Omar P. Pignataro

Interaction between arachidonic acid and cAMP signaling pathways enhances steroidogenesis and StAR gene expression in MA-10 Leydig tumor cells

Previous studies have demonstrated that trophic hormone stimulation induced cyclic AMP (cAMP) formation and arachidonic acid (AA) release from phospholipids and that both these compounds were required for steroid biosynthesis and steroidogenic acute regulatory (StAR) gene expression in MA-10 mouse Leydig tumor cells. The present study further investigates the synergistic effects of the AA and cAMP interaction on steroidogenesis. To demonstrate cAMP-induced AA release, MA-10 cells were pre-loaded with 3H-AA and subsequently treated with dibutyryl cyclic AMP (dbcAMP). Stimulation with dbcAMP significantly induced AA release in MA-10 cells to a level 145.7% higher than that of controls. Lowering intracellular cAMP concentration by expressing a cAMP-phosphodiesterase significantly reduced human chorionic gonadotrophin (hCG)-induced AA release. The dbcAMP-induced AA release was inhibited significantly by the phospholipase A(2) (PLA(2)) inhibitor dexamethasone (Dex) and also by the protein kinase A (PKA) inhibitor H89, suggesting the involvement of PKA phosphorylation and/or PLA(2) activation in cAMP-induced AA release. The effect of the interaction between AA and cAMP on StAR gene expression and steroid production was also investigated. While 0.2 mM dbcAMP induced only very low levels of StAR protein, StAR mRNA, StAR promoter activity and steroid production, all of these parameters increased dramatically as AA concentration in the culture medium was increased from 0 to 200 microM. Importantly, AA was not able to induce a significant increase in steroidogenesis at any concentration when used in the absence of dbcAMP. However, when used in concert with submaximal concentrations of dbcAMP (0.05 mm to 0.5 mm), AA was capable of stimulating StAR gene expression and increasing steroid production significantly. The results from this study demonstrate that AA and cAMP act in a highly synergistic manner to increase the sensitivity of steroid production to trophic hormone stimulation and probably do so by increasing StAR gene expression.

Lactate and short chain fatty acids produced by microbial fermentation downregulate proinflammatory responses in intestinal epithelial cells and myeloid cells.

The use of short chain fatty acids to modulate gastrointestinal inflammatory conditions such as ulcerative colitis has produced encouraging results either in animal models or also in clinical trials. Identifying the key cellular and molecular targets of this activity will contribute to establish the appropriate combinations/targeting strategies to maximize the efficacy of anti-inflammatory interventions. In the present work, we evaluated in vitro the interaction of lactate, acetate, propionate and butyrate on cells relevant for innate immune response of the gastrointestinal tract. All molecules tested regulate the production of proinflammatory cytokines by TLR-4 and TLR-5 activated intestinal epithelial cells in a dose response manner. Furthermore SCFAs and lactate modulate cytokine secretion of TLR-activated bone marrow derived macrophages and also TLR-dependent CD40 upregulation in bone marrow derived dendritic in a dose-dependent manner. Butyrate and propionate have been effective at concentrations of 1 to 5mM whereas acetate and lactate produced modulatory effects at concentrations higher than 20-50mM in different assays. Our results indicate that in concentrations similar to found in large bowel lumen, all SCFAs tested and lactate can modulate activity of relevant sentinel cell types activated by TLR signals. Modulatory activity was not inhibited by pertussis toxin treatment indicating that the effects are not related to Gi signaling. The use of these molecules in combined or separately as intervention strategy in conditions where epithelial or myeloid cells are main triggers of the inflammatory situation seems appropriate.

Involvement of nitric oxide synthase in the mechanism of histamine-induced inhibition of Leydig cell steroidogenesis via histamine receptor subtypes in Sprague-Dawley rats.

Abstract This study was conducted to shed light on the so far unexplored intracellular mechanisms underlying negative modulation of Leydig cell steroidogenesis by histamine (HA). Using the MA-10 cell line and highly purified rat Leydig cells as experimental models, we examined the effect of the amine on biochemical steps known to be modulated by HA or involved in LH/hCG action. In agreement with previous findings, HA at 10 μM showed a potent inhibitory effect on hCG-stimulated steroid synthesis, regardless of the gonadotropin concentration used. Moreover, HA decreased not only LH/hCG-induced cAMP production but also steroid synthesis stimulated by the permeable cAMP analog dibutyryl cAMP (db-cAMP). Considering the post-cAMP sites of HA action, it is shown herein that HA markedly inhibited db-cAMP-stimulated steroidogenic acute regulatory (STAR) protein expression, as well as steps catalyzed by P450-dependent enzymes, mainly the conversion of cholesterol to pregnenolone by cholesterol side-chain cleavage enzyme (CYP11A). The antisteroidogenic action of HA was blocked by addition of the phospholipase C (PLC) inhibitor U73122, and HA significantly augmented inositol triphosphate (IP3) production, suggesting a major role for the PLC/IP3 pathway in HA-induced inhibition of Leydig cell function. Finally, HA increased nitric oxide synthase (NOS) activity, and the NOS inhibitor NG-nitro-l-arginine methyl ester (l-NAME) markedly attenuated the effect of the amine on steroid synthesis. On the basis of our findings, HA antagonizes the gonadotropin action in Leydig cells at steps before and after cAMP formation. NOS activation is the main intracellular mechanism by which HA exerts its antisteroidogenic effects.

