Modulation of the activation status of Stat5a during LIF-induced differentiation of M1 myeloid leukemia cells

A dual role for oncostatin M signaling in the differentiation and death of mammary epithelial cells in vivo

Recent studies in breast cancer cell lines have shown that oncostatin M (OSM) not only inhibits proliferation but also promotes cell detachment and enhances cell motility. In this study, we have looked at the role of OSM signaling in nontransformed mouse mammary epithelial cells in vitro using the KIM-2 mammary epithelial cell line and in vivo using OSM receptor (OSMR)-deficient mice. OSM and its receptor were up-regulated approximately 2 d after the onset of postlactational mammary regression, in response to leukemia inhibitory factor (LIF)-induced signal transducer and activator of transcription-3 (STAT3). This resulted in sustained STAT3 activity, increased epithelial apoptosis, and enhanced clearance of epithelial structures during the remodeling phase of mammary involution. Concurrently, OSM signaling precipitated the dephosphorylation of STAT5 and repressed expression of the milk protein genes beta-casein and whey acidic protein (WAP). Similarly, during pregnancy, OSM signaling suppressed beta-casein and WAP gene expression. In vitro, OSM but not LIF persistently down-regulated phosphorylated (p)-STAT5, even in the continued presence of prolactin. OSM also promoted the expression of metalloproteinases MMP3, MMP12, and MMP14, which, in vitro, were responsible for OSM-specific apoptosis. Thus, the sequential activation of IL-6-related cytokines during mammary involution culminates in an OSM-dependent repression of epithelial-specific gene expression and the potentiation of epithelial cell extinction mediated, at least in part, by the reciprocal regulation of p-STAT5 and p-STAT3.

Can the protective actions of JAK-STAT in the heart be exploited therapeutically? Parsing the regulation of interleukin-6-type cytokine signaling

Activation of the transcription factor signal transducers and activators of transcription (STAT) 3 is a defining feature of the interleukin (IL)-6 family of cytokines, which include IL-6, leukemia inhibitory factor, and cardiotrophin-1. These cytokines, as well as STAT3 activation, have been shown to be protective for cardiac myocytes and necessary for ischemia preconditioning. However, the mechanisms that regulate IL-6-type cytokine signaling in cardiac myocytes are largely unexplored. We propose that the protective character of IL-6-type cytokine signaling in cardiac myocytes is determined principally by three mechanisms: redox status of the nonreceptor tyrosine kinase Janus kinase 1 (JAK) 1 that activates STAT3, phosphorylation of STAT3 within the transcriptional activation domain on serine 727, and STAT3-mediated induction of suppressor of cytokine signaling (SOCS) 3 that terminates IL-6-type cytokine signaling. Moreover, we hypothesize that hyperactivation of the JAK kinases, particularly JAK2, mismatched STAT3 serine-tyrosine phosphorylation or heightened STAT3 transcriptional activity, and SOCS3 induction may ultimately prove detrimental. Here we summarize recent evidence that supports this hypothesis, as well as additional possible mechanisms of JAK-STAT regulation. Understanding how IL-6-type cytokine signaling is regulated in cardiac myocytes has great significance for exploiting the therapeutic potential of these cytokines and the phenomenon of preconditioning.

Interleukin-6 family cytokine M17 induces differentiation and nitric oxide response of goldfish (Carassius auratus L.) macrophages

Cytokines belonging to the interleukin-6 (IL-6) family function in many biological processes and display a high degree of redundancy within the family. Although a number of mRNA transcripts from teleost fish that resemble IL-6 family cytokines have been identified none have been functionally characterized to confirm their identity. We report on the identification and functional characterization of goldfish M17, a molecule possessing sequence and mRNA expression patterns similar to the mammalian and avian ciliary neurotrophic factor and mammalian leukemia inhibitory factor. Goldfish M17 was found to induce the production of nitric oxide in goldfish macrophages and stimulate the proliferation of macrophage progenitor cells when added in combination with cell-conditioned medium. Moreover, goldfish M17 was found to facilitate the differentiation of sorted monocytes into macrophages at biologically relevant concentrations.

Cytokines in the differentiation therapy of leukemia: from laboratory investigations to clinical applications

Differentiation therapy of leukemia is the treatment of leukemia cells with biological or chemical agents that induce the terminal differentiation of the cancer cells. It is regarded as a novel and targeted approach to leukemia treatment, based on our better understanding of the hematopoietic process and the mechanisms of its deregulation during leukemogenesis. Clinically, differentiation therapy has been most successful in acute promyelocytic leukemia using all-trans-retinoic acid as the inducer, either alone or in combination with chemotherapy. This review presents evidence that a number of hematopoietic cytokines play important roles in both normal and aberrant hematopoietic processes. In vitro laboratory investigations in the past two decades using well-characterized myeloid leukemic cell lines and primary blast cells from leukemia patients have revealed that many hematopoietic cytokines can trigger lineage-specific differentiation of leukemia cells, which may have important implications in the clinical setting. Moreover, our current understanding of cytokine interactions and the molecular mechanisms of cytokine-induced leukemic cell differentiation will be discussed in the light of recent findings. Finally, ways in which laboratory research on cytokines in the differentiation therapy of leukemia can lead to the improved design of protocols for future clinical applications to leukemia therapy will also be addressed.

