SMAD3 and chronic myelogenous leukemia, BCR-ABL1 positive: Although treatment of LT-CML stem cells with Ly364947, a TGF-β type I receptor kinase inhibitor, blocked phosphorylation of Smad3 at both Ser423/425 and Ser208 (Fig. 4a–c), inhibition of p38MAPK with SB203580 decreased only Smad3–Ser208 phosphorylation (Fig. 4a,c).