Effect of synthetic peptides representing the hypervariable region of p21ras on Xenopus laevis oocyte maturation.
Ontology highlight
ABSTRACT:
SUBMITTER: Soto-Cruz I
PROVIDER: S-EPMC1136474 | biostudies-other | 1995 Feb
REPOSITORIES: biostudies-other
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Project description:Many years ago, asbestos fibers were banned and replaced by synthetic vitreous fibers because of their carcinogenicity. However, the toxicity of the latter fibers is still under debate, especially when it concerns the early fiber interactions with biological cell membranes. Here, we aimed to investigate the effects of a synthetic vitreous fiber named FAV173 on the Xenopus laevis oocyte membrane, the cell model we have already used to characterize the effect of crocidolite asbestos fiber exposure. Using an electrophysiological approach, we found that, similarly to crocidolite asbestos, FAV173 was able to stimulate a chloride outward current evoked by step membrane depolarizations, that was blocked by the potent and specific TMEM16A channel antagonist Ani9. Exposure to FAV173 fibers also altered the oocyte cell membrane microvilli morphology similarly to crocidolite fibers, most likely as a consequence of the TMEM16A protein interaction with actin. However, FAV173 only partially mimicked the crocidolite fibers effects, even at higher fiber suspension concentrations. As expected, the crocidolite fibers' effect was more similar to that induced by the co-treatment with (Fe3+ + H2O2), since the iron content of asbestos fibers is known to trigger reactive oxygen species (ROS) production. Taken together, our findings suggest that FAV173 may be less harmful that crocidolite but not ineffective in altering cell membrane properties.
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Project description:Greatwall kinase has been identified as a key element in M phase initiation and maintenance in Drosophila, Xenopus oocytes/eggs, and mammalian cells. In M phase, Greatwall phosphorylates endosulfine and related proteins that bind to and inhibit protein phosphatase 2A/B55, the principal phosphatase for Cdk-phosphorylated substrates. We show that Greatwall binds active PP2A/B55 in G2 phase oocytes but dissociates from it when progesterone-treated oocytes reach M phase. This dissociation does not require Greatwall kinase activity or phosphorylation at T748 in the presumptive T loop of the kinase. A mutant K71M Greatwall, also known as Scant in Drosophila, induces M phase in the absence of progesterone when expressed in oocytes, despite its reduced stability and elevated degradation by the proteasome. M phase induction by Scant Greatwall requires protein synthesis but is not associated with altered binding or release of PP2A/B55 as compared to wild-type Greatwall. However, in vitro studies with Greatwall proteins purified from interphase cells indicate that Scant, but not wild-type Greatwall, has low but detectable activity against endosulfine. These results demonstrate progesterone-dependent regulation of the PP2A/B55-Greatwall interaction during oocyte maturation and suggest that the cognate Scant Greatwall mutation has sufficient constitutive kinase activity to promote M phase in Xenopus oocytes.
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