Radicicol-mediated inhibition of Bcr-Abl in K562 cells induced p38-MAPK dependent erythroid differentiation and PU.1 down-regulation

摘要

Constitutive tyrosine kinase activity of the breakpoint cluster region (Bcr)-Abl fusion protein is characteristic ofchronic myelogenous leukemia (CML). As resistance against Imatinib a Bcr-abl inhibitor used in CML, was described, Heatshock protein (Hsp90) became an alternative target as inhibition of Bcr-Abl-Hsp90 complex leads to proliferation arrest. Here,we used natural product Radicicol (Rad), a macrocyclic antifungal, as an Hsp90 inhibitor to investigate the effect of Bcr-Ablinactivation on erythroid gene expression and subsequently on the transcription factors involved in their regulation. We showedthat all erythroid genes studied were over-expressed after Rad treatment while Bcr-Abl expression was inhibited. Specifictranscription factor NF-E2 was induced in Rad-treated cells as well as GATA-1 cofactors Friend of GATA (FOG)! and SPI,whereas PU.1 was downregulated. Moreover, p38 mitogen activated protein kinase (MAPK) inhibition prevented Rad-mediateddifferentiation of K562 in correlation with decreased -y-globin expression and suppression of Rad-mediated inhibition of PU. I.In conclusion, our results show that Radicicol leads to Bcr-Abl inactivation via Hsp90 inhibition inducing reactivation of theerythroid program in K562 cells.