PAK4 and breast cancer: Two cases of bone metastatic tissue stained by IHC showed the location of positive nuclear PAK4 and n/cRUNX1 (Figure 6A).To investigate how PAK4 modulates the osteolytic destruction through RUNX1 in vivo, we used the breast cancer cell line MCF-7 to establish a tumor-induced osteolysis model, which stably overexpressed RUNX1 WT, RUNX1 T207A or RUNX1 T207D.