Gene expression and cAMP

Targeting PDE4A for therapeutic potential: exploiting drug repurposing approach through virtual screening and molecular dynamics

cAMP-specific 3',5'-cyclic phosphodiesterase 4 A (PDE4A) holds a pivotal role in modulating intracellular levels of cyclic adenosine monophosphate (cAMP). Targeting PDE4A with novel therapeutic agents shows promise in addressing neurological disorders (e.g. Alzheimer's and Parkinson's diseases), mood disorders (depression, anxiety), inflammatory conditions (asthma, chronic obstructive pulmonary disease), and even cancer. In this study, we present a comprehensive approach that integrates virtual screening and molecular dynamics (MD) simulations to identify potential inhibitors of PDE4A from the existing pool of FDA-approved drugs. The initial compound selection was conducted focusing on binding affinity scores, which led to the identification of several high-affinity compounds with potential PDE4A binding properties. From the refined selection process, two promising compounds, Fluspirilene and Dihydroergocristine, emerged as strong candidates, displaying substantial affinity and specificity for the PDE4A binding site. Interaction analysis provided robust evidence of their binding capabilities. To gain deeper insights into the dynamic behavior of Fluspirilene and Dihydroergocristine in complex with PDE4A, we conducted 300 ns MD simulations, principal components analysis (PCA), and free energy landscape (FEL) analysis. These analyses revealed that Fluspirilene and Dihydroergocristine binding stabilized the PDE4A structure and induced minimal conformational changes, highlighting their potential as potent binders. In conclusion, our study systematically explores repurposing existing FDA-approved drugs as PDE4A inhibitors through a comprehensive virtual screening pipeline. The identified compounds, Fluspirilene and Dihydroergocristine, exhibit a strong affinity for PDE4A, displaying characteristics that support their suitability for further development as potential therapeutic agents for conditions associated with PDE4A dysfunction.Communicated by Ramaswamy H. Sarma.

Alteration in Cngb1 Expression upon Maternal Immune Activation in a Mouse Model and Its Possible Association with Schizophrenia Susceptibility

Objective

The cyclic nucleotide-gated channel (Cng) regulates synaptic efficacy in brain neurons by modulating Ca^2＋ levels in response to changes in cyclic nucleotide concentrations. This study investigated whether the expression of Cng channel, cyclic nucleotide-gated channel subunit beta 1 (Cngb1) exhibited any relationship with the pathophysiology of schizophrenia in an animal model and whether genetic polymorphisms of the human gene were associated with the progression of schizophrenia in a Korean population.

Methods

We investigated whether Cngb1 expression was related to psychiatric disorders in a mouse model of schizophrenia induced by maternal immune activation. A case-control study was conducted of 275 schizophrenia patients and 410 controls with single-nucleotide polymorphisms (SNPs) in the 5′-near region of CNGB1.

Results

Cngb1 expression was decreased in the prefrontal cortex in the mouse model. Furthermore, the genotype frequency of a SNP (rs3756314) of CNGB1 was associated with the risk of schizophrenia.

Conclusion

Our results suggest that CNGB1 might be associated with schizophrenia susceptibility and maternal immune activation. Consequently, it is hypothesized that CNGB1 may be involved in the pathophysiology of schizophrenia.

Overexpression of cytochrome P450 epoxygenases prevents development of hypertension in spontaneously hypertensive rats by enhancing atrial natriuretic peptide

Cytochrome P450 (P450)-derived epoxyeicosatrienoic acids (EETs) exert well recognized vasodilatory, diuretic, and tubular fluid-electrolyte transport actions that are predictive of a hypotensive effect. The study sought to determine the improvement of hypertension and cardiac function by overexpressing P450 epoxygenases in vivo. Long-term expression of CYP102 F87V or CYP2J2 in spontaneously hypertensive rats (SHR) was mediated by using a type 8 recombinant adeno-associated virus (rAAV8) vector. Hemodynamics was measured by a Millar Instruments, Inc. (Houston, TX) microtransducer catheter, and atrial natriuretic peptide (ANP) mRNA levels were tested by real-time polymerase chain reaction. Results showed that urinary excretion of 14,15-EET was increased at 2 and 6 months after injection with rAAV-CYP102 F87V and rAAV-CYP2J2 compared with controls (p < 0.05). During the course of the 6-month study, systolic blood pressure significantly decreased in P450 epoxygenase-treated rats, but the CYP2J2-specific inhibitor C26 blocked rAAV-CYP2J2-induced hypotension and the increase in EET production. Cardiac output was improved by P450 epoxygenase expression at 6 months (p < 0.05). Furthermore, cardiac collagen content was reduced in P450 epoxygenase-treated rats. ANP mRNA levels were up-regulated 6- to 14-fold in the myocardium, and ANP expression was significantly increased in both myocardium and plasma in P450 epoxygenase-treated rats. However, epidermal growth factor (EGF) receptor antagonist 4-(3'-chloroanilino)-6,7-dimethoxy-quinazoline (AG-1478) significantly attenuated the increase in the EET-induced expression of ANP in vitro. These data indicate that overexpression of P450 epoxygenases attenuates the development of hypertension and improves cardiac function in SHR, and that these effects may be mediated, at least in part, by ANP via activating EGF receptor.

Protein phosphorylation and growth control

Many growth factor receptors and retroviral transforming proteins share the property of phosphorylating proteins on tyrosine. Several substrates for both types of protein-tyrosine kinase have been identified. Treatment of quiescent cells with growth factors such as EGF and PDGF, whose receptors have ligand-stimulated protein-tyrosine kinase activities, induces tyrosine phosphorylation of three proteins, p45, p42 and p41. Two phosphorylated forms of p42 are found, the more basic of which is present in some but not all cells transformed by viral protein-tyrosine kinases. p42 is rapidly (as early as 1 min) but transiently (decreased to baseline by 2h) phosphorylated following PGDF or EGF treatment of quiescent fibroblasts. At saturating levels of mitogen the stoichiometry of p42 phosphorylation is greater than 50%. p42 is a highly conserved, rare (0.002% of total cell protein), soluble cytoplasmic protein. IGF I and insulin, whose receptors also have ligand-stimulated protein-tyrosine kinase activity, induce p42 phosphorylation in appropriate cells. In the case of insulin this effect has been observed in cells with large numbers of insulin receptors. p42 is also phosphorylated in response to mitogens whose receptors lack protein-tyrosine kinase activity, for example 12-O-tetradecanoylphorbol-13-acetate (TPA) and thrombin. For TPA there is evidence that this is an indirect effect due to the activation of a protein-serine/threonine kinase. On the basis of the highly conserved nature of this response and its generality, it seems likely that tyrosine phosphorylation of p42 is important for at least early responses to mitogens.

