Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.12.2 (MEK)
 18,161 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previously, we have shown that the addition of a constitutively-active mitogen-activated protein kinase kinase protein (MAPKK = MEK) to cycling Xenopus egg extracts activates the p42MAPK pathway, leading to a G2 or M-phase cell cycle arrest. The stage of the arrest depends on the timing of p42MAPK activation. If p42MAPK is activated prior to M-phase, or after exit from M-phase, the extract is arrested in G2. If p42MAPK is activated during entry into M-phase, the extract is arrested in M-phase. In this study, we show that the addition of recombinant Mos protein (which directly phosphorylates and activates MEK) to cycling egg extracts has the same effect as those described for MEK. The addition of Mos to the extract at the start of incubation leads to a G2 arrest with large interphase nuclei with intact nuclear envelopes. If Mos is added at later times, however, the activation of p42MAPK leads to an M-phase arrest with condensed chromosomes and mitotic arrays of microtubules. Moreover, the extent of M-phase specific phosphorylations is shown by the sustained presence of phosphoproteins that are detected by the monoclonal antibody MPM-2. Unexpectedly, in certain M-phase arrested extracts, histone H1 kinase activity levels reach a peak on entry into M-phase but then fall abruptly to interphase levels. When these extracts are analyzed by immunoblotting, Cyclin B2 is destroyed in those samples containing low maturation promoting factor activity (MPF, cyclin B/Cdc2), yet chromosomes remain condensed with associated mitotic arrays of microtubules and M-phase-specific phosphorylations are sustained. These results suggest that although MPF is required for entry into M-phase, once established, M-phase can be maintained by the p42MAPK pathway after the proteolysis of mitotic cyclins.
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PMID:Mos-induced p42 mitogen-activated protein kinase activation stabilizes M-phase in Xenopus egg extracts after cyclin destruction. 1006 1

In full-grown Xenopus oocytes, cell-cycle regulators and an inactive form of maturation/M phase promoting factor (pre-MPF) are stored ready to bring about a specific cell cycle for oocyte maturation. We examined the expression pattern of these cell-cycle regulators as well as pre-MPF formation during oogenesis. Cdc2 and Cyclin B2 were already present in stage I oocytes and pre-MPF formation was also detected in stage I oocytes. Some negative regulators of MPF, Myt1 and Chk1, were synthesized early in oogenesis. In contrast, positive regulators of MPF, MEK, MAPK and Cdc25C, were mainly synthesized late in oogenesis. Northern blotting analysis suggested that the synthesis of these cell-cycle regulators was controlled by translation.
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PMID:Expression of cell-cycle regulators during Xenopus oogenesis. 1271 44