Growth stimulation of Rous sarcoma virus‐transformed BHK cells by biotin and serum lipids

Biotin or a serum lipid extract stimulated proliferation of G1 arrested Rous sarcoma virus‐transformed BHK cells in modified Eagle's MEM (BM). The cells could be maintained continuously in BM plus biotin (BMB), but not in BM plus serum lipid extract (BM · L). Avidin inhibited growth stimulation when added to BMB, but did not inhibit growth when added to BM · L. 14 C‐acetate incorporation into total cellular lipids was stimulated in BMB, but not in BM. Thin‐layer chromatography of the labeled cellular lipid extract indicated that relatively large amounts of 14 C‐acetate were incorporated into phosphatidylserine and little into the other major phospholipids. In the neutral lipids, the largest amount of incorporation was in cholesterol. G1 arrested cells multiplied rapidly in BM supplemented with dialyzed serum (BM · DS), but they did not multiply in BM with delipidized serum (BM · DLS). The addition of biotin or serum lipid extract to BM · DLS stimulated growth. Growth stimulation in BM · DLS by biotin was inhibited by avidin, but avidin had no effect on growth stimulation by serum lipid extract. Biotin stimulated additional multiplication in BM · DS and avidin inhibited this additional growth stimulation. These results suggest that growth stimulation requires lipids supplied by serum lipids or by de novo synthesis stimulated by biotin. In the absence of serum, the stimulation of the synthesis of growth factor(s) by biotin are also required for continuous multiplication.