Multiple, PKA-dependent and PKA-independent, signals are involved in cAMP-induced PRL expression in the eosinophilic cell line Eol-1

Cyclic AMP induces reversible EPAC1 condensates that regulate histone transcription

The second messenger cyclic AMP regulates many nuclear processes including transcription, pre-mRNA splicing and mitosis. While most functions are attributed to protein kinase A, accumulating evidence suggests that not all nuclear cyclic AMP-dependent effects are mediated by this kinase, implying that other effectors may be involved. Here we explore the nuclear roles of Exchange Protein Activated by cyclic AMP 1. We find that it enters the nucleus where forms reversible biomolecular condensates in response to cyclic AMP. This phenomenon depends on intrinsically disordered regions present at its amino-terminus and is independent of protein kinase A. Finally, we demonstrate that nuclear Exchange Protein Activated by cyclic AMP 1 condensates assemble at genomic loci on chromosome 6 in the proximity of Histone Locus Bodies and promote the transcription of a histone gene cluster. Collectively, our data reveal an unexpected mechanism through which cyclic AMP contributes to nuclear spatial compartmentalization and promotes the transcription of specific genes.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Crosstalk between FSH and relaxin at the end of the proliferative stage of rat Sertoli cells

Follicle-stimulating hormone (FSH) stimulates the proliferation of immature Sertoli cells through the activation of PI3K/AKT/mTORC1 and MEK/ERK1/2 pathways. Mature Sertoli cells stop proliferating and respond to FSH by stimulating cAMP production. To gain insight into possible mechanisms involved in this switch as well as the impact of paracrine factors that stimulate cell proliferation, we analyzed the effects of FSH and relaxin on intracellular signaling pathways involved with proliferation and differentiation in Sertoli cells from 15-day-old rats, which are close to the transition between the two stages. FSH stimulated ³H-thymidine incorporation and cyclin D1 expression, changes associated with proliferation. In contrast, FSH inhibited AKT and ERK1/2 phosphorylation, activated cAMP production and induced changes in several cell cycle genes that were compatible with differentiation. Relaxin also stimulated ³H-thymidine incorporation but increased phosphorylation of ERK1/2 and AKT. When both hormones were added simultaneously, relaxin attenuated FSH-mediated inhibition of ERK1/2 and AKT phosphorylation and FSH-mediated activation of cAMP production. FSH but not relaxin increased CREB phosphorylation, and relaxin but not FSH shifted NF-κB expression from the cytoplasm to the nucleus. Relaxin did not inhibit the effects of FSH on inhibin α and Bcl2 expression. We propose that at this time of Sertoli cell development, FSH starts to direct cells to differentiation through activation of cAMP/CREB and inhibition of ERK1/2 and AKT pathways. Relaxin counteracts FSH signaling through the inhibition of cAMP and activation of ERK1/2, AKT and NF-κB, but does not block the differentiation process triggered by FSH.

The prolactin gene: a paradigm of tissue-specific gene regulation with complex temporal transcription dynamics

Transcription of numerous mammalian genes is highly pulsatile, with bursts of expression occurring with variable duration and frequency. The presence of this stochastic or 'noisy' expression pattern has been relatively unexplored in tissue systems. The prolactin gene provides a model of tissue-specific gene regulation resulting in pulsatile transcription dynamics in both cell lines and endocrine tissues. In most cell culture models, prolactin transcription appears to be highly variable between cells, with differences in transcription pulse duration and frequency. This apparently stochastic transcription is constrained by a transcriptional refractory period, which may be related to cycles of chromatin remodelling. We propose that prolactin transcription dynamics result from the summation of oscillatory cellular inputs and by regulation through chromatin remodelling cycles. Observations of transcription dynamics in cells within pituitary tissue show reduced transcriptional heterogeneity and can be grouped into a small number of distinct patterns. Thus, it appears that the tissue environment is able to reduce transcriptional noise to enable coordinated tissue responses to environmental change. We review the current knowledge on the complex tissue-specific regulation of the prolactin gene in pituitary and extra-pituitary sites, highlighting differences between humans and rodent experimental animal models. Within this context, we describe the transcription dynamics of prolactin gene expression and how this may relate to specific processes occurring within the cell.

