Effect of dietary docosahexaenoic acid on rhodopsin content and packing in photoreceptor cell membranes.

Docosahexaenoic acid (DHA) is enriched in photoreceptor cell membranes. DHA deficiency impairs vision due to photoreceptor cell dysfunction, which is caused, at least in part, by reduced activity of rhodopsin, the light receptor that initiates phototransduction. It is unclear how the depletion of membrane DHA impacts the structural properties of rhodopsin and, in turn, its activity. Atomic force microscopy (AFM) was used to assess the impact of DHA deficiency on membrane structure and rhodopsin organization. AFM revealed that signaling impairment in photoreceptor cells is independent of the oligomeric status of rhodopsin and causes adaptations in photoreceptor cells where the content and density of rhodopsin in the membrane is increased. Functional and structural changes caused by DHA deficiency were reversible.

Differential effects of inhibitory G protein isoforms on G protein-gated inwardly rectifying K+ currents in adult murine atria.

G protein-gated inwardly rectifying K+ (GIRK) channels are the major inwardly rectifying K+ currents in cardiac atrial myocytes and an important determinant of atrial electrophysiology. Inhibitory G protein α-subunits can both mediate activation via acetylcholine but can also suppress basal currents in the absence of agonist. We studied this phenomenon using whole cell patch clamping in murine atria from mice with global genetic deletion of Gαi2, combined deletion of Gαi1/Gαi3, and littermate controls. We found that mice with deletion of Gαi2 had increased basal and agonist-activated currents, particularly in the right atria while in contrast those with Gαi1/Gαi3 deletion had reduced currents. Mice with global genetic deletion of Gαi2 had decreased action potential duration. Tissue preparations of the left atria studied with a multielectrode array from Gαi2 knockout mice showed a shorter effective refractory period, with no change in conduction velocity, than littermate controls. Transcriptional studies revealed increased expression of GIRK channel subunit genes in Gαi2 knockout mice. Thus different G protein isoforms have differential effects on GIRK channel behavior and paradoxically Gαi2 act to increase basal and agonist-activated GIRK currents. Deletion of Gαi2 is potentially proarrhythmic in the atria.

Conditional Deletion of Ric-8b in Olfactory Sensory Neurons Leads to Olfactory Impairment.

The olfactory system can discriminate a vast number of odorants. This ability derives from the existence of a large family of odorant receptors expressed in the cilia of the olfactory sensory neurons. Odorant receptors signal through the olfactory-specific G-protein subunit, Gαolf. Ric-8b, a guanine nucleotide exchange factor, interacts with Gαolf and can amplify odorant receptor signal transduction in vitro To explore the function of Ric-8b in vivo, we generated a tissue specific knock-out mouse by crossing OMP-Cre transgenic mice to Ric-8b floxed mice. We found that olfactory-specific Ric-8b knock-out mice of mixed sex do not express the Gαolf protein in the olfactory epithelium. We also found that in these mice, the mature olfactory sensory neuron layer is reduced, and that olfactory sensory neurons show increased rate of cell death compared with wild-type mice. Finally, behavioral tests showed that the olfactory-specific Ric-8b knock-out mice show an impaired sense of smell, even though their motivation and mobility behaviors remain normal.SIGNIFICANCE STATEMENT Ric-8b is a guanine nucleotide exchange factor (GEF) expressed in the olfactory epithelium and in the striatum. Ric-8b interacts with the olfactory Gαolf subunit, and can amplify odorant signaling through odorant receptors in vitro However, the functional significance of this GEF in the olfactory neurons in vivo remains unknown. We report that deletion of Ric-8b in olfactory sensory neurons prevents stable expression of Gαolf. In addition, we demonstrate that olfactory neurons lacking Ric-8b (and consequently Gαolf) are more susceptible to cell death. Ric-8b conditional knock-out mice display impaired olfactory guided behavior. Our results reveal that Ric-8b is essential for olfactory function, and suggest that it may also be essential for Gαolf-dependent functions in the brain.

Autophagy-mediated catabolism of visual transduction proteins prevents retinal degeneration.

