Peptidylprolyl isomerase D circular RNA sensitizes breast cancer to trastuzumab through remodeling HER2 N4-acetylcytidine modification.

Human epidermal growth factor receptor 2 (HER2) overexpression and activation are crucial for trastuzumab resistance in HER2-positive breast cancer; however, the potential regulatory mechanism of HER2 is still largely undetermined. In this study, a novel circular RNA derived from peptidylprolyl isomerase D (PPID) is identified as a negative regulator of trastuzumab resistance. Circ-PPID is highly stable and significantly downregulated in trastuzumab-resistant cells and tissues. Restoration of circ-PPID markedly enhances HER2-positive breast cell sensitivity to trastuzumab in vitro and in vivo. Circ-PPID directly binds to N-acetyltransferase 10 (NAT10) in the nucleus and blocks the interaction between NAT10 and HER2 mRNA, reducing N4-acetylcytidine (ac4C) modification on HER2 exon 25, leading to HER2 mRNA decay. Intriguingly, the subcellular localization of circ-PPID differs between trastuzumab-sensitive and -resistant cells. Circ-PPID in trastuzumab-resistant cells is located more in the cytoplasm, mainly due to the upregulation of Exportin 4 (XPO4), which results in the loss of spatial conditions for circ-PPID to bind to nuclear NAT10. Taken together, our data suggest that circ-PPID is a previously unappreciated ac4C-dependent HER2 epigenetic regulator, providing a promising therapeutic direction for overcoming trastuzumab resistance in clinical setting.

The novel ß-TrCP protein isoform hidden in circular RNA confers trastuzumab resistance in HER2-positive breast cancer.

Trastuzumab notably improves the outcome of human epidermal growth factor receptor 2 (HER2)-positive breast cancer patients, however, resistance to trastuzumab remains a major hurdle to clinical treatment. In the present study, we identify a circular RNA intimately linked to trastuzumab resistance. circ-ß-TrCP, derived from the back-splicing of ß-TrCP exon 7 and 13, confers trastuzumab resistance by regulating NRF2-mediated antioxidant pathway in a KEAP1-independent manner. Concretely, circ-ß-TrCP encodes a novel truncated 343-amino acid peptide located in the nucleus, referred as ß-TrCP-343aa, which competitively binds to NRF2, blocks SCFß-TrCP-mediated NRF2 proteasomal degradation, and this protective effect of ß-TrCP-343aa on NRF2 protein requires GSK3 activity. Subsequently, the elevated NRF2 transcriptionally upregulates a cohort of antioxidant genes, giving rise to trastuzumab resistance. Moreover, the translation ability of circ-ß-TrCP is inhibited by eIF3j under both basal and oxidative stress conditions, and eIF3j is transcriptionally repressed by NRF2, thus forming a positive feedback circuit between ß-TrCP-343aa and NRF2, expediting trastuzumab resistance. Collectively, our data demonstrate that circ-ß-TrCP-encoded ß-TrCP protein isoform drives HER2-targeted therapy resistance in a NRF2-dependent manner, which provides potential therapeutic targets for overcoming trastuzumab resistance.

Myc derived circRNA promotes triple-negative breast cancer progression via reprogramming fatty acid metabolism.

Myc is a well-known proto-oncogene that is frequently amplified and activated in breast cancer, especially in triple-negative breast cancer (TNBC). However, the role of circular RNA (circRNA) generated by Myc remains unclear. Herein, we found that circMyc (hsa_circ_0085533) was remarkably upregulated in TNBC tissues and cell lines, which was attributed to gene amplification. Genetic knockdown of circMyc mediated by lentiviral vector significantly inhibited TNBC cell proliferation and invasion. Importantly, circMyc increased cellular triglycerides, cholesterols and lipid droplet contents. CircMyc was detected in both cytoplasm and nucleus, cytoplasmic circMyc could directly bind to HuR protein, facilitating the binding of HuR to SREBP1 mRNA, resulting in increasing SREBP1 mRNA stability. Nuclear circMyc bound to Myc protein, facilitating the occupation of Myc on SREBP1 promoter, leading to increasing SREBP1 transcription. As a result, the elevated SREBP1 increased the expression of its downstream lipogenic enzymes, enhancing lipogenesis and TNBC progression. Moreover, the orthotopic xenograft model showed that depletion of circMyc markedly inhibited lipogenesis and reduced tumor size. Clinically, high circMyc was closely related to larger tumor volume, later clinical stage and lymph node metastasis, functioning as an adverse prognostic factor. Collectively, our findings characterize a novel Myc-derived circRNA controlling TNBC tumorigenesis via regulation of metabolic reprogramming, implying a promising therapeutic target.

