CD105 prevents apoptosis in hypoxic endothelial cells

L- and S-endoglin differentially modulate TGFbeta1 signaling mediated by ALK1 and ALK5 in L6E9 myoblasts

TGFbeta regulates cellular processes by binding to type I and type II TGFbeta receptors (TbetaRI and TbetaRII, respectively). In addition to these signaling receptors, endoglin is an accessory TGFbeta receptor that regulates TGFbeta signaling. Although there are two different alternatively spliced isoforms of endoglin, L-endoglin (L, long) and S-endoglin (S, short), little is known about the effects of S-endoglin isoform on TGFbeta signaling. Here, we have analyzed the TGFbeta1 signaling pathways and the effects of L- and S-endoglin in endoglin-deficient L6E9 cells. We found that TGFbeta activates two distinct TbetaRI-Smad signaling pathways: ALK1-Smad1-Id1 and ALK5-Smad2-PAI1, in these cells. Interestingly, L-endoglin enhanced the ALK1-Id1 pathway, while S-endoglin promoted the ALK5-PAI1 route. These effects on signaling are supported by biological effects on TGFbeta1-induced collagen I expression and inhibition of cell proliferation. Thus, while L-endoglin decreased TGFbeta1-induced collagen I and CTGF expression and increased TGFbeta1-induced proliferation, S-endoglin strongly increased TGFbeta1-induced collagen I and CTGF expression, and reduced TGFbeta1-induced cell proliferation.

Endoglin in angiogenesis and vascular diseases

Endoglin is a transmembrane auxillary receptor for transforming growth factor-beta (TGF-beta) that is predominantly expressed on proliferating endothelial cells. Endoglin deficient mice die during midgestation due to cardiovascular defects. Mutations in endoglin and activin receptor-like kinase 1 (ALK1), an endothelial specific TGF-beta type I receptor, have been linked to hereditary hemorrhagic telangiectasia (HHT), an autosomal dominant vascular dysplasia characterized by telangiectases and arteriovenous malformations. Endoglin heterozygote mice develop HHT-like vascular abnormalities, have impaired tumor and post-ischemic angiogenesis and demonstrate an endothelial nitric oxide synthase-dependent deterioration in the regulation of vascular tone. In pre-eclampsia, placenta-derived endoglin has been shown to be strongly upregulated and high levels of soluble endoglin are released into the circulation. Soluble endoglin was found to cooperate with a soluble form of vascular endothelial growth factor receptor 1 in the pathogenesis of pre-eclampsia by inducing endothelial cell dysfunction. Endoglin is highly expressed in tumor-associated endothelium, and endoglin antibodies have been successfully used to target activated endothelial cells and elicit anti-angiogenic effects in tumor mouse models. These exciting advances provide opportunities for the development of new therapies for diseases with vascular abnormalities.

Pathophysiology of hypertension during preeclampsia: linking placental ischemia with endothelial dysfunction

Studies over the last decade have provided exciting new insights into potential mechanisms underlying the pathogenesis of preeclampsia. The initiating event in preeclampsia is generally regarded to be placental ischemia/hypoxia, which in turn results in the elaboration of a variety of factors from the placenta that generates profound effects on the cardiovascular system. This host of molecules includes factors such as soluble fms-like tyrosine kinase-1, the angiotensin II type 1 receptor autoantibody, and cytokines such as tumor necrosis factor-alpha, which generate widespread dysfunction of the maternal vascular endothelium. This dysfunction manifests as enhanced formation of factors such as endothelin, reactive oxygen species, and augmented vascular sensitivity to angiotensin II. Alternatively, the preeclampsia syndrome may also be evidenced as decreased formation of vasodilators such as nitric oxide and prostacyclin. Taken together, these alterations cause hypertension by impairing renal pressure natriuresis and increasing total peripheral resistance. Moreover, the quantitative importance of the various endothelial and humoral factors that mediate vasoconstriction and elevation of arterial pressure during preeclampsia remains to be elucidated. Thus identifying the connection between placental ischemia/hypoxia and maternal cardiovascular abnormalities in hopes of revealing potential therapeutic regimens remains an important area of investigation and will be the focus of this review.

