Inhibition of Plxna2

Plexins (Plxns) are the receptors encoded by the members of the plexin gene family. They are primary transducers of vertebrate semaphorin (Sema) signals. The vertebrate plexins are subdivided into four subfamilies comprising four type A plexins, three type B plexins, plexin C1 (PlEXC1) and plexin D1(Neufeld & Kessler, 2008; Tamagnone et al., 1999). The plexins are transmembrane receptors distinguished by the presence of a split gTPase-activating (gAP) cytoplasmic domain (Oinuma et al., 2004). Semaphorins are members of a large gene family of secreted and membrane-anchored proteins. There are eight subclasses of Semas. Semas 1 and 2 are found in invertebrates, 3–7 are found in vertebrates, and Sema V is found in the genome of non-neurotropic DNA viruses. They were initially characterized as axon guidance factors and are divided into eight subfamilies. The  receptors belonging to the plexin family function as semaphorin receptors (Neufeld & Kessler, 2008). Semas were initially discovered with respect to their role as repulsive guidance cues for migrating axons, although it is now appreciated that they have much broader roles in development. Semas and Plxns have tissue-specific expression patterns, and many Semas can signal through multiple Plxn family members (Luo et al., 1993).

Plxna2 is predicted to have semaphorin receptor activity. Involved in optic vesicle formation, predicted to localize to integral component of plasma membrane and semaphorin receptor complex. Is expressed in several structures, including brain; hatching gland; olfactory field; optic vesicle; and retina and is critical to zebrafish eye development. Orthologous to human PLXNA2 (plexin A2)(ZFIN Gene: Plxna2, n.d.).

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 (St. Clair et al., 2018). Phosphorylation is one of the fundamental mechanisms of cell signaling and regulation of cell growth, proliferation, differentiation, metabolism, neural function, etc. (Hanrs & Hunter, 1995; Johnson & Lewis, 2010; Mellado et al., 2001). Tyrosine phosphorylation is a pivotal post-translational protein modification that regulates intracellular signalling. Therefore, phosphorylation of tyrosines in the intracellular domain of plex-ins could determine or modify their interactions with additional signal transducers (Franco & Luca Tamagnone, 2008).

Phosphorylation changes of Plxna2 tyrosine can be detected  directly using western blot and indirectly by using ELISA method to measure Plxna2 activity. There are several antibodies available commercially. 

In (St. Clair et al., 2018) study, Fyn kinase dependent phosphorylation of plxna2 was measured with western blotting using α-Fyn (rabbit mAb), α-Flag M2 (mouse mAb), α-phosphotyrosine 4G10 (mouse mAb), and α-Src pY416 (rabbit mAb). The following secondary antibodies were used: α-rabbit-HRP (goat IgG), α-mouse-HRP (goat IgG), or for immunoprecipitation samples, α-mouse- HRP Light Chain Specific (goat IgG) .

Key event described here has been primarily established in zebrafish models (Emerson et al., 2017; St. Clair et al., 2018).

Emerson, S. E., St. Clair, R. M., Waldron, A. L., Bruno, S. R., Duong, A., Driscoll, H. E., Ballif, B. A., McFarlane, S., & Ebert, A. M. (2017). Identification of target genes downstream of semaphorin6A/PlexinA2 signaling in zebrafish. Developmental Dynamics, 246(7), 539–549. https://doi.org/10.1002/dvdy.24512

Franco, M., & Luca Tamagnone, &. (2008). review Tyrosine phosphorylation in semaphorin signalling: shifting into overdrive. EMBO Reports, 9, 865–871. https://doi.org/10.1038/embor.2008.139

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Johnson, L. N., & Lewis, R. J. (2010). ChemInform Abstract: Structural Basis for Control by Phosphorylation. ChemInform, 32(40), no--no. https://doi.org/10.1002/chin.200140284

Luo, Y., Raible, D., & Raper, J. A. (1993). Collapsin : A Protein in Brain That Induces the Collapse and Paralysis of Neuronal Growth Cones. 75(1984), 217–227.

Mellado, M., Rodríguez-Frade, J. M., Mañes, S., & Martínez-A., C. (2001). Chemokine signaling and functional responses: The role of receptor dimerization and TK pathway activation. Annual Review of Immunology, 19, 397–421. https://doi.org/10.1146/annurev.immunol.19.1.397

Neufeld, G., & Kessler, O. (2008). The semaphorins: Versatile regulators of tumour progression and tumour angiogenesis. Nature Reviews Cancer, 8(8), 632–645. https://doi.org/10.1038/nrc2404

Oinuma, I., Ishikawa, Y., Katoh, H., & Negishi, M. (2004). The Semaphorin 4D receptor Plexin-B1 is a GTPase activating protein for R-Ras. Science, 305(5685), 862–865. https://doi.org/10.1126/science.1097545

St. Clair, R. M., Emerson, S. E., D’Elia, K. P., Marion, W. E., Schmoker, A. M., Ebert, A. M., & Ballif, B. A. (2018). Fyn-dependent phosphorylation of PlexinA1 and PlexinA2 at conserved tyrosines is essential for zebrafish eye development. FEBS Journal, 285(1), 72–86. https://doi.org/10.1111/febs.14313

Tamagnone, L., Artigiani, S., Chen, H., He, Z., Ming, G. L., Song, H. J., Chedotal, A., Winberg, M. L., Goodman, C. S., Poo, M. M., Tessier-Lavigne, M., & Comoglio, P. M. (1999). Plexins are a large family of receptors for transmembrane, secreted, and GPI-anchored semaphorins in vertebrates. Cell, 99(1), 71–80. https://doi.org/10.1016/S0092-8674(00)80063-X

ZFIN Gene: plxna2. (n.d.). Retrieved March 15, 2021, from http://zfin.org/ZDB-GENE-090311-6