title: Type I collagen structure regulates cell morphology and EGF signaling in primary rat hepatocytes through cAMP-dependent protein kinase A.
abstract: Adhesion to type 1 collagen elicits different responses dependent on whether the collagen is in fibrillar (gel) or monomeric form (film). Hepatocytes adherent to collagen film spread and proliferate, whereas those adherent to collagen gel remain rounded and growth arrested. To explore the role of potential intracellular inhibitory signals responsible for collagen gel-mediated growth arrest, cAMP-dependent protein kinase A (PKA) was examined in hepatocytes adherent to collagen film or gel. PKA activity was higher in hepatocytes on collagen gel than on film during G1 of the hepatocyte cell cycle. Inhibition of PKA using H89 increased cell spreading on collagen gel in an EGF-dependent manner, whereas activation of PKA using 8-Br-cAMP decreased cell spreading on collagen film. PKA inhibition also restored ERK activation, cyclin D1 expression and G1-S progression on collagen gel, but had no effect on cells adherent to collagen film. Analysis of EGF receptor phosphorylation revealed that adhesion to collagen gel alters tyrosine phosphorylation of the EGF receptor, leading to reduced phosphorylation of tyrosine residue 845, which was increased by inhibition of PKA. These results demonstrate that fibrillar type 1 collagen can actively disrupt cell cycle progression by inhibiting specific signals from the EGF receptor through a PKA-dependent pathway.
authors.affiliation: Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, MN 55455, USA.
authors.forename: John
authors.initials: J
authors.lastname: Fassett
authors.forename: Diane
authors.initials: D
authors.lastname: Tobolt
authors.forename: Linda K
authors.initials: LK
authors.lastname: Hansen
mesh_terms: D000818:Animals; D002448:Cell Adhesion; D048430:Cell Shape; D002478:Cells, Cultured; D024042:Collagen Type I / Q000737:chemistry* / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019938:Cyclin D1 / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D004815:Epidermal Growth Factor / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism; D005786:Gene Expression Regulation; D022781:Hepatocytes / Q000378:metabolism*; D008855:Microscopy, Electron, Scanning; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D019000:Phosphotyrosine / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D024042:Collagen Type I; D047428:Protein Kinase Inhibitors; D019938:Cyclin D1; D019000:Phosphotyrosine; D004815:Epidermal Growth Factor; D004247:DNA; D066246:ErbB Receptors; D017868:Cyclic AMP-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3