Midkine (MK or MDK) is a 15 kDa heparin-binding molecule also known as neural axon growth promoter factor 2 (NEGF2), a protein encoded by the MDK gene.Midkine is pleiotropic, exerting effects on cell proliferation, cell migration, angiogenesis, and fibrinolysis. Midkine expression has been found in a variety of cancer types such as neuroblastoma, colorectal cancer, hepatocellular carcinoma, and ovarian cancer. Serum concentrations of Midkine are much higher in patients with these malignant tumors than in normal subjects. In some cases, these high levels of Midkine also portend a poorer prognosis for the disease, such as neuroblastoma, glioma, and bladder cancer.Midkine acts as a low-affinity receptor that binds to nucleolin on the cell surface. This binding inhibits HIV infection.