ADRB3 induces mobilization and inhibits differentiation of both breast cancer cells and myeloid-derived suppressor cells.

Metastatic tumors are mainly composed of neoplastic cells escaping from the primary tumor and inflammatory cells egressing from bone marrow. Cancer cell and inflammatory cell are remained in the state of immaturity during migration to distant organs. Here, we show that ADRB3 is crucial in cell mobilization and differentiation. Immunohistochemistry revealed ADRB3 expression is significantly more frequent in breast cancer tissues than in adjacent noncancerous tissues (92.1% vs. 31.5%). Expression of ADRB3 correlated with malignant degree, TNM stage and poor prognosis. Moreover, ADRB3 expression was markedly high in activated disseminated tumor cells, myeloid-derived suppressor cells (MDSCs), lymphocytes and neutrophil extracellular traps of patients. Importantly, ADRB3 promoted the expansion of MDSC through stimulation of bone marrow mobilization and inhibiting of the differentiation of immature myeloid cells. Furthermore, ADRB3 promoted MCF-7 cells proliferation and inhibited transdifferentiation into adipocyte-like cell by activating mTOR pathway. Ultimately, the MDSC-deficient phenotype of ADRB3 -/- PyMT mice was associated with impairment of mammary tumorigenesis and reduction in pulmonary metastasis. Collectively, ADRB3 promotes metastasis by inducing mobilization and inhibiting differentiation of both breast cancer cells and MDSCs.

ADRB3 expression in tumor cells is a poor prognostic factor and promotes proliferation in non-small cell lung carcinoma.

The cross-talk between cancer cells and monocyte-derived alveolar macrophages (Mo-AMs) promotes non-small cell lung carcinoma (NSCLC) progression. In this study, we report that both cancer cells and Mo-AMs robustly express beta 3-adrenergic receptor (ADRB3) in NSCLC. ADRB3 supports lung cancer cells proliferation and promotes chronic inflammation. Genetic and pharmacologic inhibition of ADRB3 reverses tumor growth and inflammation in mouse. Furthermore, we demonstrate that M5D1, a novel anti-ADRB3 monoclonal antibody, inhibits human lung cancer cells proliferation and inflammation via affecting the intracellular mTOR pathway and activating p53. In NSCLC patients, we confirmed that upregulation of ADRB3 expression correlates with tumor progression and poor prognosis. Altogether, these results shed light on the role of ADRB3 in NSCLC and suggest that M5D1 could become powerful antitumor weapons.

TRAF2 Cooperates with Focal Adhesion Signaling to Regulate Cancer Cell Susceptibility to Anoikis.

TRAF2, a RING finger adaptor protein, plays an important function in tumor necrosis factor (TNF)- and TNF-like weak inducer of apoptosis (TWEAK)-dependent signaling, in particular during inflammatory and immune responses. We identified a functional interaction of TRAF2 with focal adhesion (FA) signaling involving the focal adhesion kinase (FAK) in the regulation of cell susceptibility to anoikis. Comparison of TRAF2-proficient (TRAF2+/+) versus TRAF2-deficient (TRAF2-/-), and FAK-proficient (FAK+/+) versus FAK-deficient (FAK-/-) mouse embryonic fibroblasts and their matched reconstituted cells demonstrated that TRAF2 interacts physically with the N-terminal portion of FAK and colocalizes to cell membrane protrusions. This interaction was found to be critical for promoting resistance to cell anoikis. Similar results were confirmed in the human breast cancer cell line MDA-MB-231, where TRAF2 and FAK downregulation promoted cell susceptibility to anoikis. In human breast cancer tissues, genomic analysis of The Cancer Genome Atlas database revealed coamplification of TRAF2 and FAK in breast cancer tissues with a predictive value for shorter survival, further supporting a potential role of TRAF2-FAK cooperative signaling in cancer progression.

Left ventricular deformation associated with cardiomyocyte Ca(2+) transients delay in early stage of low-dose of STZ and high-fat diet induced type 2 diabetic rats.

