A growing amount of evidence has indicated that PSAT1 is an oncogene that plays an important role in cancer progression and metastasis. In this study, we explored the expression and function of PSAT1 in estrogen receptor (ER)-negative breast cancer. The expression level of PSAT1 in breast cancer tissues and cells was analyzed using real-time-PCR (RT-PCR), TCGA datasets or immunohistochemistry (IHC). The overall survival of patients with ER-negative breast cancer stratified by the PSAT1 expression levels was evaluated using Kaplan-Meier analysis. The function of PSAT1 was analyzed using a series of in vitro assays. Moreover, a nude mouse model was used to evaluate the function of PSAT1 in vivo. qRT-PCR and western blot assays were used to evaluate gene and protein expression, respectively, in the indicated cells. In addition, we demonstrated that PSAT1 was activated by ATF4 by chromatin immunoprecipitation (ChIP) assays. mRNA expression of PSAT1 was up-regulated in ER-negative breast cancer. A tissue microarray that included 297 specimens of ER-negative breast cancer was subjected to an immunohistochemistry assay, which demonstrated that PSAT1 was overexpressed and predicted a poor clinical outcome of patients with this disease. Our data showed that PSAT1 promoted cell proliferation and tumorigenesis in vitro and in vivo. We further found that PSAT1 induced up-regulation of cyclin D1 via the GSK3β/β-catenin pathway, which eventually led to the acceleration of cell cycle progression. Furthermore, ATF4 was also overexpressed in ER-negative breast cancers, and a positive correlation between the ATF4 and PSAT1 mRNA levels was observed in ER-negative breast cancers. We further demonstrated that knockdown of ATF4 by siRNA reduced PSAT1 expression. Finally, chromatin immunoprecipitation (ChIP) assays showed that PSAT1 was a target of ATF4. PSAT1, which is overexpressed in ER-negative breast cancers, is activated by ATF4 and promotes cell cycle progression via regulation of the GSK3β/β-catenin/cyclin D1 pathway.

Altered epigenetic reprogramming enables breast cancer cells to adapt to hypoxic stress. Hypoxic microenvironment can alter immune cell infiltration and function, limiting the effectiveness of immunotherapy. The study aimed to identify how fat mass and obesity-associated protein (FTO) helps breast cancer cells cope with the hypoxic microenvironment and the mechanisms behind breast cancer cell resistance to tumor immunity. Clinical samples were utilized to analyze the impact of FTO on breast cancer progression and the effect of programmed cell death protein 1/ programmed cell death 1 ligand 1(PD-1/PD-L1) immune checkpoint inhibitor treatment. Utilized MeRIP-seq and mRNA-seq to analyze the downstream genes regulated by FTO under hypoxia. Methylation modification regulation of PDK1 by FTO was clarified using RIP. Then mouse models were utilized to analyze the efficacy of inhibiting FTO and 3-Phosphoinositide-dependent protein kinase 1(PDK1) in combination with PD-1/PD-L1 immune checkpoint inhibitor treatment. N6-Methyladenosine(m⁶A) demethylase FTO was transcriptionally activated by hypoxia inducible factor 1α(HIF-1α). PDK1 was identified as a potential target of FTO under hypoxic conditions through high-throughput sequencing. Mechanistically, overexpression of FTO decreases m⁶A modification sites on PDK1 mRNA, preventing YTH domain family 3(YTHDF3) from recognizing and binding to these sites, thereby inhibiting the degradation of PDK1 mRNA. Overexpression of PDK1 activates the AKT/STAT3 pathway, leading to enhanced PD-L1 expression. Targeting the FTO and PDK1-AKT pathways with FB23 and BX-912 inhibit breast cancer growth, enhance cytotoxic T lymphocyte (CTL) activity, and enhance the effectiveness of the PD-1/PD-L1 checkpoint inhibitor Atezolizumab. This study reveals that HIF-1α promotes FTO transcription under hypoxic conditions, thereby increasing PD-L1 expression through the PDK1/AKT/STAT3 axis. Inhibition of FTO and PDK1 under hypoxic conditions could serve as a promising immunotherapeutic strategy for breast cancer.

Graphical In TNBC cells, the inhibition of C1QBP suppresses PKC–NF-κB signaling in cytoplasm, upregulating Iκβα expression, thereby decreasing the VCAM-1 expression by lowering p65 level in nucleus in normoxic conditions. When TNBC cells are exposed to hypoxic conditions, HIF-1α upregulates C1QBP expression. The inhibition of C1QBP notably suppresses the activation of hypoxia-induced PKC–NF-κB signaling and decreases VCAM-1 level, resulting in metastasis blocking and PTX drug chemoresistance decreasing of TNBC cells.

Understanding the causes of tumorigenesis and progression in triple-receptor negative breast cancer (TNBC) can help the design of novel and personalized therapies and prognostic assessments. Abnormal RNA modification is a recently discovered process in TNBC development. TNBC samples from The Cancer Genome Atlas database were categorized according to the expression level of NAT10, which drives acetylation of cytidine in RNA to N(4)-acetylcytidine (ac4C) and affects mRNA stability. A total of 703 differentially expressed long non-coding RNAs (lncRNAs) were found between high- and low-expressed NAT10 groups in TNBC. Twenty of these lncRNAs were significantly associated with prognosis. Two breast cancer tissues and their paired normal tissues were sequenced at the whole genome level using acetylated RNA immunoprecipitation sequencing (acRIP-seq) technology to identify acetylation features in TNBC, and 180 genes were significantly differentially ac4c acetylated in patients. We also analyzed the genome-wide lncRNA expression profile and constructed a co-expression network, containing 116 ac4C genes and 1080 lncRNAs. Three of these lncRNAs were prognostic risk lncRNAs affected by NAT10 and contained in the network. The corresponding reciprocal pairs were “LINC01614-COL3A1”, “OIP5-AS1-USP8”, and “RP5-908M14.9-TRIR”. These results indicate that RNA ac4c acetylation involves lncRNAs and affects the tumor process and prognosis of TNBC. This will aid the prediction of drug targets and drug sensitivity.