Autophagy is a lysosomal degradation pathway critical to preventing the accumulation of cytotoxic proteins. Deletion of the essential autophagy gene Atg5 from the rod photoreceptors of the retina (atg5Δrod mouse) results in the accumulation of the phototransduction protein transducin and the degeneration of these neurons. The purpose of this study is to test the hypothesis that autophagic degradation of visual transduction proteins prevents retinal degeneration. Targeted deletion of both Gnat1 (a gene encoding the α subunit of the heterotrimeric G-protein transducin) and Atg5 in the rod photoreceptors resulted in a significantly decreased rate of rod cell degeneration as compared to the atg5Δrod mouse retina, and considerable preservation of photoreceptors. Supporting this we used a novel technique to immunoprecipitate green fluorescent protein (GFP)-tagged autophagosomes from the retinas of the GFP-LC3 mice and demonstrated that the visual transduction proteins transducin and ARR/arrestin are associated with autophagosome-specific proteins. Altogether, this study shows that degradation of phototransduction proteins by autophagy is necessary to prevent retinal degeneration. In addition, we demonstrate a simple and easily reproducible immunoisolation technique for enrichment of autophagosomes from the GFP-LC3 mouse retina, providing a novel application to the study of autophagosome contents across different organs and specific cell types in vivo.

GnRH Neuron-Specific Ablation of Gαq/11 Results in Only Partial Inactivation of the Neuroendocrine-Reproductive Axis in Both Male and Female Mice: In Vivo Evidence for Kiss1r-Coupled Gαq/11-Independent GnRH Secretion.

The gonadotropin-releasing hormone (GnRH) is the master regulator of fertility and kisspeptin (KP) is a potent trigger of GnRH secretion from GnRH neurons. KP signals via KISS1R, a Gαq/11-coupled receptor, and mice bearing a global deletion of Kiss1r (Kiss1r(-/-)) or a GnRH neuron-specific deletion of Kiss1r (Kiss1r(d/d)) display hypogonadotropic hypogonadism and infertility. KISS1R also signals via ß-arrestin, and in mice lacking ß-arrestin-1 or -2, KP-triggered GnRH secretion is significantly diminished. Based on these findings, we hypothesized that ablation of Gαq/11 in GnRH neurons would diminish but not completely block KP-triggered GnRH secretion and that Gαq/11-independent GnRH secretion would be sufficient to maintain fertility. To test this, Gnaq (encodes Gαq) was selectively inactivated in the GnRH neurons of global Gna11 (encodes Gα11)-null mice by crossing Gnrh-Cre and Gnaq(fl/fl);Gna11(-/-) mice. Experimental Gnaq(fl/fl);Gna11(-/-);Gnrh-Cre (Gnaq(d/d)) and control Gnaq(fl/fl);Gna11(-/-) (Gnaq(fl/fl)) littermate mice were generated and subjected to reproductive profiling. This process revealed that testicular development and spermatogenesis, preputial separation, and anogenital distance in males and day of vaginal opening and of first estrus in females were significantly less affected in Gnaq(d/d) mice than in previously characterized Kiss1r(-/-) or Kiss1r(d/d) mice. Additionally, Gnaq(d/d) males were subfertile, and although Gnaq(d/d) females did not ovulate spontaneously, they responded efficiently to a single dose of gonadotropins. Finally, KP stimulation triggered a significant increase in gonadotropins and testosterone levels in Gnaq(d/d) mice. We therefore conclude that the milder reproductive phenotypes and maintained responsiveness to KP and gonadotropins reflect Gαq/11-independent GnRH secretion and activation of the neuroendocrine-reproductive axis in Gnaq(d/d) mice. SIGNIFICANCE STATEMENT: The gonadotropin-releasing hormone (GnRH) is the master regulator of fertility. Over the last decade, several studies have established that the KISS1 receptor, KISS1R, is a potent trigger of GnRH secretion and inactivation of KISS1R on the GnRH neuron results in infertility. While KISS1R is best understood as a Gαq/11-coupled receptor, we previously demonstrated that it could couple to and signal via non-Gαq/11-coupled pathways. The present study confirms these findings and, more importantly, while it establishes Gαq/11-coupled signaling as a major conduit of GnRH secretion, it also uncovers a significant role for non-Gαq/11-coupled signaling in potentiating reproductive development and function. This study further suggests that by augmenting signaling via these pathways, GnRH secretion can be enhanced to treat some forms of infertility.

Gαq controls rheumatoid arthritis via regulation of Th17 differentiation.

