Furin, a proprotein convertase, is located mostly in the trans-Golgi network; it intervenes in the maturation of numerous proproteins by cutting them at precisely three to four basic residues [81]; however, its exact role in increasing or decreasing the expression of MHC1 in normal, tumor, and immune system cells such as lymphocytes and APCS is under investigation. The gene discussed is FURIN; the disease is neoplasm.