Activation of Galpha s mediates induction of tissue-type plasminogen activator gene transcription by epoxyeicosatrienoic acids

The epoxyeicosatrienoic acids (EETs) are products of cytochrome P450 (CYP) epoxygenases that have vasodilatory and anti-inflammatory properties. Here we report that EETs have additional fibrinolytic properties. In vascular endothelial cells, physiological concentrations of EETs, particularly 11,12-EET, or overexpression of the endothelial epoxygenase, CYP2J2, increased tissue plasminogen activator (t-PA) expression by 2.5-fold without affecting plasminogen activator inhibitor-1 expression. This increase in t-PA expression correlated with a 4-fold induction in t-PA gene transcription and a 3-fold increase in t-PA fibrinolytic activity and was blocked by the CYP inhibitor, SKF525A, but not by the calcium-activated potassium channel blocker, charybdotoxin, indicating a mechanism that does not involve endothelial cell hyperpolarization. The t-PA promoter is cAMP-responsive, and induction of t-PA gene transcription by EETs correlated with increases in intracellular cAMP levels and, functionally, with cAMP-driven promoter activity. To determine whether increases in intracellular cAMP levels were due to modulation of guanine nucleotide-binding proteins, we assessed the effects of EETs on Galpha(s) and Galpha(i2). Treatment with EETs increased Galpha(s), but not Galpha(i2), GTP-binding activity by 3.5-fold. These findings indicate that EETs possess fibrinolytic properties through the induction of t-PA and suggest that endothelial CYP2J2 may play an important role in regulating vascular hemostasis.

Odorants induce the phosphorylation of the cAMP response element binding protein in olfactory receptor neurons

Although odorants are known to activate olfactory receptor neurons through cAMP, the long-term effects of odorant detection are not known. Our recent findings indicate that there is also a delayed and sustained cAMP response, with kinetics sufficient to mediate long-term cellular responses. This cAMP response is mediated by cGMP through activation of adenylyl cyclase by protein kinase G (PKG). Therefore, we investigated the ability of odorants to regulate gene expression in rat olfactory epithelium. The cAMP-responsive binding protein (CREB) is a well-characterized transcription factor regulated by cAMP. We examined CREB activity in rat olfactory epithelium and olfactory receptor neurons (ORNs) after stimulation with odorants. Odorants increased levels of phosphorylated CREB in olfactory epithelium in vivo, and this increase was localized to ORNs in vitro. Incubation with 8-bromo-cGMP or sodium nitroprusside, a guanylyl cyclase activator, also increased phosphorylated CREB. In vitro, cAMP-dependent protein kinase phosphorylated CREB. In contrast, PKG failed to phosphorylate CREB directly in vitro. Our results demonstrate that the delayed odorant-induced cAMP signal activates CREB, which in turn may modulate gene expression in ORNs. In addition, cGMP indirectly affects CREB activation. This effect of cGMP on CREB activity through cAMP provides another mechanism for the modulation of CREB.

Activation of guanine nucleotide-binding proteins and induction of endothelial tissue-type plasminogen activator gene transcription by alcohol

The mechanism by which moderate alcohol ingestion lowers the risk of cardiovascular disease is unknown but may be due, in part, to the ability of alcohol to increase the level of tissue-type plasminogen activator (t-PA). Human endothelial cells were treated with low concentrations of ethanol (0.25-25 mM, 0-24 h), which are associated with moderate alcohol consumption. Although treatment with ethanol alone did not affect t-PA gene transcription or mRNA expression, it augmented isoproterenol (ISO)-stimulated t-PA gene transcription and mRNA levels by 3.4- and 2.8-fold, respectively, and decreased plasminogen activator inhibitor-1 mRNA levels by 65%. These effects of ethanol correlated with 2.5- and 6.9-fold increases in ISO-stimulated cyclic AMP levels and 4x-cyclic AMP response element heterologous promoter activity, respectively. To determine whether alcohol-induced changes in agonist-stimulated cyclic AMP levels were because of modulation of guanine nucleotide-binding proteins (G proteins), we assessed the effects of ethanol on Galphas and Galphai2. Although ethanol did not affect the expression of Galphas or Galphai2, it increased ISO-stimulated Galphas GTPase and GTP binding activity by 2.2- and 2.9-fold and decreased UK14304-stimulated Galphai2 GTPase and GTP binding activity by 38 and 80%. These results indicate that treatment with relatively low concentrations of ethanol enhances agonist-stimulated cyclic AMP-dependent t-PA gene transcription in vascular endothelial cells through differential modulation of G protein.

Widespread expression of olfactory cyclic nucleotide-gated channel genes in rat brain: implications for neuronal signalling

The cyclic nucleotides cAMP and cGMP are important intracellular messengers involved in a wide variety of signal transduction events in the nervous system. It has been proposed that cAMP/cGMP elicit some of their effects through direct gating of a novel class of Ca2+ -permeable ion channels that are termed cyclic nucleotide-gated (CNG) channels. Previous studies have identified the expression of a gene encoding one major CNG channel subtype, the olfactory receptor neuron alpha subunit, in the brain [El-Husseini et al. (1995) NeuroReport 6:1331-1335; Kingston et al. (1996a) Proc. Natl. Acad. Sci. U.S.A. 93:10440-10445; Bradley et al. (1997) J. Neurosci. 17:1993-2085]. We, therefore, proposed that the actions of cAMP/cGMP on neurons in the brain might occur through the activation of these CNG channels. To determine how widespread such a function might be, the regional and cellular distribution of the olfactory CNG channel alpha subunit has been examined in detail. Primers for multiple portions of the olfactory CNG channel were used in polymerase chain reaction (PCR) to amplify cDNA reverse-transcribed from several brain regions. The identities of PCR products were confirmed with Southern blots and by sequencing. In situ hybridization experiments demonstrated localization of CNG channel mRNA in discrete neuronal populations throughout the brain. In agreement with previous work, relatively strong hybridization signals are present in neuronal cell bodies of the cerebellum, olfactory bulb, cerebral cortex, and brainstem. Additionally, somewhat lesser signals are found in thalamus, hypothalamus, midbrain, and spinal cord while no hybridization signal was detectable in the caudate nucleus. This surprisingly wide distribution throughout the rat brain strengthens the hypothesis that CNG channels may influence numerous processes as downstream effectors of cyclic nucleotide cascades. Interestingly, the distribution of CNG channels is very similar to that of the nitric oxide/cGMP system, suggesting that one function of CNG channels in the brain could be to link diffusible messengers to elevated Ca2+ entry into neurons.

