Membrane Proteome-Wide Screening of Autoantibodies in CIDP Using Human Cell Microarray Technology

BACKGROUND AND OBJECTIVES

Autoantibody discovery in complex autoimmune diseases is challenging. Diverse successful antigen identification strategies are available, but, so far, have often been unsuccessful, especially in the discovery of protein antigens in which conformational and post-translational modification are critical. Our study assesses the utility of a human membrane and secreted protein microarray technology to detect autoantibodies in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP).

METHODS

A cell microarray consisting of human embryonic kidney-293 cells expressing >5,000 human proteins was used. First, a validation step was performed with 4 serum samples from patients with autoimmune nodopathy (AN) to assess the ability of this technology to detect circulating known autoantibodies. The ability of the cell microarray technology to discover novel IgG autoantibodies was assessed incubating the array with 8 CIDP serum samples. Identified autoantibodies were subsequently validated using cell-based assays (CBAs), ELISA, and/or tissue immunohistochemistry and analyzed in a cohort of CIDP and AN (n = 96) and control (n = 100) samples.

RESULTS

Serum anti-contactin-1 and anti-neurofascin-155 were detected by the human cell microarray technology. Nine potentially relevant antigens were found in patients with CIDP without other detectable antibodies; confirmation was possible in six of them: ephrin type-A receptor 7 (EPHA7); potassium-transporting ATPase alpha chain 1 and subunit beta (ATP4A/4B); leukemia-inhibitory factor (LIF); and interferon lambda 1, 2, and 3 (IFNL1, IFNL2, IFNL3). Anti-ATP4A/4B and anti-EPHA7 antibodies were detected in patients and controls and considered unrelated to CIDP. Both anti-LIF and anti-IFNL antibodies were found in the same 2 patients and were not detected in any control. Both patients showed the same staining pattern against myelinating fibers of peripheral nerve tissue and of myelinating neuron-Schwann cell cocultures. Clinically relevant correlations could not be established for anti-LIF and anti-IFNL3 antibodies.

DISCUSSION

Our work demonstrates the utility of human cell microarray technology to detect known and discover unknown autoantibodies in human serum samples. Despite potential CIDP-associated autoantibodies (anti-LIF and anti-IFNL3) being identified, their clinical and pathogenic relevance needs to be elucidated in bigger cohorts.

Human CEACAM1 is targeted by a Streptococcus pyogenes adhesin implicated in puerperal sepsis pathogenesis

Life-threatening bacterial infections in women after childbirth, known as puerperal sepsis, resulted in classical epidemics and remain a global health problem. While outbreaks of puerperal sepsis have been ascribed to Streptococcus pyogenes, little is known about disease mechanisms. Here, we show that the bacterial R28 protein, which is epidemiologically associated with outbreaks of puerperal sepsis, specifically targets the human receptor CEACAM1. This interaction triggers events that would favor the development of puerperal sepsis, including adhesion to cervical cells, suppression of epithelial wound repair and subversion of innate immune responses. High-resolution structural analysis showed that an R28 domain with IgI3-like fold binds to the N-terminal domain of CEACAM1. Together, these findings demonstrate that a single adhesin-receptor interaction can drive the pathogenesis of bacterial sepsis and provide molecular insights into the pathogenesis of one of the most important infectious diseases in medical history.

Platelet derived growth factor receptor β (PDGFRβ) is a host receptor for the human malaria parasite adhesin TRAP

Following their inoculation by the bite of an infected Anopheles mosquito, the malaria parasite sporozoite forms travel from the bite site in the skin into the bloodstream, which transports them to the liver. The thrombospondin-related anonymous protein (TRAP) is a type 1 transmembrane protein that is released from secretory organelles and relocalized on the sporozoite plasma membrane. TRAP is required for sporozoite motility and host infection, and its extracellular portion contains adhesive domains that are predicted to engage host receptors. Here, we identified the human platelet-derived growth factor receptor β (hPDGFRβ) as one such protein receptor. Deletion constructs showed that the von Willebrand factor type A and thrombospondin repeat domains of TRAP are both required for optimal binding to hPDGFRβ-expressing cells. We also demonstrate that this interaction is conserved in the human-infective parasite Plasmodium vivax, but not the rodent-infective parasite Plasmodium yoelii. We observed expression of hPDGFRβ mainly in cells associated with the vasculature suggesting that TRAP:hPDGFRβ interaction may play a role in the recognition of blood vessels by invading sporozoites.