Gαq, the α-subunit of Gq protein, is ubiquitously expressed in mammalian cells. It initially attracted attention for its physiological significance in cardiovascular system. In recent years, studies have also indicated the important roles of Gαq in regulating immunity, supplying us a new insight into the mechanism of immune regulation. T helper type 17 (Th17) cells are potent inducers of tissue inflammation. Many studies have shown that Th17 cells are major effector cells in the pathogenesis of many experimental autoimmune diseases and human inflammatory conditions such as rheumatoid arthritis (RA). One of our previous studies has shown that Gαq negatively controls the disease activity of RA. However, how Gαq controls the pathogenesis of autoimmune disease is not clear. Whether this effect is via the regulation of Th17 differentiation is still not known. We aimed to find out the role of Gαq in control of Th17 differentiation. We investigated the relationship between Gαq and Th17 in RA patients. We then investigated the mechanism of how Gαq regulated Th17 differentiation by using Gnaq(-/-) mice. We observed that the expression of Gαq was negatively associated with interleukin-17A expression in RA patients, indicating that Gαq negatively controlled the differentiation of Th17 cells. By using Gnaq(-/-) mice, we demonstrated that Gαq inhibited the differentiation of Th17 cell via regulating the activity of extracellular signal-regulated kinase-1/2 to control the expression of STAT3 (signal transducer and activator of transcription 3) and RORα (RAR-related orphan receptor-α). These data suggest the possibility of targeting Gαq to develop a novel therapeutic regimen for autoimmune disease.

Photoresponse diversity among the five types of intrinsically photosensitive retinal ganglion cells.

Intrinsically photosensitive retinal ganglion cells (ipRGCs) mediate non-image-forming visual responses, including pupillary constriction, circadian photoentrainment and suppression of pineal melatonin secretion. Five morphological types of ipRGCs, M1-M5, have been identified in mice. In order to understand their functions better, we studied the photoresponses of all five cell types, by whole-cell recording from fluorescently labelled ipRGCs visualized using multiphoton microscopy. All ipRGC types generated melanopsin-based ('intrinsic') as well as synaptically driven ('extrinsic') light responses. The intrinsic photoresponses of M1 cells were lower threshold, higher amplitude and faster than those of M2-M5. The peak amplitudes of extrinsic light responses differed among the ipRGC types; however, the responses of all cell types had comparable thresholds, kinetics and waveforms, and all cells received rod input. While all five types exhibited inhibitory amacrine-cell and excitatory bipolar-cell inputs from the 'on' channel, M1 and M3 received additional 'off'-channel inhibition, possibly through their 'off'-sublamina dendrites. The M2-M5 ipRGCs had centre-surround-organized receptive fields, implicating a capacity to detect spatial contrast. In contrast, the receptive fields of M1 cells lacked surround antagonism, which might be caused by the surround of the inhibitory input nullifying the surround of the excitatory input. All ipRGCs responded robustly to a wide range of motion speeds, and M1-M4 cells appeared tuned to different speeds, suggesting that they might analyse the speed of motion. Retrograde labelling revealed that M1-M4 cells project to the superior colliculus, suggesting that the contrast and motion information signalled by these cells could be used by this sensorimotor area to detect novel objects and motion in the visual field.

Substrate specificity of Pasteurella multocida toxin for α subunits of heterotrimeric G proteins.

Pasteurella multocida is the causative agent of a number of epizootic and zoonotic diseases. Its major virulence factor associated with atrophic rhinitis in animals and dermonecrosis in bite wounds is P. multocida toxin (PMT). PMT stimulates signal transduction pathways downstream of heterotrimeric G proteins, leading to effects such as mitogenicity, blockade of apoptosis, or inhibition of osteoblast differentiation. On the basis of Gα(i2), it was demonstrated that the toxin deamidates an essential glutamine residue of the Gα(i2) subunit, leading to constitutive activation of the G protein. Here, we studied the specificity of PMT for its G-protein targets by mass spectrometric analyses and by utilizing a monoclonal antibody, which recognizes specifically G proteins deamidated by PMT. The studies revealed deamidation of 3 of 4 families of heterotrimeric G proteins (Gα(q/11), Gα(i1,2,3), and Gα(12/13) of mouse or human origin) by PMT but not by a catalytic inactive toxin mutant. With the use of G-protein fragments and chimeras of responsive or unresponsive G proteins, the structural basis for the discrimination of heterotrimeric G proteins was studied. Our results elucidate substrate specificity of PMT on the molecular level and provide evidence for the underlying structural reasons of substrate discrimination.

