Breast cancer (BC) comprises heterogeneous subtypes with distinct molecular drivers and clinical behaviors. Among the key signaling pathways implicated in BC progression is the mitogen-activated protein kinase (MAPK) cascade, which regulates cell proliferation, apoptosis, and stress responses. microRNAs (miRNAs), as post-transcriptional regulators, are increasingly recognized as modulators of MAPK-associated genes, yet their integrated role across BC subtypes remains incompletely understood. This study included 405 patients with histopathologically confirmed BC, stratified into luminal A (LumA), HER2-negative luminal B, HER2-positive luminal B, non-luminal HER2-positive, and triple-negative breast cancer (TNBC). Control tissues were obtained from matched surgical margins. We performed mRNA profiling (Affymetrix microarrays), reverse transcription-quantitative polymerase chain reaction (RT-qPCR), protein quantification (enzyme-linked immunosorbent assay (ELISA), and miRNA expression analysis. Predicted miRNA-mRNA interactions were analyzed using the miRDB database. Functional protein–protein interactions were explored using the STRING database. MAP3K1, MAP2K4, and TP53 were significantly downregulated across all subtypes, while PPM1D, LMTK3, and TGFB1 were upregulated, especially in TNBC. These alterations were supported by concordant changes at the protein level. Dysregulated miRNAs—miR-21-3p, miR-23c, miR-27a-3p, miR-205-3p, and miR-300—exhibited in-verse expression patterns relative to their predicted target genes. STRING analysis identified TP53 as a central hub, linking MAPK signaling with stress and apoptotic pathways. This integrated transcriptomic and miRNA profiling study reveals subtype-specific dysregulation of MAPK-associated genes and their miRNA regulators in BC, with TNBC exhibiting the most profound alterations. These findings provide insight into potential targets for personalized therapeutic strategies.

Background/Objectives: The Notch signaling pathway regulates cell fate, proliferation, and differentiation, and its dysregulation has been implicated in various cancers, including breast cancer. MicroRNAs (miRNAs) are critical post-transcriptional regulators that can modulate Notch pathway components. The aim of this study was to identify miRNAs that may potentially regulate the expression of Notch pathway-related genes across five molecular subtypes of breast cancer in Polish women. Methods: Tumor and adjacent normal tissue samples were collected from 405 patients with five breast cancer subtypes: luminal A (n = 130), HER2-negative luminal B (n = 100), HER2-positive luminal B (n = 96), non-luminal HER2-positive (n = 36), and triple-negative breast cancer (n = 43). Gene expression was profiled using mRNA microarrays and validated with RT-qPCR and ELISA. Candidate regulatory miRNAs were identified by miRNA microarrays and confirmed using the miRDB database. Results: APH1A, CTBP1, DTX1, HEY1, HEY2, JAG2, NOTCH4, TLE2, and TLE4 were consistently dysregulated across all breast cancer subtypes. Overexpression of HEY1 and JAG2 may be driven by decreased levels of miR-145, miR-98, and miR-381. Conversely, downregulation of TLE4 may be associated with elevated expression of miR-196a and miR-155. No regulatory miRNAs meeting the selection criteria were identified for APH1A, CTBP1, DTX1, HEY2, NOTCH4, or TLE2. Conclusions: The consistent alterations suggest the presence of a shared Notch-driven oncogenic signature in breast cancer, potentially driving cell proliferation, stemness, and resistance to therapy. These findings enhance our understanding of Notch signaling in breast cancer and propose novel miRNA–Notch interactions as candidate targets for therapeutic intervention.

Nuclear factor kappa B (NF-κB) signaling plays a central role in inflammation, immunity, cell survival, and cancer progression. Its constitutive activation is frequently observed in breast cancer, contributing to tumor growth, treatment resistance, and metastasis. MicroRNAs (miRNAs) are key post-transcriptional regulators of gene expression and may modulate NF-κB signaling in a subtype-specific or -independent manner. The aim of the study was to identify miRNAs that may potentially regulate the activity of genes associated with NF-κB signaling across five molecular subtypes of breast cancer in Polish women. Tumor and matched normal tissue samples were collected from 405 patients with five breast cancer subtypes: luminal A (n = 130), HER2-negative luminal B (n = 100), HER2-positive luminal B (n = 96), non-luminal HER2-positive (n = 36), and triple-negative breast cancer (TNBC, n = 43). Expression profile of selected NF-κB-related genes were evaluated using mRNA microarrays and RT-qPCR. Protein levels were assessed by ELISA. Candidate regulatory miRNAs were identified via miRNA microarrays and validated using the miRDB database. A consistent upregulation of MAP3K7, TAB2, TNFAIP3, CSNK2A1, BCL2L1, XIAP, CXCL2, and PLAU was observed across all subtypes, suggesting activation of canonical NF-κB signaling. Downregulation of specific miRNAs, miR-1297 and miR-30a (targeting MAP3K7), miR-134 (TAB2), miR-125b (TNFAIP3), and miR-4329 (XIAP), may contribute to this deregulation. For CSNK2A1, BCL2L1, CXCL2, and PLAU, no regulatory miRNAs meeting our criteria were identified. Our study reveals a subtype-independent activation of the canonical NF-κB signaling pathway in breast cancer, underpinned by consistent upregulation of key components (at both the transcript and protein levels. Dysregulation of specific miRNAs likely contributes to this altered gene expression. These findings suggest the presence of a common NF-κB-driven oncogenic program across molecular subtypes, with potential implications for developing miRNA-based therapeutic strategies targeting inflammation, survival signaling, and treatment resistance in breast cancer.

Background/Objectives: Breast cancer represents a diverse group of malignancies and continues to rank among the leading causes of cancer-related deaths in women. Altered Hippo pathway signaling has been increasingly recognized as a contributor to tumor growth, therapeutic resistance, and metastatic spread. This study aimed to identify miRNAs targeting Hippo pathway-related genes that are consistently dysregulated across all five breast cancer subtypes. Methods: The study cohort included patients representing five breast cancer subtypes: 130 luminal A, 96 HER2-positive luminal B, 100 HER2-negative luminal B, 36 non-luminal HER2-positive, and 43 triple-negative breast cancer (TNBC). Tumor samples were collected during surgery, along with adjacent healthy tissue that served as controls. Expression of Hippo-related genes was analyzed using mRNA microarrays and validated with reverse transcription quantitative polymerase chain reaction (RT-qPCR). Protein levels were assessed via enzyme-linked immunosorbent assay (ELISA), while miRNA expression profiling was performed with miRNA microarrays. Potential mRNA targets were predicted using the miRDB database. Results: We identified consistent downregulation of STK4, RASSF6, and FGF1, alongside overexpression of BIRC5 and SERPINE1. miRNA analysis revealed that STK4 is potentially regulated by miR-522-3p, SERPINE1 by miR-199b-5p and miR-30a-3p, whereas RASSF6, FGF1, and BIRC5 appeared to be predominantly regulated at the transcriptional level. These alterations reflect both the suppression of upstream Hippo activation and activation of downstream oncogenic effectors across all subtypes. Conclusions: Our findings reveal a conserved Hippo dysregulation program in breast cancer, highlighting subtype-independent Hippo-related genes and their miRNA regulators as potential universal biomarkers and therapeutic targets, complementing subtype-specific treatment strategies.