Attenuation of IGF-I receptor signaling inhibits serum-induced proliferation of prostate cancer cells

OBJECTIVE

Several studies showed that high serum levels of insulin-like growth factor-I (IGF-I) correlate with an increased risk for prostate cancer, although the causal role of IGF-I remains to be established. In this study, we addressed the role of IGF-I as a serum factor on the growth of two androgen-independent cell lines (Du145 and PC3) and one androgen-dependent cell line (LNCaP).

DESIGN

We investigated the effects of a blocking antibody against the IGF-I receptor (αIR3) on DNA synthesis in prostate cancer cells cultured in the presence of recombinant human IGF-I or normal human serum (NHS).

RESULTS

We show that in all three prostate cancer cell lines, NHS exerts a markedly stronger stimulating effect on DNA synthesis than IGF-I, and that the effect of NHS can be completely abrogated by an antibody against the IGF-I receptor (αIR3). Using pharmacological inhibitors of the two canonical IGF-I receptor signaling pathways, we show that the phosphatidylinositol-3'-kinase (PI3K) and the Mek-Erk pathways are not required for the stimulating effect of NHS.

CONCLUSION

Our observations indicate that the stimulating effect of NHS is completely dependent on IGF-I receptor signaling transduction and that IGF-I stimulates DNA synthesis in prostate cancer cells in strong synergy with other serum factors. We speculate that the role of other serum factors could explain the discrepancy between the results observed in different animal models to study the function of IGF-I in prostate cancer.

Modulation of cytokine production by cyclic adenosine monophosphate analogs in human leukocytes

Cyclic adenosine monophosphate (cAMP) is a well-known second messenger that operates through different signaling molecules, including protein kinase A (PKA) and guanine exchange proteins directly activated by cAMP (EPAC). Cell-permeable cAMP analogs such as 8-(4-chloro-phenyl-thio)-cAMP (8-pCPT-cAMP) modulate cytokine secretion by different leukocyte subsets, including T cells and monocytes. Since cAMP-modulating drugs such as phosphodiesterase inhibitors are being tested in inflammatory disorders such as asthma and chronic obstructive lung disease, it is important to obtain more insight into the regulation of cytokine production by cAMP. To address the signaling molecules involved in cAMP-mediated modulation of cytokine production, we used cAMP derivatives such as N(6)-benzoyladenosine-cAMP (6-Bnz-cAMP) and 8-pCPT-2-O-methyl cAMP (8-pCPT-2'-O-Me-cAMP), which selectively activate either PKA or EPAC, respectively. We show that in T cells, 6-Bnz-cAMP exerts similar globally inhibiting effects on cytokine secretion as 8-pCPT-cAMP, indicating that these effects are mediated by PKA. On the contrary, 8-pCPT-2'-O-Me-cAMP specifically inhibits the production of interleukin-10 (IL-10) in lipopolysaccharide-activated T-cell-depleted peripheral blood mononuclear cells, whereas the production of IL-1β, tumor necrosis factor α, and IL-12 is not or hardly affected. Inhibition by 8-pCPT-2'-O-Me-cAMP of IL-10 production was confirmed using purified monocytes. Further, in B cells 6-Bnz-cAMP, but not 8-pCPT-2'-O-Me-cAMP, stimulated IL-10 production. In conclusion, cAMP stimulates IL-10 production via PKA in activated B cells, but inhibits IL-10 production in activated monocytes through EPAC. We speculate that selective effects of PKA and EPAC on cytokine production in leukocyte subsets open up therapeutic possibilities using selective activators or inhibitors of EPAC or PKA.

What can we learn from rodents about prolactin in humans?

Prolactin (PRL) is a 23-kDa protein hormone that binds to a single-span membrane receptor, a member of the cytokine receptor superfamily, and exerts its action via several interacting signaling pathways. PRL is a multifunctional hormone that affects multiple reproductive and metabolic functions and is also involved in tumorigenicity. In addition to being a classical pituitary hormone, PRL in humans is produced by many tissues throughout the body where it acts as a cytokine. The objective of this review is to compare and contrast multiple aspects of PRL, from structure to regulation, and from physiology to pathology in rats, mice, and humans. At each juncture, questions are raised whether, or to what extent, data from rodents are relevant to PRL homeostasis in humans. Most current knowledge on PRL has been obtained from studies with rats and, more recently, from the use of transgenic mice. Although this information is indispensable for understanding PRL in human health and disease, there is sufficient disparity in the control of the production, distribution, and physiological functions of PRL among these species to warrant careful and judicial extrapolation to humans.

