טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentRosenbaum-Dekel Yifat
SubjectL-VEGF and its Cleavage Products: Intracellular Localization
and Initial Characterization of Biological
Activity
DepartmentDepartment of Biotechnology and Food Engineering
Supervisor Professor Ben-Zion Levi


Abstract

Vascular Endothelial Growth Factor (VEGF) is a potent angiogenic factor that has a pivotal role in normal as well as pathological angiogenesis. VEGF acts as a specific mitogen for vascular endothelial cells through specific receptors. The significance of VEGF is implicated from the fact that even a loss of one allele leads to embryonic lethality. VEGF is encoded by an highly conserved gene with at list 7 isoforms due to alternative splicing. VEGF has a long 5' Untranslated Region (5'UTR), which mediates alternative translation via internal ribosome entry sites (IRESes) under stress conditions such as hypoxia when normal translational machinery is halted. In addition, the 5'UTR contains a highly conserved Open Reading Frame (ORF) initiated by a CUG codon that is in-frame with VEGF coding region. This alternative translation initiation leads to the expression of a long isoform termed L-VEGF that is extended by an additional 180 amino acids (180aa). The biological function of L-VEGF is still elusive.

This research provided an evidence that L-VEGF is subjected to proteolytic cleavage leading to the detachment of the 180aa extension from the VEGF moiety. The latter is further cleaved at the leader peptide leading to a secreted mature VEGF. Using immunofluorescence staining, we show that upon hypoxia this 180aa extension of L-VEGF translocates to the nuclei of expressing cells.. The nuclear localization of the ORF upon hypoxia suggests it is involved in a regulation process and the fact it occur upon hypoxia when VEGF is crucial suggest it may be involved in the autoregulation of VEGF itself.