Through a series of inhibitor, neutralizing antibody, and knockout studies using short interfering RNA (siRNA), the authors show that GDNF-associated cancer cell migration occurs through GFRa1 receptor activation and regulation of matrix metalloproteinase (MMP)-9 and MMP-13 through a MAPK/activator protein-1 (AP-1) pathway [131]. The gene discussed is GDNF; the disease is cancer.