Multistep Change in Epidermal Growth Factor Receptors during Spontaneous Neoplastic Progression in Chinese Hamster Embryo Fibroblasts1

Whole Chinese hamster embryo lineages have been shown to undergo multistep spontaneous neoplastia progression during serial passage in culture. We have studied the binding, internalization, and degradation of 125l-labeled epidermal growth factor at four different stages of transformation. The whole Chinese hamster embryo cells lost cell surface epidermal growth factor receptors gradually during the course of neoplastia progression until only 10% of the receptor number present in the earlypassage cells (precrisis) were retained in the late-passage cells (tumorigenic). No differences in internalization rates, chloroquine sensitivity, or ability to degrade hormone between the various passage levels were seen. No evidence for the presence in conditioned medium of transforming growth factors which might mask or down-regulate epidermal growth factor receptor was obtained. These results suggest that a reduction in cell surface epidermal growth factor receptor might be an early event during spontaneous transformation in whole Chinese hamster embryo cells.