Immunohistochemical localization of calmodulin-dependent cyclic phosphodiesterase in the human brain

The amplification of cyclic nucleotide 'second messenger' signals within neurons is controlled by phosphodiesterases which are responsible for their degradation. Calmodulin-dependent phosphodiesterase (CaMPDE) is an abundant enzyme in brain which carries out this function. For the first time, we have localized CaMPDE in the normal human brain at various ages, using a mononoclonal antibody designated A6. This antibody was generated using standard techniques, purified, and applied to tissue sections. Autopsy specimens of human brain with no neuropathological abnormalities were selected representing a range of pre- and postnatal ages. Sections of various brain regions were evaluated for immunoreactivity, graded as nil, equivocal, or definite. We demonstrated definite CaMPDE immunohistochemical staining in neocortex, especially in neurons in layers 2 and 5. There was definite neuronal immunoreactivity in the hippocampus, and in the subiculum. The striatum had definite patchy neuronal staining. Definite terminal staining in the globus pallidus externa and substantia nigra pars reticulata outlined resident neurons, interpreted as axonal terminal staining. Cerebellar Purkinje cells showed definite immunoreactivity. In the developing brain, definite immunohistochemical staining was seen in the cerebellar external granular layer. The expression of CaMPDE in specific subsets of neurons suggests they may correlate with cells having dopaminergic innervation and/or high levels of neuronal integration.

Calcium-sensitive particulate guanylyl cyclase as a modulator of cAMP in olfactory receptor neurons

The second messengers cAMP and inositol-1,4,5-triphosphate have been implicated in olfaction in various species. The odorant-induced cGMP response was investigated using cilia preparations and olfactory primary cultures. Odorants cause a delayed and sustained elevation of cGMP. A component of this cGMP response is attributable to the activation of one of two kinetically distinct cilial receptor guanylyl cyclases by calcium and a guanylyl cyclase-activating protein (GCAP). cGMP thus formed serves to augment the cAMP signal in a cGMP-dependent protein kinase (PKG) manner by direct activation of adenylate cyclase. cAMP, in turn, activates cAMP-dependent protein kinase (PKA) to negatively regulate guanylyl cyclase, limiting the cGMP signal. These data demonstrate the existence of a regulatory loop in which cGMP can augment a cAMP signal, and in turn cAMP negatively regulates cGMP production via PKA. Thus, a small, localized, odorant-induced cAMP response may be amplified to modulate downstream transduction enzymes or transcriptional events.

Calcium-sensitive particulate guanylyl cyclase as a modulator of cAMP in olfactory receptor neurons

The second messengers cAMP and inositol-1,4,5-triphosphate have been implicated in olfaction in various species. The odorant-induced cGMP response was investigated using cilia preparations and olfactory primary cultures. Odorants cause a delayed and sustained elevation of cGMP. A component of this cGMP response is attributable to the activation of one of two kinetically distinct cilial receptor guanylyl cyclases by calcium and a guanylyl cyclase-activating protein (GCAP). cGMP thus formed serves to augment the cAMP signal in a cGMP-dependent protein kinase (PKG) manner by direct activation of adenylate cyclase. cAMP, in turn, activates cAMP-dependent protein kinase (PKA) to negatively regulate guanylyl cyclase, limiting the cGMP signal. These data demonstrate the existence of a regulatory loop in which cGMP can augment a cAMP signal, and in turn cAMP negatively regulates cGMP production via PKA. Thus, a small, localized, odorant-induced cAMP response may be amplified to modulate downstream transduction enzymes or transcriptional events.

Novel protein inhibitor of calmodulin-dependent cyclic nucleotide phosphodiesterase from glioblastoma multiforme

Previous investigations from our laboratory have demonstrated a significant reduction in the catalytic function of the 60 kDa and 63 kDa isozymes of calmodulin-dependent cyclic nucleotide phosphodiesterase (CaMPDE) when comparing human cerebral tissue that was free of tumor and glioblastoma multiforme (GBM) and gliosarcoma [Lal S., Raju R. V. S., Macaulay R. B. J., and Sharma R. K. (1996) Can. J. Neurol. Sci., 23, 245-250]. The results suggested the possibility of an endogenously produced inhibitor of CaMPDE expressed in these tumors. Further investigation has initially characterized the presence of a heat-labile, protein inhibitor of both the 60 kDa and 63 kDa isozymes of CaMPDE. Sephacryl S-200 gel filtration column chromatography indicated that the inhibitor has an apparent molecular weight of 22 kDa and experimental evidence demonstrates that this inhibitor protein may act independently of calmodulin, and is therefore a novel CaMPDE inhibitor. Previous work on non-CNS tumors has shown high levels of CaMPDE activity and absence of an inhibitor. This suggests that a different mechanism may exist for the proliferation of these subsets of tumors.