RUNX1-IT1 favors breast cancer carcinogenesis through regulation of IGF2BP1/GPX4 axis.

Breast cancer is the most common malignancy among women and the leading cause of cancer deaths, with complicated pathogenesis that is largely unknown. In this study, we identified a novel long non-coding RNA (lncRNA) as a critical driver of breast cancer tumorigenesis. RUNX1 intronic transcript 1 (RUNX1-IT1) was notably overexpressed in human breast cancer tissues, and knockdown of RUNX1-IT1 inhibited breast cancer cell viability and invasion, as well as tumor growth in orthotopic transplantation model. Further, RUNX1-IT1 repressed ferroptosis, a novel iron-dependent form of regulated cell death, via increasing glutathione peroxidase 4 (GPX4) expression. Specifically, RUNX1-IT1 directly bound to N6-methyladenosine m6A reader IGF2BP1 and promoted the formation of (insulin like growth factor 2 mRNA binding protein 1) IGF2BP1 liquid-liquid phase separation (LLPS) biomolecular condensates, resulting in more IGF2BP1 occupation on GPX4 mRNA, increasing GPX4 mRNA stability. Moreover, high RUNX1-IT1 was linked to poor prognosis, and a strong positive correlation between RUNX1-IT1 and GPX4 was observed in clinical breast cancer tissues. Taken together, our data reveal that RUNX1-IT1 promotes breast cancer carcinogenesis through blocking ferroptosis via elevating GPX4, targeting of the previously unappreciated regulatory axis of RUNX1-IT1/IGF2BP1/GPX4 may be a promising treatment for patient with breast cancer.

A novel circular RNA confers trastuzumab resistance in human epidermal growth factor receptor 2-positive breast cancer through regulating ferroptosis.

HER2-positive breast cancer is an aggressive subtype of breast cancer, characterized by high malignancy and poor prognosis. Trastuzumab, the first HER2-targeted monoclonal antibody therapy, has a crucial role in a curative setting in HER2-positive breast cancer. However, frequent drug resistance inhibits its clinical efficacy. Herein, by performing circular RNA (circRNA) profiling, we identified a novel circRNA, circ-BGN, as a key contributor in trastuzumab resistance. Circ-BGN was evidently increased in trastuzumab-resistant breast cancer cells and tissues, linking to poor overall survival. Knockdown of circ-BGN inhibited breast cancer cell viability and notably restored its sensitivity to trastuzumab. Further, we found that circ-BGN could directly bind to OTUB1 and SLC7A11, enhancing OTUB1-mediated SLC7A11 deubiquitination and thereby inhibiting ferroptosis, a newly recognized form of cell death that is distinct from apoptosis, necrosis, and autophagy. Moreover, erastin, a small-molecule ferroptosis inducer, could effectively restore the anti-tumor effect of trastuzumab. Pre-clinically, the orthotopic tumor model showed that erastin significantly reduced tumor volume generated by trastuzumab-resistant breast cancer cells, which was more pronounced after combined circ-BGN knockdown. Collectively, our data reveal a novel circRNA controlling trastuzumab resistance via regulation of ferroptosis, providing a promising therapeutic strategy for trastuzumab-resistant breast cancer patients.

Dysregulation of tumour microenvironment driven by circ-TPGS2/miR-7/TRAF6/NF-κB axis facilitates breast cancer cell motility.

