SMAD3 and chronic myelogenous leukemia, BCR-ABL1 positive: Cyclin-dependent kinases 8/9 (CDK8/9) also reportedly promote agonist-induced Smad3–Ser208 phosphorylation38, but we found that treatment of LT-CML stem cells in vitro with the CDK9 inhibitor Flavopiridol did not attenuate Smad3–Ser208 phosphorylation (Supplementary Fig. 10).