KIR3DL3 Is an Inhibitory Receptor for HHLA2 that Mediates an Alternative Immunoinhibitory Pathway to PD1

Blockade of the PD1 pathway is a broadly effective cancer therapy, but additional immune-inhibitory pathways contribute to tumor immune evasion. HERV-H LTR-associating 2 (HHLA2; also known as B7H5 and B7H7) is a member of the B7 family of immunoregulatory ligands that mediates costimulatory effects through its interaction with the CD28 family member transmembrane and immunoglobulin domain containing 2 (TMIGD2). However, HHLA2 has also been known to have inhibitory effects on T cells. Here, we report that we have identified killer cell immunoglobulin-like receptor, three immunoglobulin domains and long cytoplasmic tail 3 (KIR3DL3) as an inhibitory receptor for HHLA2 in T cells and natural killer (NK) cells and have generated HHLA2 and KIR3DL3 antibodies that block the immune-inhibitory activity of HHLA2, preserving the costimulatory signal. It is known that HHLA2 is frequently expressed in several tumor types, including clear cell renal cell carcinoma (ccRCC). We found that HHLA2 expression was nonoverlapping with PDL1 expression in ccRCC, suggesting that HHLA2 mediates a mechanism of tumor immune evasion that is independent from PDL1. Blockade of both the PD1 and KIR3DL3 pathways may be a more effective way to reverse tumor immune evasion.See related Spotlight on p. 128.

Affinity maturation, humanization, and co-crystallization of a rabbit anti-human ROR2 monoclonal antibody for therapeutic applications

Antibodies are widely used as cancer therapeutics, but their current use is limited by the low number of antigens restricted to cancer cells. A receptor tyrosine kinase, receptor tyrosine kinase-like orphan receptor 2 (ROR2), is normally expressed only during embryogenesis and is tightly down-regulated in postnatal healthy tissues. However, it is up-regulated in a diverse set of hematologic and solid malignancies, thus ROR2 represents a candidate antigen for antibody-based cancer therapy. Here we describe the affinity maturation and humanization of a rabbit mAb that binds human and mouse ROR2 but not human ROR1 or other human cell-surface antigens. Co-crystallization of the parental rabbit mAb in complex with the human ROR2 kringle domain (hROR2-Kr) guided affinity maturation by heavy-chain complementarity-determining region 3 (HCDR3)-focused mutagenesis and selection. The affinity-matured rabbit mAb was then humanized by complementarity-determining region (CDR) grafting and framework fine tuning and again co-crystallized with hROR2-Kr. We show that the affinity-matured and humanized mAb retains strong affinity and specificity to ROR2 and, following conversion to a T cell-engaging bispecific antibody, has potent cytotoxicity toward ROR2-expressing cells. We anticipate that this humanized affinity-matured mAb will find application for antibody-based cancer therapy of ROR2-expressing neoplasms.

New Advances in Cell Microarray Technology to Expand Applications in Target Deconvolution and Off-Target Screening

Identifying the cell surface receptors of natural ligands, and deconvoluting the receptor targets of candidate drug leads, presents a challenge in medical research and drug discovery. Traditionally, success rates have been low, and screening efforts often generate numerous false-positive hits that require extensive follow-up to either validate or disregard. If successful, receptor identification enables the discovery of previously unknown, disease-relevant targets, provides critical insights into biological pathways and disease processes, and allows for secondary targets to be uncovered. By expressing the majority of the human plasma membrane proteome in human cells on glass slides in situ, human cell microarray technology provides a powerful approach for identifying receptor target interactions. This approach significantly increases the success rates in identifying specific primary receptor targets and off-targets while limiting the number of false-positive hits. Here we describe cell microarray technology, focusing on new advances including the use of whole cells as bait for receptor interactions, and the inclusion of secreted proteins that widens the utility of the technology in off-target screening.