Novel biochemical pathways of endoglin in vascular cell physiology

The broad role of the transforming growth factor beta (TGFbeta) signaling pathway in vascular development, homeostasis, and repair is well appreciated. Endoglin is emerging as a novel, complex, and poorly understood regulatory component of the TGFbeta receptor complex, whose importance is underscored by its recognition as the site of mutations causing hereditary hemorrhagic telangiectasia (HHT) [McAllister et al., 1994]. Extensive analyses of endoglin function in normal developmental mouse models [Bourdeau et al., 1999; Li et al., 1999; Arthur et al., 2000] and in HHT animal models [Bourdeau et al., 2000; Torsney et al., 2003] exemplify the importance of understanding endoglin's biochemical functions. However, novel mechanisms underlying the regulation of these pathways continue to emerge. These mechanisms include modification of TGFbeta receptor signaling at the ligand and receptor activation level, direct effects of endoglin on cell adhesion and migration, and emerging roles for endoglin in the determination of stem cell fate and tissue patterning. The purpose of this review is to highlight the cellular and molecular studies that underscore the central role of endoglin in vascular development and disease.

Hypoxia promotes luteal cell death in bovine corpus luteum

Low oxygen caused by a decreasing blood supply is known to induce various responses of cells, including apoptosis. The present study was conducted to examine whether low-oxygen conditions (hypoxia) induce luteal cell apoptosis in cattle. Bovine midluteal cells incubated under hypoxia (3% O(2)) showed significantly more cell death than did those incubated under normoxia (20% O(2)) at 24 and 48 h of culture, and had significantly lower progesterone (P4) levels starting at 8 h. Characteristic features of apoptosis, such as shrunken nuclei and DNA fragmentation, were observed in cells cultured under hypoxia for 48 h. Hypoxia increased the mRNA expressions of BNIP3 and caspase 3 at 24 and 48 h of culture. Hypoxia had no significant effect on the expressions of BCL2 and BAX mRNA. Hypoxia also increased BNIP3 protein, and activated caspase-3. Treatment of P4 attenuated cell death, caspase-3 mRNA expression, and caspase-3 activity under hypoxia. Overall results of the present study indicate that hypoxia induces luteal cell apoptosis by enhancing the expression of proapoptotic protein, BNIP3, and by activating caspase-3, and that the induction of apoptosis by hypoxia is partially caused by a decrease in P4 production. Because hypoxia suppresses P4 synthesis in bovine luteal cells, we suggest that oxygen deficiency caused by a decreasing blood supply in bovine corpus luteum is one of the major factors contributing to both functional and structural luteolysis.

Endoglin is not critical for hematopoietic stem cell engraftment and reconstitution but regulates adult erythroid development

Endoglin is a transforming growth factor-beta (TGF-beta) accessory receptor recently identified as being highly expressed on long-term repopulating hematopoietic stem cells (HSC). However, little is known regarding its function in these cells. We have used two complementary approaches toward understanding endoglin's role in HSC biology: one that efficiently knocks down expression via lentiviral-driven short hairpin RNA and another that uses retroviral-mediated overexpression. Altering endoglin expression had functional consequences for hematopoietic progenitors in vitro such that endoglin-suppressed myeloid progenitors (colony-forming unit-granulocyte macrophage) displayed a higher degree of sensitivity to TGF-beta-mediated growth inhibition, whereas endoglin-overexpressing cells were partially resistant. However, transplantation of transduced bone marrow enriched in primitive hematopoietic stem and progenitor cells revealed that neither endoglin suppression nor endoglin overexpression affected the ability of stem cells to short-term or long-term repopulate recipient marrow. Furthermore, transplantation of cells altered in endoglin expression yielded normal white blood cell proportions and peripheral blood platelets. Interestingly, decreasing endoglin expression increased the clonogenic capacity of early blast-forming unit-erythroid progenitors, whereas overexpression compromised erythroid differentiation at the basophilic erythroblast phase, suggesting a pivotal role for endoglin at key stages of adult erythropoietic development.

Correlation between soluble endoglin, vascular endothelial growth factor receptor-1, and adipocytokines in preeclampsia

CONTEXT

Recent reports have demonstrated that soluble endoglin (sEng), an antiangiogenic protein thought to impair TGF-beta binding to receptors, and soluble vascular endothelial growth factor receptor (sVEGFR)-1 play important roles in the pathophysiology of preeclampsia (PE). Moreover, insulin resistance, which is greatly influenced by adipocytokines, characterizes PE.

