Invasive and Non-Invasive Human Salmonellosis Cases Admitted between 2015 and 2021 in Four Suburban Hospitals in the Metropolitan Area of Milan (Italy): A Multi-Center Retrospective Study

Non-Typhoidal Salmonellas (NTSs) are diffused worldwide. In Italy, more than 3500 cases are notified each year, but despite this, data about salmonellosis are scarce. Our multi-center, retrospective, descriptive study selected 252 patients with positive cultures for Salmonella spp. (feces 79.8%, blood 8.7%, feces and blood 7.5%), aiming to describe the epidemiological and clinical characteristics of this population. Bacteremic infections constituted 16.3% (41/252) of patients. Extreme ages (≤12 and ≥65 years old) accounted for 79.7%, but only elder ages were strongly associated with bacteremic infections (aOR 5.78). Invasive infections had a 7-fold higher mortality rate than non-invasive disease (9.8% vs. 1.4%, p = 0.013), with an overall rate of 2.8%. The two more represented serogroups were O:4 (52.8%) and O:9 (22.2%). The O:9 serogroup was strongly associated with a higher frequency of invasive infection (aOR 2.96, 95% CI 1.17-7.63). In particular, S. napoli, an emerging serovar in Europe, accounted for 31.7% of bacteremic infections and only 9.5% of non-bacteremic ones (p < 0.001). Antibiotic microbial resistance (AMR) observed a steep increasing trend and was detected in 60.4% of cases (122/202): amoxicillin/clavulanate, ampicillin, and gentamicin were most commonly involved (26.7%, 21.8%, 14.3%, respectively), while TMP/SMX, ciprofloxacin, and ceftriaxone were <10%. Resistance was, in general, less common in the O:9 serogroup, while amikacin resistance was significantly more common. Factors associated with an MDR Salmonella acquisition were time (OR 1.37 per year more), O:4 serogroup (OR 2.67), and being a woman (OR 2.11). The most frequent symptoms were diarrhea (90.5%) and fever (81.7%). In conclusion, our study highlights a high burden of NTS infections, leading to severe or fatal outcomes in frail patients. Furthermore, AMR shows an increasing trend with a concerning high prevalence of cephalosporine resistance compared to the rest of Europe.

Targeting PPARα in the rat valproic acid model of autism: focus on social motivational impairment and sex-related differences

BACKGROUND

The social motivational theory of autism spectrum disorder (ASD) focuses on social anhedonia as key causal feature of the impaired peer relationships that characterize ASD patients. ASD prevalence is higher in boys, but increasing evidence suggests underdiagnosis and undertreatment in girls. We showed that stress-induced motivational anhedonia is relieved by repeated treatment with fenofibrate (FBR), a peroxisome proliferator-activated receptor α (PPARα) agonist. Here, we used the valproic acid (VPA) model of ASD in rats to examine male and female phenotypes and assess whether FBR administration from weaning to young adulthood relieved social impairments.

METHODS

Male and female rats exposed to saline or VPA at gestational day 12.5 received standard or FBR-enriched diet from postnatal day 21 to 48-53, when behavioral tests and ex vivo neurochemical analyses were performed. Phosphorylation levels of DARPP-32 in response to social and nonsocial cues, as index of dopamine D1 receptor activation, levels of expression of PPARα, vesicular glutamatergic and GABAergic transporters, and postsynaptic density protein PSD-95 were analyzed by immunoblotting in selected brain regions.

RESULTS

FBR administration relieved social impairment and perseverative behavior in VPA-exposed male and female rats, but it was only effective on female stereotypies. Dopamine D1 receptor signaling triggered by social interaction in the nucleus accumbens shell was blunted in VPA-exposed rats, and it was rescued by FBR treatment only in males. VPA-exposed rats of both sexes exhibited an increased ratio of striatal excitatory over inhibitory synaptic markers that was normalized by FBR treatment.

LIMITATIONS

This study did not directly address the extent of motivational deficit in VPA-exposed rats and whether FBR administration restored the likely decreased motivation to operate for social reward. Future studies using operant behavior protocols will address this relevant issue.

CONCLUSIONS

The results support the involvement of impaired motivational mechanisms in ASD-like social deficits and suggest the rationale for a possible pharmacological treatment. Moreover, the study highlights sex-related differences in the expression of ASD-like symptoms and their differential responses to FBR treatment.

The curious case of Gαs gain-of-function in neoplasia

BACKGROUND

Mutations activating the α subunit of heterotrimeric Gs protein are associated with a number of highly specific pathological molecular phenotypes. One of the best characterized is the McCune Albright syndrome. The disease presents with an increased incidence of neoplasias in specific tissues.

MAIN BODY

A similar repertoire of neoplasms can develop whether mutations occur spontaneously in somatic tissues during fetal development or after birth. Glands are the most "permissive" tissues, recently found to include the entire gastrointestinal tract. High frequency of activating Gαs mutations is associated with precise diagnoses (e.g., IPMN, Pyloric gland adenoma, pituitary toxic adenoma). Typically, most neoplastic lesions, from thyroid to pancreas, remain well differentiated but may be a precursor to aggressive cancer.

CONCLUSIONS

Here we propose the possibility that gain-of-function mutations of Gαs interfere with signals in the microenvironment of permissive tissues and lead to a transversal neoplastic phenotype.

Transient oxytocin signaling primes the development and function of excitatory hippocampal neurons

Beyond its role in parturition and lactation, oxytocin influences higher brain processes that control social behavior of mammals, and perturbed oxytocin signaling has been linked to the pathogenesis of several psychiatric disorders. However, it is still largely unknown how oxytocin exactly regulates neuronal function. We show that early, transient oxytocin exposure in vitro inhibits the development of hippocampal glutamatergic neurons, leading to reduced dendrite complexity, synapse density, and excitatory transmission, while sparing GABAergic neurons. Conversely, genetic elimination of oxytocin receptors increases the expression of protein components of excitatory synapses and excitatory synaptic transmission in vitro. In vivo, oxytocin-receptor-deficient hippocampal pyramidal neurons develop more complex dendrites, which leads to increased spine number and reduced γ-oscillations. These results indicate that oxytocin controls the development of hippocampal excitatory neurons and contributes to the maintenance of a physiological excitation/inhibition balance, whose disruption can cause neurobehavioral disturbances.

DOI:http://dx.doi.org/10.7554/eLife.22466.001

Impaired thromboxane receptor dimerization reduces signaling efficiency: A potential mechanism for reduced platelet function in vivo

Thromboxane A₂ is a potent mediator of inflammation and platelet aggregation exerting its effects through the activation of a G protein-coupled receptor (GPCR), termed TP. Although the existence of dimers/oligomers in Class A GPCRs is widely accepted, their functional significance still remains controversial. Recently, we have shown that TPα and TPβ homo-/hetero-dimers interact through an interface of residues in transmembrane domain 1 (TM1) whose disruption impairs dimer formation. Here, biochemical and pharmacological characterization of this dimer deficient mutant (DDM) in living cells indicates a significant impairment in its response to agonists. Interestingly, two single loss-of-function TPα variants, namely W29C and N42S recently identified in two heterozygous patients affected by bleeding disorders, match some of the residues mutated in our DDM. These two naturally occurring variants display a reduced potency to TP agonists and are characterized by impaired dimer formation in transfected HEK-293T cells. These findings provide proofs that lack of homo-dimer formation is a crucial process for reduced TPα function in vivo, and might represent one molecular mechanism through which platelet TPα receptor dysfunction affects the patient(s) carrying these mutations.

