G protein-coupled estrogen receptor (GPER)/GPR30 forms a complex with the β1-adrenergic receptor, a membrane-associated guanylate kinase (MAGUK) scaffold protein, and protein kinase A anchoring protein (AKAP) 5 in MCF7 breast cancer cells

G protein-coupled receptor 30 (GPR30), also named G protein-coupled estrogen receptor (GPER), and the β1-adrenergic receptor (β1AR) are G protein-coupled receptors (GPCR) that are implicated in breast cancer progression. Both receptors contain PSD-95/Discs-large/ZO-1 homology (PDZ) motifs in their C-terminal tails through which they interact in the plasma membrane with membrane-associated guanylate kinase (MAGUK) scaffold proteins, and in turn protein kinase A anchoring protein (AKAP) 5. GPR30 constitutively and PDZ-dependently inhibits β1AR-mediated cAMP production. We hypothesized that this inhibition is a consequence of a plasma membrane complex of these receptors. Using co-immunoprecipitation, confocal immunofluorescence microscopy, and bioluminescence resonance energy transfer (BRET), we show that GPR30 and β1AR reside in close proximity in a plasma membrane complex when transiently expressed in HEK293. Deleting the GPR30 C-terminal PDZ motif (-SSAV) does not interfere with the receptor complex, indicating that the complex is not PDZ-dependent. MCF7 breast cancer cells express GPR30, β1AR, MAGUKs, and AKAP5 in the plasma membrane, and co-immunoprecipitation revealed that these proteins exist in close proximity also under native conditions. Furthermore, expression of GPR30 in MCF7 cells constitutively and PDZ-dependently inhibits β1AR-mediated cAMP production. AKAP5 also inhibits β1AR-mediated cAMP production, which is not additive with GPR30-promoted inhibition. These results argue that GPR30 and β1AR form a PDZ-independent complex in MCF7 cells through which GPR30 constitutively and PDZ-dependently inhibits β1AR signaling via receptor interaction with MAGUKs and AKAP5.

Breast cancer hypoxia in relation to prognosis and benefit from radiotherapy after breast-conserving surgery in a large, randomised trial with long-term follow-up

Background

Breast-conserving surgery followed by radiotherapy is part of standard treatment for early-stage breast cancer. Hypoxia is common in cancer and may affect the benefit of radiotherapy. Cells adapt to hypoxic stress largely via the transcriptional activity of hypoxia-inducible factor (HIF)-1α. Here, we aim to determine whether tumour HIF-1α-positivity and hypoxic gene-expression signatures associated with the benefit of radiotherapy, and outcome.

Methods

Tumour HIF-1α-status and expression of hypoxic gene signatures were retrospectively analysed in a clinical trial where 1178 women with primary T1-2N0M0 breast cancer were randomised to receive postoperative radiotherapy or not and followed 15 years for recurrence and 20 years for breast cancer death.

Results

The benefit from radiotherapy was similar in patients with HIF-1α-positive and -negative primary tumours. Both ipsilateral and any breast cancer recurrence were more frequent in women with HIF-1α-positive primary tumours (hazard ratio, HR_{0–5 yrs}1.9 [1.3–2.9], p = 0.003 and HR_{0–5 yrs} = 2.0 [1.5–2.8], p < 0.0001). Tumour HIF-1α-positivity is also associated with increased breast cancer death (HR_{0–10 years} 1.9 [1.2–2.9], p = 0.004). Ten of the 11 investigated hypoxic gene signatures correlated positively to HIF-1α-positivity, and 5 to increased rate/risk of recurrence.

Conclusions

The benefit of postoperative radiotherapy persisted in patients with hypoxic primary tumours. Patients with hypoxic primary breast tumours had an increased risk of recurrence and breast cancer death.

Plasma membrane expression of G protein-coupled estrogen receptor (GPER)/G protein-coupled receptor 30 (GPR30) is associated with worse outcome in metachronous contralateral breast cancer

Background

G protein-coupled estrogen receptor (GPER), or G protein-coupled receptor 30 (GPR30), is reported to mediate non-genomic estrogen signaling. GPR30 associates with breast cancer (BC) outcome and may contribute to tamoxifen resistance. We investigated the expression and prognostic significance of GPR30 in metachronous contralateral breast cancer (CBC) as a model of tamoxifen resistance.

Methods

Total GPR30 expression (GPR30_TOT) and plasma membrane-localized GPR30 expression (GPR30_PM) were analyzed by immunohistochemistry in primary (BC1; n_BC1 = 559) and contralateral BC (BC2; n_BC2 = 595), and in lymph node metastases (LGL; n_LGL1 = 213; n_LGL2 = 196). Death from BC (BCD), including BC death or death after documented distant metastasis, was used as primary end-point.

Results

GPR30_PM in BC2 and LGL2 were associated with increased risk of BCD (HR_BC2 = 1.7, p = 0.03; HR_LGL2 = 2.0; p = 0.02). In BC1 and BC2, GPR30_PM associated with estrogen receptor (ER)-negativity (p_BC1<0.0001; p_BC2<0.0001) and progesterone receptor (PR)-negativity (p_BC1 = 0.0007; p_BC2<0.0001). The highest GPR30_TOT and GPR30_PM were observed in triple-negative BC. GPR30_PM associated with high Ki67 staining in BC1 (p<0.0001) and BC2 (p<0.0001). GPR30_TOT in BC2 did not associate with tamoxifen treatment for BC1. However, BC2 that were diagnosed during tamoxifen treatment were more likely to express GPR30_PM than BC2 diagnosed after treatment completion (p = 0.01). Furthermore, a trend was observed that patients with GPR30_PM in an ER-positive BC2 had greater benefit from tamoxifen treatment.

Conclusion

PM-localized GPR30 staining is associated with increased risk of BC death when expressed in BC2 and LGL2. Additionally, PM-localized GPR30 correlates with prognostic markers of worse outcome, such as high Ki67 and a triple-negative subtype. Therefore, PM-localized GPR30 may be an interesting new target for therapeutic exploitation. We found no clear evidence that total GPR30 expression is affected by tamoxifen exposure during development of metachronous CBC, or that GPR30 contributes to tamoxifen resistance.

Rapid Aldosterone-Mediated Signaling in the DCT Increases Activity of the Thiazide-Sensitive NaCl Cotransporter

BACKGROUND

The NaCl cotransporter NCC in the kidney distal convoluted tubule (DCT) regulates urinary NaCl excretion and BP. Aldosterone increases NaCl reabsorption via NCC over the long-term by altering gene expression. But the acute effects of aldosterone in the DCT are less well understood.

