CD46 is a complement regulatory protein that is also called membrane cofactor protein. This protein is a type 1 membrane protein that plays an important inhibitory role in the complement system. CD46 exhibits a cofactor activity that promotes inactivation of C3b and C4b by whole antiserum factor 1, thereby protecting host cells from complement-dependent cytotoxicity. CD46 can also function as a receptor for selected bacteria and viruses, and is reportedly required for proper fusion of spermatozoa to the oocyte membrane during fertilization. CD46 is overexpressed in medulloblastoma tumors, and CD46 expression has been linked with poor prognosis in breast cancer. The upregulation of CD46 may protect cancer cells from complement-dependent cytotoxicity to facilitate cancer cell immune evasion.