The Italian national surgical site infection surveillance programme and its positive impact, 2009 to 2011

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Ectopic expression of the heterotrimeric G15 protein in pancreatic carcinoma and its potential in cancer signal transduction

G15 is a heterotrimeric G protein selectively expressed in immature cell lineages in adult tissues that feature higher cell renewal potential. It promiscuously couples a wide variety of G protein-coupled receptors (GPCRs) to phospholipase C. Intriguingly, G15 is poorly affected by GPCR desensitization. We show here that G15 α-subunit (Gα15) supports sustained stimulation of PKD1 by a constitutively desensitized GPCR co-transfected over a negative cell background. Based on the fact that PKD1 is a multifunctional protein kinase activated by PKC and known for promoting oncogenic signaling, we hypothesized that, if expressed out of its natural cell context, G15 might promote tumor growth. A screening for Gα15 mRNA expression pointed to pancreatic carcinoma among different human cancer cell types and revealed significant expression in human tumor biopsies xenografted in mice. In addition, G15 ectopic presence could functionally contribute to the transformation process since siRNA-induced depletion of Gα15 in pancreatic carcinoma cell lines dramatically inhibited anchorage-independent growth and resistance to the lack of nutrients. Altogether, our findings suggest that G15 supports tumorigenic signaling in pancreas and hence it may be considered as a novel potential target for the therapy of this form of cancer.

Mesenchymal stem cells enhance GABAergic transmission in co-cultured hippocampal neurons

Bone marrow-derived mesenchymal stem cells (MSCs) are multipotent stem cells endowed with neurotrophic potential combined with immunological properties, making them a promising therapeutic tool for neurodegenerative disorders. However, the mechanisms through which MSCs promote the neurological recovery following injury or inflammation are still largely unknown, although cell replacement and paracrine mechanisms have been hypothesized. In order to find out what are the mechanisms of the trophic action of MSCs, as compared to glial cells, on CNS neurons, we set up a co-culture system where rat MSCs (or cortical astrocytes) were used as a feeding layer for hippocampal neurons without any direct contact between the two cell types. The analysis of hippocampal synaptogenesis, synaptic vesicle recycling and electrical activity show that MSCs were capable to support morphological and functional neuronal differentiation. The proliferation of hippocampal glial cells induced by the release of bioactive substance(s) from MSCs was necessary for neuronal survival. Furthermore, MSCs selectively increased hippocampal GABAergic pre-synapses. This effect was paralleled with a higher expression of the potassium/chloride KCC2 co-transporter and increased frequency and amplitude of mIPSCs and sIPSCs. The enhancement of GABA synapses was impaired by the treatment with K252a, a Trk/neurotrophin receptor blocker, and by TrkB receptor bodies hence suggesting the involvement of BDNF as a mediator of such effects. The results obtained here indicate that MSC-secreted factors induce glial-dependent neuronal survival and trigger an augmented GABAergic transmission in hippocampal cultures, highlighting a new effect by which MSCs could promote CNS repair. Our results suggest that MSCs may be useful in those neurological disorders characterized by an impairment of excitation versus inhibition balance.

Light on the structure of thromboxane A₂receptor heterodimers

The structure-based design of a mutant form of the thromboxane A(2) prostanoid receptor (TP) was instrumental in characterizing the structural determinants of the hetero-dimerization process of this G protein coupled receptor (GPCR). The results suggest that the hetero-dimeric complexes between the TPα and β isoforms are characterized by contacts between hydrophobic residues in helix 1 from both monomers. Functional characterization confirms that TPα-TPβ hetero-dimerization serves to regulate TPα function through agonist-induced internalization, with important implications in cardiovascular homeostasis. The integrated approach employed in this study can be adopted to gain structural and functional insights into the dimerization/oligomerization process of all GPCRs for which the structural model of the monomer can be achieved at reasonable atomic resolution.

Dual modulation of inward rectifier potassium currents in olfactory neuronal cells by promiscuous G protein coupling of the oxytocin receptor

Oxytocin receptor is a seven transmembrane receptor widely expressed in the CNS that triggers G(i) or G(q) protein-mediated signaling cascades leading to the regulation of a variety of neuroendocrine and cognitive functions. We decided to investigate whether and how the promiscuous receptor/G protein coupling affects neuronal excitability. As an experimental model, we used the immortalized gonadotropin-releasing hormone-positive GN11 cell line displaying the features of immature, migrating olfactory neurons. Using RT-PCR analysis, we detected the presence of oxytocin receptors whose stimulation by oxytocin led to the accumulation of inositol phosphates and to the inhibition of cell proliferation, and the expression of several inward rectifier (IR) K+ channel subtypes. Moreover, electrophysiological and pharmacological inspections using whole-cell patch-clamp recordings evidenced that in GN11 cells, IR channel subtypes are responsive to oxytocin. In particular, we found that: (i) peptide activation of receptor either inhibited or stimulated IR conductances, and (ii) IR current inhibition was mediated by a pertussis toxin-resistant G protein presumably of the G(q/11) subtype, and by phospholipase C, whereas IR current activation was achieved via receptor coupling to a pertussis toxin-sensitive G(i/o) protein. The findings suggest that neuronal excitability might be tuned by a single peptide receptor that mediates opposing effects on distinct K+ channels through the promiscuous coupling to different G proteins.

The puzzling uniqueness of the heterotrimeric G15 protein and its potential beyond hematopoiesis

Heterotrimeric G proteins transduce the signals of the largest family of membrane receptors (G protein-coupled receptors, GPCRs) hence triggering the activation of a wide variety of physiological responses. G15 is a G protein characterized by a number of functional peculiarities that make its signaling exceptional: 1) it can couple a variety of Gs-, Gi/o-, and Gq-linked receptors to phospholipase C activation; 2) relatively to other G proteins, it is poorly affected by beta-arrestin-dependent desensitization, the general mechanism that regulates GPCR function and 3) at the protein level, its expression is only detected in highly specific cell types (hematopoietic and epithelial cells). G15 alpha-subunit displays unique structural and biochemical properties, and is phylogenetically the most recent and divergent component of the Galphaq/11 subfamily. All these aspects shed a mysterious light on G15 biological role, which remains substantially elusive. Thus, far, G15 signaling has been analyzed in the context of hematopoiesis. Here, we highlight observations supporting the view that G15 functions may extend further beyond the immune system. In addition, we describe puzzling aspects of G15 signaling that offer a novel perspective in the understanding of its physiological role.

G-protein-coupled receptors, cholesterol and palmitoylation: facts about fats

G-protein-coupled receptors (GPCRs) are integral membrane proteins, hence it is not surprising that a number of their structural and functional features are modulated by both proteins and lipids. The impact of interacting proteins and lipids on the assembly and signalling of GPCRs has been extensively investigated over the last 20-30 years, and a further impetus has been given by the proposal that GPCRs and/or their immediate signalling partners (G proteins) can partition within plasma membrane domains, termed rafts and caveolae, enriched in glycosphingolipids and cholesterol. The high content of these specific lipids, in particular of cholesterol, in the vicinity of GPCR transmembranes can affect GPCR structure and/or function. In addition, most GPCRs are post-translationally modified with one or more palmitic acid(s), a 16-carbon saturated fatty acid, covalently bound to cysteine(s) localised in the carboxyl-terminal cytoplasmic tail. The insertion of palmitate into the cytoplasmic leaflet of the plasma membrane can create a fourth loop, thus profoundly affecting GPCR structure and hence the interactions with intracellular partner proteins. This review briefly highlights how lipids of the membrane and the receptor themselves can influence GPCR organisation and functioning.

