Vascular endothelial cell growth factor activates CRE-binding protein by signaling through the KDR receptor tyrosine kinase.

Vascular endothelial cell growth factor (VEGF) plays a crucial role in the development of the cardiovascular system and in promoting angiogenesis associated with physiological and pathological processes. Although a great deal is known of the cytoplasmic signaling pathways activated by VEGF, much less is known of the mechanisms through which VEGF communicates with the nucleus and alters the activity of transcription factors. Binding of VEGF to the KDR/Flk1 receptor tyrosine kinase induces phosphorylation of the CRE-binding protein (CREB) transcription factor on serine 133 and increases CREB DNA binding and transactivation. p38 MAPK/MSK-1 and protein kinase C/p90RSK pathways mediate CREB phosphorylation. Confocal microscopy shows that VEGF-induced phosphorylation of nuclear CREB is blocked by pharmacological inhibition of protein kinase C and p38 mitogen-activated protein kinase signaling. Thus, KDR/Flk1 uses multiple pathways to transmit signals into the nucleus where CREB becomes activated. These results suggest that CREB may play a role in alterations of gene expression important to angiogenesis.

VRAP is an adaptor protein that binds KDR, a receptor for vascular endothelial cell growth factor.

A protein that binds the intracellular domain of KDR (KDR-IC), a receptor for vascular endothelial cell growth factor (VEGF), was identified by two-hybrid screening. Two-hybrid mapping showed that the VEGF receptor-associated protein (VRAP) interacted with tyrosine 951 in the kinase insert domain of KDR. Northern blot analysis identified multiple VRAP transcripts in peripheral leukocytes, spleen, thymus, heart, lung, and human umbilical vein endothelial cells (HUVEC). The predominant VRAP mRNA encodes a 389-amino acid protein that contains an SH2 domain and a C-terminal proline-rich motif. In HUVEC, VEGF promotes association of VRAP with KDR. Phospholipase C gamma and phosphatidylinositol 3-kinase, effector proteins that are downstream of KDR and important to VEGF-induced endothelial cell survival and proliferative responses, associate constitutively with VRAP. These observations identify VRAP as an adaptor that recruits cytoplasmic signaling proteins to KDR, which plays an important role in normal and pathological angiogenesis.

Utilization of distinct signaling pathways by receptors for vascular endothelial cell growth factor and other mitogens in the induction of endothelial cell proliferation.

This study was initiated to identify signaling proteins used by the receptors for vascular endothelial cell growth factor KDR/Flk1, and Flt1. Two-hybrid cloning and immunoprecipitation from human umbilical vein endothelial cells (HUVEC) showed that KDR binds to and promotes the tyrosine phosphorylation of phospholipase Cgamma (PLCgamma). Neither placental growth factor, which activates Flt1, epidermal growth factor (EGF), or fibroblast growth factor (FGF) induced tyrosine phosphorylation of PLCgamma, indicating that KDR is uniquely important to PLCgamma activation in HUVEC. By signaling through KDR, VEGF promoted the tyrosine phosphorylation of focal adhesion kinase, induced activation of Akt, protein kinase Cepsilon (PKCepsilon), mitogen-activated protein kinase (MAPK), and promoted thymidine incorporation into DNA. VEGF activates PLCgamma, PKCepsilon, and phosphatidylinositol 3-kinase independently of one another. MEK, PLCgamma, and to a lesser extent PKC, are in the pathway through which KDR activates MAPK. PLCgamma or PKC inhibitors did not affect FGF- or EGF-mediated MAPK activation. MAPK/ERK kinase inhibition diminished VEGF-, FGF-, and EGF-promoted thymidine incorporation into DNA. However, blockade of PKC diminished thymidine incorporation into DNA induced by VEGF but not FGF or EGF. Signaling through KDR/Flk1 activates signaling pathways not utilized by other mitogens to induce proliferation of HUVEC.

Transesophageal echocardiography in the diagnosis of diseases of the thoracic aorta: part II-atherosclerotic and traumatic diseases of the aorta.

Transesophageal echocardiography (TEE) has provided an accurate new window for the evaluation of diseases of the thoracic aorta. Experience with TEE has led to an increased recognition of atherosclerosis of the thoracic aorta as a source of cerebral and systemic embolism. Certain features of aortic plaque morphology detected by TEE may prove to have prognostic and therapeutic significance. The intraoperative assessment of thoracic aortic atherosclerosis by TEE may guide modifications in surgical techniques and aortic manipulations that reduce the incidence of perioperative neurologic complications. TEE has also become a valuable tool for the diagnostic evaluation of patients with blunt chest trauma. The precise role of TEE in the management of these disorders is currently under investigation.

Tumor necrosis factor employs a protein-tyrosine phosphatase to inhibit activation of KDR and vascular endothelial cell growth factor-induced endothelial cell proliferation.

Vascular endothelial cell growth factor (VEGF) binds to and promotes the activation of one of its receptors, KDR. Once activated, KDR induces the tyrosine phosphorylation of cytoplasmic signaling proteins that are important to endothelial cell proliferation. In human umbilical vein endothelial cells (HUVECs), tumor necrosis factor (TNF) inhibits the phosphorylation and activation of KDR. The ability of TNF to diminish VEGF-stimulated KDR activity was impaired by sodium orthovanadate, suggesting that the inhibitory activity of TNF was mediated by a protein-tyrosine phosphatase. KDR-initiated responses specifically associated with endothelial cell proliferation, mitogen-activated protein kinase activation and DNA synthesis, were also inhibited by TNF, and this was reversed by sodium orthovanadate. Stimulation of HUVECs with TNF induced association of the SHP-1 protein-tyrosine phosphatase with KDR, identifying this phosphatase as a candidate negative regulator of VEGF signal transduction. Heterologous receptor inactivation mediated by a protein-tyrosine phosphatase provides insight into how TNF may inhibit endothelial cell proliferative responses and modulate angiogenesis in pathological settings.

Clinical usefulness and cost of echocardiography in patients admitted to a coronary care unit.

The usefulness and cost of echocardiography was evaluated in 133 consecutive patients admitted to the Coronary Care Unit. A useful echocardiogram was one that provided new information, which influenced diagnosis, prognosis, or treatment. The cost of a useful echocardiogram was defined as the unit cost ($476 the Medicare global fee) x units (i.e., total echocardiograms / useful echocardiograms). Admission diagnoses were unstable angina (34%), arrhythmia (14%), congestive heart failure (8%), postprocedure monitoring (7%), acute myocardial infarction (6%), and miscellaneous (20%). The echocardiogram provided new information in 29% of patients. Patients without a recent echocardiogram (within 3 months) were twice as likely to have a useful echocardiogram (33 of 99, 33%) as those with a recent echocardiogram (5 of 34, 15%, p <0.05). A cardiologist predicted the overall usefulness of echocardiography with a positive predictive accuracy of 52% and a negative predictive accuracy of 94% (p < 0.0001). The overall cost of a useful echocardiogram of 3.5 units or $1,666 per useful study was decreased to $904 (1.9 units) if only studies predicted to be useful were considered. The usefulness of echocardiography varied significantly (p <0.02) within the admitting diagnostic categories. The usefulness of an echocardiogram was underestimated in patients with congestive heart failure, where it was found to be most useful (64%; $762 or 1.6 units). Thus, usefulness relates to the admission diagnosis, the availability of a recent echocardiogram, and to clinical judgment.