Specific activation of Smad1 signaling pathways by the BMP7 type I receptor, ALK2

BMP7 and activin are members of the transforming growth factor beta superfamily. Here we characterize endogenous activin and BMP7 signaling pathways in P19 embryonic carcinoma cells. We show that BMP7 and activin bind to the same type II receptors, ActRII and IIB, but recruit distinct type I receptors into heteromeric receptor complexes. The major BMP7 type I receptor observed was ALK2, while activin bound exclusively to ALK4 (ActRIB). BMP7 and activin elicited distinct biological responses and activated different Smad pathways. BMP7 stimulated phosphorylation of endogenous Smad1 and 5, formation of complexes with Smad4 and induced the promoter for the homeobox gene, Tlx2. In contrast, activin induced phosphorylation of Smad2, association with Smad4, and induction of the activin response element from the Xenopus Mix.2 gene. Biochemical analysis revealed that constitutively active ALK2 associated with and phosphorylated Smad1 on the COOH-terminal SSXS motif, and also regulated Smad5 and Smad8 phosphorylation. Activated ALK2 also induced the Tlx2 promoter in the absence of BMP7. Furthermore, we show that ALK1 (TSRI), an orphan receptor that is closely related to ALK2 also mediates Smad1 signaling. Thus, ALK1 and ALK2 induce Smad1-dependent pathways and ALK2 functions to mediate BMP7 but not activin signaling.

Association of the TLX-2 homeodomain and 14-3-3eta signaling proteins

Homeodomain proteins play important roles in various developmental processes, and their functions are modulated by polypeptide cofactors. Here we report that both in vitro and in vivo, 14-3-3eta is associated with the TLX-2 homeodomain transcription factor that is required for mouse embryogenesis. Expression of 14-3-3eta shifts the predominant localization of TLX-2 in COS cells from the cytoplasm to the nucleus. Tlx-2 and 14-3-3eta are expressed in the developing peripheral nervous system with spatially and temporally overlapping patterns, and they are also coexpressed in PC12 cells. Increased expression of either gene by transfection considerably inhibited nerve growth factor-induced neurite outgrowth of PC12 cells, and cotransfection of both genes led to a synergistic effect of suppression. These findings define 14-3-3eta as a functional modulator of the TLX-2 homeodomain transcription factor and suggest that the in vivo function of TLX-2 in neural differentiation is likely regulated by signaling mediated by 14-3-3eta.

The Tlx-2 homeobox gene is a downstream target of BMP signalling and is required for mouse mesoderm development

TGFbeta-related factors are critical regulators of vertebrate mesoderm development. However, the signalling cascades required for their function during this developmental process are poorly defined. Tlx-2 is a homeobox gene expressed in the primitive streak of mouse embryos. Exogenous BMP-2 rapidly activates Tlx-2 expression in the epiblast of E6.5 embryos. A Tlx-2 promoter element responds to BMP-2 signals in P19 cells, and this response is mediated by BMP type I receptors and Smad1. These results suggest that Tlx-2 is a downstream target gene for BMP signalling in the primitive streak where BMP-4 and other TGFbeta-related factors are expressed. Furthermore, disruption of Tlx-2 function leads to early embryonic lethality. Similar to BMP4 and ALK3 mutants, the mutant embryos display severe defects in primitive streak and mesoderm formation. These experiments thus define a BMP/Tlx-2 signalling pathway that is required during early mammalian gastrulation.

Synthetic lethality of yeast slt mutations with U2 small nuclear RNA mutations suggests functional interactions between U2 and U5 snRNPs that are important for both steps of pre-mRNA splicing