Restoration of vision after transplantation of photoreceptors.

Cell transplantation is a potential strategy for treating blindness caused by the loss of photoreceptors. Although transplanted rod-precursor cells are able to migrate into the adult retina and differentiate to acquire the specialized morphological features of mature photoreceptor cells, the fundamental question remains whether transplantation of photoreceptor cells can actually improve vision. Here we provide evidence of functional rod-mediated vision after photoreceptor transplantation in adult Gnat1−/− mice, which lack rod function and are a model of congenital stationary night blindness. We show that transplanted rod precursors form classic triad synaptic connections with second-order bipolar and horizontal cells in the recipient retina. The newly integrated photoreceptor cells are light-responsive with dim-flash kinetics similar to adult wild-type photoreceptors. By using intrinsic imaging under scotopic conditions we demonstrate that visual signals generated by transplanted rods are projected to higher visual areas, including V1. Moreover, these cells are capable of driving optokinetic head tracking and visually guided behaviour in the Gnat1−/− mouse under scotopic conditions. Together, these results demonstrate the feasibility of photoreceptor transplantation as a therapeutic strategy for restoring vision after retinal degeneration.

UNC119 is required for G protein trafficking in sensory neurons.

UNC119 is widely expressed among vertebrates and other phyla. We found that UNC119 recognized the acylated N terminus of the rod photoreceptor transducin α (Tα) subunit and Caenorhabditis elegans G proteins ODR-3 and GPA-13. The crystal structure of human UNC119 at 1.95-Å resolution revealed an immunoglobulin-like ß-sandwich fold. Pulldowns and isothermal titration calorimetry revealed a tight interaction between UNC119 and acylated Gα peptides. The structure of co-crystals of UNC119 with an acylated Tα N-terminal peptide at 2.0 Å revealed that the lipid chain is buried deeply into UNC119's hydrophobic cavity. UNC119 bound Tα-GTP, inhibiting its GTPase activity, thereby providing a stable UNC119-Tα-GTP complex capable of diffusing from the inner segment back to the outer segment after light-induced translocation. UNC119 deletion in both mouse and C. elegans led to G protein mislocalization. Thus, UNC119 is a Gα subunit cofactor essential for G protein trafficking in sensory cilia.

Rod photoreceptors drive circadian photoentrainment across a wide range of light intensities.

In mammals, synchronization of the circadian pacemaker in the hypothalamus is achieved through direct input from the eyes conveyed by intrinsically photosensitive retinal ganglion cells (ipRGCs). Circadian photoentrainment can be maintained by rod and cone photoreceptors, but their functional contributions and their retinal circuits that impinge on ipRGCs are not well understood. Using mice that lack functional rods or in which rods are the only functional photoreceptors, we found that rods were solely responsible for photoentrainment at scotopic light intensities. Rods were also capable of driving circadian photoentrainment at photopic intensities at which they were incapable of supporting a visually guided behavior. Using mice in which cone photoreceptors were ablated, we found that rods signal through cones at high light intensities, but not at low light intensities. Thus, rods use two distinct retinal circuits to drive ipRGC function to support circadian photoentrainment across a wide range of light intensities.

Deletion of GRK1 causes retina degeneration through a transducin-independent mechanism.

