SPDEF targets EMT pathway to inhibit cell migration and invasion in triple‐negative breast cancer

Background Current treatments against triple-negative breast cancer (TNBC) are ineffective due to the high rate of metastasis and therapy resistance. There is, therefore, a pressing need for novel and efficacious therapies against TNBC. The basal-like TNBC has a poor prognosis and a high metastasis rate compared to the luminal-like breast cancer subtypes. Here, set to determine the role of Sam Pointed Domain Ets Transcription Factor also known as Prostate-Derived Ets Factor (SPDEF/PDEF), in TNBC. Methods Clinical data were extracted from the METABRIC breast cancer project, hosted at the TCGA database. MDA-MB-231 and MDA 231-LM2-4175 cells were stably transfected with PDEF/control pBABE retroviral vectors. Cell migration/invasion assays were done to explore the effects of PDEF expression on the motility of TNBC cells. Proliferation was measured under 2D and 3D culture conditions. qRT-PCR and immunoblot were performed to visualize gene and protein expression. Data were graphed and analyzed using Graph Pad Prism Software 8 using one-way ANOVA and the unpaired two-tailed Student's t-test. All data were evaluated in triplicate against vector control cells. Results Basal gene and protein expression screening revealed that the expression of PDEF is significantly lower in highly metastatic breast cancer cells compared to the non-metastatic ones. Data analysis from clinical breast cancer METABRIC cohort revealed the loss of PDEF is associated with tumor metastasis, tumor grade, and poor patient survival. PDEF is lost in highly metastatic and therapy resistant TNBC cells. Re-expression of PDEF diminished cell migration and invasion in TNBC cells. Decreased migration and invasion in response to PDEF was not a result of decreased cell growth and proliferation or increased cell death but a result of suppression of EMT markers in TNBC cells. Conclusions PDEF expression inhibits cell migration and invasion partially by down-regulating EMT-related protein markers, suggesting a critical role for PDEF in suppressing TNBC cell metastasis.