METHODS

Proteomics, bioinformatics, and cell biology approaches were combined with animal models and gene-targeted mice.

RESULTS

Aldosterone significantly increases NCC activity within minutes in vivo or ex vivo. These effects were independent of transcription and translation, but were absent in the presence of high potassium. In vitro, aldosterone rapidly increased intracellular cAMP and inositol phosphate accumulation, and altered phosphorylation of various kinases/kinase substrates within the MAPK/ERK, PI3K/AKT, and cAMP/PKA pathways. Inhibiting GPR30, a membrane-associated receptor, limited aldosterone's effects on NCC activity ex vivo, and NCC phosphorylation was reduced in GPR30 knockout mice. Phosphoproteomics, network analysis, and in vitro studies determined that aldosterone activates EGFR-dependent signaling. The EGFR immunolocalized to the DCT and EGFR tyrosine kinase inhibition decreased NCC activity ex vivo and in vivo.

CONCLUSIONS

Aldosterone acutely activates NCC to modulate renal NaCl excretion.

G protein-coupled estrogen receptor 1 (GPER1)/GPR30 increases ERK1/2 activity through PDZ motif-dependent and -independent mechanisms

G protein-coupled receptor 30 (GPR30), also called G protein-coupled estrogen receptor 1 (GPER1), is thought to play important roles in breast cancer and cardiometabolic regulation, but many questions remain about ligand activation, effector coupling, and subcellular localization. We showed recently that GPR30 interacts through the C-terminal type I PDZ motif with SAP97 and protein kinase A (PKA)-anchoring protein (AKAP) 5, which anchor the receptor in the plasma membrane and mediate an apparently constitutive decrease in cAMP production independently of G_i/o Here, we show that GPR30 also constitutively increases ERK1/2 activity. Removing the receptor PDZ motif or knocking down specifically AKAP5 inhibited the increase, showing that this increase also requires the PDZ interaction. However, the increase was inhibited by pertussis toxin as well as by wortmannin but not by AG1478, indicating that G_i/o and phosphoinositide 3-kinase (PI3K) mediate the increase independently of epidermal growth factor receptor transactivation. FK506 and okadaic acid also inhibited the increase, implying that a protein phosphatase is involved. The proposed GPR30 agonist G-1 also increased ERK1/2 activity, but this increase was only observed at a level of receptor expression below that required for the constitutive increase. Furthermore, deleting the PDZ motif did not inhibit the G-1-stimulated increase. Based on these results, we propose that GPR30 increases ERK1/2 activity via two G_i/o-mediated mechanisms, a PDZ-dependent, apparently constitutive mechanism and a PDZ-independent G-1-stimulated mechanism.

C1-Inhibitor Decreases the Release of Vasculitis-Like Chemotactic Endothelial Microvesicles

The kinin system is activated during vasculitis and may contribute to chronic inflammation. C1-inhibitor is the main inhibitor of the kinin system. In this study, we investigated the presence of the kinin B1 receptor on endothelial microvesicles and its contribution to the inflammatory process. Compared with controls (n=15), patients with acute vasculitis (n=12) had markedly higher levels of circulating endothelial microvesicles, identified by flow cytometry analysis, and significantly more microvesicles that were positive for the kinin B1 receptor (P<0.001). Compared with microvesicles from wild-type cells, B1 receptor-positive microvesicles derived from transfected human embryonic kidney cells induced a significant neutrophil chemotactic effect, and a B1 receptor antagonist blocked this effect. Likewise, patient plasma induced neutrophil chemotaxis, an effect decreased by reduction of microvesicle levels and by blocking the B1 receptor. We used a perfusion system to study the effect of patient plasma (n=6) and control plasma (n=6) on the release of microvesicles from glomerular endothelial cells. Patient samples induced the release of significantly more B1 receptor-positive endothelial microvesicles than control samples, an effect abrogated by reduction of the microvesicles in the perfused samples. Perfusion of C1-inhibitor-depleted plasma over glomerular endothelial cells promoted excessive release of B1 receptor-positive endothelial microvesicles compared with normal plasma, an effect significantly decreased by addition of C1-inhibitor or B1 receptor-antagonist. Thus, B1 receptor-positive endothelial microvesicles may contribute to chronic inflammation by inducing neutrophil chemotaxis, and the reduction of these microvesicles by C1-inhibitor should be explored as a potential treatment for neutrophil-induced inflammation.

G protein-coupled receptor 30 (GPR30) forms a plasma membrane complex with membrane-associated guanylate kinases (MAGUKs) and protein kinase A-anchoring protein 5 (AKAP5) that constitutively inhibits cAMP production

GPR30, or G protein-coupled estrogen receptor, is a G protein-coupled receptor reported to bind 17β-estradiol (E2), couple to the G proteins Gs and Gi/o, and mediate non-genomic estrogenic responses. However, controversies exist regarding the receptor pharmacological profile, effector coupling, and subcellular localization. We addressed the role of the type I PDZ motif at the receptor C terminus in receptor trafficking and coupling to cAMP production in HEK293 cells and CHO cells ectopically expressing the receptor and in Madin-Darby canine kidney cells expressing the native receptor. GPR30 was localized both intracellularly and in the plasma membrane and subject to limited basal endocytosis. E2 and G-1, reported GPR30 agonists, neither stimulated nor inhibited cAMP production through GPR30, nor did they influence receptor localization. Instead, GPR30 constitutively inhibited cAMP production stimulated by a heterologous agonist independently of Gi/o. Moreover, siRNA knockdown of native GPR30 increased cAMP production. Deletion of the receptor PDZ motif interfered with inhibition of cAMP production and increased basal receptor endocytosis. GPR30 interacted with membrane-associated guanylate kinases, including SAP97 and PSD-95, and protein kinase A-anchoring protein (AKAP) 5 in the plasma membrane in a PDZ-dependent manner. Knockdown of AKAP5 or St-Ht31 treatment, to disrupt AKAP interaction with the PKA RIIβ regulatory subunit, decreased inhibition of cAMP production, and St-Ht31 increased basal receptor endocytosis. Therefore, GPR30 forms a plasma membrane complex with a membrane-associated guanylate kinase and AKAP5, which constitutively attenuates cAMP production in response to heterologous agonists independently of Gi/o and retains receptors in the plasma membrane.

