P2X7 in Cancer: From Molecular Mechanisms to Therapeutics

P2X7 is a transmembrane receptor expressed in multiple cell types including neurons, dendritic cells, macrophages, monocytes, B and T cells where it can drive a wide range of physiological responses from pain transduction to immune response. Upon activation by its main ligand, extracellular ATP, P2X7 can form a nonselective channel for cations to enter the cell. Prolonged activation of P2X7, via high levels of extracellular ATP over an extended time period can lead to the formation of a macropore, leading to depolarization of the plasma membrane and ultimately to cell death. Thus, dependent on its activation state, P2X7 can either drive cell survival and proliferation, or induce cell death. In cancer, P2X7 has been shown to have a broad range of functions, including playing key roles in the development and spread of tumor cells. It is therefore unsurprising that P2X7 has been reported to be upregulated in several malignancies. Critically, ATP is present at high extracellular concentrations in the tumor microenvironment (TME) compared to levels observed in normal tissues. These high levels of ATP should present a survival challenge for cancer cells, potentially leading to constitutive receptor activation, prolonged macropore formation and ultimately to cell death. Therefore, to deliver the proven advantages for P2X7 in driving tumor survival and metastatic potential, the P2X7 macropore must be tightly controlled while retaining other functions. Studies have shown that commonly expressed P2X7 splice variants, distinct SNPs and post-translational receptor modifications can impair the capacity of P2X7 to open the macropore. These receptor modifications and potentially others may ultimately protect cancer cells from the negative consequences associated with constitutive activation of P2X7. Significantly, the effects of both P2X7 agonists and antagonists in preclinical tumor models of cancer demonstrate the potential for agents modifying P2X7 function, to provide innovative cancer therapies. This review summarizes recent advances in understanding of the structure and functions of P2X7 and how these impact P2X7 roles in cancer progression. We also review potential therapeutic approaches directed against P2X7.

A phase I clinical trial demonstrates that nfP2X7 -targeted antibodies provide a novel, safe and tolerable topical therapy for basal cell carcinoma

BACKGROUND

Expression of P2X₇ , an ATP-gated calcium channel, increases cancer cell proliferation and invasiveness. A variant of P2X₇ (termed nfP2X₇ ), in which a normally hidden epitope (E200) is exposed for antibody binding, is observed in a variety of different cancers.

OBJECTIVES

To investigate the safety, tolerability and pharmacokinetics and assess indicative efficacy of a novel antibody ointment as a therapeutic for basal cell carcinoma (BCC).

METHODS

An open-label, phase I clinical trial was undertaken at three dermatology clinics to evaluate the safety and tolerability of topical administration of an ointment containing 10% sheep polyclonal anti-nfP2X₇ antibodies (BIL010t) to primary BCC lesions twice daily for 28 days. Twenty-one patients with primary BCC lesions at least 0·5 cm² in area and less than 2·0 cm in diameter were enrolled. The primary end points were safety, tolerability and pharmacokinetics. Change in lesion size after treatment was determined and histology was performed on pretreatment and end-of-treatment (EOT) biopsies.

RESULTS

Compliance was very high, with treatment being well tolerated. The most common adverse events were treatment site erythema, pruritus, dryness and pain. There was no evidence of systemic penetration of the sheep antibody. Lesions were measured prior to and after 28 days of treatment, with 65% of patients showing a reduction in lesion area, 20% showing no change and 15% showing an increase. Histopathology of post-treatment excision of lesion sites showed eight patients with stable disease, nine with partial response and three with complete response.

CONCLUSIONS

Antibodies against nfP2X₇ (BIL010t) provide a novel, safe and well-tolerated treatment for BCC.

P2X purinoceptor subtypes on paraventricular nucleus neurones projecting to the rostral ventrolateral medulla in the rat

