Medical and gynecological comorbidities in adult women with Turner syndrome: our multidisciplinary clinic experience.

Objective: Women with Turner syndrome (TS) are at increased risk for chronic health conditions. Reports describing the presence of comorbidities in older adult women with TS are limited. This study aimed to examine the prevalence of endocrine, gynecological, and other chronic medical conditions in a cohort of adult TS patients.Methods: A retrospective chart review was conducted on patients seen between 1 February 2015 and 1 July 2018 in a multidisciplinary TS clinic at a university-based ambulatory hospital in Toronto, Canada. All women seen at the TS clinic with a diagnosis of TS aged >18 years were included. The prevalence of diseases was determined overall and stratified by age (<40 and ≥40 years). Statistical comparisons were done using the chi-square test. The main study outcomes included the presence of comorbidities.Results: Of 122 adult women with TS, 24.5% had hypothyroidism, 16% had dysglycemia, and 27.9% had decreased bone mass. Hypothyroidism and dysglycemia were more common among older women (respectively age ≥40 years vs. age <40 years: 36.7% vs. 17.8%, p = 0.018; and 24.5% vs. 5.5%, p = 0.023). Gynecological conditions were identified in 35% of patients and were more common among older women (42.8% age ≥40 years vs. 13.7% age <40 years, p = 0.003). Overall, 41% had hearing impairment, 36.1% had cardiac abnormalities, 14.8% had hypertension, 18.8% had renal abnormalities, and 9% had celiac disease.Conclusions: The results of this study indicate a high prevalence of medical conditions in women with TS, especially those ≥40 years of age. Our study underscores the importance of multidisciplinary adult TS clinics for ongoing screening and management of comorbidities.

Managing uncertain recovery for patients nearing the end of life in hospital: a mixed-methods feasibility cluster randomised controlled trial of the AMBER care bundle.

BACKGROUND: The AMBER (Assessment, Management, Best Practice, Engagement, Recovery Uncertain) care bundle is a complex intervention used in UK hospitals to support patients with uncertain recovery. However, it has yet to be evaluated in a randomised controlled trial (RCT) to identify potential benefits or harms. The aim of this trial was to investigate the feasibility of a cluster RCT of the AMBER care bundle. METHODS: This is a prospective mixed-methods feasibility cluster RCT. Quantitative data collected from patients (or proxies if patients lack capacity) were used (i) to examine recruitment, retention and follow-up rates; (ii) to test data collection tools for the trial and determine their optimum timing; (iii) to test methods to identify the use of financial resources; and (iv) to explore the acceptability of study procedures for health professionals and patients. Descriptive statistical analyses and thematic analysis used the framework approach. RESULTS: In total, 894 patients were screened, of whom 220 were eligible and 19 of those eligible (8.6%) declined to participate. Recruitment to the control arm was challenging. Of the 728 patients screened for that arm, 647 (88.9%) were excluded. Overall, 65 patients were recruited (81.3% of the recruitment target of 80). Overall, many were elderly (≥80 years, 46.2%, n = 30, mean = 77.8 years, standard deviation [SD] = 12.3 years). Over half (53.8%) had a non-cancer diagnosis, with a mean of 2.3 co-morbidities; 24.6% patients (n = 16) died during their hospital stay and 35.4% (n = 23) within 100 days of discharge. In both trial arms, baseline IPOS subscale scores identified moderate patient anxiety (control: mean 13.3, SD 4.8; intervention: mean 13.3, SD 5.1), and howRwe identified a good care experience (control: mean 13.1, SD 2.5; intervention: mean 11.5, SD 2.1). Collecting quantitative service use and quality of life data was feasible. No patient participants regarded study involvement negatively. Focus groups with health professionals identified concerns regarding (i) the subjectivity of the intervention's eligibility criteria, (ii) the need to prognosticate to identify potential patients and (iii) consent procedures and the length of the questionnaire. CONCLUSIONS: A full trial of the AMBER care bundle is technically feasible but impractical due to fundamental issues in operationalising the intervention's eligibility criteria, which prevents optimal recruitment. Since this complex intervention continues to be used in clinical care and advocated in policy, alternative research approaches must be considered and tested. TRIAL REGISTRATION: International Standard Randomised Controlled Trial Number (ISRCTN) Register, ISRCTN36040085 .

