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Cell killing by iHAP and DT-061 is not through PP2A-B56 activation

ABSTRACT: PP2A is an abundant ser/thr protein phosphatase that act as a tumor suppressor by antagonizing multiple oncogenic kinases. For this reason, compounds able to activate PP2A holoenzymes are attractive anticancer agents. DT-061 and iHAP are phenothiazine derivatives that have recently been claimed to activate specific PP2A-B56 complexes to mediate cell killing. Here we show that iHAP and DT-061 do not activate PP2A-B56 complexes in vitro and that CRISPR removal of B56 regulatory subunits does not affect cellular toxicity of the compounds. Through genome-wide CRISPR screens we uncover the cell killing mechanism of iHAP and DT-061. We find that iHAP is a microtubule poison and removal of mitotic regulators causes hypersensitivity. In contrast, DT-061 disrupts both Golgi and ER consistent with an impact on cellular lipid composition. Indeed, we directly visualize DT-061 in cytoplasmic granules that co-localize with Golgi markers shortly after addition of the compound. Our work uncovers that well known side-effects of phenothiazine derived compounds cause cell killing by iHAP and DT-061 arguing that these compounds cannot be used for dissecting PP2A biology.

INSTRUMENT(S): Orbitrap Fusion Lumos, Q Exactive Plus

ORGANISM(S): Homo Sapiens (ncbitaxon:9606)

SUBMITTER: Arminja Kettenbach

PROVIDER: MSV000087616 | MassIVE | Fri Jun 11 14:26:00 BST 2021

SECONDARY ACCESSION(S): PXD026666

REPOSITORIES: MassIVE

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