PFN1 and breast carcinoma: First, our PIP2 immunostaining experiments revealed that silencing Pfn1 expression in human breast cancer (MDA-MB-231 [referred to as MDA-231 hereon] and BT-474) cell lines leads to a significant decrease in the PIP2 content (Figs. 2, A and B and S1 confirms siRNA-mediated knockdown of Pfn1 expression in these two cell lines).