LRPPRC promotes glycolysis by stabilising LDHA mRNA and its knockdown plus glutamine inhibitor induces synthetic lethality via m6 A modification in triple-negative breast cancer.

BACKGROUND: Targeted therapy for triple-negative breast cancer (TNBC) remains a challenge. N6-methyladenosine (m6 A) is the most abundant internal mRNA modification in eukaryotes, and it regulates the homeostasis and function of modified RNA transcripts in cancer. However, the role of leucine-rich pentatricopeptide repeat containing protein (LRPPRC) as an m6 A reader in TNBC remains poorly understood. METHODS: Western blotting, reverse transcription-polymerase chain reaction (RT-qPCR) and immunohistochemistry were used to investigate LRPPRC expression levels. Dot blotting and colorimetric enzyme linked immunosorbent assay (ELISA) were employed to detect m6 A levels. In vitro functional assays and in vivo xenograft mouse model were utilised to examine the role of LRPPRC in TNBC progression. Liquid chromatography-mass spectrometry/mass spectrometry and Seahorse assays were conducted to verify the effect of LRPPRC on glycolysis. MeRIP-sequencing, RNA-sequencing, MeRIP assays, RNA immunoprecipitation assays, RNA pull-down assays and RNA stability assays were used to identify the target genes of LRPPRC. Patient-derived xenografts and organoids were employed to substantiate the synthetic lethality induced by LRPPRC knockdown plus glutaminase inhibition. RESULTS: The expressions of LRPPRC and m6 A RNA were elevated in TNBC, and the m6 A modification site could be recognised by LRPPRC. LRPPRC promoted the proliferation, metastasis and glycolysis of TNBC cells both in vivo and in vitro. We identified lactate dehydrogenase A (LDHA) as a novel direct target of LRPPRC, which recognised the m6 A site of LDHA mRNA and enhanced the stability of LDHA mRNA to promote glycolysis. Furthermore, while LRPPRC knockdown reduced glycolysis, glutaminolysis was enhanced. Moreover, the effect of LRPPRC on WD40 repeat domain-containing protein 76 (WDR76) mRNA stability was impaired in an m6 A-dependent manner. Then, LRPPRC knockdown plus a glutaminase inhibition led to synthetic lethality. CONCLUSIONS: Our study demonstrated that LRPPRC promoted TNBC progression by regulating metabolic reprogramming via m6 A modification. These characteristics shed light on the novel combination targeted therapy strategies to combat TNBC.

LncRNA CARMN suppresses EMT through inhibiting transcription of MMP2 activated by DHX9 in breast cancer.

Long non-coding RNAs (lncRNAs) have been shown to drive cancer progression. However, the function of lncRNAs and the underlying mechanism in early-stage breast cancer(BC) have rarely been investigated. Datasets of pre-invasive ductal carcinoma in situ (DCIS), invasive ductal BC (IDC) and normal breast tissue from TCGA and GEO databases were used to conduct bioinformatics analysis. LncRNA CARMN was identified as a tumor suppressor in early-stage BC and related to a better prognosis. CARMN over-expression inhibited MMP2 mediated migration and EMT in BC. Further analysis showed that CARMN was located in the nucleus and functioned as an enhancer RNA (eRNA) in mammary epithelial cell. Mechanically, CARMN binding protein DHX9 was identified by RNA pull-down and mass spectrometry (MS) assays and it also bound to the MMP2 promoter to activate its transcription. As a decoy, CARMN competitively bound to DHX9 and blocked MMP2 transcriptional activation, thereby inhibiting metastasis and EMT of BC cells. These findings reveal the important role of CARMN as a tumor suppressor in the metastasis and a potential biomarker for progression in early-stage BC.

Transcriptionally regulated miR-26a-5p may act as BRCAness in Triple-Negative Breast Cancer.

BACKGROUND: DNA damage and DNA damage repair (DDR) are important therapeutic targets for triple-negative breast cancer (TNBC), a subtype with limited chemotherapy efficiency and poor outcome. However, the role of microRNAs in the therapy is emerging. In this study, we explored whether miR-26a-5p could act as BRCAness and enhance chemotherapy sensitivity in TNBC. METHODS: Quantitative reverse transcription polymerase chain reaction (RT-qPCR) was used to detect the expression of miR-26a-5p in breast cancer tissues and cell lines. CCK-8 was used to measure drug sensitivity in concentration gradient and time gradient. Comet assay was used to detect DNA damage. Flow cytometry was performed to examine apoptosis. Moreover, we used western blot and immunofluorescence to detect biomarkers. Luciferase reporter assay was performed to verify the combination of miR-26a-5p and 3'UTR of target gene. Hormone deprivation and stimulation assay were used to validate the effect of hormone receptors on the expression of miR-26a-5p. Chromatin immunoprecipitation (ChIP) assays were used to verify the binding sites of ER-a or PR with the promoter of miR-26a-5p. Animal experiments were performed to the effect of miR-26a-5p on Cisplatin treatment. RESULTS: The expression of miR-26a-5p was significantly downregulated in TNBC. Overexpressing miR-26a-5p enhanced the Cisplatin-induced DNA damage and following apoptosis. Interestingly, miR-26a-5p promoted the expression of Fas without Cisplatin stimulating. It suggested that miR-26a-5p provided a hypersensitivity state of death receptor apoptosis and promoted the Cisplatin sensitivity of TNBC cells in vitro and in vivo. Besides, miR-26a-5p negatively regulated the expression of BARD1 and NABP1 and resulted in homologous recombination repair defect (HRD). Notably, overexpressing miR-26a-5p not only facilitated the Olaparib sensitivity of TNBC cells but also the combination of Cisplatin and Olaparib. Furthermore, hormone receptors functioned as transcription factors in the expression of miR-26a-5p, which explained the reasons that miR-26a-5p expressed lowest in TNBC. CONCLUSIONS: Taken together, we reveal the important role of miR-26a-5p in Cisplatin sensitivity and highlight its new mechanism in DNA damage and synthetic lethal.

m6A reader HNRNPA2B1 destabilization of ATG4B regulates autophagic activity, proliferation and olaparib sensitivity in breast cancer.

N6-methyladenosine RNA (m6A) is the most extensive epigenetic modification in mRNA and influences tumor progression. However, the role of m6A regulators and specific mechanisms in breast cancer still need further study. Here, we investigated the significance of the m6A reader HNRNPA2B1 and explored its influence on autophagy and drug sensitivity in breast cancer. HNRNPA2B1 was selected by bioinformatics analysis, and its high expression level was identified in breast cancer tissues and cell lines. HNRNPA2B1 was related to poor prognosis. Downregulation of HNRNPA2B1 reduced proliferation, enhanced autophagic flux, and partially reversed de novo resistance to olaparib in breast cancer. ATG4B was determined by RIP and MeRIP assays as a downstream gene of HNRNPA2B1, by which recognized the m6A site in the 3'UTR. Overexpression of ATG4B rescued the malignancy driven by HNRNPA2B1 in breast cancer cells and increased the olaparib sensitivity. Our study revealed that the m6A reader HNRNPA2B1 mediated proliferation and autophagy in breast cancer cell lines by facilitating ATG4B mRNA decay and targeting HNRNPA2B1/m6A/ATG4B might enhance the olaparib sensitivity of breast cancer cells.