MMP9 and breast cancer: We found that treatment of MDA-MB-231 cells that express endogenous GPR54 [27] with either 10 or 100 nM of Kp-10 increases the secretion of MMP-9 (Fig. 2D), revealing for the first time that Kp-10 signaling via GPR54 in breast cancer cells stimulates the secretion of MMP-9.