Siglec-6 on Chronic Lymphocytic Leukemia Cells Is a Target for Post-Allogeneic Hematopoietic Stem Cell Transplantation Antibodies

Although the 5-year survival rate of chronic lymphocytic leukemia (CLL) patients has risen to >80%, the only potentially curative treatment is allogeneic hematopoietic stem cell transplantation (alloHSCT). To identify possible new monoclonal antibody (mAb) drugs and targets for CLL, we previously developed a phage display-based human mAb platform to mine the antibody repertoire of patients who responded to alloHSCT. We had selected a group of highly homologous post-alloHSCT mAbs that bound to an unknown CLL cell surface antigen. Here, we show through next-generation sequencing of cDNAs encoding variable heavy-chain domains that these mAbs had a relative abundance of ∼0.1% in the post-alloHSCT antibody repertoire and were enriched ∼1,000-fold after three rounds of selection on primary CLL cells. Based on differential RNA-seq and a cell microarray screening technology for discovering human cell surface antigens, we now identify their antigen as Siglec-6. We verified this finding by flow cytometry, ELISA, siRNA knockdown, and surface plasmon resonance. Siglec-6 was broadly expressed in CLL and could be a potential target for antibody-based therapeutic interventions. Our study reaffirms the utility of post-alloHSCT antibody drug and target discovery. Cancer Immunol Res; 6(9); 1008-13. ©2018 AACR.

Phenotypic screening reveals TNFR2 as a promising target for cancer immunotherapy

Antibodies that target cell-surface molecules on T cells can enhance anti-tumor immune responses, resulting in sustained immune-mediated control of cancer. We set out to find new cancer immunotherapy targets by phenotypic screening on human regulatory T (Treg) cells and report the discovery of novel activators of tumor necrosis factor receptor 2 (TNFR2) and a potential role for this target in immunotherapy. A diverse phage display library was screened to find antibody mimetics with preferential binding to Treg cells, the most Treg-selective of which were all, without exception, found to bind specifically to TNFR2. A subset of these TNFR2 binders were found to agonise the receptor, inducing iκ-B degradation and NF-κB pathway signalling in vitro. TNFR2 was found to be expressed by tumor-infiltrating Treg cells, and to a lesser extent Teff cells, from three lung cancer patients, and a similar pattern was also observed in mice implanted with CT26 syngeneic tumors. In such animals, TNFR2-specific agonists inhibited tumor growth, enhanced tumor infiltration by CD8+ T cells and increased CD8+ T cell IFN-γ synthesis. Together, these data indicate a novel mechanism for TNF-α-independent TNFR2 agonism in cancer immunotherapy, and demonstrate the utility of target-agnostic screening in highlighting important targets during drug discovery.

Mining Naïve Rabbit Antibody Repertoires by Phage Display for Monoclonal Antibodies of Therapeutic Utility

Owing to their high affinities and specificities, rabbit monoclonal antibodies (mAbs) have demonstrated value and potential primarily as basic research and diagnostic reagents, but, in some cases, also as therapeutics. To accelerate access to rabbit mAbs bypassing immunization, we generated a large naïve rabbit antibody repertoire represented by a phage display library encompassing >10 billion independent antibodies in chimeric rabbit/human Fab format and validated it by next-generation sequencing. Panels of rabbit mAbs selected from this library against two emerging cancer targets, ROR1 and ROR2, revealed high diversity, affinity, and specificity. Moreover, ROR1- and ROR2-targeting rabbit mAbs demonstrated therapeutic utility as components of chimeric antigen receptor-engineered T cells, further corroborating the value of the naïve rabbit antibody library as a rich and virtually unlimited source of rabbit mAbs.

Targeting Human Cancer by a Glycosaminoglycan Binding Malaria Protein

Plasmodium falciparum engineer infected erythrocytes to present the malarial protein, VAR2CSA, which binds a distinct type chondroitin sulfate (CS) exclusively expressed in the placenta. Here, we show that the same CS modification is present on a high proportion of malignant cells and that it can be specifically targeted by recombinant VAR2CSA (rVAR2). In tumors, placental-like CS chains are linked to a limited repertoire of cancer-associated proteoglycans including CD44 and CSPG4. The rVAR2 protein localizes to tumors in vivo and rVAR2 fused to diphtheria toxin or conjugated to hemiasterlin compounds strongly inhibits in vivo tumor cell growth and metastasis. Our data demonstrate how an evolutionarily refined parasite-derived protein can be exploited to target a common, but complex, malignancy-associated glycosaminoglycan modification.

