Pharmacologic induction of PP2A activity inhibits spontaneous NK cell–mediated cytotoxicity and granzyme B expression. (A) Primary human NK cells were first incubated (18 hours) with medium containing either DMSO vehicle control or 40μM 1,9-dideoxy-forskolin and then used as effector cells in a ⁵¹Cr release assay using K562 tumor cell targets (n = 4). *P < .03. Cell pellets from DMSO or 1,9-dideoxy-forskolin-treated cells were collected for quantification of granzyme B protein by Western blot (B) and granzyme B transcript by real-time RT-PCR (C; n = 3). **P < .03. Each experiment is representative of at least 3 performed with similar results.