A genetic screen was devised to identify Saccharomyces cerevisiae splicing factors that are important for the function of the 5' end of U2 snRNA. Six slt (stands for synthetic lethality with U2) mutants were isolated on the basis of synthetic lethality with a U2 snRNA mutation that perturbs the U2-U6 snRNA helix II interaction. SLT11 encodes a new splicing factor and SLT22 encodes a new RNA-dependent ATPase RNA helicase (D. Xu, S. Nouraini, D. Field, S. J. Tang, and J. D. Friesen, Nature 381:709-713, 1996). The remaining four slt mutations are new alleles of previously identified splicing genes: slt15, previously identified as prp17 (slt15/prp17-100), slt16/smd3-1, slt17/slu7-100, and slt21/prp8-21. slt11-1 and slt22-1 are synthetically lethal with mutations in the 3' end of U6 snRNA, a region that affects U2-U6 snRNA helix II; however, slt17/slu7-100 and slt21/prp8-21 are not. This difference suggests that the latter two factors are unlikely to be involved in interactions with U2-U6 snRNA helix II but rather are specific to interactions with U2 snRNA. Pairwise synthetic lethality was observed among slt11-1 (which affects the first step of splicing) and several second-step factors, including slt15/prp17-100, slt17/slu7-100, and prp16-1. Mutations in loop 1 of U5 snRNA, a region that is implicated in the alignment of the two exons, are synthetically lethal with slu4/prp17-2 and slu7-1 (D. Frank, B. Patterson, and C. Guthrie, Mol. Cell. Biol. 12:5179-5205, 1992), as well as with slt11-1, slt15/prp17-100, slt17/slu7-100, and slt21/prp8-21. These same U5 snRNA mutations also interact genetically with certain U2 snRNA mutations that lie in the helix I and helix II regions of the U2-U6 snRNA structure. Our results suggest interactions among U2 snRNA, U5 snRNA, and Slt protein factors that may be responsible for coupling and coordination of the two reactions of pre-mRNA splicing.

An RNA-dependent ATPase associated with U2/U6 snRNAs in pre-mRNA splicing

The hydrolysis of ATP by a group of RNA-dependent ATPases (DEAD/H proteins) is required for spliceosome assembly, but not for the subsequent transesterification reactions. Little is known about the function of these ATPases in relation to the RNA conformational changes that occur in formation of active structures, in which U2/U6 small nuclear RNA (snRNA) interactions are essential for splicing to take place. Using a synthetic lethal genetic screen, we have isolated four yeast splicing factors involved in U2/U6 snRNA interactions (D.X. et al., manuscript in preparation). The RNA-dependent ATPase activity associated with one such factor, the Slt22 protein, is stimulated preferentially by annealed U2/U6 snRNAs. Both mutant slt22-1 and U2 snRNA cause a reduction in stimulation. The slt22-1 mutation blocks splicing at or before the first step, resulting in the accumulation of an unusual complex which lacks U5 snRNA. Our results indicate that the U2/U6 snRNA interactions facilitated by Slt22 are also involved in the interaction of U5 snRNA with the spliceosome.

Regulation of topoisomerase II expression during the VM-26 induced differentiation of IW32 murine erythroleukemia cells

The effect of VM-26, a topoisomerase II targeting drug, on IW32 murine erythroleukemia cells was investigated. The VM-26 induced IW32 cells to differentiate at a non-toxic but cytostatic concentration (0.01 microgram/ml). More than 40% of the cells were induced to synthesize hemoglobin, and cells were arrested in G2/M phase of the cell cycle. Levels of beta-globin mRNA also increased significantly. Cells became committed to erythroid maturation after 16 h of continuous drug exposure. Replacement with fresh VM-26 after 48 h of drug treatment further increased the hemoglobin containing cells to greater than 80%. Unlike other drug induced erythroleukemia cell differentiation, c-myc mRNA expression was not affected by VM-26. Inhibition of topoisomerase II activity was observed during the first 12 h of VM-26 treatment; however, elevated enzyme activity was found thereafter. Northern blot analysis showed significant increase in the expression of topoisomerase IIalpha mRNA at 12 and 24 h after VM-26 addition. These findings indicate that VM-26 inhibited the activity of topoisomerase II and promoted the committed differentiation of IW32 cells along the erythroid pathway. In addition, a parallel increase in mRNA and activity levels of topoisomerase II in differentiated cells suggests that regulation of the enzyme expression occurred in the VM-26 induced erythroid maturation.