The rostral ventrolateral medulla (RVLM) is essential for the generation of sympathetic nerve activity. The RVLM receives a substantial innervation from the hypothalamic paraventricular nucleus (PVN). Activation of P2X purinoceptors via ATP has been shown to mediate fast excitatory synaptic neurotransmission. There is mounting evidence to suggest the presence of P2X purinoceptors in hypothalamic nuclei, including the PVN. In this study, we determined whether P2X1-P2X6 purinoceptor subtypes were present on PVN neurones that projected to the RVLM. Injection of the retrogradely transported tracer, rhodamine-tagged microspheres, into the pressor region of the RVLM was used to identify the neurones in the PVN that innervated the RVLM. P2X1-P2X6 purinoceptors were detected by immunohistochemistry. Double-labelled neurones were quantified and expressed as a proportion of the retrogradely labelled neurones. The proportions of double-labelled neurones for each of the P2X purinoceptor subtypes varied, on average, from 14 to 29%. The P2X3 purinoceptor subtype was found to be the dominant purinoceptor subtype present on PVN neurones projecting to the RVLM. Additionally it was apparent that more than one P2X purinoceptor subtype was present on the PVN neurones projecting to the RVLM, since the sum of the average percentages of double-labelled neurones for each P2X purinoceptor subtype exceeded 100%. These findings highlight the presence of the P2X1-P2X6 purinoceptors on PVN neurones projecting to the RVLM. The results suggest a potential role for ATP in the PVN in the regulation of sympathetic nerve activity.

Purinoceptors are involved in the induction of an osmolyte permeability in malaria-infected and oxidized human erythrocytes

In human erythrocytes, infection by the malaria parasite Plasmodium falciparum or oxidative stress induces a new organic osmolyte and anion permeability. To examine a role for autocrine purinoceptor signaling during this induction process, erythrocytic purinoceptor expression, and ATP release were determined. Furthermore, using pharmacological and genetic approaches the dependence on purinoceptor signaling of osmolyte permeability and Plasmodium development, both in vitro and in vivo, were assessed. Extracellular ATP did not induce an osmolyte permeability in non-infected or non-oxidized erythrocytes. ATP and other purinoceptor agonists increased the induction of osmolyte permeability during infection or oxidation as measured by isosmotic hemolysis and patch-clamp recording. Purinoceptor antagonists and apyrase decreased the induced permeability. The observed pharmacology suggested the involvement of P2Y purinoceptors. Accordingly, human erythrocytes expressed P2Y1 protein. Moreover, P2Y1-deficient mouse erythrocytes exhibited a delayed appearance of the osmolyte permeability during P. berghei infection- or oxidation compared with wild-type erythrocytes. Furthermore, the nonspecific purinoceptor antagonist suramin decreased in vitro growth and DNA/RNA amplification of P. falciparum in human erythrocytes and decreased in vivo growth of P. berghei. P. berghei developed slower in P2Y1-deficient mice in vivo compared with wild-type animals. In conclusion, induction of the osmolyte permeability in Plasmodium-infected erythrocytes involves autocrine purinoceptor signaling.

Differentiating keratoacanthoma from squamous cell carcinoma by the use of apoptotic and cell adhesion markers

AIMS

Keratoacanthomas (KA) are well-differentiated squamoproliferative skin lesions that grow rapidly and regress spontaneously. In contrast, squamous cell carcinomas (SCC) can have variable differentiation, inexorably progress and on occasion metastasize. Distinguishing between KA and SCC using haematoxylin and eosin-stained sections from an initial biopsy can often be difficult. There is also some debate as to whether KA is simply a variety of well-differentiated SCC or a distinct entity.

METHODS AND RESULTS

Initial biopsy sections from 25 cases of SCC and 20 of KA were labelled with markers for both the initiation (the cytolytic receptor P2X7) and end-stage (terminal deoxynucleotidyl transferase biotin-dUTP nick end labelling) of apoptosis, telomerase-associated protein (TP1) and the cell adhesion protein E-cadherin. As this was a retrospective study, the clinical outcome of each case was known. This resulted in a unique labelling pattern of each marker for SCC and KA, allowing a differential diagnosis between the two conditions. The simplest marker to use for this purpose was anti-P2X7. Sections from five cases that were initially very difficult to diagnose were correctly identified as SCC using this method.

CONCLUSIONS

These results support the view that KA has a different pathogenesis and biochemistry from that of SCC, and is a distinct entity. Anti-P2X7 labelling, using routine immunohistochemical techniques, provides a method for differentially diagnosing these conditions.

