title: alpha-Thrombin-induced early mitogenic signalling events and G0 to S-phase transition of fibroblasts require continual external stimulation.
abstract: In resting Chinese hamster fibroblasts (CCL39) alpha-thrombin rapidly stimulates several biochemical events implicated in the mitogenic response, including the breakdown of inositol phospholipids, activation of a plasma membrane Na+/H+ antiporter, phosphorylation of ribosomal protein S6 and increased expression of the proto-oncogene c-myc. Complete removal of the growth factor during cellular G0/G1 transit precludes the re-initiation of DNA synthesis. The present study was designed to examine the fate of alpha-thrombin-activated early events following growth factor inactivation. In cells stimulated for 30 min with alpha-thrombin, neutralization of the growth factor results in: (i) immediate arrest of inositol phosphate formation, (ii) rapid inactivation of Na+/H+ exchange, (iii) deactivation of the S6 phosphorylating system and (iv) strong reduction of c-myc mRNA level. Our findings that commitment for DNA synthesis as well as persistent activation of 'early' cellular events requires continual growth factor stimulation suggest that: (i) growth factor-induced transmembrane signals have a short life and (ii) the generation of these signals during the 8 h of the pre-replicative phase is required for G0-arrested cells to enter the S phase.
mesh_terms: D000818:Animals; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D006224:Cricetinae; D003412:Cricetulus; D004261:DNA Replication / Q000187:drug effects*; D005347:Fibroblasts / Q000166:cytology; D006629:Hirudins / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007399:Interphase / Q000187:drug effects*; D007700:Kinetics; D009693:Nucleic Acid Hybridization; D009857:Oncogenes / Q000187:drug effects; D010716:Phosphatidylinositols / Q000378:metabolism; D010766:Phosphorylation; D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013917:Thrombin / Q000494:pharmacology*
chemical_list: D006629:Hirudins; D010716:Phosphatidylinositols; D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins; D012964:Sodium; D013917:Thrombin