Activation of the 9E3/cCAF chemokine by phorbol esters occurs via multiple signal transduction pathways that converge to MEK1/ERK2 and activate the Elk1 transcription factor

AIRE promotes androgen-independent prostate cancer by directly regulating IL-6 and modulating tumor microenvironment

Early stage prostate cancers are dependent on androgens for their growth and survival and androgen withdrawal causes them to regress. Progressive prostate cancers eventually acquire androgen independence rendering anti-androgen therapy ineffective. However, the factors leading to this have not been adequately addressed. This study shows that AIRE finds differential expression in androgen-dependent and -independent prostate cancer cells. AIRE expression is more in androgen-independent cells due to its regulation by transcription factor Elk-1. These enhanced levels of AIRE modulate the prostate tumor microenvironment by transcriptionally activating a malignancy gene IL-6 in androgen-independent cells. Additionally, AIRE prevents the cancer cells from anticancer drug-induced death and enhances their invasiveness. Moreover, AIRE by modulating the cytokine milieu skews the tumor-associated macrophage polarization towards M2 phenotype with increased CD206 and CD163 expression. Subcutaneous mouse model of prostate cancer revealed AIRE^+/+ mice forming a palpable tumor and presents lymphadenopathy however, only a small benign tumor is observed in AIRE^−/− mice and lymph nodes appear normal in size. In conclusion, our findings suggest AIRE as a probable factor in promoting prostate cancer progression.

IL-2 imprints human naive B cell fate towards plasma cell through ERK/ELK1-mediated BACH2 repression

Plasma cell differentiation is a tightly regulated process that requires appropriate T cell helps to reach the induction threshold. To further understand mechanisms by which T cell inputs regulate B cell fate decision, we investigate the minimal IL-2 stimulation for triggering human plasma cell differentiation in vitro. Here we show that the timed repression of BACH2 through IL-2-mediated ERK/ELK1 signalling pathway directs plasma cell lineage commitment. Enforced BACH2 repression in activated B cells unlocks the plasma cell transcriptional program and induces their differentiation into immunoglobulin M-secreting cells. RNA-seq and ChIP-seq results further identify BACH2 target genes involved in this process. An active regulatory region within the BACH2 super-enhancer, under ELK1 control and differentially regulated upon B-cell activation and cellular divisions, helps integrate IL-2 signal. Our study thus provides insights into the temporal regulation of BACH2 and its targets for controlling the differentiation of human naive B cells.

T cells help B cells to differentiate into antibody-producing plasma cells. Here the authors show that T cells produce interleukin-2 to activate ERK/ELK1 and suppress BACH2 expression by modulating the BACH2 super-enhancer, thereby altering BACH2 downstream transcription programs for plasma cell differentiation.

Resveratrol upregulates Egr-1 expression and activity involving extracellular signal-regulated protein kinase and ternary complex factors

Many intracellular functions have been attributed to resveratrol, a polyphenolic phytoalexin found in grapes and in other plants. Here, we show that resveratrol induces the expression of the transcription factor Egr-1 in human embryonic kidney cells. Using a chromosomally embedded Egr-1-responsive reporter gene, we show that the Egr-1 activity was significantly elevated in resveratrol-treated cells, indicating that the newly synthesized Egr-1 protein was biologically active. Stimulus-transcription coupling leading to the resveratrol-induced upregulation of Egr-1 expression and activity requires the protein kinases Raf and extracellular signal-regulated protein kinase ERK, while MAP kinase phosphatase-1 functions as a nuclear shut-off device that interrupts the signaling cascade connecting resveratrol stimulation with enhanced Egr-1 expression. On the transcriptional level, Elk-1, a key transcriptional regulator of serum response element-driven gene transcription, connects the intracellular signaling cascade elicited by resveratrol with transcription of the Egr-1 gene. These data were corroborated by the observation that stimulation of the cells with resveratrol increased the transcriptional activation potential of Elk-1. The SRE as well as the GC-rich DNA binding site of Egr-1 function as resveratrol-responsive elements. Thus, resveratrol regulates gene transcription via activation of the stimulus-regulated protein kinases Raf and ERK and the stimulus-responsive transcription factors TCF and Egr-1.

