Perverted responses of the human granulocyte-macrophage colony-stimulating factor receptor in mouse cell lines due to cross-species beta-subunit association

Delivery of GM-CSF to Protect against Influenza Pneumonia

Background

Since adaptive immunity is thought to be central to immunity against influenza A virus (IAV) pneumonias, preventive strategies have focused primarily on vaccines. However, vaccine efficacy has been variable, in part because of antigenic shift and drift in circulating influenza viruses. Recent studies have highlighted the importance of innate immunity in protecting against influenza.

Methods

Granulocyte-macrophage colony stimulating factor (GM-CSF) contributes to maturation of mononuclear phagocytes, enhancing their capacity for phagocytosis and cytokine production.

Results

Overexpression of granulocyte macrophage-colony stimulating factor (GM-CSF) in the lung of transgenic mice provides remarkable protection against IAV, which depends on alveolar macrophages (AM). In this study, we report that pulmonary delivery of GM-CSF to wild type young and aged mice abrogated mortality from IAV.

Conclusion

We also demonstrate that protection is species specific and human GM-CSF do not protect the mice nor stimulates mouse immunity. We also show that IAV-induced lung injury is the culprit for side-effects of GM-CSF in treating mice after IAV infection, and introduce a novel strategy to deliver the GM-CSF to and retain it in the alveolar space even after IAV infection.

Up-regulation of cluster of differentiation (CD) 11b expression on the surface of canine granulocytes with human granulocyte-macrophage colony-stimulating factor (GM-CSF)

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pleiotropic cytokine, sharing a common beta subunit (CDw131) with interleukins 3 and 5. GM-CSF is important for its direct and indirect involvement in host defense. In veterinary medicine, human (h) GM-CSF has been used as a substitute for canine GM-CSF to stimulate canine granulocytes and macrophages. In this study, we compared the effects of three distinct hGM-CSFs produced by bacteria, yeasts and Chinese hamster ovary (CHO) cells with those of Escherichia (E) coli-produced canine GM-CSF on the cluster of differentiation 11b (CD11b) expression in canine granulocytes. The median effective dose (ED50) of hGM-CSFs from bacteria, yeasts and CHO cells was 3.09, 4.09 and 4.27 ng/ml, respectively, with no significant difference among three. In contrast, a significant difference was observed between ED50 of canine GM-CSF (0.56 ng/ml) and three hGM-CSFs according to the paired t-test (P<0.05). We conclude that hGM-CSF can activate canine granulocytes, but the average activity of the three rhGM-CSFs was approximately 15% of that of canine GM-CSF.

Alternative modes of GM-CSF receptor activation revealed using activated mutants of the common beta-subunit

Granulocyte/macrophage colony-stimulating factor promotes growth, survival, differentiation, and activation of normal myeloid cells and plays an important role in myeloid leukemias. The GM-CSF receptor (GMR) shares a signaling subunit, beta(c), with interleukin-3 and interleukin-5 receptors and has recently been shown to induce activation of Janus kinase 2 (JAK2) and downstream signaling via formation of a unique dodecameric receptor complex. In this study we use 2 activated beta(c) mutants that display distinct signaling capacity and have differential requirements for the GMR alpha-subunit (GMR-alpha) to dissect the signaling pathways associated with the GM-CSF response. The V449E transmembrane mutant selectively activates JAK2/signal transducer and activator of transcription 5 and extracellular signal-regulated kinase (ERK) pathways, resulting in a high level of sensitivity to JAK and ERK inhibitors, whereas the extracellular mutant (FIDelta) selectively activates the phosphoinositide 3-kinase/Akt and IkappaKbeta/nuclear factorkappaB pathways. We also demonstrate a novel and direct interaction between the SH3 domains of Lyn and Src with a conserved proline-rich motif in GMR-alpha and show a selective requirement for Src family kinases by the FIDelta mutant. We relate the nonoverlapping nature of signaling by the activated mutants to the structure of the unique GMR complex and propose alternative modes of receptor activation acting synergistically in the mature liganded receptor complex.

The Shc-binding site of the betac subunit of the GM-CSF/IL-3/IL-5 receptors is a negative regulator of hematopoiesis

Tyrosine and serine phosphorylation of the common beta chain (beta(c)) of the granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5 receptors is widely viewed as a general mechanism that provides positive inputs by coupling the receptor to signaling pathways that stimulate several cellular functions. We show here that despite the known action of Tyr577 in beta(c) to recruit Shc-PI-3 kinase (PI3K) pathway members, Tyr577 plays, surprisingly, a negative regulatory role in cell function, and that this is mediated, at least in part, through the uncoupling of SH2-containing inositol 5'-phosphatase (SHIP) from beta(c). Fetal liver cells from beta(c)/beta(IL-3)(-/-) mice expressing human GM-CSF receptor alpha chain and beta(c) Tyr577Phe mutant showed enhanced colony formation and expansion of progenitor cells in response to GM-CSF. Dissection of these activities revealed that basal survival was increased, as well as cytokine-stimulated proliferation. As expected, the recruitment and activation of Shc was abolished, but interestingly, Gab-2 and Akt phosphorylation increased. Significantly, the activation of PI3K was enhanced and prolonged, accompanied by loss of SHIP activity. These results reveal a previously unrecognized negative signaling role for Tyr577 in beta(c) and demonstrate that uncoupling Shc from cytokine receptors enhances PI3K signaling as well as survival and proliferation.

Growth factor pleiotropy is controlled by a receptor Tyr/Ser motif that acts as a binary switch

Pleiotropism is a hallmark of cytokines and growth factors; yet, the underlying mechanisms are not clearly understood. We have identified a motif in the granulocyte macrophage-colony-stimulating factor receptor composed of a tyrosine and a serine residue that functions as a binary switch for the independent regulation of multiple biological activities. Signalling occurs either through Ser585 at lower cytokine concentrations, leading to cell survival only, or through Tyr577 at higher cytokine concentrations, leading to cell survival as well as proliferation, differentiation or functional activation. The phosphorylation of Ser585 and Tyr577 is mutually exclusive and occurs via a unidirectional mechanism that involves protein kinase A and tyrosine kinases, respectively, and is deregulated in at least some leukemias. We have identified similar Tyr/Ser motifs in other cell surface receptors, suggesting that such signalling switches may play important roles in generating specificity and pleiotropy in other biological systems.

The human granulocyte/macrophage colony-stimulating factor receptor alpha2 isoform influences haemopoietic lineage commitment and divergence

A number of alternatively spliced isoforms of haemopoietic growth factor receptors (HGFRs) have been described, but their role in human haemopoiesis remains undetermined. We have investigated the relative expression of the alpha1 and alpha2 isoforms of human granulocyte/macrophage colony-stimulating factor receptor (hGM-CSFR) during haemopoietic cell differentiation, and have shown that both subunits are independently regulated during differentiation of CD34+ human haemopoietic progenitor cells. To further investigate these ex-vivo observations, we established a series of murine FDCP mix cell lines, which, as a consequence of the ectopic expression of alpha1 or alpha2 hGM-CSFR, demonstrated differential differentiation responses to hGM-CSF. In this model system, hGM-CSFR-alpha2-expressing cells showed increased hGM-CSF-mediated erythroid/megakaryocytic differentiation compared with hGM-CSFR-alpha1-expressing cells.