Hepatoma polarization limits CD81 and hepatitis C virus dynamics.

Many viruses target the polarized epithelial apex during host invasion. In contrast, hepatitis C virus (HCV) engages receptors at the basal surface of hepatocytes in the polarized liver parenchyma. Hepatocyte polarization limits HCV entry by undefined mechanism(s). Given the recent reports highlighting a role for receptor mobility in pathogen entry, we studied the effect(s) of hepatocyte polarization on viral receptor and HCV pseudoparticle (HCVpp) dynamics using real-time fluorescence recovery after photobleaching and single particle tracking. Hepatoma polarization reduced CD81 and HCVpp dynamics at the basal membrane. Since cell polarization is accompanied by changes in the actin cytoskeleton and CD81 links to actin via its C-terminus, we studied the dynamics of a mutant CD81 lacking a C-terminal tail (CD81(ΔC)) and its effect(s) on HCVpp mobility and infection. CD81(ΔC) showed an increased frequency of confined trajectories and a reduction of Brownian diffusing molecules compared to wild-type protein in non-polarized cells. However, these changes were notobserved in polarized cells. HCVpp showed a significant reduction in Brownian diffusion and infection of CD81(ΔC) expressing non-polarized cells. In summary, these data highlight the dynamic nature of CD81 and demonstrate a role for CD81 lateral diffusion to regulate HCV infection in a polarization-dependent manner.

Molecular basis of a novel oncogenic mutation in GNAO1.

Heterotrimeric G proteins are molecular switches that control signal transduction, and their dysregulation can promote oncogenesis. Somatic mutations in GNAS, GNAI2 and GNAQ genes induce oncogenesis by rendering Gα subunits constitutively activated. Recently the first somatic mutation, arginine(243) → histidine (R243H) in the GNAO1 (Gαo) gene was identified in breast carcinomas and shown to promote oncogenic transformation when introduced into cells. Here, we provide the molecular basis for the oncogenic properties of the Gαo R243H mutant. Using limited proteolysis assays, nucleotide-binding assays, and single-turnover and steady-state GTPase assays, we demonstrate that the oncogenic R234H mutation renders Gαo constitutively active by accelerating the rate of nucleotide exchange; however, this mutation does not affect Gαo's ability to become deactivated by GTPase-activating proteins (GAPs) or by its intrinsic GTPase activity. This mechanism differs from that of previously reported oncogenic mutations that impair GTPase activity and GAP sensitivity without affecting nucleotide exchange. The constitutively active Gαo R243H mutant also enhances Src-STAT3 signaling in NIH-3T3 cells, a pathway previously shown to be directly triggered by active Gαo proteins to promote cellular transformation. Based on structural analyses, we propose that the enhanced rate of nucleotide exchange in Gαo R243H results from loss of the highly conserved electrostatic interaction of R243 with E43, located in the in the P-loop that represents the binding site for the α- and ß-phosphates of the nucleotide. We conclude that the novel R234H mutation imparts oncogenic properties to Gαo by accelerating nucleotide exchange and rendering it constitutively active, thereby enhancing signaling pathways, for example, src-STAT3, responsible for neoplastic transformation.

Researching breathlessness in palliative care: consensus statement of the National Cancer Research Institute Palliative Care Breathlessness Subgroup.

Breathlessness is common in advanced disease and can have a devastating impact on patients and carers. Research on the management of breathlessness is challenging. There are relatively few studies, and many studies are limited by inadequate power or design. This paper represents a consensus statement of the National Cancer Research Institute Palliative Care Breathlessness Subgroup. The aims of this paper are to facilitate the design of adequately powered multi-centre interventional studies in breathlessness, to suggest a standardised, rational approach to breathlessness research and to aid future 'between study' comparisons. Discussion of the physiology of breathlessness is included.

Primary hepatocytes as targets for hepatitis C virus replication.

Much of our current understanding of hepatitis C virus (HCV) replication has hailed from the use of a small number of cloned viral genomes and transformed hepatoma cell lines. Recent evidence suggests that lipoproteins play a key role in the HCV life cycle and virus particles derived from the sera of infected patients exist in association with host lipoproteins. This report will review the literature on HCV replication in primary hepatocytes and transformed cell lines, focusing largely on host factors defining particle entry.

Interaction of PLD1b with actin in antigen-stimulated mast cells.