Prostaglandin E(2) induces breast cancer related aromatase promoters via activation of p38 and c-Jun NH(2)-terminal kinase in adipose fibroblasts

Aromatase is the key enzyme for estrogen biosynthesis. A distal promoter, PI.4, maintains baseline levels of aromatase in normal breast adipose tissue. In contrast, malignant breast epithelial cells secrete prostaglandin E(2) (PGE(2)), which stimulates aromatase expression via proximal promoters PI.3/PII in a cyclic AMP (cAMP)- and protein kinase C (PKC)-dependent manner in adjacent breast adipose fibroblasts (BAF), leading to increased local concentrations of estrogen. Although an effective treatment for breast cancer, aromatase inhibitors indiscriminately abolish estrogen synthesis in all tissues, causing major side effects. To identify drug targets to selectively block aromatase and estrogen production in breast cancer, we investigated PGE(2)-stimulated signaling pathways essential for aromatase induction downstream of cAMP and PKC in human BAFs. Here, we show that PGE(2) or its surrogate hormonal mixture dibutyryl cAMP (Bt(2)cAMP) + phorbol diacetate (PDA) stimulated the p38, c-jun NH(2)-terminal kinase (JNK)-1, and extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase pathways. Inhibition or small interfering RNA-mediated knockdown of p38 or JNK1, but not ERK, inhibited PGE(2)- or Bt(2)cAMP + PDA-induced aromatase activity and expression via PI.3/PII. Conversely, overexpression of wild-type p38alpha or JNK1 enhanced PGE(2)-stimulated aromatase expression via PII. PGE(2) or Bt(2)cAMP + PDA stimulated c-Jun and activating transcription factor-2 (ATF2) phosphorylation and binding to the PI.3/PII region. Specific activation of protein kinase A (PKA) or EPAC with cAMP analogues stimulated p38 and JNK1; however, only PKA-activating cAMP analogues induced aromatase expression. The PKC activator PDA effectively stimulated p38 and JNK1 phosphorylation but not aromatase expression. Taken together, PGE(2) activation of p38 and JNK1 via PKA and PKC is necessary for aromatase induction in BAFs, and p38 and JNK1 are potential new drug targets for tissue-specific ablation of aromatase expression in breast cancer.

Adipocyte prolactin: regulation of release and putative functions

Pituitary-derived prolactin (PRL) is a well-known regulator of the lactating mammary gland. However, the recent discovery that human adipose tissue produces PRL as well as expresses the PRL receptor (PRLR) highlights a previously unappreciated action of PRL as a cytokine involved in adipose tissue function. Biologically active PRL is secreted by all adipose tissue depots examined: breast, visceral and subcutaneous. The expression of adipose PRL is regulated by a non-pituitary, alternative superdistal promoter. PRL expression and release increases during early pre-adipocyte differentiation and is stimulated by cyclic AMP activators, including beta adrenergic receptor agonists. PRL release from subcutaneous adipose explants is attenuated during obesity, suggesting that adipose PRL production is altered by the metabolic state. Several lines of evidence indicate that PRL suppresses lipid storage as well as the release of adipokines such as adiponectin, interleukin-6 and possibly leptin. PRL has also been implicated in the regulation of adipogenesis. A newly developed PRL-secreting human adipocyte cell line, LS14, should allow comprehensive examination of the regulation and function of adipocyte-derived PRL. Collectively, these studies raise the prospect that PRL affects energy homeostasis through its action as an adipokine and is involved in the manifestation of insulin resistance.