Lack of G protein-coupled estrogen receptor (GPER) in the plasma membrane is associated with excellent long-term prognosis in breast cancer

G protein-coupled estrogen receptor (GPER), or GPR30, is a membrane receptor reported to mediate non-genomic estrogen responses. Tamoxifen is a partial agonist at GPER in vitro. Here, we investigated if GPER expression is prognostic in primary breast cancer, if the receptor is treatment-predictive for adjuvant tamoxifen, and if receptor subcellular localization has any impact on the prognostic value. Total and plasma membrane (PM) GPER expression was analyzed by immunohistochemistry in breast tumors from 742 postmenopausal lymph node-negative patients subsequently randomized for tamoxifen treatment for 2-5 years versus no systemic treatment, regardless of estrogen receptor (ER) status, and with a median follow-up of 17 years for patients free of event. PM GPER expression was a strong independent prognostic factor for poor prognosis in breast cancer without treatment-predictive information for tamoxifen. In the tamoxifen-treated ER-positive and progesterone receptor (PgR)-positive patient subgroup, the absence of PM GPER (53 % of all ER-positive tumors) predicted 91 % 20-year distant disease-free survival, compared to 73 % in the presence of GPER (p = 0.001). Total GPER expression showed positive correlations with ER and PgR and negative correlation with histological grade, but the correlations were biphasic. On the other hand, PM GPER expression showed strong negative correlations with ER and PgR, and strong positive correlation with HER2 overexpression and high histological grade. GPER overexpression and PM localization are critical events in breast cancer progression, and lack of GPER in the PM is associated with excellent long-term prognosis in ER-positive and PgR-positive tamoxifen-treated primary breast cancer.

The G protein-coupled estrogen receptor 1 (GPER1/GPR30) agonist G-1 regulates vascular smooth muscle cell Ca²⁺ handling

The G protein-coupled estrogen receptor GPER1/GPR30 is implicated in blood pressure regulation but the mechanisms are not identified. Here, we hypothesize that GPER1 controls blood pressure by regulating vascular smooth muscle cell Ca(2+) handling. Treatment with the GPER1 agonist G-1 (in the µM concentration range) acutely reduced spontaneous and synchronous Ca(2+) spike activity in A7r5 vascular smooth muscle cells expressing mRNA for GPER1. Furthermore, G-1 (1 µM) attenuated the thromboxane A2 analogue U46619-stimulated Ca(2+) spike activity but had no effect on the U46619-induced increase in the basal level of Ca(2+). The voltage-sensitive L-type Ca(2+) channel blocker nifedipine (100 nM) reduced Ca(2+) spike activity similar to G-1. Pharmacological, but not physiological, concentrations of the estrogen 17β-estradiol reduced Ca(2+) spike activity. The GPER1 antagonist G-15 blocked G-1-induced downregulation of Ca(2+) spike activity, supporting a GPER1-dependent mechanism. G-1 (1 µM) and nifedipine (100 nM) attenuated the 30-mM KCl-evoked rise in intracellular Ca(2+) concentration, suggesting that G-1 blocks inflow of Ca(2+) via voltage-sensitive Ca(2+) channels. In conclusion, we demonstrate that the GPER1 agonist G-1 regulates vascular smooth muscle cell Ca(2+) handling by lowering Ca(2+) spike activity, suggesting a role for this mechanism in GPER1-mediated control of blood pressure. © 2013 S. Karger AG, Basel.

G protein-coupled estrogen receptor is apoptotic and correlates with increased distant disease-free survival of estrogen receptor-positive breast cancer patients

PURPOSE

G protein-coupled estrogen receptor 1 (GPER1), previously named GPR30, is a membrane receptor reported to mediate nongenomic estrogen responses. We investigated if GPER1 expression correlates with any clinicopathologic variables and distant disease-free survival (DDFS) in patients with breast cancer, if any prognostic impact of the receptor is dependent on estrogen receptor-α (ER-α) status, and if the receptor impacts apoptotic signaling in ER-positive breast cancer cells.

EXPERIMENTAL DESIGN

GPER1 expression was analyzed by immunohistochemistry in breast tumors from 273 pre- and postmenopausal stage II patients, all treated with adjuvant tamoxifen for 2 years (cohort I) and from 208 premenopausal lymph node-negative patients, of which 87% were not subjected to any adjuvant systemic treatment (cohort II). GPER1-dependent proapoptotic signaling was analyzed in MCF7 cells with and without GPER1 knockdown, T47D cells, HEK293 cells (HEK), and HEK stably expressing GPER1 (HEK-R).

RESULTS

GPER1 positively correlates with ER and progesterone receptor expression. Multivariate analysis showed that GPER1 is an independent prognostic marker of increased 10-year DDFS in the ER-positive subgroup. HEK-R has higher basal proapoptotic signaling compared with HEK including increased cytochrome C release, caspase-3 cleavage, PARP cleavage, and decreased cell viability. Treating HEK-R with the proteasome inhibitor epoxomicin, to decrease GPER1 degradation, further increases receptor-dependent proapoptotic signaling. Also, GPER1 knockdown decreases basal and agonist-stimulated proapoptotic receptor signaling in MCF7 cells.

CONCLUSIONS

GPER1 is a prognostic indicator for increased DDFS in ER-positive breast cancer, which may be associated with constitutive GPER1-dependent proapoptotic signaling in ER-positive breast cancer cells.

The G protein-coupled oestrogen receptor 1 agonist G-1 disrupts endothelial cell microtubule structure in a receptor-independent manner

The G protein-coupled oestrogen receptor GPER1, also known as GPR30, has been implicated in oestrogen signalling, but the physiological importance of GPER1 is not fully understood. The GPER1 agonist G-1 has become an important tool to assess GPER1-mediated cellular effects. Here, we report that this substance, besides acting via GPER1, affects the microtubule network in endothelial cells. Treatment with G-1 (3 μM) for 24 h reduced DNA synthesis by about 60 % in mouse microvascular endothelial bEnd.3 cells. Treatment with 3 μM G-1 prevented outgrowth of primary endothelial cells from mouse aortic explants embedded in Matrigel. Treatment with G-1 (0.3-3 μM) for 24 h disrupted bEnd.3 cell and HUVEC microtubule structure in a concentration-dependent manner as assessed by laser-scanning confocal immunofluorescence microscopy. G-1-induced (3 μM) disruption of microtubule was observed also after acute (3 and 6 h) treatment and in the presence of the protein synthesis inhibitor cycloheximide. Disruption of microtubules by 3 μM G-1 was observed in aortic smooth muscle cells obtained from both GPER1 knockout and wild-type mice, suggesting that G-1 influences microtubules through a mechanism independent of GPER1. G-1 dose dependently (10-50 μM) stimulated microtubule assembly in vitro. On the other hand, microtubules appeared normal in the presence of 10-50 μM G-1 as determined by electron microscopy. We suggest that G-1-promoted endothelial cell anti-proliferation is due in part to alteration of microtubule organization through a mechanism independent of GPER1. This G-1-promoted mechanism may be used to block unwanted endothelial cell proliferation and angiogenesis such as that observed in, e.g. cancer.

