Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Autocrine Communication”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources
PubMed2002

Enforced expression of FGF-7 promotes epithelial hyperplasia whereas a dominant negative FGFR2iiib promotes the emergence of neuroendocrine phenotype in prostate glands of transgenic mice.

The minimal rat probasin (PB) promoter was used to target expression of human fibroblast growth factor-7 (FGF-7)/keratinocyte growth factor (KGF) directly to prostatic epithelium of transgenic mice, converting FGF-7 from a paracrine to an autocrine factor. Four independent lines were established that expressed the transgene (PKS) in the prostate. Upon histologic analysis, the prostatic epithelium of PKS mice was found to be hyperplastic. Many of the prostatic ducts were filled with secretory epithelial cells tightly associated with a highly enfolded basement membrane. Distortions of the ductal smooth muscle layer were also observed. Prostates from year-old PKS mice had significantly more abnormal ducts than their wild-type nontransgenic littermates. The minimal rat PB promoter was also used to target a truncated FGFR2iiib receptor to prostatic epithelium to functionally abrogate endogenous FGF-7 signaling. Three lines were established that expressed the transgene (KDNR) in the prostate. Upon dissection it was noted that all four lobes of the prostates of KDNR mice were present but smaller in size. Histologic analysis indicated that the epithelium in many of the prostatic ducts was disorganized and contained numerous rounded cytokeratin-positive cells that were not tightly associated with the basement membrane. The stroma was disorganized and did not form a tight layer of smooth muscle around the epithelial ducts. Surprisingly, abrogation of FGF signaling in KDNR mice correlated with the emergence of a neuroendocrine-like phenotype that was not observed as a consequence of enforced FGF-7 expression in the PKS mice.

Androgen-Binding Protein↗
PubMed1999

Role of autocrine stimulation on the effects of cyclic AMP on protein and lipid phosphorylation in collagen-activated and thrombin-activated platelets.

We compared several responses in thrombin-stimulated and collagen (type I)-stimulated platelets with and without forskolin and inhibitors of autocrine stimulation (IAS: an ADP-removing system of creatine phosphate/creatine phosphokinase, Arg-Gly-Asp-Ser peptide to prevent fibrinogen/fibronectin binding to GPIIb/IIIa, SQ 29.548 as a thromboxane A2 receptor antagonist, cyproheptadine as a serotonin receptor antagonist, BN 52021 as a platelet-activating factor receptor antagonist). The pattern of tyrosine-phosphorylated proteins, the phosphorylation of lipids in the polyphosphoinositide cycle and phosphorylation of pleckstrin (P47) were studied as markers for signal-transducing responses, exposure of CD62 (P-selectin) and CD63 (Glycoprotein 53), as well as secretion of ADP + ATP and beta-N-acetyl-glycosaminidase were studied as final activation responses. Clear differences between thrombin-stimulated and collagen-stimulated platelets were observed. First, practically all protein-tyrosine phosphorylation induced by thrombin was inhibited by IAS, while a partial inhibition was observed for collagen; the phosphorylation due to collagen alone was apparently stimulated by elevation of cAMP. Secondly, the other responses to thrombin were inhibited by increased levels of cAMP, independent of autocrine stimulation. In contrast, only the autocrine part of the collagen-induced responses was inhibited by elevation of cAMP. Thus, the inhibition by elevated cAMP seen in collagen-stimulated platelets seems to be due to removal of the G-protein-mediated activation from secreted autocrine stimulators either by IAS or forskolin. The remaining activity is a pure collagen effect which is not affected by elevated levels of cAMP.

Antigens, CD↗
PubMed2001

Sites of epidermal growth factor synthesis and action in the pituitary: paracrine and autocrine interactions.

