cAMP Gene Expression Research Articles

Regulation of the CAMP gene by 1,25(OH)2D3 in various tissues

The induction of antimicrobial peptides such as the human cathelicidin, CAMP/hCAP18, by 1,25(OH)2D3 provides a very exciting therapeutic approach in boosting immunity against infectious diseases. To explore the range of cell types and expand the number of cell models for studying the regulation of CAMP gene expression by 1,25(OH)2D3, we treated cell lines from various tissue types and determined CAMP gene expression. Also, we tested additional compounds together with 1,25(OH)2D3 to look for possible cooperative activation of the gene. We identified 1,25(OH)2D3-mediated induction of the CAMP gene in B-cell lymphomas, prostate and endometrial cancer lines and found cooperative activation with the histone deacetylase inhibitor sodium butyrate. The data suggest that regulation of CAMP by 1,25(OH)2D3 is potentially important in a wide range of tissues.

Activity-dependent hepatocyte growth factor expression and its role in organogenesis and cancer growth suppression

Studies by Murphy et al. have shown that neuronal stimulation can activate immediate early genes that code for transcription factors. Recent data suggest that Ca 2+ elevation in both neuronal cytoplasmic and nuclear compartments is responsible for the coupling of synaptic excitation to gene expression. Deisseroth et al. suggest that Ca 2+ influx through L-type voltage-sensitive Ca 2+ channels (VSCCs) activates cytoplasmic Ca 2+ targets such as calmodulin (CaM). The Ca 2+–CaM complex then translocates to the nucleus leading to Ca 2+ and cAMP response element-binding protein (CREB) phosphorylation and gene expression. Reports have shown that L-type VSCCs are found on the vagus nerve. Other studies have suggested that activation of L-type VSCCs leads to a Ca 2+ store-dependent elevation of nuclear [Ca 2+] that triggers gene expression by more direct activation of nuclear Ca 2+/CaM-dependent protein kinase (CaMK). Moreover, nuclear transcription factors such as DREAM are themselves Ca 2+-dependent, further supporting the importance of both nuclear and cytoplasmic Ca 2+ elevation in regulating gene expression. Our simulation studies suggest that intense synaptic stimulation in combination with amplification by release from intracellular Ca 2+ stores can produce elevations in nuclear Ca 2+ concentration and CaMK phosphorylation leading to CREB phosphorylation and gene expression. One of the downstream events would be the production of hepatocyte growth factor (HGF). HGF has trophic, repair, therapeutic or mitotic effect on kidney, pancreas, spleen, liver, lung, heart and spinal cord. These organs and systems' regeneration can be achieved by either upregulation of HGF release from the vagus nerve or upregulation of HGF production within the system (spinal cord). Conversely, inhibition of HGF release from the vagus nerve can inhibit cancer growth. Vagus nerve seems to be the nerve that nature intends to regulate organ growth and regeneration, it is very possible that other than HGF and injurin, other growth factors could be found in the vagus nerve. Electrical depolarization and hyperpolarization of the vagus nerve would be the most natural and effective way to induce organ regeneration and suppress cancer growth, respectively. A similar pathway seems to exist for different organs as HGF has trophic, repair, therapeutic or mitotic effect on different vagally innervated organs.

Inhibition of basal and stimulated progesterone synthesis by dichlorodiphenyldichloroethylene and methoxychlor in a stable pig granulosa cell line

The effects of the insecticide dichlorodiphenyldichloroethylene (DDE) and methoxychlor in a stable pig granulosa cell line, JC-410, were investigated. The studies of DDE and methoxychlor were conducted in combination with studies of cholera toxin, the protein kinase A activator that stimulates cAMP and progesterone synthesis and gene expression of P450 cholesterol side chain cleavage (P450scc), which converts cholesterol to pregnenolone. Administration of DDE at 3000 and 10 000 ng ml (-1) was found to decrease progesterone synthesis 0.49- and 0.25-fold, respectively, and to block the stimulatory effect of 100 ng cholera toxin ml (-1), after 24 h incubation. At 1-100 ng ml (-1), methoxychlor did not affect progesterone synthesis after 48 h incubation. However, 1000 ng methoxychlor ml (-1) decreased progesterone synthesis 0.32-fold, and both 100 and 1000 ng methoxychlor ml (-1) blocked the stimulatory effect of cholera toxin. At 3000 and 10 000 ng ml(-1), DDE decreased cAMP synthesis 0.66-and 0.36-fold, respectively. At 300, 3000 and 10 000 ng ml (-1), DDE also decreased cholera toxin-stimulated cAMP synthesis 0.84-, 0.68-, and 0.52-fold, respectively. Administration of 1-100 ng methoxychlor ml (-1) did not affect basal or cholera toxin-stimulated cAMP synthesis. Cholera toxin increased P450scc mRNA 1.4-fold after 24 h incubation, while 3000 and 10 000 ng DDE ml (-1) led to 0.39- and 0.18-fold reductions, respectively. The stimulatory effect of cholera toxin on P450scc mRNA was blocked by 3000 and 10 000 ng DDE ml(-1). Cholera toxin increased P450scc mRNA 3.48-fold after 48 h incubation, while 100 and 1000 ng methoxychlor ml (-1) increased P450scc mRNA 1.79- and 3.0-fold, respectively, and further increased the stimulatory effect of cholera toxin 6.47- and 5.44-fold, respectively. The results of the present study indicate that DDE inhibits granulosa cell steroidogenesis by affecting cAMP production and P450scc gene expression. However, methoxychlor appears to inhibit steroidogenesis by a mechanism occurring before the conversion of cholesterol into pregnenolone.

