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Metabolism of low‐density lipoprotein in differentiated and undifferentiated HT29 colon cancer cells
Author(s) -
Viallard Viviane,
Lacombe Christiane,
Trocheris Véronique,
Tabacik Christiane,
Aliau Sigrid
Publication year - 1990
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.2910460230
Subject(s) - cell culture , population , ldl receptor , receptor , low density lipoprotein , incubation , metabolism , cell , endocrinology , biology , medicine , chemistry , microbiology and biotechnology , lipoprotein , biochemistry , cholesterol , genetics , environmental health
The metabolism of human low‐density lipoproteins was studied in 2 subpopulations deriving from cells of HT29, a human colon carcinoma cell line. When grown on standard medium (25 mM glucose), about 95% of these cells are undifferentiated (G + cells). From this heterogeneous population, a subpopulation with features of differentiated small‐intestinal cells was selected by glucose deprivation (G − cells). The characteristics of the LDL receptor were first investigated. The results showed that the binding of 125 I‐LDL to G + and G − cells performed at 4°C was saturable and specific. The K d values were not statistically different in the 2 cell subpopulations. The B max of G + cells was 55 ± 6 ng 125 I‐LDL/mg cell protein and showed no changes whatever the phase of culture. In G − cells, the B max was higher during the exponential phase of culture and decreased in the post‐confluent phase (82 ± 5 versus 15 ± 6.8 ng 125 I‐LDL/mg cell protein). Cellular degradation of 125 I‐LDL was effective in both cell subpopulations but time‐course studies showed that, in post‐confluent G − cells, degradation was slowed as compared to G + cells (4 hr vs. 2 hr to reach maximal degradation). The rate of LDL processing at 37°C was enhanced by pre‐incubation with FCS‐supplemented medium, suggesting the existence of a serum component which stimulates the total degradation of 125 I‐LDL. Concerning regulation of the LDL receptor activity, we demonstrated that pre‐incubation of G + cells with LDL induced 80% down‐regulation of receptor number in both phases of culture. This was also observed in G − cells during the exponential phase while only a 20% decrease of the receptor number was observed in post‐confluent G − cells. The LDL degradation of G + cells resulted in an inhibition of the cholesterogenic activity by 30% and 60% depending on the phase of culture. In G − cells, LDL pre‐incubation inhibited cholesterol synthesis to the same extent (45%) in the exponential phase but did not affect the rate of cholesterol synthesis when cells were confluent. The defective regulatory role of LDL on receptor number and cholesterol synthesis suggests that, in the post‐confluent differentiated cells, cholesterol derived from LDL does not reach the regulatory pool. Taken together, our findings indicate the existence of functional LDL receptors in the HT29 cell line, either in the differentiated or in the undifferentiated form.