1. Epidermal growth factor (EGF) is produced by growth hormone (GH) cells and gonadotropes in normal pituitary cell populations. The studies were initiated to determine whether EGF is a paracrine or autocrine regulator of gonadotrope function. 2. The first group of studies tested for the presence of EGF receptors in gonadotropes from cycling female rats by immunolabelling. Expression varied with the stage of the cycle. At the highest point (metoestrus), only a few EGF target cells are gonadotropes, identified by their content of luteinizing hormone (LH)-beta mRNA. Expression by gonadotropes then increased to reach a peak of 50% of cells during pro-oestrus. 3. Studies investigating the regulation of expression of EGF receptor (R) showed that all culture conditions (in media with or without serum) and EGF itself both stimulated expression of the receptor by gonadotropes in populations from oestrus or metoestrus rats. Gonadotropin-releasing hormone (GnRH) also stimulated EGFR expression in follicle-stimulating hormone (FSH) gonadotropes from oestrus animals. Additional tests of expression of immediate early genes (c-fos) showed that, after 15 min, EGF stimulated expression in cells with FSH antigens. 4. Epidermal growth factor also stimulated gonadotrope proliferation, as detected by the MTT cell growth/cell death assays and bromodeoxyuridine uptake by gonadotropes during the S phase (DNA synthesis) of the cell cycle. 5. Epidermal growth factor and GnRH both stimulated a significant increase in the percentage of mitotic gonadotropes. Epidermal growth factor may be an autocrine or a paracrine growth factor to maintain and develop the gonadotrope population and EGF may also be involved in early differentiation events that prepare cells to support the LH surge.

Animals↗
PubMed2001

Autocrine expression of neurotrophins and their receptors in prostate cancer.

Previously, it has been demonstrated that the neurotrophins and their receptors are present in human prostate tissue, but neither their functional role nor localization is clearly understood. We studied the expression of neurotrophins and their receptors in prostate cancer. Between 1990 and 1999, 48 prostate cancer specimens were obtained from patients undergoing radical prostatectomy, of whom 25 received neoadjuvant hormonal therapy (NHT) and 23 were untreated. The specimens were analyzed immunohistochemically for neurotrophins (nerve growth factor, brain derived neurotrophic factor, neurotrophin 3, neurotrophin 4/5) and their receptors (TrkA, TrkB, TrkC, p75NTR). Immunohistochemical studies revealed that both benign and malignant prostate gland epithelial cells expressed the neurotrophins and their receptors to various degrees, but no obvious immunopositive reaction was observed in stromal cells. In benign epithelial cells, the neurotrophins were localized to secretory cells and the receptors were localized to basal cells. The neurotrophins, TrkA and TrkC were expressed to a similar extent in prostate cancer specimens obtained from patients both with and without NHT. In contrast, the expression of TrkB was down-regulated and the expression of p75NTR was up-regulated in prostate cancer after hormonal therapy. These findings suggest that neurotrophins are secreted by prostate cancer cells in an autocrine fashion. Neurotrophins may be involved, through their receptors, in the escape mechanism from cell death after androgen depletion found in prostate cancer.

Aged↗
PubMed1998

Immortalized gonadotropin-releasing hormone neurons secrete gamma-aminobutyric acid-evidence for an autocrine regulation.

The immortalized hypothalamic neuronal cell lines GT1-1 and GT1-7 represent unique model systems to investigate the physiological control of gonadotropin-releasing hormone (GnRH) secretion. Using immunofluorescence microscopy, key proteins of regulated exocytosis, e.g. synaptotagmin, synaptobrevin and SNAP-25 (synaptosomal associated protein of 25 kDa) were found in GT1 neurons. In addition, GT1 neurons contained synaptophysin, a marker protein for small synaptic vesicles (SSVs) which are responsible for the storage of neurotransmitters such as gamma-aminobutyric acid (GABA). Upon subcellular fractionation, a lighter vesicle population characterized by synaptophysin separated from a denser vesicle population containing GnRH. Both vesicle populations contained synaptobrevin and synaptotagmin. Besides GnRH, GT1 neurons expressed glutamic acid decarboxylase at the mRNA-level and synthesized GABA. More importantly, GT1 neurons took up and stored 3H-GABA. The stored GABA was released after stimulation with increasing K+ concentrations and by alpha-latrotoxin. Reducing the extracellular Ca2+-concentration abolished stimulated secretion, indicating that GABA was released by regulated exocytosis. Hormone secretion from GT1 neurons is controlled by GABA via GABA(A) and GABA(B) receptors reflecting the situation in vivo. Our data provide the first evidence that GT1 neurons possess a second regulated secretory pathway sustained by SSVs storing and releasing GABA. The released GABA influences GnRH secretion by an auto- or paracrine loop.

