Moreover, c-ABL, common target of these inhibitors, was highly phosphorylated in HUVEC-TIE2-L914F and VM patient-derived ECs with activating TIE2 mutations.
A <i>TIE2</i> mutation causing arginine-to-tryptophan substitution at residue 849 (<i>TIE2-R849W</i>) is commonly identified in heredofamilial venous malformation.
Recent studies have identified genetic defects that result in the constantly active endothelial cell receptor tyrosine kinase TIE2/phosphoinositide 3-kinase PI3K signalling pathway as a frequent cause for VMs.
Extracellularly, whereas angiopoietins (ANGs) are ligands of TIE2, the chaotic balance between ANG1 and ANG2 in VM is related to their effects on switching between the cell-cell/cell-extracellular matrix contact conditions and vascular quiescence/angiogenesis state, resulting in corrupted contacts.
A role for an activating TIE2 mutation in the development of the dilated luminal vessels in VM, and its proposed involvement of embryonic stem cells (ESCs), led us to investigate the expression of ESC markers in subcutaneous VM (SCVM) and intramuscular VM (IMVM).
We tested both rapamycin and a TIE2 tyrosine kinase inhibitor (TIE2-TKI) for their effects on murine VM expansion and for their ability to inhibit mutant TIE2 signaling.
Here, we report that somatic mutations in PIK3CA, the gene encoding the catalytic p110α subunit of PI3K, cause 54% (27 out of 50) of VMs with no detected TEK mutation.
Here, we report the analysis of a comprehensive collection of 22 TIE2 mutations identified in patients with VM, either as single amino acid substitutions or as double-mutations on the same allele.
Recently, somatic mutations in exon 17 of the endothelial cell tyrosine kinase receptor Tie-2 (encoded by TEK) were identified in 49.1% of patients with common sporadic venous malformation, a subtype of vascular anomalies.
These data show that a sporadic disease may be explained by somatic changes in a gene causing rare, inherited forms and pinpoint TIE2 pathways as potential therapeutic targets for venous malformations.
Homozygosity mapping excluded the following loci and/or genes: multiple cutaneous venous malformation (VMCM1; gene, TIE2) on chromosome 9p21; venous malformation with glomus cells (VMGLOM) on chromosome 1p22-p21; hereditary hemorrhagic telangiectasia type 1 (HHT1; gene, endoglin) and type 2 (HHT2; gene, activin) on chromosomes 9q34.1 and 12q11-q14, respectively; and cerebral cavernous malformation type 1 (CCM1; gene, KRIT1), type 2 (CCM2), and type 3 (CCM3) on chromosomes 7q11.2-q21, 7p15-p13, and 3q35.2-q27, respectively.
Using linkage analysis, we have established in earlier reports that some families with inherited VMs show linkage to chromosome 9p21; the mutation causes ligand-independent activation of an endothelial cell-specific receptor tyrosine kinase, TIE-2.
We conclude that an activating mutation in TIE2 causes inherited VMs in the two families and that the TIE2 signaling pathway is critical for endothelial cell-smooth muscle cell communication in venous morphogenesis.