Epileptic and developmental disorders of the speech cortex: ligand/receptor interaction of wild-type and mutant SRPX2 with the plasminogen activator receptor uPAR

Abstract

Mutations in SRPX2 (Sushi-Repeat Protein, X-linked 2) cause rolandic epilepsy with speech impairment (RESDX syndrome) or with altered development of the speech cortex (bilateral perisylvian polymicrogyria). The physiological roles of SRPX2 remain unknown to date. One way to infer the function of SRPX2 relies on the identification of the as yet unknown SRPX2 protein partners. Using a combination of interactome approaches including yeast two-hybrid screening, co-immunoprecipitation experiments, cell surface binding and surface plasmon resonance (SPR), we show that SRPX2 is a ligand for uPAR, the urokinase-type plasminogen activator (uPA) receptor. Previous studies have shown that uPAR(-/-) knock-out mice exhibited enhanced susceptibility to epileptic seizures and had brain cortical anomalies consistent with altered neuronal migration and maturation, all features that are reminiscent to the phenotypes caused by SRPX2 mutations. SPR analysis indicated that the p.Y72S mutation associated with rolandic epilepsy and perisylvian polymicrogyria, led to a 5.8-fold gain-of-affinity of SRPX2 with uPAR. uPAR is a crucial component of the extracellular plasminogen proteolysis system; two more SRPX2 partners identified here, the cysteine protease cathepsin B (CTSB) and the metalloproteinase ADAMTS4, are also components of the extracellular proteolysis machinery and CTSB is a well-known activator of uPA. The identification of functionally related SRPX2 partners provides the first and exciting insights into the possible role of SRPX2 in the brain, and suggests that a network of SRPX2-interacting proteins classically involved in the proteolytic remodeling of the extracellular matrix and including uPAR participates in the functioning, in the development and in disorders of the speech cortex.

Sushi repeat-containing protein X-linked 2 promotes angiogenesis through the urokinase-type plasminogen activator receptor dependent integrin αvβ3/focal adhesion kinase pathways

“…As referenced above, Miljkovic-Licina et al (11) proved that mouse SRPX2 directly binds to vascular uPAR on t.End.1V cells. SRPX2 is a proven ligand of cell surface uPAR located on the cell membranes of both tumor cells and HUVECs (12); therefore, the role of uPAR in the pro-angiogenic effects of SRPX2 in HUVECs was evaluated using SRPX2 recombinant protein and uPAR-neutralizing antibody. As shown in Figure 2a, in Transwell assays, the number of HUVECs that migrated through the membrane per field was markedly increased in the SRPX2 group compared with that of the control group (p < 0.001), while treating HUVECs with uPAR-neutralizing antibody before the Transwell assay significantly attenuated the number of migrating cells compared with the SRPX2 group (p < 0.01).…”

Single-Gene Determinants of Epilepsy Comorbidity

“…SRPX2 reduction impairs development of ultrasonic vocalization in mice. Interactors with SRXP2 have been identified by yeast 2-hybrid analysis of a human brain cDNA library (Royer-Zemmour et al 2008), including two other known epilepsy genes, urokinase-type plasminogen activator receptor (UPAR or PLAUR) (Powell et al 2003) and cathepsin B (CTSB) (Pennacchio et al 1998), involved in extracellular proteolysis in human and rat brain. GRIN2A has also been linked to epilepsy in the rolandic region and aphasia (Reutlinger et al 2010).…”

A Molecular Classification of Human Mesenchymal Stromal Cells

“…CCDC80 binds syndecanheparin sulphate containing proteoglycans, has been shown to inhibit WNT/beta-catenin signalling and has a regulatory role in adipogenesis (Tremblay et al, 2009;Walczak et al, 2014). SRPX2 is a secreted chondroitin sulfate proteoglycan involved in endothelial cell migration, tissue remodelling and vascular sprouting (Royer-Zemmour et al, 2008). The chaperonins HSPB5/CRYAB and HSPB6 stabilise protein complexes, and may assist in delivery of growth factor complexes where these are present in high concentrations.…”