Animals↗
PubMed1999

Axotomy results in major changes in BDNF expression by dorsal root ganglion cells: BDNF expression in large trkB and trkC cells, in pericellular baskets, and in projections to deep dorsal horn and dorsal column nuclei.

Brain derived neurotrophic factor (BDNF) is normally expressed by a small number of predominantly trkA-expressing dorsal root ganglion cells. Using immunocytochemistry and in situ hybridization, we have examined the effect of sciatic nerve section on the expression of BDNF in the adult rat. Following axotomy there was a long lasting (4-week) increase in BDNF mRNA and protein in large-diameter, trkB- and trkC-expressing dorsal root ganglion cells. By 2 days postaxotomy, expression of BDNF mRNA had increased from 2% of trkB cells to 50%, and from 18% of trkC cells to 56%. In contrast, BDNF expression in most trkA cells was unchanged, although was increased in the small population of medium- and large-sized trkA cells. Following axotomy, BDNF-immunoreactive terminals appeared in the central axonal projections of large-diameter cells, including the deep dorsal horn and gracile nucleus. Neuropeptide Y was also upregulated following axotomy and was coexpressed with BDNF in the cell bodies and central terminals of the large cells. Ultrastructural analysis in lamina IV of the spinal cord revealed that BDNF terminals in these central projections establish synaptic contacts. Immunoreactivity at 4 weeks was also observed in pericellular baskets that contained calcitonin gene-related peptide (CGRP) and surrounded trkA- and trkB-expressing cells in L4 and L5 lumbar ganglia. These baskets are likely to arise from local, highly immunoreactive, BDNF/CGRP/trkA-expressing cells. Our results identify several novel targets for BDNF and imply that it acts locally in both autocrine and paracrine modes, as well as centrally in a synaptic mode, to modulate the response of somatosensory pathways in nerve injury.

Afferent Pathways↗
PubMed1999

Voltage-independent autocrine modulation of L-type channels mediated by ATP, opioids and catecholamines in rat chromaffin cells.

The inhibition of L-type channels induced by either bath application of ATP, opioids and catecholamines or by endogenously released neurotransmitters was investigated in rat chromaffin cells with whole-cell recordings (5 mM Ba2+). In both cases, the L-type current, isolated pharmacologically using omega-toxin peptides and potentiated by Bay K 8644, was inhibited by approximately 50% with nearly no changes to the activation-inactivation kinetics. Inhibition was voltage independent at a wide range of potentials (-20 to +50 mV) and insensitive to depolarizing prepulses (+100 mV, 50 ms). Onset and offset of the inhibition were fast (time constants: tau(on) approximately 0.9 s, tau(off) approximately 3.6 s), indicating a rapid mechanism of channel modulation. Whether induced exogenously or from the released granules content in conditions of stopped cell superfusion, the neurotransmitter action was reversible and largely prevented by either intracellular GDP-beta-S, cell treatment with pertussis toxin or simultaneous application of P2y,2x delta/mu-opioidergic and alpha/beta-adrenergic antagonists. This suggests the existence of converging modulatory pathways by which autoreceptors-activated G-proteins reduce the activity of L-type channels through fast interactions. The autocrine inhibition of L-type currents, which was absent in superfused isolated cells, was effective on cell clusters, suggesting that L-type channels may be potently inhibited by cell exocytosis under physiological conditions resembling the intact adrenal glands.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed2003

A tumour necrosis factor alpha autocrine loop contributes to proliferation and nuclear factor-kappaB activation of Theileria parva-transformed B cells.

