Noncanonical UPR factor CREB3L2 drives immune evasion of triple-negative breast cancer through Hedgehog pathway modulation in T cells.

The unfolded protein response (UPR) pathway is crucial for tumorigenesis, mainly by regulating cancer cell stress responses and survival. However, whether UPR factors facilitate cell-cell communication between cancer cells and immune cells to drive cancer progression remains unclear. We found that adenosine 3',5'-monophosphate response element-binding protein 3-like protein 2 (CREB3L2), a noncanonical UPR factor, is overexpressed and activated in triple-negative breast cancer, where its cleavage releases a C-terminal fragment that activates the Hedgehog pathway in neighboring CD8+ T cells. The enhanced Hedgehog pathway represses CD8+ T cell activation and inhibits its cytotoxic effects. Consequently, overexpression of CREB3L2 not only promotes tumor growth but also causes resistance to immune checkpoint blockade (ICB). Inhibition of the Hedgehog pathway impedes the growth of CREB3L2-overexpressed tumors and sensitizes them to ICB therapy. In summary, we identified a previously unidentified mechanism by which the UPR pathway dictates cross-talk between cancer cells and immune cells, providing important anticancer therapeutic opportunities.