The expression of acidic ribosomal phosphoproteins on the surface membrane of different tissues in autoimmune and normal mice which are the target molecules for anti-double-stranded DNA antibodies

Affinity-purified polyclonal anti-double-stranded DNA (anti-dsDNA) antibodies from patients with systemic lupus erythematosus (SLE) exert a cytostatic effect on cultured rat glomerular mesangial cells (MC). The cognate antigens expressed on the surface of MC have been proved to be acidic ribosomal phosphoproteins (P proteins) in our previous study. The mesangial cytostatic effect of anti-dsDNA antibodies is attributed to the cross-reactivity of the antibodies with membrane-expressed P proteins, but not to the effect of minute amounts of anti-ribosomal P proteins antibodies contained in the anti-dsDNA preparations. Immunofluorescence staining of the native cells demonstrated that anti-dsDNA antibodies bound to the surface of rat mesangial cells, rat brain astrocytes (RBA-1) and mouse fibroblasts (3T3). Anti-dsDNA antibodies also exert potent cytostatic effects on these cells in a dose-dependent manner. In addition, the plasma membranes of different cell lines and tissues from normal and autoimmune mice were isolated and probed by anti-dsDNA antibodies in Western blot analysis. We found the actively proliferating cells such as MC, RBA-1 and 3T3 may express both P0 (38,000 MW) and P1 (19,000 MW) on the surface membrane. In addition, the kidney, liver and spleen from either autoimmune MRL-lpr/lpr or BALB/c mice may constantly express P0 protein, but the expression of P1 is inconsistent. In contrast, brain and muscle from either mice failed to express P proteins on their surface. Unexpectedly, a high molecular weight substance (larger than 205,000 MW) with unknown nature appears in the membrane of brain and muscle tissues in both mice. Immunoprecipitation of the surface-biotinylated MC-lysate by anti-dsDNA antibodies further confirmed that P1 (19,000 MW) and P2 (17,000 MW) are really expressed on the cell surface. These results suggest that P proteins expressed on the surface of different tissues become the targets for anti-dsDNA antibodies mediating pleomorphic tissue damage in patients with SLE.

Anti-dsDNA antibodies cross-react with ribosomal P proteins expressed on the surface of glomerular mesangial cells to exert a cytostatic effect

Affinity-purified human polyclonal anti-double-stranded DNA antibodies (anti-dsDNA) exerted a cytostatic effect towards human and rat glomerular mesangial cells (MC). In order to identify the cognate antigens for anti-dsDNA on the surface of MC, we used these autoantibodies to probe a human renal lambda gt11 cDNA expression library. Two cDNA clones encoding the cognate proteins for the autoantibodies were isolated. Sequencing analysis of the two cDNA showed that they had 98.6% homology with the gene of the P0 and 99.2% homology with the gene of the P1 human acidic ribosomal phosphoproteins (P protein). Two galactosidase fusion proteins (125,000 and 150,000 MW) derived from the two cDNA inserts expressed in lysogenic Escherichia coli Y1089 could react with the original screening antibodies in an immunoblotting analysis. After transformation and expression of the full-length P1 clone in prokaryotic cells, the purified P1 protein was able to react with anti-dsDNA. In a cross-inhibition experiment, the dsDNA binding activity of anti-dsDNA was inhibited by a synthetic polypeptide corresponding to the carboxyl-terminal 20 amino acids of P protein and purified P1 protein in a dose-dependent manner, but this was less potent than the inhibition caused by calf thymus dsDNA. By use of well-defined systemic lupus erythematosus (SLE) sera, we found only sera containing a high titre of anti-dsDNA activity (> 300 IU/ml) reacted with P1 of rat MC lysate. Furthermore, the 38,000 and 19,000 MW macromolecules were proved to be the cognate antigens for anti-dsDNA expression on the surface of the MC, by Western blot of the MC plasma membrane lysates. These results suggest that anti-dsDNA may cross-react with ribosomal P proteins expressed on the surface of the MC and exert cytostasis towards these cells.