Theileria infection of bovine leucocytes induces uncontrolled proliferation and a transformed phenotype comparable to tumour cells. Infected cells have many characteristics of activated leucocytes and use autocrine loops to augment proliferation. We have shown previously that, in infected B cells, PI3-K controls a granulocyte-macrophage colony-stimulating factor (GM-CSF) autocrine loop to increase both proliferation and activation of the activator protein 1 (AP-1) transcription factor. We show here that the same infected B cells also use a tumour necrosis factor (TNF) alpha autocrine loop that again contributes to proliferation and augments nuclear factor (NF)-kappaB activation. Interestingly, both pharmacological inhibition of TNF synthesis and neutralizing anti-TNF antibodies lead to a reduction in proliferation and a 50% drop in NF-kappaB activation, without inducing apoptosis.

Animals↗
PubMed1999

Changes in muscle mass and phenotype and the expression of autocrine and systemic growth factors by muscle in response to stretch and overload.

The study of the underlying mechanisms by which cells respond to mechanical stimuli, i.e. the link between the mechanical stimulus and gene expression, represents a new and important area in the morphological sciences. Several cell types ('mechanocytes'), e.g. osteoblasts and fibroblasts as well as smooth, cardiac and skeletal muscle cells are activated by mechanical strain and there is now mounting evidence that this involves the cytoskeleton. Muscle offers one of the best opportunities for studying this type of mechanotransduction as the mechanical activity generated by and imposed upon muscle tissue can be accurately controlled and measured in both in vitro and in vivo systems. Muscle is highly responsive to changes in functional demands. Overload leads to hypertrophy, whilst decreased load force generation and immobilisation with the muscle in the shortened position leads to atrophy. For instance it has been shown that stretch is an important mechanical signal for the production of more actin and myosin filaments and the addition of new sarcomeres in series and in parallel. This is preceded by upregulation of transcription of the appropriate genes some of which such as the myosin isoforms markedly change the muscle phenotype. Indeed, the switch in the expression induced by mechanical activity of myosin heavy chain genes which encode different molecular motors is a means via which the tissue adapts to a given type of physical activity. As far as increase in mass is concerned, our group have cloned the cDNA of a splice variant of IGF-1 that is produced by active muscle that appears to be the factor that controls local tissue repair, maintenance and remodelling. From its sequence it can be seen that it is derived from the IGF-1 gene by alternative splicing but it has different exons to the liver isoforms. It has a 52 base insert in the E domain which alters the reading frame of the 3' end. Therefore, this splice variant of IGF-1 is likely to bind to a different binding protein which exists in the interstitial tissue spaces of muscle, neuronal tissue and bone. This would be expected to localise its action as it would be unstable in the unbound form which is important as its production would not disturb the glucose homeostasis unduly. This new growth factor has been called mechano growth factor (MGF) to distinguish it from the liver IGFs which have a systemic mode of action. Although the liver is usually thought of as the source of circulating IGF-1, it has recently been shown that during exercise skeletal muscle not only produces much of the circulating IGF-1 but active musculature also utilises most of the IGF-I produced. We have cloned both an autocrine and endocrine IGF-1, both of which are upregulated in cardiac as well as skeletal muscle when subjected to overload. It has been shown that, in contrast to normal muscle, MGF is not detectable in dystrophic mdx muscles even when subjected to stretch and stretch combined with electrical stimulation. This is true for muscular dystrophies that are due to the lack of dystrophin (X-linked) and due to a laminin deficiency (autosomal), thus indicating that the dystrophin cytoskeletal complex may be involved in the mechanotransduction mechanism. When this complex is defective the necessary systemic as well as autocrine IGF-1 growth factors required for local repair are not produced and the ensuing cell death results in progressive loss of muscle mass. The discovery of the locally produced IGF-1 appears to provide the link between the mechanical stimulus and the activation of gene expression.

