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PubMed2004

Autocrine signaling in carcinoma: VEGF and the alpha6beta4 integrin.

This review highlights an emerging function for vascular endothelial growth factor (VEGF) in carcinoma and discusses mechanisms involved in the elaboration of VEGF autocrine loops. Evidence is provided that autocrine VEGF contributes to the two major components of invasive carcinoma: survival and migration. Moreover, the findings discussed support the hypothesis that carcinoma progression selects for cells that depend on VEGF as a survival factor. Furthermore, a related hypothesis, which is developed, is that the function of the alpha6beta4 integrin, which has been implicated in carcinoma progression, is linked to its ability to regulate VEGF translation and, consequently, autocrine VEGF signaling. The findings reviewed challenge the notion that the function of VEGF in cancer is limited to angiogenesis and suggest that VEGF and VEGF receptor-based therapeutics, in addition to targeting angiogenesis, may also impair tumor cell survival and invasion directly.

Autocrine Communication↗
PubMed2004

Oxysteroids: a new class of steroids with autocrine and paracrine functions.

Oxysteroids are a new classification for sterol intermediates in cholesterol synthesis that undergo enzyme-catalyzed stereo-specific 25R,26-hydroxylation and thus bypass cholesterol as the expected end-product. Recently, they were identified in micromolar amounts in the plasma of patients with Smith-Lemli-Opitz syndrome (SLOS). An additional three oxysteroids, the 25,26-hydroxy derivatives of lanosterol, zymosterol, and desmosterol, respectively, were generated in vitro by CYP27A1-transfected bacteria. As there are 19 steps between cholesterol and lanosterol, the first post-squalene sterol, a potentially large class of oxysteroids exists. Limited studies of 25r,26-7-dehydrocholesterol indicate a traditional role as a ligand for nuclear receptors, but complete evaluation of oxysteroids for novel biologic activities is lacking. Currently, the lack of authentic oxysteroid standards limits both their detection in biologic fluids and evaluation of their biologic effects.

Autocrine Communication↗
PubMed2005

Self-administering cannabinoids.

Endocannabinoids, which are typically released by principal cells in response to prolonged depolarization, act as retrograde messengers to inhibit synaptic transmission. A recent study shows that in a specific subtype of cortical interneuron, endocannabinoids released under similar circumstances can also act cell-autonomously. Here, endocannabinoids endow these neurons with a memory of their own activity in the form of a long-term change in excitability.

Animals↗
PubMed2004

Response of bladder smooth muscle cells to obstruction: signal transduction and the role of mechanosensors.

Bladder hypertrophy and detrusor overactivity are well-known bladder responses to outlet obstruction. Mechanical stretch stress is considered the trigger inducing these responses in the urodynamically overloaded bladder. Several studies using an in vitro model of mechanical stress demonstrate that repetitive stretch stimulation of bladder smooth muscle cells results in increased expression of a variety of growth factors and other specific proteins. In the bladder smooth muscle cell, stretch-activated ion channels (SACs) and protein kinase C (PKC) sarcolemmal proteins may function as sensors for external mechanical forces. In particular, SACs couple mechanical stress to activation of c-jun NH2-terminal kinase, which leads to a rapid induction of nuclear transcription factors. PKC also may involve an indirect or direct regulation of nuclear events. In addition, mechanical stress may induce the release of angiotensin II in an autocrine fashion. These factors in turn stimulate expression of specific gene-encoding proteins, such as heparin-binding epidermal growth factor-like growth factor, nerve growth factor, and an isomer of cyclooxygenase-2, all of which have the potential to contribute to structural and functional alterations in the bladder after obstruction.

Animals↗
PubMed2006

Granulocyte colony-stimulating receptor promotes beta1-integrin-mediated adhesion and invasion of bladder cancer cells.