Expression of the apoptotic calcium channel P2X7 in the glandular epithelium

In the current study, expression of the apoptotic calcium channel receptor P2X(7) and prostate-specific antigen (PSA) levels were studied in biopsy cores from 174 patients as well as 20 radical prostatectomy cases. In clinical biopsies, we have previously demonstrated that P2X(1 )and P2X(2) calcium channel receptors are absent from normal prostate epithelium that does not progress to prostate cancer within 5 years. In cases that did progress to prostate cancer however, P2X(1 )and P2X(2) labeling was observed in a stage-specific manner first in the nucleus, then the cytoplasm and finally on the apical epithelium, as prostate cancer developed. These markers were present up to 5 years before cancer was detectable by the usual morphological criteria (Gleason grading) as determined by H and E staining. In the current study, the apoptotic calcium channel receptor P2X(7) yielded similar results to that of P2X(1) and P2X(2). Using radical prostatectomy tissue sections as well as biopsies, these changes in calcium channel metabolism were noted throughout the prostate, indicating a field effect. This finding suggests that the presence of a prostate tumor could be detected without the need for direct sampling of tumor tissue, leading to detection of false negative cases missed by H or E stain. The reliability of PSA levels as a prognostic indicator has been questioned in recent years. In the current study, PSA levels were correlated with the P2X(7) labeling results. All patients who exhibited no P2X(7) labeling had a prostatic serum antigen (PSA) level of <2. Patients who exhibited stage-specific P2X(7) expression, and who later developed obvious prostate cancer as diagnosed by H and E stain, all had a PSA > 2. This finding suggests that increasing PSA may be an accurate indicator of cancer development.

Extracellular ATP increases cation fluxes in human erythrocytes by activation of the P2X7 receptor

Canine erythrocytes are known to undergo a reversible increase in cation permeability when incubated with extracellular ATP. We have examined the expression and function of P2X receptors on human erythrocytes using confocal microscopy and a panel of anti-P2X(1-7) antibodies and have measured monovalent cation fluxes in the presence of various nucleotide agonists. Human erythrocytes expressed P2X7 receptors on all cells examined from eight of eight subjects, as well as P2X2 at a far lower staining intensity in six of eight subjects. ATP stimulated the efflux of 86Rb+ (K+) from human erythrocytes in a dose-dependent fashion with an EC50 of approximately 95 microM. Other nucleotides also induced an efflux of 86Rb+ from erythrocytes with an order of agonist potency of 2'- and 3'-O(4-benzoylbenzoyl) ATP (BzATP) > ATP > 2-methylthio-ATP (2MeSATP) > adenosine 5'-O-(3-thiotriphosphate) (ATPgammaS), whereas ADP or UTP had no effect. ATP-induced efflux of 86Rb+ from erythrocytes was inhibited by extracellular Na+ and oxidized ATP, as well as by KN-62, an antagonist specific for the human P2X7 receptor. When erythrocytes were incubated in isotonic KCl medium, the addition of ATP stimulated an 86Rb+ influx approximately equal in magnitude to ATP-stimulated 86Rb+ efflux from the same cells. BzATP also stimulated the influx of 22Na+ into erythrocytes incubated in isotonic NaCl medium. Both ATP-induced efflux and influx of 86Rb+ and 22Na+ were impaired in erythrocytes from subjects who had inherited loss-of-function polymorphisms in the P2X7 receptor. These results suggest that the reversible permeabilization of erythrocytes by extracellular ATP is mediated by the P2X7 receptor.

An Arg307 to Gln polymorphism within the ATP-binding site causes loss of function of the human P2X7 receptor

The P2X(7) receptor is a ligand-gated channel that is highly expressed on mononuclear cells of the immune system and that mediates ATP-induced apoptosis. Wide variations in the function of the P2X receptor have been observed, explained in part by (7)loss-of-function polymorphisms that change Glu(496) to Ala (E496A) and Ile(568) to Asn (I568N). In this study, a third polymorphism, which substitutes an uncharged glutamine for the highly positively charged Arg(307) (R307Q), has been found in heterozygous dosage in 12 of 420 subjects studied. P2X(7) function was measured by ATP-induced fluxes of Rb(+), Ba(2+), and ethidium(+) into peripheral blood monocytes or various lymphocyte subsets and was either absent or markedly decreased. Transfection experiments showed that P2X(7) carrying the R307Q mutation lacked either channel or pore function despite robust protein synthesis and surface expression of the receptor. The monoclonal antibody (clone L4) that binds to the extracellular domain of wild type P2X(7) and blocks P2X(7) function failed to bind to the R307Q mutant receptor. Differentiation of monocytes to macrophages up-regulated P2X(7) function in cells heterozygous for the R307Q to a value 10-40% of that for wild type macrophages. However, macrophages from a subject who was double heterozygous for R307Q/I568N remained totally non-functional for P2X(7), and lymphocytes from the same subject also lacked ATP-stimulated phospholipase D activity. These data identify a third loss-of-function polymorphism affecting the human P2X(7) receptor, and since the affected Arg(307) is homologous to those amino acids essential for ATP binding to P2X(1) and P2X(2), it is likely that this polymorphism abolishes the binding of ATP to the extracellular domain of P2X(7).

