Enhancement of osteoclastic bone resorption and suppression of osteoblastic bone formation in response to reduced mechanical stress do not occur in the absence of osteopontin.

Reduced mechanical stress to bone in bedridden patients and astronauts leads to bone loss and increase in fracture risk which is one of the major medical and health issues in modern aging society and space medicine. However, no molecule involved in the mechanisms underlying this phenomenon has been identified to date. Osteopontin (OPN) is one of the major noncollagenous proteins in bone matrix, but its function in mediating physical-force effects on bone in vivo has not been known. To investigate the possible requirement for OPN in the transduction of mechanical signaling in bone metabolism in vivo, we examined the effect of unloading on the bones of OPN(-/-) mice using a tail suspension model. In contrast to the tail suspension-induced bone loss in wild-type mice, OPN(-/-) mice did not lose bone. Elevation of urinary deoxypyridinoline levels due to unloading was observed in wild-type but not in OPN(-/-) mice. Analysis of the mechanisms of OPN deficiency-dependent reduction in bone on the cellular basis resulted in two unexpected findings. First, osteoclasts, which were increased by unloading in wild-type mice, were not increased by tail suspension in OPN(-/-) mice. Second, measures of osteoblastic bone formation, which were decreased in wild-type mice by unloading, were not altered in OPN(-/-) mice. These observations indicate that the presence of OPN is a prerequisite for the activation of osteoclastic bone resorption and for the reduction in osteoblastic bone formation in unloaded mice. Thus, OPN is a molecule required for the bone loss induced by mechanical stress that regulates the functions of osteoblasts and osteoclasts.

Antisense RNA-induced reduction in murine TIMP levels confers oncogenicity on Swiss 3T3 cells.

Mouse 3T3 cell lines capable of constitutively synthesizing an RNA complementary to the messenger RNA encoding TIMP, tissue inhibitor of metalloproteinases, were constructed by transfection with appropriate plasmid constructs. Many of the lines were down-modulated for TIMP messenger RNA levels and secreted less TIMP into the culture medium. In comparison to noninvasive, nontumorigenic controls, these cells not only were invasive in a human amnion invasion assay, but also were tumorigenic and metastatic in athymic mice. These results indicate that TIMP suppresses oncogenicity, at least in immortal murine 3T3 cells.

The influence of the proinflammatory cytokine, osteopontin, on autoimmune demyelinating disease.

Multiple sclerosis is a demyelinating disease, characterized by inflammation in the brain and spinal cord, possibly due to autoimmunity. Large-scale sequencing of cDNA libraries, derived from plaques dissected from brains of patients with multiple sclerosis (MS), indicated an abundance of transcripts for osteopontin (OPN). Microarray analysis of spinal cords from rats paralyzed by experimental autoimmune encephalomyelitis (EAE), a model of MS, also revealed increased OPN transcripts. Osteopontin-deficient mice were resistant to progressive EAE and had frequent remissions, and myelin-reactive T cells in OPN-/- mice produced more interleukin 10 and less interferon-gamma than in OPN+/+ mice. Osteopontin thus appears to regulate T helper cell-1 (TH1)-mediated demyelinating disease, and it may offer a potential target in blocking development of progressive MS.

Eta-1 (osteopontin): an early component of type-1 (cell-mediated) immunity.

Cell-mediated (type-1) immunity is necessary for immune protection against most intracellular pathogens and, when excessive, can mediate organ-specific autoimmune destruction. Mice deficient in Eta-1 (also called osteopontin) gene expression have severely impaired type-1 immunity to viral infection [herpes simplex virus-type 1 (KOS strain)] and bacterial infection (Listeria monocytogenes) and do not develop sarcoid-type granulomas. Interleukin-12 (IL-12) and interferon-gamma production is diminished, and IL-10 production is increased. A phosphorylation-dependent interaction between the amino-terminal portion of Eta-1 and its integrin receptor stimulated IL-12 expression, whereas a phosphorylation-independent interaction with CD44 inhibited IL-10 expression. These findings identify Eta-1 as a key cytokine that sets the stage for efficient type-1 immune responses through differential regulation of macrophage IL-12 and IL-10 cytokine expression.