Identification of anti-tumour biologics using primary tumour models, 3-D phenotypic screening and image-based multi-parametric profiling

Background

Monolayer cultures of immortalised cell lines are a popular screening tool for novel anti-cancer therapeutics, but these methods can be a poor surrogate for disease states, and there is a need for drug screening platforms which are more predictive of clinical outcome. In this study, we describe a phenotypic antibody screen using three-dimensional cultures of primary cells, and image-based multi-parametric profiling in PC-3 cells, to identify anti-cancer biologics against new therapeutic targets.

Methods

ScFv Antibodies and designed ankyrin repeat proteins (DARPins) were isolated using phage display selections against primary non-small cell lung carcinoma cells. The selected molecules were screened for anti-proliferative and pro-apoptotic activity against primary cells grown in three-dimensional culture, and in an ultra-high content screen on a 3-D cultured cell line using multi-parametric profiling to detect treatment-induced phenotypic changes. The targets of molecules of interest were identified using a cell-surface membrane protein array. An anti-CUB domain containing protein 1 (CDCP1) antibody was tested for tumour growth inhibition in a patient-derived xenograft model, generated from a stage-IV non-small cell lung carcinoma, with and without cisplatin.

Results

Two primary non-small cell lung carcinoma cell models were established for antibody isolation and primary screening in anti-proliferative and apoptosis assays. These assays identified multiple antibodies demonstrating activity in specific culture formats. A subset of the DARPins was profiled in an ultra-high content multi-parametric screen, where 300 morphological features were measured per sample. Machine learning was used to select features to classify treatment responses, then antibodies were characterised based on the phenotypes that they induced. This method co-classified several DARPins that targeted CDCP1 into two sets with different phenotypes. Finally, an anti-CDCP1 antibody significantly enhanced the efficacy of cisplatin in a patient-derived NSCLC xenograft model.

Conclusions

Phenotypic profiling using complex 3-D cell cultures steers hit selection towards more relevant in vivo phenotypes, and may shed light on subtle mechanistic variations in drug candidates, enabling data-driven decisions for oncology target validation. CDCP1 was identified as a potential target for cisplatin combination therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0415-0) contains supplementary material, which is available to authorized users.

Genetic engineering of the glucocorticoid receptor by fusion with the herpes viral protein VP22 causes selective loss of transactivation

The development of methods for engineering proteins with novel properties opens the way to manipulating intracellular processes in a therapeutically useful way. Glucocorticoids, acting via glucocorticoid receptors (GR), are potent anti-inflammatory agents, acting to oppose nuclear factor kappa B (NF kappa B) function. The herpes viral protein, VP22, has been reported to confer intercellular trafficking activity on 'cargo' proteins, potentially facilitating gene therapy with intracellular proteins. VP22GR, resulting from the addition of VP22 to the N terminal of GR, was equipotent with the wild-type GR in opposing NF kappa B p65-driven expression of an NF kappa B reporter gene. Surprisingly, VP22GR was incapable of inducing transactivation of positive glucocorticoid reporter genes (MMTV-luc and TAT3-luc). Furthermore, the VP22GR had powerful dominant negative activity on both endogenous and exogenous GR transactivation. VP22GR was cytoplasmic in quiescent cells, and after hormone addition underwent nuclear translocation to share the same distribution as the GR. The ability of the VP22GR to selectively confer and enhance glucocorticoid-dependent transrepression of NF kappa B may be of use therapeutically in e.g. transplant rejection, inflammatory arthritis or asthma.

Serum insulin-like growth factor-I, IGF binding protein-3 and IGFBP-3 protease activity after cranial irradiation

The relationship between peak growth hormone (GH), insulin-like growth factor I (IGF-I), IGF-I binding protein 3 (IGFBP-3) and IGFBP-3 protease activity was studied in 28 children and adolescents undergoing investigation of pituitary function 0.4-14.2 years after cranial or craniospinal irradiation for the treatment of CNS tumours distant from the hypothalamic-pituitary axis (n = 16) or prophylaxis against CNS leukaemia (n = 12). Seven out of 15 patients with GH deficiency (GHD) (defined as a peak GH concentration <7.5 ng/ml in a stimulation test) had IGF-I <-2 standard deviation score (SDS). None of the 28 patients had serum IGFBP-3 concentrations measured by radioimmunoassay (RIA) <-1.5 SDS with no difference between those with and without GHD. IGFBP-3 concentrations measured by RIA were strongly correlated to IGFBP-3 band density on Western ligand blot (WLB) (r = 0.71; p < 0.0001). IGFBP-3 protease activity was negatively correlated to IGFBP-3 by RIA (r = -0.55; p < 0.01) and to IGFBP-3 by WLB (r = -0.51; p < 0.01). Twenty-two patients had normal IGFBP-3 protease activity (<30% of the activity in pregnancy serum) indicating that serum IGFBP-3 protease activity does not account for the normal levels of IGFBP-3 in RIA. Low serum IGF-I but normal IGFBP-3 concentrations and in the majority normal IGFBP-3 protease activity was found in patients in the years after CNS irradiation. Neither serum IGF-I nor IGFBP-3 can be used as a reliable index of the development of radiation-induced GHD.

