The enzyme l-isoaspartyl (d-aspartyl) methyltransferase is required for VEGF-dependent endothelial cell migration and tubulogenesis

The protein l -isoaspartyl ( d -aspartyl) methyltransferase (PIMT) methylates proteins carrying altered aspartyl residues in their structure. PIMT is postulated to limit the accumulation of these damaged proteins with abnormal aspartyl residues. However, little is known about the role of PIMT in tumor growth and almost nothing about its involvement in angiogenic processes. We previously reported that PIMT was up-regulated when endothelial cells were detached from extracellular matrix, leading us to postulate that PIMT could play a critical role during angiogenic steps, since the contacts between endothelial cells and the extracellular matrix are intensively regulated during this process. Here, we demonstrated that PIMT down-regulation by siRNA in human umbilical vein endothelial cells (HUVECs) inhibited both cell migration and tube formation in vitro when stimulated by vascular endothelial growth factor (VEGF). Conversely, overexpression of wild-type PIMT promoted HUVEC migration in the presence of VEGF, while this response was prevented in cells transfected with the inactive mutant PIMT(D83V). Similar results were obtained with the two forms of PIMT regarding their capacity to regulate the action of VEGF during the formation of capillary-like structures in vitro. Together, these data highlight the importance of the catalytic activity of PIMT to mediate VEGF effects during endothelial cell migration and tube formation in angiogenesis. Furthermore, these results identify a new function for PIMT as an enzyme involved in pro-angiogenic processes.