OBJECTIVES: To determine whether granulocyte colony-stimulating factor receptor (G-CSFR) autocrine signaling promotes endothelial cell adhesion and invasion of bladder cancer cells through a beta1-integrin-mediated pathway. A significant fraction of invasive bladder carcinomas express both G-CSF and G-CSFR. Bladder carcinoma cell line 5637 constitutively secretes G-CSF but lacks G-CSFR expression. Thus, we studied the effects of G-CSFR expression on cell adhesion and invasion in this unique model system. METHODS: Flow cytometry and adhesion assay were performed to detect expression of beta1-integrin in G-CSFR-expressing 5637 cells and adhesion of these cells to human umbilical vein endothelial cell, respectively. Furthermore, an invasion chamber assay was done with the 5637 cells. Next, we used the G-CSF-specific antibody, siRNA, and a truncated version of G-CSFR (GR19) to block G-CSFR autocrine loop in these cells. We also used a beta1-integrin-specific neutralizing antibody in the adhesion and invasion assays with the 5637 cells. RESULTS: G-CSFR-mediated increased expression (approximately threefold) of beta1-integrin is significantly abrogated by G-CSF specific antibody or siRNA in 5637 cells. GR19 also completely blocked beta1-integrin expression. G-CSFR signaling increased adhesion (approximately 2.5-fold) of 5637 cells to human umbilical vein endothelial cells, which are potently blocked by beta1-integrin-specific antibody. G-CSF/G-CSFR autocrine signaling significantly increased the invasiveness of 5637 cells (approximately 10-fold), which was reduced by either attenuating G-CSF production (G-CSF-specific antibody and siRNA) or interfering with G-CSFR signaling (GR19). Furthermore, beta1-integrin-specific antibody completely blocked G-CSFR-mediated invasion of 5637 cells. CONCLUSIONS: Autocrine G-CSF/G-CSFR signaling in bladder cancer can significantly contribute to cancer cell adhesion and invasion in a beta1-integrin-dependent manner.

Adhesiveness↗
PubMedDate not supplied

A buffer temperature controlled perifusion system to study temperature dependence and kinetics of insulin secretion in MIN6 pseudoislets.

INTRODUCTION: The perifusion of pancreatic islets is a well-known method to investigate the kinetics of insulin secretion. Nevertheless, little interest has been attributed to a precise temperature control in perifusion systems. Insulin secretion from MIN6 cells, cultured as monolayers, differs substantially from pancreatic islets, at least partly due to missing beta-to-beta cell contacts. These cellular contacts are abundant in MIN6 pseudoislets, which show a more pronounced glucose-induced insulin release. Here, a perifusion system that directly and dynamically controls the perifusion buffer temperature inside the reaction chamber is described. Additionally, the influence of small temperature changes, glucagon-like peptide 1 (GLP-1) and tolbutamide on insulin release from MIN6 pseudoislets is examined. METHODS: MIN6 cells were cultured in suspension culture dishes to generate MIN6 pseudoislets. The pseudoislets were perifused using a newly developed 12-channel perifusion system. The buffer temperature inside the reaction chambers was dynamically controlled by a programmable proportional plus integral plus differential (PID) controller. Insulin was determined by radioimmunoassay. RESULTS: After adjusting the PID controller, the temperature inside the reaction chambers was constant in a very narrow range. The first phase of the glucose-induced insulin secretion was enhanced from 1.0+/-0.1 to 2.8+/-0.2 ng insulin/ml and the second phase from 5.4+/-0.9 to 17.8+/-1.3 ng insulin/ml, when the temperature was elevated by 1 degrees C, from 37 to 38 degrees C. GLP-1 concentration dependently increased insulin release at 15.0 mM and was ineffective at 0.0 mM glucose. Tolbutamide induced a concentration-dependent increase in both phases of the insulin secretion. DISCUSSION: MIN6 pseudoislets are a useful tool to study insulin secretion from beta-cells, which are arranged in clusters like pancreatic beta-cells in the islet. The strong influence of temperature on insulin release from these pseudoislets requires a perifusion system, which precisely controls the buffer temperature.

Animals↗
PubMedDate not supplied

Differential effects of rapamycin, cyclosporine A, and FK506 on human coronary artery smooth muscle cell proliferation and signalling.

BACKGROUND: Immunosuppressive agents are at the forefront of preventing organ rejection after transplantation. However, their effects on vascular smooth muscle cell-mediated intimal hyperplasia that occurs in post-transplant coronary artery disease are less well known. METHODS AND RESULTS: We investigated the in vitro effects of three immunosuppressive agents cyclosporine A (CsA), FK506 (tacrolimus), and rapamycin (sirolimus, Rapa) on cultured human coronary artery smooth muscle cells (cSMC). CsA inhibited both platelet-derived growth factor (PDGF)-stimulated DNA synthesis and serum-induced proliferation at high concentrations (> or =1000 ng/ml). The growth-inhibitory effect of CsA was not altered by anti-TGF-beta neutralising antibodies nor was autocrine TGF-beta release detected in CsA-treated culture medium. At inhibitory doses, CsA inhibited ERK kinase activation by PDGF, although cytotoxicity was also apparent. Most notably, CsA visibly prevented PDGF-induced altered cell morphology. Rapa was a highly potent and effective inhibitor of cSMC proliferation (reduction in DNA synthesis by >50% from 0.01 ng/ml), acting through inhibition of 70-kDa S6 kinase (p70S6k). FK506 (1-1000 ng/ml) did not affect cSMC proliferation alone, although a > or =250-fold excess of FK506 over Rapa completely reversed the inhibitory effect of Rapa, confirming that these two agents share a common intracellular receptor, the FK506-binding protein (FKBP). CONCLUSION: Rapa is a powerful inhibitor of cSMC proliferation, while CsA slighly inhibits cSMC proliferation, although only at higher concentrations that may be toxic. These results indicate that therapeutic immunosuppression with Rapa may be additionally useful in prevention or delay of posttransplant coronary artery disease.

