Endothelin-1 induces vascular endothelial growth factor synthesis in osteoblasts: involvement of p38 mitogen-activated protein kinase

The impact of implant abutment surface treatment with TiO2 on peri-implant levels of angiogenesis and bone-related markers: a randomized clinical trial

The goal of this randomized, blinded, split-mouth controlled clinical trial was to assess the influence of abutment surface treatment on tissue healing. Fifteen patients received two implants distributed randomly to two groups: test (TiO₂ abutment surface), control (standard abutment surface). Levels of epidermal growth factor (EGF), bone morphogenetic protein 9 (BMP-9), endothelin 1 (ET-1), fibroblast growth factor (FGF), placental growth factor (PlGF), and vascular endothelial growth factor (VEGF) were quantified in the peri-implant fluid after 3, 14, 30, and 60 days. Inter-group comparisons indicated higher levels of EGF, BMP-9, ET-1, FGF, and PlGF in the test group after 30days (P<0.05). PlGF levels were also higher in the test group after 60 days. In the test group, intra-group analysis revealed different levels of ET-1 and FGF between days 3 and 30, and days 3 and 60 (P<0.05); furthermore, VEGF levels were significantly higher on day 60 than on day 3 (P <0.05). In the control group, intra-group analysis demonstrated significantly different levels of ET-1, FGF, and PlGF between days 3 and 60 and of PlGF between days 14 and 60 (P<0.05). In conclusion, abutment surfaces treated with TiO₂ influenced the levels of angiogenesis and bone-related markers.

Ginkgolide B enhances the differentiation of preosteoblastic MC3T3-E1 cells through VEGF: Involvement of the p38 MAPK signaling pathway

Ginkgolide B (GB) is one of the ginkgolides isolated from the leaves of the Ginkgo biloba tree. Our previous study indicated that GB promotes the proliferation, migration and adhesion of endothelial progenitor cells, and the induction of angiogenesis through vascular endothelial factor (VEGF). In the present study, the effects of GB on the differentiation of MC3T3‑E1 cells and the signaling pathway involved were investigated in vitro. The MC3T3‑E1 cell viability activities were assessed using an MTS assay. Measurements of alkaline phosphatase activity and Alizarin Red staining were used to identify osteoblastic differentiation of the MC3T3‑E1 cells. The mRNA and secretion levels of VEGF were detected using reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) analysis and enzyme-linked immunosorbent assays, respectively. The protein expression levels of phosphorylation‑associated markers were detected using western blot analysis and associated gene expression was determined using RT‑qPCR analysis. It was found that GB significantly promoted alkaline phosphatase activity and osteoblastic mineralization in the MC3T3‑E1 cells. In addition, the mRNA expression and secretion levels of VEGF in the MC3T3‑E1 cells were significantly increased in MC3T3‑E1 cells treated with GB. SB203580, a specific inhibitor of p38 mitogen‑activated protein (MAP) kinase, markedly suppressed the GB‑induced p38 kinase phosphorylation and GB‑induced synthesis of VEGF. PD98059, an inhibitor of the upstream kinase, which activates p44/p42 MAP kinase, had minimal effect on the GB‑induced phosphorylation of p44/p42 MAP kinase or the GB‑induced synthesis of VEGF. Taken together, these results indicated that GB promoted osteoblastic differentiation of the MC3T3‑E1 cells through VEGF, and that the p38, but not the p44/p42 MAP kinase signaling pathway, was involved in the GB‑induced synthesis of VEGF.