Analysis of c-fos expression in the butyrate-induced F-98 glioma cell differentiation

The functional induction of c-fos in the sodium butyrate-induced differentiation of F-98 glioma cells was studied. Fos protein level was increased by butyrate. In contrast, c-Jun protein was constitutively expressed and was not affected by butyrate. Gel-retardation assay indicates Fos as a component of the complex formed between the consensus oligonucleotide of the TPA (PMA, phorbol 12-myristate 13-acetate) response element (TRE) and nuclear extract prepared from butyrate-treated cells. Transfection studies showed that butyrate increased transcription from a multimeric TRE-driven reporter construct, and the effect was mimicked by transfecting cells with fos-expression plasmid. Furthermore, under conditions of c-fos over-expression, transactivation by butyrate was essentially abolished. These data suggest that Fos induction had a functional role in gene activation. Characterization of stable c-fos transfectants demonstrated that these cells displayed alterations in morphology, showed serum-dependent growth, had slower growth rates and grew to lower saturation densities than did untransfected F-98 cells or transfected cells that did not express c-fos. Immunofluorescent staining indicated that fos transfectants also had elevated glial fibrillary acidic protein ('GFAP') expression. Transfection of the c-fos promoter-chloramphenicol acetyltransferase fusion gene into F-98 cells revealed that activation of c-fos by butyrate was exerted at the promoter level, and sequences located within nucleotides -757 to -402 of the c-fos promoter were responsible for butyrate induction. Our data indicate that transcriptional activation of c-fos through its promoter by butyrate resulted in increased Fos protein expression. Transfection studies show that both c-fos and butyrate activate TRE-containing genes, and fos may be a downstream mediator of butyrate. Furthermore, expression of c-fos plays a major role in modulating the growth properties of F-98 cells.

[A clinical research of three dimensional computerized imaging in the aid of operative design for reconstructive surgery of the face]

This article reports the utilization of three dimensional imaging technique of computer in reconstructive surgery of the face. In 312 cases, the technique has been proved that it can make the preoperative analysis computerized, quantitated and picturized. The measurement and analysis through computer are quick and exact, rendering operative designs feasible. The use of the evaluation system can also help enhance the communication and understanding between the surgeon and his patient. The surgical simulation system can replace the traditional preoperative manual work such as paper molds, plaster casts, and wax mold, and it is therefore much valuable for practical use.

Expression of c-myc proto-oncogene during podophyllotoxin induced IW32 erythroleukemia cell differentiation

The effect of hemin or podophyllotoxin on the differentiation of the erythropoietin (epo)-producing IW32 erythroleukemia cells was investigated. Podophyllotoxin induced IW32 cells to differentiate, and hemin potentiated the differentiation. Hemin had no effect on cell proliferation whereas podophyllotoxin inhibited cell growth. c-myc mRNA levels decreased biphasically by hemin or podophyllotoxin, while the combined treatment of hemin plus podophyllotoxin did not result in the initial decrease in c-myc mRNA level. Our data suggested that down-regulation of c-myc expression was not a prerequisite of IW32 cell differentiation induced by hemin and podophyllotoxin combined.

Induction of fos and sis proto-oncogenes and genes of the extracellular matrix proteins during butyrate induced glioma differentiation

Sodium butyrate has been shown to inhibit the growth and induce the differentiation of F-98 rat glioma cells. In agreement with the morphological changes, we have found that mRNAs for fibronectin and collagen in these cells could be reversibly induced by butyrate. While Ki-ras mRNA levels remained relatively unchanged, mRNAs for fos and sis increased significantly during the course of butyrate induced differentiation. c-fos induction can be detected 30 min after butyrate addition, a peak level (greater than 20 fold) was reached at 2 h, with a subsequent gradual decline. c-sis induction was detectable 24 h after butyrate exposure, at which time the cells have assumed morphological transition. Interestingly, the sis mRNA induction was not reversible upon butyrate withdrawal. The sis mRNA half-life increased from 40 min in the untreated cells to 100 min in the butyrate induced cells indicating that the increase in the stability of sis mRNA contributed, at least in part, to the elevated levels of sis expression. These findings demonstrate a coordinated induction of fibronectin and collagen genes in the butyrate-treated F-98 cells. In addition, fos and sis transcripts were differentially induced; a rapid and transient induction of fos followed by an irreversible induction of sis at a later stage of differentiation.