Department of Biology, University of Vermont, Burlington, VT, USA.
FEBS J. 2018 Jan;285(1):72-86. doi: 10.1111/febs.14313. Epub 2017 Nov 17.
Plexins (Plxns) are semaphorin (Sema) receptors that play important signaling roles, particularly in the developing nervous system and vasculature. Sema-Plxn signaling regulates cellular processes such as cytoskeletal dynamics, proliferation, and differentiation. However, the receptor-proximal signaling mechanisms driving Sema-Plxn signal transduction are only partially understood. Plxn tyrosine phosphorylation is thought to play an important role in these signaling events as receptor and nonreceptor tyrosine kinases have been shown to interact with Plxn receptors. The Src family kinase Fyn can induce the tyrosine phosphorylation of PlxnA1 and PlxnA2. However, the Fyn-dependent phosphorylation sites on these receptors have not been identified. Here, using mass spectrometry-based approaches, we have identified highly conserved, Fyn-induced PlexinA (PlxnA) tyrosine phosphorylation sites. Mutation of these sites to phenylalanine results in significantly decreased Fyn-dependent PlxnA tyrosine phosphorylation. Furthermore, in contrast to wild-type human PLXNA2 mRNA, mRNA harboring these point mutations cannot rescue eye developmental defects when coinjected with a plxnA2 morpholino in zebrafish embryos. Together these data suggest that Fyn-dependent phosphorylation at two critical tyrosines is a key feature of vertebrate PlxnA1 and PlxnA2 signal transduction.
衔接蛋白（Plexins，Plxns）是一种 semaphorin（Sema）受体，在神经系统和脉管系统的发育中发挥着重要的信号作用。Sema-Plxn 信号调节细胞过程，如细胞骨架动力学、增殖和分化。然而，驱动 Sema-Plxn 信号转导的受体近端信号机制仅部分被理解。受体酪氨酸磷酸化被认为在这些信号事件中起着重要作用，因为已经表明受体和非受体酪氨酸激酶与 Plxn 受体相互作用。Src 家族激酶 Fyn 可以诱导 PlxnA1 和 PlxnA2 的酪氨酸磷酸化。然而，这些受体上的 Fyn 依赖性磷酸化位点尚未确定。在这里，我们使用基于质谱的方法鉴定了高度保守的、由 Fyn 诱导的 PlexinA（PlxnA）酪氨酸磷酸化位点。将这些位点突变为苯丙氨酸会导致 Fyn 依赖性 PlxnA 酪氨酸磷酸化显著减少。此外，与野生型人 PLXNA2 mRNA 相反，当与 zebrafish 胚胎中的 plxnA2 形态发生素共注射时，携带这些点突变的 mRNA 不能挽救眼部发育缺陷。这些数据表明，两个关键酪氨酸上的 Fyn 依赖性磷酸化是脊椎动物 PlxnA1 和 PlxnA2 信号转导的关键特征。
