miRNAs in Signal Transduction of SMAD Proteins in Breast Cancer

The aim of this study was to identify miRNAs that could potentially influence the activity of SMAD proteins involved in TGFβ signal transduction in five types of breast cancer in Polish women. Patients with five breast cancer subtypes were included in the study: luminal A (<i>n</i> = 130), luminal B HER2- (<i>n</i> = 100), luminal B HER2+ (<i>n</i> = 96), non-luminal HER2+ (<i>n</i> = 36), and TNBC (<i>n</i> = 43). During surgery, tumor tissue was removed along with a margin of healthy tissue (control). Molecular analysis included determination of the expression of genes related to SMAD protein signal transduction using mRNA microarrays and reverse transcription quantitative polymerase chain reaction (RT-qPCR). Protein expression was determined using an enzyme-linked immunosorbent assay (ELISA). The miRNA profiling was performed using miRNA microarrays and the miRDB database. SMAD3 and SMAD5 were overexpressed in all types of breast cancer, which could be related to the reduced expression of miR-145, and the findings for SMAD4 and miR-155 were similar. Additionally, the level of SMAD7 was reduced, which may be due to the low activity of miR-15b and miR21b. This study determined the gene expression profiles involved in SMAD protein signal transduction across five different types of breast cancer and identified the miRNAs potentially regulating their activity. Overexpression of SMAD3, SMAD4, and SMAD5 suggests excessive activation of the TGFβ pathway, potentially promoting tumor growth and development. Concurrently, a significant reduction in SMAD7 expression removes inhibitory control in the TGFβ pathway, a phenomenon that is particularly evident in more aggressive breast cancer types.