Immediate-early transcriptional response to angiotensin II in human adrenocortical cells

Angiotensin II binds to the angiotensin II receptors type 1 (AT1 receptors) in adrenocortical cells and triggers an intracellular signaling cascade leading to changes in the gene expression pattern. Here, we show that stimulation with angiotensin II induces the expression of biologically active early growth response (Egr)-1, a zinc finger transcription factor, in human H295R adrenocortical cells. Expression of a dominant-negative mutant of the ternary complex factor Elk-1, a key transcriptional regulator of serum response element-driven gene transcription, prevented Egr-1 expression in angiotensin II-stimulated H295R cells, indicating that Ets-like protein-1 (Elk-1) or related ternary complex factors connect the intracellular signaling cascade elicited by activation of AT1 receptors with transcription of the Egr-1 gene. These data were corroborated by the fact that angiotensin II stimulation increased the transcription activation potential of Elk-1. In addition, activator protein-1 transcriptional activity was significantly elevated in angiotensin II-treated H295R cells. Expression of c-Jun and c-Fos was increased as well as the transcription activation potential of c-Fos. Expression of a dominant-negative mutant of Elk-1 reduced c-Fos expression in angiotensin II-stimulated adrenocortical cells, suggesting that the serum response element within the c-Fos promoter functions as an angiotensin II-response element. Expression of a dominant-negative mutant of c-Jun reduced activator protein-1 activity in angiotensin II-stimulated adrenocortical cells and reduced the up-regulation of c-Jun after angiotensin II stimulation. Thus, c-Jun regulates its own expression in adrenocortical cells. Together, the data show that angiotensin II stimulation activates the transcription factors Egr-1, Elk-1, c-Jun, and c-Fos in adrenocortical cells, leading to stimulus-dependent changes in the gene expression pattern.

Genome-wide analysis reveals PADI4 cooperates with Elk-1 to activate c-Fos expression in breast cancer cells

Peptidylarginine deiminase IV (PADI4) catalyzes the conversion of positively charged arginine and methylarginine residues to neutrally charged citrulline, and this activity has been linked to the repression of a limited number of target genes. To broaden our knowledge of the regulatory potential of PADI4, we utilized chromatin immunoprecipitation coupled with promoter tiling array (ChIP-chip) analysis to more comprehensively investigate the range of PADI4 target genes across the genome in MCF-7 breast cancer cells. Results showed that PADI4 is enriched in gene promoter regions near transcription start sites (TSSs); and, surprisingly, this pattern of binding is primarily associated with actively transcribed genes. Computational analysis found potential binding sites for Elk-1, a member of the ETS oncogene family, to be highly enriched around PADI4 binding sites; and coimmunoprecipitation analysis then confirmed that Elk-1 physically associates with PADI4. To better understand how PADI4 may facilitate gene transactivation, we then show that PADI4 interacts with Elk-1 at the c-Fos promoter and that, following Epidermal Growth Factor (EGF) stimulation, PADI4 catalytic activity facilitates Elk-1 phosphorylation, histone H4 acetylation, and c-Fos transcriptional activation. These results define a novel role for PADI4 as a transcription factor co-activator.

Protein kinase C regulates urea permeability in the rat inner medullary collecting duct

Hypertonicity increases urea transport independently of, as well as synergistically with, vasopressin in the inner medullary collect duct (IMCD). We previously showed that hypertonicity does not increase the level of cAMP in the IMCD, but it does increase the level of intracellular calcium. Since we also showed that hypertonicity increases both the phosphorylation and biotinylation of the urea transporters UT-A1 and UT-A3, this would suggest involvement of a calcium-dependent protein kinase in the regulation of urea transport in the inner medulla. In this study, we investigated whether protein kinase C (PKC), which is present in the IMCD, is a regulator of urea permeability. We tested the effect of PKC inhibitors and activators on urea permeability in the isolated, perfused rat terminal IMCD. Increasing osmolality from 290 to 690 mosmol/kgH(2)O significantly stimulated (doubled) urea permeability; it returned to control levels on inhibition of PKC with either 10 μM chelerythrine or 50 μM rottlerin. To determine the potential synergy between vasopressin and PKC, phorbol dibutyrate (PDBu) was used to stimulate PKC. Vasopressin stimulated urea permeability 247%. Although PDBu alone did not change basal urea permeability, in the presence of vasopressin, it significantly increased urea permeability an additional 92%. The vasopressin and PDBu-stimulated urea permeability was reduced to AVP alone levels by inhibition of PKC. We conclude that hypertonicity stimulates urea transport through a PKC-mediated phosphorylation. Whether PKC directly phosphorylates UT-A1 and/or UT-A3 or phosphorylates it as a consequence of a cascade of activations remains to be determined.

Post-translational modifications influence transcription factor activity: a view from the ETS superfamily

Transcription factors provide nodes of information integration by serving as nuclear effectors of multiple signaling cascades, and thus elaborate layers of regulation, often involving post-translational modifications, modulating and coordinate activities. Such modifications can rapidly and reversibly regulate virtually all transcription factor functions, including subcellular localization, stability, interactions with cofactors, other post-translational modifications and transcriptional activities. Aside from analyses of the effects of serine/threonine phosphorylation, studies on post-translational modifications of transcription factors are only in the initial stages. In particular, the regulatory possibilities afforded by combinatorial usage of and competition between distinct modifications on an individual protein are immense, and with respect to large families of closely related transcription factors, offer the potential of conferring critical specificity. Here we will review the post-translational modifications known to regulate ETS transcriptional effectors and will discuss specific examples of how such modifications influence their activities to highlight emerging paradigms in transcriptional regulation.

