Arsenic and benzo[α]pyrene (BaP) are widespread carcinogens and important etiology factors for lung cancer. Moreover, arsenic and BaP co-exposure displays a significantly stronger effect in inducing lung cancer than arsenic or BaP exposure alone. This study was performed to investigate the basic mechanism of the synergistic carcinogenic effect of arsenic and BaP co-exposure. It was found that integrin α4 (ITGA4) expression levels are significantly up-regulated and the Hedgehog pathway is highly activated in arsenic plus BaP co-exposure-transformed human bronchial epithelial cells. Either ITGA4 downregulation or Hedgehog pathway inhibition in the co-exposure-transformed cells significantly reduced their cancer stem cell (CSC)-like property and tumorigenicity. It was determined that ITGA4 downregulation leads to the inhibition of the Hedgehog pathway activation, which is achieved by increasing suppressor of fused (SUFU) protein stability through reducing the PI3K/Akt signaling. Moreover, stably overexpressing SUFU in the co-exposure-transformed cells significantly reduces their CSC-like property and tumorigenicity. These findings indicate that ITGA4 up-regulation activates the Hedgehog pathway to enhance the CSC-like property and tumorigenicity of arsenic and BaP co-exposure-transformed cells, offering new mechanistic insight for the synergistic carcinogenic effect of arsenic and BaP co-exposure.Copyright © 2020. Published by Elsevier B.V.