In 2022, breast cancer (BC) accounted for 31% of all newly diagnosed cancers in women, making it the most prevalent female malignancy [1], [2]. As the most common type of cancer in women, BC is the leading cause of cancer-related death among women worldwide [3]. Triple-negative breast cancer (TNBC), a subtype of BC, constitutes approximately 15–20% of invasive breast cancer cases worldwide and displays heterogeneous molecular characteristics [4], [5]. Neoadjuvant chemotherapy administered preoperatively and postoperative chemotherapy are standard treatments for TNBC [6]. Although these drugs have improved disease outcomes, chemotherapy efficacy remains constrained due to primary and acquired drug resistance [7].

Doxorubicin (DOX) is an anthracycline chemotherapeutic agent that has demonstrated effectiveness in treating various malignancies, including breast cancer [8]. Doxorubicin-induced cancer cell apoptosis is considered a fundamental aspect of breast cancer chemotherapy [9], [10]. Cellular resistance to DOX generally develops in breast cancer patients with relapsed and advanced stages. However, the molecular mechanisms underlying this resistance remain incompletely understood [11]. Thus, exploring the molecular mechanism of DOX-induced tumor cell apoptosis to enhance breast cancer patients' sensitivity to DOX chemotherapy holds significant potential for improving patient treatment and survival rates.

The ubiquitin-proteasome system (UPS)-mediated protein posttranslational modification plays a critical role in protein localization, regulation, metabolism, and degradation, thereby maintaining cellular protein homeostasis [12]. Ubiquitination is implicated in various diseases, including numerous cancers, and is considered a promising therapeutic target [13]. Deubiquitinating enzymes (DUBs) can alter and reverse the ubiquitination modification of proteins [14]. Notably, DUBs are strongly linked to sensitivity to antitumor chemotherapeutic agents [15]. Ovarian tumor-associated proteases domain-containing proteins (OTUDs) belong to the deubiquitination enzyme family and play a pivotal role in the oncogenesis of solid tumors [16]. OTU domain-containing protein 1 (OTUD1), a member of the OTU protein family, significantly impacts various biological processes, including immune response, chemotherapy resistance, and cancer progression by modulating different substrates [17], [18], [19]. However, the specific role and mechanism of OTUD1 in chemotherapy resistance of TNBC remain unclear.

In this study, we examined the clinical significance of OTUD1 in BC. Our results revealed that OTUD1 expression was significantly downregulated in TNBC, and low expression of OTUD1 was closely associated with poor prognosis in BC patients. Furthermore, cell and animal experiment results demonstrated that OTUD1 inhibited TNBC cell proliferation and sensitized them to DOX. Mechanistically, P16 was identified as a novel downstream target of OTUD1 and positively regulated by OTUD1. Moreover, functional rescue experiments confirmed that OTUD1 impedes the malignant progression of TNBC by regulating P16. Consequently, our findings highlight a functional OTUD1/P16 axis in TNBC tumorigenesis, offering a promising prognostic biomarker and therapeutic target for TNBC treatment.