Structure/function of the human glucocorticoid receptor: tyrosine 735 is important for transactivation

Ligand-induced activation of the glucocorticoid receptor (GR) is not well understood. The GR ligand-binding domain was modeled, based on homology with the progesterone receptor. Tyrosine 735 interacts with the D ring of dexamethasone, and substitution of D ring functional groups results in partial agonist steroids with reduced ability to direct transactivation. Loss of the Tyr735 hydroxyl group by substitution to phenylalanine (Tyr735Phe) did not reduce ligand binding affinity [dissociation constant (Kd) 4.3 nM compared with Kd 4.6 nM for wild-type] and did not alter transrepression of an nuclear factor-kappaB (NF-kappaB reporter. But, there was a significant 30% reduction in maximal transactivation of a mouse mammary tumor virus (MMTV) reporter, although with an unchanged EC50 (8.6 nM compared with 6 nM). Substitution to a nonaromatic hydrophobic amino acid, valine (Tyr735Val), retained high-affinity ligand binding for dexamethasone (Kd 6 nM compared with 4.6 nM) and did not alter transrepression of NF-kappaB. However, there was a 36% reduction in MMTV activity with a right shift in EC50 (14.8 nM). The change to serine, a small polar amino acid (Tyr735Ser), caused significantly lower affinity for dexamethasone (10.4 nM). Maximal transrepression of NF-kappaB was unaltered, but the IC50 for this effect was increased. Tyr735Ser had a major shift in EC50 (118 nM) for transactivation of an MMTV reporter. Maximal transactivation of MMTV induced by the natural ligand cortisol was reduced to 60% by Tyr735Phe and Tyr735Val and was completely absent by Tyr735Ser. These data suggest that tyrosine 735 is important for ligand interpretation and transactivation.

Iodide-dependent regulation of thyroid follicular cell proliferation: a mediating role of autocrine insulin-like growth factor-I

An inhibitory action of intracellular iodide on the autocrine production of insulin-like growth factor-I (IGF-I) by thyroid follicular cells (TFCs) in vitro has been investigated as a possible mechanism underlying the iodide-dependent control of TFC proliferation. IGF-I release from primary monolayer cultures of porcine TFCs increased 5-fold between 24 and 168 h of incubation. Confirmation of a mediating role of IGF-I in TFC proliferation was obtained by exposing TFCs to an immunoadsorbing IGF-I antiserum, which led to a significant (P < 0.05) decline in [methyl-3H]thymidine incorporation, relative to TFCs exposed to preimmune serum. Exposure of TFCs to sodium iodide (NaI; 0.1-100 mumol/l) led to an attenuation of the IGF-I content of the cell-conditioned medium. This was accompanied by a reduction in [methyl-3H]thymidine incorporation that was affected by IGF-I immunoneutralization. The inhibitory effect of NaI on IGF-I production and [methyl-3H]thymidine incorporation were reversed by the thionamide compound methimazole (MMI; 1 mmol/l), exposure to which also led to significant (P < 0.001) increases above control values. However, a residual suppressive effect of NaI on [methyl-3H]thymidine incorporation suggested that certain of the TFC growth-attenuating effects of iodide may not be dependent upon organification. While providing evidence, therefore, for a direct relationship between iodide exposure, suppression of autocrine IGF-I production and a regulation of TFC proliferation, the present studies also suggest that suppression of TFC proliferation by iodide may be partially mediated by MMI-insensitive events.

