Reduced lymphomyeloid repopulating activity from adult bone marrow and fetal liver of mice lacking expression of STAT5

Abstract

IntroductionThe functional roles of janus kinases (JAKs) and signal transducers and activators of transcription (STATs) have been characterized in both hematopoietic and nonhematopoietic tissues. 1 The JAK/STAT signaling axis allows a diverse set of extracellular signals to result in modification of gene expression patterns in the appropriate target cells. This process is initiated when, on cytokine binding, JAKs come into close proximity and become activated by autophosphorylation on tyrosine residues. Activated JAKs then phosphoryate among many other substrates, the STAT proteins. STATs form homodimers or heterodimers via SH2 domain phosphotyrosine interactions and translocate to the nucleus where they bind to transcriptional elements on DNA. 2,3 Activated STAT proteins regulate their target genes often with tissue specificity. In the hematopoietic system, JAK/STAT signaling has been extensively described in a variety of lymphoid and myeloid cell types. Four mammalian JAKs and 7 STAT proteins have been identified and characterized by generation of knockout mice. 4 These studies have revealed a large diversity in the role of STATs in hematopoiesis with some STATs showing phenotypes primarily in restricted cytokine pathways (eg, interferons, interleukin [IL]-4, IL-12, and IL-13) that are primarily involved in immune responses (STAT1, STAT2, STAT4, and STAT6). In contrast, the complex phenotypes of STAT3-and STAT5-deficient mice demonstrate a broad cytokine activation and function profile for many individual cell lineages.STAT5a and STAT5b are 2 very homologous transcription factors with variability between these 2 proteins being primarily in the transactivation domain. Mice deficient in either STAT5a or STAT5b have been generated and characterized. The STAT5a knockout mouse is characterized by defects in responses to granulocyte-macrophage colony-stimulating factor (GM-CSF) 5 and mammary gland development. 6 The STAT5b knockout mouse is characterized by defects in growth hormone signaling and expression of male-characteristic liver gene expression patterns. 7 To study the effects of STAT5 on hematopoiesis and also to eliminate any compensating function between the 2 STAT isoforms, homozygous mutant mice lacking both STAT5a and STAT5b were generated. These female mice were infertile, but heterozygous mice could breed normally and give viable STAT5ab Ϫ/Ϫ mice, but at a lower than expected frequency because of various phenotypes affecting survival. An important role for STAT5a and STAT5b in T-cell function 8,9 and terminal myeloid differentiation/apoptosis 10 has been shown by using tissues from these STAT5ab Ϫ/Ϫ mice. Comparable results have also been obtained in cytokine-inducible SH2-containing protein-1 transgenic mice. 11 Somewhat surprisingly, the peripheral hematology of the STAT5ab Ϫ/Ϫ mice was not dramatically altered, although reductions in the numbers of IL-3-and GM-CSF-responsive myeloid progenitors 12 and IL-7-responsive B-lymphoid 12,13 [25][26][27][28] have been shown to stimulate primitive hematopoi...

Abnormal hematopoiesis in Gab2 mutant mice

“…Our prior studies also observed preservation of the KLS pool in STAT5-deficient mice. 22 We found that serial competitive repopulation with Gab2 Ϫ/Ϫ BM was deficient relative to wild-type BM, but that defects observed in primary recipients were not augmented by secondary and tertiary transplantations. These data support a decreased functional ability of transplanted progenitor cells to respond to cytokine growth factors in the BM microenvironment rather than a reduction in either the absolute number or function of stem cells.…”

“…22,25 The inability of Gab2 deficiency to affect STAT5 phosphorylation by IL-3 in primitive progenitor cells indicates that STAT5 is not tyrosine phosphorylated downstream of Gab2 in this cytokine-signaling pathway. However, the interactions among Gab2, SHP-2, and STAT5 are not well defined, and clearly the hematopoietic phenotypes are overlapping in some respects but divergent in others.…”

“…22 The antiGab2 antibody was obtained from Toshio Hirano and has been previously described. 8,13 Hematology and CFU assays Peripheral blood was obtained from the retro-orbital sinus following puncture using microcapillary tubes.…”

“…22 Briefly, BM cells were harvested from both hind limbs of donor mice and mixed with competitor CD45.1 cells at a donor equivalent ratio of 1:1. The mixed BM cells were injected into lethally irradiated recipient CD45.1 mice (11 Gy [1100 rad], 137 Cs source).…”

Loss of Tolerance and Autoimmunity Affecting Multiple Organs inSTAT5A/5B-Deficient Mice

“…These observations suggest that defects in STAT5A/5B Ϫ/Ϫ lymphocytes, probably within CD4 ϩ cells in particular, are responsible for the observed pathology. The complex effects of STAT5 deficiency on other cell types such as the bone marrow progenitors (18,24,25,(27)(28)(29)(30)(31) may also play a role in the pathology observed in these organs.…”