Heterotrimeric G proteins demonstrate differential sensitivity to beta-arrestin dependent desensitization

G15 is a heterotrimeric G protein of the Gq/11 family. In this study, we describe its exceptional poor sensitivity to the general regulatory mechanism of G protein-coupled receptor (GPCR) desensitization. Enhancing beta2 adrenergic receptor desensitization by arrestin overexpression, did not affect signalling to G15. Similarly, increased levels of arrestin did not affect G15 signalling triggered by the activation of V2 vasopressin and delta opioid receptors. Furthermore, co-immunoprecipitation experiments showed that G15 alpha subunit (as opposed to Galphaq and Galphas) is recruited to a V2 vasopressin receptor mutant that is constitutively desensitized by beta-arrestin. Interestingly, co-expression of Galpha15 partially rescued cell surface localization and signalling capabilities of the same mutant receptor and reduced beta2 adrenergic receptor internalization. Taken together, these findings provide evidence for a novel mechanism whereby GPCR desensitization can be bypassed and G15 can support sustained signalling in cells chronically exposed to hormones or neurotransmitters.

G protein-coupled receptor oligomerization provides the framework for signal discrimination

The idea that G protein-coupled receptors (GPCRs) may undergo homo- or hetero-oligomerization, although highly controversial up to a few years ago, has recently gained wide acceptance. The recognition that GPCRs may exhibit either dimeric or oligomeric structures is based upon a large body of biochemical and biophysical evidence. While much effort has been spent to demonstrate the mechanism(s) by which GPCRs interact with each other, the physiological relevance of this phenomenon remains rather elusive. GPCR oligomerization has been proposed to play a role in receptor ontogeny by either chaperoning protein folding or controlling trafficking to the cell surface. However, the acquisition of these roles does not rule out the possibility that oligomeric receptors may have additional functions, once they are brought to the cell surface. Herein, we propose that protein-protein as well as protein-lipid interactions may provide the structural basis for organizing distinct cell compartments along the plasma membrane where different extracellular signals may be perceived and discriminated.

Polarization of caveolins and caveolae during migration of immortalized neurons

During CNS development neurons undergo directional migration to achieve their adult localizations. To study neuronal migration, we used a model cell line of immortalized murine neurons (gonadotropin-releasing hormone expressing neurons; GN11), enriched with caveolins and caveolae invaginations that show in vitro chemotaxis upon serum exposure. Cholesterol depletion with methyl-beta-cyclodextrin induced the loss of caveolae and the inhibition of chemotaxis, thus suggesting that GN11 migration depends upon the structural integrity of caveolae. Polarization of proteins and organelles is a hallmark of cell migration. Accordingly, GN11 cells transmigrating through filter pores exhibited a polarized distribution of caveolin-1 isoform (cav-1) in the leading processes. In contrast, during two-dimensional migration cav-1 and caveolae polarized at the trailing edge. As caveolae are enriched with signaling molecules, we suggest that asymmetrical localization of caveolae may spatially orient GN11 neurons to incoming migratory signals thereby transducing them into directional migration.

Presence of delta opioid receptors on a subset of hypothalamic gonadotropin releasing hormone (GnRH) neurons

Opioid peptides exert an inhibitory effect on hypothalamic gonadotropin releasing hormone (GnRH) secretion mainly by interacting with mu-opioid receptors. Although a direct role for opioids via delta-opioid receptors (DORs) has been suggested, the presence of these receptors on GnRH neurons has never been demonstrated. In the present study, we determined the distribution of DORs in the basal hypothalamus of rat with special focus on their relation to GnRH neurons. Double-labelling immunofluorescence and confocal microscopy revealed that DORs are exclusively present in a subpopulation of GnRH nerve terminals, with the highest density in the external layer of the median eminence. We then studied the functional characteristics of DORs in an immortalized GnRH-secreting neuronal cell line (GT1-1) known to endogenously express this receptor. Here, pertussis toxin pretreatment abolished the delta-agonist (DPDPE) inhibitory effect on cAMP accumulation. We also analyzed the type of G proteins involved in the signal transduced by the DOR and showed that GT1-1 cells express the inhibitory Go and Gi2 alpha-subunits. However, only Go was down-regulated under chronic DPDPE exposure. Finally, since DOR is expressed postnatally in brain, we compared GnRH neuronal cells immortalized at different developmental stages (the more mature GT1-1 and GT1-7 cells, versus the more immature GN11 cells), evidencing that only mature neurons express DOR. In conclusion, our study indicates that a direct control of opioids via delta-receptors occurs on GnRH neurons and validates the use of GT1 cells to further investigate the nature of the DOR present on GnRH neurons.

Caveolin-1 expression and membrane cholesterol content modulate N-type calcium channel activity in NG108-15 cells

Caveolins are the main structural proteins of glycolipid/cholesterol-rich plasmalemmal invaginations, termed caveolae. In addition, caveolin-1 isoform takes part in membrane remodelling as it binds and transports newly synthesized cholesterol from endoplasmic reticulum to the plasma membrane. Caveolin-1 is expressed in many cell types, including hippocampal neurons, where an abundant SNAP25-caveolin-1 complex is detected after induction of persistent synaptic potentiation. To ascertain whether caveolin-1 influences neuronal voltage-gated Ca2+ channel basal activity, we stably expressed caveolin-1 into transfected neuroblastoma x glioma NG108-15 hybrid cells [cav1(+) clone] that lack endogenous caveolins but express N-type Ca2+ channels upon cAMP-induced neuronal differentiation. Whole-cell patch-clamp recordings of cav1(+) cells demonstrated that N-type current density was reduced in size by approximately 70% without any significant change in the time course of activation and inactivation and voltage dependence. Moreover, the cav1(+) clone exhibited a significantly increased proportion of membrane cholesterol compared to wild-type NG108-15 cells. To gain insight into the mechanism underlying caveolin-1 lowering of N-current density, and more precisely to test whether this was indirectly caused by caveolin-1-induced enhancement of membrane cholesterol, we compared single N-type channel activities in cav1(+) clone and wild-type NG108-15 cells enriched with cholesterol after exposure to a methyl-beta-cyclodextrin-cholesterol complex. A lower Ca2+ channel activity was recorded from cell-attached patches of both cell types, thus supporting the view that the increased proportion of membrane cholesterol is ultimately responsible for the effect. This is due to a reduction in the probability of channel opening caused by a significant decrease of channel mean open time and by an increase of the frequency of null sweeps.

The oxytocin receptor antagonist atosiban inhibits cell growth via a "biased agonist" mechanism

In human myometrial cells, the promiscuous coupling of the oxytocin receptors (OTRs) to G(q) and G(i) leads to contraction. However, the activation of OTRs coupled to different G protein pathways can also trigger opposite cellular responses, e.g. OTR coupling to G(i) inhibits, whereas its coupling to G(q) stimulates, cell proliferation. Drug analogues capable of promoting a selective receptor-G protein coupling may be of great pharmacological and clinical importance because they may target only one specific signal transduction pathway. Here, we report that atosiban, an oxytocin derivative that acts as a competitive antagonist on OTR/G(q) coupling, displays agonistic properties on OTR/G(i) coupling, as shown by specific (35)S-labeled guanosine 5'-3-O-(thio) trisphosphate ([(35)S]GTPgammaS) binding. Moreover, atosiban, by acting on a G(i)-mediated pathway(,) inhibits cell growth of HEK293 and Madin-Darby canine kidney cells stably transfected with OTRs and of DU145 prostate cancer cells expressing endogenous OTRs. Notably, atosiban leads to persistent ERK1/2 activation and p21(WAF1/CIP1) induction, the same signaling events leading to oxytocin-mediated cell growth inhibition via a G(i) pathway. Finally, atosiban exposure did not cause OTR internalization and led to only a modest decrease (20%) in the number of high affinity cell membrane OTRs, two observations consistent with the finding that atosiban did not lead to any desensitization of the oxytocin-induced activation of the G(q)-phospholipase C pathway. Taken together, these observations indicate that atosiban acts as a "biased agonist" of the human OTRs and thus belongs to the class of compounds capable of selectively discriminating only one among the multiple possible active conformations of a single G protein-coupled receptor, thereby leading to the selective activation of a unique intracellular signal cascade.