Roles of protein kinase A and C in spontaneous maturation and in forskolin or 3-isobutyl-1-methylxanthine maintained meiotic arrest of bovine oocytes

Four hypotheses were tested using isolated bovine oocytes. (1) Cumulus oocyte complexes (COCs) or denuded oocytes (DOs) were cultured with the protein kinase A (PKA) inhibitor, H-89, to test if meiotic arrest induced by forskolin or IBMX was due to cAMP-stimulated PKA activity or nonspecific effects of these cAMP elevators. (2) COCs were cultured with a protein kinase C (PKC) stimulator (PDD beta) or inhibitor (GF109203x) to test if PKC modulation altered oocyte maturation. (3) COCs were prestimulated for 15 min with (a) PDD beta followed by cotreatment with forskolin, or (b) with H-89 or H-7 followed by cotreatment with GF109203x, to test for interaction between the PKA and PKC signal transduction pathways. (4) H-89 was added to spontaneously maturing COCs at intervals of 0-18 hr to test if H-89 interfered with the transition between meiosis I and II. The results were as follows: H-89 interfered with forskolin or IBMX arrested oocytes in dose-response manner (IBMX ED50 = 41 microM for COCs; forskolin ED50 = 9 microM for denuded oocytes). Prestimulation with PKC induced meiotic resumption in COCs in spite of the presence of forskolin [PDD beta followed by PDD beta + forskolin: 41-47% germinal vesicle (GV) oocytes; forskolin alone: 90-95% GV], while PKC inhibition induced meiotic arrest to a similar extent as forskolin (GF109203x, 85% GV; forskolin, 67-80% GV). Additionally, pretreatment of COCs with H-89 interfered with GF109203x induced arrest (41% vs. 90% GV, respectively). Finally, H-89 interfered with the timely progression of COCs from meiosis I and II. These results indicate that the PKA and PKC pathways can modulate the maturation of bovine oocytes in vitro.

Nutritional and hormonal regulation of expression of the gene for malic enzyme

We have provided a historical and personal description of the analysis of physiological and molecular mechanisms by which diet and hormones regulate the activity of hepatic malic enzyme. For the most part, our analyses have been reductionist in approach, striving for increasingly simpler systems in which we can ask more direct questions about the molecular nature of the signaling pathways that regulate the activity of malic enzyme. The reductionist approaches that were so successful at analyzing molecular mechanisms in cells in culture may now provide the means to analyze more definitively questions about the physiological mechanisms involved in nutritional regulation of gene expression. In addition to physiological questions, however, there are still many aspects of the molecular mechanisms that have not been elucidated. Despite considerable effort from many laboratories, the molecular mechanisms by which T3 regulates transcription are not clear. Similarly, the molecular details for the mechanisms by which glucagon, insulin, glucocorticoids, and fatty acids regulate gene expression remain to be determined. The role of fatty acids is particularly interesting because it may provide a model for mechanisms by which genes are regulated by metabolic intermediates; this is a form of transcriptional regulation widely used by prokaryotic organisms and extensively analyzed in prokaryotic systems, but poorly understood in higher eukaryotes. At any specific time, there is, of course, only one rate of transcription for each copy of the malic-enzyme gene in a cell. Our long-term objective is to understand how signals from all of the relevant regulatory pathways are integrated to bring about that rate.

Point mutation of the autophosphorylation site or in the nuclear location signal causes protein kinase A RII beta regulatory subunit to lose its ability to revert transformed fibroblasts

The RII beta regulatory subunit of cAMP-dependent protein kinase (PKA) contains an autophosphorylation site and a nuclear location signal, KKRK. We approached the structure-function analysis of RII beta by using site-directed mutagenesis. Ser114 (the autophosphorylation site) of human RII beta was replaced with Ala (RII beta-P) or Arg264 of KKRK was replaced with Met (RII beta-K). ras-transformed NIH 3T3 (DT) cells were transfected with expression vectors for RII beta, RII beta-P, and RII beta-K, and the effects on PKA isozyme distribution and transformation properties were analyzed. DT cells contained PKA-I and PKA-II isozymes in a 1:2 ratio. Over-expression of wild-type or mutant RII beta resulted in an increase in PKA-II and the elimination of PKA-I. Only wild-type RII beta cells demonstrated inhibition of both anchorage-dependent and -independent growth and phenotypic change. The growth inhibitory effect of RII beta overexpression was not due to suppression of ras expression but was correlated with nuclear accumulation of RII beta. DT cells demonstrated growth inhibition and phenotypic change upon treatment with 8-Cl-cAMP. RII beta-P or RII beta-K cells failed to respond to 8-Cl-cAMP. These data suggest that autophosphorylation and nuclear location signal sequences are integral parts of the growth regulatory mechanism of RII beta.

The role of protein phosphorylation in the regulation of cyclic nucleotide phosphodiesterases

The cyclic nucleotide phosphodiesterases constitute a complex superfamily of enzymes responsible for catalyzing the hydrolysis of cyclic nucleotides. Regulation of cyclic nucleotide phosphodiesterases is one of the two major mechanisms by which intracellular cyclic nucleotide levels are controlled. In many cases the fluctuations in cyclic nucleotide levels in response to hormones is due to the hormone responsiveness of the phosphodiesterase. Isozymes of the cGMP-inhibited, cAMP-specific, calmodulin-stimulated and cGMP-binding phosphodiesterases have been demonstrated to be substrates for protein kinases. Here we review the evidence that hormonally responsive phosphorylation acts to regulate cyclic nucleotide phosphodiesterases. In particular, the cGMP-inhibited phosphodiesterases, which can be phosphorylated by at least two different protein kinases, are activated as a result of phosphorylation. In contrast, phosphorylation of the calmodulin-stimulated phosphodiesterases, which coincides with a decreased sensitivity to activation by calmodulin, results in decreased phosphodiesterase activity.

Differential effects of peptide hormones bombesin, vasoactive intestinal polypeptide and somatostatin analog RC-160 on the invasive capacity of human prostatic carcinoma cells

The effects of bombesin, vasoactive intestinal polypeptide (VIP), and a somatostatin analog (RC-160) on the in vitro invasion of reconstituted basement membrane (Matrigel) by two human prostatic carcinoma cell lines were examined. Aggressively growing PC-3 cells were found to be invasive in this assay in contrast to the relatively indolent LNCaP cells. Bombesin increased penetration of basement membrane by both cell lines. Although VIP had no effect on invasion by PC-3 cells, it enhanced invasion by LNCaP cells in a dose-dependent manner. In agreement with these results, VIP stimulated adenylate cyclase activity only in LNCaP cells. In contrast to bombesin and VIP, RC-160 did not alter invasion by either cell line. Our results suggest that certain neuroendocrine peptides can increase the invasive potential of prostatic carcinoma cells and may thereby contribute to the rapid progression and aggressive clinical course of prostate tumors containing neuroendocrine elements.