Pulmonary artery smooth muscle cells from normal subjects and IPAH patients show divergent cAMP-mediated effects on TRPC expression and capacitative Ca2+ entry

Pulmonary vascular remodeling due to overgrowth of pulmonary artery smooth muscle cells (PASMC) is a major cause for the elevated vascular resistance in patients with idiopathic pulmonary arterial hypertension (IPAH). Increased cytosolic Ca(2+) concentration, resulting from enhanced capacitative Ca(2+) entry (CCE) and upregulated transient receptor potential (TRP) channel expression, is involved in stimulating PASMC proliferation. The current study was designed to determine the impact of cAMP, a second messenger that we hypothesized would blunt aspects of PASMC activity, as a possible contributor to IPAH pathophysiology. Short-term (30 min) pretreatment with forskolin (FSK; 10 muM), a direct activator of adenylyl cyclase, in combination with the cyclic nucleotide phosphodiesterase inhibitor isobutylmethylxanthine (IBMX; 200 muM), attenuated CCE in PASMC from normal subjects, patients without pulmonary hypertension (NPH), and patients with IPAH. The FSK-mediated CCE inhibition was independent of protein kinase A (PKA), because the PKA inhibitor H89 negligibly affected the decrease in CCE produced by cAMP. By contrast, longer (4 h) treatment with FSK (with IBMX) attenuated CCE in normal and NPH PASMC but enhanced CCE in IPAH PASMC. This enhancement of CCE was abolished by PKA inhibition and associated with an upregulation of TRPC3. In addition, cAMP increased TRPC1 mRNA expression in IPAH (but not in normal or NPH) PASMC, an effect blunted by H89. Furthermore, iloprost, a prostacyclin analog that increases cAMP, downregulated TRPC3 expression in IPAH PASMC and FSK-mediated cAMP increase inhibited IPAH PASMC proliferation. Although a rapid rise in cellular cAMP decreases CCE by a PKA-independent mechanism, sustained cAMP increase inhibits CCE in normal and NPH PASMC but increases CCE via a PKA-dependent pathway in IPAH PASMC. The divergent effect of cAMP on CCE parallels effects on TRPC expression. The results suggest that the combined use of a PKA inhibitor and cAMP-elevating drugs may provide a novel approach for treatment of IPAH.

Modulation of the production of reactive oxygen species (ROS) by cAMP-elevating agents in granulocytes from diabetic patients: an Akt/PKB-dependent phenomenon

BACKGROUND

Granulocytes from healthy subjects and from patients suffering from diabetes mellitus present differences in reactivity to stimulation with cyclic nucleotide-elevating agents. The production of reactive oxygen species (ROS) is inhibited in cells from non-diabetic subjects following such stimulation, but activated through a PKA-independent signaling pathway in granulocytes from type 1 and type 2 diabetic patients. The aim of the present study was to understand better the changes in signaling mechanisms induced by the disease.

METHODS

ROS production in granulocytes from healthy subjects and from type 1 and type 2 diabetic patients was measured using a luminol-dependent chemiluminescence assay. Granulocytes were stimulated by the addition of the cAMP-elevating agent dibutyryl cAMP. In some experiments, granulocytes were pre-treated with an inhibitor of PKA or Akt/PKB prior to cAMP stimulation.

RESULTS

Intracellular elevation of cAMP induced a PKA-dependent and Akt/PKB-independent inhibition of ROS production in granulocytes from healthy subjects, but a significant activation in cells from both type 1 and type 2 diabetic patients. Most significantly, activation of ROS generation in cells from diabetic patients was shown to be Akt/PKB-dependent and PKA-independent.

CONCLUSIONS

These results suggest that chronic hyperglycaemia could induce metabolic adaptation in cAMP-related signaling mechanisms. Epac (exchange protein directly activated by cAMP) is a novel cAMP receptor besides PKA involved in different signaling pathways. The cAMP-stimulated inverse ROS response in granulocytes from type 1 and type 2 diabetic patients may be due to a change in signaling pathways from cAMP/PKA to cAMP/Epac/Akt/PKB. These preliminary results require further studies in order to evaluate their consequences on innate immunity and pathogenesis of diabetes mellitus.

Gene expression profiling of acute myeloid leukemia with translocation t(8;16)(p11;p13) and MYST3-CREBBP rearrangement reveals a distinctive signature with a specific pattern of HOX gene expression

