MSK2 and MSK1 mediate the mitogen- and stress-induced phosphorylation of histone H3 and HMG-14

Cells respond to mitogenic or stress stimuli by the rapid induction of immediate-early (IE) genes, which occurs concomitantly with the phosphorylation of histone H3 and the high-mobility-group protein HMG-14. In mammalian cells this response is mediated via ERK and p38 MAP kinase pathways, but the identity of the downstream kinase that phosphorylates histone H3 has been contentious. One study, based on Coffin- Lowry cells defective in RSK2, reported that RSK2 was the histone H3 kinase, while a second study, based on the efficiency of RSKs and MSKs as in vitro histone H3 kinases, and their relative susceptibility to kinase inhibitors, suggested that MSKs were responsible. We show here that the histone H3 phosphorylation response is normal in Coffin-Lowry cells. Further more, we show that histone H3 and HMG-14 phosphorylation is severely reduced or abolished in mice lacking MSK1 and MSK2. We also show that, despite this, histone H3 acetylation is unimpaired in these cells and that IE genes can be induced, although at a reduced efficiency. We conclude that MSKs are the major kinases for histone H3 and HMG-14 in response to mitogenic and stress stimuli in fibroblasts.     

90-kDa ribosomal S6 kinase is a direct target for the nuclear fibroblast growth factor receptor 1 (FGFR1): role in FGFR1 signaling

Fibroblast growth factor receptor 1 (FGFR1) is a transmembrane protein capable of transducing stimulation by secreted FGFs. In addition, newly synthesized FGFR1 enters the nucleus in response to cellular stimulation and during development. Nuclear FGFR1 can transactivate CRE (cAMP responsive element), activate CRE-binding protein (CREB)-binding protein (CBP) and gene activities causing cellular growth and differentiation. Here, a yeast two-hybrid assay was performed to identify FGFR1-binding proteins and the mechanism of nuclear FGFR1 action. Ten FGFR1-binding proteins were identified. Among the proteins detected with the intracellular FGFR1 domain was a 90-kDa ribosomal S6 kinase (RSK1), a regulator of CREB, CBP, and histone phosphorylation. FGFR1 bound to the N-terminal region of RSK1. The FGFR1-RSK1 interaction was confirmed by co-immunoprecipitation and colocalization in the nucleus and cytoplasm of mammalian cells. Predominantly nuclear FGFR1-RSK1 interaction was observed in the rat brain during neurogenesis and in cAMP-stimulated cultured neural cells. In TE671 cells, transfected FGFR1 colocalized and coimmunoprecipitated, almost exclusively, with nuclear RSK1. Nuclear RSK1 kinase activity and RSK1 activation of CREB were enhanced by transfected FGFR1. In contrast, kinase-deleted FGFR1 (TK-), which did not bind to RSK1 failed to stimulate nuclear RSK1 activity or RSK1 activation of CREB. Kinase inactive FGFR1 (K514A) bound effectively to nuclear RSK1, but it failed to stimulate RSK1. Thus, active FGFR1 kinase regulates the functions of nuclear RSK1. The interaction of nuclear FGFR1 with pluripotent RSK1 offers a new mechanism through which FGFR1 may control fundamental cellular processes.     

Histone acetylation induced by granulocyte colony-stimulating factor in a map kinase-dependent manner

Histone acetylation has been shown to affect chromatin structure and gene expression. The mitogen-activated protein (MAP) kinase pathway is activated by a number of cytokines and plays critical roles in hematopoietic cell survival, proliferation, and differentiation. We focused on the part of the MAP kinase cascade and granulocyte colony-stimulating factor (G-CSF)in histone acetylation at one of the critical myeloid differentiation-associated genes, myeloperoxidase (MPO). G-CSF caused rapid acetylation of histone H3 and H4 at the promoter of MPO as revealed by chromatin immunoprecipitation. In addition, CBP and p300 were recruited to the promoter in response to G-CSF. Furthermore, we showed that rapid histone acetylation induced by G-CSF is MAP kinase-dependent. These results illustrate how myeloid-differentiating signals via G-CSF may be coupled with histone acetylation during the process of gene expression.     

Activation of tachykinin,neurokinin 3 receptors affects chromatin structure and gene expression by means of histone acetylation

The tachykinin, neurokinin 3 receptor (NK3R) is a g-protein coupled receptor that is broadly distributed in the nervous system and exerts its diverse physiological actions through multiple signaling pathways. Despite the role of the receptor system in a range of biological functions, the effects of NK3R activation on chromatin dynamics and gene expression have received limited attention. The present work determined the effects of senktide, a selective NK3R agonist, on chromatin organization, acetylation, and gene expression, using qRT-PCR, in a hypothalamic cell line (CLU 209) that expresses the NK3R. Senktide (1 nM, 10 nM) caused a relaxation of chromatin, an increase in global acetylation of histone H3 and H4, and an increase in the expression of a common set of genes involved in cell signaling, cell growth, and synaptic plasticity. Pretreatment with histone acetyltransferase (HAT) inhibitor (garcinol and 2-methylene y-butylactone), that inhibits p300, p300/CREB binding protein (CBP) associated factor (PCAF), and GCN 5, prevented the senktide-induced increase in expression of most, but not all, of the genes upregulated in response to 1 nM and 10 nM senktide. Treatment with 100 nM had the opposite effect: a reduction in chromatin relaxation and decreased acetylation. The expression of four genes was significantly decreased and the HAT inhibitor had a limited effect in blocking the upregulation of genes in response to 100 nM senktide. Activation of the NK3R appears to recruit multiple pathways, including acetylation, and possibly histone deactylases, histone methylases, or DNA methylases to affect chromatin structure and gene expression.