Early prostate cancer detected using expression of non-functional cytolytic P2X7 receptors

AIMS

To detect early prostate cancer reliably by monitoring the expression of non-functional P2X(7) cytolytic purinergic receptors.

METHODS AND RESULTS

P2X(7) receptors were absent from normal prostate epithelium obtained from post mortem tissue and tissue from cases of transurethral resection collected from young men (n = 23) who were confirmed to be free of cancer at later procedures 5-10 years after collection of the original samples. However, P2X(7) was present in every case of 116 confirmed prostate cancers regardless of Gleason grade or patient age. P2X(7) was present in apparently normal epithelial cells in acini well outside the tumour margins, but appeared in a distinct stage-specific manner commencing with the nucleus, progressing to the cytoplasm and collecting finally on the apical membrane of the epithelial cells in morphologically distinct cancer. The pattern of P2X(7) receptor localization in the epithelial cells was recorded in earlier biopsies obtained from the same patient cohort. One hundred and fourteen of 116 prostates stained positively for P2X(7) at the earliest biopsy, though generally with a less advanced pattern of distribution.

CONCLUSIONS

The appearance of P2X(7) receptors in normal prostate tissue adjacent to prostate tumours makes direct tumour biopsy less critical for positive cancer diagnosis and enables cancer progression to be monitored.

Differentiation between Cancerous and Normal Hyperplastic Lobules in Breast Lesions

Determining the risk that a particular area of hyperplastic breast tissue will progress to cancer is difficult and is currently expressed only as a general risk factor within the population. Using an antibody against the apoptotic purinergic receptor P2X7, we examined 40 cases each of the following histological categories: normal, moderate, florid and atypical hyperplasia, lobular carcinoma in situ, ductal carcinoma in situ, invasive lobular and invasive ductal carcinoma. These were previously diagnosed by H&E and supplied by clinical laboratories as tissue sections. Normal and mildly hyperplastic epithelium was devoid of the cytolytic P2X7 receptors whereas all epithelial cells in all cases of in situ or invasive lobular or ductal carcinoma labelled intensely. The lobular and ductal in situ cases labelled intracellularly while the invasive epithelial cancer cells showed intense cell surface label indicating an attempt was being made to induce apoptosis. All these receptors however are non-functional and thus unable to induce apoptosis. Approximately 10% of all hyperplastic lobules examined in the biopsied tissue, regardless of H&E classification, labelled for P2X7, which is suggestive of early metabolic cancerous change. The acini within lobules were either completely labelled with P2X7 or were completely devoid of the receptor. A potential advantage of this method lies in identifying early cancerous change in hyperplastic lobules and in establishing the true extent of cancerous spread in infiltrating lesions, thus facilitating the task of reporting clear surgical margins.

Loss of purinergic P2X receptor innervation in human detrusor and subepithelium from adults with sensory urgency

Purinergic P2X receptors associated with the parasympathetic nerves supplying human bladder smooth muscle (detrusor) are implicated in control of detrusor contractility. The relative abundance of all seven subtypes colocalised with synaptic vesicles on parasympathetic nerves was examined in specimens from normal adult bladder and in adults with the urodynamics findings of sensory urgency (SU) to determine how receptor distribution varied in patients with a small bladder capacity. Alteration in control of detrusor innervation was examined with P2X subtype-specific antibodies and an antibody (SV2) against synaptic vesicles, using immunofluorescence and confocal microscopy. Detrusor samples were taken from: controls, at cystectomy for cancer or cystoscopic biopsy for haematuria (n=22, age 33-88 years) and adults with sensory urgency at cystoscopy/cystodistension (n=11, age 37-70 years). Normal adult specimens contained detrusor muscle innervated by parasympathetic nerves possessing large varicosities (1.2 microm) distributed along their length. These mostly all showed colocalised patches of presynaptic P2X(1,2,3,5) subtypes while presynaptic subtypes P2X(4,6,7) were present in only 6-18% of varicosities. Detrusor nerve varicosities from SU patients revealed general loss of all presynaptic P2X subtypes with the proportion containing receptors reducing to only 0.5-5% depending on P2X subtype. The same loss was recorded from the sensory nerves in the surrounding lamina propria. This specific loss of P2X receptors may impair control of detrusor distension and contribute to the pathophysiology of sensory urgency.