The emerging role of endothelin-1 in the pathogenesis of subchondral bone disturbance and osteoarthritis

Mounting evidence suggests reconceptualizing osteoarthritis (OA) as an inflammatory disorder. Trauma and obesity, the common risk factors of OA, could trigger the local or systemic inflammatory cytokines cascade. Inflammatory bone loss has been well documented; yet it remains largely unknown about the link between the inflammation and hypertrophic changes of subchondral bone seen in OA, such as osteophytosis and sclerosis. Amid a cohort of inflammatory cytokines, endothelin-1 (ET-1) could stimulate the osteoblast-mediated bone formation in both physiological (postnatal growth of trabecular bone) and pathological conditions (bone metastasis of prostate or breast cancer). Also, ET-1 is known as a mitogen and contributes to fibrosis in various organs, e.g., skin, liver, lung, kidney heart and etc., as a result of inflammatory or metabolic disorders. Subchondral bone sclerosis shared the similarity with fibrosis in terms of the overproduction of collagen type I. We postulated that ET-1 might have a hand in the subchondral bone sclerosis of OA. Meanwhile, ET-1 was also able to stimulate the production of matrix metalloproteinase (MMP)-1 and 13 by articular chondrocytes and synoviocytes, by which it might trigger the enzymatic degradation of articular cartilage. Taken together, ET-1 signaling may play a role in destruction of bone-cartilage unit in the pathogenesis of OA; it warrants further investigations to potentiate ET-1 as a novel diagnostic biomarker and therapeutic target for rescue of OA.

Link between cancer and Alzheimer disease via oxidative stress induced by nitric oxide-dependent mitochondrial DNA overproliferation and deletion

Nitric oxide- (NO-) dependent oxidative stress results in mitochondrial ultrastructural alterations and DNA damage in cases of Alzheimer disease (AD). However, little is known about these pathways in human cancers, especially during the development as well as the progression of primary brain tumors and metastatic colorectal cancer. One of the key features of tumors is the deficiency in tissue energy that accompanies mitochondrial lesions and formation of the hypoxic smaller sized mitochondria with ultrastructural abnormalities. We speculate that mitochondrial involvement may play a significant role in the etiopathogenesis of cancer. Recent studies also demonstrate a potential link between AD and cancer, and anticancer drugs are being explored for the inhibition of AD-like pathology in transgenic mice. Severity of the cancer growth, metastasis, and brain pathology in AD (in animal models that mimic human AD) correlate with the degree of mitochondrial ultrastructural abnormalities. Recent advances in the cell-cycle reentry of the terminally differentiated neuronal cells indicate that NO-dependent mitochondrial abnormal activities and mitotic cell division are not the only important pathogenic factors in pathogenesis of cancer and AD, but open a new window for the development of novel treatment strategies for these devastating diseases.

Molecular profiling of pancreatic neuroendocrine tumors in sporadic and Von Hippel-Lindau patients

PURPOSE

Von Hippel-Lindau (VHL) disease is an inherited syndrome caused by germline mutations in the VHL tumor suppressor gene, predisposing to a variety of neoplasms including pancreatic neuroendocrine tumors (PanNET). In VHL disease, PanNET probably progress according to a specific pathway of carcinogenesis. Our aim was to characterize by molecular quantitative analysis a panel of molecules implicated in the VHL pathway and in tumor progression in the PanNET of patients with VHL.

EXPERIMENTAL DESIGN

The expression of 52 genes was studied by quantitative reverse transcriptase PCR in 18 patients with VHL operated on for PanNET and compared with 16 non-VHL PanNET. The VHL and non-VHL tumors were matched according to their size and cell proliferation. For some genes, we looked for differences in the protein expression in VHL PanNET (n = 31), microadenomas (n = 22), and non-VHL PanNET (n = 16), included in tissue microarray blocks.

RESULTS

Nineteen (36%) genes were significantly upregulated and three (6%) downregulated in VHL PanNET. The upregulated genes were related to (i) hypoxia-inducible factor (HIF) molecules (CA9, HIF2A, and GLUT1), (ii) angiogenesis (CDH5, VEGFR1, EDNRA, ANGPT2, CD34, VEGFR2, VEGFA, and ANGPT1), (iii) the processes of epithelial-mesenchymal transition (VIM) and/or metastasis (LAMA4 and CXCR4), (iv) growth factors and receptors (PDGFB, IRS1, and ERBB1), or (v) cell cycle (CCND1 and CDKN2A). The downregulated genes were related to (i) EMT (OCLN) and (ii) signaling pathways (RPS6KB1 and GADD45B).

