Resistance exercise reduces muscular substrates in women.

The purpose of this investigation was to examine the influence of an acute bout of resistance exercise (RE) on intramuscular triglyceride (IMTG) and muscle glycogen concentrations and intracellular signaling in women with high body fat content. Six overweight women with a high percent body fat (age 29+/-3 yr; BMI 28+/-3 kg/m(2), body fat 38+/-4%) performed 6 sets of 10 repetitions of knee extension exercise at 70% 1RM. Muscle biopsies were obtained from the vastus lateralis before, 1 min after (POST1), and 2 h after (POST2) exercise. Acute RE reduced (p<0.05) IMTG content approximately 40% at POST1 and POST2 (75+/-5; 45+/-6; 50+/-10 mmol/kg/dry wt). Muscle glycogen was also reduced (p<0.05) approximately 25% at POST1 and remained lower at POST2 (317+/-14; 241+/-30; 235+/-26 mmol/kg/dry wt). ERK1/2, SAPK/JNK, and p38 phosphorylation were increased (p<0.05) approximately 2-3-fold at POST1 and ERK1/2 remained elevated and POST2 whereas SAPK/JNK and p38 returned to basal levels. AMPKalpha phosphorylation was unchanged in response to RE. These results show that both IMTG and muscle glycogen stores serve as an important energy source during RE in overweight women and the MAP kinase signaling response to RE is not compromised by high levels of body fat.

Identification of a soluble form of the angiopoietin receptor TIE-2 released from endothelial cells and present in human blood.

The transmembrane tyrosine kinase TIE-2, the receptor for the angiopoietins-1 and -2, has been shown to be involved in angiogenic processes. Investigating the regulation of TIE-2 expression on endothelial cells, we found that stimulators such as PMA induce a decrease of TIE-2 protein from the cell surface without affecting TIE-2 mRNA. In conditioned media of PMA stimulated endothelial cells, a soluble form of this receptor comprising parts of the extracellular domain can be detected. Using a sandwich ELISA, we were able to detect and quantify TIE-2 receptors in cell lysates (representing the whole transmembrane receptor) and in cell culture supernatants (representing a soluble form of this receptor, sTIE-2). Several factors influencing the shedding process e.g. basic FGF could be identified. Finally, the soluble form of TIE-2 could also be detected in human biological fluids such as sera and plasma from healthy controls.

Active interaction of human A375 melanoma cells with the lymphatics in vivo.

We have used the avian chorioallantoic membrane (CAM) to study the interaction of tumor cells with the lymphatics in vivo. The vascular endothelial growth factor-C (VEGF-C) has been shown to be lymphangiogenic. We have therefore grown VEGF-C-expressing human A375 melanoma cells on the CAM. These tumors induced numerous lymphatics at the invasive front, and compressed or destroyed VEGF receptor (R)-3-positive lymphatics were observed within the solid tumors. The lymphatics in the CAM and in the A375 melanomas could also be demonstrated with an antibody against Prox 1, a highly specific marker of lymphatic endothelial cells. Proliferation studies revealed a BrdU labeling index of 11.6% of the lymphatic endothelial cells in the tumors and at their margins. A great number of melanoma cells invaded the lymphatics. Such interactions were not observed with VEGF-C-negative Malme 3 M melanoma cells. Lymphangiogenesis was inhibited to some extent when A375 melanoma cells were transfected with cDNA encoding soluble VEGFR-3 (sflt4), and the BrdU labeling index of the lymphatics in these tumors was 3.9%. Invasion of lymphatics and growth of blood vascular capillaries were not inhibited by the transfection. Therefore, tumor-induced lymphangiogenesis seems to be dependent to some extent on VEGF-C/flt4 interactions, but invasion of lymphatics seems to be a distinct mechanism.

Two independent mechanisms essential for tumor angiogenesis: inhibition of human melanoma xenograft growth by interfering with either the vascular endothelial growth factor receptor pathway or the Tie-2 pathway.

Protein ligands and receptor tyrosine kinases that specifically regulate endothelial cell function are mainly involved in physiological as well as in disease-related angiogenesis. These ligand/receptor systems include the vascular endothelial growth factor (VEGF) and the angiopoietin (Ang) families, and their receptors, the VEGF receptor family and the tyrosine kinase with immunoglobulin-like and epidermal growth factor homology domains (Tie) family. In the present study, the contribution of these endothelium-specific ligand/receptor systems to tumor angiogenesis was evaluated. A375v human melanoma cells, which express at least the angiogenic growth factors VEGF, VEGF-C, and Ang-1, were stably transfected to overexpress the extracellular ligand-binding domains of the endothelium-specific receptor tyrosine kinases fms-like tyrosine kinase-1 (Flt-1), Flt-4, Tie-1, and Tie-2, respectively. In vitro proliferation and colony formation assays confirmed that expression of the extracellular receptor domains inhibited neither tumor cell mitogenesis nor the ability to produce anchorage-independent growth. Nude mouse xenografts revealed that interference with either the VEGF receptor pathway or the Tie-2 pathway resulted in a significant inhibition of tumor growth and tumor angiogenesis. In contrast, interference with the Flt-4 pathway or the Tie-1 pathway was without significant effect. Our results show that both the VEGF receptor pathway and the Tie-2 pathway are essential for A375v melanoma xenograft growth. The inhibition of the VEGF receptor pathway cannot be compensated by the Tie-2 pathway, nor vice versa. These findings suggest that the VEGF receptor pathway and the Tie-2 pathway have to be considered as two independent mediators essential for the process of in vivo angiogenesis.

