CLT1 targets angiogenic endothelium through CLIC1 and fibronectin

Angiogenesis. 2012 Mar;15(1):115-29. doi: 10.1007/s10456-011-9247-8. Epub 2011 Dec 28.


Angiogenesis is important for tumor growth and metastasis. CLT1 (CGLIIQKNEC), a peptide that binds to tumor interstitial spaces in the presence of fibrin-fibronectin, has structural similarity to the anti-angiogenic β-sheet peptides anastellin and anginex. This similarity is reflected in the ability of CLT1 to form co-aggregates with fibronectin that induce an unfolded protein response and cause autophagic cell death in proliferating endothelial cells. CLT1 cytotoxicity is mediated at least in parts by a novel CLT1 binding protein, Chloride Intracellular Channel 1 (CLIC1), which promotes internalization of CLT1-fibronectin co-aggregates in a mechanism that depends on the LIIQK amino acid sequence of CLT1. LIIQK encompasses amino acid residues relevant for CLT1 binding to CLIC1 and in addition, facilitates the formation of CLT1-fibronectin co-aggregates, which in turn promote translocation of CLIC1 to the endothelial cell surface through ligation of integrin αvβ3. Paralleling the in vitro results, we found that CLT1 co-localizes with CLIC1 and fibronectin in angiogenic blood vessels in vivo, and that CLT1 treatment inhibited angiogenesis and tumor growth. Our findings show that CLT1 is a new anti-angiogenic compound, and its mechanism of action is to form co-aggregates with fibronectin, which bind to angiogenic endothelial cells through integrins, become internalized through CLIC1 and elicit a cytotoxic unfolded protein response. The simple structure and high potency of CLT1 make it a potentially useful compound for anti-angiogenic treatments.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Angiogenesis Inhibitors / chemistry
  • Angiogenesis Inhibitors / pharmacology
  • Angiogenesis Inhibitors / therapeutic use
  • Animals
  • Antineoplastic Agents / chemistry
  • Antineoplastic Agents / pharmacology
  • Antineoplastic Agents / therapeutic use
  • Cell Death / drug effects
  • Cell Line, Tumor
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Cell Proliferation / drug effects
  • Chloride Channels / metabolism*
  • Endocytosis / drug effects
  • Endothelium, Vascular / drug effects*
  • Endothelium, Vascular / metabolism*
  • Fibronectins / chemistry
  • Fibronectins / metabolism*
  • Human Umbilical Vein Endothelial Cells / cytology
  • Human Umbilical Vein Endothelial Cells / drug effects
  • Human Umbilical Vein Endothelial Cells / metabolism
  • Humans
  • Lysosomes / drug effects
  • Lysosomes / metabolism
  • Male
  • Mice
  • Mice, Nude
  • Molecular Sequence Data
  • Neovascularization, Pathologic / drug therapy
  • Neovascularization, Pathologic / pathology
  • Neovascularization, Physiologic / drug effects*
  • Peptides, Cyclic / chemistry
  • Peptides, Cyclic / pharmacology*
  • Peptides, Cyclic / therapeutic use
  • Protein Structure, Quaternary


  • Angiogenesis Inhibitors
  • Antineoplastic Agents
  • CLIC1 protein, human
  • Chloride Channels
  • Fibronectins
  • Peptides, Cyclic
  • cyclo(cysteinyl-glycyl-leucyl-isoleucyl-isoleucyl-glutaminyl-lysyl-asparaginyl-glutamyl-cysteinyl)