CONCLUSION

This study shows that the progression of PanNET in patients with VHL tumors follows a specific pathway and supports that targeting molecules specifically involved may be of therapeutic importance.

Regulation of postnatal trabecular bone formation by the osteoblast endothelin A receptor

Endothelin-1 (ET-1) is a potent vasoconstrictor that also stimulates cells in the osteoblast lineage by binding to the endothelin A receptor (ETAR). ET-1 ligand is widely secreted, particularly by the vasculature. However, the contributions of ETAR signaling to adult bone homeostasis have not been defined. ETAR was inactivated in osteoblasts by crossing ETAR-floxed and osteocalcin-Cre mice. Histomorphometric analyses were performed on 4-, 8-, and 12-week-old osteoblast-targeted ETAR knockout (KO) and wild-type (WT) male and female mice. Tibial trabecular bone volume was significantly lower from 12 weeks in KO versus WT mice in both males and females. Bone-formation rate, osteoblast density, and in vitro osteoblast differentiation were reduced by targeted inactivation of ETAR. A separate longitudinal analysis was performed between 8 and 64 weeks to examine the effect of aging and castration on bone metabolism in ETAR KO mice. Hypogonadism did not change the rate of bone accrual in WT or KO females. However, eugonadal KO males had a significantly larger increase in tibial and femoral bone acquisition than WT mice. Male mice castrated at 8 weeks of age showed the reverse: KO mice had reduced rates of tibial and femoral BMD acquisition compared with WT mice. In vitro, ET-1 increased osteoblast proliferation, survival, and differentiation. Dihydrotestosterone also increased osteoblast differentiation using a mechanism distinct from the actions of ET-1. These results demonstrate that endothelin signaling in osteoblasts is an important regulator of postnatal trabecular bone remodeling and a modulator of androgen effects on bone.

Role of hypoxia-inducible factor-1alpha in angiogenic-osteogenic coupling

Angiogenesis and osteogenesis are tightly coupled during bone development and regeneration. The vasculature supplies oxygen to developing and regenerating bone and also delivers critical signals to the stroma that stimulate mesenchymal cell specification to promote bone formation. Recent studies suggest that the hypoxia-inducible factors (HIFs) are required for the initiation of the angiogenic-osteogenic cascade. Genetic manipulation of individual components of the HIF/vascular endothelial growth factor (VEGF) pathway in mice has provided clues to how coupling is achieved. In this article, we review the current understanding of the cellular and molecular mechanisms responsible for angiogenic-osteogenic coupling. We also briefly discuss the therapeutic manipulation of HIF and VEGF in skeletal repair. Such discoveries suggest promising approaches for the development of novel therapies to improve bone accretion and repair.

Metastasis: the seed and soil theory gains identity

The metastatic spread of tumor cells to distant sites represents the major cause of cancer-related deaths. Cancer metastasis involves a series of complex interactions between tumor cells and microenvironment that influence its biological effectiveness and facilitate tumor cell arrest to distant organs. More than a century since Paget developed the theory of seed and soil, the enigma of tissue specificity observed in metastatic colonization of tumor cells begins to unfold itself. The advent of new technologies has led to the discovery of novel molecules and pathways that confer metastasis-associated properties to the cancer cells, mediating organ specificity and unique genetic signatures have been developed using microarray studies. Future clinical studies and new antimetastatic compounds aiming to improve survival of patients with metastasis will most probably be based on these signatures. This review summarizes the plethora of old and new molecules that are strongly correlated with organ-specific metastases and which provide now an identity to the theory of seed and soil.