BACKGROUND: In the early stage of diabetes, the cardiac ejection fraction is preserved, despite the existence of the subclinical cardiac dysfunction to some extent. However, the detailed phenotype of this dysfunction and the underlying mechanism remain unclear. To improve our understanding of this issue, we used low-dose STZ and high-fat diet to induce type 2 diabetic models in rats. The effects and the mechanism associated with the early stages of the disease were analyzed. METHODS: The type 2 diabetic mellitus (T2DM) in SD rats were induced through 30 mg/kg STZ and high-fat diet. Two-dimensional spackle-tracking echocardiography (STE) and the dobutamine test were performed to examine the cardiac function. Calcium transients of left ventricular myocytes were detected and the related intracellular signalling factors were analyzed by western blotting. RESULTS: After 6-weeks, T2DM rats in left ventricular (LV) diastole showed decreased global and segment strain(S) levels (P < 0.05), both in the radial and circumferential directions. Strain rate (Sr) abatement occurred in three segments in the radial and circumferential directions (P < 0.05), and the radial global Sr also decreased (P < 0.05). In the systolic LV, radial Sr was reduced, except the segment of the anterior septum, and the Sr of the lateral wall and post septum decreased in the circumferential direction (P < 0.05). Conventional M-mode echocardiography failed to detect significant alterations of cardiac performance between the two groups even after 12 weeks, and the decreased ejection fraction (EF%), fractional shortening (FS%) and end-systolic diameters (ESD) could be detected only under stress conditions induced by dobutamine (P < 0.05). In terms of calcium transients in cardiac myocytes, the Tpeak in model rats at 6 weeks was not affected, while the Tdecay1/2 was higher than that of the controls (P < 0.05), and both showed a dose-dependent delay after isoproterenol treatment (P < 0.05). Western blot analysis showed that in 6-week T2DM rats, myocardial p-PLB expression was elevated, whereas p-CaMKII, p-AMPK and Sirt1 were significantly down-regulated (P < 0.05). CONCLUSION: A rat model of T2DM was established by low dose STZ and a high-fat diet. LV deformation was observed in the early stages of T2DM in association with the delay of Ca(2+) transients in cardiomyocytes due to the decreased phosphorylation of CaMKII. Myocardial metabolism remodeling might contribute to the early LV function and calcium transportation abnormalities.

Fn14, a Downstream Target of the TGF-ß Signaling Pathway, Regulates Fibroblast Activation.

Fibrosis, the hallmark of human injuries and diseases such as serious burns, is characterized by excessive collagen synthesis and myofibroblast accumulation. Transforming growth factor-ß (TGF-ß), a potent inducer of collagen synthesis, has been implicated in fibrosis in animals. In addition to TGF-ß, fibroblast growth factor-inducible molecule 14 (Fn14) has been reported to play an important role in fibrotic diseases, such as cardiac fibrosis. However, the function and detailed regulatory mechanism of Fn14 in fibrosis are unclear. Here, we investigated the effect of Fn14 on the activation of human dermal fibroblasts. In normal dermal fibroblasts, TGF-ß signaling increased collagen production and Fn14 expression. Furthermore, Fn14 siRNA blocked extracellular matrix gene expression; even when TGF-ß signaling was activated by TGF-ß1, fibroblast activation remained blocked in the presence of Fn14 siRNA. Overexpressing Fn14 increased extracellular matrix gene expression. In determining the molecular regulatory mechanism, we discovered that SMAD4, an important TGF-ß signaling co-mediator, bound to the Fn14 promoter and activated Fn14 transcription. Taken together, these results indicate that the TGF-ß signaling pathway activates Fn14 expression through the transcription factor SMAD4 and that activated Fn14 expression increases extracellular matrix synthesis and fibroblast activation. Therefore, Fn14 may represent a promising approach to preventing the excessive accumulation of collagen or ECM in skin fibrosis.

Dynamin 2 interacts with connexin 26 to regulate its degradation and function in gap junction formation.

Connexin 26 (Cx26), a protein involved in gap junctional intercellular communication, has an essential function during organ and tissue development. Its deregulation, in part due to inherent mutations, is associated with pathological conditions including congenital deafness. Regulation of Cx26 protein level is critical for its function but the molecular mechanisms involved are partially understood. This study identifies dynamin 2 (Dyn2) as a Cx26 interactor in yeast and mammalian cells. Deletion studies revealed that Cx26-Dyn2 interaction involves the C-terminus of Cx26 and the GTPase effector domain of Dyn2, which is of particular importance for the regulation of the endocytic pathway. Dyn2 inhibition using siRNA or dynasore resulted in reduced Cx26 degradation at the plasma membrane and this was associated with change in gap junctional intercellular communication (GJIC). Furthermore, we demonstrate that Dyn2 regulates Cx26 endocytosis and ubiquitination. These results establish Dyn2 as a Cx26 partner in the regulation of GJIC.

