Interaction of p38 and Sp1 in a mechanical force-induced, beta 1 integrin-mediated transcriptional circuit that regulates the actin-binding protein filamin-A.
Connective tissue cells in mechanically active environments survive applied physical forces by modifying actin cytoskeletal structures that stabilize cell membranes. In fibroblasts, tensile forces induce the expression of filamin-A, a mechanoprotective actin-binding protein, but the mechanisms and protein interactions by which force activates filamin-A transcription are not defined. We found that in fibroblasts, application of tensile forces through collagen-coated magnetite beads to cell surface beta(1) integrins induced filamin-A expression. This induction required actin filaments and selective activation of the p38 mitogen-activated protein kinase. Force promoted the redistribution of p38 to the integrin/bead locus and the nucleus as well as enhanced binding of the transcription factor Sp1 to proximal, regulatory domains of the filamin-A promoter. Force application increased association of Sp1 with p38 and phosphorylation of Sp1. Transcriptional activation of filamin-A in force-treated fibroblasts was subsequently mediated by Sp1-binding sites on the filamin-A promoter. These results provide evidence for a mechanically coupled transcriptional circuit that originates at the magnetite bead/integrin locus, activates p38, tethers p38 to actin filaments, promotes binding of p38 to Sp1 in the nucleus, and induces filamin-A expression.
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003285:Contractile Proteins / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000378:metabolism; D064448:Filamins; D006801:Humans; D019012:Integrin beta1 / Q000378:metabolism*; D048669:MAP Kinase Kinase 6; D051379:Mice; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012313:RNA / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D013314:Stress, Mechanical; D013997:Time Factors; D014162:Transfection; D014466:Ultraviolet Rays; D048051:p38 Mitogen-Activated Protein Kinases
D003285:Contractile Proteins; D064448:Filamins; D019012:Integrin beta1; D008840:Microfilament Proteins; D016329:Sp1 Transcription Factor; D012313:RNA; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048669:MAP Kinase Kinase 6; C482566:MAP2K6 protein, human; C482567:Map2k6 protein, mouse