Autocrine Communication↗
PubMed2006

Evidence that autocrine signaling through Bmpr1a regulates the proliferation, survival and morphogenetic behavior of distal lung epithelial cells.

Lung development requires reciprocal epithelial/mesenchymal interactions, mediated by signaling factors such as Bmps made in both cell populations. To address the role of Bmp signaling in the epithelium, we have exploited the fact that Bmp receptor type Ia (Alk3) is expressed in the epithelium during branching morphogenesis. Deletion of Bmpr1a in the epithelium with an Sftpc-cre transgene leads to dramatic defects in lung development. There is reduced epithelial proliferation, extensive apoptosis, changes in cell morphology and extrusion of cells into the lumen. By E18.5, there are fewer Type II cells than normal, and the lung contains large fluid-filled spaces. If cell death is prevented by making embryos homozygous null for the proapoptotic gene, Bax, the epithelial cells that are rescued can apparently differentiate, but normal morphogenesis is not restored. To determine whether Bmps made by the epithelium can function in an autocrine manner, mesenchyme-free endoderm was cultured in Matrigel with Fgfs. Under these conditions, the mutant epithelium fails to undergo secondary budding. Abnormal development was also seen when Bmp4 was specifically deleted in the epithelium using the Sftpc-cre transgene. Our results support a model in which Bmp signaling primarily regulates the proliferation, survival and morphogenetic behavior of distal lung epithelial cells.

Animals↗
PubMed2006

Activin A is an endogenous inhibitor of ureteric bud outgrowth from the Wolffian duct.

Development of metanephric kidney begins with ureteric bud outgrowth from the Wolffian duct (WD). GDNF is believed to be a crucial positive signal in the budding process, but the negative regulation of this process remains unclear. Here, we examined the role of activin A, a member of TGF-beta family, in bud formation using an in vitro WD culture system. When cultured with the surrounding mesonephros, WDs formed many ectopic buds in response to GDNF. While the activin signaling pathway is normally active along the non-budding WD (as measured by expression of activin A and phospho-Smad2/3), activin A was absent and phospho-Smad2/3 was undetectable in the ectopic buds induced by GDNF. To examine the role of activin A in bud formation, we attempted to inactivate activin action. Interestingly, the addition of neutralizing anti-activin A antibody potentiated GDNF action. To further clarify the role of activin A, we also tested the effect of activin blockade on the WD cultured in the absence of mesonephros. WDs without mesonephros did not form ectopic buds even in the presence of GDNF. In contrast, blockade of activin action with a variety of agents acting through different mechanisms (natural antagonist, neutralizing antibodies, siRNA) enabled GDNF to induce ectopic buds. Inhibition of GDNF-induced bud formation by activin A was accompanied by inhibition of cell proliferation, reduced expression of Pax-2, and decreased phosphorylation of PI3-kinase and MAP kinase in the WD. Our data suggest that activin A is an endogenous inhibitor of bud formation and that cancellation of activin A autocrine action may be critical for the initiation of this process.

Activins↗
PubMed2006

Levels of mesenchymal FGFR2 signaling modulate smooth muscle progenitor cell commitment in the lung.