G protein-coupled oestrogen receptor 1 (GPER1)/GPR30: a new player in cardiovascular and metabolic oestrogenic signalling

Oestrogens are important sex hormones central to health and disease in both genders that have protective effects on the cardiovascular and metabolic systems. These hormones act in complex ways via both genomic and non-genomic mechanisms. The genomic mechanisms are relatively well characterized, whereas the non-genomic ones are only beginning to be explored. Two oestrogen receptors (ER), ERα and ERβ, have been described that act as nuclear transcription factors but can also associate with the plasma membrane and influence cytosolic signalling. ERα has been shown to mediate both anti-atherogenic effects and pro-survival effects in pancreatic β-cells. In recent years, a third membrane-bound ER has emerged, G protein-coupled receptor 30 or G protein-coupled oestrogen receptor 1 (GPER1), which mediates oestrogenic responses in cardiovascular and metabolic regulation. Both GPER1 knock-out models and pharmacological agents are now available to study GPER1 function. These tools have revealed that GPER1 activation may have several beneficial effects in the cardiovascular system including vasorelaxation, inhibition of smooth muscle cell proliferation, and protection of the myocardium against ischaemia/reperfusion injury, and in the metabolic system including stimulation of insulin release and protection against pancreatic β-cell apoptosis. Thus, GPER1 is emerging as a candidate therapeutic target in both cardiovascular and metabolic disease.

17β-Estradiol induces nongenomic effects in renal intercalated cells through G protein-coupled estrogen receptor 1

Steroid hormones such as 17β-estradiol (E2) are known to modulate ion transporter expression in the kidney through classic intracellular receptors. Steroid hormones are also known to cause rapid nongenomic responses in a variety of nonrenal tissues. However, little is known about renal short-term effects of steroid hormones. Here, we studied the acute actions of E2 on intracellular Ca(2+) signaling in isolated distal convoluted tubules (DCT2), connecting tubules (CNT), and initial cortical collecting ducts (iCCD) by fluo 4 fluorometry. Physiological concentrations of E2 induced transient increases in intracellular Ca(2+) concentration ([Ca(2+)](i)) in a subpopulation of cells. The [Ca(2+)](i) increases required extracellular Ca(2+) and were inhibited by Gd(3+). Strikingly, the classic E2 receptor antagonist ICI 182,780 also increased [Ca(2+)](i), which is inconsistent with the activation of classic E2 receptors. G protein-coupled estrogen receptor 1 (GPER1 or GPR30) was detected in microdissected DCT2/CNT/iCCD by RT-PCR. Stimulation with the specific GPER1 agonist G-1 induced similar [Ca(2+)](i) increases as E2, and in tubules from GPER1 knockout mice, E2, G-1, and ICI 182,780 failed to induce [Ca(2+)](i) elevations. The intercalated cells showed both E2-induced concanamycin-sensitive H(+)-ATPase activity by BCECF fluorometry and the E2-mediated [Ca(2+)](i) increment. We propose that E2 via GPER1 evokes [Ca(2+)](i) transients and increases H(+)-ATPase activity in intercalated cells in mouse DCT2/CNT/iCCD.

The GPER1 agonist G-1 attenuates endothelial cell proliferation by inhibiting DNA synthesis and accumulating cells in the S and G2 phases of the cell cycle

G protein-coupled receptor 30 (GPR30) or G protein-coupled estrogen receptor 1 (GPER1) is expressed in the vasculature, but the importance of vascular GPER1 remains to be clarified. Here we investigate effects of the GPER1 agonist G-1 on endothelial cell proliferation using mouse microvascular endothelial bEnd.3 cells. The bEnd.3 cells express mRNA for GPER1. The bEnd.3 cells expressed both ERα and ERβ immunoreactivities. Treatment with G-1 reduced DNA synthesis and cell number with IC(50) values of about 2 μM. GPER1 siRNA prevented G-1-induced attenuation of DNA synthesis. G-1 accumulated cells in S and G2 phases of the cell cycle, suggesting that G-1 blocks transition between G2 and M. G-1 had no effect on DNA synthesis in COS-7 cells only weakly expressing GPER1 mRNA. 17β-Estradiol had no effect on DNA synthesis in physiological concentrations (nM). The ER blocker ICI182780 reduced DNA synthesis with similar potency as G-1. Treatment with the ERK/MAP kinase inhibitor PD98059 had no effect on G-1-induced attenuation of DNA synthesis. G-1- induced antiproliferation was observed not only in bEnd.3 cells but also in human umbilical vein endothelial cells and HMEC-1 endothelial cells. We conclude that the GPER1 agonist G-1 attenuates endothelial cell proliferation via inhibition of DNA synthesis and by accumulation of cells in S and G2.

G protein-coupled estrogen receptor 1/G protein-coupled receptor 30 localizes in the plasma membrane and traffics intracellularly on cytokeratin intermediate filaments

G protein-coupled receptor 30 [G protein-coupled estrogen receptor 1 (GPER1)], has been introduced as a membrane estrogen receptor and a candidate cancer biomarker and therapeutic target. However, several questions surround the subcellular localization and signaling of this receptor. In native cells, including mouse myoblast C(2)C(12) cells, Madin-Darby canine kidney epithelial cells, and human ductal breast epithelial tumor T47-D cells, G-1, a GPER1 agonist, and 17β-estradiol stimulated GPER1-dependent cAMP production, a defined plasma membrane (PM) event, and recruitment of β-arrestin2 to the PM. Staining of fixed and live cells showed that GPER1 was localized both in the PM and on intracellular structures. One such intracellular structure was identified as cytokeratin (CK) intermediate filaments, including those composed of CK7 and CK8, but apparently not endoplasmic reticulum, Golgi, or microtubules. Reciprocal coimmunoprecipitation of GPER1 and CKs confirmed an association of these proteins. Live staining also showed that the PM receptors constitutively internalize apparently to reach CK filaments. Receptor localization was supported using FLAG- and hemagglutinin-tagged GPER1. We conclude that GPER1-mediated stimulation of cAMP production and β-arrestin2 recruitment occur in the PM. Furthermore, the PM receptors constitutively internalize and localize intracellularly on CK. This is the first observation that a G protein-coupled receptor is capable of associating with intermediate filaments, which may be important for GPER1 regulation in epithelial cells and the relationship of this receptor to cancer.

