Pathway maps

Cell adhesion_Integrin inside-out signaling
Cell adhesion_Integrin inside-out signaling

Object List (links open in MetaCore):

alpha-5/beta-1 integrin, Ca('2+) endoplasmic reticulum lumen, FAK1, G-protein alpha-12 family, alpha-2/beta-1 integrin, IP3 receptor, Angiotensin II, Thrombin, Fibronectin, Fibrinogen, IP3, TBXA2R, PKC-epsilon, Actin cytoskeletal, PtdIns(3,4,5)P3, Collagen II, alpha-L/beta-2 integrin, <endoplasmic reticulum lumen> Ca('2+) = <cytosol> Ca('2+), Calmodulin, alpha-V/beta-3 integrin, SDF-1, PtdIns(4)P, G-protein alpha-i family, PAR1, ITGB1, DAG, Erk (MAPK1/3), c-Src, CaMK II, NRIF3, PtdIns(4,5)P2, ITGA2B, PLC-beta, CXCR4, AGTR1, alpha-1/beta-1 integrin, PI3K cat class IB (p110-gamma), G-protein alpha-q/11, G-protein beta/gamma, ITGB3,,, Thromboxane A2, alpha-IIb/beta-3 integrin, Cytohesin3, PtdIns(4,5)P2, PIPKI gamma, Cytohesin1, Talin, ICAP-1, Calmyrin,, PAR4, Collagen I, Ca('2+) cytosol, alpha-10/beta-1 integrin, ITGB2


Integrin inside-out signaling

The integrin family of transmembrane adhesion receptors mediates both cell-cell and cell- extracellular matrix (ECM) adhesion. One important, rapid and reversible mechanism for regulating adhesion is increasing the affinity of integrin receptors for their extracellular ligands (integrin activation). This is controlled by intracellular signals that, through their action on integrin cytoplasmic domains, induce conformational changes in integrin extracellular domains that result in increased affinity for ligand (inside-out signaling) [1], [2].

Several such inside-out signal pathways could be activated by a host of G-protein-coupled receptors (GPCRs), including the Thromboxane A2 receptor ( TBXA2R ), Thrombin receptors PAR1 and PAR4, Angiotensin II receptor type-1 ( AGTR1 ), and receptor for the C-X-C chemokine SDF-1 ( CXCR4 ).

Ligand binding triggers conformational changes that promote receptor/G-protein coupling and catalyzes the exchange of GTP for GDP on the G-alpha subunit of the heterotrimeric G protein, leading to dissociation of the GTP-bound G-alpha subunit from the G - beta/gamma subunit heterodimer [3].

The G alpha-q family of G-proteins ( G-protein alpha-q/11 ) and G-protein beta/gamma subunits activate different phosphoinositide-specific phospholipase C PLC-beta isozymes [4], [5]. These enzymes in turn catalyze the hydrolysis of phosphatidylinositol 4,5-bisphosphate ( PtdIns(4,5)P2 ) to inositol 1,4,5-trisphosphate ( IP3 ) and diacylglycerol ( DAG ) [6].

IP3 stimulates Ca(2+) release from endoplasmic reticulum storage sites via the inositol 1,4,5-trisphosphate receptor ( IP3 receptor ) [7]. Ca(2+), in turn, activates diverse downstream targets, including Calmodulin [8] and Calmyrin [9].

DAG activates protein kinase C PKC-epsilon, that phosphorylates the cytoplasmatic tail of the beta-1 integrin subunit ( ITGB1 ) [10].

PKC-epsilon is also activated in G-protein alpha-12 family signaling pathway [11]. G-protein alpha-12 family subunits, in turn, are stimulated by the activity of TBXA2R [12] and AGTR1 [13].

The Phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit, gamma isoform ( PI3K cat class IB, gamma ) is activated by G-protein beta/gamma subunits upon stimulation of GPCRs AGTR1 and CXCR4. PI3K cat class IB (p110-gamma) phosphorylates the membrane lipid PtdIns(4,5)P2 to generate phosphatidylinositol 3,4,5-trisphosphate PtdIns(3,4,5)P3 [14].

