REUPTAKE OF NASCENT LOW-DENSITY LIPOPROTEINS BY HEPG2 CELLS

The kinetics and specificity of the interaction of nascent HepG2 LDL w ith the HepG2 LDL receptor were examined. I-125-Labeled HepG2 LDL and plasma LDL were bound by HepG2 cells in a specific and saturable manne r at 4-degrees-C. Competition studies with HepG2 LDL and plasma LDL in dicated that both ligands bound to the same receptor. Scatchard analys es of the specific 4-degrees-C-binding data revealed a K(d) of 75 nM f or HepG2 LDL and a K(d) of 30 nM for plasma LDL suggesting that HepG2 LDL bind less efficiently to the HepG2 LDL receptor than plasma LDL. B inding, internalization and degradation studies carried out at 37-degr ees-C indicated that HepG2 cells are capable of catabolizing their own nascent LDL; however, under normal experimental conditions re-uptake of nascent LDL is quantitatively insignificant.