GPR30/GPER1: searching for a role in estrogen physiology

Estrogens are sex hormones that are central to health and disease in both genders. These hormones have long been recognized to act in complex ways, both through relatively slow genomic mechanisms and via fast non-genomic mechanisms. Several recent in vitro studies suggest that GPR30, or G protein-coupled estrogen receptor 1 (GPER1), is a functional membrane estrogen receptor involved in non-genomic estrogen signaling. However, this function is not universally accepted. Studies concerning the role of GPER1 in vivo are now beginning to appear but with divergent results. In this review we discuss current knowledge on the physiological role of GPER1 in the nervous system as well as in reproduction, metabolism, bone, and in the cardiovascular and immune systems.

The role of the G protein-coupled receptor GPR30 in the effects of estrogen in ovariectomized mice

In vitro studies suggest that the membrane G protein-coupled receptor GPR30 is a functional estrogen receptor (ER). The aim of the present study was to determine the possible in vivo role of GPR30 as a functional ER primarily for the regulation of skeletal parameters, including bone mass and longitudinal bone growth, but also for some other well-known estrogen-regulated parameters, including uterine weight, thymus weight, and fat mass. Three-month-old ovariectomized (OVX) GPR30-deficient mice (GPR30(-/-)) and wild-type (WT) mice were treated with either vehicle or increasing doses of estradiol (E(2); 0, 30, 70, 160, or 830 ng.mouse(-1).day(-1)). Body composition [bone mineral density (BMD), fat mass, and lean mass] was analyzed by dual-energy-X ray absorptiometry, while the cortical and trabecular bone compartments were analyzed by peripheral quantitative computerized tomography. Quantitative histological analyses were performed in the distal femur growth plate. Bone marrow cellularity and distribution were analyzed using a fluorescence-activated cell sorter. The estrogenic responses on most of the investigated parameters, including increase in bone mass (total body BMD, spine BMD, trabecular BMD, and cortical bone thickness), increase in uterine weight, thymic atrophy, fat mass reduction, and increase in bone marrow cellularity, were similar for all of the investigated E(2) doses in WT and GPR30(-/-) mice. On the other hand, E(2) treatment reduced longitudinal bone growth, reflected by decreased femur length and distal femur growth plate height, in the WT mice but not in the GPR30(-/-) mice compared with vehicle-treated mice. These in vivo findings demonstrate that GPR30 is not required for normal estrogenic responses on several major well-known estrogen-regulated parameters. In contrast, GPR30 is required for a normal estrogenic response in the growth plate.

Deletion of the G protein-coupled receptor 30 impairs glucose tolerance, reduces bone growth, increases blood pressure, and eliminates estradiol-stimulated insulin release in female mice

In vitro studies suggest that the G protein-coupled receptor (GPR) 30 is a functional estrogen receptor. However, the physiological role of GPR30 in vivo is unknown, and it remains to be determined whether GPR30 is an estrogen receptor also in vivo. To this end, we studied the effects of disrupting the GPR30 gene in female and male mice. Female GPR30((-/-)) mice had hyperglycemia and impaired glucose tolerance, reduced body growth, increased blood pressure, and reduced serum IGF-I levels. The reduced growth correlated with a proportional decrease in skeletal development. The elevated blood pressure was associated with an increased vascular resistance manifested as an increased media to lumen ratio of the resistance arteries. The hyperglycemia and impaired glucose tolerance in vivo were associated with decreased insulin expression and release in vivo and in vitro in isolated pancreatic islets. GPR30 is expressed in islets, and GPR30 deletion abolished estradiol-stimulated insulin release both in vivo in ovariectomized adult mice and in vitro in isolated islets. Our findings show that GPR30 is important for several metabolic functions in female mice, including estradiol-stimulated insulin release.

Activation of TAFI on the surface of Streptococcus pyogenes evokes inflammatory reactions by modulating the kallikrein/kinin system

Bacteria-controlled regulation of host responses to infection is an important virulence mechanism that has been demonstrated to contribute to disease progression. Here we report that the human pathogen Streptococcus pyogenes employs the procarboxypeptidase TAFI (thrombin-activatable fibrinolysis inhibitor) to modulate the kallikrein/kinin system. To this end, bacteria initiate a chain of events starting with the recruitment and activation of TAFI. This is followed by the assembly and induction of the contact system at the streptococcal surface, eventually triggering the release of bradykinin (BK). BK is then carboxyterminally truncated by activated TAFI, which converts the peptide from a kinin B(2) receptor ligand to a kinin B(1) receptor (B1R) agonist. Finally, we show that streptococcal supernatants indirectly amplify the B1R response as they act on peripheral blood mononuclear cells to secrete inflammatory cytokines that in turn stimulate upregulation of the B1R on human fibroblasts. Taken together our findings implicate a critical and novel role for streptococci-bound TAFI, as it processes BK to a B1R agonist at the bacterial surface and thereby may redirect inflammation from a transient to a chronic state.

Kinins Promote B2Receptor Endocytosis and Delay Constitutive B1Receptor Endocytosis

Upon sustained insult, kinins are released and many kinin responses, such as inflammatory pain, adapt from a B2 receptor (B2R) type in the acute phase to a B1 receptor (B1R) type in the chronic phase. In this study, we show that kinins modulate receptor endocytosis to rapidly decrease B2R and increase B1R on the cell surface. B2Rs, which require agonist for activity, are stable plasma membrane components without agonist but recruit beta-arrestin 2, internalize in a clathrin-dependent manner, and recycle rapidly upon agonist treatment. In contrast, B1Rs, which are inducible and constitutively active, constitutively internalize without agonist via a clathrin-dependent pathway, do not recruit beta-arrestin 2, bind G protein-coupled receptor sorting protein, and target lysosomes for degradation. Agonist delays B1R endocytosis, thus transiently stabilizing the receptor. Most of the receptor trafficking phenotypes are transplantable from one receptor to the other through exchange of the C-terminal receptor tails, indicating that the tails contain epitopes that are important for the binding of protein partners that participate in the endocytic and postendocytic receptor choices. It is noteworthy that the agonist delay of B1R endocytosis is not transplanted to the B2R via the B1R tail, suggesting that this property of the B1R requires another domain. These events provide a rapid kinin-dependent mechanism for 1) regulating the constitutive B1R activity and 2) shifting the balance of accessible receptors in favor of B1R.