Phosphatidic acid, the product of phospholipase D catalysed phosphatidylcholine hydrolysis is an important signalling molecule that has been implicated in regulation of actin cytoskeleton remodelling and secretion from mast cells. We show that human PLD1b (hPLD1b) is an actin-binding protein and the N-terminus is predominantly involved in this interaction. Protein kinase C (PKC) is a major upstream regulator of PLD activity and PKC phosphorylation sites have been identified within the N-terminus of PLD1b at serine 2 and threonine 147. Over-expression of wild type hPLD1b in mast cells showed that antigen stimulation significantly enhanced co-localisation of PLD1b with actin structures. Mutation of serine 2 to alanine abolished antigen-induced co-localisation whereas mutation of threonine 147 had less dramatic effects on co-localisation. The absence of co-localisation of PLD1b (S2A) with actin coincides with a significant decrease in PLD activity in cells expressing the PLD1b (S2A) mutant. In resting RBL-2H3 cells, mutation of serine 2 to aspartate resulted in constitutive co-localisation of PLD with the actin cytoskeleton, coincident with restored PLD activity. These results reveal that serine 2 is an important regulatory site involved in controlling PLD enzyme activity and the interaction between PLD and actin.

Measurement of breathlessness in advanced disease: a systematic review.

BACKGROUND: There is a plethora of assessment tools available to measure breathlessness, the most common and disabling symptom of advanced cardio-respiratory disease. The aim of this systematic review was to identify all measures available via standard search techniques and review their usefulness for patients with advanced disease. METHODS: A systematic literature search was performed in Medline. All studies focusing on the development or evaluation of tools for measuring breathlessness in chronic respiratory disease, cardiac disease, cancer, or MND were identified. Their characteristics with regard to validity, reliability, appropriateness and responsiveness to change were described. The tools were then examined for their usefulness in measuring significant aspects of breathlessness in advanced disease. RESULTS: Thirty-five tools were initially identified, two were excluded. Twenty-nine were multidimensional of which 11 were breathlessness-specific and 18 disease-specific. Four tools were unidimensional, measuring the severity of breathlessness. The majority of disease-specific scales were validated for chronic obstructive pulmonary disease (COPD), few were applicable in other conditions. No one tool assessed all the dimensions of this complex symptom, which affects the psychology and social functioning of the affected individual and their family--most focused on physical activity. CONCLUSION: As yet there is no one scale that can accurately reflect the far-reaching effects of breathlessness on the patient with advanced disease and their family. Therefore, at present, we would recommend combining a unidimensional scale (e.g. VAS) with a disease-specific scale (where available) or a multidimensional scale in conjunction with other methods (such as qualitative techniques) to gauge psychosocial and carer distress for the assessment of breathlessness in advanced disease.

Barriers to effective communication across the primary/secondary interface: examples from the ovarian cancer patient journey (a qualitative study).

Effective communication across the primary/secondary interface is vital for the planning and delivery of appropriate patient care throughout the cancer patient journey. This study describes GPs' views of the communication issues across the primary/secondary interface in relation to ovarian cancer patients using qualitative interviews with purposively sampled general practitioners (GPs) and an audit of hospital medical records of 30 deceased ovarian cancer patients. Issues raised by the GPs related to the content and format of communications, but of most concern was the tardiness. The time lag between dictation and typing letters ranged from 0 to 27 days, with a delay of up to 8 days for signing before transit through various mail systems to the GP. Three stages in the patient journey were characterized by particular issues: (1) in the pre-diagnostic and diagnostic stage was a need for prompt information regarding the results of tests and diagnoses, and clearer guidance on the use of tests and fast-track referrals; (2) in the active treatment phase, when GPs could lose touch with their patients, they needed effective communication in order to provide moral support and crisis management; and (3) when oncology withdrew and the focus of care switched back to the community for the terminal phase, GPs needed information to enable them to pick up the baton of care. There is a need to develop and evaluate interventions aimed at improving the content and speed of communications between secondary and primary care. Such interventions are likely to be complex and might include the greater use of telephone or fax for more selected communications, a review of secretarial support, the use of email, the development of GP designed proformas, the feasibility of patient/carer letter delivery options, nurse-led communication, universal electronic patient records, or a revisiting of the patient-held record.