Osteopontin is elevated during neointima formation in rat arteries and is a novel component of human atherosclerotic plaques.

In an earlier report, we used differential cloning to identify genes that might be critical in controlling arterial neointima formation (Giachelli, C., N. Bae, D. Lombardi, M. Majesky, and S. Schwartz. 1991. Biochem. Biophys. Res. Commun. 177:867-873). In this study, we sequenced the complete cDNA and conclusively identified one of these genes, 2B7, as rat osteopontin. Using immunochemistry and in situ hybridization, we found that medial smooth muscle cells (SMC) in uninjured arteries contained very low levels of osteopontin protein and mRNA. Injury to either the adult rat aorta or carotid artery using a balloon catheter initiated a qualitatively similar time-dependent increase in both osteopontin protein and mRNA in arterial SMC. Expression was transient and highly localized to neointimal SMC during the proliferative and migratory phases of arterial injury, suggesting a possible role for osteopontin in these processes. In vitro, basic fibroblast growth factor (bFGF), transforming growth factor-beta (TGF-beta), and angiotensin II (AII), all proteins implicated in the rat arterial injury response, elevated osteopontin expression in confluent vascular SMC. Finally, we found that osteopontin was a novel component of the human atherosclerotic plaque found most strikingly associated with calcified deposits. These data implicate osteopontin as a potentially important mediator of arterial neointima formation as well as dystrophic calcification that often accompanies this process.

Regulation of the mRNA for monocyte-derived neutrophil-activating peptide in differentiating HL60 promyelocytes.

A cDNA library was constructed from HL60 human promyelocyte poly(A)+ RNA harvested 3 h after induction of macrophage differentiation with 12-O-tetradecanoyl phorbol-13-acetate in the presence of cycloheximide. We isolated from this library a 1.6-kilobase full-length clone designated b4 whose corresponding mRNA was greatly increased in abundance in cytoplasmic RNA under these conditions. Dideoxy sequencing revealed that this mRNA encoded MONAP (monocyte-derived neutrophil-activating peptide), a 10-kilodalton monokine with neutrophil-specific chemotactic and enzyme-releasing activities. The 3' untranslated region of this mRNA was found to be 1.2 kilobases long and possessed nine copies of the AUUUA sequence known to be associated with regulation of mRNA stability. Actinomycin D chase experiments yielded evidence that cytoplasmic stabilization was one of the means of regulation of MONAP expression. Analysis of cytoplasmic poly(A)- RNA revealed the presence of several discrete truncated species that shared a common 5' end and appeared to be intermediates of degradation. S1 mapping showed that the 3' ends of these molecules were distributed throughout the 3' untranslated region, preferentially in A + U-rich regions, broadly correlating with the distribution of AUUUA sites. Nuclear run-on experiments indicated that transcriptional induction accounted for less than 15% of the accumulation of MONAP mRNA. This mRNA was induced in HL60 cells by treatment with several differentiation-inducing agents: 12-O-tetradecanoyl phorbol-13-myristate alone, sodium butyrate, vitamin D3, and dimethyl sulfoxide. It was also induced in quiescent diploid lung fibroblasts stimulated to divide by serum, and it was constitutively overexpressed by some human tumor lines.

Transcriptional regulation of two serum-induced RNAs in mouse fibroblasts: equivalence of one species to B2 repetitive elements.

