Oncostatin M (OSM) is a multifunctional cytokine, a member of the interleukin-6/leukemia inhibitory factor (IL-6/LIF) family, that can regulate a number of connective-tissue cell types in vitro including cartilage and synovial tissue-derived fibroblasts, however its role in joint inflammation in vivo is not clear. We have analyzed murine OSM (muOSM) activity in vitro and in vivo in mouse joint tissue, to determine the potential role of this cytokine in local joint inflammation and pathology. The effects of muOSM and other IL-6/LIF cytokines on mouse synovial fibroblast cultures were assessed in vitro and showed induction of monocyte chemotactic protein-1, interleukin-6, and tissue inhibitor metalloproteinase-1, as well as enhancement of colony growth in soft agarose culture. Other IL-6/LIF cytokines including IL-6, LIF, or cardiotrophin-1, did not have such effects when tested at relatively high concentrations (20 ng/ml). To assess effects of muOSM in articular joints in vivo, we used recombinant adenovirus expressing muOSM cDNA (AdmuOSM) and injected purified recombinant virus (10(6) to 10(8) pfu) intra-articularly into the knees of various mouse strains. Histological analysis revealed dramatic alterations in the synovium but not in synovium of knees treated with the control virus Ad-dl70 or knees treated with Adm-IL-6 encoding biologically active murine IL-6. AdmuOSM effects were characterized by increases in the synovial cell proliferation, infiltration of mononuclear cells, and increases in extracellular matrix deposition that were evident at day 4, but much more marked at days 7, 14, and 21 after administration. The synovium took on characteristics similar to pannus and appeared to contact and invade cartilage. Collectively, these results provide good evidence that OSM regulates synovial fibroblast function differently than other IL-6-type cytokines, and can induce a proliferative invasive phenotype of synovium in vivo in mice on overexpression. We suggest that OSM may contribute to pathology in arthritis.

Oncostatin M (OSM) is a member of the IL-6/LIF (or gp130) cytokine family, and its potential role in inflammation is supported by a number of activities identified in vitro. In this study, we investigate the action of murine OSM on expression of the CC chemokine eotaxin by fibroblasts in vitro and on mouse lung tissue in vivo. Recombinant murine OSM stimulated eotaxin protein production and mRNA levels in the NIH 3T3 fibroblast cell line. IL-6 could regulate a small induction of eotaxin in NIH 3T3 cells, but other IL-6/LIF cytokines (LIF, cardiotrophin-1 (CT-1)) had no effect. Cell signaling studies showed that murine OSM, LIF, IL-6, and CT-1 stimulated the tyrosine phosphorylation of STAT-3, suggesting STAT-3 activation is not sufficient for eotaxin induction in NIH 3T3 cells. OSM induced ERK-1,2 and p38 mitogen-activated protein kinase phosphorylation in NIH 3T3 cells, and inhibitors of ERK (PD98059) or p38 (SB203580) could partially reduce OSM-induced eotaxin production, suggesting partial dependence on mitogen-activated protein kinase signaling. OSM (but not LIF, IL-6, or CT-1) also induced eotaxin release by mouse lung fibroblast cultures derived from C57BL/6 mice. Overexpression of murine OSM in lungs of C57BL/6 mice using an adenovirus vector encoding murine OSM resulted in a vigorous inflammatory response by day 7 after intranasal administration, including marked extracellular matrix accumulation and eosinophil infiltration. Elevated levels of eotaxin mRNA in whole lung were detected at days 4 and 5. These data strongly support a role of OSM in lung inflammatory responses that involve eosinophil infiltration.

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Objective. To measure levels of oncostatin M (OSM) in the synovial fluid of rheumatoid arthritis (FU) patients and to examine the activities of human OSM in the regulation of human synovial fibroblast (HSF) production of chemokines and matrix metalloproteinases (MMP-1 and MMP-3) in vitro.Methods. We examined the levels of OSM in the synovial fluids of patients with arthritis by an enzymelinked immunosorbent assay (ELISA). ELISA of cell culture supernatants and Northern blots were used to assess responses of HSF to interleukin-la (IL-la), OSM, and other members of the IL-6/leukemia inhibitory factor (IL-6/LIF) family of cytokines.Results. We detected variable levels of OSM antigen in 9 of 10 RA patient synovial fluids, but levelswere not detectable in 9 of 10 osteoarthritis (OA) patient fluids. Upon examining the responses of HSF in culture, OSM stimulated monocyte chemoattractant protein 1 (MCP-l), whereas RANTES secretion (regulated upon activation, normal T expressed and presumably secreted) was not altered by OSM alone. In IL-lainduced cells, OSM costimulation further enhanced MCP-1 release, but inhibited the release of RANTES and IL-8. Other members of the IL-6/LIF family of cytokines did not show these effects. OSM induced a small elevation of MMP-1 production over 2 and 3 days of stimulation (2-fold), and acted significantly to enhance IL-la-induced production of MMP-1 (to 8-fold Submitted for publication December 20, 1096; acccptcd in revised form July 15, 1097. and 9-fold at 48 and 72 hours, respectively). No effect of OSM was seen on MMP-3 secretion, either alone or in IL-la-costimulated cells.Conclusion. These results suggest that OSM has potentially important functions in the modulation of chemokine and metalloproteinase production by synovial cells of the joint.