Kinin receptor expression during Staphylococcus aureus infection

An inappropriate host response to invading bacteria is a critical parameter that often aggravates the outcome of an infection. Staphylococcus aureus is a major human Gram-positive pathogen that causes a wide array of community- and hospital-acquired diseases ranging from superficial skin infections to severe conditions such as staphylococcal toxic shock. Here we find that S aureus induces inflammatory reactions by modulating the expression and response of the B1 and B2 receptors, respectively. This process is initiated by a chain of events, involving staphylococcal-induced cytokine release from monocytes, bacteria-triggered contact activation, and conversion of bradykinin to its metabolite desArg(9)bradykinin. The data of the present study implicate an important and previously unknown role for kinin receptor regulation in S aureus infections.

Lysophosphatidic acid binds to and activates GPR92, a G protein-coupled receptor highly expressed in gastrointestinal lymphocytes

Here, the ligand binding, activation, and tissue distribution of the orphan G protein-coupled receptor (GPCR) GPR92 were studied. GPR92 binds and is activated by compounds based on the lysophosphatidic acid (LPA) backbone. The binding of LPA to GPR92 was of high affinity (K(D) = 6.4 +/- 0.9 nM) and led to an increase in both phosphoinositide hydrolysis and cAMP production. GPR92 is atypical in that it has a low sequence homology with the classic LPA(1-3) receptors (21-22%). Expression of GPR92 is mainly found in heart, placenta, spleen, brain, lung, and gut. Notably, GPR92 is highly expressed in the lymphocyte compartment of the gastrointestinal tract. It is the most abundant GPCR activated by LPA found in the small intestinal intraepithelial CD8+ cytotoxic T cells.

International union of pharmacology. XLV. Classification of the kinin receptor family: from molecular mechanisms to pathophysiological consequences

Kinins are proinflammatory peptides that mediate numerous vascular and pain responses to tissue injury. Two pharmacologically distinct kinin receptor subtypes have been identified and characterized for these peptides, which are named B1 and B2 and belong to the rhodopsin family of G protein-coupled receptors. The B2 receptor mediates the action of bradykinin (BK) and lysyl-bradykinin (Lys-BK), the first set of bioactive kinins formed in response to injury from kininogen precursors through the actions of plasma and tissue kallikreins, whereas the B(1) receptor mediates the action of des-Arg9-BK and Lys-des-Arg9-BK, the second set of bioactive kinins formed through the actions of carboxypeptidases on BK and Lys-BK, respectively. The B2 receptor is ubiquitous and constitutively expressed, whereas the B1 receptor is expressed at a very low level in healthy tissues but induced following injury by various proinflammatory cytokines such as interleukin-1beta. Both receptors act through G alpha(q) to stimulate phospholipase C beta followed by phosphoinositide hydrolysis and intracellular free Ca2+ mobilization and through G alpha(i) to inhibit adenylate cyclase and stimulate the mitogen-activated protein kinase pathways. The use of mice lacking each receptor gene and various specific peptidic and nonpeptidic antagonists have implicated both B1 and B2 receptors as potential therapeutic targets in several pathophysiological events related to inflammation such as pain, sepsis, allergic asthma, rhinitis, and edema, as well as diabetes and cancer. This review is a comprehensive presentation of our current understanding of these receptors in terms of molecular and cell biology, physiology, pharmacology, and involvement in human disease and drug development.

Infection-Induced Kinin B1Receptors in Human Pulmonary Fibroblasts: Role of Intact Pathogens and p38 Mitogen-Activated Protein Kinase-Dependent Signaling

Kinin B(1) receptors (B(1)R) are involved in many pathophysiological processes, and its expression is up-regulated in inflammatory pulmonary disease. Although bacteria can generate kinin peptides, the molecular signaling mechanisms regulating B(1)R during infection by intact pathogens is unknown. The serious opportunistic clinical isolate Burkholderia cenocepacia (B. cen.) belongs to the important B. cepacia complex (Bcc) of gram-negative pathogens that rapidly causes fatal pulmonary disease in hospitalized and immunocompromised patients and those with cystic fibrosis. We demonstrate here that B. cen. infection induced a rapid increase in B(1)R mRNA (1 h) proceeded by an increase in B(1)R protein expression (2 h), without affecting B(2) receptor expression in human pulmonary fibroblasts. The B(1)R response was dose-dependent and maximal by 6 to 8 h (3- to 4-fold increase), however, brief B. cen. infection could sustain B(1)R up-regulation. In contrast, nonclinical Bcc phytopathogens were much less B(1)R inducive. The protein synthesis inhibitor cycloheximide and transcriptional inhibitor actinomycin D abrogated the B(1) response to B. cen. indicating de novo B(1)R synthesis. B. cen. activated p38 mitogen-activated protein kinase (MAPK), and blocking p38 MAPK with the specific inhibitor 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB 203580) dramatically reduced B. cen.-induced B(1)R. Furthermore, B. cen. regulation of B(1)R was diminished by the anti-inflammatory glucocorticoid dexamethasone. In conclusion, this study is the first demonstration that infection with intact pulmonary pathogens like B. cen. positively modulates the selective expression of B(1)R. Thus, providing evidence that B(1)R regulation may be an important and novel mechanism in the inflammatory cascade in response to chronic pulmonary infection and disease.

B1Bradykinin Receptor Homo-Oligomers in Receptor Cell Surface Expression and Signaling: Effects of Receptor Fragments

The human B(1) bradykinin receptor is an inducible and constitutively active G protein-coupled receptor that is involved in the inflammatory and pain responses to injury. Here, we investigated the role of B(1) receptor homo-oligomerization in cell surface receptor expression. B(1) receptors tagged with either the FLAG or hemagglutinin epitope were monitored immunologically and by radio-ligand binding, biotinylation, and phosphoinositide hydrolysis in human embryonic kidney 293 cells. Selective immunoprecipitation, immunoblotting, and immunoelectron microscopy with epitope-specific antibodies together provided evidence for constitutively formed cell surface receptor homo-oligomers. Truncation of the receptor from the N- and C-terminal ends indicated that the epitope for oligomerization seems to be located between Leu(26) on top of transmembrane helix 1 and Val(71) at the bottom of helix 2. A receptor construct terminating at Asp(134) at the bottom of helix 3, B1stop135, was expressed in the cell. It is interesting that this construct behaved as a dominant-negative mutant by competitively preventing formation of intact B(1) receptor homo-oligomers, and redistributing B(1) receptors from the cell surface to a common intracellular compartment. In contrast, expression of a construct containing the residues downstream of Asp(134), B1del(2-134), was inactive in this regard. Together, these results are consistent with a mechanism where constitutive B(1) receptor homooligomerization is required for expression of receptors on the cell surface and subsequent constitutive receptor signaling. This may be a novel mechanism by which the cell regulates the presentation of this constitutively highly active receptor at various stages of injury.

