We have determined a functional link to the inverse expression of SETDB1 and FosB following anticancer drug treatment. Doxorubicin treatment caused decreased SETDB1 expression and FosB overexpression both at the mRNA and protein levels. The decreased HMTase activity of SETDB1 coincided with altered occupancy across the promoter region of the FosB gene. SETDB1 overexpression decreased the luciferase reporter activity containing the FosB promoter region, but siSETDB1 increased the luciferase reporter activity, suggesting that SETDB1 directly and negatively regulated FosB expression. In addition, MEK inhibitor (PD98059) blocked the SETDB1 regulation of the FosB promoter activity via ERK2 activation during doxorubicin treatment. A microscopic analysis reveals that FosB expression was observed in living cells in spite of doxorubicin treatment. Ectopic FosB/Delta FosB expression increased the number of colonies and the migration of A549 cells compared to that in control. These results suggest that the ERK2-SETDB1-FosB signaling pathway might have an anti-therapeutic regulatory mechanism that increases the transformation and migration activity of cancer cells during anticancer drug treatment. (C) 2017 Elsevier Inc. All rights reserved.