In most eukaryotes, families of tubulin genes give rise to multiple isoforms of tubulin, which may be modified post-translationally. The synthesis of isotubulins is spatially and temporally regulated, leading to the presence of different tubulins within an organism. The cellular localization of tubulin is also nonrandom with discrete isoforms residing in specific regions of some cells. Much work, dependent upon interrelated molecular and immunological technologies, has gone into determining why cells produce multiple isotubulins. One proposal would have us believe that isotubulins are functionally discrete and that the isotubulin composition of a microtubule determines its function. A second idea is that tubulin multigene families arose by gene duplication and subsequent genetic drift. The duplicated genes survive in modified form, as they provide the cell with the ability to effectively regulate tubulin synthesis at the transcriptional level while yielding multifunctional tubulins. Analysis of mutant tubulin genes is revealing functionally important regions of tubulin, prompting a return to the consideration of those properties of the molecule that are fundamental to microtubule formation rather than function per se. A model for autoregulation of tubulin synthesis has been developed, but little is yet known of other molecular signals or mechanisms involved in regulation of tubulin production. Further study of flagella formation promises to change this situation. Complementing the genetic studies is the examination of tubulin posttranslational modifications including detyrosination/tyrosination, acetylation/deacetylation, and phosphorylation. Enzymatic mechanisms mediating tubulin posttranslational changes are partially elucidated, as are the influences of the modifications on microtubule properties. Potential functions of the posttranslational changes are the modulation of microtubule-associated protein binding to microtubules, the provision of a mechanism to indicate microtubule age, or as mediators of cellular morphogenesis, a role which could be dependent upon the first two functions. Despite the progress that has been made, the physiological significance of having several isotubulins within a single cell and the molecular details of microtubule function remain obscure.

Mouse oncostatin M (MuOSM) regulates the production of acute-phase proteins by hepatocytes as well as tissue inhibitor of metalloproteinases-1 (TIMP-1) production by fibroblasts in vitro. We have generated an adenovirus (Ad) encoding MuOSM and tested the effects of administration of recombinant AdMuOSM to mice in vivo. On intramuscular injection, AdMuOSM (5 X 10(7) plaque-forming units, pfu) induced an increase in serum levels of interleukin-6 (IL-6) as well as the acute-phase proteins serum amyloid A (SAP) and alpha1-acid glycoprotein (AGP) at day 1. SAP and AGP concentrations were elevated to greater levels at day 3 and decreased to near control levels at day 7. Intratracheal treatment with AdMuOSM induced TIMP-1 mRNA levels (as assessed by Northern blots) that corresponded to the presence of transgene MuOSM mRNA levels. TIMP-1 was elevated at day 1 and day 3 and less consistently at day 7 after administration. Intraperitoneal treatment with AdMuOSM also resulted in elevation of TIMP-1 mRNA in lung tissue. These results show that AdMuOSM can induce both local and systemic effects and demonstrate in vivo effects of OSM that are consistent with in vitro studies on acute-phase protein and TIMP-1 expression.

In many differentiated cells, posttranslationally modified tubulins exhibit restricted subcellular distribution, leading to the proposal that they are required for the production and maintenance of polarity. To study this possibility, we used immunological approaches to examine tubulin isoforms in developing Artemiu larvae and to determine their location in several types of cells within the organism. The amount of tubulin in relation to total protein remained relatively constant during early larval development while detyrosinated tubulin increased, an event correlated with the differentiation of larval gut muscle cells. Except for epidermal cells of the developing thorax, each type of cell within the Artemiu larvae exhibited characteristic staining patterns which were very similar for each antitubulin antibody. Within epidermal cells, microtubules containing acetylated tubulin appeared patchy or punctate in their distribution, an image not seen with the other antibodies. In most polarized cells, staining for tubulin and actin colocalized in discrete areas, demonstrating enrichment of both proteins within the same cellular compartment and suggesting functional interactions. Mitotic figures were stained with qualitatively equal intensity by all of the antitubulin antibodies, but asters were not observed. Midbodies were intensely stained with phalloidin as well as the antibodies to tubulin. It was clear that microtubules exhibited a preferential localization in cells of Arfernia but in no case was a tubulin isoform found exclusively in one area of a cell. The results support the contention that microtubules influence the organization of polarized cell structure and function but they do not permit the conclusion that this capability is dependent on the localization of posttranslationally modified tubulins to restricted subcellular positions.

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