We obtained eight cDNA clones that define five genes whose expression (appearance of transcripts in the cytoplasm) is enhanced when quiescent mouse fibroblasts are stimulated with serum to divide. Two of these clones (designated 49C8 and 16C8) correspond to RNA species that are present in the cytoplasm of quiescent cells at very low levels. After serum stimulation, the level of 16C8 mRNA rose more rapidly than that of 49C8 RNA, reaching a maximum around 6 to 12 h. The data suggest that 49C8 and 16C8 RNAs are induced as a result of independent stimuli. Either fibroblast growth factor or 12-tetradecanoylphorbol-13-acetate alone could induce 16C8 expression almost as effectively as serum; in contrast, 49C8 was not efficiently induced by epidermal growth factor, fibroblast growth factor, insulin, or 12-tetradecanoylphorbol-13-acetate. Inhibitors of transcription and translation diminished the induction of 16C8, while 49C8 expression was sensitive to actinomycin D but not cycloheximide or 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole. In vitro transcription experiments with isolated nuclei revealed a peak in transcriptional activity of the 16C8 gene at around 3 h after serum stimulation. Sequence analysis of the 49C8 cDNA clone showed greater than 90% homology of a large portion to a consensus rodent B2 repetitive element.

Characterization of a cDNA clone encoding murine mitogen-regulated protein: regulation of mRNA levels in mortal and immortal cell lines.

Mitogen-regulated protein (MRP) is secreted by certain immortal murine cell lines (Swiss 3T3, BNL) stimulated with serum or particular growth factors. We have identified a cDNA clone that encodes part of the protein and have confirmed that MRP is closely related to, if not identical to, the prolactin-related protein designated proliferin. MRP is not produced by primary mouse embryo fibroblasts to nearly the same extent as it is produced by many immortal or transformed lines. Control of expression of this protein by growth factors is achieved both by regulating the extent of transcription and by regulating the processing of the protein.

Identification of a ras-activated enhancer in the mouse osteopontin promoter and its interaction with a putative ETS-related transcription factor whose activity correlates with the metastatic potential of the cell.

The role of RAS in transducing signals from an activated receptor into altered gene expression is becoming clear, though some links in the chain are still missing. Cells possessing activated RAS express higher levels of osteopontin (OPN), an alpha v beta 3 integrin-binding secreted phosphoprotein implicated in a number of developmental, physiological, and pathological processes. We report that in T24 H-ras-transformed NIH 3T3 cells enhanced transcription contributes to the increased expression of OPN. Transient transfection studies, DNA-protein binding assays, and methylation protection experiments have identified a novel ras-activated enhancer, distinct from known ras response elements, that appears responsible for part of the increase in OPN transcription in cells with an activated RAS. In electrophoretic mobility shift assays, the protein-binding motif GGAGGCAGG was found to be essential for the formation of several complexes, one of which (complex A) was generated at elevated levels by cell lines that are metastatic. Southwestern blotting and UV light cross-linking studies indicated the presence of several proteins able to interact with this sequence. The proteins that form these complexes have molecular masses estimated at approximately 16, 28, 32, 45, 80, and 100 kDa. Because the approximately 16-kDa protein was responsible for complex A formation, we have designated it MATF for metastasis-associated transcription factor. The GGANNNAGG motif is also found in some other promoters, suggesting that they may be similarly controlled by MATF.

p21ras and protein kinase C function in distinct and interdependent signaling pathways in C3H 10T1/2 fibroblasts.

Both p21ras and protein kinase C (PKC) are believed to function downstream of plasma membrane-associated tyrosine kinases in cellular signal transduction pathways. However, it has remained controversial whether they function in the same pathway and, if so, what their relative position and functional relationship in such a pathway are. We investigated the possibilities that p21ras and PKC function either upstream or downstream of each other in a common linear pathway or that they function independently in colinear signal pathways. Either decreased expression of endogenous normal ras in fibroblasts transfected with an inducible antisense ras construct or overexpression of a mutant ras gene reduced the capacity of the phorbol ester tetradecanoyl phorbol acetate to trigger expression of the tetradecanoyl phorbol acetate-responsive and ras-dependent reporter gene osteopontin (OPN). PKC depletion decreased basal OPN mRNA levels, and the overexpression of ras restored OPN expression to the level of non-PKC-depleted cells. We propose a model in which ras and PKC function in distinct and interdependent signaling pathways.