Jak2 and Ca2+/calmodulin are key intermediates for bradykinin B2 receptor-mediated activation of Na+/H+ exchange in KNRK and CHO cells

Na(+)/H(+) exchangers are ubiquitous in mammalian cells, carrying out key functions, such as cell volume defense, acid-base homeostasis, and regulation of the cytoskeleton. We used two screening technologies (FLIPR and microphysiometry) to characterize the signal transduction pathway used by the bradykinin B(2) receptor to activate Na(+)/H(+) exchange in two cell lines, KNRK and CHO. In both cell types, B(2) receptor activation resulted in rapid increases in the rate of proton extrusion that were sodium-dependent and could be blocked by the Na(+)/H(+) exchange inhibitors EIPA and MIA or by replacing extracellular sodium with TMA. Activation of Na(+)/H(+) exchange by bradykinin was concentration-dependent and could be blocked by the selective B(2) receptor antagonist HOE140, but not by the B(1) receptor antagonist des-Arg10-HOE140. Inhibitors of Jak2 tyrosine kinase (genistein and AG490) and of CAM (W-7 and calmidazolium) attenuated bradykinin-induced activation of Na(+)/H(+) exchange. Bradykinin induced formation of a complex between CAM and Jak2, supporting a regulatory role for Jak2 and CAM in the activation of Na(+)/H(+) exchange in KNRK and CHO cells. We propose that this pathway (B(2) receptor --> Jak2 --> CAM --> Na(+)/H(+) exchanger) is a fundamental regulator of Na(+)/H(+) exchange activity.

Spontaneous Formation of a Proteolytic B1 and B2 Bradykinin Receptor Complex with Enhanced Signaling Capacity

B1 bradykinin receptor (B1R) induction is critical in the adaptation of the kinin-mediated inflammatory response from a B2 bradykinin receptor (B2R) subtype to a B1R subtype that occurs during chronic insult. Here, we show that B1R spontaneously forms a proteolytic plasma membrane complex with B2R along with increased receptor signaling capacity. Co-expression of hemagglutinin-tagged B2R with FLAG-tagged B1R in HEK293 cells resulted in degradation of B2R as determined by the diminution of the intact 65-kDa B2R species and the appearance of proteolytic B2R products at 30-40 kDa and by the reduction in B2R bradykinin binding sites. On the other hand, the 35-kDa B1R remained intact. Receptor co-expression also led to an increase in constitutive and agonist-stimulated receptor signaling. Selective immunoprecipitation with epitope-specific antibodies revealed a spontaneously formed heterologous receptor complex, which was composed of the intact 35-kDa B1R and the B2R degradation products. Cellular fractionation, cell surface biotinylation, and immunoelectron microscopy showed that B2R.B1R complexes were present on the cell surface. This is the first evidence that a heterologous G protein-coupled receptor complex in the plasma membrane is linked to proteolytic degradation of a participating receptor, and this mechanism may contribute to the adaptation of the kinin response from a B2 type to a B1 type during chronic insult.

Calcium-sensing Receptor-mediated ERK1/2 Activation Requires Gαi2 Coupling and Dynamin-independent Receptor Internalization

The calcium-sensing receptor (CaR) recently has been shown to activate MAP kinase (ERK1/2) in various cell types as well as in heterologous expression systems. In this study we show that the CaR agonist NPS R-467 (1 microm), which does not activate the CaR by itself, robustly activates ERK1/2 in the presence of a low concentration of Ca(2+) (0.5 mm CaCl(2)) in human embryonic kidney (HEK) cells permanently expressing the human CaR (HEK-hCaR). Ca(2+) (4 mm) also activates ERK1/2 but with differing kinetics. CaR-dependent ERK1/2 activation begins to desensitize to 4 mm Ca(2+) after 10 min, whereas there is no desensitization to NPS R-467/CaCl(2) as late as 4 h. Moreover, recovery from desensitization occurs as rapidly as 30 min with 4 mm CaCl(2). Pretreatment of HEK-hCaR cells with concanavalin A (250 microg/ml) to block CaR internalization completely eliminated the NPS R-467/CaCl(2)-mediated ERK1/2 activation but did not block the 2-min time point of 4 mm Ca(2+)-mediated ERK1/2 activation. Neither dominant-negative dynamin (K44A) nor dominant-negative beta-arrestin inhibited ERK1/2 activation by either CaR agonist treatment, suggesting that CaR-elicited ERK1/2 signaling occurs via a dynamin-independent pathway. Pertussis toxin pretreatment partially attenuated the 4 mm Ca(2+)-ERK1/2 activation; this attenuated activity was completely restored by co-expression of the Galpha(i2) (C351I) but not Galpha(i1) (C351I) or Galpha(i3) (C351I) G proteins, PTX-insensitive G protein mutants. Taken together, these data suggest that both 4 mm Ca(2+) and NPS R-467/CaCl(2) activate ERK1/2 via distinguishable pathways in HEK-hCaR cells and may represent a nexus to differentially regulate differentiation versus proliferation via CaR activation.

Bradykinin receptor subtype 1 expression and function in prostate cancer

Kinins exert multiple pathophysiological functions, including vascular permeability and mitogenesis, by activating their cognate receptors, bradykinin subtype 1 receptor (B1R) and bradykinin subtype 2 receptor (B2R), which belong to the superfamily of G protein-coupled receptors. Tissue-specific expression pattern or contribution of the individual kinin receptors to pathological prostate cell growth is not known. We report here the differential expression of B1R and B2R in human benign and malignant prostate specimens. Whereas B2R is ubiquitously expressed, the B1R is detected only in prostatic intraepithelial neoplasia and malignant lesions and not in benign prostate tissues. Using androgen-insensitive prostate cancer PC3 cells, we show that specific stimulation of endogenous B1R promotes cell growth, migration, and invasion. These findings identify B1R as an early marker for pathological growth of the prostate and suggest its potential utility as a drug target effective for the treatment of prostate cancer.

