Erythropoietin receptor mutations associated with familial erythrocytosis cause hypersensitivity to erythropoietin in the heterozygous state.
(57/1703)
Inherited mutations in the erythropoietin receptor (EPOR) causing premature termination of the receptor cytoplasmic region are associated with dominant familial erythrocytosis (FE), a benign clinical condition characterized by hypersensitivity of erythroid progenitor cells to EPO and low serum EPO (S-EPO) levels. We describe a Swedish family with dominant FE in which erythrocytosis segregates with a new truncation in the negative control domain of the EPOR. We show that cells engineered to concomitantly express the wild-type (WT) EPOR and mutant EPORs associated with FE (FE EPORs) are hypersensitive to EPO-stimulated proliferation and activation of Jak2 and Stat5. These results demonstrate that FE is caused by hyperresponsiveness of receptor-mediated signaling pathways and that this is dominant with respect to WT EPOR signaling. (+info)
ErbB4 signaling in the mammary gland is required for lobuloalveolar development and Stat5 activation during lactation.
(58/1703)
Signaling by members of the epidermal growth factor receptor family plays an important role in breast development and breast cancer. Earlier work suggested that one of these receptors, ErbB4, is coupled to unique responses in this tissue. To determine the function of ErbB4 signaling in the normal mouse mammary gland, we inactivated ErbB4 signaling by expressing a COOH terminally deleted dominant-negative allele of ErbB4 (ErbB4DeltaIC) as a transgene in the mammary gland. Despite the expression of ErbB4DeltaIC from puberty through later stages of mammary development, an ErbB4DeltaIC-specific phenotype was not observed until mid-lactation. At 12-d postpartum, lobuloalveoli expressing ErbB4DeltaIC protein were condensed and lacked normal lumenal lactation products. In these lobuloalveoli, beta-casein mRNA, detected by in situ hybridization, was normal. However, whey acidic protein mRNA was reduced, and alpha-lactalbumin mRNA was undetectable. Stat5 expression was detected by immunohistochemistry in ErbB4DeltaIC-expressing tissue. However, Stat5 was not phosphorylated at Y694 and was, therefore, probably inactive. When expressed transiently in 293T cells, ErbB4 induced phosphorylation of Stat5. This phosphorylation required an intact Stat5 SH2 domain. In summary, our results demonstrate that ErbB4 signaling is necessary for mammary terminal differentiation and Stat5 activation at mid-lactation. (+info)
Integrin-mediated adhesion of endothelial cells induces JAK2 and STAT5A activation: role in the control of c-fos gene expression.
(59/1703)
Integrin-mediated adhesion induces several signaling pathways leading to regulation of gene transcription, control of cell cycle entry and survival from apoptosis. Here we investigate the involvement of the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) pathway in integrin-mediated signaling. Plating primary human endothelial cells from umbilical cord and the human endothelial cell line ECV304 on matrix proteins or on antibody to beta1- or alphav-integrin subunits induces transient tyrosine phosphorylation of JAK2 and STAT5A. Consistent with a role for the JAK/STAT pathway in regulation of gene transcription, adhesion to matrix proteins leads to the formation of STAT5A-containing complexes with the serum-inducible element of c-fos promoter. Stable expression of a dominant negative form of STAT5A in NIH3T3 cells reduces fibronectin-induced c-fos mRNA expression, indicating the involvement of STAT5A in integrin-mediated c-fos transcription. Thus these data present a new integrin-dependent signaling mechanism involving the JAK/STAT pathway in response to cell-matrix interaction. (+info)
STAT5b down-regulates peroxisome proliferator-activated receptor alpha transcription by inhibition of ligand-independent activation function region-1 trans-activation domain.
(60/1703)
Growth hormone-activated STAT5b inhibits by up to 80% the transcriptional activity of peroxisome proliferator-activated receptor (PPAR) alpha, a nuclear receptor activated by diverse environmental chemicals and hypolipidemic drugs classified as peroxisome proliferators. This inhibitory cross-talk between STAT5b and PPAR is now reported for PPAR forms gamma and delta and for thyroid hormone receptor, indicating a more general potential for inhibitory cross-talk between JAK/STAT and nuclear receptor signaling pathways. Further investigations revealed that SOCS-3, a growth hormone-inducible negative regulator of cytokine signaling to STAT5b, abolished the STAT5b inhibitory response. A constitutively active STAT5b mutant failed to inhibit PPARalpha activity, indicating that STAT5b does not induce synthesis of a more proximal PPARalpha inhibitor. STAT5b inhibition was not reversed by overexpression of the heterodimerization partner of PPAR (retinoid X receptor) or the nuclear receptor coactivators P300 and SRC-1, suggesting that STAT5b does not inhibit PPARalpha by competing for these limiting cellular cofactors. STAT5b did not inhibit a chimeric receptor comprised of yeast GAL4 DNA-binding domain linked to the ligand binding/AF-2 trans-activation domain of PPARalpha, indicating that the COOH-terminal AF-2 domain of PPAR is not the target of STAT5b inhibition. Rather, STAT5b inhibited transcription driven by the NH(2)-terminal ligand-independent AF-1 trans-activation domain of PPARalpha in a GAL4-linked chimera by approximately 80%. The conservation of this AF-1 trans-activation function in many nuclear receptors suggests that AF-1 may serve as an important target for inhibitory cross-talk between STAT transcription factors and nuclear receptors in a variety of signaling pathways. (+info)
CIS associates with the interleukin-2 receptor beta chain and inhibits interleukin-2-dependent signaling.