Rpe65(-/-) mice are unable to produce 11-cis-retinal, the chromophore of visual pigments. Consequently, the pigment is present as the apoprotein opsin with a minute level of pigment containing 9-cis-retinal as chromophore. Notably, a 10-20% fraction of this opsin is mono-phosphorylated independently of light conditions. To determine the role of rhodopsin kinase (GRK1) in phosphorylating this opsin and to test whether eliminating this phosphorylation would accelerate photoreceptor degeneration, we generated the Rpe65(-/-)Grk1(-/-) mouse. The retinae of Rpe65(-/-)Grk1(-/-) mice had negligible opsin phosphorylation, extensive degeneration with decreased opsin levels, and diminished light-evoked rod responses relative to Rpe65(-/-) mice. These data show that opsin phosphorylation in the Rpe65(-/-) mouse is due to the action of GRK1 and is neuroprotective. However, despite the higher activity of unphosphorylated opsin, the severe loss of opsin in the rapidly degenerating Rpe65(-/-)Grk1(-/-) mice resulted in lower overall opsin activity and in higher rod sensitivity compared with Rpe65(-/-) mice. In Rpe65(-/-)Grk1(-/-)Gnat1(-/-) mice where transduction activation was blocked, degeneration was only partially prevented. Therefore, increased opsin activity in the absence of phosphorylation was not the only mechanism for the accelerated retinal degeneration. Finally, the deletion of GRK1 triggered retinal degeneration in Grk1(-/-) mice after 1 month, even in the absence of apo-opsin. This degeneration was independent of light conditions and occurred even in the absence of transducin in Grk1(-/-)Gnat1(-/-) mice. Taken together, our results demonstrate a light-independent mechanism for retinal degeneration in the absence of GRK1, suggesting a second, not previously recognized role for that kinase.

The OFF-pathway dominance of P2X(2)-purinoceptors is formed without visual experience.

Visual input in the critical period is an important determinant of the functions of the visual system, affecting for example the formation of the ocular dominance column in the visual cortex. The final map of columnar organization is usually determined by plastic changes in the critical period, but organization is distorted without adequate visual input. Here, we examined whether formation of the OFF-pathway dominance of P2X(2)-purinoceptor signaling in the mouse retina is the result of visual experience. The P2X(2)-purinoceptor signaling pathway developed during the critical period. However, visual experience in this period produced no plastic change in the formation of the OFF-pathway dominance of P2X(2)-purinoceptor signaling. Our findings suggest that the OFF-pathway dominance of P2X(2)-signaling in the mouse retina is intrinsically programmed.

Influence of the rod photoresponse on light adaptation and circadian rhythmicity in the cone ERG.

PURPOSE: In the mammalian retina, rod and cone pathways are fundamentally intertwined, with signals from both converging on cone bipolar cells to reach retinal ganglion cells. Psychophysical and electrophysiological data suggests that, as a consequence, rod signal transduction has a suppressive effect on the activity of cone pathways. It therefore might be assumed that the balance between rod and cone input to cone bipolar cells would be subject to dynamic regulation. There is evidence of light and time-of-day dependent alterations in this parameter. Here we set out to determine the extent to which such changes in rod-cone pathway convergence explain alterations in cone pathway function associated with light adaptation and circadian phase by recording cone electroretinograms (ERGs) in mice deficient in rod phototransduction. METHODS: Cone-isolated ERGs elicited by bright flashes superimposed on a rod saturating background light were recorded from wild-type and rod transducin deficient (Gnat1(-/-)) mice. The process of light adaptation was observed by tracing changes in the ERG waveform over 20 min exposure to the background light in these genotypes, and circadian control by comparing responses at subjective midday and midnight. RESULTS: The cone ERG b-wave exhibited significantly enhanced amplitude and reduced latency (implicit time) in Gnat1(-/-) mice under all conditions. Light adaptation was associated with a robust increase in b-wave amplitude in Gnat1(-/-) mice but, in contrast to wild types, almost no change in implicit time. Gnat1(-/-) mice retained circadian rhythms in the cone ERG with b-wave amplitudes larger and latencies reduced during the subjective day. CONCLUSIONS: Rod phototransduction has a strong suppressive effect on the cone ERG. Light adaptation in cone pathways relies in part on reductions in this effect, although mechanisms intrinsic to cone pathways also play an important role. Similarly, while changes in coupling between rod and cone pathways over the course of the day may contribute to circadian regulation of the cone pathway they are not sufficient to explain circadian rhythms in the wild-type cone ERG.

A Dictyostelium chalone uses G proteins to regulate proliferation.