Mutational analysis of the highly conserved ERY motif of the thromboxane A2 receptor: alternative role in G protein-coupled receptor signaling

The presence of highly conserved amino acid stretches in G protein-coupled receptors (GPCRs) usually predicts an important role in receptor function. Considerable attention has therefore been focused on the involvement of the highly conserved Glu/Asp-Arg-Tyr (E/DRY) motif at the cytoplasmic end of transmembrane domain 3 in the regulation of GPCR conformational states and/or the mediation of G protein activation. In the present study, we investigated the role of Glu129 and Arg130 in the ERY of thromboxane A2 receptor alpha (TPalpha) in transfected human embryonic kidney 293 cells. We show that no conservative or nonconservative substitutions of Glu129 and Arg130 generated a constitutively active TPalpha mutant, but a nonconservative mutation of Arg130 (R130V) yielded a mutant receptor with significantly impaired 9,11-dideoxy-9alpha,11alpha-methanoepoxy-prosta-5Z,13E-dien-1-oic acid (U46619)-induced accumulation of inositol phosphates (IPs). This loss-of-function phenotype seems to be caused by the uncoupling of the TPalpha receptor from Gq, as demonstrated by the loss of high-affinity agonist binding, and not by receptor internalization, as shown by localization studies with the R130V-green fluorescent protein fusion protein. It is interesting to note that U46619-induced activation of the nonconservative E129V mutant stimulated the production of IPs with a approximately 10-fold lower EC50 and a approximately 2-fold higher Emax than in the wild-type receptor. Collectively, these data demonstrate that, unlike other GPCRs, mutations of Glu129 do not induce constitutive activity, whereas Arg130 is involved in G protein coupling or recognition, and they suggest the existence within class A GPCRs of at least two different subclasses that make different uses of the highly conserved E/DRY motif.

Long-term agonist stimulation of IP prostanoid receptor depletes the cognate G(s)alpha protein in membrane domains but does not change the receptor level

Iloprost (IP) stimulation (1 microM, 2 h) of Flag-epitope-tagged human IP prostanoid receptor (FhIPR) expressed in HEK293 cells resulted in specific decrease of endogenous G(s)alpha protein in detergent-insensitive, caveolin-enriched, membrane domains (DIMs). Receptor protein FhIPR, caveolin, G(i)alpha and GPI-linked, domain markers CD55 and CD59 were unchanged. The same result was obtained in HEK293 cells expressing FhIPR-G(s)alpha fusion protein. The endogenous G(s)alpha decreased, but the level of Flag-hIPR-G(s)alpha protein did not change. The specific depletion of domain-bound pool of G(s)alpha as consequence of iloprost stimulation was also demonstrated in membrane domains prepared according to alkaline treatment plus sonication protocol (detergent-free procedure of Song et al.). Our data further indicated that in control, quiescent cells only a very small amount of IP prostanoid receptor was present in DIMs together with large amount of its cognate G(s)alpha protein. Expressed in quantitative terms, DIMs contained 30-40% of the total cellular amount of G proteins whereas the content of IP prostanoid receptors was 1-3%. The dominant portion (>95%) of FhIPR as well as FhIPR-G(s)alpha was localised in high-density area of the gradient containing detergent-solubilised proteins. FhIPR and FhIPR-G(s)alpha distribution was similar to that of transmembrane plasma membrane (PM) markers (CD147, MHCI, CD29, Tapa1, the alpha subunit of Na,K-ATPase, transmembrane form of CD58 and CD44). All these proteins are known to be fully solubilised by detergent and thus unable to float in density gradient. Our data indicate that (i) long-term agonist stimulation of IP prostanoid receptor is associated with preferential decrease of its cognate G protein G(s)alpha from membrane domains; receptor level is unchanged. (ii) Very small fraction (1-3%) of total cellular amount of receptors is recovered in DIMs together with roughly 40% of G proteins. These data suggest a "supra-stoichiometric" arrangement of G proteins and corresponding receptors in DIMs.

G-protein coupled receptors in lipid rafts and caveolae: how, when and why do they go there?

This review describes the advances in our understanding of the role of G-protein coupled receptor (GPCR) localisation in membrane microdomains known as lipid rafts and caveolae. The growing interest in these specialised regions is due to the recognition that they are involved in the regulation of a number of cell functions, including the fine-tuning of various signalling molecules. As a number of GPCRs have been found to be enriched in lipid rafts and/or caveolae by means of different experimental approaches, we first discuss the pitfalls and uncertainties related to the use of these different procedures. We then analyse the addressing signals that drive and/or stabilise GPCRs in lipid rafts and caveolae, and explore the role of rafts/caveolae in regulating GPCR trafficking, particularly in receptor exo- and endocytosis. Finally, we review the growing evidence that lipid rafts and caveolae participate in the regulation of GPCR signalling by affecting both signalling selectivity and coupling efficacy.

CysLT1 signal transduction in differentiated U937 cells involves the activation of the small GTP-binding protein Ras

We investigated the signal transduction pathway(s) of leukotriene D(4) (LTD(4)) in the human promonocytic U937 cells, a cell line known to constitutively express CysLT(1) receptors. Herein, we demonstrate that LTD(4) specifically acts on a CysLT(1) receptor to dose-dependently increase (three to five-fold over basal) RasGTP through a G(i/o) protein. In fact, while cytosolic Ca(2+) ([Ca(2+)](i)) increase was only partially sensitive to pertussis toxin (PTx), Ras activation was almost completely inhibited by the same toxin. Furthermore, the phospholipase C (PLC) inhibitor U73122 completely inhibited both [Ca(2+)](i) and RasGTP increase, suggesting that in these cells PLC is the point of convergence for both PTx insensitive and sensitive pathways leading to [Ca(2+)](i) release and Ras activation. Indeed, chelating intracellular Ca(2+) strongly (>70%) prevented LTD(4)-induced Ras activation, indicating that this ion plays an essential role for CysLT(1)-induced downstream signaling in differentiated U937 (dU937) cells. In addition, while Src did not appear to be substantially involved in CysLT(1)-induced signaling, genistein was able to partially inhibit LTD(4)-induced [Ca(2+)](i) transient ( approximately 34%) and almost completely prevented Ras activation (>90%), suggesting a potential role for other Ca(2+)-dependent tyrosine kinases in LTD(4)-induced signaling. Finally, agonist-induced CysLT(1) stimulation was followed by a specific extracellular regulated kinase (ERK) 1/2 phosphorylation, an event with a pharmacological profile similar to that of Ras activation, partially ( approximately 40%) sensitive to Clostridium sordellii lethal toxin and totally blocked by PTx. In conclusion, LTD(4)-induced CysLT(1) receptor activation in dU937 cells leads to Ras activation and ERK phosphorylation mostly through a PTx-sensitive G(i/o) protein, PLC, and Ca(2+)-dependent tyrosine kinase(s).

Oxytocin receptor elicits different EGFR/MAPK activation patterns depending on its localization in caveolin-1 enriched domains

We have recently shown that oxytocin inhibits cell proliferation when the vast majority of oxytocin receptors are excluded from caveolin-1-enriched microdomains, and that, on the contrary, it has a mitogenic effect when the receptors are targeted to these plasma membrane domains. In this study, we investigated whether the receptors located inside and outside caveolar microdomains initiate different signalling pathways and how this may lead to opposite effects on cell proliferation. Our data indicate that, depending on their localization, oxytocin receptors transactivate EGFR and activate ERK1/2 using different signalling intermediates. The final outcome is a different temporal pattern of EGFR and ERK1/2 phosphorylation, which is more persistent when the receptors are located outside caveolar microdomains and inhibit cell growth, and very transient when they are located in caveolar microdomains and stimulate cell growth. Finally, only the activation of receptors located outside caveolar microdomains correlates with the activation of the cell cycle inhibitor p21(WAF1/CIP1), thus suggesting that the antiproliferative OTR effects may, in this case, be achieved by a sustained activation of EGFR and MAPK leading to the induction of this cell cycle regulator.

