Targeting the PRSS3-PAR2-ERK1/2 Axis Inhibits Malignancy and Regulates Chemosensitivity and Resistance through Ferroptosis in Breast Cancer.

Breast cancer (BRCA) heterogeneity contributes to malignancy progression and therapeutic resistance, yet the role of proteases in this process remains elucidated. In this study, we identified serine protease 3 (PRSS3), an indispensable member of the serine protease family, as an oncogenic driver in BRCA through its ability to inhibit ferroptosis. Immunohistochemical analysis of 90 paired BRCA tissue samples revealed high PRSS3 expression in 76.47% of HER2-positive subtypes, 87.30% of luminal A/B cases, and 90% of TNBC tumors. Elevated PRSS3 levels were significantly associated with advanced clinical stages, lymph node metastasis, and increased Ki-67 expression. Transcriptomic analysis integrated with functional studies using gain- and loss-of-function BRCA cell models demonstrated that PRSS3 promotes tumor progression mainly attributed to its splicing isoform 1 (PRSS3-V1), which interacted with protease-activated receptor 2 (PAR2) and enhances ERK1/2 phosphorylation both in vitro and in vivo. Silencing PRSS3 significantly induced cell cycle arrest and ferroptotic cell death via multiple mechanisms, including increased levels of malondialdehyde and lactate dehydrogenase levels, accumulation of labile iron via regulation of transferrin receptor 1 (TfR1) and ferritin heavy chain 1 and reactive oxygen species, mitochondrial membrane dysfunction, and activation of NLRP3 inflammasome. These effects were mediated by downregulation of SLC7A11 and GPX4, two key regulators of ferroptosis, resulting in increased lipid peroxidation. Treatment with the PAR2 agonist SLIGKV-NH2 or the TfR1 inhibitor ferrostatin II attenuated these effects. Furthermore, PRSS3 knockdown improved chemosensitivity to paclitaxel and doxorubicin and alleviated resistance to trastuzumab in BRCA cells. Our findings uncover a novel PRSS3-mediated mechanism underlying ferroptotic evasion in BRCA. Targeting the PRSS3-PAR2-ERK1/2 axis may offer therapeutic potential, with PRSS3-V1 serving as a valuable biomarker for BRCA subtype stratification.