Identification of exchange mechanisms for the regulation of intracellular pH in rat thyroid FRTL-5 cells

pH is maintained in cells by plasma membrane exchange mechanisms. In the absence of HCO3- ions, FRTL-5 cells regulate intracellular pH (pHi) by an Na+/H+ antiport but HCO3(-)-dependent exchangers cannot operate. We have investigated pHi regulation (by microfluorimetry and the pH sensitive dye 2',7'-bis(2-carboxyethyl)-5(6')-carboxyfluorescein) in small groups (five to six cells) of FRTL-5 thyroid cell monolayers held in Krebs-Ringer buffer (pH 7.4) with or without HCO3- ions. The exchangers were investigated with inhibitors (amiloride or its derivative dimethylamiloride for the Na+/H+ antiporter and the stilbene derivative disodium 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) for HCO3(-)-dependent mechanisms), ionic substitution and by NH4+/NH3 (10 mM) acid loading. Basal pHi was lower in the presence (7.3 +/- 0.058, mean +/- S.D., n = 14) than in the absence (7.59 +/- 0.078, n = 10) of HCO3- ions. In HCO3(-)-free media, cells recovered from acid load by 0.34 +/- 0.04 pH units in the first 2 min and finally reached a pHi of 7.35 +/- 0.06. This recovery was Na(+)-dependent and blocked by dimethylamiloride during the 15 min following intracellular acidification. In HCO3(-)-containing media, cells recovered from an acid load at a similar rate, but reached 99 +/- 10% (n = 9) of the baseline pH; this recovery was also dependent on Na+ ions. Moreover, although dimethylamiloride and DIDS reduced the rate of recovery to 0.06 +/- 0.02 and 0.18 +/- 0.04 pH units respectively during the 2-min period, the cells returned to the basal pHi within 15 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term effects of thyroid stimulating hormone and insulin on intracellular pH in FRTL-5 cells

We have studied the chronic effects of TSH (100 microU/ml) and insulin (10 micrograms/ml) on intracellular pH (pH(i)) in FRTL-5 cells using the pH sensitive probe 2'7-bis (2-carboxyethyl-5'-6') carboxyfluorescein. FRTL-5 cells were cultured on Petri dishes either in the presence of 4H, ie. Coons F-12 containing cortisol (10 nM), transferrin (0.5 microgram/ml), glycyl-histidyl lysine acetate (10 ng/ml) and somatostatin (10 micrograms/ml), or with 4H + insulin (5H), 4H + TSH, or 4H + TSH + insulin (6H). pH(i) was measured in small groups of cells by microspectrofluorimetry both in the presence and absence of bicarbonate ions after cells had been deprived of serum for at least a day. In the absence of TSH, insulin and bicarbonate ions, pH(i) was 7.26 +/- 0.18 (mean +/- SD, n = 49) rising to 7.89 +/- 0.09 (n = 59) and 7.43 +/- 0.1 (n = 55) in the presence of TSH (4H + TSH) and insulin (5H) respectively. Addition of both insulin and TSH (6H) resulted in a pH(i) of 7.75 +/- 0.09 (n = 40). In the absence of TSH and insulin, but the presence of bicarbonate ions, pH(i) was 7.29 +/- 0.12 (mean +/- SD n = 47) rising to 7.72 +/- 0.07 (n = 59) in 4H + TSH and 7.48 +/- 0.08 (n = 60) in 5H. pH(i) in the presence of both TSH and insulin was 7.81 +/- 0.03 (n = 60). In conclusion, both insulin and TSH caused an intracellular alkalinization, TSH markedly so, even in the presence of bicarbonate ions.

H(+)-dependent ATPase and K+ channel activities in the rat thyroid cell strain FRTL-5