Role of osterix in endothelin-1-induced downregulation of vascular endothelial growth factor in osteoblastic cells

Endothelin-1 (ET-1) is produced by vascular endothelial cells to play an important role during bone development, remodeling and repair. ET-1 promotes osteoblastic cell proliferation and differentiation, but has the unique effect of downregulating vascular endothelial growth factor (VEGF) and may thereby control angiogenesis during bone production. Our objectives were to identify the intracellular mechanisms by which ET-1 controls VEGF expression during osteoblastic proliferation and differentiation. ET-1 induced osteoblastic differentiation in rat SBMC-D8 osteoblastic cells, but downregulated expression of VEGF mRNA isoforms (VEGF120, 164 and 188) as demonstrated by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) and by use of a luciferase reporter construct containing the promoter region of the VEGF gene. Co-transfection with the endothelin receptor A (ETRA) had the same effect. ET-1 and ETRA both upregulated the transcription factor osterix (Osx). RNA silencing of Osx resulted in an upregulation of VEGF. This study supports the novel inhibitory role for ET-1, via Osx, on VEGF synthesis in osteoblastic cells as a possible mechanism in the temporal and spatial feedback of angiogenesis to bone formation and resorption.

Endothelin-1 and ETA/ETB Receptor Protein and mRNA

PURPOSE

Neovascularization of the cornea causes blindness and increases the risk of immune rejections after keratoplasty. The purpose of this study was to investigate involvement of the potent angiogenic growth factor endothelin (ET)-1 and its receptors, ETA and ETB, in corneal neovascularization.

METHODS

ET-1, ETA, and ETB receptor protein expression was evaluated in nonvascularized and vascularized human corneas by immunohistochemistry. Epithelial ET-1 protein expression of both groups was compared using a semiquantitative scoring system. Double immunofluorescence was used to colocalize ETA and ETB receptor with CD31. In situ hybridization and immunoelectron microscopy analyzed ET-1 and its receptors in normal and vascularized corneas.

RESULTS

Nonvascularized corneas displayed ET-1 and ETA/ETB receptor protein and mRNA in epithelial and some corneal endothelial cells. ETA more than ETB receptors were expressed on some keratocytes. In vascularized corneas, ET-1 and ETA/ETB receptor expression was found in the endothelial lining of new blood vessels (as shown by CD31-colocalization). ET-1 protein expression was significantly increased in the epithelium of vascularized corneas (P < 0.001). Immunogold localized ET-1 and its receptors to the nuclear/perinuclear space and to the luminal side of endothelial cells of new blood vessels.

CONCLUSIONS

In corneal neovascularization, ET-1 protein and mRNA expression is upregulated in epithelial cells. Together with ET-1, ETA, and ETB receptor expression on endothelial cells of ingrown new blood vessels, this points to an involvement of ET-1 and its receptors in corneal angiogenesis. As potent ETA and ETB receptors are available, the endothelin system may represent an additional target for corneal antiangiogenic therapy.

Interferon alpha 2a down-regulates VEGF expression through PI3 kinase and MAP kinase signaling pathways

An earlier report demonstrated that interferon alpha (IFN-alpha) inhibited tumor growth and recurrence in an MHCC97 xenograft model in nude mice by suppressing tumor angiogenesis rather than by inhibiting tumor cell proliferation. However, the underlying molecular mechanism was not fully elucidated. In this study, we demonstrated that IFN-alpha 2a could down-regulate VEGF expression both in mRNA and in protein levels, as well as down-regulating HIF-1 alpha mRNA expression in MHCC97 cells in vitro. A cDNA micro array analysis followed by Northern and Western blot analysis revealed that PI3 kinase and MAP kinase signaling pathways might be inhibited by IFN-alpha 2a. Blocking the function of IFN-alpha receptor with a specific peptide could eliminate the inhibitory effects of IFN-alpha 2a on VEGF expression. In addition, wortmannin and PD098059, respective inhibitors of the PI3 kinase and the MAP kinase signaling pathways, when used independently or in combination, could also down-regulate the VEGF synthesis and secretion in a similar pattern of IFN-alpha 2a. These observations may lead to the conclusion that IFN-alpha 2a could suppress VEGF synthesis and secretion by down-regulating HIF-1 alpha expression, via inhibition of the PI3 kinase and/or the MAP kinase signaling pathways.

