Abstract
Plasma membrane carboxypeptidase-D (CPD) hydrolyzes C-terminal arginine (Arg) from extracellular substrates, and Arg is converted into nitric oxide (NO) in the cell. CPD is upregulated by prolactin (PRL) and androgens in breast cancer (BCa) cells, increasing NO production to promote cell survival. EDD E3 ubiquitin ligase, upregulated by PRL/androgens, is implicated in TORC1 signaling. This study investigated CPD and EDD in triple-negative (TNBC) and HER2+ BCa. Kaplan-Meier analysis showed a negative correlation between CPD or EDD mRNA expression in TNBC patients and relapse-free survival. Immunohistochemistry showed that benign and malignant breast tissues stained abundantly for the PRL receptor (PRLR) and androgen receptor (AR). CPD and EDD staining were elevated in TNBC and HER2+ tumors as compared to benign tissues. In TNBC/HER2+ cell lines, CPD and EDD protein expression were upregulated by PRL or synthetic androgen methyltrienolone (R1881) at 3-6 h. PRL/R1881-induced CPD in TNBC and HER2+ cells increased intracellular NO production, which was abolished by PRLR antagonist ∆1-9-G129R-hPRL and AR antagonist flutamide. In turn, treatment with NO increased viability and decreased apoptosis in Arg-deprived TNBC cells. Cell viability and apoptosis were also affected in HER2+ cells with CPD knockdown. Lastly, EDD knockdown decreased PRL/R1881-induced phosphorylation of initiation factor 4E binding protein-1 and decreased 4E release in TNBC cells. In summary, PRL/R1881-induced CPD promotes TNBC/HER2+ cell survival through production of NO, and EDD promotes TNBC cell survival by TORC1 activation. This study implicates CPD and EDD as useful therapeutic targets for TNBC/HER2+ tumors, and suggests that PRLR and AR blockade are also beneficial to these patients.