ATP modulates intracellular Ca2+ and firing rate through a P2Y1 purinoceptor in cane toad pacemaker cells

The effect of extracellular ATP (10-100 microM) on intracellular Ca2+ concentration ([Ca2+]i) and firing rate has been studied in single pacemaker cells isolated from the sinus venosus of cane toads. In spontaneously firing cells, ATP initially increased peak [Ca2+]i by 43 +/- 5 %, increased diastolic [Ca2+]i by 20 + 3 % and increased the firing rate by 58 +/- 8 %. These early effects were followed by a late phase in which both the peak [Ca2+]i and the firing rate declined. Adenosine, and UTP (respectively, P1- and P2Y2,4,6-selective agonists) caused no significant change in [Ca2+]i or firing rate, while alphabeta-methylene ATP (a P2X1,3 agonist) caused a small increase in firing rate but no changes in [Ca2+]i. In contrast the P2Y1-selective agonist 2-MesADP (1 microM) mimicked the biphasic effects of ATP and these effects were inhibited by the purinoceptor antagonists suramin and PPADS and by the P2Y1-selective antagonist MRS 2179. Immunohistochemistry established that P2Y1 purinoceptors were present on the cell surface. Western blotting analysis demonstrated that the P2Y1 antibody recognised a 57 kDa protein. After sarcoplasmic reticulum Ca2+ release was prevented with caffeine or ryanodine, ATP no longer had any effect on [Ca2+]i or firing rate. Furthermore, the SR Ca2+ store content was decreased during the late phase of 2-MesADP application. The effect of ATP was coupled to phospholipase C (PLC) activity because the PLC inhibitor U-73122 eliminated the effects of ATP. Our study shows that in toad pacemaker cells, the biphasic effects of ATP on pacemaker activity are mainly through P2Y1 purinoceptors, which are able to modulate Ca2+ release from the SR Ca2+ store.

Effects of pathophysiological concentrations of albumin on NHE3 activity and cell proliferation in primary cultures of human proximal tubule cells

The progression of renal disease correlates strongly with hypertension and the degree of proteinuria, suggesting a link between excessive Na+ reabsorption and exposure of the proximal tubule to protein. The present study investigated the effects of albumin on cell growth and Na+ uptake in primary cultures of human proximal tubule cells (PTC). Albumin (1.0 mg/ml) increased cell proliferation to 134.1 +/- 11.8% (P < 0.001) of control levels with no change in levels of apoptosis. Exposure to 0.1 and 1.0 mg/ml albumin increased total 22Na+ uptake to 119.1 +/- 6.3% (P = 0.005) and 115.6 +/- 5.3% (P < 0.006) of control levels, respectively, because of an increase in Na+/H+ exchanger isoform 3 (NHE3) activity. This was associated with an increase in NHE3 mRNA to 161.1 +/- 15.1% (P < 0.005) of control levels in response to 0.1 mg/ml albumin. Using confocal microscopy with a novel antibody raised against the predicted extracellular NH2 terminus of human NHE3, we observed in nonpermeabilized cells that exposure of PTC to albumin (0.1 and 1.0 mg/ml) increased NHE3 at the cell surface to 115.4 +/- 2.7% (P < 0.0005) and 122.4 +/- 3.7% (P < 0.0001) of control levels, respectively. This effect was paralleled by significant increases in NHE3 in the subplasmalemmal region as measured in permeabilized cells. These albumin-induced increases in expression and activity of NHE3 in PTC suggest a possible mechanism for Na+ retention in response to proteinuria.