BACKGROUND: Several studies have shown that organ size, and the proliferation of tumor metastases, may be regulated by negative feedback loops in which autocrine secreted factors called chalones inhibit proliferation. However, very little is known about chalones, and how cells sense them. We previously identified two secreted proteins, AprA and CfaD, which act as chalones in Dictyostelium. Cells lacking AprA or CfaD proliferate faster than wild-type cells, and adding recombinant AprA or CfaD to cells slows their proliferation. RESULTS: We show here that cells lacking the G protein components Galpha8, Galpha9, and Gbeta proliferate faster than wild-type cells despite secreting normal or high levels of AprA and CfaD. Compared with wild-type cells, the proliferation of galpha8-, galpha9- and gbeta- cells are only weakly inhibited by recombinant AprA (rAprA). Like AprA and CfaD, Galpha8 and Gbeta inhibit cell proliferation but not cell growth (the rate of increase in mass and protein per nucleus), whereas Galpha9 inhibits both proliferation and growth. galpha8- cells show normal cell-surface binding of rAprA, whereas galpha9- and gbeta- cells have fewer cell-surface rAprA binding sites, suggesting that Galpha9 and Gbeta regulate the synthesis or processing of the AprA receptor. Like other ligands that activate G proteins, rAprA induces the binding of [3H]GTP to membranes, and GTPgammaS inhibits the binding of rAprA to membranes. Both AprA-induced [3H]GTP binding and the GTPgammaS inhibition of rAprA binding require Galpha8 and Gbeta but not Galpha9. Like aprA- cells, galpha8- cells have reduced spore viability. CONCLUSION: This study shows that Galpha8 and Gbeta are part of the signal transduction pathway used by AprA to inhibit proliferation but not growth in Dictyostelium, whereas Galpha9 is part of a differealnt pathway that regulates both proliferation and growth, and that a chalone signal transduction pathway uses G proteins.

Histone H3 phosphorylation is under the opposite tonic control of dopamine D2 and adenosine A2A receptors in striatopallidal neurons.

The antipsychotic agent haloperidol regulates gene transcription in striatal medium spiny neurons (MSNs) by blocking dopamine D2 receptors (D2Rs). We examined the mechanisms by which haloperidol increases the phosphorylation of histone H3, a key step in the nucleosomal response. Using bacterial artificial chromosome (BAC)-transgenic mice that express EGFP under the control of the promoter of the dopamine D1 receptor (D1R) or the D2R, we found that haloperidol induced a rapid and sustained increase in the phosphorylation of histone H3 in the striatopallidal MSNs of the dorsal striatum, with no change in its acetylation. This effect was mimicked by raclopride, a selective D2R antagonist, and prevented by the blockade of adenosine A2A receptors (A2ARs), or genetic attenuation of the A2AR-associated G protein, Galpha(olf). Mutation of the cAMP-dependent phosphorylation site (Thr34) of the 32-kDa dopamine and cAMP-regulated phosphoprotein (DARPP-32) decreased the haloperidol-induced H3 phosphorylation, supporting the role of cAMP in H3 phosphorylation. Haloperidol also induced extracellular signal-regulated kinase (ERK) phosphorylation in striatopallidal MSNs, but this effect was not implicated in H3 phosphorylation. The levels of mitogen- and stress-activated kinase 1 (MSK1), which has been reported to mediate ERK-induced H3 phosphorylation, were lower in striatopallidal than in striatonigral MSNs. Moreover, haloperidol-induced H3 phosphorylation was unaltered in MSK1-knockout mice. These data indicate that, in striatopallidal MSNs, H3 phosphorylation is controlled by the opposing actions of D2Rs and A2ARs. Thus, blockade of D2Rs promotes histone H3 phosphorylation through the A2AR-mediated activation of Galpha(olf) and inhibition of protein phosphatase-1 (PP-1) through the PKA-dependent phosphorylation of DARPP-32.

Frequent somatic mutations of GNAQ in uveal melanoma and blue naevi.

BRAF and NRAS are common targets for somatic mutations in benign and malignant neoplasms that arise from melanocytes situated in epithelial structures, and lead to constitutive activation of the mitogen-activated protein (MAP) kinase pathway. However, BRAF and NRAS mutations are absent in a number of other melanocytic neoplasms in which the equivalent oncogenic events are currently unknown. Here we report frequent somatic mutations in the heterotrimeric G protein alpha-subunit, GNAQ, in blue naevi (83%) and ocular melanoma of the uvea (46%). The mutations occur exclusively in codon 209 in the Ras-like domain and result in constitutive activation, turning GNAQ into a dominant acting oncogene. Our results demonstrate an alternative route to MAP kinase activation in melanocytic neoplasia, providing new opportunities for therapeutic intervention.

Ca2+-dependent activator proteins of secretion promote vesicular monoamine uptake.

