Biphasic effect of PTK7 on KDR activity in endothelial cells and angiogenesis

Abstract

Protein tyrosine kinase 7 (PTK7) is a member of the defective receptor protein tyrosine kinase family which lacks catalytic activity. Expression of PTK7 is increased in various cancers but its role in carcinogenesis is not well understood. We previously showed that disruption of PTK7 function suppresses VEGF-induced angiogenic phenotypes in HUVECs and mice. Here, we investigated molecular mechanisms for modulating VEGF-induced physiological effects by PTK7. Treatment with a high concentration of extracellular domain of PTK7 (soluble PTK7; sPTK7) or knockdown of PTK7 inhibited VEGF-induced phosphorylation of kinase insert domain receptor (KDR) but did not inhibit phosphorylation of fms-related tyrosine kinase 1 (FLT-1) in HUVECs. PTK7, more specifically sPTK7, interacted with KDR but not with FLT-1 in HUVECs and HEK293 cells. In vitro binding assay showed that sPTK7 formed oligomers with the extracellular domain of KDR (sKDR) up to an approximately 1:3 molar ratio, and vice versa. sPTK7 at lower molar ratios than sKDR enhanced the binding of VEGF to sKDR. At the same or higher molar ratios, it reduced the binding of VEGF to sKDR. Increasing concentrations of sPTK7 or increasing levels of PTK7 expression first increased and then decreased VEGF-induced KDR phosphorylation, migration, and capillary-like tube formation of HUVECs, as well as in vivo angiogenesis. Taken together, our data demonstrates that PTK7 regulates the activity of KDR biphasically by inducing oligomerization of KDR molecules at lower concentrations and by surrounding KDR molecules at higher concentrations.

Catalytically defective receptor protein tyrosine kinase PTK7 enhances invasive phenotype by inducing MMP-9 through activation of AP-1 and NF-κB in esophageal squamous cell carcinoma cells

“…The mechanism(s) underlying the contradictory roles played by PTK7 in different cancer types is unclear. Recently, we demonstrated that PTK7 displays phenotypes ranging from oncogenic to tumor-suppressive depending on its concentration relative to those of its binding partners, such as kinase insert domain receptor (KDR) [17]. Our finding of a biphasic function of PTK7 explains in part the discrepancy in the expression-level-dependent oncogenic functions of PTK7.…”

“…It was well known that HER3, a catalytically defective RPTK, can heterodimerize with other EGFR family members upon ligand binding such as neuregulin and activates downstream signaling proteins such as Akt and Erk [28]. We have previously demonstrated that PTK7 binds to and activates KDR, one of VEGF receptor [17]. However, KDR expression was not detectable in TE-10 cells.…”

“…Expression vectors pcDNA3.1-TIMP-1 [42] and pcDNA3.1-TIMP-2 [43] encoding human TIMP-1 and TIMP-2, respectively, and pcDNA3-hPTK7-FLAG [17] encoding human PTK7 with a C-terminal Flag tag were described previously. Expression vector encoding K297R/Y529F dominant-negative mouse Src (pLNCX-mSrc [K297R/Y529F]) was generated by site-directed mutagenesis using pLNCX-mSrc, which was a generous gift from Professor E.-S. Oh (Ewha Womans University, Korea), as a template and primer pairs listed in Supplementary Table S1.…”

“…PTK7 enhances proliferation, survival, and migration of various cancer cells [8, 11, 13, 16]. PTK7 increases activation of ERKs, JNK, and p38 in ESCC and vascular endothelial cells [8, 17], and decreases expression of BAX and cleavage of caspase-3, −8, and −9 in cholangiocarcinoma [15]. In colon cancer and ovarian cancer, PTK7 sensitizes canonical Wnt and non-canonical Wnt/PCP pathways, respectively [6, 18].…”

Therapeutic Targeting of PTK7 is Cytotoxic in Atypical Teratoid Rhabdoid Tumors

“…Alternately, the therapeutic effect of Vatalanib may be due to inhibition of KDR. There is a biphasic relationship between PTK7 expression and KDR activity such that there is an optimal PTK7 concentration that leads to higher KDR activity (38). The therapeutic effect of Vatalanib might be due to the inhibition of KDR, which in ATRT cells may have higher activity due to increased levels of PTK7.…”