Follicle-stimulating hormone stimulates protein kinase A-mediated histone H3 phosphorylation and acetylation leading to select gene activation in ovarian granulosa cells

Phorbol ester promotes histone H3-Ser10 phosphorylation at the LDL receptor promoter in a protein kinase C-dependent manner

Histone modification is emerging as a major regulatory mechanism for modulating gene expression by altering the accessibility of transcription factors to DNA. This study unravels the relationship between histone H3 modifications and LDL receptor induction, focusing also on routes by which phosphorylation is mediated in human hepatoma HepG2 cells. We show that while histone H3 is constitutively acetylated at LDL receptor chromatin, 12-O-tetradecanoylphorbol-13-acetate (TPA) causes rapid hyperphosphorylation of histone H3 on serine 10 (histone H3-Ser10), despite global reduction in its phosphorylation levels. Ser10 hyperphosphorylation precedes LDL receptor induction and is independent of the p42/44MAPK, p38MAPK, pp90RSK, or MSK-1 cascade. Interestingly, inhibition of protein kinase C (PKC) blocks Ser10 hyperphosphorylation and also compromises LDL receptor induction by TPA. Consistent with its role, recombinant purified PKC phosphorylate purified histone H3-Ser10. Collectively, our findings highlight a novel role for PKC in regulating histone H3-Ser10 phosphorylation and suggest that histone modification provides numerous regulatory opportunities to set the overall range of control attainable for LDL receptor gene induction.

Phosphorylation of histone H3: a balancing act between chromosome condensation and transcriptional activation

In recent years, the covalent modification of histone tails has emerged as a crucial step in controlling the transcription of eukaryotic genes. Phosphorylation of the serine 10 residue of the N-terminal tail of histone H3 is crucial for chromosome condensation and cell-cycle progression during mitosis and meiosis. In addition, this modification is important during interphase because it enables the transcription of an increasing number of genes that are activated as a consequence of a variety of cell-signaling events. The location of the serine 10 residue in close proximity to other modifiable amino acids in the histone H3 tail enables the possibility of an interaction between phosphorylation of serine 10 and methylation and/or acetylation of lysine 9 and lysine 14. Finally, the finding that the histone H3.3 variant, which has a conserved N-terminal tail, can replace histone H3 at sites of active transcription, adds a new layer of complexity and possibilities to the regulation of transcription through changes in chromatin structure.

Follicle-stimulating hormone activation of hypoxia-inducible factor-1 by the phosphatidylinositol 3-kinase/AKT/Ras homolog enriched in brain (Rheb)/mammalian target of rapamycin (mTOR) pathway is necessary for induction of select protein markers of follicular differentiation

We sought to elucidate the role of AKT in follicle-stimulating hormone (FSH)-mediated granulosa cell (GC) differentiation. Our results define a signaling pathway in GCs whereby the inactivating phosphorylation of tuberin downstream of phosphatidylinositol (PI) 3-kinase/AKT activity leads to Rheb (Ras homolog enriched in brain) and subsequent mTOR (mammalian target of rapamycin) activation. mTOR then stimulates translation by phosphorylating p70 S6 kinase and, consequently, the 40 S ribosomal protein S6. Activation of this pathway is required for FSH-mediated induction of several follicular differentiation markers, including luteinizing-hormone receptor (LHR), inhibin-alpha, microtubule-associated protein 2D, and the PKA type IIbeta regulatory subunit. FSH also promotes activation of the transcription factor hypoxia-inducible factor-1 (HIF-1). FSH-stimulated HIF-1 activity is inhibited by the PI 3-kinase inhibitor LY294002, the Rheb inhibitor FTI-277 (farnesyltransferase inhibitor-277), and the mTOR inhibitor rapamycin. Finally, we find that the FSH-mediated up-regulation of reporter activities for LHR, inhibin-alpha, and vascular endothelial growth factor is dependent upon HIF-1 activity, because a dominant negative form of HIF-1alpha interferes with the up-regulation of these genes. These results show that FSH enhances HIF-1 activity downstream of the PI 3-kinase/AKT/Rheb/mTOR pathway in GCs and that HIF-1 activity is necessary for FSH to induce multiple follicular differentiation markers.