OBJECTIVES

We examined possible links between sEng, VEGF, sVEGFR, and adipocytokines in the pathophysiology of PE.

STUDY DESIGN

We performed a cross-sectional study in 30 PE patients and controls matched for gestational age and body mass index. Blood samples were collected soon after disease onset. We measured serum concentrations of leptin, adiponectin, sEng, VEGF, placental growth factor (PlGF), and sVEGFR [soluble fms-like tyrosine kinase 1 (sFlt-1) and soluble fetal liver kinase 1 (sFlk-1)], and examined the placental protein content of sEng and sFlt-1.

RESULTS

sEng concentrations in PE patients (60.9 +/- 28.8 ng/ml) were significantly higher than those in controls (11.2 +/- 4.4 ng/ml). There was a significant correlation between sEng and sFlt-1 or PlGF. Moreover, there were significant differences in mean blood pressure between the high and low sEng groups, and in proteinuria between the high and low sFlt-1 groups, and significant differences in placental sEng and sFlt-1 contents between patients with and without severe hypertension or proteinuria. sEng was also correlated positively with adiponectin levels and negatively with the leptin to adiponectin ratio.

CONCLUSIONS

Along with sFlt-1 and PlGF, sEng might play a role in the pathophysiology of PE, especially in elevating blood pressure, while the association with hypoadiponectinemia and the high leptin to adiponectin ratio in pregnancy seem to be risk factors for PE.

Reduced tumor growth and angiogenesis in endoglin-haploinsufficient mice

Endoglin is a transforming growth factor-beta(1) (TGF-beta(1)) accessory receptor which is highly expressed in tumor vessels. To study the role of endoglin in tumor growth and angiogenesis we induced a highly vascularized tumor in mice heterozygous for endoglin (Eng+/-) and in their control littermates (Eng+/+) by injecting 10(6) Lewis lung carcinoma (3LL) cells subcutaneously. Nine days after injection, the tumor was removed and weighed. Capillary density (CD31 immunohistochemistry), hemoglobin content and vascular cell adhesion molecule-1 (VCAM-1) expression were used to assess tumor vascularization. Tumor perfusion rate was measured by laser-Doppler technique. Expression of the hypoxia-inducible factor (HIF), endothelial nitric oxide synthase (eNOS) and vascular endothelial growth factor (VEGF) were determined by Western blot analysis. The aerobic metabolism and oxygen dependency were inferred from the measurement of ATP in tumoral tissue. Tumor weight, capillary density, hemoglobin and VCAM-1 were reduced by about 30% in Eng+/- compared to Eng+/+ littermates. The protein levels of eNOS and phosphorylated eNOS were significantly reduced in Eng+/- compared to Eng+/+ mice. HIF expression was slightly reduced whereas VEGF level was slightly increased in Eng+/- compared to Eng+/+. Tumor tissue levels of ATP and ADP were similar in both types of mice. These data demonstrate that endoglin plays a major role in tumor neoangiogenesis.

Role of endoglin and transforming growth factor-beta in progressive white matter damage after an ischemic stroke

We morphologically examined human brains several years after a territorial ischemic stroke to assess the development of progressing white matter damage and its pathomechanisms. Our investigations focused on the role of TGF-beta, one of the factors whose expression increases after tissue damage, and its receptor endoglin in the propagation of postischemic injury. Examination of the white matter adjacent to the postapoplectic cavity revealed structural changes in the capillary vessels, disturbed microcirculation, and deep endothelial cell damage with DNA fragmentation in the TUNEL reaction. Many oligodendrocytes also revealed DNA damage and an increased expression of caspase-3. In the rarefied white matter, the microvessel immune reaction to TGF-beta was diminished while the expression of endoglin was heterogeneous: absent in some capillaries but increased in others in comparison to the vessels located more peripherally from the cavity and in the control material. We conclude that endoglin and TGF-beta can be involved in the development of the microangiopathy responsible for the propagation of postischemic white matter injury in humans. We suggest that disturbances in endoglin expression can influence TGF-beta signaling and, consequently, vessel structure and function. Pronounced endoglin expression can lead to decreased vessel wall integrity while a lack of the constitutively expressed protein is probably a mirror of deep vessel damage.