Requirement for direct cross-talk between B1 and B2 kinin receptors for the proliferation of androgen-insensitive prostate cancer PC3 cells

Stimulation of endogenous kinin receptors promotes growth of androgen-independent prostate cancer PC3 cells via activation of the mitogenic extracellular-signal-regulated kinase (ERK) pathway. In the present study, we show that kinin-mediated mitogenic signalling and prostate-cell growth involves two subtypes of bradykinin (BK) receptors, B1R and B2R. Specific stimulation of either B1R or B2R by their respective agonists des-Arg(9)-BK and Lys-BK promoted ERK activation and cell growth, whereas selective blockade with specific antagonists des-Arg(9)-[Leu(8)]BK and Hoe 140 respectively obliterated this effect, indicating the presence of both receptor subtypes. However, blockade of B1R also inhibited B2R-mediated ERK activation and cell growth, and, similarly, antagonism of B2R inhibited the B1R-mediated response. Furthermore, both B1R and B2R agonists promoted internalization of B1R, whereas both receptor antagonists blocked this effect. The B1R ligands des-Arg(9)-BK and des-Arg(9)-[Leu(8)]BK had no effect on the binding of BK to B2R, as demonstrated by radioligand competitive binding studies. However, blockade of either B1R or B2R impaired the ability of the reciprocal receptor to produce inositol phosphates, suggesting that the interaction between B1R and B2R is proximal to activation of phospholipase C. These results provide evidence for the existence of B1R-B2R complexes in prostate cancer PC3 cells and demonstrate that antagonism of one receptor interferes with the signalling ability of the other, possibly at the level of receptor-Galpha(q) protein coupling. Selective inhibition of B1R, which is up-regulated in injured and cancerous tissue, may be beneficial for the treatment of advanced prostate cancer.

Human B1 and B2 bradykinin receptors and their agonists target caveolae-related lipid rafts to different degrees in HEK293 cells

To address the targeting of G protein-coupled receptors to caveolae-related lipid rafts (CLR), we studied the human B2 (B2R) and B1 (B1R) bradykinin receptor subtypes in HEK293 cells. CLR were enriched on the basis of their unique buoyant density and composition of cholesterol, caveolin-1, and flotillin-1 but not clathrin. CLR contained B2R and B1R as determined by both receptor immunoblotting and the increase in specific activity of receptor agonist binding to cells at both 4 and 37 degrees C when binding was followed by CLR enrichment. B2R was highly enriched in this fraction, whereas B1R was not enriched. Furthermore, acid washing of cells prior to cell disruption minimally affected the CLR-associated B2R agonist binding, whereas it dissociated a major portion of the CLR-associated B1R agonist binding. In addition, when agonist binding at 4 degrees C was followed by an increase in the temperature to 37 degrees C, B2R agonist binding in CLR transiently increased, and this increase was dependent on the C-terminal domain. On the other hand, B1R agonist binding remained unchanged and was independent of the C-terminal domain. Our results show that B2R is constitutively targeted to CLR in HEK293 cells and appears to shuttle the agonist through these domains, whereas B1R may be there by default.

Negative and positive regulatory epitopes in the C-terminal domains of the human B1 and B2 bradykinin receptor subtypes determine receptor coupling efficacy to G(q/11)-mediated [correction of G(9/11)-mediated] phospholipase Cbeta activity

The human B1 bradykinin (BK) receptor (B1R) is more efficacious than the human B2 BK receptor (B2R) in both ligand-independent and agonist-dependent coupling to G(q/11)-mediated phospholipase Cbeta activity. In fact, B1R is constitutively active, whereas B2R exhibits little if any constitutive activity. To evaluate the role of the C-terminal domain in receptor G(q/11) coupling, we constructed chimeric and C-terminally truncated receptors. The slopes of the increase in basal and agonist-dependent cellular phosphoinositide hydrolysis as a function of receptor density in transiently transfected human embryonic kidney 293 cells provided parameters of receptor coupling. Exchanging the C-terminal domains between the two receptors revealed that these domains are largely responsible for the difference in coupling. B1R truncation showed that this receptor does not directly depend on the C-terminal domain for efficient coupling, although coupling is dramatically augmented by residues in the membrane-distal portion of the domain downstream from Tyr(327). On the other hand, coupling of B2R is absolutely dependent on a membrane-proximal epitope in the C-terminal domain upstream from Lys(315). This epitope is adjacent to a basic residue, Arg(311), which exerts an inhibitory effect on coupling. Arg(311) is not conserved in B1R, and complementary mutations in B2R and B1R showed that this residue, together with previously identified serines and threonines, acts to attenuate the coupling efficacy of B2R. Therefore, the C-terminal domain participates intimately in the efficacy of B1R and B2R G(q/11) coupling by contributing both positive and negative regulatory epitopes.

PI 3-kinase regulation of dopamine uptake

The magnitude and duration of dopamine (DA) signaling is defined by the amount of vesicular release, DA receptor sensitivity, and the efficiency of DA clearance, which is largely determined by the DA transporter (DAT). DAT uptake capacity is determined by the number of functional transporters on the cell surface as well as by their turnover rate. Here we show that inhibition of phosphatidylinositol (PI) 3-kinase with LY294002 induces internalization of the human DAT (hDAT), thereby reducing transport capacity. Acute treatment with LY294002 reduced the maximal rate of [(3) H]DA uptake in rat striatal synaptosomes and in human embryonic kidney (HEK) 293 cells stably expressing the hDAT (hDAT cells). In addition, LY294002 caused a significant redistribution of the hDAT from the plasma membrane to the cytosol. Conversely, insulin, which activates PI 3-kinase, increased [(3)H]DA uptake and blocked the amphetamine-induced hDAT intracellular accumulation, as did transient expression of constitutively active PI 3-kinase. The LY294002-induced reduction in [(3)H]DA uptake and hDAT cell surface expression was inhibited by expression of a dominant negative mutant of dynamin I, indicating that dynamin-dependent trafficking can modulate transport capacity. These data implicate DAT trafficking in the hormonal regulation of dopaminergic signaling, and suggest that a state of chronic hypoinsulinemia, such as in diabetes, may alter synaptic DA signaling by reducing the available cell surface DATs.