Adaptation, Physiological↗
PubMed1998

Interleukin-6-mediated autocrine growth promotion in human glioblastoma multiforme cell line U87MG.

Human glioblastoma multiforme cell lines, brain tumor biopsy tissue, and normal human fetal brain synthesize interleukin (IL)-6 and IL-6 receptor (IL-6R). Neither of these is expressed in human neurons or neuroblastoma cell lines in culture. Astrocytes from fetal brain grown in culture retain the ability to synthesize IL-6 but do not express IL-6R as inferred from RT-PCR and Southern blot studies. Coexpression of IL-6 and IL-6R in the glioblastoma cell line U87MG is confirmed by immunofluorescence staining. Both specific monoclonal antibodies against IL-6 and IL-6R and antisense oligonucleotide to IL-6 mRNA inhibit the growth of U87MG cells in culture, suggesting the existence of a functional autocrine growth loop. Anti-IL-6 antibodies also inhibit the growth of glioblastoma cell lines U373 and U118. The expression of IL-6 by human fetal astrocytes in culture is highly suggestive of its role as an oncofetal protein responsible for rapid proliferation of fetal and tumor cells but not cells of adult brain.

Animals↗
PubMed2000

Delayed and sustained activation of p42/p44 mitogen-activated protein kinase induced by proteasome inhibitors through p21(ras) in PC12 cells.

Proteolysis by the ubiquitin/proteasome pathway regulates the intracellular level of several proteins, some of which control cell proliferation and cell cycle progression. To determine what kinds of signaling cascades are activated or inhibited by proteasome inhibition, we treated PC12 cells with specific proteasome inhibitors and subsequently performed in-gel kinase assays. N-Acetyl-Leu-Leu-norleucinal and lactacystin, which inhibit the activity of the proteasome, induced the activation of p42/p44 mitogen-activated protein (MAP) kinases [extracellular signal-regulated kinases (ERKs) 1 and 2]. In contrast, N-acetyl-Leu-Leu-methional, which inhibits the activity of calpains, but not of the proteasome, failed to induce ERK activation. Uniquely, the kinetics of MAP kinase activation induced by proteasome inhibitors are very slow compared with those resulting from activation by nerve growth factor; ERK activation is detectable only after a 5-h treatment with the inhibitors, and its activity remained unchanged for at least until 27 h. Proteasome inhibitor-initiated ERK activation is inhibited by pretreatment with the ERK kinase inhibitor PD 98059, as well as by overexpression of a dominant-negative form of Ras. Thus, proteasome inhibitors induce sustained ERK activation in a Ras-dependent manner. Proteasome inhibitor-induced neurite outgrowth, however, is not inhibited by PD 98059, indicating that sustained activation of ERKs is not the factor responsible for proteasome inhibitor-induced morphological differentiation. Our data suggest the presence of a novel mechanism for activation of the MAP kinase cascade that involves proteasome activity.

Acetylcysteine↗
PubMed2000

Brevetoxin-induced autocrine excitotoxicity is associated with manifold routes of Ca2+ influx.

