title: Role of cdc25-C phosphatase in the immediate G2 delay induced by the exogenous factors epidermal growth factor and phorbolester.
abstract: Studies on the link between cellular signalling and cell cycle control at the G2 checkpoint have shown that, in HeLa cells, epidermal growth factor (EGF) and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) rapidly inhibit the G2-M transition by preventing the key component of mitosis-promoting factor (MPF), p34cdc2, from expressing protein kinase activity. The kinase activity of active MPF is not inhibited; rather, the conversion of pre-MPF to MPF, i.e., the activating dephosphorylation of p34cdc2, at tyrosine is rapidly blocked (Barth and Kinzel, 1994, Exp. Cell Res. 212:383-388; 1995, J. Cell. Physiol., 162:44-51). The phosphatase responsible, cdc25-C, is activated by phosphorylation in mitotic cells starting at the G2-M transition in an autocatalytic loop with MPF (Hoffmann et al., 1993, EMBO J. 12:53-63). We now show that, concomitant with the prevention of MPF activation, EGF and TPA induced a reduction of the activity of cdc25-C in synchronized cultures. Furthermore, treatment of mitotic HeLa cells with TPA did not influence the kinase activity of MPF but caused a rapid decrease of the specific enzyme activity of cdc25-C, probably due to dephosphorylation of the enzyme, as indicated by reduced binding of monoclonal MPM-2 antibody specific for phosphoepitopes in M phase. Because of its inability to induce signalling during division, EGF failed to influence the activity of cdc25-C in mitotic cells. The scenario in cells late in G2 that are committed to enter mitosis may be as follows: In those cells where the signalling pathways responding to EGF as well as those responding to TPA are still open, cdc25-C is prevented by dephosphorylation from exceeding the threshold level of activity required to initiate the activation of and the autocatalytic feedback loop with p34cdc2 and to enter mitosis. Therefore, cdc25-C appears to represent part of an interface between cellular signalling and cell cycle control in G2 phase.
authors.affiliation: Department of Pathochemistry, German Cancer Research Center, Heidelberg, Federal Republic of Germany.
authors.forename: H
authors.initials: H
authors.lastname: Barth
authors.forename: I
authors.initials: I
authors.lastname: Hoffmann
authors.forename: S
authors.initials: S
authors.lastname: Klein
authors.forename: M
authors.initials: M
authors.lastname: Kaszkin
authors.forename: J
authors.initials: J
authors.lastname: Richards
authors.forename: V
authors.initials: V
authors.lastname: Kinzel
mesh_terms: D016203:CDC2 Protein Kinase / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000502:physiology; D016195:G2 Phase; D006367:HeLa Cells; D006801:Humans; D008024:Ligands; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D020687:cdc25 Phosphatases
chemical_list: D018797:Cell Cycle Proteins; D008024:Ligands; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D016203:CDC2 Protein Kinase; D010749:Phosphoprotein Phosphatases; D017027:Protein Tyrosine Phosphatases; D020687:cdc25 Phosphatases; D013755:Tetradecanoylphorbol Acetate