Localisation of p2x2 receptor subunit immunoreactivity on nitric oxide synthase expressing neurones in the brain stem and hypothalamus of the rat: a fluorescence immunohistochemical study

A large body of evidence suggests that nitric oxide (NO) and ATP act as neurotransmitters in the regulatory mechanisms concerning several autonomic functions at the level of both the hypothalamus and the brain stem. In the present study, we investigated whether neuronal NO synthase containing neurones also express P2X(2) receptor subunit of the ATP-gated ion channel via double-labelling fluorescence immunohistochemistry. Our data demonstrate that a high percentage of neuronal NO synthase-immunoreactive neurones are also P2X(2)-immunoreactive in the rostral ventrolateral medulla (98%) and supraoptic nucleus of the hypothalamus (92%). Significant numbers of neuronal NO synthase-immunoreactive neurones are also P2X(2)-immunoreactive in the subpostremal (48%) and commissural (65%) subdivisions of the nucleus tractus solitarius. In the caudal ventrolateral medulla and raphe obscurus, 96% and 89%, respectively, of neuronal NO synthase containing neurones also express P2X(2) receptor subunit. In contrast to the supraoptic nucleus, there was a lower percentage of co-localisation between NO synthase and P2X(2) receptor subunit in the paraventricular nucleus of the hypothalamus. In summary, this study demonstrates for the first time that there is a widespread co-localisation of neuronal NO synthase and P2X(2) receptor subunit in the hypothalamus and brain stem of the rat. Further studies are required to elucidate whether NO and ATP functionally interact within the hypothalamus and the brain stem.

An Ile-568 to Asn polymorphism prevents normal trafficking and function of the human P2X7 receptor

The P2X(7) receptor is a ligand-gated channel that is highly expressed on mononuclear cells and that mediates ATP-induced apoptosis of these cells. Wide variations in the function of the P2X(7) receptor have been observed, in part because of a loss-of-function polymorphism that changes Glu-496 to Ala without affecting the surface expression of the receptor on lymphocytes. In this study a second polymorphism (Ile-568 to Asn) has been found in heterozygous dosage in three of 85 normal subjects and in three of 45 patients with chronic lymphocytic leukemia. P2X(7) function was measured by ATP-induced fluxes of Rb(+), Ba(2+), and ethidium(+) into various lymphocyte subsets and was decreased to values of approximately 25% of normal. The expression of the P2X(7) receptor on lymphocytes was approximately half that of normal values as measured by the binding of fluorescein-conjugated monoclonal antibody. Transfection experiments showed that P2X(7) carrying the Ile-568 to Asn mutation was non-functional because of the failure of cell surface expression. The differentiation of monocytes to macrophages with interferon-gamma up-regulated P2X(7) function in cells heterozygous for the Ile-568 to Asn mutation to a value around 50% of normal. These data identify a second loss-of-function polymorphism within the P2X(7) receptor and show that Ile-568 is critical to the trafficking domain, which we have shown to lie between residues 551 and 581.

Increased expression of apoptotic markers in melanoma

Extensive labelling for the apoptotic markers calcium channel receptor P2X(7) and caspase-3 and telomerase activity was co-localized at a similar intensity in areas affected by superficial spreading melanoma obtained from 80 patients. Labelling for each of these markers also extended 2 microm from the melanoma into the keratinocyte layer of the adjacent normal epidermis. Conversely, the calcium-regulating receptors P2X(1-3) and P2Y(2) (found in normal but not neoplastic skin) were fully de-expressed within 2 microm of the melanoma but fully expressed beyond that distance. The cell adhesion protein E-cadherin (also only present in normal skin) was progressively de-expressed from a point 2 microm from the melanoma until full de-expression within the lesion. These results show that telomerase-induced proliferation and defensive apoptosis are co-localized and simultaneous processes in melanoma tissue. Melanoma cell proliferation appears to overwhelm the apoptotic defence, perhaps due to the anti-apoptotic effects of telomerase. In addition, keratinocyte regulation of the epidermis and dermis is severely compromised by the loss of E-cadherin and P2X(1-3) and P2Y(2) receptors, resulting in a lesion that is aggressive and malignant.

Specific detection of non-functional human P2X(7) receptors in HEK293 cells and B-lymphocytes

P2X(7) receptor/channels mediate ATP-induced apoptosis in a range of cells including lymphocytes. HEK293 cells were transfected with wild-type human P2X(7) receptor or site-directed mutant constructs (K193A, K311A and E496A) known to be non-functional from measurements of barium/ethidium influx in the presence of ATP or 2',3'-O-(4-benzoylbenzoyl)-ATP. An antibody was designed against an epitope from a loop adjacent to the extracellular ATP site. The epitope was unavailable in cells expressing normal functional surface receptors. Non-functional surface receptors as well as intracellular receptors selectively bound the antibody. So did B-lymphocytes from chronic lymphocytic leukemia patients expressing non-functional (E496A) mutant receptor.

