Heat shock proteins and other components of cellular machinery for protein synthesis are up-regulated in vascular endothelial cell growth factor-activated human endothelial cells

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Abstract
Proteome analysis of human umbilical endothelial cells was performed to identify proteins that are modified during vascular endothelial cell growth factor (VEGF)-induced transition from the quiescent into the proliferating-migrative phenotype. Subtractive analysis of two-dimensional gel patterns of human endothelial cells, before and after stimulation with VEGF165, revealed differences in 85 protein spots. All proteins were identified by peptide sequencing and peptide mass fingerprinting using an electrospray spectrometer. The proteins identified were members of specific families including Ca2+-binding proteins, fatty-acid binding proteins, structural proteins, and chaperones. Remarkably, there was a massive activation of cellular machinery for both protein synthesis and protein degradation. Thus, among up-regulated proteins there were members of all groups of heat shock proteins (HSPs; HSP 27, HSP 60, HSP 70p5, HSP 70p8, HSP 90, and HSP 96) and some other proteins showing either chaperone activity or which participate in assembly of multimolecular structures (TCP-1, desmoplakins, junction plakoglobin, GRP 94, thioredoxin related protein, and peptidylprolyl isomerase). The increased expression of HSPs was confirmed at the mRNA level at different stages of treatment with VEGF. Similarly, components of the proteolytic machinery for the degradation of misfolded proteins (ER-60, cathepsin D, proteasome subunits, and protease inhibitor 6) were also up-regulated. On the other hand, changes in the expression of structural proteins (T-plastin, vimentin, α tubulin, actin, and myosin) could account, at least in part, for the different morphologies displayed by migrating endothelial cells. In summary, our data show that VEGF levels similar to those during physiological stresses induce a number of genes and multiple endogenous pathways seem to be engaged in restoring cellular homeostasis. To ensure cell survival, the molecular chaperones (the heat shock family of stress proteins) are highly up-regulated providing protein-folding machinery to repair or degrade misfolded proteins.

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