Characterization of a new potent, in vivo neutralizing monoclonal antibody to human vascular endothelial growth factor.

Vascular endothelial growth factor (VEGF) is an important mediator of tumor-induced angiogenesis and represents a potential target for anticancer therapy. Therefore, we prepared a panel of monoclonal antibodies (mAb) against both the VEGF121 and VEGF165 isoforms. Three of them completely neutralized the mitogenic stimulation by VEGF of human umbilical vein endothelial cells at mAb concentrations below 0.1 microg/ml. The most potent one, with a dissociation constant (Kd) of 8 pM, inhibited, in a dose-dependent manner, VEGF-induced angiogenesis in a growth factor implant model in mice. A complete inhibition of the angiogenic response was obtained by daily intraperitoneal injections of 10 microg mAb/mouse. Angiogenesis induced by basic fibroblast growth factor was not inhibited by the mAb. Epitope mapping of the mAb, performed by competitive enzyme-linked immunosorbent assay and Western blot analysis, showed that it did not bind to the reduced and denatured monomer of VEGF. Substitutions of three residues (Q87R, G88K, Q89K), located on the major surface loop beta5 to beta6 of VEGF, resulted in the complete loss of binding (more than 400-fold reduction). The results suggest that the mAb binds primarily to a conformation-dependent epitope on the VEGF dimeric form, encompassing one of the loop regions involved in KDR receptor binding. The mAb with its strong neutralizing properties represents a useful agent for effective blocking of VEGF-mediated tumor neovascularization.

Vascular endothelial growth factor in the sera and effusions of patients with malignant and nonmalignant disease.

BACKGROUND: Clinical data clearly indicate a correlation between tumor neovascularization, aggressiveness of tumor growth, and metastatic spread. One of the key factors capable of stimulating tumor angiogenesis is vascular endothelial growth factor (VEGF). Using an immunoassay for VEGF, we assessed the levels of soluble VEGF in the sera and effusions of patients with malignant and nonmalignant disease as well as in the sera of healthy controls. METHODS: Using a sandwich enzyme-linked immunoadsorbent assay, the concentration of VEGF was measured in serum specimens (n=445) and effusions (n=56) collected from a total of 212 patients with various types of cancer, 88 patients with nonmalignant disease, and 145 healthy individuals. RESULTS: Low and rather stable levels of VEGF were detected in the serum of healthy individuals (median, 294 pg/mL; range, 30-1752 pg/mL; 95th percentile, 883 pg/mL). Compared with healthy individuals, serum levels in patients with acute infections were elevated (P=0.03), whereas patients with chronic cirrhosis had lower serum VEGF levels. Among patients with various types of neoplasia, VEGF serum levels in patients with ovarian or gastrointestinal carcinoma were significantly higher than in healthy individuals. Moreover, VEGF concentrations in sera from patients with metastatic disease were higher than in sera from patients with localized tumors. Maximum serum concentrations of VEGF (median, 1022 pg/mL; range, 349-7821 pg/mL) were found in patients with metastatic ovarian carcinoma. Median VEGF levels (and ranges) in malignant effusions were up to 10-fold higher than in matched serum samples: 5528 pg/mL (468-49269 pg/mL) in ovarian carcinoma, 885 pg/mL (77-14,337 pg/mL) in breast carcinoma, and 813 pg/mL (372-18,331 pg/mL) in gastrointestinal carcinoma. In contrast, ascitic fluid from patients with cirrhosis contained only 303 pg/mL (median, range 116-676 pg/mL) of VEGF, corresponding to the low serum levels in this patient group. CONCLUSIONS: Depending on the tumor type, elevated levels of VEGF are detectable in the serum of only 0-20% of patients with localized cancer but in 11-65% of patients with metastatic cancer. Of cytology-proven malignant ascites or peritoneal exudates from various malignancies, 46-96% show VEGF levels above the upper limit (95th percentile, 676 pg/mL) of nonmalignant ascites. Maximum VEGF concentrations in malignant effusions indicate abundant local release of VEGF within the pleural or peritoneal cavity. These results suggest that VEGF might play an important role in tumor progression and the formation of malignant effusions. Further studies are warranted to determine the clinical value of soluble VEGF as a tumor marker, a prognostic factor, and a surrogate indicator of tumor angiogenesis.

Inhibition of Th1 development mediated by GATA-3 through an IL-4-independent mechanism.

