Stimulation of low density lipoprotein receptor activity by conditioned medium from a human cancer cell line.

Low density lipoprotein receptor activity in cultured rabbit aortic smooth muscle cells was enhanced by the addition of the conditioned medium derived from the serum-free culture of a human lung cancer cell line. By gel filtration, two peaks of low density lipoprotein receptor-enhancing fractions were obtained, and the molecular weights were 140,000 and greater than 850,000. These fractions also stimulated [3H]thymidine incorporation into DNA. Maximal stimulations of the low density lipoprotein receptor activity and [3H]thymidine incorporation were observed at 16 and 20 h after the addition of the conditioned medium, respectively. The apparent Km (about 10 micrograms/ml) was not changed by the addition of the conditioned medium. De novo cholesterol synthesis was also stimulated by the conditioned medium. It is speculated that certain factors released from the cancer cells affect cholesterol metabolism in normal cells.