Possible Coordinate Regulation of Apolipoproteins B-100 (LDL) and A-1 (HDL) Via the LDL Receptor Pathway
Vaishampayan, Nitin G.
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One of the major factors contributing to coronary heart disease is high plasma levels of cholesterol. Studies of hypercholesterolemia have focused on the role of lipoprotein particles: Low Density Lipoproteins (LDL), which contain the apolipoprotein B-100, appear to play a causal role in the development of cholesterol plaques; High Density Lipoproteins (HDL), which contain the apolipoprotein A-I, appear to prevent this process. In this study, the levels of apolipoprotein B-100 and apolipoprotein A-I messenger RNA levels were measured using specific cDNA probes. Hepatoma G2 cells were grown in media containing lipoprotein deficient serum to which low density lipoprotein was added to some flasks. The RNA was extracted and the levels of the specific mRNAs determined by Northern Blot or Dot Blot hybridizations. The results indicated that the level of apolipoprotein B-100 mRNA was lower in cells grown in the presence of LDL than cells grown in lipoprotein deficient serum alone. The levels of apolipoprotein A-I mRNA, on the other hand, were variable and could not be related to the presence of LDL. While the results suggest that exogenous LDL can repress apolipoprotein B-100 formation, further studies would be required to determine whether LDL and HDL biosynthesis are coordinately regulated.