THE ROLE OF MICROTUBULES AND INOSITOL TRIPHOSPHATE INDUCED CA2-ACTIVATED PROTEIN-KINASE IN EXTRACTS OF XENOPUS-LAEVIS OOCYTES( RELEASE IN THE TYROSINE PHOSPHORYLATION OF MITOGEN)
Ns. Duesbery et Y. Masui, THE ROLE OF MICROTUBULES AND INOSITOL TRIPHOSPHATE INDUCED CA2-ACTIVATED PROTEIN-KINASE IN EXTRACTS OF XENOPUS-LAEVIS OOCYTES( RELEASE IN THE TYROSINE PHOSPHORYLATION OF MITOGEN), Zygote, 4(1), 1996, pp. 21-30
Microsomal fractions of Xenopus oocytes release preloaded Ca-45(2+) wh
en treated with inositol triphosphate (InsP(3)). The effective concent
ration of InsP(3) required for half-maximal release (EC(50)) is 59 nM
and maximal release occurs at similar to 2 mu M InsP(3). Uptake and re
lease of Ca-45(2+) are not altered by the catalytic subunit of protein
kinase A, dibutyrl cyclic adenosine monophosphate, protein kinase A p
eptide inhibitor or nocodazole. In contrast, taxol decreases the sensi
tivity of the microsomal fraction to InsP(3), shifting the EC(50) for
InsP(3)-induced Ca2+ release from 59 to 259 nM. In lysates of oocytes,
InsP(3)-induced Ca2+ release causes the tyrosine phorphorylation of a
42000 (M(r) 42k) protein identified as 42k mitogen-activated protein
(MAP) kinase. InsP(3)-induced tyrosine phosphorylation of MAP kinase i
s prevented by BAPTA and taxol, but not by nocodazole. Thus, microtubu
le polymerisation modifies InsP(3)-induced Ca2+ release, thereby inhib
iting phosphorylation of MAP kinase.