The over-expression of the wild type or mutant forms of the presenilin-1 protein alters glycoprotein processing in a human neuroblastoma cell line.

Mutations in the presenilin proteins (PS1 and PS2) are responsible for more than 70% of the cases of the familial form of Alzheimer's disease (FAD). The proteins are expressed in the cell at a low level, primarily in the endoplasmic reticulum and cis Golgi, where they have been proposed to play a role in protein processing. As protein glycosylation is a key post-translational event that occurs within the Golgi, we have investigated the effect of altered PS1 expression levels on the protein glycosylation pattern using the SH-SY5Y human neuroblastoma cell line. In cells over-expressing either the wild type or mutant (M146L) PS1-FAD proteins, there was a decrease in the expression levels of protein-bound alpha2,3-linked sialic acid residues at the level of the cell membrane. This was particularly manifest as a significant decrease in the expression of the polysialic acid chain that is linked to the core oligosaccharide of the neural cell adhesion molecule in an alpha2,3 bond. These results suggest that the over-expression of either the wild type or mutant PS1 disturbs glycoprotein processing within the Golgi.

Defining patients as palliative: hospital doctors' versus general practitioners' perceptions.

There appears to be a lack of consensus on the classification of individual patients as 'for palliative care', although the extent of this is unknown. General practitioners (GPs) of 213 patients with a palliative diagnosis of lung or colo-rectal cancer were sent a one-page questionnaire to assess information sent by hospital doctors, and to establish the GPs' perception of patients' palliative status. A total of 185 questionnaires were returned (87% response rate). Of those GPs receiving information from the hospital, one in four rated the adequacy as less than positive; 26% reportedly received no information or received it 'too late'. In 20% of cases, GPs did not perceive patients as palliative, although hospital records suggested that they were, and death certificates received later potentially confirmed this. There was, however, no significant difference between GPs allocating a patient to palliative status or not, in terms of the promptness or adequacy of information received from the hospital, as rated by the GP. There was a significant difference in survival between patients whom GPs perceived as for palliative care and those they did not ('palliative' patients died, on average, 117 days earlier). Possible explanations of the differing perceptions of patients' palliative status are discussed. The findings have implications for patient care in the community, patients' informed choices, and palliative care research.

General practitioners' and district nurses' views of hospital at home for palliative care.

Cambridge Hospital at Home (CH@H) provides 24-h nursing in a patient's own home to patients requiring terminal and palliative respite care. To investigate views of the service, we surveyed all GPs and district nurses (DNs) in the catchment area of the scheme. Responses were received from 85% of DNs and 65% of GPs. The majority of DNs (93%) and GPs (57%) had patients referred to CH@H, whereas 90% of DNs and 42% GPs had patients admitted. The most commonly reported reason for non-referral was lack of availability of places (GPs 62%; DNs 63%). Ninety per cent DNs and 84% GPs rated continuation of the scheme as important. The most important reported benefits were 24-h care (GPs 84%; DNs 82%) and help in keeping patients at home (GPs 69%; DNs 83%). Seventy-four DNs also considered help in arranging discharge to be important. Almost half GPs and DNs considered CH@H worse than other NHS services in terms of availability and limits on the duration of care. Whilst 65% of DNs thought CH@H had reduced workload, 77% GPs reported it had made no difference or had increased it. Most indicated that CH@H made a difference in allowing patients to die at home (GPs 60%; DNs 68%). The CH@H scheme is viewed as beneficial for patients requiring palliative care at home, although GPs and DNs expressed realistic reservations about specific aspects of the scheme. With the emergence of Primary Care Trusts, NHS commissioning of hospice at home services will more firmly rest with primary care practitioners, who on balance clearly prize them.

Galpha i3 binding to calnuc on Golgi membranes in living cells monitored by fluorescence resonance energy transfer of green fluorescent protein fusion proteins.

