Phorbol esters inhibit the binding of low-density lipoproteins (LDL) to U-937 monocytelike cells

Publisher Website
Google Scholar
Abstract
The present study demonstrates that U‐937 monocytelike human cells possess specific LDL receptors. 125I‐LDL binds at 4°C on the cell surface. The bound molecules are releasable by heparin. The reaction requires Ca2+ and the binding sites are sensitive to proteolysis. Unlabeled LDL compete with 125I‐LDL, whereas HDL are ineffective. At 37°C, LDL are internalized and degraded by a chloroquine‐sensitive pathway. Tumor‐promoting phorbol esters inhibit the binding of 125I‐LDL to its receptor on U‐937 cells. This inhibition exhibits temperature, time, and concentration dependence. At 37°C, inhibition is 50% at 5 × 10−9 M of TPA. After removal of phorbol esters, treated cells recover their 125I‐LDL‐binding activity in 60 min. The inhibitory activities of various phorbol esters are proportional to their tumor‐promoting activities. Inhibition appears to be due to a reduction in the number of available LDL receptors rather than a decrease in receptor affinity.

This publication has 56 references indexed in Scilit: