Human and murine oncostatin M (OSM) induce their bioactivities through a heterodimeric receptor complex consisting of gp130 and the OSM receptor (OSMR), which initiates a signaling pathway involving Janus kinases (JAKs) and transcription factors of the signal transducers and activators of transcription (STAT) family. In contrast to the signal transducing receptor subunit gp130, the OSMR allows strong activation of STAT5B. The underlying molecular mechanism, however, remained unclear. Here we demonstrate that the human and murine OSM receptors use distinct mechanisms for STAT5B activation. The human receptor contains a STAT5B recruiting tyrosine motif (Tyr 837 /Tyr 839 ) C-terminal to the box 1/2 region, which is absent in the mouse receptor. In contrast, the murine receptor initiates STAT5 activation directly via the receptor bound Janus kinases. Intriguingly, the murine receptor preferentially recruits JAK2, whereas the human receptor seems to have a higher affinity for JAK1. We identify a single amino acid (Phe 820 ) in the human receptor that is responsible for this preference. Exchange by the murine counterpart (Cys 815 ) allows recruitment of JAK2 by the human receptor and consequently activation of STAT5B independently of receptor tyrosine motifs. STAT5B interacts directly with JAK2 only in response to activation of the murine OSMR or the mutated human OSMR. Additionally, we show that OSM-induced STAT1 phosphorylation occurs independently of receptor tyrosine motifs and is mediated directly by Janus kinases, whereas the two C-terminally located tyrosine residues Tyr 917 /Tyr 945 of the OSMR are crucial for STAT3 activation.

Objective. To investigate the molecular mechanisms of CCL13/monocyte chemoattractant protein 4 (MCP-4) chemokine expression through proinflammatory cytokines in different primary human fibroblasts and the contribution of CCL13 to monocyte migration.Methods. Using RNase protection assays and enzyme-linked immunosorbent assays, we quantified the expression of CCL13 compared with that of CCL2/ MCP-1 in primary human fibroblasts. Boyden chamber assays were performed to determine the importance of CCL13 for migration of primary monocytes. Pharmacologic inhibitors as well as small interfering RNA knockdown approaches were used to investigate the signaling pathways regulating CCL13 expression.Results. The interleukin-6 (IL-6)-type cytokine oncostatin M (OSM) was a powerful inducer of CCL13 expression in primary synovial fibroblasts from patients with rheumatoid arthritis (RA) as well as those from healthy control subjects but not in other types of fibroblasts. Neither IL-6 nor tumor necrosis factor ␣ could stimulate the expression of CCL13 in synovial fibroblasts; IL-1␤ was a very weak inducer. Synovial fibroblasts from patients with RA constitutively produced low amounts of CCL13, which was partially dependent on constitutive production of OSM. By investigating the underlying molecular mechanism, we identified STAT-5, ERK-1/2, and p38 as critical factors involved in OSM-dependent transcription and messenger RNA stabilization of CCL13.Conclusion. In contrast to other prominent cytokines involved in the pathogenesis of RA, OSM can strongly up-regulate the expression of CCL13, a chemokine recently identified in the synovial fluid of patients with RA. Despite potent OSM-induced signal transduction in all types of fibroblasts analyzed, only synovial fibroblasts secreted CCL13, which might be indicative of tissue-specific imprinting of different fibroblasts during development.

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The recruitment of leukocytes to injured tissue is crucial for the initiation of inflammatory responses as well as for immune surveillance to fight tumor progression. In this study, we show that oncostatin M, a member of the IL-6-type cytokine family and potent proinflammatory cytokine stimulates the expression of the chemokines CCL1, CCL7, and CCL8 in primary human dermal fibroblasts at a faster kinetic than IL-1␤ or TNF-␣. The production of CCL1 and CCL8 is important for migration of monocytes, while specific Abs against CCL1 additionally inhibit the migration of T lymphocytes. We identify the mitogen-activated protein kinases ERK1/2 and p38 as crucial factors for the enhanced expression of CCL1 and CCL8. T he appropriate immune response relies on the interaction of various cell types orchestrated by direct cell contact or soluble factors. As an initial step, recruitment of leukocytes to sites of tissue damage or invaded pathogens occurs. This process is mainly controlled by members of the chemokine superfamily, in particular by the inducible "inflammatory" chemokines (1-3). This subfamily comprises the majority of the so far known 50 chemokines in humans and is distinguished from the constitutively expressed "homeostatic" chemokines. Apart from their function, chemokines can be sorted according to their structure into four groups, designated C, CX 3 C, CXC, and CC depending on the number and spacing of conserved cysteines (1-3). The family of monocyte-chemoattractant proteins (CCL2/MCP-1, CCL7/ MCP-3, CCL8/MCP-2, and CCL13/MCP-4) has mainly proinflammatory activities and exerts its biologic effects through binding to the G-protein coupled receptors CCR1 and CCR2, which are present on the cell surface of a variety of cell types (1, 3). CCL1/ I-309 has been originally identified as a gene expressed in activated T cell lines (4) and specifically binds to CCR8, which is expressed on the cell surface of polarized Th2 cells and regulatory T cells as well as macrophages (5-8).CCL1 as well as the MCP family members CCL7 and CCL8 are considered to play an important role in the recruitment of monocytes and T lymphocytes to sites of inflammation (9 -11). Their enhanced expression during inflammatory processes is stimulated by different cytokines in various cell types, i.e., by IL-1, TNF-␣, and IFN-␥ in human airway smooth-muscle cells (12), by IL-1 and IFN-␥ in both fibroblasts and epithelial cells (13) and by endogenous IL-1 in monocytes (14).In this study, we describe the regulation of CCL1, CCL7, and CCL8 by the IL-6-type cytokine oncostatin M (OSM) 3 in primary human dermal fibroblasts. OSM is a known proinflammatory cytokine, which is secreted by activated monocytes, neutrophils, and T lymphocytes (15). The human cytokine can signal through two receptor complexes: the type I receptor complex consisting of gp130, the common receptor subunit of all IL-6-type cytokines, and the LIF receptor or the type II receptor complex composed of gp130 and the OSM receptor ␤ subunit (16). In contrast, murine OSM only signals throu...