Involvement of prenylated proteins in calcium signaling induced by LTD4 in differentiated U937 cells

We investigated signal transduction pathways for LTD4 in the human promonocytic cell line U937 known, upon differentiation, to express CysLT1 receptors. We confirmed the presence of high-affinity binding sites for 3H-LTD4, which, in functional studies, displayed the features of CysLT1 receptor. In fact, three potent and selective CysLT1 receptor antagonists were able to completely inhibit LTD4-induced response. In turn, cytosolic Ca2+ ([Ca2+]i) increase (EC50 = 3.4 nM +/- 27% CV) was only partially sensitive to pertussis toxin (PTx) as well as to the prenylation inhibitor fluvastatin and to the specific geranylgeranylation and farnesylation inhibitors BAL 9504 and FPT II. Finally, Clostridium sordellii lethal toxin, inhibitor of the Ras family of GTPases, and FTS, a potent methyltransferase inhibitor, were both able to partially inhibit LTD4-induced [Ca2+] increase, suggesting a role for a Ras family member in [Ca2+]i regulation. In conclusion, in dU937 LTD4 signal transduction involves: (a) at least two pathways, one sensitive and one insensitive to PTx; (b) isoprenylated proteins, such as betagamma subunits and, possibly, a small G protein of the Ras family.

Palmitic is the main fatty acid carried by lipids of detergent-resistant membrane fractions from neural and non-neural cells

Lipids extracted from detergent-resistant membrane fractions, thought to derive from membrane domains, were analyzed for fatty acid composition. The proportion of palmitic acid in fractions isolated from neurons (cerebellar granule cells) and from neural-like cell lines (neuroblastomaglioma NG108-15) nearly doubled (reaching about 54% of total fatty acids) with respect to cell WCL, indicating their enrichment in palmitic acid-carrying lipids. The proportion of palmitic acid in detergent-resistant fractions obtained from caveolin-transfected NG108-15 cells was comparable with that obtained from caveolin-negative cells, ruling out a specific role of this protein in recruiting palmitoylated lipid species. The enrichment in palmitic acid was remarked also in membrane fractions isolated from non-neuronal cell lines (A431) using either detergents or detergent-free techniques. Lipid fractionation and mass spectrometry experiments show that palmitic acid-rich phosphatidylcholine species are responsible of the peculiar fatty acid composition of these fractions. All together these results suggest that the enrichment in palmitic acid-rich phosphatidylcholine species is a common feature of neural and non-neural cell lines and may play a major role in the biogenesis of membrane domains.

Sphingolipid metabolism and caveolin expression in gonadotropin-releasing hormone-expressing GN11 and gonadotropin-releasing hormone-secreting GT1-7 neuronal cells

In this paper, we show that caveolin-1 is abundantly present in a cell line of immortalized gonadotropin-releasing hormone-expressing neurons (GN11). In contrast to GN11, caveolin is undetectable in a cognate cell line of immortalized gonadotropin-releasing hormone-secreting neurons (GT1-7). These two cell lines are characterized by a radically different sphingolipid metabolism. After incubation in the presence of tracer amount of [1-(3)H]sphingosine, GN11 and GT1-7 neurons incorporated similar amounts of radioactivity. In GT1-7 neurons, [1-(3)H]sphingosine metabolism was markedly oriented toward the biosynthesis of complex sphingolipids. In fact, almost all the radioactivity in the lipid extracts from GT1-7 cells was associated with biosynthetic products (ceramide, sphingomyelin, and glycosphingolipids). In particular glycosphingolipids represented more than 65% of total lipid radioactivity in these cells, and the main glycosphingolipid was GM3 ganglioside (about 47% of total lipid radioactivity). In the case of GN11 neurons, a high portion of [1-(3)H]sphingosine underwent complete degradation, as indicated by the formation of high levels of radioactive phosphatidylethanolamine (about 23% of lipid radioactivity). Moreover, the main complex sphingolipid in GN11 neurons was not a glycolipid, but sphingomyelin (its level in these cells, about 54% of lipid radioactivity, was two-fold higher than in GT1-7). Glycolipids, gangliosides in particular, were present in low amount (9.5% of lipid radioactivity) if compared with the cognate GT1-7 cell line, and GM3 was almost absent in GN11 neurons. Despite the radical differences in ganglioside and caveolin content, from both cell types a membrane fraction similarly enriched in sphingolipids was prepared. In the case of GN11 cells, this fraction was also enriched in caveolin. The presence of caveolin or GM3 may correlate with different functional properties linked to the stage of neuronal maturation, since GN11 and GT1-7 are representative, respectively, of immature, migrating, and differentiated, postmigratory gonadotropin-releasing hormone-positive neurons.

Localization of the human oxytocin receptor in caveolin-1 enriched domains turns the receptor-mediated inhibition of cell growth into a proliferative response

In this study, we investigated the functional role of the localization of human OTR in caveolin-1 enriched membrane domains. Biochemical fractionation of MDCK cells stably expressing the WT OTR-GFP indicated that only minor quantities of receptor are partitioned in caveolin-1 enriched domains. However, when fused to caveolin-2, the OTR protein proved to be exclusively localized in caveolin-1 enriched fractions, where it bound the agonist with increased affinity and efficiently coupled to Galpha(q/11). Interestingly, the chimeric protein was unable to undergo agonist-induced internalization and remained confined to the plasma membrane even after prolonged agonist exposure (120 min). A striking difference in receptor stimulation was observed when the OT-induced effect on cell proliferation was analysed: stimulation of the human WT OTR inhibited cell growth, whereas the chimeric protein had a proliferative effect. These data indicate that the localization of human OTR in caveolin-1 enriched microdomains radically alters its regulatory effects on cell growth; the fraction of OTR residing in caveolar structures may therefore play a crucial role in regulating cell proliferation.

Attenuation of G protein-mediated inhibition of N-type calcium currents by expression of caveolins in mammalian NG108-15 cells

1. Caveolins are integral proteins of glycolipid/cholesterol-rich plasmalemmal caveolae domains, where, they may function as a plasma membrane scaffold onto which many classes of signalling molecules, including receptors and heterotrimeric G proteins, can assemble. To ascertain whether caveolins influence G protein-mediated signal transduction, we stably expressed caveolin-1 and -3 isoforms in the neuroblastoma x glioma NG108-15 hybrid cell line, lacking endogenous caveolins. Subsequently, using whole-cell voltage clamp methods, we examined whether the modulation of N-type voltage-gated Ca2+ channels by G(o) protein-coupled, delta-type opioid receptors might be affected by recombinant caveolin expression. 2. In transfected NG108-15 cells, caveolins localized at the plasma membrane and, upon subcellular fractionation on sucrose density gradients, they co-localized in Triton-resistant, low buoyancy fractions, with endogenous G(o) protein alpha-subunits. 3. The voltage-dependent inhibition of omega-conotoxin GVIA-sensitive Ba2+ currents following either activation of delta-opioid receptors by the agonist [o-pen2,o-pen5]-enkephalin (DPDPE), or direct stimulation of G proteins with guanosine 5'-O-(thiotriphosphate) (GTPgammaS) was significantly attenuated in caveolin-expressing cells. The kinetics of Ca2+ channel inhibition were also modified by caveolins. 4. Overall, these results suggest that caveolins may negatively affect G protein-dependent regulation of voltage-gated N-type Ca2+ channels, presumably by causing a reduction of the available pool of activated G proteins.

