The role of microtubules and inositol triphosphate induced Ca2+ release in the tyrosine phosphorylation of mitogen-activated protein kinase in extracts of Xenopus laevis oocytes.
Microsomal fractions of Xenopus oocytes release preloaded 45 Ca2+ when treated with inositol triphosphate (InsP3). The effective concentration of InsP3 required for half-maximal release (EC50) is 59 nM and maximal release occurs at approximately 2 microM InsP3. Uptake and release of 45 Ca2+ are not altered by the catalytic subunit of protein kinase A, dibutyrl cyclic adenosine monophosphate, protein kinase A peptide inhibitor or nocodazole. In contrast, taxol decreases the sensitivity of the microsomal fraction to InsP3, shifting the EC50 for InsP3-induced Ca2+ release from 59 to 259 nM. In lysates of oocytes, InsP3-induced Ca2+ release causes the tyrosine phosphorylation of a 42,000 (M(r) 42k) protein identified as 42k mitogen-activated protein (MAP) kinase. InsP3-induced tyrosine phosphorylation of MAP kinase is prevented by BAPTA and taxol, but not by nocodazole. Thus, microtubule polymerisation modifies InsP3-induced Ca2+ release, thereby inhibiting phosphorylation of MAP kinase.
Duesbery
N S
NS
Department of Zoology, University of Toronto, Canada. duesbery@zoo.toronto.edu
Masui
Y
Y
D000818:Animals; D001704:Biopolymers; D002118:Calcium / Q000378:metabolism*; D004789:Enzyme Activation; D005260:Female; D007295:Inositol Phosphates / Q000502:physiology*; D008861:Microsomes / Q000378:metabolism / Q000648:ultrastructure; D008870:Microtubules / Q000187:drug effects / Q000502:physiology*; D015739:Nocodazole / Q000494:pharmacology; D009865:Oocytes / Q000201:enzymology*; D017239:Paclitaxel / Q000494:pharmacology; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism*; D014982:Xenopus laevis
D001704:Biopolymers; D007295:Inositol Phosphates; D014443:Tyrosine; D011494:Protein Kinases; D017239:Paclitaxel; D015739:Nocodazole; D002118:Calcium