Okadaic acid (OA)-resistant variants of Chinese hamster ovary cells, clones CHO/OAR6-6 and CHO/OAR2-3, were isolated from a CHO-K1 culture. These variant cells were 17- to 26-fold more resistant to OA than the parental cells. The phosphorylase phosphatase activity of the variant cell extracts was 2- to 4-fold more resistant to OA than that of the parental cells in the presence of inhibitor 2, a specific inhibitor of type 1 protein serine/threonine phosphatase (PP1). Nucleotide sequencing of PP2Aα (an isotype of PP2A catalytic subunit) cDNA demonstrated that both variants have a T → G transversion at the first base of codon 269 (805 nt), which results in substitution of glycine for cysteine. We expressed in COS-1 cells a mutant PP2Aα tagged with the influenza hemagglutinin epitope. The recombinant mutant PP2Aα protein immunoprecipitated with an anti-influenza hemagglutinin antibody was more resistant than the wild type to OA, their IC50 values being 0.65 nM and 0.15 nM, and their IC80 values being 4.0 nM and 0.45 nM, respectively. The cysteine at residue 269 present only in highly OA-sensitive protein serine/threonine phosphatase catalytic subunit isozymes, PP2Aα, PP2Aβ, and PPX, is suggested to be involved in the binding of OA. CHO/OAR6- 6 and CHO/OAR2-3 cells also overexpressed the P-glycoprotein, and the efflux of OA was more rapid. It is suggested that the PP2Aα mutation in cooperation with a high level of P-glycoprotein makes the CHO-K1 variants highly resistant to OA.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Sep 27 1994|
- protein serine
- threonine phosphatase
ASJC Scopus subject areas