Using the fluorescent indicators 2',7'-bis(2-carboxyethyl)-5'-(6')-carboxyfluorescein and Oxonol V to monitor intracellular pH (pHi) and cell membrane potential respectively, we have investigated the involvement of H(+)-dependent ATPase and H(+)-dependent K+ channels in the recovery of the rat thyroid cell strain FRTL-5 from experimentally induced cytosolic acidification and membrane hyperpolarization events. Following exposure of cells to the weak acid sodium butyrate (24 mmol/l) under bicarbonate-free incubation conditions, cytoplasmic acidification was maximal after 3 min, attaining a pHi of 6.42. The subsequent recovery of pHi was unimpaired by the absence of extracellular K+, but was reduced in the presence of the Na+ antagonist amiloride (1 mmol/l), recovering by 0.11 +/- 0.003 units, compared with 0.27 +/- 0.02 units under amiloride-free conditions. In the presence of the H(+)-dependent ATPase antagonist N,N'-dicyclohexylcarbodiimide (DCC), the pHi recovery observed in amiloride-containing, K(+)-free buffer was abolished. The recovery of pHi in Na(+)- and K(+)-containing buffer was accompanied by hyperpolarization of the cell membrane, the later stage of which was reduced after blockade of K+ channels with BaCl2, implying a major contribution of transmembrane K+ movement to such events. In contrast to its attenuating effect on pHi recovery, DCC was ineffective in reducing butyrate-dependent membrane hyperpolarization, suggesting that H(+)-dependent ATPase may not be a major contributory factor to this event. However, when K+ channels were blocked by addition of BaCl2, addition of DCC abolished the butyrate-induced membrane depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factor-I production and action in porcine thyroid follicular cells in monolayer: regulation by transforming growth factor-beta

The regulation of thyroid follicular cell growth in vitro involves autocrine or paracrine actions of insulin-like growth factor-I (IGF-I), which are partially suppressed by transforming growth factor-beta (TGF-beta). Using subconfluent monolayers of porcine thyroid follicular cells, the aims of this study were to establish whether the actions of TGF-beta involve changes in the synthesis of, or response to, IGF-I. We also investigated the extent to which inhibitory actions of iodide on IGF-I-dependent proliferation of thyroid follicular cells may be attributable to the production of TGF-beta by follicular cells, as opposed to iodide-mediated autoregulation events. Exposure of porcine thyroid follicular cells in subconfluent monolayer culture to TGF-beta over a 7-day period reduced both IGF-I release and the incorporation of [methyl-3H]thymidine into trichloroacetic acid-precipitable cellular material, while preincubation of cells with NaI (0.1 mmol/l) for 24 h prior to the addition of TSH reduced the stimulatory effect of the latter on IGF-I release over the following 7 days. Preincubation of cells with iodide also reduced basal (i.e. autonomous) [methyl-3H]thymidine incorporation. This effect was partially reversed when, following initial exposure to follicular cells, iodide-containing preincubation medium was immunoadsorbed with a neutralizing TGF-beta antiserum, and subsequently re-added to the cells. Furthermore, similar immunoadsorption of iodide-free preincubation medium resulted in an enhancement of the control level of [methyl-3H]thymidine incorporation when the treated medium was returned to the original cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Transmembrane Na+/H+ exchange in the rat thyroid cell strain FRTL-5: a possible role in insulin-like growth factor-I-mediated proliferation

Using the fluorescent pH indicator 2'7'-bis(2-carboxyethyl)-5'-(6')-carboxyfluorescein to monitor intracellular pH (pHi), we have investigated whether transmembrane Na+/H+ exchange, as measured by experimental changes in pHi under bicarbonate-free incubation conditions, may be involved in the early growth-promoting actions of insulin-like growth factor-I (IGF-I) on the rat thyroid cell stain FRTL-5. In initial studies to characterize Na+/H+ exchange in FRTL-5 cell suspensions, the recovery of a resting pHi in acid-loaded cells was shown to be dependent upon the presence of extracellular Na+, was enhanced by the presence of the sodium ionophore monensin and was abolished by amiloride, an antagonist of Na+/H+ antiport activity. Unlike TSH, which was without effect on the pHi of FRTL-5 cells for up to 15 min after addition, IGF-I (1000 micrograms/l) caused a rapid and sustained increase within 3 min, which was abolished in medium in which Na+ had been replaced with an iso-osmotic level of choline chloride. The change in pHi in response to IGF-I was mimicked by phorbol 12-myristate 13-acetate (PMA; 100 nmol/l), an activator of thyroid cell proliferation. In the presence of TSH, exposure of cells to IGF-I or PMA had no additional effect on the cytoplasmic alkalinization induced by either of these two agonists alone. However, blockade of transmembrane Na+/H+ exchange with amiloride inhibited both the individual actions of IGF-I and PMA on [methyl-3H]thymidine incorporation, and the synergistic interaction between TSH and IGF-I.(ABSTRACT TRUNCATED AT 250 WORDS)