Inhibition of basal and stimulated progesterone synthesis by dichlorodiphenyldichloroethylene and methoxychlor in a stable pig granulosa cell line

The effects of the insecticide dichlorodiphenyldichloroethylene (DDE) and methoxychlor in a stable pig granulosa cell line, JC-410, were investigated. The studies of DDE and methoxychlor were conducted in combination with studies of cholera toxin, the protein kinase A activator that stimulates cAMP and progesterone synthesis and gene expression of P450 cholesterol side chain cleavage (P450scc), which converts cholesterol to pregnenolone. Administration of DDE at 3000 and 10 000 ng ml (-1) was found to decrease progesterone synthesis 0.49- and 0.25-fold, respectively, and to block the stimulatory effect of 100 ng cholera toxin ml (-1), after 24 h incubation. At 1-100 ng ml (-1), methoxychlor did not affect progesterone synthesis after 48 h incubation. However, 1000 ng methoxychlor ml (-1) decreased progesterone synthesis 0.32-fold, and both 100 and 1000 ng methoxychlor ml (-1) blocked the stimulatory effect of cholera toxin. At 3000 and 10 000 ng ml(-1), DDE decreased cAMP synthesis 0.66-and 0.36-fold, respectively. At 300, 3000 and 10 000 ng ml (-1), DDE also decreased cholera toxin-stimulated cAMP synthesis 0.84-, 0.68-, and 0.52-fold, respectively. Administration of 1-100 ng methoxychlor ml (-1) did not affect basal or cholera toxin-stimulated cAMP synthesis. Cholera toxin increased P450scc mRNA 1.4-fold after 24 h incubation, while 3000 and 10 000 ng DDE ml (-1) led to 0.39- and 0.18-fold reductions, respectively. The stimulatory effect of cholera toxin on P450scc mRNA was blocked by 3000 and 10 000 ng DDE ml(-1). Cholera toxin increased P450scc mRNA 3.48-fold after 48 h incubation, while 100 and 1000 ng methoxychlor ml (-1) increased P450scc mRNA 1.79- and 3.0-fold, respectively, and further increased the stimulatory effect of cholera toxin 6.47- and 5.44-fold, respectively. The results of the present study indicate that DDE inhibits granulosa cell steroidogenesis by affecting cAMP production and P450scc gene expression. However, methoxychlor appears to inhibit steroidogenesis by a mechanism occurring before the conversion of cholesterol into pregnenolone.

Can GHRH or GH secretagogues re-initiate pituitary GH pulsatility?

Can GHRH or GH secretagogues re-initiate pituitary GH pulsatility?

Regulation of the cAMP cascade, gene expression and immune function by cannabinoid receptors

The objective of this article is to discuss the putative role of cannabinoid receptors in immune modulation by cannabinoid compounds. The primary focus is on the signal transduction events that are initiated following ligand binding to cannabinoid receptors and how these events lead to detrimental effects on the normal responsiveness of immunocompetent cells. Toward this end, signalling events are traced from the cannabinoid receptor to the transcription factors which are adversely regulated in the presence of cannabinoid compounds during leukocyte activation. Moreover, this aberrant regulation of transcription factors is discussed in the context of altered gene expression and the impact this has on leukocyte function. Lastly, an important goal of this article is to dispel a long standing myth that the cyclic adenosine 3′:5′-monophosphate (cAMP) cascade is a negative regulatory pathway for immunocompetent cells. This chapter examines two major immunologic cell-types which are well established as exhibiting altered function following cannabinoid treatment, helper T-cells and the macrophage. Not discussed are the effects of cannabinoids on B-cell function. This is primarily due to the rather refractory nature of B-cells to inhibition by cannabinoids in spite of the fact that this cell-type expresses functional cannabinoid receptors [Schatz, A.R., Koh, W.S., Kaminski, N.E., 1993. Δ 9-tetrahydrocannabinol selectively inhibits T-cell dependent humoral immune responses through direct inhibition of accessory T-cell function. Immunopharmacol., 26, pp. 129–137.]. One cautionary note, although the focus of this article is on cannabinoid receptor mediated signalling events, immune modulation by cannabinoid compounds is likely multi-factorial presumably involving receptor as well as receptor-nonrelated events. Effects on leukocytes by cannabinoids which are believed to be mediated by receptor-nonrelated events are outside the scope of this paper and will not be discussed. One last introductory point is that even though their is presumably little overlap in the genes which are regulated by cannabinoids in leukocytes as compared to other cell-types (e.g., neural cells), the major signalling pathways involved in cellular regulation are ubiquitous. With that in mind, it is likely that their is a considerable amount of similarity in the signalling pathways regulated by cannabinoids in cell-types of different lineage, given that they express cannabinoid receptors. In this context, signalling events observed in leukocytes can provide important insight into which genes may be modulated by cannabinoid in other cell types.