Osteopontin deficiency produces osteoclast dysfunction due to reduced CD44 surface expression.

Osteopontin (OPN) was expressed in murine wild-type osteoclasts, localized to the basolateral, clear zone, and ruffled border membranes, and deposited in the resorption pits during bone resorption. The lack of OPN secretion into the resorption bay of avian osteoclasts may be a component of their functional resorption deficiency in vitro. Osteoclasts deficient in OPN were hypomotile and exhibited decreased capacity for bone resorption in vitro. OPN stimulated CD44 expression on the osteoclast surface, and CD44 was shown to be required for osteoclast motility and bone resorption. Exogenous addition of OPN to OPN-/- osteoclasts increased the surface expression of CD44, and it rescued osteoclast motility due to activation of the alpha(v)beta(3) integrin. Exogenous OPN only partially restored bone resorption because addition of OPN failed to produce OPN secretion into resorption bays as seen in wild-type osteoclasts. As expected with these in vitro findings of osteoclast dysfunction, a bone phenotype, heretofore unappreciated, was characterized in OPN-deficient mice. Delayed bone resorption in metaphyseal trabeculae and diminished eroded perimeters despite an increase in osteoclast number were observed in histomorphometric measurements of tibiae isolated from OPN-deficient mice. The histomorphometric findings correlated with an increase in bone rigidity and moment of inertia revealed by load-to-failure testing of femurs. These findings demonstrate the role of OPN in osteoclast function and the requirement for OPN as an osteoclast autocrine factor during bone remodeling.

Mechanisms of cellular invasiveness: a comparison of amnion invasion in vitro and metastatic behavior in vivo.

We employed a sensitive in vitro amnion invasion assay to examine the relationship of the invasive ability of numerous mouse and human tumor cell lines and their variants to their ability to spontaneously or artificially metastasize; we also studied possible enzymatic activities involved in the in vitro invasion process. In vitro invasive ability of tumor cells was strongly correlated with spontaneous metastatic ability from the subcutaneous site, regardless of the ability of tumor cells to form artificial metastases when introduced intravenously. However, normal nontumorigenic human trophoblast cells were also highly invasive. Various collagenase inhibitors totally abrogated amnion penetration by all invasive cells; various inhibitors of plasmin, plasminogen, and plasminogen activators prevented invasion in most, but not all, cases. Thus, amnion penetration provides a rigorous test for tumor cell invasiveness required for spontaneous metastasis in vivo, and invasiveness is strongly dependent on metalloproteinase activity, which usually follows plasmin activation.

Suppression by cathepsin L inhibitors of the invasion of amnion membranes by murine cancer cells.

Cysteine proteinases, particularly cathepsins B and L, have been strongly implicated in fostering metastasis in mice. In this work four different inhibitors of cysteine proteinases have been shown to inhibit the invasion of the human amnion by murine melanoma and mammary carcinoma cells in vitro. Two of the inhibitors are synthetic peptides [ZPhePheCHN2 (benzyloxycarbonyl-L-phenylalanyl-L-phenylalanyldiazomethane) and ZPheAlaCH2F [3-(N-benzyloxycarbonylphenylalanylamido)-DL-1-fluoro-2-butanone]] and two are thiol protease inhibitors (TPIn, TPId) isolated from the skeletal muscle of the hind limbs of normal and dystrophic mice, respectively. The inhibitors (ZPhePheCHN2, TPId), with apparent selectivity for cathepsin L, blocked invasion as effectively as inhibitors (ZPheAlaCH2F, TPIn) effective on both cathepsins. The data reveal that in these cell lines the cysteine proteinases contribute significantly to the invasive capacity of the cells, but to a lesser extent than do the metalloproteinases. We suggest that the cysteine proteinases facilitate the action of metalloproteinases (collagenase, gelatinase, and stromelysin), possibly by activating them, by inactivating the tissue inhibitor of metalloproteinases, and/or by making basement membrane matrix more accessible.

