Upregulation of Bcl-x and Bfl-1 as a potential mechanism of chemoresistance, which can be overcome by NF-kappaB inhibition.

In A549 human lung adenocarcinoma cells, we found that TNF-alpha and several commonly used chemotherapeutic agents upregulated the expression of Bcl-x and/or Bfl-1/A1 through an NF-kappaB-dependent pathway. While parental A549 cells were resistant to the cytotoxic effects of both TNF-alpha and chemotherapy agents, NF-kappaB-blocked A549 cells were sensitized to both. Expression of either Bcl-x or Bfl-1/A1 in the NF-kappaB-deficient cells at physiological levels provided differential protection against TNF-alpha and chemotherapeutic treatment. These studies provide a potential mechanism for the phenomenon of chemotherapy-induced chemoresistance, and also reveal a potential strategy by which chemoresistance can be overcome.