Fn14 promotes differentiation of human mesenchymal stem cells into heart valvular interstitial cells by phenotypic characterization.

Despite the fact that tissue engineered heart valves (TEHV) hold great promise for heart valve disease treatment, one of the challenges is to find suitable seeding cells. Bone marrow derived mesenchymal stem cells (MSCs) were considered to be one of the best seed cell sources. In this study we propose a novel approach to promote stem cell differentiation into the seed cells of TEHV, valvular interstitial cells (VICs). Newly induced MSCs (iMSCs) were created from a co-culture niche in which healthy human donor derived MSCs were co-cultured with cardiac fibroblasts (H9C2 cell line). Then iMSCs were transfected with either a mock vector (iMSCs(mock) ) as controls or with a vector that overexpresses thefibroblast inducible factor 14 (Fn14) gene (iMSCs(Fn14) ). Immunofluorescence staining was performed to assay VIC differentiation. Western blot analysis was performed to analyze the involved signaling pathway. The results demonstrate that the expression of α-smooth muscle actin (SMA) was significantly higher in iMSCs(Fn14) as compared with iMSC(mock) , and MSC, and also had higher co-alignment of α-actinin and stress fiber (F-actin) in bundles. Additionally, increased biosynthesis of extracellular matrix (ECM) proteins including collagen I, collagen III, and fibronection were observed in iMSCs(Fn14) in comparison with iMSCs(mock) . These data observed in iMSCs(Fn14) were in accordance with VIC phenotype from normal heart valves. In addition, the PI3K/Akt signaling pathway was activated in iMSCs(Fn14) which allowed higher Akt phosphorylation (p-Akt) levels and SMA levels, whereas, it was attenuated by LY294002 (PI3K/Akt inhibitor). These new findings of the effect of Fn14 on VIC-like cell differentiation may provide a novel therapeutic strategy for heart valve disease treatment.

mTOR regulates TGF-ß2-induced epithelial-mesenchymal transition in cultured human lens epithelial cells.

BACKGROUND: Post-cataract surgery fibrosis in the lens capsule is caused by epithelial to mesenchymal transition (EMT) of the lens epithelium. Mammalian target of rapamycin (mTOR) has been demonstrated to be a key regulator of EMT. The aim of this study was to investigate the role of mTOR in transforming growth factor ß2 (TGF-ß2)-induced EMT in human lens epithelial cells (HLECs). METHODS: Human lens epithelial B-3 (HLEB-3) cells were cultured with 10 ng/ml TGF-ß2 for different periods of time. The expression of E-cadherin, connexin 43, fibronectin and α-smooth muscle actin (α-SMA), and activation of mTOR were determined by Western blots. Cell migration was assessed by wound healing assay. An inhibition test was performed using two kinds of mTOR inhibitors. RESULTS: E-cadherin and connexin 43 expressions were suppressed, whereas fibronectin and α-SMA expressions were increased in HLEB-3 cells after treatment with TGF-ß2. mTOR was activated during the TGF-ß2-induced EMT in a time-dependent manner. Rapamycin or Ku-0063794 with 100 nM was able to inhibit the phosphorylation of mTOR and impaired EMT induced by TGF-ß2. Cell motility enhanced by TGF-ß2 for 24 h was attenuated by both rapamycin and Ku-0063794. CONCLUSIONS: mTOR is activated during TGF-ß2-induced EMT in HLECs, suggesting that it is involved in the regulation of TGF-ß2-induced EMT and may contribute to the development of posterior capsule opacification.

Silencing of desmoplakin decreases connexin43/Nav1.5 expression and sodium current in HL­1 cardiomyocytes.

Desmosomes and gap junctions are situated in the intercalated disks of cardiac muscle and maintain the integrity of mechanical coupling and electrical impulse conduction between cells. The desmosomal plakin protein, desmoplakin (DSP), also plays a crucial role in the stability of these interconnected components as well as gap junction connexin proteins. In addition to cell­to­cell junctions, other molecules, including voltage­gated sodium channels (Nav1.5) are present in the intercalated disk and support the contraction of cardiac muscle. Mutations in genes encoding desmosome proteins may result in fatal arrhythmias, including arrhythmogenic right ventricular cardiomyopathy (ARVC). Therefore, the aim of the present study was to determine whether the presence of DSP is necessary for the normal function and localization of gap junction protein connexin43 (Cx43) and Nav1.5. To examine this hypothesis, RNA interference was utilized to knock down the expression of DSP in HL­1 cells and the content, distribution and function of Cx43 and Nav1.5 was assessed. Western blotting and flow cytometry experiments revealed that Cx43 and Nav1.5 expression decreased following DSP silencing. In addition, immunofluorescence studies demonstrated that a loss of DSP expression led to an abnormal distribution of Cx43 and Nav1.5, while scrape­loading dye/transfer revealed a decrease in dye transfer in DSP siRNA­treated cells. The sodium current was also recorded by the whole­cell patch clamp technique. The results indicated that DSP suppression decreased sodium current and slowed conduction velocity in cultured cells. The present study indicates that impaired mechanical coupling largely affects electrical synchrony, further uncovering the pathogenesis of ARVC.