Markers for the development of early prostate cancer

Biochemical and genetic changes precede histologically identifiable changes accompanying cell transformation often by months or years. De-expression of the extracellular matrix adhesive glycoprotein tenascin and the cell-to-cell adherent protein E-cadherin have been suggested as markers of early neoplastic change in prostate epithelial cells. Previous studies have been inconclusive, probably due to epitope masking. This study examined 2,378 biopsy cores from 289 prostates using a heat antigen retrieval protocol at low pH to improve the accuracy of detection. Tenascin and E-cadherin de-expression was correlated with purinergic receptor and telomerase-associated protein labelling, as well as prostate-specific antigen (PSA) levels and Gleason scores. E-cadherin was a poor marker, as it was expressed in all lesions except carcinomas of the highest Gleason score. Tenascin was maximally expressed in the extracellular matrix and acinar basement membrane in normal and prostatic intraepithelial neoplasia tissue. In prostate cancer tissue, tenascin expression did not correlate with Gleason score but was significantly de-expressed as purinergic receptor and telomerase-associated protein expression increased. Marked changes in tenascin, telomerase-associated protein, and purinergic receptor expression were apparent before any histological abnormalities were visible by haematoxylin and eosin (H&E) stain, making these potential markers for early and developing prostate cancer. Moreover, the potential increased accuracy of diagnosis of underlying prostate cancer using purinergic receptor translocation (PRT) assessment suggests that PSA levels may be more accurate than has generally been supposed when apparent false negatives arising from H&E-based diagnoses are correctly categorized.

Detection of preneoplasia in histologically normal prostate biopsies

P2X immunolabeling of prostate detected preneoplastic changes in apparently normal tissue. Labeling occurred in two well-defined stages before the diagnostic histological markers of cancer were visible. As cancer progressed, the location of P2X expression changed from confinement within individual nuclei in the acini (stage 1) to a cytoplasmic punctate label in the acinal epithelium, with an associated removal of nuclear stain (stage 2). Finally, in advanced cases, where clear morphological evidence of cancer was apparent, the P2X label condensed exclusively on the apical epithelium (stage 3). BPH/normal tissue was entirely devoid of P2X label. Biopsy samples (77) were tested in three categories. One group (35) were diagnosed as normal benign prostatic hyperplasia (BPH) on the basis of haematoxylin and eosin (H&E) stain, although underlying disease was suspected. Of these, 14 (40%) were clearly normal and appeared entirely devoid of label, 13 (37%) exhibited the first stage of P2X receptor labeling and the remaining eight (23%) exhibited second stage labeling. The accompanying H&E-stained sections of all these cases had a normal appearance. Low grade cancer biopsy samples with Gleason scores G4-7 (25) all revealed widespread second stage receptor labeling in areas of both normal and cancerous morphology, while 17 high grade cancer biopsy samples (Gleason G8-10) all showed third stage labeling along with some residual second stage labeling. The features of each P2X labeling stage occupied the entire histological area affected, offering more opportunity to diagnose the tissue than was supplied by the more-localised diagnostic features identified by H&E-stain. Besides detecting cases of preneoplasia in biopsies with a normal H&E appearance, this technique was also able to rule out the presence of neoplasia in purely hyperplasic prostates by the absence of any P2X labeling.Prostate Cancer and Prostatic Diseases (2001) 4, 92-96

Antisense co-suppression of G(alpha)(q) and G(alpha)(11) demonstrates that both isoforms mediate M(3)-receptor-activated Ca(2+) signalling in intact epithelial cells

We used replication-deficient adenoviruses overexpressing antisense against G(q) class alpha-subunits to determine the roles of G(q) and G(11) in mediating M(3)-receptor-coupled Ca(2+) mobilization in intact HT29 human colonic carcinoma epithelial cells. Western blot analysis and confocal microscopy showed that the viruses expressing antisense directed against the alpha-subunits of G(q) or G(11) produced isoform-specific reductions in the levels of these alpha-subunits. Fura-2 was used to measure changes in the Ca(2+) response following activation of the M(3) receptors by carbachol. The G(alpha)(q) antisense virus suppressed the peak Ca(2+) response by 70%, whereas the G(alpha)(11) antisense virus reduced it by 34%. We then used co-infection with both viruses to determine the effect of concomitant suppression of both G(alpha)(q) and G(alpha)(11). Overexpression of antisense to both alpha-subunits reduced by approximately 50% the levels of both G(alpha)(q) and G(alpha)(11). It also almost completely inhibited the Ca(2+) response to carbachol. These data show that both G(q) and G(11) are involved in mediating the action of the M(3) receptor on cytosolic Ca(2+) in HT29 cells. Furthermore, they suggest that the coupling of the M(3) receptor to these G proteins is specific, in that G(alpha)(q) cannot substitute for G(alpha)(11), and vice versa.