Reduced malignancy of ras-transformed NIH 3T3 cells expressing antisense osteopontin RNA.

Osteopontin (OPN) is a secreted, calcium-binding phosphoprotein that frequently has been associated with the transformed phenotype. To clarify the function of OPN in tumor cells, we designed experiments to: (a) express antisense OPN RNA in murine PAP2 cells (metastatic, ras-transformed NIH 3T3 cells) and (b) examine the effects of antisense OPN expression on the tumorigenic and metastatic properties of the cells. PAP2 cells were transfected with pNMH-asOPN, an inducible, mammalian expression vector that can generate antisense OPN RNA complementary to the OPN mRNA. Two clones have been identified that expressed antisense OPN RNA in vitro. While reduced OPN protein secretion was not detected when the cells were grown in vitro, the in vivo expression of antisense OPN RNA was associated with reduced tumorigenicity. Tumors that did arise, with greatly extended lag time, had lost expression of antisense OPN RNA in vivo, suggesting that antisense OPN RNA expression was associated with reduced tumorigenicity of these cells.

Close relationship of the major excreted protein of transformed murine fibroblasts to thiol-dependent cathepsins.

Complementary DNA clones corresponding to 638 nucleotides of the messenger RNA encoding the major portion of murine major excreted protein have been isolated and sequenced. The amino acid sequence of a part of the murine major excreted protein deduced from the DNA sequence reveals substantial and significant homology with the cysteine proteases actinidin, rat cathepsin H, and papain. Since the amount of murine major excreted protein secreted by cultured cells is often enhanced by transformation, it is implicated in oncogenic phenomena and may play a role in the metastatic process by virtue of its proteolytic activity.

p53 mutations in spontaneously immortalized 3T12 but not 3T3 mouse embryo cells.

We have asked whether p53 mutations are involved in the process of spontaneous immortalization of mouse embryo cells. Cells from Swiss mouse embryos were used to prepare 3T3 and 3T12 lines according to the protocol of Todaro & Green [(1963). J. Cell Biol., 17, 299-313]. After the cells emerged from crisis, p53 sequences were amplified by polymerase chain reaction (PCR) from both RNA and DNA. The sequence of the aggregated cDNA from each of six 3T3 lines showed no evidence of mutation. PCR-amplified p53 cDNA from two 3T3 lines was cloned, and individual clones in M13mp19 were partially sequenced. One cell ine showed a single, non-coding nucleotide change in 2/8 independent clones. Nine cDNA clones from the second 3T3 lines were sequenced, and no single nucleotide changes appeared more than once. The mutations which appeared only once were not detected in clones of genomic DNA. Since these apparent mutations are probably reverse transcriptase or Taq polymerase errors, we conclude that both the 3T3 lines contained only wild-type p53. In two out of three independent 3T12 lines however, missense mutations were readily observed in the aggregate cDNA sequence. Restriction fragment length polymorphism and Southern blot analyses of the genomic DNA indicated that these cells were homozygous for the mutations. The p53 protein molecules in four cell lines were analysed by immunoprecipitation: one 3T12 line showed the pattern of antibody reactivity characteristic of some p53 mutants, while the others displayed the wild-type pattern. We conclude that p53 mutations arise and are strongly selected for during immortalization according to the 3T12 but not the 3T3 protocol.

Cysteine proteinase cathepsin L expression correlates closely with the metastatic potential of H-ras-transformed murine fibroblasts.

