Effects of YAP Inhibitors and Activators on the Growth of Leukemia Cells

The Hippo signaling pathway is involved in cell proliferation through the regulation of its downstream molecule YAP. The dysregulation of Hippo signaling is associated with cancer cell proliferation. This study aimed to investigate the effects of YAP inhibitors and activators on the proliferation of human leukemia cell lines in vitro to examine whether YAP functions as a tumor suppressor or promoter. In total, six leukemia cell lines (THP-1, HL-60, and U-937, derived from acute myeloid leukemia; K-562 from chronic myeloid leukemia; and KOPT-K1 and Jurkat from T-lymphoblastic leukemia) were treated with the YAP inhibitors CA3, Peptide17, and Verteporfin or YAP activators SBP-3264 and XMU-MP-1. Colorimetric assay was conducted to assess cell growth. Immunoblotting was used to evaluate the expression of signaling proteins. Treatment with YAP activators suppressed cell growth in all cell lines, with apoptotic induction involving an increase in cleaved caspase-3. Moreover, the treatment down-regulated NOTCH1, cleaved NOTCH1, and MYC expression. Treatment with the YAP inhibitor CA3 suppressed the growth of HL-60 and KOPT-K1 cells without inducing apoptosis, accompanied by decreased MYC expression. As the other two YAP inhibitors did not suppress growth, off-target effects might contribute to inhibition by CA3. YAP activators suppressed the growth of leukemia cells through induction of apoptosis. This suggested that YAP might function as a tumor suppressor in leukemia. SBP-3264 and XMU-MP-1 could be novel candidate molecular-targeted drugs for leukemia; however, further investigations are required.