Leukemia-inhibitory factor-neuroimmune modulator of endocrine function

Leukemia-inhibitory factor (LIF) is a pleiotropic cytokine expressed by multiple tissue types. The LIF receptor shares a common gp130 receptor subunit with the IL-6 cytokine superfamily. LIF signaling is mediated mainly by JAK-STAT (janus-kinase-signal transducer and activator of transcription) pathways and is abrogated by the SOCS (suppressor-of cytokine signaling) and PIAS (protein inhibitors of activated STAT) proteins. In addition to classic hematopoietic and neuronal actions, LIF plays a critical role in several endocrine functions including the utero-placental unit, the hypothalamo-pituitary-adrenal axis, bone cell metabolism, energy homeostasis, and hormonally responsive tumors. This paper reviews recent advances in our understanding of molecular mechanisms regulating LIF expression and action and also provides a systemic overview of LIF-mediated endocrine regulation. Local and systemic LIF serve to integrate multiple developmental and functional cell signals, culminating in maintaining appropriate hormonal and metabolic homeostasis. LIF thus functions as a critical molecular interface between the neuroimmune and endocrine systems.

STAT3 activation in stromal/osteoblastic cells is required for induction of the receptor activator of NF-kappaB ligand and stimulation of osteoclastogenesis by gp130-utilizing cytokines or interleukin-1 but not 1,25-dihydroxyvitamin D3 or parathyroid hormone

Interleukin (IL)-6-type cytokines stimulate osteoclastogenesis by activating gp130 in stromal/osteoblastic cells and may mediate some of the osteoclastogenic effects of other cytokines and hormones. To determine whether STAT3 is a downstream effector of gp130 in the osteoclast support function of stromal/osteoblastic cells and whether the gp130/STAT3 pathway is utilized by other osteoclastogenic agents, we conditionally expressed dominant negative (dn)-STAT3 or dn-gp130 in a stromal/osteoblastic cell line (UAMS-32) that supports osteoclast formation. Expression of either dominant negative protein abolished osteoclast formation stimulated by IL-6 + soluble IL-6 receptor, oncostatin M, or IL-1 but not by parathyroid hormone or 1,25-dihydroxyvitamin D3. Because previous studies suggested that IL-6-type cytokines may stimulate osteoclastogenesis by inducing expression of the tumor necrosis factor-related protein, receptor activator of NF-kappaB ligand (RANKL), we conditionally expressed RANKL in UAMS-32 cells and found that this was sufficient to stimulate osteoclastogenesis. Moreover, dn-STAT3 blocked the ability of either IL-6 + soluble IL-6 receptor or oncostatin M to induce RANKL. These results establish that STAT3 is essential for gp130-mediated osteoclast formation and that the target of STAT3 during this process is induction of RANKL. In addition, this study demonstrates that activation of the gp130-STAT3 pathway in stromal/osteoblastic cells mediates the osteoclastogenic effects of IL-1, but not parathyroid hormone or 1, 25-dihydroxyvitamin D3.

Stat5a and Stat5b: fraternal twins of signal transduction and transcriptional activation

Stat5a and Stat5b are discretely encoded transcription factors that mediate signals for a broad spectrum of cytokines. Their activation is often an integral component of redundant cytokine signal cascades involving complex cross-talk and pleiotropic gene regulation by Stat5 has been implicated in cellular functions of proliferation, differentiation and apoptosis with relevance to processes of hematopoiesis and immunoregulation, reproduction, and lipid metabolism. Although Stat5a and Stat5b show peptide sequence similarities of > 90%, targeted gene disruptions in mice yield distinctive phenotypes. Prolactin-directed mammary gland maturation fails without functional Stat5a, while disruption of Stat5b in males mitigates growth hormone effects on hepatic function and body mass. The molecular basis for this biologic dichotomy is probably multifaceted. Limited structural dissimilarities between the Stat5a and Stat5b transactivation domains, or subtle differences in the DNA-binding affinities of Stat5 dimer pairs undoubtedly influence gene regulation, but cell-dependent asymmetries in availability of phosphorylated Stat5 can be an underlying factor. Differences in serine phosphorylation(s) of Stat5a and Stat5b, or Stat5 associations with adaptor proteins or co-transcription factors are other potential sources of functional disparity and the signal amplitude, frequency or duration also can be significant. In addition to Stat5 signal attenuation by phosphatase actions or classical feedback inhibition, truncated forms of Stat5 lacking in transactivation capacity may compete upstream for activation and diminish access of full length molecules to DNA binding sites.

Reconstitution of IL6-inducible differentiation of a myeloid leukemia cell line by activated Stat factors

Differentiation of the myeloid leukemia cell line M1 by treatment with IL6-type cytokines depends on activation of the Jak/Stat (Janus kinase/signal transducer and activator of transcription) pathway. Defects in this cascade are correlated with an impaired cytokine-inducible differentiation of various other myeloid cell lines. Although treatment with IL-6 increased the amount of activated transcription factor Stat3 in the myeloid leukemia line C, differentiation was not induced. However, after cotransfection with expression constructs for the tyrosine kinase Jak2 and Stat factors 3 or 5a, treatment of the cells with IL-6 caused a decrease in the number of viable cells. In parallel, an increase in the percentage of differentiated cells occurred. These findings are consistent with the hypothesis that the Jak/Stat signaling cascade plays an important role in cytokine-induced differentiation of myeloid leukemia cells.