Tumour microenvironment (TME) is frequently remodelled and deregulated in cancer development and progression. The underlying mechanisms are complex, multifactorial and largely unknown. Circular RNA (circRNA) is an endogenous RNA with a covalently closed loop that plays critical roles in the pathological and physiological processes of the organism. Here, we identified a TME-associated circRNA, circ-TPGS2, which promoted breast cancer (BC) cell dissemination via altering TME. High circ-TPGS2 was observed in metastatic BC tissues and cell lines in comparison to respective normal controls, which was linked to poor overall and recurrence-free survival. Overexpression of circ-TPGS2 notably promoted cell migration, while silencing of circ-TPGS2 resulted in an opposite trend. Moreover, circ-TPGS2 increased pro-inflammatory chemokine production and evoked tumour-associated inflammation by recruiting neutrophils via autocrine and paracrine manners. In terms of mechanism, circ-TPGS2 acted as a sponge of miR-7 and elevated TRAF6, leading to p65 phosphorylation and nuclear translocation, ultimately activating NF-κB signalling. In addition, p65 was abundantly occupied on circ-TPGS2 promoter, activating circ-TPGS2 transcription, thus, forming a positive feedback loop that amplified the pro-metastasis effect of circ-TPGS2. Taken together, our data for the first time reveal the biological implication of circ-TPGS2 in BC, it triggers TME reshaping that facilitates BC metastasis through the miR-7/TRAF6/NF-κB signalling cascade.

Upregulation of circ-UBAP2 predicts poor prognosis and promotes triple-negative breast cancer progression through the miR-661/MTA1 pathway.

Recently, a large number of studies have shown that circular RNA (circRNA) is involved in the development and progression of human cancer. However, its role in triple-negative breast cancer (TNBC) remains largely unknown. In this study, a novel circRNA, circ-UBAP2 (hsa_circ_0001846), was shown to be markedly upregulated in TNBC. Moreover, high circ-UBAP2 expression was closely associated with larger tumour size (p = 0.003), advanced TNM stage (p = 0.005), lymph node metastasis (p = 0.002), and unfavourable prognosis (p = 0.0256). Functionally, lentivirus-mediated stable knockdown of circ-UBAP2 dramatically weakened the ability of TNBC cells to proliferate and migrate and induced apoptosis in vitro and in vivo. Regarding the mechanism, we found that circ-UBAP2 was mainly observed in the cytoplasm and was capable of sponging miRNA-661 to increase the expression of the oncogene MTA1. Additionally, silencing of miRNA-661 or overexpression of MTA1 could partially rescue the attenuated malignant phenotype caused by circ-UBAP2 knockdown. Taken together, our data reveal that circ-UBAP2 plays a vital regulatory role in TNBC via the miR-661/MTA1 axis and may serve as a promising therapeutic target for TNBC patients.

CircZNF609 promotes breast cancer cell growth, migration, and invasion by elevating p70S6K1 via sponging miR-145-5p.

BACKGROUND: Accumulating evidence suggests that circular RNAs (circRNAs) play critical roles in carcinomas. However, the contributions of circRNAs to breast cancer remain unclear. Herein, we determined the role of circZNF609 in breast cancer. METHODS: A total of 143 breast cancer and 38 normal tissues were collected to assess the expression of circZNF609 and its relationship with breast cancer prognosis. A series of in vitro and in vivo functional experiments were carried out to elucidate the role of circZNF609 in breast cancer progression and its underlying molecular mechanisms. RESULTS: CircZNF609 was markedly over-expressed in breast cancer tissues and cell lines, and high circZNF609 expression was closely associated with poor outcome. Silencing of circZNF609 inhibited the malignant phenotype of breast cancer in vitro and in vivo. Mechanistically, circ-ZNF609 served as a sponge of miR-145-5p to elevate p70S6K1 expression. Moreover, miR-145-5p overexpression or p70S6K1 knockdown abrogated the oncogenic effects of circZNF609 in breast cancer. In addition, clinically, a strong negative correlation was observed between the expression of circZNF609 and miR-145-5p in breast cancer tissues (r=-0.597, P<0.001), whereas a positive correlation between circZNF609 and p70S6K1 expression (r=0.319, P<0.001). CONCLUSION: These data suggest that circZNF609 contributes to breast cancer progression, at least partly, by modulating the miR-145-5p/p70S6K1 axis, and it may be a potential therapeutic target for breast cancer.