Acute myeloid leukemia (AML) with translocation t(8;16)(p11;p13) is an infrequent leukemia subtype with characteristic clinicobiological features. This translocation leads to fusion of MYST3 (MOZ) and CREBBP (CBP) genes, probably resulting in a disturbed transcriptional program of a myelomonocytic precursor. Nonetheless, its gene expression profile is unknown. We have analyzed the gene expression profile of 23 AML patients, including three with molecularly confirmed MYST3-CREBBP fusion gene, using oligonucleotide U133A arrays (Affymetrix). MYST3-CREBBP cases clustered together and clearly differentiated from samples with PML-RARalpha, RUNX1-RUNX1T1, and CBFbeta-MYH11 rearrangements. The relative expression of 46 genes, selected according to their differential expression in the high-density array study, was analyzed by low-density arrays in an additional series of 40 patients, which included 7 MYST3-CREBBP AML cases. Thus, genes such as prolactin (PRL) and proto-oncogene RET were confirmed to be specifically overexpressed in MYST3-CREBBP samples whereas genes such as CCND2, STAT5A, and STAT5B were differentially underexpressed in this AML category. Interestingly, MYST3-CREBBP AML exhibited a characteristic pattern of HOX expression, with up-regulation of HOXA9, HOXA10, and cofactor MEIS1 and marked down-regulation of other homeobox genes. This profile, with overexpression of FLT3, HOXA9, MEIS1, AKR7A2, CHD3, and APBA2, partially resembles that of AML with MLL rearrangement. In summary, this study shows the distinctive gene expression profile of MYST3-CREBBP AML, with overexpression of RET and PRL and a specific pattern of HOX gene expression.

Induction of prolactin expression and release in human preadipocytes by cAMP activating ligands

In addition to the pituitary, prolactin (PRL) in humans is produced at non-pituitary sites where it acts as a cytokine. We previously reported that PRL is expressed and released from breast adipose explants, raising the question as to the dynamics of its production and its regulation. Preadipocytes were isolated from breast adipose tissue obtained during breast reduction. PRL expression was transiently increased during early preadipocyte differentiation. Both isoproterenol, a beta-adrenergic receptor agonist, and PACAP, pituitary adenylate cyclase activating peptide, increased PRL expression, and release from preadipocytes. This stimulation was suppressed by several protein kinase inhibitors, suggesting involvement of multiple signaling pathways. Transfection of preadipocytes with a superdistal PRL promoter/luciferase reporter revealed two stimulatory domains and an inhibitory domain. These data establish the transcriptional regulation of adipocyte PRL by the superdistal PRL promoter, its transient expression during adipogenesis, and the stimulatory effect of catecholamines and PACAP.

Multiple cAMP-induced signaling cascades regulate prolactin expression in T cells

Beside its pivotal role in reproduction, the pituitary hormone prolactin (PRL) has been attributed an immunomodulatory function. Here we report that cAMP is an important stimulator of PRL transcription in primary human T lymphocytes. Inhibition of both protein kinase A (PKA) and p38 MAPK partially abrogated cAMP-induced PRL expression. In addition, cAMP-induced phosphorylation of p38 was shown to occur independently of PKA and could be mimicked by a methylated cAMP analogue which specifically activates the recently discovered cAMP receptor EPAC (exchange protein directly activated by cAMP). Our findings suggest that cAMP induces PRL expression in T lymphocytes via cooperation of at least two different signaling pathways: a PKA-dependent pathway leading to the phosphorylation of cAMP response element-binding protein, and a PKA-independent pathway leading to p38 phosphorylation.

Insulin-like growth factor-I augments interleukin-8 promoter activity through induction of activator protein-1 complex formation

We previously established that stimulation by IGF-I of interleukin (IL)-8 expression in leukocytes required activation of extracellular-regulated kinase (ERK) and basal activity of c-Jun N-terminal kinase (JNK). In this study, we tested the hypothesis that IGF-I stimulates IL-8 expression at the transcriptional level through induction of Fos/Jun activator protein (AP)-1 complex formation. Inhibition studies using the transcriptional inhibitor actinomycin D and IL-8 promoter activation studies indicate that IGF-I act at the transcriptional level. Using gel shift assays we demonstrate that IGF-I induces the formation of active c-Jun/c-Fos AP-1 complexes. Promoter activation studies using mutated IL-8 promoter constructs show that the AP-1 response element is required for promoter activation by IGF-I whereas CAAT-enhancer binding protein (C/EBP) and nuclear factor of kappa B (NFkappaB) sites were not essential. These results indicate that IGF-I can augment IL-8 expression through activation of AP-1 independent of other inducible transcription factors which have shown to be involved in IL-8 regulation by immune stimuli. This finding is in agreement with our previous observation that IGF-I is able to enhance basal IL-8 production in peripheral blood mononuclear cells (PBMC) in the absence of other stimuli.