Fibroblast growth factor (FGF) signaling has been shown to regulate lung epithelial development but its influence on mesenchymal differentiation has been poorly investigated. To study the role of mesenchymal FGF signaling in the differentiation of the mesenchyme and its impact on epithelial morphogenesis, we took advantage of Fgfr2c(+/Delta) mice, which due to a splicing switch express Fgfr2b in mesenchymal tissues and manifest Apert syndrome-like phenotypes. Using a set of in vivo and in vitro studies, we show that an autocrine FGF10-FGFR2b signaling loop is established in the mutant lung mesenchyme, which has several consequences. It prevents the entry of the smooth muscle progenitors into the smooth muscle cell (SMC) lineage and results in reduced fibronectin and elastin deposition. Levels of Fgf10 expression are raised within the mutant mesenchyme itself. Epithelial branching as well as epithelial levels of FGF and canonical Wnt signaling is dramatically reduced. These defects result in arrested development of terminal airways and an "emphysema like" phenotype in postnatal lungs. Our work unravels part of the complex interactions that govern normal lung development and may be pertinent to understanding the basis of respiratory defects in Apert syndrome.

Animals↗
PubMed2006

Purinergic signaling regulates neural progenitor cell expansion and neurogenesis.

Neural stem and progenitor cells typically exhibit a density-dependent survival and expansion, such that critical densities are required below which clonogenic progenitors are lost. This suggests that short-range autocrine factors may be critical for progenitor cell maintenance. We report here that purines drive the expansion of ventricular zone neural stem and progenitor cells, and that purine receptor activation is required for progenitor cells to be maintained as such. Neural progenitors expressed P2Y purinergic receptors and mobilized intracellular calcium in response to agonist. Receptor antagonists suppressed proliferation and permitted differentiation into neurons and glia in vitro, while subsequent removal of purinergic inhibition restored progenitor cell expansion. Real-time bioluminescence imaging of extracellular ATP revealed that the source of extracellular nucleotides are the progenitor cells themselves, which appear to release ATP in episodic burst events. Enzyme histochemistry of the adult rat brain for ectonucleotidase activity revealed that NTDPase, which acts to degrade active ATP and thereby clears it from areas of active purinergic transmission, was selectively localized to the subventricular zone and the dentate gyrus, regions in which neuronal differentiation proceeds from the progenitor cell pool. These data suggest that purine nucleotides act as proliferation signals for neural progenitor cells, and thereby serve as negative regulators of terminal neuronal differentiation. As a result, progenitor cell-derived neurogenesis is thus associated with regions of both active purinergic signaling and modulation thereof.

Animals↗
PubMed2004

Lysophosphatidic acid regulates murine blastocyst development by transactivation of receptors for heparin-binding EGF-like growth factor.

Transient elevation of intracellular calcium (Ca2+(i)) by various means accelerates murine preimplantation development and trophoblast differentiation. Several G-protein-coupled receptors (GPCRs), including the lysophosphatidic acid (LPA) receptor (LPAR), induce Ca2+(i) transients and transactivate the EGF receptor (ErbB1) through mobilization of EGF family members, including heparin-binding EGF-like growth factor (HB-EGF). Because HB-EGF accelerates blastocyst differentiation in vitro, we examined whether crosstalk between LPA and HB-EGF regulates peri-implantation development. During mouse blastocyst differentiation, embryos expressed LPAR1 mRNA constitutively, LPAR2 only in late stage blastocysts and no LPAR3. Consistent with a mechanism based on Ca2+(i) signaling, LPA rapidly accelerated the rate of trophoblast outgrowth, an index of blastocyst differentiation, and chelation of Ca2+(i) with BAPTA-AM blocked LPA stimulation. Interfering with HB-EGF signaling through ErbB1 or ErbB4 also attenuated LPA stimulation. We established that mouse blastocysts indeed express HB-EGF and that LPA induces the transient accumulation of HB-EGF on the embryo surface, which was blocked by treatment with either BAPTA-AM or the protein trafficking inhibitor, brefeldin A. We conclude that LPA accelerates blastocyst differentiation through its ability to induce Ca2+(i) transients and HB-EGF autocrine signaling. Transactivation of ErbB1 or ErbB4 by HB-EGF could represent a convergent signaling pathway accessed in the trophoblast by stimuli that mobilize Ca2+(i).

Animals↗
PubMed2004

Erythropoietin-dependent autocrine secretion of tumor necrosis factor-alpha in hematopoietic cells modulates proliferation via MAP kinase--ERK-1/2 and does not require tyrosine docking sites in the EPO receptor.

