Decrease in epidermal growth factor receptor levels and production of material enhancing epidermal growth factor binding accompany the temperature-dependent changes from normal to transformed phenotype.

Abstract

Normal rat kidney (NRK) cells infected with a temperature-sensitive mutant of Kirsten sarcoma virus (Ts cells) exhibited normal monolayer morphology identical to that observed for uninfected cells (NRK cells) at the nonpermissive temperature, 39 degrees C, but grew as multilayered foci resembling NRK cells transformed by the wild-type virus (KNRK cells) at 32 degrees C, the permissive temperature. NRK cell division was stimulated by epidermal growth factor (EGF), and these cells showed high levels of EGF receptors, as determined by 125I-labeled EGF binding. KNRK cells were unresponsive to EGF and no EGF receptors were detectable. Ts cells also were unresponsive to EGF at both temperatures, but exhibited just detectable EGF binding at 32 degrees C and 10-15% of NRK cell binding at 39 degrees C. Use of EGF added to the culture medium by these cells paralleled the receptor levels. Crossfeeding experiments among NRK, KNRK, and Ts cultures indicated that Ts cells at the permissive temperature and KNRK cells at both temperatures produced a heat-stable substance(s) which stimulated DNA synthesis in NRK cells independent of the presence of serum or of EGF. Conditioned medium from the transformed cultures also significantly enhanced EGF binding to NRK cells. These studies demonstrated a correlation between the transformed phenotype and the receptor levels of a potent cell mitogen, EGF, which was readily reversible in the Ts cultures. In addition, cultures expressing the transformed phenotype produced material that did not compete for the EGF receptor but did enhance EGF binding, in contrast to other reports involving sarcoma virus-transformed cells.