[Expression of thioredoxin-2 for monitoring minimal residual disease in acute leukemia].

OBJECTIVE: To investigate the significance of human thioredoxin-2 (TRX-2) in monitoring minimal residual disease (MRD) in acute leukemia (AL). METHODS: We used real-time quantitative PCR to serially quantitize TRX-2 expression levels in the bone marrow of AL patients at diagnosis (n=68), at complete hematologic remission (CHR, n=57) and at relapse (n=25). Another 25 normal donors served as normal controls. The upper limit of the bone marrow at 91 was regarded as the reference. TRX-2 expression level at CHR with <5% blast cells in the bone marrow of relapse patients was analyzed and compared with MRD by flow cytometry. RESULTS: The TRX-2 levels between the CHR patients and newly diagnosed patients, and between the CHR patients and the relapse patients had significant difference. TRX-2 expression level of 21(21/25) relapse patients at CHR with <5% blast cells in the bone marrow was higher than the reference (>91). TRX-2 level was correlated to the expression level of MRD. CONCLUSION: TRX-2 may be the marker for AL and used in MRD monitoring.

Mechanism of macrophage migration inhibitory factor-induced decrease of T-type Ca(2+) channel current in atrium-derived cells.

The T-type Ca(2+) current (I(Ca,T)) plays an important role in the pathogenesis of atrial fibrillation (AF). The present study sought to investigate the role of macrophage migration inhibitory factor (MIF), a pleiotropic cytokine, in the regulation of T-type Ca(2+) channels (TCCs) in atrial myocytes. We used the whole-cell voltage-clamp technique and biochemical assays to study the regulation and expression of I(Ca,T) in atrial myocytes. Gene levels of the α1G and α1H subunit of TCCs were decreased in human atrial tissue of patients with AF. In cultured atrium-derived myocytes (HL-1 cells), mouse recombinant MIF (20 or 40 nm, 24 h) suppressed peak I(Ca,T) in a concentration-dependent manner, impaired the voltage-dependent activation of I(Ca,T) and downregulated TCC α1G and α1H mRNA. The Src inhibitors genistein and PP1 significantly enhanced I(Ca,T). The reduction of I(Ca,T) and TCC subunit mRNA induced by recombinant MIF could be reversed by genistein and PP1. The TCC α1G associated with Src in HL-1 cells and mouse cardiomycytes. Macrophage migration inhibitory factor is involved in the pathogenesis of AF, probably by decreasing the T-type calcium current in atrium-derived myocytes through impairment of channel function and activation of c-Src kinases, representing a potential pathogenic mechanism in atrial fibrillation.

High glucose induces apoptosis in AC16 human cardiomyocytes via macrophage migration inhibitory factor and c-Jun N-terminal kinase.

1. It is known that high glucose can induce cardiomyocyte apoptosis and that macrophage migration inhibitory factor (MIF) may be involved in the development of diabetes. However, the relationship between high glucose and MIF in diabetic cardiomyopathy remains unclear. 2. In the present study, AC16 human cardiomyocytes were cultured in the presence of 25 mmol/L glucose for 20, 30 and 60 min before being subjected to western blot analyses to determine MIF expression and c-Jun N-terminal kinase (JNK) activation. In addition, AC16 cells were pretreated with 2.5 µmol/L SP600125 (a JNK inhibitor), 40 µmol/L (s,r)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid methyl ester (ISO-1; an MIF antagonist) or 0.1% dimethylsulphoxide (DMSO; vehicle) for 1 h prior to exposure to 25 mmol/L glucose and culture for 72 h, followed by annexin V-fluorescein isothiocyanate/propidium iodide staining and flow cytometry analysis. Caspase 3 activity and phosphorylation of JNK were also analysed by western blotting. 3. The high concentration of glucose increased expression of endogenous MIF and JNK phosphorylation in AC16 cardiomyocytes. Pretreatment of cells with SP600125 and ISO-1 reduced glucose-induced apoptosis and caspase 3 activity. Furthermore, JNK phosphorylation was attenuated by inhibition of endogenous MIF. 4. In conclusion, myocardial cell apoptosis induced by high glucose involves the overexpression of MIF and activation of the JNK signalling pathway. The identification of a high glucose-MIF-JNK pathway will help determine potential new targets in the treatment of diabetic cardiomyopathy.