Chromatin remodeling and neuronal response: multiple signaling pathways induce specific histone H3 modifications and early gene expression in hippocampal neurons

Plasticity in gene expression is achieved by a complex array of molecular mechanisms by which intracellular signaling pathways directly govern transcriptional regulation. In addition to the remarkable variety of transcription factors and co-regulators, and their combinatorial interaction at specific promoter loci, the role of chromatin remodeling has been increasingly appreciated. The N-terminal tails of histones, the building blocks of nucleosomes, contain conserved residues that can be post-translationally modified by phosphorylation, acetylation, methylation and other modifications. Depending on their nature, these modifications have been linked to activation or silencing of gene expression. We wanted to investigate whether neuronal stimulation by various signaling pathways elicits chromatin modifications that would allow transcriptional activation of immediate early response genes. We have analysed the capacity of three drugs - SKF82958 (a dopaminergic receptor agonist), pilocarpine (a muscarinic acetylcholine receptor agonist) and kainic acid (a kainate glutamate receptor agonist) - to induce chromatin remodeling in hippocampal neurons. We show that all stimulations induce rapid, transient phosphorylation of histone H3 at serine 10. Importantly, the same agonists induce rapid activation of the mitogen-activated protein kinase pathway with similar kinetics to extracellular-regulated-kinase phosphorylation. In the same neurons where this dynamic signaling cascade is activated, there is induction of c-fos transcription. Histone H3 Ser10 phosphorylation is coupled to acetylation at the nearby Lys14 residue, an event that has been linked to local opening of chromatin structure. Our results underscore the importance of dynamic chromatin remodeling in the transcriptional response to various stimuli in neuronal cells.

Deactylase inhibitors disrupt cellular complexes containing protein phosphatases and deacetylases

Affinity isolation of protein serine/threonine phosphatases on the immobilized phosphatase inhibitor microcystin-LR identified histone deacetylase 1(HDAC1), HDAC6, and HDAC10 as novel components of cellular phosphatase complexes. Other HDACs, specifically HDAC2, -3, -4, and -5, were excluded from such complexes. In vitro biochemical studies showed that recombinant HDAC6, but not HDAC4, bound directly to the protein phosphatase (PP)1 catalytic subunit. No association was observed between HDAC6 and PP2A, another major protein phosphatase. PP1 binding was mapped to the second catalytic domain and adjacent C-terminal sequences in HDAC6, and treatment of cells with trichostatin A (TSA) disrupted endogenous HDAC6.PP1 complexes. Consistent with the inhibition of tubulin deactylase activity of HDAC6, TSA enhanced cellular tubulin acetylation, and acetylated tubulin was present in the PP1 complexes from TSA-treated cells. Trapoxin B, a weak HDAC6 inhibitor, and calyculin A, a cell-permeable phosphatase inhibitor, had no effect on the stability of the HDAC6.PP1 complexes or on tubulin acetylation. Mutations that inactivated HDAC6 prevented its incorporation into cellular PP1 complexes and suggested that when bound together both enzymes were active. Interestingly, TSA disrupted all the cellular HDAC.phosphatase complexes analyzed. This study provided new insight into the mechanism by which HDAC inhibitors elicited coordinate changes in cellular protein phosphorylation and acetylation and suggested that changes in these protein modifications at multiple subcellular sites may contribute to the known ability of HDAC inhibitors to suppress cell growth and transformation.

Phosphorylation at serine 28 and acetylation at lysine 9 of histone H3 induced by trichostatin A

Trichostatin A (TSA), a histone deacetylase inhibitor, strongly increases acetylation of the N-terminal tails of histone H3. Many studies have correlated the function of TSA with the hyperacetylation of histone. Although histone H3 is known to be phosphorylated, the effect of acetylation on phosphorylation is not known. Here, we report that in JB6 cells, TSA induces both acetylation at lysine 9 and phosphorylation at serine 28 of histone H3. UVB irradiation, which is known to induce phosphorylation at serine 28, did not significantly affect phosphorylation of histone H3 in TSA-pretreated JB6 cells. In contrast, TSA markedly increased phosphorylation and acetylation of histone H3 in UVB-pretreated JB6 cells. TSA strongly activated MAP kinases. Moreover, PD98059 and SB202190 inhibited TSA-induced phosphorylation but not acetylation of histone H3. Dominant negative mutant ERK2 and dominant negative mutant p38 kinase blocked TSA-stimulated phosphorylation of histone H3 at serine 28. The results indicate that TSA-induced phosphorylation of histone H3 at serine 28 occurs through activation of the MAP kinase pathway and phosphorylated histone H3 is more sensitive to TSA-induced hyperacetylation. The facilitation of phosphorylation and acetylation of histone H3 induced by TSA may play a critical regulatory role in chromatin remodeling and gene expression.

