ABSTRACT
Vascular endothelial growth factor (VEGF)-induced endothelial cell migration is a key step in the angiogenic response and is mediated, in part, by an accelerated rate of focal adhesion complex assembly and disassembly. We investigated the signaling pathway by which VEGF regulates focal adhesion complex assembly by examining the signaling proteins involved. VEGF stimulated the tyrosine phosphorylation of the SH2 domain-containing signaling proteins NCK and CRK in human umbilical vein endothelial cells. The signaling pathways that couple the kinase insert domain-containing receptor to NCK and CRK is most likely mediated by another cellular protein, as NCK and CRK were tyrosine-phosphorylated in response to VEGF in cells expressing receptors mutated at each of several candidate SH2 domain-interacting cytosolic tyrosines. In the absence of VEGF treatment, NCK (but not CRK) associated with the p21 GTPase-activated kinase PAK. PAK catalytic activity was augmented after VEGF treatment; an association of PAK with 60- and 90-kDa tyrosine-phosphorylated proteins accompanied this. VEGF stimulated the recruitment of PAK to focal adhesions, and FAK immunoprecipitated with both NCK and PAK in VEGF-treated (but not untreated) human umbilical vein endothelial cells. Inhibition of NCK protein expression using antisense oligonucleotides led to the inhibition of both VEGF-induced focal adhesion assembly and VEGF-induced cell migration, demonstrating a necessary role of NCK in these cellular responses.
Subject(s)
Endothelial Growth Factors/physiology , Lymphokines/physiology , Oncogene Proteins/physiology , Protein Serine-Threonine Kinases/physiology , Protein-Tyrosine Kinases/metabolism , Signal Transduction/physiology , Adaptor Proteins, Signal Transducing , Base Sequence , Cells, Cultured , DNA Primers , Endothelium, Vascular/cytology , Endothelium, Vascular/metabolism , Enzyme Activation , Focal Adhesion Kinase 1 , Focal Adhesion Protein-Tyrosine Kinases , Humans , Mutagenesis, Site-Directed , Receptor Protein-Tyrosine Kinases/genetics , Receptor Protein-Tyrosine Kinases/metabolism , Receptors, Growth Factor/genetics , Receptors, Growth Factor/metabolism , Receptors, Vascular Endothelial Growth Factor , Vascular Endothelial Growth Factor A , Vascular Endothelial Growth Factors , p21-Activated KinasesABSTRACT
Corpus luteum formation is characterized by a period of extensive vascularization, as capillaries in the thecal layer of the collapsed follicle following ovulation invade the previously avascular granulosa layer. In order to study these processes in vitro we have developed an endothelial cell preparation from the specific microvasculature of the ovarian follicle. Follicular aspirates, obtained at oocyte collection for in-vitro fertilization (IVF), were filtered to obtain fragments of follicle wall. These were set in Matrigel and then cultured allowing the growth of capillary-like structures through the matrix. Upon emergence from the Matrigel the growing cells formed monolayers with the characteristic cobble-stone morphology of endothelial cells. Immunocytochemistry demonstrated the presence of a range of endothelial-specific markers including von Willebrand factor (vWF), Ulex europeus agglutinin (UEA)-1, CD31 and E-selectin, as well as VCAM-1, which is normally associated with stimulated endothelial cells. RT-PCR analysis showed the expression of two receptors for vascular endothelial growth factor (flt-1 and KDR), and the endothelial nitric oxide synthase, adding further evidence of their identity as human ovarian microvascular endothelial cells (HOMEC). Thus, the novel preparative procedure described now allows the generation of HOMEC cultures from readily available material resulting from IVF procedures.
