The requirements for G1 checkpoint progression of Trypanosoma brucei S 427 clone 1.
Trypanosoma brucei S 427 clone 1 accumulated in G1 when incubated under growth-limiting conditions. Further incubation of the G1-restricted organisms in medium containing 10% fetal bovine serum (FBS) and 2 mM hydroxyurea resulted in their reversible arrest after a G1 checkpoint beyond which serum was not required for progress into and through S. Progress of the G1-restricted T. brucei through the G1 checkpoint was linear and required continuous incubation with exogenous serum growth factors. These were principally low and high density lipoproteins; both lipoproteins triggered G1 progression in a dose- and time-dependent manner whilst their removal by immunoaffinity chromatography severely reduced the capacity of FBS to stimulate G1 progression. Serum-induced progress of T. brucei through G1 was Ca(2+)-independent, but required gene transcription, protein synthesis, and continuous kinase activity that was inhibited by tyrphostin 51 and DAPH 1 which typically inhibit epidermal growth factor receptor protein tyrosine kinase activity. The tyrphostin 51-sensitive catalytic activity was not required for T. brucei protein synthesis, glycolysis, or S phase progression but was required for tyrosine phosphorylation of several polypeptides, none of which was specifically associated with serum-induced G1 progression.
Morgan
G A
GA
Department of Microbiology, Ohio State University, Columbus 43210, USA.
Hamilton
E A
EA
Black
S J
SJ
D000818:Animals; D002417:Cattle; D003470:Culture Media; D016054:DNA, Protozoan / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016193:G1 Phase / Q000187:drug effects / Q000502:physiology*; D006918:Hydroxyurea / Q000494:pharmacology; D007700:Kinetics; D008074:Lipoproteins / Q000494:pharmacology; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D047428:Protein Kinase Inhibitors; D015800:Protozoan Proteins / Q000096:biosynthesis; D019289:Pyruvic Acid / Q000378:metabolism; D016196:S Phase / Q000187:drug effects / Q000502:physiology; D014346:Trypanosoma brucei brucei / Q000166:cytology* / Q000254:growth & development / Q000378:metabolism
D003470:Culture Media; D016054:DNA, Protozoan; D004791:Enzyme Inhibitors; D008074:Lipoproteins; D019384:Nucleic Acid Synthesis Inhibitors; D047428:Protein Kinase Inhibitors; D015800:Protozoan Proteins; D019289:Pyruvic Acid; D006918:Hydroxyurea