Galphai3 is found both on the plasma membrane and on Golgi membranes. Calnuc, an EF hand protein, binds both Galphai3 and Ca(2+) and is found both in the Golgi lumen and in the cytoplasm. To investigate whether Galphai3 binds calnuc in living cells and where this interaction takes place we performed fluorescence resonance energy transfer (FRET) analysis between Galphai3 and calnuc in COS-7 cells expressing Galphai3-yellow fluorescent protein (YFP) and calnuc-cyan fluorescent protein (CFP). The tagged proteins have the same localization as the endogenous, nontagged proteins. When Galphai3-YFP and calnuc-CFP are coexpressed, a FRET signal is detected in the Golgi region, but no FRET signal is detected on the plasma membrane. FRET is also seen within the Golgi region when Galphai3 is coexpressed with cytosolic calnuc(DeltaN2-25)-CFP lacking its signal sequence. No FRET signal is detected when Galphai3(DeltaC12)-YFP lacking the calnuc-binding region is coexpressed with calnuc-CFP or when Galphai3-YFP and calnuc(DeltaEF-1,2)-CFP, which is unable to bind Galphai3, are coexpressed. Galphai3(G2AC3A)-YFP lacking its lipid anchors is localized in the cytoplasm, and no FRET signal is detected when it is coexpressed with wild-type calnuc-CFP. These results indicate that cytosolic calnuc binds to Galphai3 on Golgi membranes in living cells and that Galphai3 must be anchored to the cytosolic surface of Golgi membranes via lipid anchors for the interaction to occur. Calnuc has the properties of a Ca(2+) sensor protein capable of binding to and potentially regulating interactions of Galphai3 on Golgi membranes.

RGS-PX1, a GAP for GalphaS and sorting nexin in vesicular trafficking.

Heterotrimeric GTP-binding proteins (G proteins) control cellular functions by transducing signals from the outside to the inside of cells. Regulator of G protein signaling (RGS) proteins are key modulators of the amplitude and duration of G protein-mediated signaling through their ability to serve as guanosine triphosphatase-activating proteins (GAPs). We have identified RGS-PX1, a Galpha(s)-specific GAP. The RGS domain of RGS-PX1 specifically interacted with Galpha(s), accelerated its GTP hydrolysis, and attenuated Galpha(s)-mediated signaling. RGS-PX1 also contains a Phox (PX) domain that resembles those in sorting nexin (SNX) proteins. Expression of RGS-PX1 delayed lysosomal degradation of the EGF receptor. Because of its bifunctional role as both a GAP and a SNX, RGS-PX1 may link heterotrimeric G protein signaling and vesicular trafficking.

Loss of glomerular foot processes is associated with uncoupling of podocalyxin from the actin cytoskeleton.

Podocalyxin (PC), the major sialoprotein of glomerular epithelial cells (GECs), helps maintain the characteristic architecture of the foot processes and the patency of the filtration slits. PC associates with actin via ezrin, a member of the ERM family of cytoskeletal linker proteins. Here we show that PC is linked to ezrin and the actin cytoskeleton via Na(+)/H(+)-exchanger regulatory factor 2 (NHERF2), a scaffold protein containing two PDZ (PSD-95/Dlg/ZO-1) domains and an ERM-binding region. The cytoplasmic tail of PC contains a C-terminal PDZ-binding motif (DTHL) that binds to the second PDZ domain of NHERF2 in yeast two-hybrid and in vitro pull-down assays. By immunocytochemistry NHERF2 colocalizes with PC and ezrin along the apical domain of the GEC plasma membrane. NHERF2 and ezrin form a multimeric complex with PC, as they coimmunoprecipitate with PC. The PC/NHERF2/ezrin complex interacts with the actin cytoskeleton, and this interaction is disrupted in GECs from puromycin aminonucleoside-, protamine sulfate-, or sialidase-treated rats, which show a dramatic loss of foot processes, comparable to that seen in the nephrotic syndrome. Thus NHERF2 appears to function as a scaffold protein linking PC to ezrin and the actin cytoskeleton. PC/NHERF2/ezrin/actin interactions are disrupted in pathologic conditions associated with changes in GEC foot processes, indicating their importance for maintaining the unique organization of this epithelium.

RGS12 and RGS14 GoLoco motifs are G alpha(i) interaction sites with guanine nucleotide dissociation inhibitor Activity.