MAP kinase-mediated phosphoacetylation of histone H3 and inducible gene regulation

That signalling pathways, particularly the mitogen-activated protein kinase cascades, elicit modification of chromatin proteins such as histone H3 by phosphorylation and/or acetylation concomitant with gene activation is now well established. The picture that is emerging is one of a complex and dynamic pattern of multiple modifications at the H3 tail. Here, we review the inducible gene systems where H3 modifications have been reported and re-evaluate the controversy as to the kinase(s) that phosphorylates it as well as the proposed coupling between H3 phosphorylation and acetylation.

Activin a signaling induces Smad2, but not Smad3, requiring protein kinase a activity in granulosa cells from the avian ovary

Activin A signaling is an important regulator of ovarian granulosa cell function. The cytosolic signal transducer Smad2 is most highly expressed in chicken granulosa cells (cGC) of preovulatory follicles. Moreover, Smad2 shows predominant nuclear localization in freshly isolated cGC, indicating active Smad signaling in vivo. Primary cGC cultured in vitro require activin A to sustain high Smad2 levels, which otherwise drop dramatically in the absence of activin A. This activin A-dependent Smad2 expression is abrogated by protein kinase A (PKA) inhibitors, suggesting a role for PKA in activin signaling. In the absence of activin A, strong PKA activators such as follicle-stimulating hormone (FSH) and 8-bromo-cyclic AMP fail to elicit Smad2 induction. However, FSH and 8-bromo-cyclic AMP boost activin A-dependent Smad2 up-regulation, giving rise to Smad2 levels similar to expression in vivo levels. Interestingly, the effect is specific for Smad2, since expression of the structurally and functionally closely related Smad3 remains entirely unaffected. Hence, activin A induces Smad2, but not Smad3, to high levels requiring PKA activation. Since Smad2 and Smad3 target distinct yet overlapping sets of TGF-beta/activin-responsive genes, the selective Smad2 induction by FSH/activin A could allow FSH to efficiently modulate the transcriptional readout of activin A signaling in avian granulosa cells.

BIR-1, a Caenorhabditis elegans homologue of Survivin, regulates transcription and development

bir-1, a Caenorhabditis elegans inhibitor-of-apoptosis gene homologous to Survivin is organized in an operon with the transcription cofactor C. elegans SKIP (skp-1). Because genes arranged in operons are frequently linked functionally, we have asked whether BIR-1 also functions in transcription. bir-1 inhibition resulted in multiple developmental defects that overlapped with C. elegans SKIP loss-of-function phenotypes: retention of eggs, dumpy, movement defects, and lethality. bir-1 RNA-mediated interference decreased expression of several gfp transgenes and the endogenous genes dpy-7 and hlh-1. Immunoblot analysis revealed decreased phosphoacetylated histones in bir-1 RNA-mediated interference-treated worms. In a heterologous transfection system, BIR-1 augments thyroid hormone-regulated transcription and has an additive effect with SKIP. These results show that BIR-1 functions in the regulation of transcription and development.

Transcriptional induction of the osteocalcin gene during osteoblast differentiation involves acetylation of histones h3 and h4

The remodeling of chromatin is required for tissue-specific gene activation to permit interactions of transcription factors and coregulators with their cognate elements. Here, we investigate the chromatin-mediated mechanisms by which the bone-specific osteocalcin (OC) gene is transcriptionally activated during cessation of cell growth in ROS 17/2.8 osteosarcoma cells and during normal osteoblast differentiation. Acetylation of histones H3 and H4 at the OC gene promoter was assayed during the proliferative and postproliferative stages of cell growth by using chromatin immunoprecipitation assays with antibodies that recognize different acetylated forms of histones H3 or H4. The results show that the promoter and coding regions of the OC gene contain very low levels of acetylated histones H3 and H4 during the proliferative period of osteoblast differentiation when the OC gene is inactive. Active expression of the OC gene in mature osteoblasts and confluent ROS 17/2.8 cells is functionally linked to preferential acetylation of histone H4 and, to a lesser extent, to acetylation of histone H3. Histone acetylation at the loci for RUNX2 (CBFA1), alkaline phosphatase, bone sialoprotein, osteopontin, and the cell growth regulator p21, which are expressed throughout osteoblast differentiation, is not altered postproliferatively. We conclude that acetylation of histones H3 and H4 is functionally coupled to the chromatin remodeling events that mediate the developmental induction of OC gene transcription in bone cells.