Purinergic receptor distribution in endothelial cells in blood vessels: a basis for selection of coronary artery grafts

Expression levels of the purinergic P2X receptor subunits (P2X(1) to P2X(7)) and P2Y(2) were examined in the endothelial cell layer of internal mammary artery (Ann. Thorac. Surg. 54 (1992) 652), radial artery (Ann. Thorac. Surg. 16 (1973) 111) and saphenous vein (Ann. Thorac. Surg. 20 (1975) 628) samples obtained at surgery for coronary artery bypass grafts using immunohistochemistry and confocal microscopy. Similar levels of P2X(1), P2X(2), P2X(3), P2X(7) and P2Y(2) were found in the endothelial cells in all vessels examined while the levels of P2X(5) and P2X(6) were uniformly lower. A clear difference was measured in P2X(4) expression between arteries and veins. Both radial and internal mammary arteries exhibited very low levels of P2X(4) whereas the level in the saphenous vein was 14.6 fold higher (P<0.0001), approaching that of the major receptor subtypes. These data showing strong expression of P2X(4) in veins have implications for the choice of vessels used in coronary artery bypass grafts given that P2X(4) is involved in calcium influx into endothelial cells, modulates blood vessel contractility and is up-regulated in situations involving intima proliferation suggesting vein grafts are more susceptible to developing atherosclerosis.

Purinergic receptor expression in the apical plasma membrane of rat uterine epithelial cells during implantation

We examined the expression of the metabotropic P2Y(1), P2Y(2), P2Y(4), and ionotropic P2X(7) purinergic receptor subtypes in the uterine epithelium during early pregnancy in the rat. On Day 1 of pregnancy, there was no expression of P2X(7), P2Y(2), or P2Y(4) in the uterine epithelium. P2Y(1) was detected only as a diffuse label. On Day 3, P2X(7) and P2Y(2) receptor distribution was confined to the lateral plasma membranes in the epithelium. There was no expression of P2Y(4) while P2Y(1) was again detected only as a diffuse label throughout the epithelium. At the time of implantation on Day 6, a strong, continuous and area-specific P2X(7) and P2Y(2) label was noted along the entire surface of the apical epithelium suggesting a major role in calcium-modified events preceding and facilitating attachment and implantation of the blastocyst. P2Y(1) and P2Y(4) were present as a ubiquitous and nonspecific label, although the latter exhibited a minor apical deposition. These and earlier experiments with P2X subtype-specific antibodies indicate that both P2X and P2Y purinergic receptors play a role in conditioning the entire uterine epithelium for blastocyst implantation regardless of the site of attachment.

Bioactivity of PTH/PTHrP analogs lacking the 1-14 N-terminal domain

The N-terminal regions of 1-34 parathyroid hormone (PTH) and 1-34 parathyroid hormone related protein (PTHrP) are thought to be required for full agonist activity of these molecules and for signal transduction by cyclic AMP (cAMP). The C-terminal regions are thought to be involved in receptor binding and protein kinase C activation. In this study, two analogs of PTH/PTHrP lacking the segment 1-14 exhibited agonist activity in opossum kidney (OK) 3B2 cells. Analogs cPTHrP(15-34) and ANA NPY(13-36), an analog of neuropeptide Y, which both have amphipathic alpha helices, inhibited phosphate uptake and stimulated cAMP production in a dose-dependent manner, with half maximal activity in the microM range, compared to the nM range for hPTHrP(1-34) and hPTH(1-34). They also exhibited proportionately lower receptor binding affinities. cAMP production by these analogs was suppressed by the antagonist hPTHrP(7-34). Inhibition of phosphate uptake in response to the analogs was partially suppressed by H-89, but not by bisindolylmaleimide. The analogs also inhibited phosphate uptake and stimulated cAMP in parent OK cells and stimulated cAMP production in UMR-106 cells. These studies present the novel finding that in these cell types, a C-terminal region encompassing PTH/PTHrP(24-31), with the alpha-helical structure maintained, is sufficient for full activity at reduced potency.