P2RX7 and breast carcinoma: As depicted in the diagram (Figure 7), our data unveil a new regulatory mechanism by which persistent extracellular ATP released by osteocyte Cx43 hemichannels [9], through its binding to purinergic receptor P2Y11R, down-regulates the CXCR4 receptor, a critical factor for breast cancer growth in the bone, leading to the inhibition of breast cancer cell migration and bone metastasis.