Identification and characterization of regulator of G protein signaling 4 (RGS4) as a novel inhibitor of tubulogenesis: RGS4 inhibits mitogen-activated protein kinases and vascular endothelial growth factor signaling

Tubulogenesis by epithelial cells regulates kidney, lung, and mammary development, whereas that by endothelial cells regulates vascular development. Although functionally dissimilar, the processes necessary for tubulation by epithelial and endothelial cells are very similar. We performed microarray analysis to further our understanding of tubulogenesis and observed a robust induction of regulator of G protein signaling 4 (RGS4) mRNA expression solely in tubulating cells, thereby implicating RGS4 as a potential regulator of tubulogenesis. Accordingly, RGS4 overexpression delayed and altered lung epithelial cell tubulation by selectively inhibiting G protein-mediated p38 MAPK activation, and, consequently, by reducing epithelial cell proliferation, migration, and expression of vascular endothelial growth factor (VEGF). The tubulogenic defects imparted by RGS4 in epithelial cells, including its reduction in VEGF expression, were rescued by overexpression of constitutively active MKK6, an activator of p38 MAPK. Similarly, RGS4 overexpression abrogated endothelial cell angiogenic sprouting by inhibiting their synthesis of DNA and invasion through synthetic basement membranes. We further show that RGS4 expression antagonized VEGF stimulation of DNA synthesis and extracellular signal-regulated kinase (ERK)1/ERK2 and p38 MAPK activation as well as ERK1/ERK2 activation stimulated by endothelin-1 and angiotensin II. RGS4 had no effect on the phosphorylation of Smad1 and Smad2 by bone morphogenic protein-7 and transforming growth factor-beta, respectively, indicating that RGS4 selectively inhibits G protein and VEGF signaling in endothelial cells. Finally, we found that RGS4 reduced endothelial cell response to VEGF by decreasing VEGF receptor-2 (KDR) expression. We therefore propose RGS4 as a novel antagonist of epithelial and endothelial cell tubulogenesis that selectively antagonizes intracellular signaling by G proteins and VEGF, thereby inhibiting cell proliferation, migration, and invasion, and VEGF and KDR expression.

Endothelin-1 down-regulates the expression of vascular endothelial growth factor-A associated with osteoprogenitor proliferation and differentiation

Endothelin-1 (ET-1) is implicated in the signaling between vascular endothelial cells (VECs) and osteoblasts during bone development, remodeling and repair. Vascular endothelial growth factor (VEGF) also plays an important role in these intercellular interactions. Our objectives were to identify which specific VEGF isoforms were produced during osteoblastic proliferation and differentiation and to determine the effects of ET-1 on VEGF mRNA and protein production by osteoblastic cells. Semiquantitative reverse transcription polymerase chain reaction (RT-PCR) and ELISA were used to evaluate VEGF mRNA isoform expression and protein synthesis at different stages of ET-1-induced osteoblastic differentiation in fetal rat calvaria (FRC) osteoblastic cells. Three VEGF mRNA isoforms were identified corresponding to VEGF(120), VEGF(164) and VEGF(188). Predominant isoforms VEGF(120) and VEGF(164) had a bimodal expression that increased in the early proliferation and late mineralization phases. ET-1 stimulated osteoblastic proliferation and differentiation, but surprisingly, ET-1 down-regulated VEGF mRNA and protein expression and sustained the down-regulation over time in long-term cultures. Time course studies showed that ET-1 inhibited VEGF mRNA expression after incubation for 3 h in 7- and 14-day FRC cell cultures. Similarly, ET-1 inhibited VEGF protein secretion by 5.8- and 2.8-fold in 7- and 14-day FRC cells, respectively. VEGF-A protein secretion was inhibited by ET-1 in a dose-dependent manner with a maximal effect at 10(-7) M. This study supports a novel inhibitory role for ET-1 on VEGF synthesis in osteoblastic cells as a feedback mechanism in the temporal and spatial coupling of angiogenesis to bone formation and resorption.