Real-time alterations in intracellular Ca2+ ([Ca2+]i) were monitored in fluo-3-loaded cerebellar granule neurons (CGNs) exposed to the brevetoxin PbTx-1. [Ca2+]i was measured using a fluorescent plate reader (FLIPR), which measures simultaneously the mean intracellular Ca2+ change in a population of cultured cells in each well of a 96-well plate. PbTx-1 produced rapid and concentration-dependent increases in neuronal [Ca2+]i with a potency nearly identical to that determined previously for PbTx-1-induced neurotoxicity. The NMDA receptor antagonists MK-801, dextrorphan, and D(-)-2-amino-5-phosphonopentanoic acid, and tetanus toxin, an inhibitor of Ca2+-dependent exocytotic neurotransmitter release, effected significant reductions in both the integrated fluo-3 fluorescence response and excitatory amino acid release and protected CGNs against PbTx-1 neurotoxicity. The L-type Ca2+ channel antagonist nifedipine produced a modest reduction in the fluo-3 response but reduced substantially the plateau phase of the PbTx-1 increment in [Ca2+]i when combined with MK-801. When nifedipine and MK-801 were combined with the Na+/Ca2+ exchanger (reversed mode) inhibitor KB-R7943, the PbTx-1 increment in [Ca2+]i was nearly completely attenuated. These data show that Ca2+ entry into PbTx-1-exposed CGNs occurs through three primary routes: NMDA receptor ion channels, L-type Ca2+ channels, and reversal of the Na+/Ca2+ exchanger. There was a close correlation between reduction of the integrated fluo-3 fluorescence response and the level of neuroprotection afforded by blockers of each Ca2+ entry pathway; however, simultaneous blockade of L-type Ca2+ channels and the Na+/Ca2+ exchanger, although reducing the integrated [Ca2+]i response to a level below that provided by NMDA receptor blockade alone, failed to completely attenuate PbTx-1 neurotoxicity. This finding suggests that in addition to total [Ca2+]i load, neuronal vulnerability is governed principally by the NMDA receptor Ca2+ influx pathway.

2-Amino-5-phosphonovalerate↗
PubMed2001

Neurotrophin-3 mediates the autocrine survival of the catecholaminergic CAD CNS neuronal cell line.

The mechanisms for neuronal survival in the CNS are not well understood, but are likely to be complex due to possible autocrine and redundant neurotrophic support. Most studies have focused on the nerve growth factor (NGF)/TrkA pathway in peripheral neurons, and little is known regarding the other neurotrophins, particularly neurotrophin-3 (NT3)/TrkC. Progress has also been hampered by the paucity of homogenous and accessible CNS neuronal experimental models. We now report that the novel catecholaminergic CNS cell line, CAD, is capable of autocrine survival mediated by NT3. The CAD cell is of CNS neuronal origin and can survive and morphologically differentiate in the absence of exogenously provided trophic factors. However, neutralizing reagents against NT3 (the neutralizing TrkC-IgG fusion protein and anti-NT3 antibodies), but not those that block the other neurotrophins, inhibited survival of differentiating CAD cells. Moreover, Trk phosphorylation was detected in CAD cells and its inhibition by K252a was correlated with K252a-induced apoptosis. Finally, endogenous NT3 was detectable in CAD cell extracts by a specific ELISA assay. Thus, CAD cells possess an autocrine survival capability mediated by NT3, and may provide a valuable model system for studying the signaling pathways that mediate the actions of this little understood neurotrophin.

Animals↗
PubMed2002

Autocrine activation of adenosine A1 receptors blocks D1A but not D1B dopamine receptor desensitization.

Adenosine is known to modulate dopamine responses in several brain areas. Here, we show that tonic activation of adenosine receptors is able to impede desensitization of D1 dopamine receptors. As measured by cAMP accumulation in transfected COS-7 cells, long-term exposure to dopamine agonists promoted desensitization of D1B receptor but not that of D1A receptor. The inability of D1A receptor to desensitize was a result of the adenosine present in culture medium acting through activation of adenosine A1 receptors. Cell incubation with either adenosine deaminase, CGS-15943, a generic adenosine receptor antagonist, or the A1 antagonist DPCPX restored the long-term desensitization time-course of D1A receptors. In Ltk cells stably expressing A1 adenosine receptors and D1A dopamine receptors, pre-treatment of cells with R(-)-PIA, a full A1 receptor agonist, did not significantly inhibit the acute increase in cAMP levels induced by D1 receptor agonists, but blocked desensitization of D1A receptors. However, simultaneous activation of A1 and D1A receptors promoted a delayed D1A receptor desensitization. This suggests that functional interaction between A1 and D1A receptors may depend on the activation kinetics of components regulating D1 receptor responses, acting differentially on D1A and D1B receptors.

