Abstract
Triple-negative breast cancer (TNBC) cells are often resistant to FAS (CD95)-mediated apoptosis, but the underlying molecular mechanism(s) is not fully understood yet. Notably, the expression of the type II transmembrane protein, CD74, is correlated with chemotherapy-resistant and more invasive forms of cancers via unknown mechanisms. Here, we analyzed gene expression pattern of cancer patients and/or patient-derived xenograft (PDX) models and found that mRNA and protein levels of CD74 are highly expressed in TNBC and correlated with cancer stem cells (CSCs) and epithelial-mesenchymal transition (EMT) properties. Mechanistically, we found that AKT activation is likely critical for maintaining CD74 expression and protein stability to favor its oncogenic functions. Physiologically, epidermal growth factor (EGF) along with CD74 could activate AKT signaling, likely through binding of phosphorylated AKT (S473) to CD74, whereas inhibition of AKT could impair stability of CD74. We also revealed that CD74 binds to FAS and interferes with the intrinsic signaling of FAS-mediated apoptosis. As such, selective targeting of the CD74/FAS complex using the AKT inhibitor along with the CD74-derived peptide could synergistically restore and activate FAS-mediated apoptosis. Therefore, our approach of mobilizing apoptosis pathways likely provides a rationale for TNBC treatment by targeting the CD74/FAS and CD74-AKT axes.