STAT5A-Deficient Mice Demonstrate a Defect in Granulocyte-Macrophage Colony-Stimulating Factor–Induced Proliferation and Gene Expression

Abstract

Responses of cells to cytokines typically involve the activation of a family of latent DNA binding proteins, referred to as signal transducers and activators of transcription (STAT) proteins, which are critical for the expression of early response genes. Of the seven known STAT proteins, STAT5 (originally called mammary gland factor) has been shown to be activated by several cytokines, such as granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5, which are known to play important roles in growth and differentiation of hematopoietic precursors. In this report we have used mice that are deficient in STAT5A (one of two homologues of STAT5) to study the role of STAT5A in GM-CSF stimulation of cells. When bone marrow–derived macrophages were generated by differentiation with macrophage-CSF (M-CSF), exposure of cells from wild-type mice to GM-CSF resulted in a typical pattern of assembly of DNA binding proteins specific for the gamma activation sequence (GAS) element within the β-casein promoter. However, in cells from the STAT5A null mouse one of the shifted bands was absent. Immunoblotting analysis in the null mice showed that lack of STAT5A protein resulted in no alteration in activation of STAT5B by tyrosine phosphorylation. Proliferation experiments revealed that, when exposed to increasing concentrations of GM-CSF, cells derived from the null mice grew considerably more slowly than cells derived from the wild-type mice. Moreover, expression of GM-CSF–dependent genes, CIS and A1, was markedly inhibited in cells derived from null mice as compared with those of wild-type mice. The decreased expression observed with A1, a bcl-2 like gene, may account in part for the suppression of growth in cells from the null mice. These data suggest that the presence of STAT5A during the GM-CSF–induced assembly of STAT5 dimers is critical for the formation of competent transcription factors that are required for both gene expression and cell proliferation.

Chemokines, chemokine receptors and hematopoiesis

“…In addition to CDK, CDKi and cyclins that directly influence cell cycle progression, a number of other intracellular molecules have been implicated in cytokine-mediated cell growth regulation. This includes members of the RAS, RAF, mitogen-activated protein kinase (MAPK) (31,(101)(102)(103)(104)(105) and alternate pathways (106), the protein phosphatases Src homology 2 (SH2)-containing tyrosine phosphatase (SHP)-1 (107-113), SHP-2 (22,25,(115)(116)(117)(118)(119)(120) and SH 2 domain-containing inositol phosphatase (SHIP) (121)(122)(123)(124)(125)(126)(127)(128)(129)(130) and transcription factors such as signal transducers and activators of transcription (Stats) and their associated Janus kinases (JAK) (131)(132)(133)(134)(135)(136)(137)(138)(139)(140)(141)(142)(143)(144), and possibly B-cell lymphoma gene product (BCL)-6 (145), amongst others.…”

Transcriptional regulation of the cyclin D1 promoter by STAT5: its involvement in cytokine-dependent growth of hematopoietic cells

“…In contrast, mutant forms of EPO and IL-2 receptors, both of which were unable to activate STAT5, were shown to transmit mitogenic signals as efficiently as wild-type receptors (Fujii et al, 1995;Quelle et al, 1996). It has been reported recently that, although STAT5A-targeted mice undergo normal development without apparent hematopoietic abnormalities (Lie et al, 1997), macrophages obtained from the bone marrow of STAT5Atargeted mice showed a 33% decreased proliferative response to GM-CSF compared with that of those from normal mice (Feldman et al, 1997). Furthermore, Teglund et al (1998) have reported that STAT5A -/-/5B -/mice reveal no abnormality in numbers of peripheral hematopoietic cells, but the number and proliferative potential of myeloid progenitor cells assayed by in vitro culture with IL-3, IL-5, TPO or GM-CSF were reduced by~50% in the bone marrow cells of these mice.…”

IFN‐γ regulates survival and function of tumor‐induced CD11b+Gr‐1high myeloid derived suppressor cells by modulating the anti‐apoptotic molecule Bcl2a1

“…Here, we demonstrate how IFN‐γ−induced STAT1 phosphorylation modulates the induction of Bcl2a1 by GM‐CSF in tumor‐induced myeloid cells. Therefore, while GM‐CSF increases Bcl2a1 expression in a STAT5 dependent manner , IFN‐γ simultaneously blocks it, providing T cells with an accelerator and brake mechanism to control granulocytic MDSC function in the tumor environment. IFN‐γ has been previously shown to display diverse effects on MDSC subsets .…”