Tyrosine-protein kinase c-Src is activated by G-protein alpha-q/11, G-protein alpha-12 family, and G-protein beta/gamma subunits. In most cell types, c-Src stimulation is involved in GPCR-mediated activation of the Focal adhesion kinase FAK1 and the mitogen-activated protein kinases ERK1 / 2 [3].

Talin, a major cytoskeletal Actin -binding protein, plays a crucial role in integrin activation. Talin binding to integrin beta-1 ( ITGB1 ), integrin beta-2 (ITGB2 ), integrin beta-3 ( ITGB3 ) cytoplasmic tails induces conformational changes in their extracellular domains, increasing integrin affinity for ligands. Mechanisms that regulate Talin binding may therefore control integrin activation [1].

The binding of PtdIns(4,5)P2 to Talin induces a conformational change that enhances its association with integrin beta subunits. Talin binds to and activates the PtdIns(4,5)P2 -producing enzyme: phosphatidylinositol phosphate kinase type I gamma ( PIPKI gamma ). Therefore, Talin can stimulate PtdIns(4,5)P2 production that enhances Talin - Integrin interactions, which suggests that PIPKI gamma may positively regulate integrin activation. PIPKI gamma is also stimulated by c-Src [15] and FAK1 phosphorylation [16]. However, PIPKI gamma and integrin beta-1 tails compete for overlapping binding sites on the Talin and so, under some conditions, PIPKI gamma might inhibit integrin activation by displacing Talin from beta-1 tails [1].

PtdIns(4,5)P2 also stimulates the transient, direct interactions of diverse cytoskeleton actin-binding protein and couple adhesion to Actin assembly [17].

The integrin beta-1 binding protein ICAP-1 inhibits Integrin - Talin association [18]. Calcium/calmodulin-dependent protein kinase II CaMK II phosphorylates ICAP-1 and this phosphorylation negatively regulates integrin-mediated processes [19].

Beta-3-endonexin ( NRIF3 ) binds specifically to ITGB3 and activates alpha-IIb/beta-3 integrin [20]. However, in the absence of Talin, this activation is very weak. Therefore, NRIF3 may cooperate with Talin during alpha-IIb/beta-3 integrin activation in platelets [1].

Calcium - and integrin-binding protein Calmyrin, which interacts directly with the alpha-IIb ( ITGA2B ) tail, inhibits alpha-IIb/beta-3 integrin activation by competing with talin for binding to integrin [21].

Guanine nucleotide exchange factors Cytohesin-1 and Cytohesin-3, activated by PI(3,4,5)P3, bind ITGB2 which leads to an increase cell adhesion through an affinity-independent processes, such as integrin clustering, rather than integrin activation [1].

Intracellular signals induce conformational changes in the integrin extracellular domains that result in their increased affinity for ligands, focal adhesion formation and integrin signal transduction (outside-in signaling) [1].


