The source of cellular lipid in the human diploid cell strain WI-38

Abstract

The extent of lipid biosynthesis in cultures of WI-38 cells was assayed using radioactive precursors, and it was found that the lipid present in these cells under normal culture conditions is not biosynthesized but is derived from the medium. The results of experiments designed to determine which of the serum lipids is the source of the cell lipid indicate that free fatty acid is probably the source of all the nonsterol lipid in the cells. The data suggest that the serum-free fatty acid is taken up by the cells and that then cellular triglycerides and phospholipids are assembled from the preformed fatty acid. It was further demonstrated that, during the course of culture, hydrolysis of serum triglycerides occurs, replenishing the free fatty acid levels in the medium. This hydrolysis was shown to occur in the absence of cells; its rate was decreased by heating the serum, which suggests the mediation of a serum enzyme.