Cyclic Adenosine 3′,5′-Monophosphate (cAMP)-Dependent and cAMP-Independent Regulation of Parathyroid Hormone Receptors on UMR 106–01 Osteoblastic Osteosarcoma Cells

The osteoblast-like cells, UMR 106-01, express PTH receptors that are coupled to adenylate cyclase. Recently, we reported the isolation of a UMR 106-01 subclone, UMR 4-7, that is stably transfected with a Zn(++)-inducible mutant of the regulatory subunit of protein kinase A. Incubation of UMR 4-7 cells with Zn++ renders the cells unresponsive to cAMP agonists. This subclone, therefore, seemed particularly suitable for studies of PTH receptor regulation. In UMR 106-01 cells, PTH receptors are strikingly down-regulated by pretreatment with 8-Br-cAMP or 3-isobutyl-1-methylxanthine for 2 days. In UMR 4-7 cells, this effect is totally prevented by prior and concurrent treatment with Zn++. Zn++ addition to UMR 106 cells does not modify these responses. Treatment with the PTH agonist [Nle8,18,Tyr34]bovine PTH(1-34)NH2 [(NlePTH(1-34)] also markedly down-regulates PTH receptors in UMR 106 cells, but this effect is only partially inhibited in Zn(++)-induced UMR 4-7 cells. At high doses, the PTH antagonist, [Nle8,18,Tyr34]bovine PTH(3-34)NH2 [NlePTH(3-34)] also (partially) reduces PTH receptor availability. Receptor regulation by NlePTH(3-34) is not blocked in the cAMP-resistant cells, however. Coincubation of submaximal doses of NlePTH(1-34) (1 nM) with NlePTH(3-34) (1 microM) reduces receptor availability more than when the cells are exposed to either ligand alone. This decrease is only partially inhibited in Zn(++)-induced UMR 4-7 cells. In contrast to its additive effect on receptor regulation, NlePTH(3-34) efficiently competes for binding to the PTH receptor in UMR 106-01 cells and antagonizes the stimulatory effects of NlePTH(1-34) on both intracellular cAMP accumulation and gene expression driven by a transiently transfected synthetic cAMP-responsive enhancer. In conclusion, homologous down-regulation of PTH receptors is mediated by activation of both cAMP-dependent (via protein kinase A) and cAMP-independent pathways. PTH activates both pathways, whereas the effect of NlePTH(3-34) appears to be exclusively cAMP-independent. These results give new insights into mechanisms of PTH receptor regulation.

Caffeine blocks activation of cyclic AMP synthesis in Dictyostelium discoideum

Cyclic AMP (cAMP) appears to play multiple roles in the development of the social ameba Dictyostelium discoideum, serving as the chemoattractant mediating aggregation, and perhaps also regulating gene transcription in both early and late stages of differentiation. Progress in understanding the mechanism of activation of the adenylate cyclase in D. discoideum has been frustrated by the inability to obtain its activation in vitro. Also, the lack of defined cAMP-defective mutants has prevented a causal relationship from being established between cAMP levels and gene expression. As an alternative approach to studying the role of cAMP in D. discoideum development, we have sought a compound which inhibits cAMP synthesis in a reasonably specific manner. Here we identify caffeine as a compound which rapidly and reversibly inhibits cAMP-dependent activation of the adenylate cyclase without affecting either cell viability or intracellular levels of ATP or GTP. Using this drug, we show that cAMP synthesis is not required for the cAMP-stimulated decrease in lightscattering, the increase in cyclic GMP synthesis, or for chemotaxis toward cAMP. Studies of the mechanism of action of caffeine show that the drug does not act by inhibiting a cAMP phosphodiesterase, by inhibiting binding of cAMP to its receptor, by itself binding to a physiological adenosine receptor, or by directly inhibiting the adenylate cyclase. Instead, caffeine blocks the cAMP-dependent activation of the adenylate cyclase. Since similar effects are obtained with the cation ionophore A23187, it is possible that caffeine exerts its effect by altering intracellular calcium distribution.