A causal role for endothelin-1 in the pathogenesis of osteoblastic bone metastases

Osteoblastic bone metastases are common in prostate and breast cancer patients, but mechanisms by which tumor cells stimulate new bone formation are unclear. We identified three breast cancer cell lines that cause osteoblastic metastases in a mouse model and secrete endothelin-1. Tumor-produced endothelin-1 stimulates new bone formation in vitro and osteoblastic metastases in vivo via the endothelin A receptor. Treatment with an orally active endothelin A receptor antagonist dramatically decreased bone metastases and tumor burden in mice inoculated with ZR-75-1 cells. Tumor-produced endothelin-1 may have a major role in the establishment of osteoblastic bone metastases, and endothelin A receptor blockade represents effective treatment.

Involvement of MAP kinases in TGF-beta-stimulated vascular endothelial growth factor synthesis in osteoblasts

Transforming growth factor-beta (TGF-beta) reportedly induces vascular endothelial growth factor (VEGF) synthesis in osteoblast-like MC3T3-E1 cells. We have recently shown that TGF-beta activates p44/p42 mitogen-activated protein (MAP) kinase and p38 MAP kinase in these cells. In the present study, we investigated the exact mechanism of TGF-beta behind the synthesis of VEGF in MC3T3-E1 cells. PD98059 and U-0126, specific inhibitors of MEK, suppressed the VEGF synthesis induced by TGF-beta. U-0126 inhibited the TGF-beta-induced p44/p42 MAP kinase phosphorylation. SB203580 and PD169316, inhibitors of p38 MAP kinase, reduced the TGF-beta-stimulated VEGF synthesis. SB202474, a negative control for p38 MAP kinase inhibitor, did not affect the VEGF synthesis. A combination with PD98059 and SB203580 almost completely suppressed the TGF-beta-induced VEGF synthesis. Retinoic acid, which alone failed to affect VEGF synthesis, markedly enhanced the VEGF synthesis stimulated by TGF-beta. Retinoic acid enhanced the TGF-beta-increased levels of VEGF mRNA. The amplifications by retinoic acid of TGF-beta-increased VEGF synthesis and levels of VEGF mRNA were reduced by PD98059 or SB203580. The combination of PD98059 and SB203580 almost completely suppressed the enhancement by retinoic acid of VEGF synthesis induced by TGF-beta. Taken together, our results strongly suggest that both p44/p42 MAP kinase and p38 MAP kinase take part in TGF-beta-stimulated VEGF synthesis in osteoblasts, and that retinoic acid upregulates the VEGF synthesis.

Stress-activated protein kinase/c-Jun N-terminal kinase (JNK) plays a part in endothelin-1-induced vascular endothelial growth factor synthesis in osteoblasts

