TGFB1 and chronic myelogenous leukemia, BCR-ABL1 positive: Furthermore, TGF-β stimulates the expression of plasminogen activator inhibitor-1 (PAI-1), a significant physiologic serine protease inhibitor (serpin) of the fibrinolytic network, leading to decrease membrane type-1 metalloprotease (MT1-MMP) activity and mobility of CML LSCs.