Interactions between Testicular Serotoninergic, Catecholaminergic, and Corticotropin-Releasing Hormone Systems Modulating cAMP and Testosterone Production in the Golden Hamster

We previously reported the presence of serotonin (5-HT) in testes from golden hamster, a photoperiodic species which is a useful model for the study of states of male (in)fertility. The aims of this study were to investigate: (1) the presence of intrinsic sources of 5-HT in the testis; (2) the role of 5-HT in in vitro androgen production; (3) the serotoninergic receptor subtypes in the testis, and (4) the existence of interactions among the 5-HT receptors and the testicular catecholaminergic and corticotropin-releasing hormone (CRH) systems. Immunohistochemical studies revealed the presence of tryptophan hydroxylase, a 5-HT-biosynthetic enzyme, in interstitial cells which show the characteristic punctate chromatin pattern of Leydig cells. We describe an inhibitory action of 5-HT on testosterone, dihydrotestosterone, and androstane-3α,17β-diol production from testes of peripubertal and adult hamsters maintained in a long photoperiod (14/10 h light/dark), and adult animals exposed to a short photoperiod (6/18 h light/dark). By using several agonists and antagonists of 5-HT receptors, we characterized 5-HT1A and 5-HT2A receptor subtypes involved in the inhibitory action of this neurotransmitter on human chorionic gonadotropin stimulated cyclic adenosine monophosphate and testosterone production. CRH also produced a negative modulation of both parameters, but epinephrine and norepinephrine, through α1/β1-adrenergic receptors, exerted a stimulatory action. 5-HT1A, 5-HT2, and CRH antagonists showed that the testicular activity of the serotoninergic system, but also the α1/β1-adrenergic receptor system, is mediated by CRH. Moreover, interactions between the 5-HT2A receptor system and α1/β-adrenergic receptors have been established. Thus, these data suggest that α1/β1-adrenergic receptors are involved in the local regulatory action exerted by 5-HT on steroidogenesis through a 5-HT2-receptor-mediated response and the CRH system.

Heregulin inhibits proliferation via ERKs and phosphatidyl-inositol 3-kinase activation but regulates urokinase plasminogen activator independently of these pathways in metastatic mammary tumor cells.

Heregulin (HRG) and type I receptor tyrosine kinase (RTK) expression was investigated in the highly invasive and metastatic LM3 cell line, our previously described model of metastasis for mammary cancer (Bal de Kier Joffe et al. [1986] Invasion Metastasis 6:302–12; Urtreger et al. [1997] Int J Oncol 11:489–96). Although LM3 cells do not express HRG, they exhibit high levels of ErbB‐2 and ErbB‐3 as well as moderate expression of ErbB‐4. Addition of exogenous HRGβ1 resulted in inhibition of both proliferation and migration of LM3 cells. HRGβ1 was also able to decrease the activity of urokinase‐type plasminogen activator (uPA) and matrix metalloproteinase 9 (MMP‐9), 2 key enzymes in the invasion and metastatic cascade. HRGβ1 treatment of LM3 cells induced tyrosine phosphorylation of ErbB‐2, ErbB‐3 and ErbB‐4 as well as the formation of ErbB‐2/ErbB‐3 and ErbB‐2/ErbB‐4 heterodimers. Assessment of the signaling pathways involved in HRGβ1 action indicated that the addition of HRGβ1 to LM3 cells resulted in activation of phosphatidylinositol 3‐ kinase (PI‐3K) and in strong induction of the association of the p85 subunit of PI‐3K with ErbB‐3. HRGβ1 also caused the rapid activation of ERK1/ERK2 and Stat3 and Stat5 (signal transducers and activators of transcription [STAT]). This is the first demonstration of the ability of HRGβ1 to activate STATs in mammary tumor cells. Blockage of PI‐3K activity with its chemical inhibitor wortmannin, or of MEK1/ERKs activity with PD98059, resulted in suppression of the ability of HRGβ1 to inhibit LM3 cell growth. Notwithstanding the suppression of these 2 signaling pathways, HRGβ1 still proved capable of inhibiting uPA activity. Therefore, our results provide evidence that signaling pathways involved in HRGβ1‐induced proliferation appear to be distinct from those involved in HRGβ1 regulation of uPA, a protease that plays a pivotal role in invasion and metastasis.

