Fa. Suprynowicz et al., CA2-KINASE IN PERMEABILIZED SEA-URCHIN EMBRYOS( TRIGGERS PREMATURE INACTIVATION OF THE CDC2 PROTEIN), Proceedings of the National Academy of Sciences of the United Statesof America, 91(13), 1994, pp. 6176-6180
Exit from mitosis requires inactivation of the cyclin B-p34(cdc2) prot
ein kinase complex. Since increased cytosolic Ca2+ has been implicated
as a potential trigger of mitotic progression, we directly tested the
possibility that Ca2+ triggers the pathway responsible for inactivati
ng the cdc2 kinase, using sea urchin embryos permeabilized at various
stages of the cell cycle. In cells permeabilized during late interphas
e and prophase, micromolar Ca2+ induced premature inactivation of the
cdc2 kinase without affecting the absolute amount of p34(cdc2) protein
. Inactivation was selective for the cdc2 kinase, as elevated Ca2+ had
no effect on cAMP-dependent protein kinase activity. Premature cdc2 k
inase inactivation did not require cyclin B destruction, but did coinc
ide with the dissociation of cyclin B-q34(cdc2) complexes. In cells pe
rmeabilized during prometaphase and metaphase, cdc2 kinase inactivatio
n was Ca2+-independent, presumably because at these later times the in
activating pathway had been enabled prior to permeabilization. This wo
rk provides evidence that Ca2+ is the physiological trigger enabling c
dc2 kinase inactivation during mitosis.