Cell adhesion - Ephrin signaling

Ephrin signaling

The Ephrin receptor tyrosine kinases and their Ephrin ligands play a pivotal role during axon guidance, synaptogenesis, neuronal circuitry formation, angiogenesis and proliferation of neuronalstem cells [1]. Ephrin receptors and Ephrin ligands transduce intracellular responses only upon binding and clustering in the membrane [2].

Ephrin-A receptors (Ephrin-A receptors 1-8) bind glycosylphosphatidyl-anchored Ephrin-A ligands (Ephrin-A1-5), whereas Ephrin-B receptors (Ephrin-B receptors 1-6) bind transmembrane Ephrin-B ligands (Ephrin-B1-3) [3].

Ephrin receptors signaling occurs through specific Guanine nucleotide exchange factors (GEFs) and therby can activate multiple Rho family GTPases including RhoA, Rac1 and CDC42.

Ephrin-A stimulation of Ephrin-A receptors activates three exchange factors: Ephexin [4], VAV-2 [5] and Tiam 1 [6]. VAV-2 can also bind to Ephrin-B receptors.

In the absence of Ephrin-A stimulation, Ephrin-A receptors alternatively engage Ephexin at the plasma membrane. This interaction induces Ephexin phosphorylation by c-Src tyrosine kinase [7] and this phosphorylation enhances Ephexin activity toward the GTPase RhoA and not Rac1 or CDC42 [8].

VAV-2 is rapidly phosphorylated by c-Src upon Ephrin stimulation of both Ephrin-A receptors and Ephrin-B receptors [5] leading to RhoA activation [9].

RhoA-dependent signaling in both cases leads to the growth cone retraction and collapse.

The growth cone collapse may be due to Rac1-dependent endocytosis events. Following Ephrin-A activation, VAV-2 induces activation of Rac1 which leads to actin cytoskeleton reorganization and endocytosis [3].

Ephrin-A receptors also signal through the Rac1 exchange factor Tiam 1 to promote neurite outgrowth [6].

Ephrin-A receptor 8 localizes p110gamma isoform of phosphatidylinositol 3-kinase (PI3K cat class IB (p110-gamma)) to the plasma membrane, thereby allowing access to lipid substrates that facilitate integrin-mediated cell adhesion [10].

Src-like adapter protein SLAP binds to activated Ephrin-A receptor 2 [11] and this interaction leads to the inhibiting c-Src signaling [12].

Guanine exchange factors Kalirin and Intersectin are downstream effectors of Ephrin-B receptors. Kalirin and Intersectin promote dendritic spine morphogenesis by modulating Rac1 and CDC42 activity, respectively [13]. Intersectin binds to Ephrin-B receptors independently of activation by Ephrins, while Kalirin appear to require Ephrin stimulation. Kalirin is also phosphorylated on tyrosine residues following Ephrin-B receptors activation [14].

The majority of Ephrin receptors negatively regulate the Ras/ MAP-kinase pathways in most cell types [15]. For instance, Ephrin-B receptor 2 via GTPase activated protein (GAP), p120GAP, down-regulates H-Ras activity and MAP kinase phosphorylation and induces neurite retraction in some neuronal cell lines [16] However the phosphorylation of p120GAP by c-Src inhibites its GAP activity [17]. Ephrin-A1 stimulation leads to Ras-related protein Rap-1A activation [18] and inhibits MAPK signaling cascade by decreasing c-Raf-1 kinase activation [19]. Alternatively c-Raf-1 can also be phosphorylated and activated by PAK1 [20]. Recruitment of the adaptor proteins GRB2 and GRB10 to the activated Ephrin-B receptor 1 also promotes MAP-kinase activation [21], [22].

Ephrin-B receptor 1 also associates with GRB7 [23], that specifically activates RHO6, a member of Rho family GTPases, and promotes axon growth repulsion [24].

Ephrin-B receptor 1 and Ephrin-B receptor 2 bind adaptor protein NCK1, thereby increasing the activity of specifically Nck-interacting kinase HGK [25]. HGK-induced JNK (stress-activated protein kinases) activation leads to the phosphorylation of Paxillin by JNK, which is essential for maintaining the dynamic cytoskeletal remodeling required for rapid cell migration [26].

Ephrin receptors also maintain feedback mechanisms that reverse signaling through their Ephrin ligands [15].