FGF-1 and S100A13 possibly contribute to angiogenesis in endometriosis

Endometriosis is referred often as an angiogenic disease. The pivotal role of angiogenesis in the pathophysiology of this disease has been confirmed by many studies. This process has several steps, and VEGF is probably the most important in its initiation. There are others involved in its continuation and maintenance of the tight balance between a quiescent and activated blood vessel state. In the process of formation of new blood capillaries and arterioles, many different factors are involved in sometimes distinct pathways. Such factors are TGF-beta and endoglin--the latter being one of the main modulators of the TGF-beta signaling pathway. Endoglin is now not only established as a marker of active neo-angiogenesis and activated endothelium, but also turns to be an active player in the very process of endometriotic angiogenesis. Its signaling pathway of hypoxic activation is tightly interconnected with that of VEGF, and also some of the FGFs. FGF-1 and S100A13 are members of two distinct families of proteins -- the FGFs, growth and angiogenic factors, and that of the S100 proteins, -- Ca(2+)-binding proteins involved in cell function regulation, motility and signaling. These two particular members are quite unique in having no signal peptide sequence and being involved in common export pathway. Our hypothesis is that these two factors are involved in vascular remodeling in endometriotic angiogenesis, playing a role in vascular wall formation and migration of endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). We believe also that endoglin is tightly involved in the new arteriolar formation in endometriosis, being expressed in VSMCs but not on the ECs of the middle-sized vessels.

Differential kinetics of plasma CD105 and transforming growth factor beta expression early in human acute pancreatitis

OBJECTIVES

The interaction of transforming growth factor beta (TGF-beta) with CD105 (endoglin) is an essential step in the maintenance of endothelial cell quiescence. The importance of this interaction during the critical early phases of acute pancreatitis is unknown. This study explores patterns of expression of CD105 and TGF-beta in plasma during human acute pancreatitis.

METHODS

Forty-one patients with a clinical diagnosis of acute pancreatitis constitute the study population. Venous blood samples were taken at admission and on the fifth day. Enzyme-linked immunosorbent assay was performed for CD105, TGF-beta1, TGF-beta3, CD105/TGF-beta1, and CD105/TGF-beta3 complexes.

RESULTS

TGF-beta1 levels were significantly elevated on admission in the acute pancreatitis group compared with controls and were further elevated in delayed samples. In contrast, admission CD105 levels were similar to those in controls, but in delayed samples, there was a significant reduction in CD105. Levels of TGF-beta3, CD105/TGF-beta1, and CD105/TGF-beta3 did not differ between groups.

CONCLUSIONS

This is the first report to investigate the interplay between plasma expression of CD105, TGF-beta1, TGF-beta3, and ligand complexes in acute pancreatitis. The results of this study confirm previous findings that increased expression of TGF-beta1 is a feature of severe acute pancreatitis. The absence of a parallel elevation in CD105 or CD105/TGF-beta ligand complexes is previously unreported and may suggest that angiogenesis mediated by the interaction between CD105 and TGF-beta is not an early feature of this disease.

Elevated plasma CD105 and vitreous VEGF levels in diabetic retinopathy

Diabetic retinopathy is the leading cause of blindness in the industrialized world. Hyperglycaemia induces retinal hypoxia that upregulates a range of vasoactive factors which may lead to macular oedema and/or angiogenesis and hence potentially sight threatening retinopathy. In this study, we have focused on the association of CD105 and vascular endothelial growth factor (VEGF) with the development and progression of diabetic retinopathy by means of quantifying their expression in the plasma and vitreous of diabetic patients. CD105 levels were quantified in the plasma of 38 type I diabetic patients at various stages of retinopathy and 15 non-diabetic controls. In an additional cohort of 11 patients with advanced proliferative retinopathy and 23 control subjects, CD105 and VEGF were measured in the vitreous. The values were expressed as median (range) and statistical analysis was carried out using the non-parametric Mann-Whitney U test. Plasma CD105 levels were significantly increased in diabetic patients [1.8 (1.1-2.4) ng/ml] compared with non-diabetic controls [0.7 (0.3-1.8) ng/ml] (p<0.01). Plasma CD105 levels were elevated in diabetic patients with all stages of retinopathy, the highest level was observed in background retinopathy [2.3 (2.1-2.5) ng/ml] followed by proliferative retinopathy [2.1 (0.9-2.8) ng/ml] and advanced proliferative retinopathy [1.4 (0.6-1.8) ng/ml]. Vitreous contents of CD105 did not differ between controls and patients with advanced proliferative retinopathy, but vitreous levels of VEGF were elevated by approximately 3-fold in patients with advanced proliferative retinopathy [7.2 (1.90-15.60) ng/ml] compared with the control subjects [1.80 (1.10-2.210)] (p<0.01). These observations indicate that plasma levels of CD105 and vitreous levels of VEGF are associated with diabetic retinopathy, suggesting that CD105 and the angiogenic factor VEGF may play a critical role in the development and progression of diabetic retinopathy. Further studies are required to determine whether circulating CD105 levels could serve as a surrogate marker for early stage retinopathy and for monitoring disease progression.