Adenosine↗
PubMed2004

The neurotrophic effect of oleic acid includes dendritic differentiation and the expression of the neuronal basic helix-loop-helix transcription factor NeuroD2.

We have shown recently that the presence of albumin in astrocytes triggers the synthesis and release of oleic acid, which behaves as a neurotrophic factor for neurons. Thus, oleic acid promotes axonal growth together with the expression of the axonal growth-associated protein, GAP-43. Here we attempted to elucidate whether the neurotrophic effect of oleic acid includes dendritic differentiation. Our results indicate that oleic acid induces the expression of microtubule associated protein-2 (MAP-2), a marker of dendritic differentiation. In addition, the presence of oleic acid promotes the translocation of MAP-2 from the soma to the dendrites. The time course of MAP-2 expression during brain development coincides with that of stearoyl-CoA desaturase, the limiting enzyme of oleic acid synthesis, indicating that both phenomena coincide during development. The effect of oleic acid on MAP-2 expression is most probably independent of autocrine factors synthesized by neurons because this effect was also observed at low cellular densities. As oleic acid is an activator of protein kinase C, the possible participation of this transduction pathway was studied. Our results indicate that added oleic acid or oleic acid endogenously synthesized by astrocytes exerts its neurotrophic effect through a protein kinase C-dependent mechanism as the effect was inhibited by sphingosine or two myristoylated peptide inhibitors of protein kinase C. The transduction pathway by which oleic acid induces the expression of genes responsible for neuronal differentiation appears to be mediated by the transcription factor NeuroD2, a regulator of terminal neuronal differentiation.

Animals↗
PubMed2001

An autocrine loop mediates expression of vascular endothelial growth factor in human dermal microvascular endothelial cells.

The expression of vascular endothelial growth factor mRNA and protein is regulated by a number of agents including growth factors, cytokines, and phorbol esters. Here we report that vascular endothelial growth factor is able to increase its own level in cultured human dermal microvascular endothelial cells. Accumulation of vascular endothelial growth factor mRNA and polypeptide can be detected as early as 4 h after addition of vascular endothelial growth factor to the cell culture medium. The autocrine action of vascular endothelial growth factor appears to be mediated by the KDR receptor. The increase of its own message by vascular endothelial growth factor is blocked by the transcription inhibitor actinomycin D. Transient transfection experiments performed with human dermal microvascular endothelial cells and using a 3.2 kb human vascular endothelial growth factor promoter fragment showed that vascular endothelial growth factor auto-induction can be mimicked at the promoter level. This indicates that the observed vascular endothelial growth factor mRNA increase after vascular endothelial growth factor treatment is occurring at the level of transcription. Furthermore, vascular endothelial growth factor auto-induction is inhibited by PD 098059, showing that phosphorylation events, catalyzed by mitogen activated protein kinases, are a prerequisite for the vascular endothelial growth factor effect. Examination of extracellular signal-regulated kinase and c-Jun N-terminal protein kinase catalytic activities showed that both enzymes have to be activated to mediate the vascular endothelial growth factor signal. Our data demonstrate for the first time the existence of an autocrine loop for vascular endothelial growth factor in endothelial cells. Most probably this represents an amplification mechanism for the action of vascular endothelial growth factor in the microvascularization process.

Autocrine Communication↗
PubMed2003

The heregulin/human epidermal growth factor receptor as a new growth factor system in melanoma with multiple ways of deregulation.