Ca(2+)-dependent activator proteins of secretion (CAPS) 1 and 2 are essential regulators of synaptic vesicle and large dense core vesicle priming in mammalian neurons and neuroendocrine cells. CAPS1 appears to have an additional and as yet unexplained function in vesicular catecholamine uptake or storage as CAPS1-deficient chromaffin cells exhibit strongly reduced vesicular catecholamine levels. Here we describe a role of CAPS proteins in vesicular monoamine uptake. Both CAPS1 and CAPS2 promote monoamine uptake and storage mediated by the vesicular monoamine transporters VMAT1 and VMAT2. Monoamine uptake of vesicular preparations from embryonic brains of CAPS1 deletion mutants is decreased as compared with corresponding preparations from wild type littermates, and anti-CAPS1 or anti-CAPS2 antibodies inhibit monoamine sequestration by synaptic vesicles from adult mouse brain. In addition, overexpression of CAPS1 or CAPS2 enhances vesicular monoamine uptake in Chinese hamster ovary cells that stably express VMAT1 or VMAT2. CAPS function has been linked to the heterotrimeric GTPase G(o), which modulates vesicular monoamine uptake. We found that the expression of CAPS1 is decreased in brain membrane preparations from mice lacking G(o2)alpha, which may explain the reduced monoamine uptake by G(o2)alpha-deficient synaptic vesicles. Accordingly, anti-CAPS1 antibodies do not further reduce monoamine uptake by G(o2)alpha-deficient synaptic vesicles, whereas antibodies directed against CAPS2, whose expression is not altered in G(o2)alpha-deficient brain, still reduce monoamine uptake into G(o2)alpha-deficient vesicles. We conclude that CAPS proteins are involved in optimizing vesicular monoamine uptake and storage mediated by VMAT1 and VMAT2.

Role for epithelial dysregulation in early-onset colitis-associated colon cancer in Gi2-alpha-/- mice.

BACKGROUND: Inflammatory bowel disease (IBD) is a risk factor for developing colorectal cancer but the mechanisms are poorly characterized. Mice lacking the G-protein alpha subunit Gi2-alpha spontaneously develop colitis and colon cancer with high penetrance. Compared to canonical Wnt/APC signaling-based animal models of colon cancer, the tumors in Gi2-alpha-/- mice more closely recapitulate the features of IBD-associated cancers seen in humans. They are predominantly right-sided, multifocal, mucinous, and arise from areas of flat dysplasia. METHODS: In evaluating the potential contribution of epithelial Gi2-alpha signaling to this phenotype, we found that Gi2-alpha-/- colonic epithelium is hyperproliferative even before the onset of colitis, and resistant to the induction of apoptosis. We generated colon cancer cell lines overexpressing dominant-negative Gi2-alpha. RESULTS: Like other cells lacking Gi2-alpha, these cells release less arachidonic acid, an important antiinflammatory and epithelial growth regulator. They are also hyperproliferative and resistant to camptothecin-induced apoptosis and caspase-3 activation. CONCLUSIONS: The colitis-associated cancers in Gi2-alpha-/- mice appear very similar to those seen in human IBD patients, and Gi2-alpha is a direct negative regulator of colonic epithelial cell growth.

Postsynaptic mechanisms underlying responsiveness of amygdaloid neurons to cholecystokinin are mediated by a transient receptor potential-like current.

Projection neurons of mouse basolateral amygdala responded to CCK with an inward current at a holding potential of -70 mV. This response was mediated by CCK2 receptors as indicated by agonist and antagonist effectiveness, and conveyed via G-proteins of the G(q/11) family as it was abolished in gene knockout mice. Maximal current amplitude was insensitive to extracellular potassium, cesium, and calcium ions, respectively, whereas amplitude and reversal potential critically depended upon extracellular sodium concentration. The current reversed near -20 mV consistent with activation of a mixed cationic channel reminiscent of transient receptor potential (TRP) channels. Extracellular application of the non-selective TRP channel blockers 2-APB, flufenamic acid, Gd3+, and ruthenium red, respectively, inhibited CCK induced inward currents. Single cell PCR confirmed the expression of TRPC1,4,5 and coexpression of TRPC1 with TRPC4 or TRPC5 in some cells. CCK responses were associated with depolarization leading to an increase in cell excitability.