Regulation of niemann-pick c1 gene expression by the 3'5'-cyclic adenosine monophosphate pathway in steroidogenic cells

The Niemann Pick-C1 (NPC-1) protein is essential for intracellular transport of cholesterol derived from low-density lipoprotein import in mammalian cells. The role of the protein kinase A (PKA) pathway in regulation of expression of the NPC-1 gene was investigated. NPC-1 promoter activity was induced by treatment with dibutryl cAMP (dbcAMP), alone or in combination with the cAMP response element (CRE) binding protein (CREB) overexpressed in adrenal Y-1 cells. When the catalytic subunit of PKA was overexpressed in Y-1 cells, there were similar increases in NPC-1 promoter activity in the presence of CREB. Responses were attenuated by blockade of the PKA pathway, and in the Kin-8 cell line deficient in PKA. Promoter deletion analysis revealed that this response was present in promoter fragments of 186 bp and larger but not present in the 121-bp fragment. Two promoter regions, one at -430 and one at -120 upstream of the translation initiation site, contained CRE consensus sequences. These bound recombinant CREB in EMSA, confirming their authenticity as CREB response elements. Promoters bearing mutations of both CRE displayed no response to dbcAMP. The orphan nuclear receptor, steroidogenic factor-1 (SF-1), was implicated in NPC-1 transactivation by the presence of SF-1 target sequence that formed a complex with recombinant SF-1 in EMSA. Furthermore, transfection of a plasmid that overexpressed SF-1 into ovarian granulosa cells increased promoter activity in response to dbcAMP, an effect abrogated by mutation of the SF-1 target sequence. Chromatin immunoprecipitation assays demonstrated that the CRE region of the endogenous and transfected NPC-1 promoter associated with both acetylated and phosphorylated histone H-3 and that this association was increased by dbcAMP treatment. Treatment with dbcAMP also increased the association of the CRE region of the promoter with CREB binding protein, which has histone acetyltransferase activity. Together, these results demonstrate a mechanism of regulation of NPC-1 expression by the cAMP-PKA pathway that includes PKA phosphorylation of CREB, recruitment of the coactivator CREB binding protein and the phosphorylation and acetylation of histone H-3 to transactivate the NPC-1 promoter.

A dominant negative PPARgamma mutant shows altered cofactor recruitment and inhibits adipogenesis in 3T3-L1 cells

AIMS/HYPOTHESIS

PPARgamma, a member of the nuclear hormone receptor family of transcription factors, plays a key role in adipocyte differentiation and insulin sensitivity. The aim of this study was to identify a potential dominant negative murine PPARgamma mutant and to characterize the in vitro functional properties of this mutant.

METHODS

In vitro transient transfections and mammalian two-hybrid assays in TSA201 cells were used to characterize the transcriptional activity of the L466A mutant and to study the molecular interaction of transcriptional cofactors with the L466A mutant in an attempt to elucidate the mechanism of its dominant negative activity. Adenoviral constructs expressing PPARgamma wild-type (AdWT) or the L466A mutant (AdL466A) were infected into the murine 3T3-L1 cell line to study the mutant's effect on adipogenesis.

RESULTS

The L466A mutant alone is transcriptionally defective. However, it retains DNA binding and inhibits the ligand-dependent and -independent activity of the wild-type receptor, consistent with dominant negative properties. In mammalian two-hybrid studies, the L466A mutant does not bind nuclear receptor coactivators. However, it more avidly recruits corepressors due to enhanced binding to the corepressor ID1 domain, leading to pronounced transcriptional repression. The AdL466A mutant inhibits adipogenesis induced by either a differentiation cocktail or by thiazolidinedione ligand. AdL466A infection also blocked the upregulation of the adipocyte marker genes aP2 and adipsin.

CONCLUSION

We conclude that the L466A PPARgamma mutant possesses potent dominant negative activity based on preferential corepressor recruitment and it inhibits adipogenesis and the expression of adipocyte-specific genes.