MAP kinase phosphorylation-dependent activation of Elk-1 leads to activation of the co-activator p300

CBP/p300 recruitment to enhancer-bound complexes is a key determinant in promoter activation by many transcription factors. We present a novel mechanism of activating such complexes and show that pre-assembled Elk-1-p300 complexes become activated following Elk-1 phosphorylation by changes in Elk-1-p300 interactions rather than recruitment. It is known that Elk-1 binds to promoter in the absence of stimuli. However, it is unclear how activation of Elk-1 by mitogen-acivated protein kinase (MAPK)-mediated phosphorylation leads to targeted gene transactivation. We show that Elk-1 can interact with p300 in vitro and in vivo in the absence of a stimulus through the Elk-1 C-terminus and the p300 N-terminus. Phosphorylation on Ser383 and Ser389 of Elk-1 by MAPK enhances this basal binding but, most importantly, Elk-1 exhibits new interactions with p300. These interaction changes render a strong histone acetyltransferase activity in the Elk-1-associated complex that could play a critical role in chromatin remodeling and gene activation. The pre-assembly mechanism may greatly accelerate transcription activation, which is important in regulation of expression of immediate-early response genes, in particular those involved in stress responses.

Novel nuclear target for thrombin: activation of the Elk1 transcription factor leads to chemokine gene expression

Thrombin is primarily known for its role in homeostasis and thrombosis. However, this enzyme also plays important roles in wound healing and pathologic situations such as inflammation and tumorigenesis. Among the molecules stimulated by thrombin in these latter processes are the stress response proteins, chemokines. Chemokines are also known for their roles in inflammatory responses and tumor development. These correlative observations strongly suggest that chemokines may be mediators of some of thrombin's functions in these processes. Elucidation of the molecular mechanisms of stimulation of chemokines by thrombin may help to unravel the ways in which their expression can be modulated. Up-regulation of the chemokine 9E3/cCAF by thrombin occurs via its proteolytically activated receptor with subsequent transactivation of the epidermal growth factor receptor tyrosine kinase. This study shows that stimulation by thrombin very rapidly activates this chemokine at the transcriptional level, that 2 Elk1 binding elements located between −534 and −483 bp of the promoter are major thrombin response elements, that activation occurs via the Elk1 transcription factor, and that the latter is directly activated by MEK1/ERK2. The common occurrence of Elk1 binding domains in the promoters of immediate early response genes suggests that it may be characteristically involved in gene activation by stress-inducing agents.

Novel nuclear target for thrombin: activation of the Elk1 transcription factor leads to chemokine gene expression

Thrombin is primarily known for its role in homeostasis and thrombosis. However, this enzyme also plays important roles in wound healing and pathologic situations such as inflammation and tumorigenesis. Among the molecules stimulated by thrombin in these latter processes are the stress response proteins, chemokines. Chemokines are also known for their roles in inflammatory responses and tumor development. These correlative observations strongly suggest that chemokines may be mediators of some of thrombin's functions in these processes. Elucidation of the molecular mechanisms of stimulation of chemokines by thrombin may help to unravel the ways in which their expression can be modulated. Up-regulation of the chemokine 9E3/cCAF by thrombin occurs via its proteolytically activated receptor with subsequent transactivation of the epidermal growth factor receptor tyrosine kinase. This study shows that stimulation by thrombin very rapidly activates this chemokine at the transcriptional level, that 2 Elk1 binding elements located between −534 and −483 bp of the promoter are major thrombin response elements, that activation occurs via the Elk1 transcription factor, and that the latter is directly activated by MEK1/ERK2. The common occurrence of Elk1 binding domains in the promoters of immediate early response genes suggests that it may be characteristically involved in gene activation by stress-inducing agents.

Isolation and characterization of a new chemokine receptor gene, the putative chicken CXCR1