We previously reported that endothelin-1 (ET-1) activates both p44/p42 mitogen-activated protein (MAP) kinase and p38 MAP kinase in osteoblast-like MC3T3-E1 cells, and that not p44/p42 MAP kinase but p38 MAP kinase participates in the ET-1-induced vascular endothelial growth factor (VEGF) synthesis. In the present study, we investigated the involvement of stress-activated protein kinase/c-Jun N-terminal kinase (JNK) in ET-1-induced VEGF synthesis in these cells. ET-1 significantly induced the phosphorylation of JNK in a dose-dependent manner in the range between 0.1 and 100 nM. SP600125, an inhibitor of JNK, markedly reduced the ET-1-induced VEGF synthesis. A combination of SP600125 and SB203580 additively reduced the ET-1-stimulated VEGF synthesis. SP600125 suppressed the ET-1-induced phosphorylation of JNK, while having no effect on the phosphorylation of p38 MAP kinase elicited by ET-1. SB203580, an inhibitor of p38 MAP kinase, hardly affected the ET-1-induced phosphorylation of JNK. These results strongly suggest that JNK plays a role in ET-1-induced VEGF synthesis in addition to p38 MAP kinase in osteoblasts.

Maternal dexamethasone increases endothelin-1 sensitivity and endothelin a receptor expression in ovine foetal placental arteries

Despite National Institutes of Health recommendations to administer antenatal steroids as a single course to women threatening preterm delivery, repeated treatments are often given. We investigated effects of repeated dexamethasone (DM) administered to the ewe on small maternal and foetal placental arteries. We hypothesized that DM would increase responsiveness to endothelin-1 (ET-1) and norepinephrine (NE) and that foetal arteries would react differently to ET-1 and NE compared to maternal arteries. Ewes received three treatments beginning at 103, 110, and 117 days of gestation (dGA). Each treatment consisted of four IM injections of 2mg DM or saline at 12-h intervals. At 119 dGA, in vitro functional studies were performed using Mulvany wire myography and endothelin receptor (ETR) expression was quantified using real-time RTPCR and receptor ligand autoradiography. Foetal placental arteries demonstrated greater maximal contractility to ET-1 and lesser maximal contractility to NE compared to maternal arteries. DM increased the maximal contraction elicited by ET-1 and NE in foetal but not maternal placental arteries. DM also increased the abundance of type-A ETR but not type-B ETR mRNA in foetal but not maternal placental arteries. However, within the whole placentome, DM increased the abundance of type-B ETR and decreased type-A ETR mRNA, which was confirmed by similar changes in ETR binding specifically within the labyrinth region. In summary, repeated DM treatment results in agonist and vascular bed specific responses within the placenta.

Emerging role of endothelin-1 in tumor angiogenesis

Tumor vessels express distinct molecular markers that are functionally relevant in the angiogenic process. Although tyrosine kinase receptor agonists are the major mediators of angiogenesis, several G-protein-coupled receptor agonists have also been shown to have a role. Among these, endothelin-1 (ET-1), by acting directly on endothelial cells via the ET(B) receptor, modulates different stages of neovascularization, including proliferation, migration, invasion, protease production and morphogenesis, and also stimulates neovascularization in vivo. ET-1 can also modulate tumor angiogenesis indirectly through the induction of vascular endothelial growth factor (VEGF). Engagement of the ET(A) receptor by ET-1 induces VEGF production by increasing levels of hypoxia-inducible factor 1 alpha. Moreover, tumor cells themselves, predominantly expressing the ET(A) receptor, might form vessel-like channels within the tumors. The role of ET-1 and its signaling network in tumor angiogenesis suggests that new therapeutic strategies using specific ET(A)-receptor antagonists could improve antitumor treatment by inhibiting both neovascularization and tumor cell growth.

Oxidative stress and stress-activated signaling pathways: a unifying hypothesis of type 2 diabetes

In both type 1 and type 2 diabetes, the late diabetic complications in nerve, vascular endothelium, and kidney arise from chronic elevations of glucose and possibly other metabolites including free fatty acids (FFA). Recent evidence suggests that common stress-activated signaling pathways such as nuclear factor-kappaB, p38 MAPK, and NH2-terminal Jun kinases/stress-activated protein kinases underlie the development of these late diabetic complications. In addition, in type 2 diabetes, there is evidence that the activation of these same stress pathways by glucose and possibly FFA leads to both insulin resistance and impaired insulin secretion. Thus, we propose a unifying hypothesis whereby hyperglycemia and FFA-induced activation of the nuclear factor-kappaB, p38 MAPK, and NH2-terminal Jun kinases/stress-activated protein kinases stress pathways, along with the activation of the advanced glycosylation end-products/receptor for advanced glycosylation end-products, protein kinase C, and sorbitol stress pathways, plays a key role in causing late complications in type 1 and type 2 diabetes, along with insulin resistance and impaired insulin secretion in type 2 diabetes. Studies with antioxidants such as vitamin E, alpha-lipoic acid, and N-acetylcysteine suggest that new strategies may become available to treat these conditions.

