Epidermal growth factor‐dependent growth of human KB cells in a defined medium and altered growth factor requirements of KB mutants resistant to EGF‐Pseudomonas exotoxin conjugates

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Abstract
A serum-free culture system was established for human KB carcinoma (HeLa) cells that consisted of a chemically defined medium and several growth factors including epidermal growth factor (EGF), insulin, transferrin, hydrocortisone, and ethanolamine. EGF and insulin showed the greatest effects on the growth rate of KB cells. Insulin-like growth factor l (IGF-l) at the same concentration as insulin stimulated cell growth less than insulin. Transferrin, hydrocortisone, or ethanolamine had no growth-stimulatory effects alone but were stimulatory when combined with EGF and/or insulin. Transforming growth factor-beta inhibited growth and triiodothyronine stimulated growth. The growth factor requirements were established for several KB mutants with low EGF receptor levels that had been selected for resistance to a conjugate of EGF with Pseudomonas exotoxin (EGF-PE). Three of five KB mutants did not respond to EGF; two other mutants responded to a lesser extent than the parental KB cells. Four mutants had a reduced response to insulin and responded to T3; one mutant (ET-30) responded to neither. These results indicate that KB cells selected for EGF-PE resistance have lost their growth response to EGF and illustrate the usefulness of serum-free medium for studying the growth factor requirements of mutants with altered receptor levels.