Follicle-stimulating hormone activates extracellular signal-regulated kinase but not extracellular signal-regulated kinase kinase through a 100-kDa phosphotyrosine phosphatase

In this report we sought to elucidate the mechanism by which the follicle-stimulating hormone (FSH) receptor signals to promote activation of the p42/p44 extracellular signal-regulated protein kinases (ERKs) in granulosa cells. Results show that the ERK kinase MEK and upstream intermediates Raf-1, Ras, Src, and L-type Ca(2+) channels are already partially activated in vehicle-treated cells and that FSH does not further activate them. This tonic stimulatory pathway appears to be restrained at the level of ERK by a 100-kDa phosphotyrosine phosphatase that associates with ERK in vehicle-treated cells and promotes dephosphorylation of its regulatory Tyr residue, resulting in ERK inactivation. FSH promotes the phosphorylation of this phosphotyrosine phosphatase and its dissociation from ERK, relieving ERK from inhibition and resulting in its activation by the tonic stimulatory pathway and consequent translocation to the nucleus. Consistent with this premise, FSH-stimulated ERK activation is inhibited by the cell-permeable protein kinase A-specific inhibitor peptide Myr-PKI as well as by inhibitors of MEK, Src, a Ca(2+) channel blocker, and chelation of extracellular Ca(2+). These results suggest that FSH stimulates ERK activity in immature granulosa cells by relieving an inhibition imposed by a 100-kDa phosphotyrosine phosphatase.

Acute signaling by the LH receptor is independent of protein kinase C activation

LH receptor activation leads to the phosphorylation/activation of p42/44 MAPK in preovulatory granulosa cells. As the LH receptor can activate both adenylyl cyclase and phospholipase C, we hypothesized that the LH receptor could elicit phosphorylation of p42/44 MAPK through activation of protein kinase A (PKA) and/or protein kinase C (PKC). Preovulatory granulosa cells in serum-free primary cultures were treated with ovulatory concentrations of human chorionic gonadotropin (hCG), an LH receptor agonist, with or without various inhibitors. The PKA inhibitor H89 as well as the myristoylated PKA inhibitor peptide PKI strongly inhibited hCG-stimulated p42/44 MAPK phosphorylation, whereas the PKC inhibitor GF109203X had no effect on p42/44 MAPK phosphorylation. LH receptor-stimulated phosphorylation of cAMP response element-binding protein (CREB), histone H3, and MAPK kinase (MEK) was also strongly inhibited by H89 and not by GF109203X. The extent of PKC activation was assessed in preovulatory granulosa cells using three criteria: translocation of PKC isoforms to the membrane fraction, phosphorylation of a known PKC substrate, and autophosphorylation of PKC delta on an activation-related site. By all three criteria PKCs were partially activated before hCG stimulation, and hCG treatment failed to elicit further PKC activation, in vitro or in vivo. Taken together, these results indicate that, under primary culture conditions where physiological levels of signaling proteins are present, hCG signals to activate MEK, p42/44 MAPK, CREB, and histone H3 in a predominantly PKA-dependent and PKC-independent manner. Unexpectedly, PKCs were partially activated in the absence of LH receptor activation, and LH receptor activation did not elicit further detectable PKC activation.

Histone H3 phosphorylation during Xenopus oocyte maturation: regulation by the MAP kinase/p90Rsk pathway and uncoupling from DNA condensation

Here we show that during the meiotic maturation of Xenopus oocytes, histone H3 becomes phosphorylated on serine-10 at about the time of maturation promoting factor activation and meiosis I entry. However, overexpression of cAMP-dependent protein kinase that blocks entry into M phase, also leads to massive serine-10 phosphorylation of histone H3 in intact Xenopus oocytes but does not cause chromosome condensation. We also show that the phosphorylation of histone H3 during oocyte maturation requires the activation of the mitogen-activated protein kinase/p90Rsk pathway. Our results indicate that in G2-arrested oocytes, which are about to enter M phase, histone H3 phosphorylation is not sufficient for chromosome condensation.

Independent dynamic regulation of histone phosphorylation and acetylation during immediate-early gene induction

Induction of c-fos and c-jun is associated with phosphoacetylation of histone H3 and acetylation of histone H4. Upon induction, a large population of nucleosomes becomes highly acetylated on histones H3 and H4, whereas a much smaller population of comparable nucleosomes at similar positions along the gene becomes phosphoacetylated. Inhibiting histone H3 phosphorylation with kinase inhibitors does not measurably alter the enhanced acetylation of these nucleosomes. Finally, whereas H3 phosphorylation is a MAP kinase-mediated inducible event, we found acetylation to be continuously turning over by the targeted action of HATs and HDACs in the absence of any stimulation or gene transcription. These studies suggest that phosphorylation and acetylation are independently and dynamically regulated at these genes and reveal the complexity of multiple histone modifications at immediate-early gene chromatin.