The regulators of G-protein signaling (RGS) proteins accelerate the intrinsic guanosine triphosphatase activity of heterotrimeric G-protein alpha subunits and are thus recognized as key modulators of G-protein-coupled receptor signaling. RGS12 and RGS14 contain not only the hallmark RGS box responsible for GTPase-accelerating activity but also a single G alpha(i/o)-Loco (GoLoco) motif predicted to represent a second G alpha interaction site. Here, we describe functional characterization of the GoLoco motif regions of RGS12 and RGS14. Both regions interact exclusively with G alpha(i1), G alpha(i2), and G alpha(i3) in their GDP-bound forms. In GTP gamma S binding assays, both regions exhibit guanine nucleotide dissociation inhibitor (GDI) activity, inhibiting the rate of exchange of GDP for GTP by G alpha(i1). Both regions also stabilize G alpha(i1) in its GDP-bound form, inhibiting the increase in intrinsic tryptophan fluorescence stimulated by AlF(4)(-). Our results indicate that both RGS12 and RGS14 harbor two distinctly different G alpha interaction sites: a previously recognized N-terminal RGS box possessing G alpha(i/o) GAP activity and a C-terminal GoLoco region exhibiting G alpha(i) GDI activity. The presence of two, independent G alpha interaction sites suggests that RGS12 and RGS14 participate in a complex coordination of G-protein signaling beyond simple G alpha GAP activity.

Direct binding of occupied urokinase receptor (uPAR) to LDL receptor-related protein is required for endocytosis of uPAR and regulation of cell surface urokinase activity.

Low-density lipoprotein receptor-related protein (LRP) mediates internalization of urokinase:plasminogen activator inhibitor complexes (uPA:PAI-1) and the urokinase receptor (uPAR). Here we investigated whether direct interaction between uPAR, a glycosyl-phosphatidylinositol-anchored protein, and LRP, a transmembrane receptor, is required for clearance of uPA:PAI-1, regeneration of unoccupied uPAR, activation of plasminogen, and the ability of HT1080 cells to invade extracellular matrix. We found that in the absence of uPA:PAI-1, uPAR is randomly distributed along the plasma membrane, whereas uPA:PAI-1 promotes formation of uPAR-LRP complexes and initiates redistribution of occupied uPAR to clathrin-coated pits. uPAR-LRP complexes are endocytosed via clathrin-coated vesicles and traffic together to early endosomes (EE) because they can be coimmunoprecipitated from immunoisolated EE, and internalization is blocked by depletion of intracellular K(+). Direct binding of domain 3 (D3) of uPAR to LRP is required for clearance of uPA-PAI-1-occupied uPAR because internalization is blocked by incubation with recombinant D3. Moreover, uPA-dependent plasmin generation and the ability of HT1080 cells to migrate through Matrigel-coated invasion chambers are also inhibited in the presence of D3. These results demonstrate that GPI-anchored uPAR is endocytosed by piggybacking on LRP and that direct binding of occupied uPAR to LRP is essential for internalization of occupied uPAR, regeneration of unoccupied uPAR, plasmin generation, and invasion and migration through extracellular matrix.

GIPC and GAIP form a complex with TrkA: a putative link between G protein and receptor tyrosine kinase pathways.

NGF initiates the majority of its neurotrophic effects by promoting the activation of the tyrosine kinase receptor TrkA. Here we describe a novel interaction between TrkA and GIPC, a PDZ domain protein. GIPC binds to the juxtamembrane region of TrkA through its PDZ domain. The PDZ domain of GIPC also interacts with GAIP, an RGS (regulators of G protein signaling) protein. GIPC and GAIP are components of a G protein-coupled signaling complex thought to be involved in vesicular trafficking. In transfected HEK 293T cells GIPC, GAIP, and TrkA form a coprecipitable protein complex. Both TrkA and GAIP bind to the PDZ domain of GIPC, but their binding sites within the PDZ domain are different. The association of endogenous GIPC with the TrkA receptor was confirmed by coimmunoprecipitation in PC12 (615) cells stably expressing TrkA. By immunofluorescence GIPC colocalizes with phosphorylated TrkA receptors in retrograde transport vesicles located in the neurites and cell bodies of differentiated PC12 (615) cells. These results suggest that GIPC, like other PDZ domain proteins, serves to cluster transmembrane receptors with signaling molecules. When GIPC is overexpressed in PC12 (615) cells, NGF-induced phosphorylation of mitogen-activated protein (MAP) kinase (Erk1/2) decreases; however, there is no effect on phosphorylation of Akt, phospholipase C-gamma1, or Shc. The association of TrkA receptors with GIPC and GAIP plus the inhibition of MAP kinase by GIPC suggests that GIPC may provide a link between TrkA and G protein signaling pathways.