HSP90 associates with and stabilizes STK33. (a) Anti-Flag IPs were performed with KRAS WT BT-20 and KRAS mutant MDA-MB-231 breast cancer cell lines stably transduced with empty vector (EV), N-terminally Flag-tagged STK33 (Flag-STK33), or C-terminally Flag-tagged STK33 (STK33-Flag), and the resulting protein complexes were separated by PAGE and stained with Coomassie. Peptides isolated from each lane were analyzed by mass spectrometry. The STK33 band is indicated by an asterisk. SM, size marker. (b) Number of peptides representing proteins highly enriched in STK33-containing IPs. (c) Anti-HA IPs were performed with MDA-MB-231 cells stably transduced with empty vector (EV), N-terminally HA-tagged STK33 (HA-STK33), or C-terminally HA-tagged STK33 (STK33-HA), and immunoblots were probed with antibodies against HSP90A/B, CDC37, and HA. One of three independent experiments is shown. (d) Protein expression of HSP90A, HSP90B, STK33, and cleaved PARP in lung (NCI-H520, A549) and colon (Caco-2, HCT-116) carcinoma cells transduced with a nontargeting control shRNA or a shRNA-targeting HSP90A or HSP90B. One of two independent experiments is shown.