Recently, the transcription factor GATA-3 was shown to be selectively expressed in Th2 but not Th1 cells and to augment Th2-specific cytokines. Here, we show that loss of GATA-3 expression by developing Th1 cells requires IL-12 signaling through Stat4 and does not simply result from an absence of IL-4. Moreover, we demonstrate a novel role for GATA-3 in directly repressing Th1 development distinct from its positive actions on Th2-specific cytokines. GATA-3 inhibits Th1 cytokines by a cell-intrinsic mechanism that is not dependent on IL-4 and that may involve repression of IL-12 signaling. Thus, GATA-3 expression and IL-12 signaling are mutually antagonistic, which facilitates rapid dominance of one pathway during early Th development, producing a stable divergence in cytokine profiles.

Vascular endothelial growth factor up-regulates its receptor fms-like tyrosine kinase 1 (FLT-1) and a soluble variant of FLT-1 in human vascular endothelial cells.

The growth of solid tumors and the formation of metastases are dependent on neoangiogenesis. One of the most important factors in inducing the formation of new blood vessels is the vascular endothelial growth factor (VEGF), which acts specifically on endothelial cells. VEGF is expressed and secreted by almost all solid tumors. The molecular mechanisms leading to enhanced production of this angiogenic mitogen are manyfold and have been elucidated to some degree. Two VEGF receptors, fms-like tyrosine kinase 1 (FLT-1) and KDR, have been identified almost specifically on human endothelial cells. They are expressed preferentially in the proliferating endothelium of vessels lining and/or penetrating solid tumors, whereas they are almost undetectable by convenient methods in vessels of healthy tissue. However, the underlying mechanisms are not understood. We could show that media conditioned by various cancer cell lines grown under hypoxic conditions were able to up-regulate expression of FLT-1 mRNA and protein but not of KDR mRNA. Furthermore, up-regulation of a shorter mRNA species was observed that most probably codes for the soluble variant of FLT-1. These effects were completely inhibited by VEGF-neutralizing extracellular VEGF receptor domains. The effect could be mimicked by adding recombinant VEGF instead of conditioned cancer cell medium to the endothelial cell cultures. Both mutant VEGF, which activates only KDR, and placenta growth factor, which activates only FLT-1, were able to enhance FLT-1 expression. VEGF-stimulated FLT-1 mRNA expression was inhibited by actinomycin D. These data suggest that VEGF itself is the main factor secreted by tumor cells that is able to enhance the expression of its receptor FLT-1 and of a soluble variant of FLT-1 in endothelial cells.

Schwannoma cells induce a tumor-cell-specific cytotoxic-T-cell response upon transplantation into syngeneic rats but escape elimination through the secretion of immunosuppressive factors.

Tumor cells often express antigens that can be recognized by the immune system. Despite induction of an immune response, the tumor cells escape their elimination. We have studied the mechanisms and factors which mediate these events in a syngeneic tumor model. NV2Cd rat schwannoma cells were transplanted into BDIX rats. After injection of 10(7) to 2 x 10(7) cells, tumors grew very slowly for 10 to 12 days. After that time, rapid growth was observed. The tumors consisted of compact areas of spindle-shaped cells with small cysts, many blood vessels and central necrotic areas. During tumor growth, the number of spleen cells and T lymphocytes increased, and cytotoxic T cells with specificity for the NV2Cd tumor cells were detected. The strong specific cellular immune response did not prevent the increase in tumor volume. We studied the biological activity of the fluid present in the cysts of the tumor. At a concentration of 1 ng to 10 microg protein per ml, the cyst fluid inhibited the proliferation of splenic T lymphocytes and B lymphocytes and of lymphoma cells, but enhanced the proliferation of NV2Cd tumor cells. The cyst fluids contain the immunosuppressive transforming growth factors (TGF)-beta1, -beta2 and -beta3, also the vascular endothelial growth factor (VEGF) and epidermal growth factor (EGF). Antibodies directed against TGF-beta relieved the suppression of T-cell growth by cyst fluid, but did not influence the proliferation of NV2Cd cells. The growth-modulating factors present in the tumor cyst fluid were also detected in conditioned medium from NV2Cd cells cultured in vitro. Our data suggest that tumors can escape the cellular immune response by the production of factors that inhibit lymphocytes. They also enhance their own growth environment by secreted factors.

Reversion of deregulated expression of vascular endothelial growth factor in human renal carcinoma cells by von Hippel-Lindau tumor suppressor protein.

Mutations or loss of both alleles of the von Hippel-Lindau (VHL) tumor suppressor gene has been documented in sporadic renal cell carcinomas and neoplasms that arise in individuals having the VHL syndrome. The well-vascularized phenotype of tumors that form in VHL disease let us consider vascular endothelial growth factor (VEGF) as a mediator of tumor growth in VHL disease. Human renal carcinoma cells that either lacked endogenous wild-type VHL or were transfected with an inactive mutant VHL showed deregulated expression of VEGF on the mRNA and protein level that was reverted by introduction of wild-type VHL. Stimulation of proliferation of endothelial cells by conditioned medium of cells expressing mutant VHL was almost abolished by neutralizing the VEGF. In contrast, expression of basic fibroblast growth factor and of c-myc proto-oncogene was not affected by VHL. Our data suggest VEGF as the key tumor angiogenesis factor in VHL disease.