Thioacylation is required for targeting G-protein subunit G(o1alpha) to detergent-insoluble caveolin-containing membrane domains

alpha-Subunits of heterotrimeric G(i)-like proteins (alpha(i), alpha(o) and alpha(z)) associate with the cytoplasmic leaflet of the plasma membrane by means of N-terminally linked myristic acid and palmitic acid. An additional role for palmitate has been recently suggested by the observation that fusion with the palmitoylated N-terminus of alpha(i1) relocalizes cytosolic green-fluorescent-protein reporter to low buoyancy, Triton-insoluble membrane domains (TIFF; Triton-insoluble floating fraction), enriched with caveolin-1 [Galbiati, Volonté, Meani, Milligan, Lublin, Lisanti and Parenti (1999) J. Biol. Chem 274, 5843-5850]. Here we show that, upon transient expression in transfected COS-7 cells, myristoylated and palmitoylated alpha(o) (alpha(o)wt, where wt is wild-type) is exclusively found in TIFF, from where non-palmitoylated alpha(o)wt and alpha(o)C3S (Cys(3)-->Ser) mutant are excluded. Moreover, alpha(o) fused to N-terminally truncated human vasopressin V2 receptor (V2TR-alpha(o)), lacking myristate and palmitate, still localizes at the plasma membrane by means of first transmembrane helix of V2R, but is excluded from TIFF. Likewise, alpha(o)C3S does not partition into TIFF, even when its membrane avidity is enhanced by co-expression of betagamma-subunits. Thus membrane association, in the absence of added palmitate, is not sufficient to confer partitioning of alpha(o) within TIFF, suggesting that palmitoylation is a signal for membrane compartmentalization of dually acylated alpha-subunits.

Nephrogenic diabetes insipidus: functional analysis of new AVPR2 mutations identified in Italian families

The aim of this study was to identify loss-of-function mutations of the V2 vasopressin receptor gene (AVPR2) in Italian patients affected by X-linked nephrogenic diabetes insipidus (NDI). Mutations were found in 15 of the 18 unrelated families investigated: nine of these mutations were previously unknown, including two affecting residues located in regions known to be important for determining the pharmacologic properties of the receptor, which were therefore functionally investigated. The first (A84D) involves a residue located near an aspartic acid (D85) that is highly conserved in all G protein-coupled receptors and that is believed to play a role in the process of their isomerization into functionally active and inactive states. The present study indicates that this mutation not only affects receptor folding in such a way as to lead to its retention inside the intracellular compartments but, as expected, also has profound effects on its binding and coupling properties. The second was a mutation of a tryptophan located at the beginning of the first extracellular loop (W99R) that greatly impaired the binding properties of the receptor and had a minor effect on its intracellular routing. Molecular analysis of the first extracellular loop bearing this mutation suggests that this residue plays a fundamental role in stabilizing the peptide/receptor interactions responsible for the high-affinity binding of agonists to the V2 receptor.

Interaction between HIV-1 NEF and G(o) proteins in transfected COS-7 cells

Nef protein of HIV/SIV lentiviruses affects G-protein-mediated signaling, and physically associates to Lck, a myristoylated and palmitoylated Src-like tyrosine kinase. To assess whether Nef interacts with alpha-subunits of heterotrimeric G proteins (Galpha), carrying the same lipidation motif as Lck, we transiently expressed Nef and G(o)alpha (wild-type or nonpalmitoylated C3S mutant), individually or in combination, in transfected COS-7 cells. Recombinant Nef was mostly recovered in particulate fractions, and a Nef-Green Fluorescent Protein chimera was localized at the plasmalemma by in vivo fluorescence imaging. Moreover, Nef and C3S were entirely solubilized by cold Triton X-100, and excluded from low buoyant density sucrose gradient fractions, containing caveolin-1, whereas wild-type G(o)alpha was partially resistant to Triton extraction, and colocalized with caveolin-1. After coexpression, Nef recruited soluble C3S to membranes, and the two proteins were coimmunoprecipitated by G(o)alpha and Nef antisera. We conclude that Nef interacts with nonpalmitoylated G(o)alpha, presumably outside caveolin-rich microdomains of the plasma membrane.

Tubulin anchoring to glycolipid-enriched, detergent-resistant domains of the neuronal plasma membrane

After incubation of intact living cultured rat cerebellar granule cells at 37 degrees C with a new GM1 ganglioside analog, carrying a diazirine group and labeled with (125)I in the ceramide moiety, followed by photoactivation, a relatively small number of radiolabeled proteins were detected in a membrane-enriched fraction. A protein of about 55 kDa with a pI of about 5 carried a large portion of the radioactivity even if incubation and cross-linking were performed at 4 degrees C and in the presence of inhibitors of endocytosis, suggesting that it is cross-linked at the plasma membrane. Immunoprecipitation and Western blotting experiments showed the positivity of this protein for tubulin. Trypsin treatment of intact cells ruled out the involvement of a plasma membrane surface tubulin. Release of radioactivity from cross-linked tubulin after KOH treatment (but not hydroxylamine treatment) suggested that the photoactivated ganglioside reacts with an ester-linked fatty acid anchor of tubulin. Low buoyancy, detergent-resistant membrane fractions, isolated from cells after incubation with the GM1 analogue and photoactivation, proved their enrichment in endogenous and radioactive GM1 ganglioside, sphingomyelin, cholesterol, signal transduction proteins, and tubulin. It is noteworthy that radioactive tubulin was also detected in this fraction, indicating the presence of tubulin molecules carrying a fatty acid anchor in detergent-resistant, ganglioside-enriched domains of the plasma membrane. Parallel experiments carried out with a phosphatidylcholine analogue, also carrying a diazirine group and labeled with (125)I in the fatty acid moiety, showed the specificity of tubulin interaction with GM1. Taken together, these results indicate that some tubulin molecules are associated with a lipid anchor to detergent-resistant glycolipid-enriched domains of the plasma membrane. This novel feature of membrane domains can provide a key for a better understanding of their biological role.

The luteinizing hormone-releasing hormone receptor in human prostate cancer cells: messenger ribonucleic acid expression, molecular size, and signal transduction pathway

Evidence has accumulated indicating that LHRH might behave as an autocrine/paracrine growth inhibitory factor in some peripheral tumors. However, LHRH receptors in tumor cells have not been fully characterized, so far. The present experiments were performed to analyze: 1) the messenger RNA expression; 2) the molecular size; and 3) the signal transduction pathway of LHRH receptors in prostate cancer. For these studies, the human androgen-dependent LNCaP and androgen-independent DU 145 prostate cancer cell lines were used. 1) By RT-PCR, a complementary DNA product, which hybridized with a 32P-labeled oligonucleotide probe specific for the pituitary LHRH receptor complementary DNA, was found both in LNCaP and in DU 145 cells. 2) Western blot analysis, using a monoclonal antibody raised against the human pituitary LHRH receptor, revealed the presence of a protein band of approximately 64 kDa (corresponding to the molecular mass of the pituitary receptor) in both cell lines. 3) In LNCaP and DU 145 cells, pertussis toxin completely abrogated the antiproliferative action of a LHRH agonist (LHRH-A). Moreover, LHRH-A substantially antagonized the pertussis toxin-catalyzed ADP-ribosylation of a Galpha(i) protein. Finally, LHRH-A significantly counteracted the forskolin-induced increase of intracellular cAMP levels in both cell lines. These data demonstrate that the LHRH receptor, which is present in prostate cancer cells, independently of whether they are androgen-dependent or not, corresponds to the pituitary receptor, in terms of messenger RNA expression and protein molecular size. However, at variance with the receptor of the gonadotrophs, prostate cancer LHRH receptor seems to be coupled to the Galpha(i) protein-cAMP signal transduction pathway, rather than to the Galpha(q/11)-phospholipase C signaling system. This might be responsible for the different actions of LHRH in anterior pituitary and in prostate cancer.

