title: Activation of S6 kinase by repeated cycles of stretching and relaxation in rat glomerular mesangial cells. Evidence for involvement of protein kinase C.
abstract: Quiescent rat glomerular mesangial cells were exposed to repeated cycles of stretching and relaxation, and the effects on the rate of collagen production, proliferation, and S6 kinase activity were investigated. Stretch/relaxation induced increases in production of both collagen and non-collagenous proteins. Proliferation of mesangial cells was stimulated by stretch/relaxation and epidermal growth factor, but not by angiotensin II; however, administration of angiotensin II augmented stretch/relaxation-induced cell proliferation. Cytosolic S6 kinase activity was stimulated by stretch/relaxation, angiotensin II, epidermal growth factor, or phorbol 12-myristate 13-acetate. The increased S6 kinase activity was detectable within 30 min after initiation of stretch/relaxation and was blocked by either inhibitors of protein kinase C or prior down-regulation of protein kinase C following prolonged incubation with phorbol 12-myristate 13-acetate. Both translocation of protein kinase C from the cytosolic to the membrane fraction and phosphorylation of an endogenous 80-kDa protein were observed within 5 min of initiation of stretch/relaxation. These results demonstrate that in mesangial cells, mechanical factors alone can induce increases in production of collagen and non-collagenous proteins and in cell proliferation. The observation that stretch/relaxation induced stimulation of S6 kinase activity through protein kinase C-dependent mechanisms suggests that activation of protein kinase C may be a key event in initiating adaptive responses of mesangial cells to increased workload.
authors.affiliation: Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
authors.forename: T
authors.initials: T
authors.lastname: Homma
authors.forename: Y
authors.initials: Y
authors.lastname: Akai
authors.forename: K D
authors.initials: KD
authors.lastname: Burns
authors.forename: R C
authors.initials: RC
authors.lastname: Harris
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D003094:Collagen / Q000096:biosynthesis*; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005920:Glomerular Mesangium / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008970:Molecular Weight; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D011392:Proline / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051381:Rats; D038601:Ribosomal Protein S6; D019893:Ribosomal Protein S6 Kinases; D012269:Ribosomal Proteins / Q000302:isolation & purification / Q000378:metabolism; D013314:Stress, Mechanical; D014316:Tritium
chemical_list: D010761:Phosphorus Radioisotopes; D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins; D014316:Tritium; D000804:Angiotensin II; D004815:Epidermal Growth Factor; D000255:Adenosine Triphosphate; D003094:Collagen; D011392:Proline; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D011493:Protein Kinase C