Multiple signaling pathways involved in activation of matrix metalloproteinase-9 (MMP-9) by heregulin-beta1 in human breast cancer cells

Matrix metalloproteinase-9 (MMP-9) plays important roles in tumor invasion and angiogenesis. Secretion of MMP-9 has been reported in various cancer types including lung cancer, colon cancer, and breast cancer. In our investigation of MMP-9 regulation by growth factors, MMP-9 was activated by heregulin-beta1 as shown by zymography in both SKBr3 and MCF-7 breast cancer cell lines. Increase in MMP-9 activity was due to increased MMP-9 protein and mRNA levels, which mainly results from transcriptional upregulation of MMP-9 by heregulin-beta1. Heregulin-beta1 activates multiple signaling pathways in breast cancer cells, including Erk, p38 kinase, PKC, and PI3-K pathways. We examined the pathways involved in heregulin-beta1-mediated MMP-9 activation using chemical inhibitors that specifically inhibit each of these heregulin-beta1-activated pathways. The PKC inhibitor RO318220 and p38 kinase inhibitor SB203580 completely blocked heregulin-beta1-mediated activation of MMP-9. MEK-1 inhibitor PD098059 partially blocked MMP-9 activation, whereas PI3-K inhibitor wortmannin had no effect on heregulin-beta1-mediated MMP-9 activation. Therefore, at least three signaling pathways are involved in the activation of MMP-9 by heregulin-beta1. Since MMP-9 is tightly associated with invasion/metastasis and angiogenesis, our studies suggest that blocking heregulin-beta1-mediated activation of MMP-9 by inhibiting the related signaling pathways may provide new strategies for inhibition of cancer metastasis and angiogenesis.

Identification of novel hypoxia dependent and independent target genes of the von Hippel-Lindau (VHL) tumour suppressor by mRNA differential expression profiling

The von Hippel-Lindau tumour suppressor gene (VHL) targets hypoxia inducible factor (HIF)-alpha subunits for ubiquitin dependent proteolysis. To better understand the role of this and other putative pathways of gene regulation in VHL function we subjected mRNA from VHL defective renal carcinoma cells and transfectants re-expressing a wild type VHL allele to differential expression profiling, and analysed VHL target genes for oxygen regulated expression. Among a group of newly identified VHL target genes the majority but not all were regulated by oxygen, indicating that whilst dysregulation of the HIF system makes a dominant contribution to alterations in transcription, VHL has other influences on patterns of gene expression. Genes newly defined as targets of the VHL/hypoxia pathway (conditionally downregulated by VHL in normoxic cells) include aminopeptidase A, collagen type V, alpha 1, cyclin G2, DEC1/Stra13, endothelin 1, low density lipoprotein receptor-related protein 1, MIC2/CD99, and transglutaminase 2. These genes have a variety of functions relevant to tumour biology. However, not all are connected with the promotion of tumour growth, some being pro-apoptotic or growth inhibitory. We postulate that co-ordinate regulation as part of the HIF pathway may explain this paradox, and that evolution of anti-apoptotic pathways may be required for tumour growth under VHL-dysregulation. Our results indicate that it will be necessary to consider the effects of abnormal activity in integral regulatory pathways, as well as the effects of individual genes to understand the role of abnormal patterns of gene expression in cancer.