[Identification of the interactions between the truncated fragments of macrophage migration inhibitory factor and CD74 using a yeast two-hybrid system].

OBJECTIVE: To investigate the interaction domains between macrophage migration inhibitory factors (MIF) and the extracellular segment of type-II trans-membrane protein CD74 using a yeast two-hybrid system. METHODS: By using molecular cloning techniques, the DNA fragments encoding MIF, MIF(50-65) and MIF(1-50/65-115) were introduced into the pGBKT7 vector to construct the corresponding recombinant bait plasmids, and the DNA fragments encoding CD74(73-232), CD74(73-109), CD74(1109-149) and CD74(149-232) into the pGADT7 vector to construct the recombinant activation domain (AD) plasmids. PEG/LiAC method was employed to transform the above 3 recombinant bait plasmids paired with each of the 4 recombinant AD plasmids into the chemical competent yeast AH109 cells. The transformed yeast AH109 cells were screened consecutively on SD/-Trp-Leu and SD/-Trp-Leu-Ade-His/X-alpha-gal nutritional media. RESULTS: The results of restriction endonuclease digestion and DNA sequencing verified the correct construction of all the recombinant plasmids. The yeast AH109 cells transformed with each of the 3 recombinant bait plasmids could grow on SD/-trp nutritional media without autonomous activation effect on the reporter gene MEL1. The cells transformed with each of the 4 recombinant AD plasmids could also grow on SD/-leu nutritional media without activation of the reporter gene MEL1. Only the yeast AH109 cells co-transformed with MIF, MIF(50-65), or MIF(1-50/65-115) plasmid and CD74(73-232) plasmid could grow on SD/-Trp-Leu-Ade-His nutritional media with transcription activation of the reporter gene MEL1. CONCLUSION: MIF interacts with the intact extracellular segment of CD74 (CD74(73-232)) independent of the functional domain of MIF(50-65).

[An efficient method for screening effective siRNAs using dual-luciferase reporter assay system].

OBJECTIVE: To establish an efficient method for screening effective small interference RNA (siRNA) using dual-luciferase reporter assay system. METHODS: Based on the siRNA expression vector pSilencer-4.1, 3 candidate green fluorescence protein (GFP) gene siRNA expression plasmids, namely pSi-GFPsiRNA1, pSi-GFPsiRNA2, and pSi-GFPsiRNA3, along with the negative control pSi-Negative, were constructed. Using the pGL3-promoter vector, the GFP-luciferase (GFP-LUC) expression plasmid pGL3-GFPf was constructed with the same Kozak consensus translation initiation site and start codon ATG for GFP-LUC coding sequence. The GFP fragment containing the target sequences of 3 GFP siRNAs was introduced into the 3' untranslate region of LUC in the modified pGL3-promoter vector to construct the plasmid pGL3-GFPp. The GFP siRNAs expression plasmids and Renilla luciferase reporter vector pRL-TK were co-transfected with pGL3-GFPf or pGL3-GFPp into the HEK293 cells, respectively. The luciferase activities were determined by dual-luciferase reporter assay, and the GFP mRNA expressions were detected by real-time quantitative PCR. RESULTS: In the groups cotransfected with GFP siRNAs expression plasmids and pGL3-GFPf, the luciferase activities were reduced obviously, and the reduction was more significant in cells transfected with GFPsiRNA1 compared with the control cells (P<0.01).GFP mRNA levels were also markedly lowered in cells transfected with GFPsiRNA1 as shown by real-time PCR (P<0.01). In addition, the results of dual-luciferase reporter assay and real-time PCR showed that among the groups cotransfected with GFP siRNAs expression plasmids and pGL3-GFPp, the GFP expression was inhibited most obviously by GFPsiRNA1 (P<0.01). CONCLUSION: The dual-luciferase reporter assay system provides a useful method for screening effective siRNAs targeting specific genes.

Involvement of Src in L-type Ca2+ channel depression induced by macrophage migration inhibitory factor in atrial myocytes.