Src family kinases are responsible for Ephrin-B phosphorylation upon Ephrin receptor engagement [27]. The adaptor protein GRB4 links Ephrin-B to a vast signaling network that modifies cell morphology through reorganization of the actin cytoskeleton. Phosphorylated Ephrin-B recruits the phosphotyrosine phosphatase FAP-1, that dephosphorylates the cytoplasmic domain of Ephrin-B [27].

The GTPase-activating protein RGS3, can also transduce Ephrin-B signaling by catalyzing the hydrolysis of GTP to GDP in the alpha-i-subunits of G-proteins (G-protein alpha-i family). This signaling mechanism has broad implications for cell migratory behavior in different systems [15].

Ephrin-A ligands can also induce signals that modify cell behavior. Clustering of Ephrin-A molecules with Ephrin-A receptors recruits the Src family kinase Fyn to lipid rafts. This is accompanied by activation of MAP kinases and leading to an increase in cellular adhesion [15], [28].

Inhibition of Ephrin-A signaling may be modulated at the cell surface by induction of ligand-receptor dissociation by the metalloprotease ADAM10. Upon binding of Ephrin-A receptors, ADAM10 cleaves Ephrin-A2 ligands from the cell surface [29], serving two functions: 1) Ephrin-A cleavage allows Ephrin-A-receptor-bearing structures such as growth cones to revert from cellular adhesion to repulsion, and 2) ligand cleavage leads to direct inhibition of receptor activation [15].

References:

1. Palmer A, Klein R
   Multiple roles of ephrins in morphogenesis, neuronal networking, and brain function. Genes & development 2003 Jun 15;17(12):1429-50
2. Poliakov A, Cotrina M, Wilkinson DG
   Diverse roles of eph receptors and ephrins in the regulation of cell migration and tissue assembly. Developmental cell 2004 Oct;7(4):465-80
3. Murai KK, Pasquale EB
   New exchanges in eph-dependent growth cone dynamics. Neuron 2005 Apr 21;46(2):161-3
4. Shamah SM, Lin MZ, Goldberg JL, Estrach S, Sahin M, Hu L, Bazalakova M, Neve RL, Corfas G, Debant A, Greenberg ME
   EphA receptors regulate growth cone dynamics through the novel guanine nucleotide exchange factor ephexin. Cell 2001 Apr 20;105(2):233-44
5. Cowan CW, Shao YR, Sahin M, Shamah SM, Lin MZ, Greer PL, Gao S, Griffith EC, Brugge JS, Greenberg ME
   Vav family GEFs link activated Ephs to endocytosis and axon guidance. Neuron 2005 Apr 21;46(2):205-17
6. Tanaka M, Ohashi R, Nakamura R, Shinmura K, Kamo T, Sakai R, Sugimura H
   Tiam1 mediates neurite outgrowth induced by ephrin-B1 and EphA2. The EMBO journal 2004 Mar 10;23(5):1075-88
7. Knoll B, Drescher U
   Src family kinases are involved in EphA receptor-mediated retinal axon guidance. The Journal of neuroscience : the official journal of the Society for Neuroscience 2004 Jul 14;24(28):6248-57
8. Sahin M, Greer PL, Lin MZ, Poucher H, Eberhart J, Schmidt S, Wright TM, Shamah SM, O'connell S, Cowan CW, Hu L, Goldberg JL, Debant A, Corfas G, Krull CE, Greenberg ME
   Eph-dependent tyrosine phosphorylation of ephexin1 modulates growth cone collapse. Neuron 2005 Apr 21;46(2):191-204
9. Schmidt A, Hall A
   Guanine nucleotide exchange factors for Rho GTPases: turning on the switch. Genes & development 2002 Jul 1;16(13):1587-609
10. Gu C, Park S
    The EphA8 receptor regulates integrin activity through p110gamma phosphatidylinositol-3 kinase in a tyrosine kinase activity-independent manner. Molecular and cellular biology 2001 Jul;21(14):4579-97
11. Pandey A, Duan H, Dixit VM
    Characterization of a novel Src-like adapter protein that associates with the Eck receptor tyrosine kinase. The Journal of biological chemistry 1995 Aug 18;270(33):19201-4
12. Manes G, Bello P, Roche S
    Slap negatively regulates Src mitogenic function but does not revert Src-induced cell morphology changes. Molecular and cellular biology 2000 May;20(10):3396-406
13. Noren NK, Pasquale EB
    Eph receptor-ephrin bidirectional signals that target Ras and Rho proteins. Cellular signalling 2004 Jun;16(6):655-66
14. Irie F, Yamaguchi Y
    EPHB receptor signaling in dendritic spine development. Frontiers in bioscience : a journal and virtual library 2004 May 1;9:1365-73
15. Murai KK, Pasquale EB
    'Eph'ective signaling: forward, reverse and crosstalk. Journal of cell science 2003 Jul 15;116(Pt 14):2823-32
16. Elowe S, Holland SJ, Kulkarni S, Pawson T
    Downregulation of the Ras-mitogen-activated protein kinase pathway by the EphB2 receptor tyrosine kinase is required for ephrin-induced neurite retraction. Molecular and cellular biology 2001 Nov;21(21):7429-41
17. Giglione C, Gonfloni S, Parmeggiani A
    Differential actions of p60c-Src and Lck kinases on the Ras regulators p120-GAP and GDP/GTP exchange factor CDC25Mm. European journal of biochemistry / FEBS 2001 Jun;268(11):3275-83
18. Aoki M, Yamashita T, Tohyama M
    EphA receptors direct the differentiation of mammalian neural precursor cells through a mitogen-activated protein kinase-dependent pathway. The Journal of biological chemistry 2004 Jul 30;279(31):32643-50
19. Hu CD, Kariya K, Kotani G, Shirouzu M, Yokoyama S, Kataoka T
    Coassociation of Rap1A and Ha-Ras with Raf-1 N-terminal region interferes with ras-dependent activation of Raf-1. The Journal of biological chemistry 1997 May 2;272(18):11702-5
20. Coles LC, Shaw PE
    PAK1 primes MEK1 for phosphorylation by Raf-1 kinase during cross-cascade activation of the ERK pathway. Oncogene 2002 Mar 28;21(14):2236-44
21. Stein E, Cerretti DP, Daniel TO
    Ligand activation of ELK receptor tyrosine kinase promotes its association with Grb10 and Grb2 in vascular endothelial cells. The Journal of biological chemistry 1996 Sep 20;271(38):23588-93
22. Vindis C, Cerretti DP, Daniel TO, Huynh-Do U
    EphB1 recruits c-Src and p52Shc to activate MAPK/ERK and promote chemotaxis. The Journal of cell biology 2003 Aug 18;162(4):661-71
23. Han DC, Shen TL, Miao H, Wang B, Guan JL
    EphB1 associates with Grb7 and regulates cell migration. The Journal of biological chemistry 2002 Nov 22;277(47):45655-61
24. Oinuma I, Katoh H, Harada A, Negishi M
    Direct interaction of Rnd1 with Plexin-B1 regulates PDZ-RhoGEF-mediated Rho activation by Plexin-B1 and induces cell contraction in COS-7 cells. The Journal of biological chemistry 2003 Jul 11;278(28):25671-7
25. Becker E, Huynh-Do U, Holland S, Pawson T, Daniel TO, Skolnik EY
    Nck-interacting Ste20 kinase couples Eph receptors to c-Jun N-terminal kinase and integrin activation. Molecular and cellular biology 2000 Mar;20(5):1537-45
26. Huang C, Rajfur Z, Borchers C, Schaller MD, Jacobson K
    JNK phosphorylates paxillin and regulates cell migration. Nature 2003 Jul 10;424(6945):219-23
27. Palmer A, Zimmer M, Erdmann KS, Eulenburg V, Porthin A, Heumann R, Deutsch U, Klein R
    EphrinB phosphorylation and reverse signaling: regulation by Src kinases and PTP-BL phosphatase. Molecular cell 2002 Apr;9(4):725-37
28. Davy A, Gale NW, Murray EW, Klinghoffer RA, Soriano P, Feuerstein C, Robbins SM
    Compartmentalized signaling by GPI-anchored ephrin-A5 requires the Fyn tyrosine kinase to regulate cellular adhesion. Genes & development 1999 Dec 1;13(23):3125-35
29. Hattori M, Osterfield M, Flanagan JG
    Regulated cleavage of a contact-mediated axon repellent. Science (New York, N.Y.) 2000 Aug 25;289(5483):1360-5