Primary erythroid cells and erythroid cell lines may synthesize and secrete tumor necrosis factor-alpha (TNF-alpha) following stimulation with erythropoietin (EPO). The effect of triggering TNF-alpha synthesis and secretion was investigated in erythroleukemia and myeloid cell lines: HCD57, DA3-EPOR, and BAF3-EPOR. The EPO-induced, membrane-bound form of autocrine TNF-alpha seemed to enhance proliferation of HCD57 and DA3-EPOR cells; however, the concentration of secreted autocrine/paracrine TNF-alpha was never sufficient to have an effect. Autocrine TNF-alpha acts through TNFRII receptors to stimulate proliferation. Modulation of mitogen-activated protein kinase (MAPK)/extracellular signal-related kinase (ERK-1/2) activity by the membrane-bound form of autocrine TNF-alpha apparently played a central role in the control of EPO-dependent proliferation of HCD57 and DA3-EPOR cells. Primary erythroid cells and DA3-EPOR cells were found to express similar, high levels of both TNFRI and TNFRII, showing that differential expression of TNF-alpha receptors does not explain why primary cells are inhibited and DA3-EPOR cells are stimulated by autocrine TNF-alpha. BAF3 cells expressing a mutant EPOR with no cytoplasmic tyrosine residues were capable of triggering EPO-dependent TNF-alpha synthesis and secretion, indicating that tyrosine-docking sites in the EPOR were not required for EPO-dependent TNF-alpha secretion.

Animals↗
PubMed2004

DU145 human prostate carcinoma invasiveness is modulated by urokinase receptor (uPAR) downstream of epidermal growth factor receptor (EGFR) signaling.

Tumor cell motility and invasion have been linked to upregulated signaling from both the epidermal growth factor receptor (EGFR) and that for urokinase-type plasminogen activator (uPAR). However, we do not know whether these events are interdependent or unrelated, despite the obvious diagnostic and therapeutic implications. Gene microarray analyses have suggested that EGFR signaling via phospholipase C-gamma (PLCgamma) induces uPAR transcription. We utilized two sublines of the DU145 human prostate carcinoma cell line that are genetically engineered to differentially activate the EGFR/PLCgamma cascade and are variously invasive in vitro and in vivo. uPAR protein levels in these cells were found to be dependent on PLC signaling, pharmacologic inhibition of PLC signaling reduced uPAR expression. To determine whether uPAR was a required element in EGFR-mediated invasion, we stably expressed uPAR cDNA in either sense or antisense orientation in the two DU145 sublines. Interestingly, uPA production was modulated in parallel, although to a lesser degree, with uPAR in these sublines. Antisense to uPAR significantly restricted invasion of the highly invasive DU145 WT cells through Matrigel and reduced aggressiveness of tumors in nude mice. Up-regulation of uPAR significantly increased the invasiveness of the moderately invasive DU145 parental (DU145 P) cells through Matrigel, but this increased invasiveness was not seen in mice. uPA activity appears to contribute to invasiveness at least through Matrigel, as antibody to uPA or amiloride limited the transmigration. These results support a model of tumor invasion promoted by autocrine EGFR signaling involving reinforcing altered gene expression, of uPAR at least, that further induces cell motility. Herein, a number of key molecules whose expression levels are interrelated, including both EGFR and uPAR, are required but none are sufficient in the absence of other keys molecules in promoting tumor progression.

Amiloride↗
PubMed2004

Effects of PGF2alpha on human melanocytes and regulation of the FP receptor by ultraviolet radiation.

Prostaglandins are potent lipid hormones that activate multiple signaling pathways resulting in regulation of cellular growth, differentiation, and apoptosis. In the skin, prostaglandins are rapidly released by keratinocytes following ultraviolet radiation and are chronically present in inflammatory skin lesions. We have shown previously that melanocytes, which provide photoprotection to keratinocytes through the production of melanin, express several receptors for prostaglandins, including the PGE2 receptors EP1 and EP3 and the PGF2alpha receptor FP, and that PGF2alpha stimulates melanocyte dendricity. We now show that PGF2alpha stimulates the activity and expression of tyrosinase, the rate-limiting enzyme in melanin synthesis. Analysis of FP receptor regulation showed that the FP receptor is regulated by ultraviolet radiation in melanocytes in vitro and in human skin in vivo. We also show that ultraviolet irradiation stimulates production of PGF2alpha by melanocytes. These results show that PGF2alpha binding to the FP receptor activates signals that stimulate a differentiated phenotype (dendricity and pigmentation) in melanocytes. The regulation of the FP receptor and the stimulation of production of PGF2alpha in melanocytes in response to ultraviolet radiation suggest that PGF2alpha could act as an autocrine factor for melanocyte differentiation.

Autocrine Communication↗
PubMed2005

Autocrine regulation of human urothelial cell proliferation and migration during regenerative responses in vitro.