This study delineates the isolation and characterization of a novel chemokine receptor gene, the putative chicken CXC receptor 1 (cCXCR1). Using a human CXCR1 probe, we isolated several positive clones from a chicken genomic library. One of the clones contained a fragment of approximately 5000bp that hybridized strongly with the hCXCR1 probe. This fragment was sequenced and subjected to a variety of computer analyses. The open reading frame for this gene predicts a seven transmembrane domain protein with all the characteristics of a chemokine receptor and with 67% sequence homology to hCXCR1, 65% to hCXCR2 and also with considerable sequence homology to other human chemokine receptors such as hCXCR4 (50%), hCCR2 (49%) and hCCR1 (49%). However, the homology to a previously isolated potential G-protein-coupled receptor for chickens (AvCRL1) is only 47%. Using 5' RACE, two transcription initiation sites were identified suggesting the potential for the expression of two protein isoforms (I and II) in vivo. The promoter for the putative cCXCR1 contains a variety of consensus transcription factor binding elements that can potentially be involved in the expression of this chicken receptor upon stimulation by stress-inducing agents. RT-PCR analysis was used to determine the pattern of expression of the larger isoform (I) of this receptor in a variety of tissues. This form of the receptor is expressed primarily in the organs of the gastrointestinal tract, tissues that are frequently exposed to stress-inducing agents, but not in the central nervous system, tissues that are protected from insult by the blood barrier. Using the same RT-PCR approach we show that stress-inducing agents, such as 'first-hand' and 'second-hand' cigarette smoke components, tumor promoters and thrombin, differentially stimulate the expression of the isoform I in primary fibroblasts. Thrombin is an enzyme that plays many important roles in thrombosis, angiogenesis and wound healing and exposure to both cigarette smokes and/or to tumor promoters can lead to tumorigenesis. Therefore, upregulation of chemokines and their receptors by stress-inducing agents can confer highly regulated modulation of cellular responses to traumatic and pathological situations.

Disparate effects of phorbol esters, CD3 and the costimulatory receptors CD2 and CD28 on RANTES secretion by human T lymphocytes

This study has examined the stimuli required for secretion of regulated upon activation, normal T-cell expressed, presumed secreted (RANTES) from T lymphocytes and found that stimuli such as phorbol 12-myristate 13-acetate (PMA), which are unable to support T-cell proliferation and interleukin-2 (IL-2) production, are nevertheless able to elicit strong secretion of RANTES. Conversely, stimuli such as CD2 and CD28 ligation, which are able to support T-cell proliferation, are unable to elicit RANTES secretion. Coligation of CD3 and CD28 drives T-cell proliferation to a similar degree as CD2 and CD28 coligation, yet also supports modest RANTES secretion. Furthermore, CD28 ligation enhances the secretion of RANTES stimulated by PMA and this costimulatory effect is abrogated by the phosphoinositide 3-kinase inhibitor wortmannin. Our data also indicate that the observed effects of PMA on RANTES secretion are probably due to activation of protein kinase C (PKC) isoenzymes, since RANTES secretion was unaffected by the non-PKC activating 4alpha-phorbol ester, whilst the general PKC inhibitor Ro-32-0432 inhibits PMA-stimulated RANTES secretion. Moreover, the effect of PMA appears to be chemokine-specific because PMA was unable to increase secretion of the related CC chemokine MIP-1alpha. Under stimulation conditions where increases in [Ca2+]i occur (e.g. PMA plus ionomycin or CD3 plus CD28 ligation) RANTES secretion can be severely reduced compared with the levels observed in response to the phorbol ester PMA. Hence, whilst PKC-dependent pathways are sufficient for strong RANTES secretion, a calcium-dependent factor is activated which negatively regulates RANTES secretion. This correlates well with the observation that ligation of cytolytic T lymphocyte-associated antigen-4 (CTLA-4) (expression of which has been reported to be dependent on a sustained calcium signal), inhibits RANTES secretion induced by CD3/CD28, but has no effect on PMA-stimulated RANTES secretion.

Tissue specific expression of Yrk kinase: implications for differentiation and inflammation

The Src family of proto-oncogenes is a highly conserved group of non-receptor tyrosine kinases with very similar, but not identical, tissue distributions and functions. Yrk is a recently discovered new member of this family. Here we report the patterns of expression of this kinase in a variety of chicken tissues during development and after hatching, and experiments that correlate some of the observed patterns of expression with potential functions. The results show that the Yrk protein is primarily found in neuronal and epithelial cells and in monocyte/macrophages. In neuronal tissues of hatched chicks, Yrk is expressed in Purkinje cells, in the gigantocellularis of the brain-stem, and in retinal ganglion cells. In addition, staining for this kinase is also seen as thread-like and punctate patterns suggesting staining in neurites and growth cones. Epithelial cells express Yrk in the stomach during late developmental stages and after hatching but, in other epithelia such as in the peridermis, intestine and kidney, expression is high during development but low (skin) or undetectable (intestine and kidney) after hatching. These results suggest that Yrk may have several functional roles, specifically in cell migration and or differentiation during neuronal and epithelial cell development and in maintenance of the differentiated phenotype. In this study we also show that significant levels of Yrk are detected in monocytes of the blood and in tissue macrophages. Analysis of chicken hematopoietic cell lines confirmed the expression of Yrk in cells of monocyte/macrophage lineage and show for the first time in experimentally-induced inflammation that Yrk kinase activity is high during the period of monocyte infiltration, raising the possibility that this kinase plays a role in inflammation and/or response to injury.