PINCH, Beta-catenin, Ca(2+) cytosol, Ephrin-B, H-Ras, Tau (MAPT), G-protein beta/gamma, WIRE, FAK1, Paxillin, PAK1, Tubulin alpha, c-Raf-1, GSK3 beta, FAP-1, N-WASP, WaspIP, PINCH-2, Arp2/3, Ephrin-B receptors, Grb4, G-protein alpha-i family, SDF-1, CXCR4, ILK, Axin, RGS3, Actin cytoskeletal, c-Src, SOS, Tubulin (in microtubules)
Reverse signaling by Ephrin B
Ephrin receptors and Ephrins are both membrane bound, and following their interaction and clustering, each can transduce signals that regulate cell responses .
Ephrin receptors activate reverse signaling through their Ephrin ligands .
Ephrin-B receptors induce Ephrin-B tyrosine phosphorylation. Src family kinases are responsible for Ephrin-B phosphorylation, but this activation is transient. At later time points Ephrin-B ligands recruit phosphotyrosine Phosphatase protein-tyrosine phosphatase PTPL1 ( FAP-1 ) to the membrane and become dephosphorylated. This is suggested the presence of a switch mechanism that allows Ephrin-B ligands to shift from fast phosphotyrosine/Src-dependent signaling to delayed signaling .
Tyrosine phosphorylation of Ephrin-B results in binding of the NCK adaptor protein 2 ( Grb4), which links Ephrin-B to a vast signaling network that modifies cell morphology through reorganization of Actin cytoskeleton .
Grb4 could associate with a number of signaling molecules. It can bind to G-factor Son of sevenless homolog ( SOS ) , followed by activation of transforming protein v-Ha-ras Harvey rat sarcoma viral oncogene homolog ( H-RAS ), protein kinase V-raf-1 murine leukemia viral oncogene homolog ( c-Raf ) and MAPK-cascade signaling.
Grb4 binding to p21 protein-activated kinase 1 ( PAK1 )  and to the WAS/WASL interacting protein family, member 2 ( WIRE ) with subsequent activation of Wiskott-Aldrich syndrome protein ( N-WASP ) promotes complex of ARP actin-related proteins homologs ( Arp2/3 ) activation and Actin polymerization . Activity of the N-WASP is also facilitated by another WASP interacting protein WAS/WASL interacting protein family member 1 ( WaspIP ) .
Binding of Grb4 to LIM and senescent cell antigen-like domains 1 ( PINCH) and to Axin regulates Beta-catenin activity and Wingless-type MMTV integration site family ( WNT ) proteins signaling.
PINCH is a binding protein for Integrin-linked kinase ( ILK ) , which phosphorylates downstream glycogen synthase kinase 3 ( GSK3 ) and down-regulates its activity . PINCH-2, another member of the PINCH protein family, forms a complex with ILK and significantly inhibits the PINCH/ ILK interaction .
Axin forms a complex with Glycogen synthase kinase 3 beta ( GSK3 beta ) and Beta-catenin and promotes GSK3 beta -dependent phosphorylation of Beta-catenin, thereby stimulating degradation of Beta-catenin. GSK3 beta in turn phosphorylates Axin in the complex, which is important for the regulation of its stability .
GSK3 beta also phosphorylates neuronal microtubule-associated protein Microtubule-associated protein tau ( Tau (MAPT) ) . This phosphorylation does not alter Tau 's ability to bind to Tubulin in microtubules but appears to be required for the maintenance of the anterograde organelle transport in differentiated cells .
Paxillin is a focal adhesion-associated protein that also could bind to both Tubulin alpha and gamma of the cellular microtubule cytoskeleton .
Activation of Ephrin-B1 leads to phosphorylation of focal adhesion kinase (FAK1 ) by V-src sarcoma viral oncogene homolog ( c-Src), which increases FAK1 activity, and leads to redistribution of the FAK1 -binding protein Paxillin and disassembly of focal adhesions .
These signaling pathways lead to rounding of cell morphology and cell repulsion.
A mechanism that may serve to turn off phosphorylation-dependent Ephrin-B reverse signals involves delayed recruitment of the FAP-1, which then dephosphorylates the cytoplasmic domain of Ephrin-B .
Ephrin-B ligands, even after dephosphorylating, can initiate reverse signaling through binding to the Regulator of G-protein signaling 3 ( RGS3 ), which catalyzes hydrolysis of GTP to GDP in the Guanine nucleotide binding protein alpha inhibiting activity polypeptide 1 ( G-protein alpha-i )-subunits, thereby inhibiting their activity. RGS3 might inhibit Stromal cell derived factor 1 ( SDF1 )-mediated cerebellar granule cell chemotaxis through Chemokine receptor 4 ( CXCR4 ) G-protein -coupled chemokine receptor . This signaling mechanism may have broad implications for cell migratory behavior in different systems .