NTAK (neural- and thymus-derived activator for ErbB kinases), also known as neuregulin-2, is a member of the epidermal growth factor (EGF) family, which binds directly to ErbB3 and ErbB4 and transactivates ErbB2. Because ErbB signaling has been implicated in various angiogenic mechanisms, the effect of NTAK (which has at least nine isoforms due to alternative splicing) in angiogenesis is explored. One isoform, NTAKγ, inhibited cell growth in terms of DNA synthesis and cell numbers in vascular endothelial cells specifically, whereas NTAKα and β had no activity. On the other hand, NTAKγ secreted by transfected MDA-MB-231 cells inhibited endothelial cell growth, and NTAKγ expressed in endothelial cells by adenovirus infection suppressed cell growth in a dose-dependent manner. The EGF-like domain of NTAKγ did not have this activity. The NTAKδ isoform, which had the Ig-like domain but not the EGF-like domain, inhibited proliferation of endothelial cells. NTAKδ prevented hyper-phosphorylation of the retinoblastoma tumor suppressor protein and caused G1 arrest in endothelial cells. Both NTAKγ and δ isoforms displayed anti-angiogenic activity in the chick embryo chorioallantoic membrane in vivo. These results suggest that the active site of NTAK is localized outside of the EGF-like domain but within the N-terminal region, including the Ig-like domain, of NTAK.
This work was supported in part by the Charitable Trust Osaka Cancer Researcher Fund. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.