A set of H-ras-transfected mouse C3H 10T1/2 cell lines that vary in their experimental and spontaneous metastatic potential has been analysed for the level of expression of the cysteine proteinase cathepsin L, also known as the major excreted protein (MEP). We found a good positive correlation between the extent of ras expression, the metastatic potential, and the amount of the secreted protease in nine independently isolated lines. There was an increased abundance of the MEP mRNA in cells with increased ras expression, suggesting that this gene is under ras control. Expression of glyceraldehyde phosphate dehydrogenase mRNA was also elevated.

The mechanism of replication of phi X 174. XVIII. Gene A and A* proteins of phi X 174 bind tightly to phi X 174 replicative form DNA.

Evidence is presented that the gene A and A * proteins of bacteriophage phi X 174 form covalent associations with the 5' ends of the DNA molecules when superhelical phi X replicative form DNA is nicked by a combination of these proteins in vitro. This evidence is: 1, The 5' ends of the DNA molecules nicked by the gene A protein and reacted with bacterial alkaline phosphatase were protected against subsequent phosphorylation by polynucleotide kinase even after treatment of the nicked DNA with SDS and pronase followed by centrifugation on a high-salt neutral sucrose gradient. 2, Iodinated pronase-sensitive material remained attached to the nicked replicative form DNA and could not be removed by exposure to SDS or 2 M NaCl, either by sedimentation through high-salt neutral sucrose gradients, or by CsCl equilibrium centrifugation. 3, Iodinated pronase-sensitive material was detected on DNA that had been nicked during the reaction, but not on unreacted DNA. 4, Electrophoresis of the iodinated pronase-sensitive, DNA-bound material in SDS-polyacrylamide gels after DNAse digestion revealed that it was composed almost entirely polypeptides with electrophoretic mobilities similar to those of the gene A and A * proteins. We speculate that the gene * protein may be essential for normal progeny single-stranded DNA synthesis in vivo.

Adenovirus DNA replication in vivo: properties of short DNA molecules extracted from infected cells.

Adenovirus type 5 (Ad5) DNA replicating in intact HeLa cells was pulse-labeled with [3H]thymidine extracted by the procedure of Hirt and analyzed on neutral sucrose gradients. In addition to viral replicative forms (over 33 kb), slowly sedimenting species of DNA (0.05-3 kb) was observed. Hybridization analysis showed that this DNA contained about 30% Ad5 DNA sequences. Analysis of the sensitivity of this DNA to the 5' OH-specific spleen exonuclease after alkali or RNAase treatment revealed that about 80% of these molecules contained ribonucleotides. DNA in this fraction was labeled at the 5' end with 32P and hybridized together with control 3H-labeled Ad5 DNA to Hpa I restriction fragments immobilized on nitrocellulose paper. Many of these small molecules were located near the termini. Alkali treatment prior to hybridization decreased the 32P/3H ratio throughout the genome. This suggests that some of these Ad5 molecules possess ribonucleotides and therefore may be intermediates in discontinuous DNA replication. Longer molecules (over 0.5 kb) were found sedimenting with viral replicative forms and mature DNA. The Ad5 molecules in this fraction showed no evidence of alkali-labile termini.

Characterization of a mouse mitogen-regulated protein/proliferin gene and its promoter: a member of the growth hormone/prolactin gene superfamily.

A genomic clone containing the complete gene, designated mrp/plf3, of a member of the mitogen-regulated protein/proliferin (MRP/PLF) multi-gene family was isolated from a mouse genomic library constructed in lambda L47.1. The DNA sequences of the 5' flanking region, the exons, and the exon/intron boundaries have been determined. The size and organization of the five exons in the murine mrp/plf3 gene are very similar to those of members of the prolactin/growth hormone family, confirming that mrp/plf3 is a part of this superfamily. Removal of an upstream negative regulatory element revealed an active mrp/plf promoter that was responsive to TGF-alpha and contains known regulatory elements. Intracellular mrp/plf mRNA levels were increased by 17 beta-estradiol and reduced by dexamethasone.