Prenatal Hyperandrogenization Induces Metabolic and Endocrine Alterations Which Depend on the Levels of Testosterone Exposure

Prenatal hyperandrogenism is able to induce polycystic ovary syndrome (PCOS) in rats. The aim of the present study was to establish if the levels of prenatal testosterone may determine the extent of metabolic and endocrine alterations during the adult life. Pregnant Sprague Dawley rats were prenatally injected with either 2 or 5 mg free testosterone (groups T2 and T5 respectively) from day 16 to day 19 day of gestation. Female offspring from T2 and T5 displayed different phenotype of PCOS during adult life. Offspring from T2 showed hyperandrogenism, ovarian cysts and ovulatory cycles whereas those from T5 displayed hyperandrogenism, ovarian cysts and anovulatory cycles. Both group showed increased circulating glucose levels after the intraperitoneal glucose tolerance test (IPGTT; an evaluation of insulin resistance). IPGTT was higher in T5 rats and directly correlated with body weight at prepubertal age. However, the decrease in the body weight at prepubertal age was compensated during adult life. Although both groups showed enhanced ovarian steroidogenesis, it appears that the molecular mechanisms involved were different. The higher dose of testosterone enhanced the expression of both the protein that regulates cholesterol availability (the steroidogenic acute regulatory protein (StAR)) and the protein expression of the transcriptional factor: peroxisome proliferator-activated receptor gamma (PPAR gamma). Prenatal hyperandrogenization induced an anti-oxidant response that prevented a possible pro-oxidant status. The higher dose of testosterone induced a pro-inflammatory state in ovarian tissue mediated by increased levels of prostaglandin E (PG) and the protein expression of cyclooxygenase 2 (COX2, the limiting enzyme of PGs synthesis). In summary, our data show that the levels of testosterone prenatally injected modulate the uterine environment and that this, in turn, would be responsible for the endocrine and metabolic abnormalities and the phenotype of PCOS during the adult life.

Early cell cycle diacylglycerol (DAG) content and protein kinase C (PKC) activity enhancement potentiates prostaglandin F2α (PGF2α) induced mitogenesis in Swiss 3T3 cells

R59022, a diacylglycerol kinase inhibitor, enhances the prostaglandin F2α (PGF2α)‐induced diacylglycerol (DAG) synthesis in Swiss 3T3 cells. It also potentiates the PGF2α‐mediated protein kinase C (PKC)‐dependent 80 kDa protein (80K) phosphorylation and initiation of DNA replication. R 59022 enhances the PGF2α mitogenic response by increasing the rate of entry into the S phase. Insulin does not cause 80K phosphorylation, and does not enhance its induction but it potentiates the PGF2α mitogenic response. These results suggest that mitogenically triggered fluctuations in DAG content and PKC activity play a pivotal role in controlling the PGF2α‐induced DNA synthesis while insulin acts via a different mechanism.

Defining the role of a FYVE domain in the localization and activity of a cAMP phosphodiesterase implicated in osmoregulation in Trypanosoma cruzi

Intracellular levels of cyclic nucleotide second messengers are regulated predominantly by a large superfamily of phosphodiesterases (PDEs). Trypanosoma cruzi, the causative agent of Chagas disease, encodes four different PDE families. One of these PDEs, T. cruzi PDE C2 (TcrPDEC2) has been characterized as a FYVE domain containing protein. Here, we report a novel role for TcrPDEC2 in osmoregulation in T. cruzi and reveal the relevance of its FYVE domain. Our data show that treatment of epimastigotes with TcrPDEC2 inhibitors improves their regulatory volume decrease, whereas cells overexpressing this enzyme are unaffected by the same inhibitors. Consistent with these results, TcrPDEC2 localizes to the contractile vacuole complex, showing strong labelling in the region corresponding to the spongiome. Furthermore, transgenic parasites overexpressing a truncated version of TcrPDEC2 without the FYVE domain show a failure in its targeting to the contractile vacuole complex and a marked decrease in PDE activity, supporting the importance of this domain to the localization and activity of TcrPDEC2. Taking together, the results here presented are consistent with the importance of the cyclic AMP signalling pathway in regulatory volume decrease and implicate TcrPDEC2 as a specifically localized PDE involved in osmoregulation in T. cruzi.