cAMP-mediated differential regulation of lignin peroxidase and manganese-dependent peroxidase production in the white-rot basidiomycete Phanerochaete chrysosporium

Lignin peroxidases (LIPs) and manganese-dependent peroxidases (MNPs) are major components of the lignin-degrading enzyme system of Phanerochaete chrysosporium and typically appear during secondary metabolism. The involvement of cAMP in the regulation of production of LIPs and MNPs was investigated in this study. Production of LIPs and MNPs was preceded by a sharp rise in intracellular cAMP concentration. Addition of atropine, theophylline, or histamine to cultures resulted in a drop in intracellular cAMP concentration and a concomitant inhibition of production of LIPs only or of both LIPs and MNPs, depending on the concentration of the inhibitor added. These results were independently confirmed by fast protein liquid chromatographic profiles of the LIPs and MNPs in the extracellular fluid of the inhibitor-treated and untreated control cultures. LIP production was generally more sensitive to the inhibitors than MNP production. Northern blot analyses showed that the inhibitors affect the production of LIPs and MNPs at the level of transcription. Furthermore, LIP and MNP gene expression appears to be differentially regulated depending on the intracellular concentration of cAMP. These results show that cAMP plays a key role in the regulation of production of LIPs and MNPs in P. chrysosporium.

Structure/function relationships of CREB/ATF proteins

Signal-transduction pathways converge ultimately at the level of transcriptional activation to produce specific patterns of gene expression in response to environmental stimuli. The initiation of transcription mediated by these signaling pathways is regulated by the coordinate expression and/or activation of specific transcription factors that bind to the control regions of genes. Specific insights into the mechanisms underlying transcriptional activation have recently arisen from studies of the structure and functions of these transcription factors. The CREB/ATF family of transcriptional transactivating proteins has only recently been discovered and appears to provide a link between the regulation of gene expression in response to activators of cellular signaling pathways and the regulation of gene expression by viral transactivating proteins. In addition, these proteins may be involved in the normal regulation of growth and differentiation. Understanding the nature and importance of the role(s) of these proteins in the normal regulation of growth and differentiation will have profound influences on the understanding of the aberrant regulation of these processes during oncogenesis.

Ablation of stimulation of a cAMP-responsive promoter in CHO cell lines defective in their cAMP-dependent protein kinase system

We have studied the requirement for an intact cAMP-dependent protein kinase (PKA) system to regulate cAMP-mediated gene transcription in Chinese hamster ovary (CHO) cells. Wild-type CHO cells and mutant CHO cell lines selected for their resistance to the growth inhibitory effect of 8-Br-cAMP and defective in their PKA system were transiently transfected with reporter plasmids containing 2.5 and 3.0 kb of the 5'-flanking sequence of the rat tyrosine aminotransferase (TAT) gene promoter. This segment of DNA contains no CRE-like sequences, yet wild-type transfectants exhibited a specific increase in TAT promoter activity following growth in medium containing 8-Br-cAMP. In CHO cell lines defective in their PKA, the transfected TAT promoter failed to respond to cAMP treatment. We conclude that an intact PKA system is necessary for the cAMP-mediated increase in TAT promoter activity in CHO cells and that there is no requirement for a CRE to see this effect.

Effects of histamine and activators of the cyclic AMP system on protein synthesis in and release of high molecular weight glycoproteins from isolated gastric non-parietal cells

1. Glycoprotein and protein synthesis in and release from pig isolated, enriched gastric mucous cells were measured by the incorporation of N-acetyl-[14C]-D-glucosamine and [3H]-L-leucine, respectively, into cellular and released acid precipitable material. 2. Histamine and activators of the adenosine 3':5'-cyclic monophosphate (cyclic AMP) system maximally stimulated total protein and glycoprotein synthesis in and release from the cells at concentrations of histamine (10 microM), forskolin (10-100 microM), 3-isobutyl-1-methylxanthine (100 microM), and dibutyryl cyclic AMP (1-3 mM), respectively. In the presence of 3-isobutyl-1-methylxanthine (30 microM) histamine stimulation was enhanced. 3. As shown by gel chromatography, stimulation by histamine (100 microM), forskolin (10 microM), 3-isobutyl-1-methylxanthine (100 microM) and dibutyryl cyclic AMP (1 mM) resulted in a release of high molecular weight (approximately 2 x 10(6) daltons) glycoproteins from the cells. The histamine H2-receptor antagonist, ranitidine (100 microM), blocked the effect of histamine. 4. We conclude that cyclic AMP-dependent processes are involved in the regulation of protein and glycoprotein synthesis in and the release of high molecular weight (mucous) glycoproteins from pig gastric non-parietal cells and that histamine may be a physiological activator of this system.

Genesis of hadacidin-induced cleft palate in hamster: morphogenesis, electron microscopy, and determination of DNA synthesis, cAMP, and enzyme acid phosphatase

A morphological, electron microscopic, and biochemical study was undertaken to analyze the genesis of hadacidin-induced cleft palate in hamster fetuses. Gross and light microscopic observations indicated that hadacidin affected the growth of vertical palatal shelves to induce cleft palate. Electron microscopic observations showed that initial hadacidin-induced changes were seen in the mesenchymal cells. Within 12 hr of drug administration, the perinuclear space was swollen and a lysosomal response injury was evident in the mesenchymal cells. Subsequently, 24 hr after hadacidin treatment, lysosomes appeared in the epithelial cells; changes were also seen in the basal lamina which included separation of the lamina densa from the basal cells, duplication of lamina densa, and complete loss of basal lamina. Between 36 and 42 hr post-treatment, the cellular and basal lamina changes subsided, and the epithelium of vertical shelves underwent stratification. Biochemical determination of enzyme acid phosphatase indicated that the levels of enzyme activity in both the control and treated palatal tissues corresponded to the appearance of lysosomes. Measurement of cAMP levels suggested that the peak activity of cAMP corresponded to that of enzyme acid phosphatase and cell injury. The cAMP activity in hadacidin-injured cells, however, was significantly lower in comparison to that of the dying cells of control palates. Hadacidin treatment also affected DNA synthesis in the developing primordia of the palate. It was suggested that hadacidin injures the precursor cells of the palate prior to the appearance of the primordia, and subsequently affects their proliferative behavior, stunting the vertical growth of the palatal shelves and inducing a cleft palate.