Association of hereditary hemorrhagic telangiectasia and hereditary nonpolyposis colorectal cancer in the same kindred

Endoglin (CD105) is a proliferation-associated protein that is strongly expressed in endothelial tissue and has a role in tumor angiogenesis. Mutations in endoglin are also linked to Hereditary Hemorrhagic Telangiectasia type 1 (HHT1), an autosomal dominant disease associated with aberrant angiogenesis. We report an unusual association of HHT1 and Hereditary Nonpolyposis Colorectal Cancer (HNPCC) in the same kindred. Genetic analysis indicates that these 2 syndromes are genetically unrelated and separately segregated within the family. The mutation in the endoglin gene leads to a truncated protein. The mutation in the mismatch repair gene MLH1 causes a splicing defect, giving synthesis to an unstable mRNA from this mutated allele. The potential protective role of an endoglin mutation in patients with HNPCC is discussed.

Interaction and functional interplay between endoglin and ALK-1, two components of the endothelial transforming growth factor-beta receptor complex

Transforming growth factor-beta (TGF-beta) signaling in endothelial cells is able to modulate angiogenesis and vascular remodeling, although the underlying molecular mechanisms remain poorly understood. Endoglin and ALK-1 are components of the TGF-beta receptor complex, predominantly expressed in endothelial cells, and mutations in either endoglin or ALK-1 genes are responsible for the vascular dysplasia known as hereditary hemorrhagic telangiectasia. Here we find that the extracellular and cytoplasmic domains of the auxiliary TGF-beta receptor endoglin interact with ALK-1 (a type I TGF-beta receptor). In addition, endoglin potentiates TGF-beta/ALK1 signaling, with the extracellular domain of endoglin contributing to this functional cooperation between endoglin and ALK-1. By contrast, endoglin appears to interfere with TGF-beta/ALK-5 signaling. These results suggest that the functional association of endoglin with ALK-1 is critical for the endothelial responses to TGF-beta.

CEACAM engagement by human pathogens enhances cell adhesion and counteracts bacteria-induced detachment of epithelial cells

Exfoliation, which is the detachment of infected epithelial cells, is an innate defense mechanism to prevent bacterial colonization. Indeed, infection with Neisseria gonorrhoeae induced epithelial detachment from an extracellular matrix (ECM) substrate in vitro. Surprisingly, variants of N. gonorrhoeae that bind to human carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) failed to induce detachment and, instead, promoted enhanced host cell adhesion to the ECM. Microarray analysis revealed that CEACAM engagement by several human pathogens triggers expression of CD105. Blockage of CD105 expression by antisense oligonucleotides abolished infection-induced cell adhesion. The expression of full-length CD105 promoted cell adhesion to the ECM and was sufficient to prevent infection-induced detachment. The CD105-mediated increase in cell adhesion was dependent on the presence and function of integrin β1. CD105 expression did not elevate cellular integrin levels but caused a dramatic increase in the ECM-binding capacity of the cells, suggesting that CD105 affects integrin activity. The exploitation of CEACAMs to trigger CD105 expression and to counteract infection-induced cell detachment represents an intriguing adaptation of pathogens that are specialized to colonize the human mucosa.

Mutation Analysis in Spanish Patients with Hereditary Hemorrhagic Telangiectasia: Deficient Endoglin Up-regulation in Activated Monocytes

Background: Mutations in the endoglin (ENG) or ALK1 genes are responsible for hereditary hemorrhagic telangiectasia types 1 and 2 (HHT1 and HHT2), respectively, a dominant vascular dysplasia caused by haploinsufficiency. No formal mutation studies of patients with HHT have been conducted in Spain.

