and sequence-specific DNA affinity column chromatography yielded a highly purified preparation of MGF. The purification from nuclear extract was more than 2400-fold, and the yield of MGF activity was 11%. A protein of 89 kDa was visualized by silver staining after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The apparent molecular weight was confirmed by UV cross-linking of the factor to its cognate DNA binding sequence and subsequent gel electrophoresis. Excision of the 89-kDa band from the gel and renaturation of the protein restored its specific DNA binding ability. This indicates that MGF is composed of a single polypeptide.

Topography of the Escherichia coli ribosomal 30S subunit-initiation factor 2 complex

The specific effect of the binding of initiation factor IF2 on E coli 16S rRNA within the [IF2/30S/GTP] complex has been probed by crosslinking experiment with trans-diamminedichloro platinum (II) and by phosphate alkylation with ethylnitrosourea. Several 16S rRNA fragments crosslinked to IF2 have been identified and are mostly located in the head and the lateral protrusion of the 30S subunit. The study of the effect of IF2 binding to the 30S subunit reveals that the factor does not tightly bind to the 16S rRNA and induces both isolated reductions and enhancements of phosphate reactivity in the 16S rRNA. Several of them are located near the binding site of IF2 and weak effects are observed in distant parts of the subunit. These results are discussed in the light of current knowledge of the topographical localization of IF2 with the 30S subunit and of its relation with function.

Binding of initiation factor 2 and initiator tRNA to the Escherichia coli 30S ribosomal subunit induces allosteric transitions in 16S rRNA

The specific effect of the binding of IF2 and initiator fMET-tRNA(fMet) on Escherichia coli 16S rRNA has been probed by phosphate alkylation with ethylnitrosourea. The results show that IF2 does not significantly shield portions of 16S rRNA but induces both reductions and enhancements of reactivity scattered in the entire molecule. Most of them are topographically constrained in a region corresponding to the cleft, the lateral protrusion, and the part of the head facing the protrusion (positions 694, 771, 791, 1225, 1268, 1398, 1401, 1504, and 1527). Weak effects are also observed in distant parts of the subunit (positions 301, 302, 492, and 1428). All the reactivity changes induced by the binding of IF2 are still observed in the presence of the initiator tRNA and AUG as messenger. The additional changes induced by the tRNA are mostly centered around the cleft-head-lateral protrusion region, near positions affected by IF2 binding. Most of the changes correspond to reduced reactivities (positions 791, 1222, 1263, 1393, 1395, 1430, 1431, 1504, 1528, and 1529), while enhanced reactivities are observed at positions 708, 709, and 1398. Functional implications are discussed, which stress the dynamic properties of the ribosome.

The conformation of the initiator tRNA and of the 16S rRNA from Escherichia coli during the formation of the 30S initiation complex

The conformation of the E. coli initiator tRNA and of the 16S rRNA at different steps leading to the 30S.IF2.fMet-ARN(fMet).AUG.GTP complex has been investigated using several structure-specific probes. As compared to elongator tRNA, the initiator tRNA exhibits specific structural features in the anticodon arm, the T and D loops and the acceptor arm. Initiation factor 2 (IF2) interacts with the T-loop and the minor groove of the T stem of the RNA, and induces an increased flexibility in the anticodon arm. In the 30S initiation complex, additional protection is observed in the acceptor stem and in the anticodon arm of the tRNA. Within the 30S subunit, IF2 does not significantly shield defined portions of 16S rRNA, but induces both reduction and enhancement of reactivity scattered in the entire molecule. Most are constrained in a region corresponding to the cleft, the lateral protrusion and the part of the head facing the protrusion. All the reactivity changes induced by the binding of IF2 are still observed in the presence of the initiator tRNA and AUG message. The additional changes induced by the tRNA are mostly centered around the cleft-head-lateral protrusion region, near positions affected by IF2 binding.

The solution structure of the Escherichia coli initiator tRNA and its interactions with initiation factor 2 and the ribosomal 30 S subunit

The conformation of the Escherichia coli initiator tRNA has been investigated using enzymatic and chemical probes. This study was conducted on the naked tRNA and on the tRNA involved in the various steps leading to the formation of the 30 S.IF-2.GTP.fMet-tRNA.AUG complex. A three-dimensional model of the initiator tRNA is presented, which displays several differences with yeast tRNAPhe: (i) the anticodon arm is more rigid; (ii) the presence of an additional nucleotide in the D loop results in specific features in both T and D loops; (iii) C1 and A72 might form a noncanonical base pair. Aminoacylation and formylation induce subtle conformational adjustments near the 3' end, the T arm and the D loop. Initiation factor (IF) 2 interacts with a rather limited portion of the tRNA, covering the T loop and the minor groove of the T stem, and induces an increased flexibility in the anticodon arm. The specific structural features observed in the T loop are probably recognized by IF-2. In the 30 S.IF-2.GTP.fMet-tRNA.AUG complex, additional protections are observed in the acceptor stem and in the anticodon arm, resulting from a strong steric hindrance and from the codon-anticodon interaction within the subunit decoding site.

Technetium-99m pertechnetate and gallium-67 imaging in salivary gland disease

Thirty-two patients with salivary gland tumors or sialadenitis were studied with Tc-99m pertechnetate and Ga-67 imaging and, in some instances, sialography. The diagnostic algorithm presented allows the correct categorization of the salivary gland pathology in the vast majority of patients. The patients were studied serially with Tc-99m pertechnetate, Ga-67 and in certain situations sialography (or CT-sialography). Use of the algorithm can distinguish benign salivary tumors from malignant tumors and malignant tumors from inflammatory disease. The limitations and pitfalls of interpretation are discussed.

The relationship between 67Ga accumulation and ATP metabolism in tumor cells in vitro

Previously, we reported that the deposition of 67Ga into malignant tumors may be a sensitive index of proliferative activity in tumor cells. For the purpose of elucidation of this hypothesis, we investigated the relationship between the accumulation of 67Ga into malignant tumor cells and the intra cellular ATP metabolism in vitro. The uptake of 67Ga into tumor cells was inhibited by adding NaF which is an inhibitor of ATP production. Furthermore, the uptake of 67Ga into tumor cells was strongly inhibited by adding ouabain which is a specific inhibitor of Na+-K+-ATPase. From these in vitro results, it was concluded that there is a correlation between 67Ga uptake and intra cellular ATP metabolism in tumor cells.