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that controls inflammatory processes, and inflammation is known to play an important role in the pathogenesis of atrial fibrillation (AF). The present study sought to investigate whether MIF expression is responsible for the changes in L-type Ca2+ currents (I(Ca,L)) seen in AF. Whole-cell voltage-clamp recordings and biochemical assays were used to study the regulation and expression of I(Ca,L) in human atrial myocytes and in HL-1 cells. Basal I(Ca,L) was reduced in AF compared to sinus rhythm (SR) controls, mRNA and protein levels of the pore-forming alpha1C subunit of L-type Ca2+ channel (LCC alpha1C) were also decreased, while MIF expression levels were increased in AF. Levels of Src and activated Src (p-Src Y416) were higher in AF than in SR. Treatment of atrial myocytes from a patient with SR with human recombinant MIF (rMIF) (40 nM, 1 h) was found to depress I(Ca,L) amplitudes, while mouse rMIF (20 or 40 nM, 24 h) suppressed peak I(Ca,L) in HL-1 cells by approximately 69% and approximately 83% in a concentration-dependent manner. Mouse rMIF impaired the time-dependent recovery from inactivation of I(Ca,L) and down-regulated LCC alpha1C subunit levels. The depression of I(Ca,L) and decrease of LCC protein levels induced by rMIF were prevented by the Src inhibitors genistein and PP1. These results implicate MIF in the electrical remodeling that accompanies AF, probably by decreasing I(Ca,L) amplitudes through impairment of channel function, down-regulation of LCC alpha1C subunit levels, and the activation of c-Src kinases in atrial myocytes.

FAK signaling is critical for ErbB-2/ErbB-3 receptor cooperation for oncogenic transformation and invasion.

The overexpression of members of the ErbB tyrosine kinase receptor family has been associated with cancer progression. We demonstrate that focal adhesion kinase (FAK) is essential for oncogenic transformation and cell invasion that is induced by ErbB-2 and -3 receptor signaling. ErbB-2/3 overexpression in FAK-deficient cells fails to promote cell transformation and rescue chemotaxis deficiency. Restoration of FAK rescues both oncogenic transformation and invasion that is induced by ErbB-2/3 in vitro and in vivo. In contrast, the inhibition of FAK in FAK-proficient invasive cancer cells prevented cell invasion and metastasis formation. The activation of ErbB-2/3 regulates FAK phosphorylation at Tyr-397, -861, and -925. ErbB-induced oncogenic transformation correlates with the ability of FAK to restore ErbB-2/3-induced mitogen-activated protein kinase (MAPK) activation; the inhibition of MAPK prevented oncogenic transformation. In contrast, the inhibition of Src but not MAPK prevented ErbB-FAK-induced chemotaxis. In migratory cells, activated ErbB-2/3 receptors colocalize with activated FAK at cell protrusions. This colocalization requires intact FAK. In summary, distinct FAK signaling has an essential function in ErbB-induced oncogenesis and invasiveness.

Differential regulation of tumor angiogenesis by distinct ErbB homo- and heterodimers.

Interactions between cancer cells and their microenvironment are critical for the development and progression of solid tumors. This study is the first to examine the role of all members of the ErbB tyrosine kinase receptors (epidermal growth factor receptor [EGFR], ErbB-2, ErbB-3, or ErbB-4), expressed singly or as paired receptor combinations, in the regulation of angiogenesis both in vitro and in vivo. Comparison of all receptor combinations reveals that EGFR/ErbB-2 and ErbB-2/ErbB-3 heterodimers are the most potent inducers of vascular endothelial growth factor (VEGF) mRNA expression compared with EGFR/ErbB-3, EGFR/ErbB-4, ErbB-2/ErbB-4, and ErbB-3/ErbB-4. Immunohistochemistry of tumor xenografts overexpressing these heterodimers shows increased VEGF expression and remarkably enhanced vascularity. Enhanced VEGF expression is associated with increased VEGF transcription. Deletional analysis reveals that ErbB-mediated transcriptional up-regulation of VEGF involves a hypoxia-inducible factor 1-independent responsive region located between nucleotides -88 to -66 of the VEGF promoter. Mutational analysis reveals that the Sp-1 and AP-2 transcription factor binding elements within this region are required for up-regulation of VEGF by heregulin beta1 and that this up-regulation is dependent on the activity of extracellular signal-related protein kinases. These results emphasize the biological implications of cell signaling diversity among members of the ErbB receptor family in regulation of the tumor microenvironment.