Methods: ENG and ALK1 mutation analyses were carried out in 13 Spanish HHT patients diagnosed according to the Curaçao criteria. Because endoglin is up-regulated at the cell surface during the monocyte-macrophage transition, endoglin concentrations in activated monocytes were determined by immunofluorescence flow cytometry in a systematic analysis. As controls, 40 non-HHT volunteers were studied for up-regulation of endoglin in activated monocytes.

Results: The mutation responsible for HHT was identified in eight patients belonging to two unrelated families. One of the families has a nonsense mutation in exon 4 (c.511C&gt;T; R171X) of the ENG gene, and accordingly the disorder was identified as HHT1. The other family has a missense mutation affecting exon 8 (c.1120C&gt;T; R374W) of the ALK1 gene, and hence is a HHT2 family. Interestingly, endoglin up-regulation was deficient in activated monocytes of both HHT1 and HHT2 patients compared with controls. By contrast, endoglin up-regulation was age-independent in control donors across a broad range of ages. The extent of endoglin up-regulation in activated monocytes was most diminished in those patients with the most severe symptoms.

Conclusions: Endoglin up-regulation in activated monocytes is impaired in HHT1 and HHT2 patients and is age-dependent in both HHT types. Endoglin expression may predict the clinical severity of HHT.

Highlights on endoglin (CD105): from basic findings towards clinical applications in human cancer

Antibody targeting of tumor-associated vasculature is a promising therapeutic approach in human cancer; however, a specific cell membrane marker for endothelial cells of tumor vasculature has not been discovered yet. Endoglin (CD105) is a cell-surface glycoprotein most recently identified as an optimal indicator of proliferation of human endothelial cells. The finding that CD105 is over-expressed on vascular endothelium in angiogenetic tissues has prompted several pre-clinical studies designed to get a deeper understanding on the role of CD105 in angiogenesis, and to evaluate the most appropriate clinical setting(s) to utilize CD105 as a therapeutic target. In this review, the foreseeable clinical applications of CD105 in human cancer are discussed.

Antiapoptotic action of hypoxia-inducible factor-1 alpha in human endothelial cells

Hypoxia-inducible factor-1 (HIF-1) is the major transcription factor involved in the adaptive response to hypoxia and consists of HIF-1 alpha and HIF-1 beta subunits. Indirect evidence suggests that HIF-1 alpha may exert both proapoptotic and antiapoptotic actions in response to hypoxia. In this study, we evaluated the effects of RNA interference (RNAi) targeting HIF-1 alpha messenger RNA (mRNA) on apoptosis in primary cultured human umbilical vascular endothelial cells (HUVECs) exposed to anoxia and reoxygenation (A/R). HUVECs were transfected with specific 21-nt small interfering RNA (siRNA) duplexes targeting HIF-1 alpha mRNA sequences or scrambled RNA duplexes and subjected either to normoxia for 251/2 h or to anoxia for 11/2 h, and subsequently normoxia for 24 h (A/R). Control samples were subjected to A/R but not transfected. HUVECs apoptosis was evaluated by Tdt-mediated dUTP nick end-labeling (TUNEL) assay and by activated caspase-3 immunostaining and immunoblotting. The efficacy of RNAi was assessed by knockdown of HIF-1 alpha mRNA and protein expression via in situ hybridization, real-time quantitative PCR, immunohistochemistry, and Western blotting. When compared with normoxic cultures, A/R significantly upregulated HIF- 1 alpha mRNA and protein expression in HUVECs, but did not appreciably alter the percentage of apoptotic cells. In contrast, a significantly greater proportion of HUVECs transfected with specific siRNA duplexes and exposed to A/R demonstrated evidence of apoptosis when compared with nontransfected cells. Transfection with specific siRNA duplexes knocked down HIF-1 alpha mRNA and protein expression in A/R-treated cells by approximately 60%, whereas transfection with scrambled siRNA duplexes had no noticeable effect on HIF-1 alpha expression. These findings strongly suggest that HIF-1 alpha exerts an antiapoptotic role in HUVECs stressed by anoxia.