α2‐Adrenergic effect on human breast cancer MCF‐7 cells

Abstract(-)Epinephrine (Epi) and –Norepinephrine (NEpi) significantly stimulated tritiated Thymidine incorporation in MCF‐7 cells at concentrations 10–30 pM to 10 nM, with an EC50 of 10 pM for Epi and 14.2 pM for NEpi. To characterize this action, cells were incubated in the presence of NEpi or Epi and different antagonists. The β‐adrenergic antagonist Propanolol showed no effect on the agonists stimulation, whereas the α‐adrenergic antagonist Phentolamine, reverted it completely at high concentrations (100 μM). The α1‐adrenergic antagonist Prazosin (Pra) acted only at high concentrations, while the α2‐adrenergic antagonist Yohimbine (Yo) reverted the stimulation at an EC50 of 0.11μM. Likewise, when the cells were incubated in the presence of the specific α2‐adrenergic agonist Clonidine (Clo), Thymidine incorporation was significantly stimulated at an EC50 of 0.298 pM. Again, the incubation of the cells in the presence of the α1‐adrenergic antagonist Pra exerted its action at high concentrations, whereas the α2‐adrenergic antagonist Yo showed a clear reversal of the agonists enhancement at an EC50 of 0.136 μM.Moreover, Clo caused a clear and significant inhibition of stimulated cAMP levels both in the intracellular and the extracellular fractions. Yo showed a complete reversion of cAMP levels to control values in the presence of Clo, while Pra had the opposite effect. These data suggest that the stimulation provoked in Thymidine incorporation by the agonists Epi, NEpi, and Clo is, at least in part, due to an α2‐adrenergic mechanism directly on tumoral cells, and that the effect is coupled with inhibition of cAMP levels, as described for this kind of receptors.

GABAB Receptors in Anterior Pituitary Cells

Fil: Lux, Victoria Adela R.. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Instituto de Biologia y Medicina Experimental. Fundacion de Instituto de Biologia y Medicina Experimental. Instituto de Biologia y Medicina Experimental; Argentina. Universidad de Buenos Aires. Facultad de Medicina; ArgentinaThe activation of pituitary GABA_B receptors by the specific agonist baclofen inhibits pituitary hormone secretion in vitro. Here we studied the mechanism of action of GABA_B receptors in rat adenohypophysis. Anterior pituitary cells were obtained by trypsinization and were either plated for hormonal studies and cAMP determination or incubated in FURA 2AM for calcium measurements. Baclofen (BACL: 1·10^–5 M) significantly inhibited basal and thyrotropic releasing hormone (TRH)-stimulated (1·10^–7 M) PRL secretion in anterior pituitary cells from proestrous rats. In the presence of pertussis toxin (PTX: 150 ng/ml, 20 h), which leads to the uncoupling of the G_i/o-protein from the receptor, both effects of BACL were abolished while the effect of dopamine (DA: 1·10^–8 M), used as an inhibitory control, was reduced from 70 to 25%. PTX also reversed BACL-induced inhibition of gonadotropin-releasing hormone (GnRH)-elicited luteinizing hormone (LH) secretion in anterior pituitary cells from 15-day-old female rats. In addition, though working in a pituitary mixed cell population, in which only some cell types possess GABA_B receptors, BACL (1·10^–5 M) attenuated the forskolin-induced (0.5 µM) increase in cAMP. This effect was prevented by co-incubation with the antagonist 2 hydroxysaclofen and by preincubation with PTX. BACL (5· 10^–5 M) and DA (5·10^–7 M) inhibited basal intracellular calcium concentrations ([Ca²⁺]_i) in pituitary cells and the effect of the latter was significantly stronger. The effect of BACL on [Ca²⁺]_i was abolished after preincubation with PTX. In the presence of the potassium channel blocking agents barium (200 µM and 1 mM) and tetraethylammonium (10 mM), BACL was still able to inhibit [Ca²⁺]_i. Blockade of voltage-sensitive calcium channels (VSCC) with either verapamil (5·10^–6 M) or nifedipine (1·10^–6 M) completely abolished the effect of BACL on [Ca²⁺]_i. In the presence of 12.5 mM potassium concentration baclofen significantly inhibited [Ca²⁺]_i. In conclusion, our results describe the negative coupling of adenohypophyseal GABA_B receptors to VSCC through PTX-sensitive G-proteins. These characteristics suggest a resemblance of these receptors to the typical presynaptic GABA_B sites described in the central nervous system.