Disintegrins:integrin selective ligands which activate integrin-coupled signaling and modulate leukocyte functions Auth

1. Disintegrins:integrin selective ligands which activate integrin-coupled signaling and modulate leukocyte functionsAuthorsC.Bajra-Fidalgo,A.L.j.coelho,R.Saldanha-Gama, E.Helal-Neto,and M.S.de Freitas Presented By: P.Vipula

2. Background: Integrins are a large family of heterodimeric glycoproteins that attach cells to ECM proteins of the basement or to ligands on other cells , with out which cell migration is not possible. Integrins are the adhesion molecules. As they integrate the function of cell with the outside world they got that name. The interaction between integrins and ECM regulates cell survival , cell growth, gene expression and function. �-Barrel shaped integrins are made of 120-170 KDa of a subunit and 90-100 KDa of �-subunit.

3. Background contin. In mammals nearly 18-a subunits and 8-� subunits were cloned leading to 24 a� Heterodimers. Integrins are Bidirectional signaling molecules. Extracellular matrix molecules �Fibronectin , laminins. Intracellular ligands � talin, a � actinin. Integrins are linked to structural proteins like Vinculin, actin microfilaments,FAK�s etc.

4. Integrin Structure

6. Integrins and Signal Transduction: Integrins play an important role not only in structure & architecture of tissues, but also for signal transduction leading to regulation of functions in cell. Focal adhesion kinase (FAK) becomes tyrosine phosphorylated during integrin - mediated cell adhesion. FAK is a non-receptor tyrosine kinase interacting with C- src, PI3-K,Rho GTPase,Grb-2 and p130 CAS . FAK-generated signaling is involved in cell survival and essential for development.

7. FAK can be phosphorylated on different tyrosine residues like tyr397 conforms to consensus binding for SH-2 domains for C-Src and p85 regulatory subunit of PI3-K and activates the PI3-K. Integrins-mediated cell adhesion can activate MAPK including Erk-1, c-Jun kinase, and p38 which leads to transcriptional regulation of certain genes � cell growth, differentiation and apoptosis. I.M.C.A also stimulates Rho family members including RhoA,Rac1, CDC42 and bring Actin Polymerization. Activation of Rho family is important for actin rearrangement.

9. Activated FAK is associated with PI3-K through Tyr397 residue, Phosphorylating the P85 subunit and activating the PI3-K. PI3-K-effector proteins are involved in regulation of integrin mediated leukocyte migration and immune cell proliferation, differentiation and survival. Regulation of catalytic activity of FAK signaling site specific dephosphorylation of tyrosine residues.

13. A family of Cysteine rich peptide with RGD motif .This tripeptide sequence is the cell attachment site recognized by integrins. Through RGD motifs Disintegrins bind to integrins inhibiting integrin related functions. Integrin inhibitory proteins were first discovered in snake venom, and are potent antagonists of platelet aggregation and integrins cellular adhesive functions. In snake venom disintegrins peptides had other active sequences like KGD,MVD,MLD,VGD,ECD,or MDG in integrin motifs. Different disintegrins are eristostatin, echistatin,kistrin, and flavoridin are able to bind to aIIb�3 potent inhibitors of platelet aggregation and tumor cell metastasis.

14. Leukocytes and integrin signaling: Integrins are dominant family of cell adhesion receptors involved in leukocyte interactions with endothelium and ECM . Integrin signaling pathways mediate important functions in leukocytes, including migration, spreading, activation of the respiratory burst, complement binding, cell adhesion, cytokines and chemokine expression, and apoptosis . During inflammation, neutrophils roll along the endothelial wall of postcapillary venules producing different inflammatory signals. FAK, recruits signaling proteins-PI3-K and signaling via PI3K regulates the migration and immune T-cell proliferation ,survival and differentiation.

16. Triggering of several intracellular signaling pathways linked to FAK and PI3-K activation includes Ras/Raf/MAPK pathway which can control various neutrophil functions. Once leukocytes are guided to sites of infection, inflammation ,or antigen presentation, integrins can participate in the initiation, maintainence, or termination of the immune and inflammatory responses. Disintegrins like Jarastatin(JT) were able to bind to aM�2 integrin on neutrophils and inhibit their migration. Disintegrins are tools that can be used to understand the cellular events mediated by adhesion molecules.

17. Conclusions: In FAK deficient mice developmental defect associated with impairment of cell migration and enhancement of cell adhesion. Integrin mediated c-Jun kinase activation is dependent on FAK and is involved in cell cycle progression and cell spreading and cell survival. Activation of p38 MAPK by integrins regulate collagen gene expression and cell motility. Integrin- mediated cell adhesion also stimulates RHO family members including RhoA, Rac1, and CDC42. Disintegrins ,ligands of aIIb�3 is a potent inhibitors of platelet aggregation and tumor cell metastasis, and ligands of a5 �1 and av�3 inhibits angiogenesis and induce apoptosis in cells.

18. ACKNOWLEDGEMENTS : Dr. RINEHART BIOLOGY DEPARTMENT, WKU. PRABHAVATHI and SANKARA REDDY PETLURU.