Comparison of three assays for HIV antibodies detection in urine to be applied to epidemiological setting

Three immune-enzymatic tests for urinary HIV antibodies were examined in order to assess their sensibility, specificity and delta value. The highest sensibility was noticed for the Seradyn test (98.8%), followed by the Wellcozyme test (98.1%) and finally the SUDS rapid test (56.8%). The resultant specificity was 98.5% for the Seradyn test, 91.3% for the Wellcozyme test and 97.3% for the SUDS test. The measurement of delta value showed a higher capability of discrimination for Seradyn test, that could be considered the most reliable for epidemiological purposes.

The dually acylated NH2-terminal domain of gi1alpha is sufficient to target a green fluorescent protein reporter to caveolin-enriched plasma membrane domains. Palmitoylation of caveolin-1 is required for the recognition of dually acylated g-protein alpha subunits in vivo

Here we investigate the molecular mechanisms that govern the targeting of G-protein alpha subunits to the plasma membrane. For this purpose, we used Gi1alpha as a model dually acylated G-protein. We fused full-length Gi1alpha or its extreme NH2-terminal domain (residues 1-32 or 1-122) to green fluorescent protein (GFP) and analyzed the subcellular localization of these fusion proteins. We show that the first 32 amino acids of Gi1alpha are sufficient to target GFP to caveolin-enriched domains of the plasma membrane in vivo, as demonstrated by co-fractionation and co-immunoprecipitation with caveolin-1. Interestingly, when dual acylation of this 32-amino acid domain was blocked by specific point mutations (G2A or C3S), the resulting GFP fusion proteins were localized to the cytoplasm and excluded from caveolin-rich regions. The myristoylated but nonpalmitoylated (C3S) chimera only partially partitioned into caveolin-containing fractions. However, both nonacylated GFP fusions (G2A and C3S) no longer co-immunoprecipitated with caveolin-1. Taken together, these results indicate that lipid modification of the NH2-terminal of Gi1alpha is essential for targeting to its correct destination and interaction with caveolin-1. Also, a caveolin-1 mutant lacking all three palmitoylation sites (C133S, C143S, and C156S) was unable to co-immunoprecipitate these dually acylated GFP-G-protein fusions. Thus, dual acylation of the NH2-terminal domain of Gi1alpha and palmitoylation of caveolin-1 are both required to stabilize and perhaps regulate this reciprocal interaction at the plasma membrane in vivo. Our results provide the first demonstration of a functional role for caveolin-1 palmitoylation in its interaction with signaling molecules.

Expression of caveolin-1 and -2 in differentiating PC12 cells and dorsal root ganglion neurons: caveolin-2 is up-regulated in response to cell injury

Caveolae are cholesterol/sphingolipid-rich microdomains of the plasma membrane that have been implicated in signal transduction and vesicular trafficking. Caveolins are a family of caveolae-associated integral membrane proteins. Caveolin-1 and -2 show the widest range of expression, whereas caveolin-3 expression is restricted to muscle cell types. It has been previously reported that little or no caveolin mRNA species are detectable in the brain by Northern blot analyses or in neuroblastoma cell lines. However, it remains unknown whether caveolins are expressed within neuronal cells. Here we demonstrate the expression of caveolin-1 and -2 in differentiating PC12 cells and dorsal root ganglion (DRG) neurons by using mono-specific antibody probes. In PC12 cells, caveolin-1 expression is up-regulated on day 4 of nerve growth factor (NGF) treatment, whereas caveolin-2 expression is transiently up-regulated early in the differentiation program and then rapidly down-regulated. Interestingly, caveolin-2 is up-regulated in response to the mechanical injury of differentiated PC12 cells; up-regulation of caveolin-2 under these conditions is strictly dependent on continued treatment with NGF. Robust expression of caveolin-1 and -2 is also observed along the entire cell surface of DRG neurons, including high levels on growth cones. These findings demonstrate that neuronal cells express caveolins.

A cysteine-3 to serine mutation of the G-protein Gi1 alpha abrogates functional activation by the alpha 2A-adrenoceptor but not interactions with the beta gamma complex

Pertussis toxin-resistant (C351G) and also palmitoylation-negative (C3S/C351G), myristoylation-negative (G2A/C351G) and combined acylation-negative (G2A/C3S/C351G) forms of the G-protein Gi1 alpha were expressed in COS-7 cells along with the porcine alpha 2A-adrenoceptor. G2A/C3S/C351G Gi1 alpha and G2A/C351G Gi1 alpha were largely cytosolic and failed to interact with the agonist-occupied alpha 2A-adrenoceptor in membrane preparations. In contrast, C351G Gi1 alpha was almost entirely particulate and the alpha 2-adrenoceptor agonist UK14304 caused a marked stimulation of its GTPase activity and binding of [35S]GTP gamma S which was not prevented by pertussis toxin treatment of the cells. C3S/C351G Gi1 alpha was present in both the particulate and cytosolic fractions but the GTPase activity of the membrane bound fraction was only slightly activated by the alpha 2A-adrenoceptor. Coexpression of C3S/C351G Gi1 alpha and the alpha 2A-adrenoceptor along with beta 1 and gamma 2 subunits increased the P2 membrane complement of the alpha subunit and increased substantially the ratio of membrane bound to cytosolic protein. However, this also failed to allow marked stimulation of high-affinity GTPase activity by the alpha 2A-adrenoceptor despite the increased proportion of G-protein in the P2 membrane fraction. Despite the low fractional activation of C3S/C351G Gi1 alpha by the alpha 2A-adrenoceptor compared to C351G Gi1 alpha, the palmitoylation-resistant G-protein caused a marked reduction in pertussis toxin-resistant, agonist (UK14304)-mediated stimulation of adenylyl cyclase activity. UK14304 caused the same degree of effect on adenylyl cyclase activity in pertussis toxin-treated cells following transfection of the same amounts of C351G Gi1 alpha and C3S/C351G Gi1 alpha, as both appear to act to sequester beta gamma subunits. By contrast, neither G2A/C351G Gi1 alpha nor G2A/C3S/C351G Gi1 alpha resulted in effective regulation of adenylyl cyclase activity.

Interaction of the G-protein G11alpha with receptors and phosphoinositidase C: the contribution of G-protein palmitoylation and membrane association

Wild-type and palmitoylation defective mutants of the murine G protein G11alpha were transfected into HEK293 cells. Wild-type G11alpha was membrane associated, Cys9Ser Cys10Ser G11alpha was present in the soluble fraction whilst both Cys9Ser G11alpha and Cys10Ser G11alpha were distributed between the fractions. Expression of the rat TRH receptor resulted in agonist stimulation of inositol phosphate accumulation. The degree of stimulation produced by TRH following co-transfection of the palmitoylation-resistant forms of G11alpha compared to the wild-type protein correlated with the amount of membrane-associated G protein.