Regeneration of the urothelium is rapid and effective in order to maintain a barrier to urine following tissue injury. Whereas normal human urothelial (NHU) cells are mitotically quiescent and G0 arrested in situ, they rapidly enter the cell cycle upon seeding in primary culture and show reversible growth arrest at confluency. We have used this as a model to investigate the role of EGF receptor signaling in urothelial regeneration and wound-healing. Transcripts for HER-1, HER-2, and HER-3 were expressed by quiescent human urothelium in situ. Expression of HER-1 was upregulated in proliferating cultures, whereas HER-2 and HER-3 were more associated with a growth-arrested phenotype. NHU cells could be propagated in the absence of exogenous EGF, but autocrine signaling through HER-1 via the MAPK and PI3-kinase pathways was essential for proliferation and migration during urothelial wound repair. HB-EGF was expressed by urothelium in situ and HB-EGF, epiregulin, TGF-alpha, and amphiregulin were expressed by proliferating NHU cells. Urothelial wound repair in vitro was attenuated by neutralizing antibodies against HER-1 ligands, particularly amphiregulin. By contrast, the same ligands applied exogenously promoted migration, but inhibited proliferation, implying that HER-1 ligands provoke differential effects in NHU cells depending upon whether they are presented as soluble or juxtacrine ligands. We conclude that proliferation and migration during wound healing in NHU cells are mediated through an EGFR autocrine signalling loop and our results implicate amphiregulin as a key mediator.

Amphiregulin↗
PubMed2005

Oncostatin M induces an acute phase response but does not modulate the growth or maturation-status of liver progenitor (oval) cells in culture.

Following acute injury, the liver regenerates through hepatocyte division. If this pathway is impaired, liver repair depends on the recruitment of adult liver progenitor (oval) cells. Mice fed a choline deficient, ethionine supplemented (CDE) diet possess substantial numbers of oval cells, which can be isolated, or examined in vivo. Oncostatin M (OSM) has been shown to induce maturation of murine fetal hepatoblasts into hepatocytes. We recently confirmed this in human fetal liver cultures. Here, we show that liver OSM expression increases in mice fed a CDE diet and CDE-derived oval cell isolates express OSM and its receptor (OSMR). Oval cell lines (PIL cells), as well as primary oval cell cultures, displayed STAT-3 phosphorylation following OSM stimulation. OSM had no effect on the growth of primary oval cells, but it was pro-apoptotic to PIL cells, suggesting that the two cell models are not directly comparable. Expression of PCNA and cyclin D1 was not affected by OSM treatment. No evidence was obtained to suggest an effect on oval cell maturation with OSM treatment. However, decreased albumin production, accompanied by increased expression of haptoglobin and fibrinogen, suggests that OSM induced an acute phase reaction in cultured oval cells.

Acute-Phase Reaction↗
PubMed2005

Autocrine EGF receptor activation mediates endothelial cell migration and vascular morphogenesis induced by VEGF under interstitial flow.

We show here that autocrine ligand activation of epidermal growth factor (EGF) receptor in combination with interstitial flow is critically involved in the morphogenetic response of endothelial cells to VEGF stimulation. Human umbilical vein endothelial cell (HUVEC) monolayers cultured on a collagen gel and exposed to low interstitial flow in the absence of EGF and VEGF remained viable and mitotic but exhibited little evidence of vascular morphogenesis. Addition of VEGF produced a flow-dependent morphogenetic response within 48 to 72 h, characterized by branched capillary-like structures. The response was substantially abolished by inhibitors related to the autocrine EGF receptor pathway including Galardin, AG1478, PD98059, and an EGF receptor-blocking antibody, indicating that regulation of the morphogenetic process operates via autocrine EGF receptor activation. Moreover, we observed that in our system the EGF receptor was always activated independently of the interstitial flow, and, in addition, the EGF receptor inhibitors used above reduced the phosphorylation state of the receptor, correlating with inhibition of capillary morphogenesis. Finally, 5'bromo-2'-deoxyuridine (BrdU) labeling identified dividing cells at the monolayer but not in the extending capillary-like structures. EGF pathway inhibitors Galardin and AG1478 did not reduce BrdU incorporation in the monolayer, indicating that the EGF-receptor-mediated morphogenetic behavior is mainly due to cell migration rather than proliferation. Based on these results, we propose a two-step model for in vitro capillary morphogenesis in response to VEGF stimulation with interstitial fluid flow: monolayer maintenance by mitotic activity independent of EGF receptors and a migratory response mediated by autocrine EGF receptor activation wherein cells establish capillary-like structures.

Autocrine Communication↗