(61/1703)
CIS is a cytokine-induced SH2-containing protein that was originally cloned as an interleukin (IL)-3-inducible gene. CIS is known to associate with the IL-3 receptor beta chain and erythropoietin receptor and to inhibit signaling mediated by IL-3 and erythropoietin. We now demonstrate that CIS also interacts with the IL-2 receptor beta chain (IL-2Rbeta). This interaction requires the A region of IL-2Rbeta (residues 313-382), which also mediates the association of IL-2Rbeta with Lck and Jak3. Correspondingly, CIS inhibits functions associated with both of these kinases: Lck-mediated phosphorylation of IL-2Rbeta and IL-2-mediated activation of Stat5. Thus, we demonstrate that CIS can negatively control at least two independent IL-2 signaling pathways. Although a functional SH2 binding domain of CIS was not required for its interaction with IL-2Rbeta in vitro, its phosphotyrosine binding capability was essential for the inhibitory action of CIS. On this basis, we have generated a mutant form of CIS protein with an altered SH2 domain that acts as a dominant negative and should prove useful in further understanding CIS action. (+info)
In vitro expression of long and short ovine prolactin receptors: activation of Jak2/STAT5 pathway is not sufficient to account for prolactin signal transduction to the ovine beta-lactoglobulin gene promoter.
(62/1703)
The recent finding that sheep had long (l-oPRLR) and short (s-oPRLR) prolactin receptors provided new tools to further explore prolactin signaling to target genes. Here we used CHO cells transfected with l-oPRLR or s-oPRLR cDNAs to compare the activation of known key steps of prolactin signaling by the two receptors. We found that prolactin stimulated l-oPRLR tyrosine phosphorylation, although it lacked the last tyrosine residue found in other long prolactin receptors. In addition, l-oPRLR and s-oPRLR both responded to prolactin stimulation by (1) Janus kinase 2 (Jak2) tyrosine phosphorylation, (2) DNA-binding activation of signal transducer and activator of transcription 5 (STAT5), (3) stimulation of transcription from a promoter made of six repeats of STAT5-responsive sequence. However, although it contains STAT5-binding consensus sequences, the ovine beta-lactoglobulin promoter (-4000 to +40) was transactivated by l-oPRLR, but not by s-oPRLR. Taken together, our results indicate that activation of Jak2/STAT5 pathway alone is not sufficient to account for prolactin-induced transcription of this milk protein gene, and that sequences of its promoter, other than STAT5-specific sequences, account for the opposite transcriptional activation capabilities of l-oPRLR and s-oPRLR. (+info)
Targeted disruption of the murine fps/fes proto-oncogene reveals that Fps/Fes kinase activity is dispensable for hematopoiesis.
(63/1703)
The fps/fes proto-oncogene encodes a cytoplasmic protein-tyrosine kinase that is functionally implicated in the survival and terminal differentiation of myeloid progenitors and in signaling from several members of the cytokine receptor superfamily. To gain further insight into the physiological function of fps/fes, we targeted the mouse locus with a kinase-inactivating missense mutation. Mutant Fps/Fes protein was expressed at normal levels in these mice, but it lacked detectable kinase activity. Homozygous mutant animals were viable and fertile, and they showed no obvious defects. Flow cytometry analysis of bone marrow showed no statistically significant differences in the levels of myeloid, erythroid, or B-cell precursors. Subtle abnormalities observed in mutant mice included slightly elevated total leukocyte counts and splenomegaly. In bone marrow hematopoietic progenitor cell colony-forming assays, mutant mice gave slightly elevated numbers and variable sizes of CFU-granulocyte macrophage in response to interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Tyrosine phosphorylation of Stat3 and Stat5A in bone marrow-derived macrophages was dramatically reduced in response to GM-CSF but not to IL-3 or IL-6. This suggests a distinct nonredundant role for Fps/Fes in signaling from the GM-CSF receptor that does not extend to the closely related IL-3 receptor. Lipopolysaccharide-induced Erk1/2 activation was also reduced in mutant macrophages. These subtle molecular phenotypes suggest a possible nonredundant role for Fps/Fes in myelopoiesis and immune responses. (+info)
Inhibition of interleukin 2 signaling and signal transducer and activator of transcription (STAT)5 activation during T cell receptor-mediated feedback inhibition of T cell expansion.
(64/1703)
Limitation of clonal expansion of activated T cells is necessary for immune homeostasis, and is achieved by growth arrest and apoptosis. Growth arrest and apoptosis can occur passively secondary to cytokine withdrawal, or can be actively induced by religation of the T cell receptor (TCR) in previously activated proliferating T cells. TCR-induced apoptosis appears to require prior growth arrest, and is mediated by death receptors such as Fas. We tested whether TCR religation affects T cell responses to interleukin (IL)-2, a major T cell growth and survival factor. TCR ligation in activated primary human T cells blocked IL-2 induction of signal transducer and activator of transcription (STAT)5 DNA binding, phosphorylation of STAT5, Janus kinase (Jak)1, Jak3, and Akt, and kinase activity of Jak1 and Jak3. Inhibition was mediated by the mitogen-activated protein kinase kinase (MEK)-extracellular stimulus-regulated kinase (ERK) signaling pathway, similar to the mechanism of inhibition of IL-6 signaling we have described previously. TCR ligation blocked IL-2 activation of genes and cell cycle regulatory proteins, and suppressed cell proliferation and expansion. These results identify TCR-induced inhibition of IL-2 signaling as a novel mechanism that underlies antigen-mediated feedback limitation of T cell expansion, and suggest that modulation of cytokine activity by antigen receptor signals plays an important role in the regulation of lymphocyte function. (+info)