The effect of cyclic AMP on the growth of Toxoplasma gondii in vitro

To assess the role of cAMP on the growth and proliferation of Toxoplasma in HL-60 cells we tested the effect of exogenous cAMP and cAMP analogues to the co-culture system of Toxoplasma and HL-60 cells. cAMP, dbcAMP, and br-cAMP stimulated the growth of Toxoplasma at a specific concentration, i.e., 10(0) mM, 10(0) mM, and 10(-1) mM, respectively. There were differences in growth induction kinetics and in the rate of promotion. These results were further verified by treating the co-culture with adenylate cyclase activator, pNHppG, cAMP phosphodiesterase activators, imidazole and A23187, and cAMP phosphodiesterase inhibitors, IBMX, compound 48/80, and theophylline, separately. When the cytosolic cAMP levels increased by the reagents mentioned above, Toxoplasma in the cytoplasm of HL-60 cells stimulated to proliferate more rapidly with concentration-dependent modes compared to the control, and vice versa. It is suggested that some mechanisms are activated by the high levels of cAMP in the cytoplasm, which result in the stimulation of Toxoplasma proliferation.

Induction of glutamine synthetase by 8-bromo cyclic AMP in primary cultures of rat brain astrocytes

Glutamine synthetase (GS) is the key enzyme in cerebral glutamine production. Understanding the regulation of the expression of GS is important for definition of the control of glutamine metabolism in brain. Therefore, we studied the control of GS expression by 8-bromo cyclic AMP in primary cultures of astrocytes prepared from brains of neonatal rats. GS activity was increased by 8-bromo cyclic AMP in a dose- and time-dependent manner. This increase was associated with a corresponding increase in the steady-state level of GS mRNA.

Defective cAMP-dependent phosphorylation of intact T lymphocytes in active systemic lupus erythematosus

The present study was undertaken to establish whether cAMP-dependent phosphorylation of endogenous substrates is impaired in T lymphocytes from subjects with active systemic lupus erythematosus (SLE). In normal human T lymphocytes, the cell-permeable cAMP analog, N6,O2'-dibutyryladenosine 3',5'-cyclic monophosphate, induced phosphorylation of substrates with molecular masses of 17.5, 23/25, 33.5 kDa on one-dimensional SDS/PAGE. Maximal phosphorylation occurred at 60 min. In contrast to healthy T cells, the extent of substrate phosphorylation achieved in active SLE T cells (n = 8) was only 15% at 60 min in the 17.5-kDa substrate, 21% in the 23/25-kDa substrate, and 9% in the 33.5-kDa substrate. The rheumatic disease controls (rheumatoid arthritis; primary Sjögren syndrome; n = 8) exhibited a mean 72%, 124%, and 85%, respectively, of phosphorylation observed in healthy T cells. Because the only known mechanism by which cAMP acts is via cAMP-dependent protein kinase (protein kinase A), these data raise the possibility of a defect at the level of this kinase in SLE T lymphocytes.

Multiple cAMP-binding proteins in Aplysia tissues

While it is recognized that cAMP is able to regulate distinct cellular processes differentially, the molecular basis for the diversity of its effects remains unclear. Using photoaffinity labeling with 32P-8 azido-cAMP and two-dimensional gel analysis, we have identified 26 electrophoretic variants of cAMP-binding proteins in the six different tissues of the marine mollusc Aplysia californica sampled. Some of these proteins are found in most tissues, others only in a few; still others appear to be restricted to a single tissue. All of these proteins bind cAMP specifically. The two-dimensional polyacrylamide gel electrophoretic patterns of binding proteins seen in the different tissues fall into three classes. One pattern is shared by the nervous system and embryos. The second is found in muscular tissues (heart, buccal muscle, siphon, and gill). The third pattern is specific to sperm. The presence of distinct subsets of cAMP-binding proteins in different tissues suggests that at least some of the diversity in cAMP's regulatory function may result from diversity in the proteins that bind it.

Site-selective 8-Cl-cAMP which causes growth inhibition and differentiation increases DNA (CRE)-binding activity in cancer cells

Control mechanisms of normal differentiation are disrupted in cancer cells but can be restored by treatment with site-selective cAMP analogs. The cellular events associated with such changes entail compartmental redistribution of the cAMP-dependent protein kinase type II regulatory subunit, RII beta. The results of this study indicate that the molecular mechanisms of action involve changes in specific DNA-binding activity of putative transcription factors. Gel retardation analyses revealed that nuclear extracts from cells of various human cancer cell lines [colon cancer (LS-174T), gastric cancer (TMK-1), and leukemia (K-562)] and rodent pheochromocytoma (PC12) show a concentration-dependent increase in binding activity to a synthetic DNA that contained the cAMP-responsive element 5'-TGACGTCA-3' after treatment with 8-Cl-cAMP. Such an increase in cAMP-responsive element binding activity was not observed in the 8-C1-cAMP-unresponsive MKN-1 gastric cancer cells. These findings indicate that the antitumor activity of site-selective cAMP analogs may reside in the induction of transcription factors that restore normal gene regulation in cancer cells.

Similarities between prokaryotic and eukaryotic cyclic AMP-responsive promoter elements

Organisms as diverse as bacteria and man contain genes that show transcriptional induction when the intracellular concentration of cAMP is increased. This regulated transcriptional response is mediated through specific promoter elements located, in general, upstream from the transcription start site. In Escherichia coli the element responsible for cAMP-mediated transcriptional induction is the binding site for the cAMP-receptor protein (CAP). In mammalian cells the cAMP regulatory element is composed of one or more binding sites for various transcription factors. In many instances the cAMP regulatory element contains binding sites for a family of proteins referred to as ATF. Here we provide evidence that some prokaryotic and mammalian cAMP-response elements are functionally related. First, we show that mammalian ATF binds specifically to some E. coli CAP sites, and conversely E. coli CAP binds specifically to some mammalian ATF sites. Second, we demonstrate that an E. coli CAP binding site can confer cAMP-inducibility onto a mammalian gene when assayed in transfected mammalian cells.