  1. Calderwood DA
    Integrin activation. Journal of cell science 2004 Feb 15;117(Pt 5):657-66
  2. Kinashi T
    Intracellular signalling controlling integrin activation in lymphocytes. Nature reviews. Immunology. 2005 Jul;5(7):546-59
  3. Luttrell DK, Luttrell LM
    Not so strange bedfellows: G-protein-coupled receptors and Src family kinases. Oncogene 2004 Oct 18;23(48):7969-78
  4. Lee CH, Park D, Wu D, Rhee SG, Simon MI
    Members of the Gq alpha subunit gene family activate phospholipase C beta isozymes. The Journal of biological chemistry 1992 Aug 15;267(23):16044-7
  5. Litosch I
    Regulation of phospholipase C-beta activity by phosphatidic acid: isoform dependence, role of protein kinase C, and G protein subunits. Biochemistry 2003 Feb 18;42(6):1618-23
  6. Rhee SG
    Regulation of phosphoinositide-specific phospholipase C. Annual review of biochemistry 2001;70:281-312
  7. Miyakawa T, Mizushima A, Hirose K, Yamazawa T, Bezprozvanny I, Kurosaki T, Iino M
    Ca(2+)-sensor region of IP(3) receptor controls intracellular Ca(2+) signaling. The EMBO journal 2001 Apr 2;20(7):1674-80
  8. Kwiatkowski AP, McGill JM
    Alternative splice variant of gamma-calmodulin-dependent protein kinase II alters activation by calmodulin. Archives of biochemistry and biophysics 2000 Jun 15;378(2):377-83
  9. Naik UP, Patel PM, Parise LV
    Identification of a novel calcium-binding protein that interacts with the integrin alphaIIb cytoplasmic domain. The Journal of biological chemistry 1997 Feb 21;272(8):4651-4
  10. Stawowy P, Margeta C, Blaschke F, Lindschau C, Spencer-Hansch C, Leitges M, Biagini G, Fleck E, Graf K
    Protein kinase C epsilon mediates angiotensin II-induced activation of beta1-integrins in cardiac fibroblasts. Cardiovascular research 2005 Jul 1;67(1):50-9
  11. Lopez I, Mak EC, Ding J, Hamm HE, Lomasney JW
    A novel bifunctional phospholipase c that is regulated by Galpha 12 and stimulates the Ras/mitogen-activated protein kinase pathway. The Journal of biological chemistry 2001 Jan 26;276(4):2758-65
  12. Klages B, Brandt U, Simon MI, Schultz G, Offermanns S
    Activation of G12/G13 results in shape change and Rho/Rho-kinase-mediated myosin light chain phosphorylation in mouse platelets. The Journal of cell biology 1999 Feb 22;144(4):745-54
  13. Nishida M, Tanabe S, Maruyama Y, Mangmool S, Urayama K, Nagamatsu Y, Takagahara S, Turner JH, Kozasa T, Kobayashi H, Sato Y, Kawanishi T, Inoue R, Nagao T, Kurose H
    Galpha12/13- and reactive oxygen species-dependent activation of c-Jun NH2-terminal Kinase and p38 mitogen-activated protein kinase by angiotensin receptor stimulation in rat neonatal cardiomyocytes. The Journal of biological chemistry 2005 May 6;280(18):18434-41
  14. Brock C, Schaefer M, Reusch HP, Czupalla C, Michalke M, Spicher K, Schultz G, Nurnberg B
    Roles of G beta gamma in membrane recruitment and activation of p110 gamma/p101 phosphoinositide 3-kinase gamma. The Journal of cell biology 2003 Jan 6;160(1):89-99
  15. Lee SY, Voronov S, Letinic K, Nairn AC, Di Paolo G, De Camilli P
    Regulation of the interaction between PIPKI gamma and talin by proline-directed protein kinases. The Journal of cell biology 2005 Feb 28;168(5):789-99
  16. Ling K, Doughman RL, Firestone AJ, Bunce MW, Anderson RA
    Type I gamma phosphatidylinositol phosphate kinase targets and regulates focal adhesions. Nature 2002 Nov 7;420(6911):89-93
  17. Nayal A, Webb DJ, Horwitz AF
    Talin: an emerging focal point of adhesion dynamics. Current opinion in cell biology 2004 Feb;16(1):94-8
  18. Bouvard D, Vignoud L, Dupe-Manet S, Abed N, Fournier HN, Vincent-Monegat C, Retta SF, Fassler R, Block MR
    Disruption of focal adhesions by integrin cytoplasmic domain-associated protein-1 alpha. The Journal of biological chemistry 2003 Feb 21;278(8):6567-74
  19. Bouvard D, Block MR
    Calcium/calmodulin-dependent protein kinase II controls integrin alpha5beta1-mediated cell adhesion through the integrin cytoplasmic domain associated protein-1alpha. Biochemical and biophysical research communications 1998 Nov 9;252(1):46-50
  20. Shattil SJ, O'Toole T, Eigenthaler M, Thon V, Williams M, Babior BM, Ginsberg MH
    Beta 3-endonexin, a novel polypeptide that interacts specifically with the cytoplasmic tail of the integrin beta 3 subunit. The Journal of cell biology 1995 Nov;131(3):807-16
  21. Yuan W, Leisner TM, McFadden AW, Wang Z, Larson MK, Clark S, Boudignon-Proudhon C, Lam SC, Parise LV
    CIB1 is an endogenous inhibitor of agonist-induced integrin alphaIIbbeta3 activation. The Journal of cell biology 2006 Jan 16;172(2):169-75