The formin FMNL3 is a cytoskeletal regulator of angiogenesis.

The process of angiogenesis requires endothelial cells (ECs) to undergo profound changes in shape and polarity. Although this must involve remodelling of the EC cytoskeleton, little is known about this process or the proteins that control it. We used a co-culture assay of angiogenesis to examine the cytoskeleton of ECs actively undergoing angiogenic morphogenesis. We found that elongation of ECs during angiogenesis is accompanied by stabilisation of microtubules and their alignment into parallel arrays directed at the growing tip. In other systems, similar microtubule alignments are mediated by the formin family of cytoskeletal regulators. We screened a library of human formins and indentified formin-like 3 (FMNL3; also known as FRL2) as a crucial regulator of EC elongation during angiogenesis. We showed that activated FMNL3 triggers microtubule alignment and that FMNL3 is required for this alignment during angiogenic morphogenesis. FMNL3 was highly expressed in the ECs of zebrafish during development and embryos that were depleted for FMNL3 showed profound defects in developmental angiogenesis that were rescued by expression of the human gene. We conclude that FMNL3 is a new regulator of endothelial microtubules during angiogenesis and is required for the conversion of quiescent ECs into their elongated angiogenic forms.

Farnesyltransferase inhibitors target multiple endothelial cell functions in angiogenesis.

Farnesyltransferase inhibitors (FTIs) are novel anticancer drugs that inhibit the secretion of pro-angiogenic factors by Ras-transformed cancer cells. FTIs also inhibit angiogenesis in a rat corneal model, suggesting that FTIs have anti-angiogenic properties that extend beyond targeting cancer cells. Our hypothesis was that FTIs may directly target endothelial cell functions in angiogenesis. We examined the effects of FTI treatment on a range of assays designed to pick apart the individual functions of endothelial cells during angiogenesis. We found that FTIs inhibit endothelial cell proliferation, causing a failure of mitosis and accumulation of binucleate cells. FTIs also block the directional migration of endothelial cells toward VEGF, the major pro-angiogenic factor in adult tissues. In a co-culture assay of angiogenesis, FTI treatment significantly inhibits tube formation, but has no effect on pre-existing structures. Defects in tube formation could be replicated by specific targeting of endothelial cell farnesyltransferase using RNA interference. Our data show that FTIs directly target endothelial cells in angiogenesis, explaining previous in vivo findings. Importantly, these results suggest that the therapeutic use of FTIs may extend beyond cancer to include the treatment of other diseases involving pathological angiogenesis.