Ligand-specific, transient interaction between integrins and calreticulin during cell adhesion to extracellular matrix proteins is dependent upon phosphorylation/dephosphorylation events.
As transmembrane heterodimers, integrins bind to both extracellular ligands and intracellular proteins. We are currently investigating the interaction between integrins and the intracellular protein calreticulin. A prostatic carcinoma cell line (PC-3) was used to demonstrate that calreticulin can be found in the alpha3 immunoprecipitates of cells plated on collagen type IV, but not when plated on vitronectin. Conversely, alphav immunoprecipitates contained calreticulin only when cells were plated on vitronectin, i. e. not when plated on collagen IV. The interactions between these integrins and calreticulin were independent of actin cytoskeleton assembly and were transient, being maximal approx. 10-30 min after the cells came into contact with the substrates prior to complete cell spreading and formation of firm adhesive contacts. We demonstrate that okadaic acid, an inhibitor of intracellular serine/threonine protein phosphatases, inhibited the alpha3beta1-mediated adhesion of PC-3 cells to collagen IV and the alpha2beta1-mediated attachment of Jurkat cells to collagen I. This inhibition by okadaic acid was accompanied by inhibition of the ligand-specific interaction of calreticulin with the respective integrins in the two cell types. Additionally, we found that pharmacological inhibition of mitogen-activated protein kinase kinase (MEK) resulted in prolongation of the calreticulin-integrin interaction, and enhancement of PC-3 cell attachment to collagen IV. We conclude that calreticulin interacts transiently with integrins during cell attachment and spreading. This interaction depends on receptor occupation, is ligand-specific, and can be modulated by protein phosphatase and MEK activity.
Coppolino
M G
MG
Department of Cell Biology, Hospital for Sick Children, 555 University Ave., Toronto, ON, Canada M5G 1X8.
Dedhar
S
S
D000199:Actins / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D037282:Calreticulin; D002448:Cell Adhesion / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D003094:Collagen / Q000378:metabolism; D015638:Cytochalasin D / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000378:metabolism*; D006801:Humans; D039201:Integrin alpha3beta1; D016023:Integrins / Q000378:metabolism*; D019169:Jurkat Cells; D008024:Ligands; D048369:MAP Kinase Kinase 1; D008297:Male; D020929:Mitogen-Activated Protein Kinase Kinases; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011471:Prostatic Neoplasms; D011485:Protein Binding / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D038981:Receptors, Collagen; D012261:Ribonucleoproteins / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D019096:Vitronectin / Q000378:metabolism
D000199:Actins; D002135:Calcium-Binding Proteins; D037282:Calreticulin; D016326:Extracellular Matrix Proteins; D039201:Integrin alpha3beta1; D016023:Integrins; D008024:Ligands; D038981:Receptors, Collagen; D012261:Ribonucleoproteins; D019096:Vitronectin; D019319:Okadaic Acid; D015638:Cytochalasin D; D003094:Collagen; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; D010749:Phosphoprotein Phosphatases