Cyr61 expression confers resistance to apoptosis in breast cancer MCF-7 cells by a mechanism of NF-kappaB-dependent XIAP up-regulation

The aggressiveness of a tumor is partly attributed to its resistance to chemotherapeutic agent-induced apoptosis. Cysteine-rich 61 (Cyr61), from the CCN gene family, is a secreted and matrix-associated protein, which is involved in many cellular activities such as growth and differentiation. Here we established a cell model system to examine whether stable expression of Cyr61 in MCF-7 cells can confer resistance to apoptosis and identify possible participating mechanisms. We showed that stable cell lines overexpressing Cyr61 had acquired a remarkable resistance to apoptosis induced by paclitaxel, adriamycin, and beta-lapachone. Most interesting, gel shift and reporter assays showed that the Cyr61-overexpressing cells had significantly increased NF-kappaB activity compared with neo control cells. Blockage of NF-kappaB activity in Cyr61-expressing cells by transfecting with a dominant negative (DN)-IkappaB or with an NF-kappaB decoy rendered them more susceptible to anti-cancer drugs-induced apoptosis. In addition, several NF-kappaB-regulated anti-apoptotic genes were examined, and we found that only XIAP showed a significant 3-4-fold increase in mRNA and protein in Cyr61-overexpressing cells but not in neo control cells. Treatment with inhibitor of apoptosis protein (XIAP)-specific antisense, but not sense, oligonucleotides abolished the apoptosis resistance of the Cyr61-overexpressing cells. At the same time, transfection of these stable cells with DN-IkappaB to block NF-kappaB activity also effectively reduced the elevated XIAP level. Function-neutralizing antibodies to alpha(v)beta(3) and alpha(v)beta(5) could inhibit Cyr61-mediated NF-kappaB activation as well as XIAP expression. Taken together, our data suggested that Cyr61 plays an important role in resistance to chemotherapeutic agent-induced apoptosis in human breast cancer MCF-7 cells by a mechanism involving the activation of the integrins/NF-kappaB/XIAP signaling pathway.

Effect of vascular endothelial growth factor on functional recovery after hepatectomy in lean and obese mice

BACKGROUND/AIMS

Liver regeneration is dependent upon coordinated proliferation of hepatocytes and endothelial cells. Vascular endothelial growth factor (VEGF) promotes angiogenesis. Hepatic steatosis delays regeneration and increases liver resection morbidity. We hypothesized that VEGF overexpression stimulates hepatic regeneration.

METHODS

Recombinant adenovirus expressing human VEGF165 or adenovirus control-vector (LacZ) were administered before 2/3 hepatectomy in lean and ob/ob mice. Galactose elimination capacity, a quantitative liver function test, was repeatedly measured before and after hepatectomy. Expression of VEGF receptors (flt1, flk1), endoglin and hypoxia inducible factor-1alpha (HIF-1alpha) was assessed by quantitative RT-PCR and for endoglin also by immunohistochemistry.

RESULTS

After 2/3 hepatectomy, VEGF gene transfer increased galactose elimination capacity in lean and ob/ob mice. HIF-1alpha, endoglin and VEGF receptor mRNA increased during regeneration in lean but not in obese mice. Staining of endothelial cells by endoglin immunohistochemistry returned to baseline reactivity in lean mice by day 6 and remained decreased in ob/ob mice. VEGF treatment decreased HIF-1alpha and increased flk1 response in lean mice.

CONCLUSIONS

Hepatic resection elicits an angiogenic response in the remnant liver, which is impaired in case of steatosis. Adenovirus-mediated transfer of VEGF hastens functional hepatic recovery in lean, and more importantly also, in obese mice after partial hepatectomy.

Endoglin regulates nitric oxide‐dependent vasodilatation

Endoglin is a membrane glycoprotein that plays an important role in cardiovascular development and angiogenesis. We examined the role of endoglin in the control of vascular tone by measuring nitric oxide (NO)-dependent vasodilation in haploinsufficient mice (Eng+/-) and their Eng+/+ littermates. The vasodilatory effect of acetylcholine, bradykinin, and sodium nitroprusside was assessed in anesthetized mice; in isolated, perfused hindlimbs; and in aortic rings. The substantial hypotensive and vasodilatory response induced by acetylcholine and bradykinin in Eng+/+ was markedly reduced in Eng+/- mice. Both kinds of animals had similar responses to sodium nitroprusside, suggesting that the deficient vasodilatory effect is not due to a NO response impairment. Urinary and plasma concentrations of nitrites, a NO metabolite, were lower in Eng+/- than in Eng+/+ mice. The levels of endothelial nitric oxide synthase (eNOS) in kidneys and femoral arteries were about half in Eng+/- than in Eng+/+ mice and were also reduced in primary cultures of aortic endothelial cells from Eng+/- compared with those from Eng+/+ mice. Furthermore, overexpression or suppression of endoglin in cultured cells induced a marked increase or decrease in the protein levels of eNOS, respectively. Thus, our results in vivo and in vitro demonstrate a relationship between endoglin and NO-dependent vasodilation mediated by the regulation of eNOS expression.