Regulation of transcription by cyclic AMP-dependent protein kinase

cAMP-dependent protein kinase (PKA; ATP: protein phosphotransferase; EC 2.7.1.37) appears to be the major mediator of cAMP responses in mammalian cells. We have investigated the role of PKA subunits in the regulation of specific genes in response to cAMP by cotransfection of wild-type or mutant subunits of PKA together with cAMP-inducible reporter genes. Overexpression of catalytic subunit induced expression from three cAMP-regulated promoters (alpha-subunit, c-fos, E1A) in the absence of elevated levels of cAMP but did not affect expression from two unregulated promoters (Rous sarcoma virus, simian virus 40). Cotransfection of a regulatory subunit gene containing mutations in both cAMP binding sites strongly repressed both basal and induced expression from the cAMP-responsive alpha-subunit promoter without affecting expression from the Rous sarcoma virus promoter. These experiments indicate that cAMP induces gene expression through phosphorylation by the catalytic subunit and that the ambient degree of phosphorylation dictates the level of basal as well as induced expression of the cAMP-regulated alpha-subunit gene.

Levels of RNA from a family of putative serine protease genes are reduced in Drosophila melanogaster dunce mutants and are regulated by cyclic AMP

We have isolated several genes expressed at abnormal levels in the memory mutant, dunce (dnc), of Drosophila melanogaster. These mutants have an elevated cyclic AMP (cAMP) content due to a mutation in the structural gene for cAMP phosphodiesterase, so the isolated genes are potentially ones regulated by cAMP. Here, we describe the characterization of a genomic clone and corresponding cDNA clones which contain sequences that are underexpressed in dnc mutants. Sequence analysis of portions of the genomic clone and representative cDNAs revealed the presence of two uninterrupted and complete open reading frames (SER1 and SER2) and part of a third (SER3). The predicted amino acid sequences of all of these were found to be homologous to the serine protease family of enzymes. The genomic clone was localized to the polytene chromosome region 99C-D, although genome-blotting experiments indicated the existence of several other genes related to the cloned serine protease-like genes. Hybridization experiments with probes representing each of the three sequenced genes showed that only the SER1-related genes were differentially expressed in dnc mutants. The putative serine protease genes were abundantly expressed in the larval gut, suggesting a major function in digestion. Feeding normal flies cAMP, isobutylmethylxanthine, or forskolin resulted in a decreased RNA level of the SER1-related genes. Thus, RNA levels of this serine protease gene family are negatively regulated by cAMP.

Levels of RNA from a family of putative serine protease genes are reduced in Drosophila melanogaster dunce mutants and are regulated by cyclic AMP

We have isolated several genes expressed at abnormal levels in the memory mutant, dunce (dnc), of Drosophila melanogaster. These mutants have an elevated cyclic AMP (cAMP) content due to a mutation in the structural gene for cAMP phosphodiesterase, so the isolated genes are potentially ones regulated by cAMP. Here, we describe the characterization of a genomic clone and corresponding cDNA clones which contain sequences that are underexpressed in dnc mutants. Sequence analysis of portions of the genomic clone and representative cDNAs revealed the presence of two uninterrupted and complete open reading frames (SER1 and SER2) and part of a third (SER3). The predicted amino acid sequences of all of these were found to be homologous to the serine protease family of enzymes. The genomic clone was localized to the polytene chromosome region 99C-D, although genome-blotting experiments indicated the existence of several other genes related to the cloned serine protease-like genes. Hybridization experiments with probes representing each of the three sequenced genes showed that only the SER1-related genes were differentially expressed in dnc mutants. The putative serine protease genes were abundantly expressed in the larval gut, suggesting a major function in digestion. Feeding normal flies cAMP, isobutylmethylxanthine, or forskolin resulted in a decreased RNA level of the SER1-related genes. Thus, RNA levels of this serine protease gene family are negatively regulated by cAMP.

Negative control elements and cAMP responsive sequences in the tissue-specific expression of mouse renin genes

The 5' flanking regions of the mouse renin genes (Ren1d and Ren2d) contain putative negative control and cAMP responsive elements. Sequence analysis shows additionally that these putative control elements in the Ren2d gene are interrupted by a 160-base-pair insertion. To document the functions of these elements, we isolated these regions and fused them to the reporter gene chloramphenicol acetyltransferase (CAT), which was linked upstream to a thymidine kinase (TK) promoter (pUTKAT1). The chimeric constructs were transfected into mouse pituitary tumor AtT-20 and human choriocarcinoma JEG-3 cells. At the basal unstimulated condition, Ren1d 5' flanking sequence in the sense orientation inhibited basal CAT expression from the TK promoter of pUTKAT1, whereas the same sequence in the antisense orientation did not. The 5' flanking region of Ren2d had no inhibitory effect on basal CAT expression. These data demonstrate that the negative control element is functional in Ren1d but is nonfunctional in Ren2d, suggesting that the 160-base-pair insertion in Ren2d interferes with the function of the negative control elements. In response to 8-bromo-cAMP, both renin genes increased transcription 3-fold, suggesting a functional cis action of the cAMP responsive element in both genes. These data may be important in the understanding of the regulation of the tissue-specific expression of mouse renin genes.

Regulatory aspects of cellulase biosynthesis and secretion

The cellulase enzyme system consists of cellobiohydrolase, endoglucanase, and beta-glucosidase and has been extensively studied with respect to its biosynthesis, properties, mode of action, application, and, most recently, secretion mechanisms. A knowledge of the factors governing the biosynthesis and secretion of these enzymes at the molecular level will be useful in maximizing enzyme productivity in extracellular fluid. Among other topics, the regulatory effects of sorbose (a noninducing sugar which is not a product of cellulose hydrolysis) on cellulase synthesis and release are described. Cellulase genes have recently been cloned into a number of microorganisms with a view to understanding the gene structure and expression and to obtaining the enzyme components in pure form. The factors governing biosynthesis and secretion of cellulases in recombinant cells are also discussed. Cellulases are known to be glycoproteins, therefore, the role of O- and N-linked glycosylation on enzyme stability and secretion is also detailed.

