Role of Autophagy in Cd(II) Carcinogenesis

  • Zhang, Zhuo (PI)
  • Shi, Xianglin (CoPI)

Grants and Contracts Details


Although the mechanism of Cd(II)-induced carcinogenesis remains to be investigated, recent studies have indicated that autophagy plays a significant role. Our preliminary studies have shown that exposure of human lung bronchial epithelial BEAS-2B cells to Cd(II) generates reactive oxygen species (ROS), which are responsible for Cd(II)-induced malignant cell transformation. We have also shown that Cd(II) is able to induce autophagy in normal BEAS-2B cells. The activation of autophagy by Cd(II) is likely to be a cell self-defense mechanism against Cd(II)-induced oxidative damage. We have shown that Cd(II)-transformed BEAS-2B cells exhibit autophagy deficiency (autophagy incompetence), resulting in accumulations of autophagosomes and p62. The p62 protein causes a constitutive activation of Nrf2, which upregulates its target antioxidant proteins, superoxide dismutase 1 (SOD1) and superoxide dismutase 2 (SOD2), and apoptotic proteins Bcl-2 and Bcl-xL, most likely due to binding of Nrf2 to the antioxidant response elements (AREs) of these two target proteins. The upregulations of these antioxidants and anti-apoptotic proteins result in decreased ROS level and development of apoptosis resistance of Cd(II)-transformed cells. The constitutively elevated p62 and Nrf2 are responsible for growth and survival of Cd(II)-transformed cells. Natural compound sulforaphane increased autophagy in normal cells exposed to Cd(II) and restored autophagy competence in Cd(II)-transformed cells. The central hypothesis of this application is that autophagy is a cell defense mechanism in Cd(II)-induced malignant cell transformation and that autophagy deficiency is responsible for tumorigenesis of Cd(II)-transformed cells. Aim 1 will investigate the protective role of autophagy in Cd(II)-induced malignant cell transformation. The hypothesis of this aim is that autophagy protects Cd(II)-induced malignant cell transformation by decreasing ROS generation through facilitating mitochondrial turnover in normal cells and that sulforaphane enhances autophagy and decreases the cell transformation. Aim 2 will demonstrate that autophagy deficiency in Cd(II)-transformed cells increases cell survival through constitutive activation of p62/Nrf2 signaling. The hypothesis of this aim is that Cd(II)-transformed cells are autophagy deficient, resulting in constitutive activations of p62/Nrf2, elevated level of antioxidants, decreased levels of ROS, increased levels of Bcl-2 and Bcl-xL, and acquisition of apoptosis resistance. Aim 3 will investigate roles of autophagy deficiency, accumulation of p62, constitutive activation of Nrf2, and apoptosis resistance in tumorigenesis of Cd(II)-transformed cells and protection by sulforaphane in vivo. The hypothesis of this aim is that autophagy deficiency in Cd(II)-transformed cells promotes tumorigenesis through accumulation of p62, constitutive activation of Nrf2, and acquisition of apoptosis resistance and that sulforaphane restores autophagy competence and inhibits tumorigenesis.
Effective start/end date12/15/178/22/19


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