Perfusion of99Tcm-labeled CD105 Mab into kidneys from patients with renal carcinoma suggests that CD105 is a promising vascular target

There is strong published and unpublished evidence that our CD105 Mab E9, which is highly reactive with angiogenic endothelial cells, could be a useful reagent to target the vasculature of solid tumors in man. Since Mab E9 does not cross-react with animal tissues, we undertook here to evaluate its localization using human kidney as an ex vivo model. Perfusion was performed through the renal artery of 99Tcm-labeled purified CD105 Mab in freshly excised kidneys from 7 patients with renal carcinoma. In all 7 cases, immunoscintigraphs showed the presence of well-defined radioactive hot spots, which matched the positions of the tumors as identified by presurgery MRI scans and subsequent histopathologic examination. Importantly, in one instance, where a presurgery MRI scan had identified only one tumor, immunoscintigraphs showed 2 distinct hot spots of radioactivity. The pathology report confirmed that the additional hot spot corresponded to a small secondary well-vascularized tumor. The implication of this finding is that the radiolabeled Mab, E9, may be of use in the detection of metastatic disease. That the labeling of tumors was specific was confirmed when prior perfusion of unlabeled mab E9 in 2 kidneys completely blocked the localization of 99Tcm-conjugated Mab E9. Radioactivity in samples of tumor and normal tissue taken from 7 kidneys was counted in a gamma counter. In all cases, there was a greater uptake of radioactivity in tumors compared with the corresponding normal kidneys. The median values, adjusted per gram wet weight, for 99Tcm were 14.8 times (range, 4.8-113.0) greater in kidney tumors than in normal kidney tissue (p < 0.007). Immunofluorescent staining of cryostat sections of tumor tissues in each of the 7 cases showed strong and uniform localization of Mab E9 in tumor microvessels. Interestingly, chimeric staining of endothelial cells (ECs) was seen in an occasional microvessel segment. That is, while most of the ECs lining a microvessel were strongly stained, an occasional EC was negative. This was not an artifact of staining. Unstained ECs may be nonangiogenic or apoptotic since CD105 is a proliferation/activation-associated antigen. Further investigations are warranted to establish the pharmacokinetics of 99Tcm-labeled CD105 antibody in vivo. This would enable us to determine whether an apparently highly successful ex vivo study has the potential for tumor imaging/therapeutic vascular targeting in patients with cancer.

EndoPDI, a novel protein-disulfide isomerase-like protein that is preferentially expressed in endothelial cells acts as a stress survival factor

We have identified a novel protein-disulfide isomerase and named it endothelial protein-disulfide isomerase (EndoPDI) because of its high expression in endothelial cells. Isolation of the full-length cDNA showed EndoPDI to be a 48 kDa protein that has three APWCGHC thioredoxin motifs in contrast to the two present in archetypal PDI. Ribonuclease protection and Western analysis has shown that hypoxia induces EndoPDI mRNA and protein expression. In situ hybridization analysis showed that EndoPDI expression is rare in normal tissues, except for keratinocytes of the hair bulb and syncytiotrophoblasts of the placenta, but was present in the endothelium of tumors and in other hypoxic lesions such as atherosclerotic plaques. We have compared the function of EndoPDI to that of PDI in endothelial cells using specific siRNA. PDI was shown to have a protective effect on endothelial cells under both normoxia and hypoxia. In contrast, EndoPDI has a protective effect only in endothelial cells exposed to hypoxia. The loss of EndoPDI expression under hypoxia caused a significant decrease in the secretion of adrenomedullin, endothelin-1, and CD105; molecules that protect endothelial cells from hypoxia-initiated apoptosis. The identification of an endothelial PDI further extends this increasing multigene family and EndoPDI, unlike archetypal PDI, may be a molecule with which to target tumor endothelium.