Parathyroid hormone-related protein: isolation, molecular cloning, and mechanism of action

Many factors, such as interleukin 1, TGF alpha, tumor necrosis factor alpha and beta, and PGs, have been implicated in etiological roles in HHM (Martin and Mundy, 1987). Much interest in the past has also centered upon the likelihood of ectopic secretion of PTH in this condition. We have purified a protein (PTHrP) implicated in HHM from a human lung cancer cell line (BEN). Full-length cDNA clones have been isolated and were found to encode a prepropeptide of 36 amino acids and a mature protein of 141 amino acids. Eight of the first 13 amino acids were identical with human PTH, although antisera directed to the NH2 terminus of PTHrP do not recognize PTH; this homology is not maintained in the remainder of the molecule. PTHrP therefore represents a previously unrecognized hormone, possibly related to the PTH gene by a gene duplication mechanism. In support of this notion, the PTHrP gene has been localized to the short arm of chromosome 12; it is believed that chromosome 11, containing the PTH gene, and chromosome 12 are evolutionarily related. In addition, the human PTHrP gene has been isolated, characterized, and shown to have a similar intron--exon organization as the PTH gene. It is possible that the original ancestral gene is indeed the PTHrP gene; resolution of this question awaits studies in lower species. Peptides synthesized to the predicted protein sequence have enabled detailed structure-function studies that have identified NH 2-terminal sequences to be responsible for the biological effects of the molecule. Antibodies raised against the various synthetic peptides have led to the immunohistochemical localization of PTHrP in many human squamous cell carcinomas as well as in a subpopulation of keratinocytes of normal skin. The availability of these antibodies has opened the way for the development of a radioimmunoassay to detect PTHrP in the sera of cancer patients at risk of developing hypercalcemia. The recent characterization of PTHrP-like activity in the ovine fetus suggests some physiological function for PTHrP. It is possible that PTHrP, as the fetal counterpart of PTH, has the role of maintaining the maternal-fetal calcium gradient. The isolation and characterization of PTHrP have added to our understanding of the mechanisms of hypercalcemia and may contribute to the understanding of other metabolic bone diseases, such as osteoporosis and Paget's disease. Finally, and perhaps most importantly, PTHrP may play a hitherto unrecognized role in normal cell physiology.

Cyclic AMP-responsive DNA-binding protein: structure based on a cloned placental cDNA

Cyclic AMP (cAMP) is an intracellular second messenger that activates transcription of many cellular genes. A palindromic consensus DNA sequence, TGACGTCA, functions as a cAMP-responsive transcriptional enhancer (CRE). The CRE binds a cellular protein of 38 kD in placental JEG-3 cells. A placental lambda gt11 library was screened for expression of specific CRE-binding proteins with the CRE sequence as a radioactive probe. A cDNA encoding a protein of 326 amino acids with the binding properties of a specific CRE-binding protein (CREB) was isolated. The protein contains a COOH-terminal basic region adjacent to a sequence similar to the "leucine zipper" sequence believed to be involved in DNA binding and in protein-protein contacts in several other DNA-associated transcriptional proteins including the products of the c-myc, c-fos, and c-jun oncogenes and GCN4. The CREB protein also contains an NH2-terminal acidic region proposed to be a potential transcriptional activation domain. The putative DNA-binding domain of CREB is structurally similar to the corresponding domains in the phorbol ester-responsive c-jun protein and the yeast transcription factor GCN4.

Temporal relationship between nerve-stump-length-dependent changes in the autophosphorylation of a cyclic AMP-dependent protein kinase and the acetylcholine receptor content in skeletal muscle

The acetylcholine receptor (AChR) content and the autophosphorylation of the regulatory subunit of cyclic AMP-dependent protein kinase type II (R-II) were evaluated in rats soleus muscles at 24, 30 and 66 hr after surgical denervation by cutting the nerve at a short distance (short-nerve-stump) and at a long distance (long-nerve-stump) from the muscle. AChR content was based on the specific binding of [125I]alpha-bungarotoxin (BUTX); changes in the autophosphorylation of R-II were based upon the predominant in vitro 32P-phosphorylation of a 56-Kd soluble protein in cytosolic fractions of solei. The AChR content and the 32P-autophosphorylation of R-II were increased in samples from short-nerve-stump solei, but not from long-nerve-stump solei, after a denervation-time of 30 hr. This nerve-stump-length dependency indicates that the two denervation effects are not related to the immediate halt of impulse-evoked muscle contractility. Furthermore, the results show that alterations in the 32P-autophosphorylation of R-II occurred before, as well as whenever, increases in the AChR content were found. Speculatively, this temporal relationship may be significant with respect to the potential role of R-II in gene expression.

A model to account for the effects of oncogenes, TPA, and retinoic acid on the regulation of genes involved in metastasis

We have postulated that signals from the microenvironment can induce shifts in tumor cell phenotypes and that microenvironmental factors are therefore important for cancer metastasis. In this article we expand on this hypothesis and propose a model to explain (a) how extracellular signals can lead to changes in tumor phenotypes, and (b) how cytoplasmic oncogenes, which influence signal transducing pathways as well as nuclear oncogenes regulating gene expression via DNA binding transacting factors, might affect metastatic competence.

The catalytic subunit of cAMP-dependent protein kinase induces expression of genes containing cAMP-responsive enhancer elements

Transcriptional regulation of eukaryotic genes by cyclic AMP requires a cAMP-dependent protein kinase (A kinase). Two hypotheses have been proposed to explain how the holoenzyme of the A kinase induces transcription. The regulatory subunits of the A kinase, which bind cAMP and DNA, and have amino-acid homology with the Escherichia coli catabolite activator protein could directly stimulate gene expression. Alternatively, phosphorylation by the catalytic subunits could induce transcription by activating proteins involved in gene transcription. To distinguish between these models, we microinjected purified preparations of the catalytic and regulatory subunits of A kinase into tissue culture cells and monitored expression of a stably integrated fusion gene containing a cAMP-responsive human promoter fused to a bacterial reporter gene, or of the endogenous c-fos gene. The catalytic subunit stimulated expression of these genes, whereas the regulatory subunit did not. These results indicate that the catalytic subunit of A kinase is sufficient to induce expression of two cAMP-responsive genes, without increasing levels of cAMP.