Clusterin/Apo J

At least 9 distinct polymorphic forms of apolipoproteins are known. The apolipoproteins act as stabilizers of the intact lipoprotein particles. Quantitative measurements of HDL, LDL and VLDL particles in human serum are often used to estimate an individual's relative risk of coronary heart disease. In addition, quantitative immunological measurements of certain apolipoproteins (especially A-1 and B) have been suggested to be more accurate estimators of coronary heart disease than measurements of lipoprotein particles (especially HDL and LDL).

Clusterin/Apolipoprotein J (ApoJ)is the major secreted product of Sertoli cells and is thought to play a critical role in spermatogenesis. The protein was shown to be a normal constituent of human blood and is also thought to be a control mechanism of the complement cascade. It prevents the binding of a C5b-C7 complex to the membrane of the target cell and in this way inhibits complement-mediated cytolysis.

Apo J is overexpressed in human prostate and breast cancers and in squamous cell carcinomas. Suppression of Apolipoprotein J renders these cells sensitive to chemotherapeutic drug-mediated apoptosis. It has been proposed that elevated levels of Apolipoprotein J may promote oncogenic transformation and tumor progression by interfering with BAX proapoptotic activities.