In a screening for new growth factors released by melanoma cells, we found that the p185-phosphorylating capacity of a medium conditioned by a melanoma cell line was due to the secretion of heregulin, a ligand for the human epidermal growth factor receptor (HER) family of receptor tyrosine kinases. Expression of heregulin, including a new isoform, and secretion of functionally active protein was found in several cell lines. Receptor activation by heregulin, either autocrine or paracrine, resulted in a potent growth stimulation of both melanocytes and melanoma cells. Heregulin receptor HER3 and coreceptor HER2 were the main receptors expressed by these cells. Nevertheless, none of the cell lines in our panel overexpressed HER2 or HER3. In contrast, loss of HER3 was found in two cell lines, whereas one cell line showed loss of functional HER2, both types of deregulations resulting in unresponsiveness to heregulin. This implies the heregulin/HER system as a possible important physiologic growth regulatory system in melanocytes in which multiple deregulations may occur during progression toward melanoma, all resulting in, or indicating, growth factor independence.

Apoptosis↗
PubMed2000

PTHrP enhances the secretory response of PTH to a hypocalcemic stimulus in rat parathyroid glands.

BACKGROUND: The secretion of parathyroid hormone (PTH) from the parathyroid glands might be regulated by autocrine/paracrine factors, and a feedback regulatory mechanism of PTH on the secretion of PTH has been suggested. Because of the existence of a common receptor between PTH and PTH-related peptide (PTHrP), the aim of the present study was to examine the possible effects of PTHrP 1-40 and 1-86 on PTH secretion in rats. METHODS: In vivo, the effect of PTHrP on Ca++-regulated PTH secretion was examined by the induction of hypocalcemia and hypercalcemia by an infusion of EGTA and Ca++, with and without PTHrP. The eventual effects of PTHrP on the peripheral metabolism of PTH were examined by infusion of human PTH (hPTH) with and without PTHrP. hPTH was measured by an intact hPTH assay not cross reacting with rat PTH or PTHrP. To examine whether near physiological levels of circulating PTH have an autoregulatory effect in vivo on PTH secretion from the parathyroid gland, an acute reduction of the circulating PTH was induced by an acute unilateral parathyroidectomy (UPTX). PTH secretion from the remaining parathyroid gland was followed in response to EGTA-induced hypocalcemia. In vitro investigations on the effect of PTHrP 1-40 on PTH secretion from whole rat parathyroid glands incubated in media containing a calcium concentration of 0.6 or 1.35 mmol/L were performed to confirm whether the effect of PTHrP was directly on the gland. The rat PTH assay was examined for cross reaction with PTHrP. RESULTS: In vivo, the same rate of decrease of plasma Ca++ was induced in the experimental groups. The maximal response of PTH to hypocalcemia (218 +/- 16 pg/mL, N = 6) was significantly enhanced by PTHrP 1-40 (525 +/- 79 pg/mL, N = 6) and by PTHrP 1-86 (465 +/- 29 pg/mL, N = 6, P < 0.001). No effect of PTHrP on PTH secretion was found during normocalcemia or hypercalcemia. UPTX resulted in a 50% reduction of PTH secretion, and no compensatory increase of PTH was observed. PTHrP had no effect on the metabolism of PTH. In vitro, low-Ca++-induced PTH secretion was significantly augmented by 300% (P < 0.01) when the medium contained PTHrP 1-40. PTHrP did not cross react with the PTH assay. CONCLUSIONS: PTHrP significantly enhanced the low-Ca++-stimulated PTH secretion in vivo and in vitro. An autocrine/paracrine role of PTHrP in the parathyroid glands is suggested. An autoregulatory effect of circulating PTH on the PTH secretion from parathyroid glands seems unlikely. The "maximal secretory capacity" of the parathyroid glands induced by hypocalcemia in vivo and in vitro is not the maximum, as PTH secretion can be increased even further, by several-fold.

Animals↗