Targeting of a G alpha subunit (Gi1 alpha) and c-Src tyrosine kinase to caveolae membranes: clarifying the role of N-myristoylation

Many signaling molecules contain the consensus protein sequence Met-Gly at their N-termini that specifies N-myristoylation. Additionally, some of these proteins contain a cysteine at position-3 (Met-Gly-Cys) that can undergo palmitoylation. As many acylated proteins [G-protein subunits (alpha and beta gamma); c-Src and Src-family tyrosine kinases; H-Ras and Ras-related GTPases; endothelial nitric oxide synthase] are known to be targeted to caveolae membranes, it has been suggested that acylation is required or greatly facilitates this targeting event. However, it remains unclear whether myristoylation of Src-family kinases is necessary or sufficient for caveolar targeting. Our current study aims at clarifying the role of myristoylation in caveolar targeting using well-characterized acylation mutants of two model proteins, namely Gi1 alpha and c-Src. Here, we have used: i) detergent-free subcellular fractionation and ii) acylation mutants of Gi1 alpha and c-Src to systematically evaluate the relative contribution of myristoylation and palmitoylation to their caveolar targeting. Myristoylation (G2A) and palmitoytation (C3S) mutants of Gi1 alpha were poorly targeted to caveolae-enriched membrane fractions, while approximately 35% of total wild-type Gi1 alpha co-fractionated with caveolin, a caveolar marker protein. Similarly, a myristoylation minus mutant of c-Src was quantitatively excluded from caveolae. In contrast to a previous study, we conclude that myristoylation of Gi1 alpha and c-Src proteins is required for their correct caveolar targeting. However, the caveolar targeting of Gi1 alpha is dramatically augmented approximately 4-fold by palmitoylation. Our current studies are directly supported by the earlier in vivo observation that N-terminal myristoylation of v-Src is required for v-Src to phosphorylate caveolin on tyrosine residues in intact cells.

Chronic treatment with a synthetic cannabinoid CP-55,940 alters G-protein expression in the rat central nervous system

Prolonged exposure of rats to the synthetic cannabinoid receptor ligand, CP-55,940 (0.4 mg/kg, i.p. for 11 days), induced tolerance to analgesia, to the reduction in spontaneous locomotor activity and the incidence of splayed hind limbs. One hour after the last injection on day 11, the rats were killed and in situ hybridization was used to investigate the effect of treatment on G-protein alpha-subunit expression throughout the brain. Chronic cannabinoid exposure markedly reduced G alpha(s), G alpha(i) and G alpha(o) mRNA levels. The message for the alpha(s)-subunit was decreased in all the brain areas containing the basal autoradiographic signal; the decrease ranging from 25% in the thalamus to 45% in the mesencephalon. Also the basal G alpha(i) expression was reduced in tolerant rats showing the greatest decrease in the forebrain (63%) in the cerebellum (58%) and in the mesencephalon (38%). The reduction in G alpha(o) expression (25%) was more localized, being present only in the rostral portion of the brain (cortex, striatum and olfactory area). The alterations in alpha-subunits gene expression were not followed by any change in the amount of proteins. Our results indicate that, besides the receptor modification, alteration to the G-protein expression could be a molecular event associated with the development of cannabinoid tolerance.

Cholera toxin effects on body temperature changes induced by morphine

The present study evaluates the influence of cholera toxin and its B-subunit on thermic responses to morphine in the rats. The holotoxin (1 microg/rat) and the B-subunit (5 microg) were administered ICV and three days later rats were challenged ICV with morphine and tested for changes of body temperature. Cholera toxin, but not its B-subunit, modified the time course of the hyperthermic response induced by a low dose of morphine (2.5 microg), converted the hypothermia due to a higher dose of morphine (18 microg) to a consistent hyperthermia and only partially reduced the greater hypothermia induced by 36 microg of morphine. Cholera toxin-induced modifications of thermic responses to morphine were paralleled with a decreased Gs(alpha) immunoreactivity and a reduced ability for the toxin to catalyse the "in vitro" ADP-ribosylation of Gs(alpha) in hypothalamic membranes. In contrast, at the same time when morphine-induced effects on body temperature were assessed, no changes in pertussis toxin-mediated ADP-ribosylation of Gi(alpha)/Go(alpha), or basal adenylate cyclase activity, or binding of mu-opioid receptor selective ligand [3H]-DAMGO were observed in hypothalamic areas from rats treated with cholera toxin. These findings suggest that adaptative events secondary to prolonged activation of Gs(alpha) play a role in the modifications of thermic responses to morphine induced by CTX.

Pulmonary sporotrichosis with hyphae in a human immunodeficiency virus-infected patient. A case report

BACKGROUND

Pulmonary sporotrichosis is a rare event. Sporothrix schenckii is a dimorphic fungus and develops at 37 degrees C in yeast form. Usually hyphae are not observed in tissues, although their presence has been occasionally demonstrated in biopsies.

CASE

A 37-year-old man, human immunodeficiency virus-1 positive, with a CD4 cell count of 345/mm3, developed a productive cough. A sputum smear revealed the presence of a large amount of long, thin, septated micelia. The hyphae bore oval, sessile conidia. Cultures of sputum yielded numerous colonies of S schenckii.

CONCLUSION

This is the first report of hyphae of S schenckii in sputum. This case emphasizes the possibilities of cytology for the diagnosis of mycotic infections. Fungi have typical morphologies, and it is possible, on the basis of microscopic evidence, to suspect the nature of the infection early and thus to direct culture procedures.

Albendazole treatment of human hydatid tissue

The effect of albendazole was studied in 12 patients with cystic hydatid disease (CHD) of the liver. Six patients received albendazole continuously for 6 months, while 6 patients received albendazole for 6 courses of 4 weeks with a 2 week drug-free interval between cycles. The continuous therapy proved successful, with stable involution at the follow-up at 24 months, while the patients treated with discontinuous therapy showed improvement or relapse. In our experience, continuous therapy was more effective and can be considered to be a suitable alternative or percutaneous therapy in uncomplicated hydatid liver disease, as an initial treatment.

Chemical inhibition of myristoylation of the G-protein Gi1 alpha by 2-hydroxymyristate does not interfere with its palmitoylation or membrane association. Evidence that palmitoylation, but not myristoylation, regulates membrane attachment

The alpha-subunit of the G-protein Gi1 alpha is normally dually acylated at its N-terminus with the saturated fatty acids myristate and palmitate. Inhibition of protein myristoylation by treatment with 2-hydroxymyristate prevented neither the incorporation of [3H]palmitate nor the membrane association of this protein when expressed in the COS cells. Construction of a mutant of Gi1 alpha in which serine-6 was replaced by aspartic acid prevented both myristoylation and palmitoylation, and the expressed protein was found primarily in the cytoplasmic fraction. These data indicate the myristoylation is not an absolute requirement for palmitoylation of Gi1 alpha and that palmitoylation, but not myristoylation, plays a key role in membrane association of this G-protein alpha-subunit.

Morphine withdrawal syndrome and G protein expression: a study of the time course in the rat central nervous system

We followed the changes in G protein alpha subunit expression and levels throughout the brain during the naltrexone-precipitated withdrawal syndrome in morphine-dependent rats. Intraperitoneally injected naltrexone (10 mg/kg) in rats made tolerant to morphine resulted in sustained withdrawal. Additional naltrexone doses 6, 24 and 72 h later still induced a significant abstinence syndrome. At the fifth naltrexone injection (8 days later) counted signs were completely resolved but checked ones were not. Besides the behavioural modifications, opiate withdrawal affected G protein expression in the central nervous system. In situ hybridization showed that G alpha s and G alpha o mRNA, whose levels are increased in tolerance, changed further during opiate withdrawal. Specifically, as alpha s mRNA in the hypothalamus was reduced after the first naltrexone injection and reached the control level with subsequent doses. However, alpha a mRNA expression in the olfactory system remained elevated after repeated naltrexone injections, declining to the control value of only after the fifth dose. The amounts of G alpha s and G alpha o protein closely followed the time course of mRNA. The relationship between behavioural and biochemical parameters is discussed, together with the regional selectivity of the modifications.